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Real-world labs hold the potential to catalyse rapid urban transformations through real-world experimentation. Characterised by a rather radical, responsive, and location-specific nature, real-world labs face constraints in the scaling of experimental knowledge. To make a significant contribution to urban transformation, the produced knowledge must go beyond the level of a building, street, or small district where real-world experiments are conducted. Thus, a conflict arises between experimental boundaries and the stimulation of broader implications. The challenges of scaling experimental knowledge have been recognised as a problem, but remain largely unexplained. Based on this, the article will discuss the applicability of the “typology of amplification processes” by Lam et al. (2020) to explore and evaluate the potential of scaling experimental knowledge from real-world labs. The application of the typology is exemplified in the case of the Bauhaus.MobilityLab. The Bauhaus.MobilityLab takes a unique approach by testing and developing cross-sectoral mobility, energy, and logistics solutions with a distinct focus on scaling knowledge and innovation. For this case study, different qualitative research techniques are combined according to “within-method triangulation” and synthesised in a strengths, weaknesses, opportunities, and threats (SWOT) analysis. The analysis of the Bauhaus.MobilityLab proves that the “typology of amplification processes” is useful as a systematic approach to identifying and evaluating the potential of scaling experimental knowledge.
For the safe and efficient operation of dams, frequent monitoring and maintenance are required. These are usually expensive, time consuming, and cumbersome. To alleviate these issues, we propose applying a wave-based scheme for the location and quantification of damages in dams.
To obtain high-resolution “interpretable” images of the damaged regions, we drew inspiration from non-linear full-multigrid methods for inverse problems and applied a new cyclic multi-stage full-waveform inversion (FWI) scheme. Our approach is less susceptible to the stability issues faced by the standard FWI scheme when dealing with ill-posed problems. In this paper, we first selected an optimal acquisition setup and then applied synthetic data to demonstrate the capability of our approach in identifying a series of anomalies in dams by a mixture of reflection and transmission tomography. The results had sufficient robustness, showing the prospects of application in the field of non-destructive testing of dams.
With the growing importance of the World Wide Web, the major challenges our society faces are also increasingly affecting the digital areas of our lives. Some of the associated problems can be addressed by computer science, and some of these specifically by data-driven research. To do so, however, requires to solve open issues related to archive quality and the large volume and variety of the data contained.
This dissertation contributes data, algorithms, and concepts towards leveraging the big data and temporal provenance capabilities of web archives to tackle societal challenges. We selected three such challenges that highlight the central issues of archive quality, data volume, and data variety, respectively:
(1) For the preservation of digital culture, this thesis investigates and improves the automatic quality assurance of the web page archiving process, as well as the further processing of the resulting archive data for automatic analysis.
(2) For the critical assessment of information, this thesis examines large datasets of Wikipedia and news articles and presents new methods for automatically determining quality and bias.
(3) For digital security and privacy, this thesis exploits the variety of content on the web to quantify the security of mnemonic passwords and analyzes the privacy-aware re-finding of the various seen content through private web archives.
The objective of this thesis was to understand the 20th-century history of informal urbanisation in Europe and its origins in Madrid and Paris. The concept of informal urbanisation was employed to refer to the process of developing shacks and precarious single-family housing areas that were not planned by the public powers and were considered to be substandard because of their below-average materials and social characteristics. Our main hypothesis was that despite being a phenomenon with ancient roots, informal urbanisation emerged as a public problem and was subsequently prohibited in connection with another historical process occurred: the birth of contemporary urban planning. Therefore, its transformation into a deviant and illegal urban growth mechanism would have been a pan-European process occurring at the same pace that urban planning developed during the first decades of the 20th century.
Analysing the 20th-century history of informal urbanisation in Europe was an ambitious task that required using a large number of sources. To contend with this issue, this thesis combined two main methods: historiographical research about informal urbanisation in Europe and archival research of two case studies, Madrid and Paris, to make the account more precise by analysing primary sources of the subject.
Our research of these informal areas, which were produced mainly through poor private allotments and housing developed on land squats, revealed two key moments of explosive growth across Europe: the 1920s and 1960s. The near disappearance of informal urbanisation throughout the continent seemed to be a consequence not of the historical development of urban planning—which was commonly transgressed and bypassed—but of the exacerbation of global economic inequalities, permitting the development of a geography of privilege in Europe.
Concerning the cases of Paris and Madrid, the origins of informal urbanisation—that is, the moment the issue started to be problematised—seemed to occur in the second half of the 19th century, when a number of hygienic norms and surveillance devices began to control housing characteristics. From that moment onwards, informal urbanisation areas formed peripheral belts in both cities. This growth became the object of an illegalisation process of which we have identified three phases: (i) the unregulated development of the phenomenon during the second half of the 20th century, (ii) the institutional production of “exception regulations” to permit a controlled development of substandard housing in the peripheral fringes of both cities, and (iii) the synchronic prohibition of informal urbanisation in the 1920s and its illegal reproduction.
In this work, the degradation performance for the photocatalytic oxidation of eight micropollutants (amisulpride, benzotriazole, candesartan, carbamazepine, diclofenac, gabapentin, methlybenzotriazole, and metoprolol) within real secondary effluent was investigated using three different reactor designs. For all reactor types, the influence of irradiation power on its reaction rate and energetic efficiency was investigated. Flat cell and batch reactor showed almost similar substance specific degradation behavior. Within the immersion rotary body reactor, benzotriazole and methylbenzotriazole showed a significantly lower degradation affinity. The flat cell reactor achieved the highest mean degradation rate, with half time values ranging from 5 to 64 min with a mean of 18 min, due to its high catalysts surface to hydraulic volume ratio. The EE/O values were calculated for all micro-pollutants as well as the mean degradation rate constant of each experimental step. The lowest substance specific energy per order (EE/O) values of 5 kWh/m3 were measured for benzotriazole within the batch reactor. The batch reactor also reached the lowest mean values (11.8–15.9 kWh/m3) followed by the flat cell reactor (21.0–37.0 kWh/m3) and immersion rotary body reactor (23.9–41.0 kWh/m3). Catalyst arrangement and irradiation power were identified as major influences on the energetic performance of the reactors. Low radiation intensities as well as the use of submerged catalyst arrangement allowed a reduction in energy demand by a factor of 3–4. A treatment according to existing treatment goals of wastewater treatment plants (80% total degradation) was achieved using the batch reactor with a calculated energy demand of 7000 Wh/m3.
One of the most important renewable energy technologies used nowadays are wind power turbines. In this paper, we are interested in identifying the operating status of wind turbines, especially rotor blades, by means of multiphysical models. It is a state-of-the-art technology to test mechanical structures with ultrasonic-based methods. However, due to the density and the required high resolution, the testing is performed with high-frequency waves, which cannot penetrate the structure in depth. Therefore, there is a need to adopt techniques in the fields of multiphysical model-based inversion schemes or data-driven structural health monitoring. Before investing effort in the development of such approaches, further insights and approaches are necessary to make the techniques applicable to structures such as wind power plants (blades). Among the expected developments, further accelerations of the so-called “forward codes” for a more efficient implementation of the wave equation could be envisaged. Here, we employ electromagnetic waves for the early detection of cracks. Because in many practical situations, it is not possible to apply techniques from tomography (characterized by multiple sources and sensor pairs), we focus here on the question of whether the existence of cracks can be determined by using only one source for the sent waves.
The goal of architecture is changing in response to the expanding role of cities, rapid urbanization, and transformation under changing economic, environmental, social, and demographic factors. As cities increased in the early modern era, overcrowding, urbanization, and pollution conditions led reformers to consider the future shape of the cities. One of the most critical topics in contemporary architecture is the subject of the future concepts of living. In most cases, domed cities, as a future concept of living, are rarely considered, and they are used chiefly as “utopian” visions in the discourse of future ways of living. This paper highlights the reviews of domed cities to deepen the understanding of the idea in practice, like its approach in terms of architecture. The main aim of this paper is to provide a broad overview for domed cities in the face of pollution as one of the main concerns in many European cities. As a result, the significance of the reviews of the existing projects is focused on their conceptual quality. This review will pave the way for further studies in terms of future developments in the realm of domed cities. In this paper, the city of Celje, one of the most polluted cities in Slovenia, is taken as a case study for considering the concept of Dome incorporated due to the lack of accessible literature on the topic. This review’s primary contribution is to allow architects to explore a broad spectrum of innovation by comparing today’s achievable statuses against the possibilities generated by domed cities. As a result of this study, the concept of living under the Dome remains to be developed in theory and practice. The current challenging climatic situation will accelerate the evolution of these concepts, resulting in the formation of new typologies, which are a requirement for humanity.
Bolted connections are widely employed in structures like transmission poles, wind turbines, and television (TV) towers. The behaviour of bolted connections is often complex and plays a significant role in the overall dynamic characteristics of the structure. The goal of this work is to conduct a fatigue lifecycle assessment of such a bolted connection block of a 193 m tall TV tower, for which 205 days of real measurement data have been obtained from the installed monitoring devices. Based on the recorded data, the best-fit stochastic wind distribution for 50 years, the decisive wind action, and the locations to carry out the fatigue analysis have been decided. A 3D beam model of the entire tower is developed to extract the nodal forces corresponding to the connection block location under various mean wind speeds, which is later coupled with a detailed complex finite element model of the connection block, with over three million degrees of freedom, for acquiring stress histories on some pre-selected bolts. The random stress histories are analysed using the rainflow counting algorithm (RCA) and the damage is estimated using Palmgren-Miner's damage accumulation law. A modification is proposed to integrate the loading sequence effect into the RCA, which otherwise is ignored, and the differences between the two RCAs are investigated in terms of the accumulated damage.
The floods in 2002 and 2013, as well as the recent flood of 2021, caused billions Euros worth of property damage in Germany. The aim of the project Innovative Vulnerability and Risk Assessment of Urban Areas against Flood Events (INNOVARU) involved the development of a practicable flood damage model that enables realistic damage statements for the residential building stock. In addition to the determination of local flood risks, it also takes into account the vulnerability of individual buildings and allows for the prognosis of structural damage. In this paper, we discuss an improved method for the prognosis of structural damage due to flood impact. Detailed correlations between inundation level and flow velocities depending on the vulnerability of the building types, as well as the number of storeys, are considered. Because reliable damage data from events with high flow velocities were not available, an innovative approach was adopted to cover a wide range of flow velocities. The proposed approach combines comprehensive damage data collected after the 2002 flood in Germany with damage data of the 2011 Tohoku earthquake tsunami in Japan. The application of the developed methods enables a reliable reinterpretation of the structural damage caused by the August flood of 2002 in six study areas in the Free State of Saxony.
A safe and economic structural design based on the semi-probabilistic concept requires statistically representative safety elements, such as characteristic values, design values, and partial safety factors. Regarding climate loads, the safety levels of current design codes strongly reflect experiences based on former measurements and investigations assuming stationary conditions, i.e. involving constant frequencies and intensities. However, due to climate change, occurrence of corresponding extreme weather events is expected to alter in the future influencing the reliability and safety of structures and their components. Based on established approaches, a systematically refined data-driven methodology for the determination of design parameters considering nonstationarity as well as standardized targets of structural reliability or safety, respectively, is therefore proposed. The presented procedure picks up fundamentals of European standardization and extends them with respect to nonstationarity by applying a shifting time window method. Taking projected snow loads into account, the application of the method is exemplarily demonstrated and various influencing parameters are discussed.
Design-related reassessment of structures integrating Bayesian updating of model safety factors
(2022)
In the semi-probabilistic approach of structural design, the partial safety factors are defined by considering some degree of uncertainties to actions and resistance, associated with the parameters’ stochastic nature. However, uncertainties for individual structures can be better examined by incorporating measurement data provided by sensors from an installed health monitoring scheme. In this context, the current study proposes an approach to revise the partial safety factor for existing structures on the action side, γE by integrating Bayesian model updating. A simple numerical example of a beam-like structure with artificially generated measurement data is used such that the influence of different sensor setups and data uncertainties on revising the safety factors can be investigated. It is revealed that the health monitoring system can reassess the current capacity reserve of the structure by updating the design safety factors, resulting in a better life cycle assessment of structures. The outcome is furthermore verified by analysing a real life small railway steel bridge ensuring the applicability of the proposed method to practical applications.
Determining the earthquake hazard of any settlement is one of the primary studies for reducing earthquake damage. Therefore, earthquake hazard maps used for this purpose must be renewed over time. Turkey Earthquake Hazard Map has been used instead of Turkey Earthquake Zones Map since 2019. A probabilistic seismic hazard was performed by using these last two maps and different attenuation relationships for Bitlis Province (Eastern Turkey) were located in the Lake Van Basin, which has a high seismic risk. The earthquake parameters were determined by considering all districts and neighborhoods in the province. Probabilistic seismic hazard analyses were carried out for these settlements using seismic sources and four different attenuation relationships. The obtained values are compared with the design spectrum stated in the last two earthquake maps. Significant differences exist between the design spectrum obtained according to the different exceedance probabilities. In this study, adaptive pushover analyses of sample-reinforced concrete buildings were performed using the design ground motion level. Structural analyses were carried out using three different design spectra, as given in the last two seismic design codes and the mean spectrum obtained from attenuation relationships. Different design spectra significantly change the target displacements predicted for the performance levels of the buildings.
The seismic vulnerability assessment of existing reinforced concrete (RC) buildings is a significant source of disaster mitigation plans and rescue services. Different countries evolved various Rapid Visual Screening (RVS) techniques and methodologies to deal with the devastating consequences of earthquakes on the structural characteristics of buildings and human casualties. Artificial intelligence (AI) methods, such as machine learning (ML) algorithm-based methods, are increasingly used in various scientific and technical applications. The investigation toward using these techniques in civil engineering applications has shown encouraging results and reduced human intervention, including uncertainties and biased judgment. In this study, several known non-parametric algorithms are investigated toward RVS using a dataset employing different earthquakes. Moreover, the methodology encourages the possibility of examining the buildings’ vulnerability based on the factors related to the buildings’ importance and exposure. In addition, a web-based application built on Django is introduced. The interface is designed with the idea to ease the seismic vulnerability investigation in real-time. The concept was validated using two case studies, and the achieved results showed the proposed approach’s potential efficiency
In the wake of the news industry’s digitization, novel organizations that differ considerably from traditional media firms in terms of their functional roles and organizational practices of media work are emerging. One new type is the field repair organization, which is characterized by supporting high‐quality media work to compensate for the deficits (such as those which come from cost savings and layoffs) which have become apparent in legacy media today. From a practice‐theoretical research perspective and based on semi‐structured interviews, virtual field observations, and document analysis, we have conducted a single case study on Science Media Center Germany (SMC), a unique non‐profit news start‐up launched in 2016 in Cologne, Germany. Our findings show that, in addition to field repair activities, SMC aims to facilitate progress and innovation in the field, which we refer to as field advancement. This helps to uncover emerging needs and anticipates problems before they intensify or even occur, proactively providing products and tools for future journalism. This article contributes to our understanding of novel media organizations with distinct functions in the news industry, allowing for advancements in theory on media work and the organization of journalism in times of digital upheaval.
Paper-based data acquisition and manual transfer between incompatible software or data formats during inspections of bridges, as done currently, are time-consuming, error-prone, cumbersome, and lead to information loss. A fully digitized workflow using open data formats would reduce data loss, efforts, and the costs of future inspections. On the one hand, existing studies proposed methods to automatize data acquisition and visualization for inspections. These studies lack an open standard to make the gathered data available for other processes. On the other hand, several studies discuss data structures for exchanging damage information among different stakeholders. However, those studies do not cover the process of automatic data acquisition and transfer. This study focuses on a framework that incorporates automatic damage data acquisition, transfer, and a damage information model for data exchange. This enables inspectors to use damage data for subsequent analyses and simulations. The proposed framework shows the potentials for a comprehensive damage information model and related (semi-)automatic data acquisition and processing.
This dataset presents the numerical analysis of the heat and moisture transport through a facade equipped with a living wall system designated for greywater treatment. While such greening systems provide many environmental benefits, they involve pumping large quantities of water onto the wall assembly, which can increase the risk of moisture in the wall as well as impaired energetic performance due to increased thermal conductivity with increased moisture content in the building materials. This dataset was acquired through numerical simulation using the coupling of two simulation tools, namely Envi-Met and Delphin. This coupling was used to include the complex role the plants play in shaping the near-wall environmental parameters in the hygrothermal simulations. Four different wall assemblies were investigated, each assembly was assessed twice: with and without the living wall. The presented data include the input and output parameters of the simulations, which were presented in the co-submitted article [1].
Der Aufruf, die Begriffe Stadt und Kritik in das Zentrum einer Debatte zu stellen, bietet die große Chance, uns weit über begriffliche Klärungen unseres gemeinsamen Arbeitsgegenstands hinaus – die ja auch für sich selbst sehr fruchtbar sein können – über die Funktion zu verständigen, die wir in der Gesellschaft ausüben, wenn wir räumliche Planung praktizieren, erforschen und lehren. Da in der Bundesrepublik nicht nur ein großer Bedarf, sondern auch eine beträchtliche Nachfrage nach öffentlicher Planung besteht und die planungsbezogenen Wissenschaften sich eines insgesamt stabilen institutionellen Standes erfreuen, laufen wir Gefahr, die gesellschaftspolitische Legitimation von Berufsfeld und Wissenschaft zu vernachlässigen, sie als gegeben zu behandeln. Wir müssen uns ja kaum rechtfertigen.
In ten chapters, this thesis presents information retrieval technology which is tailored to the research activities that arise in the context of corpus-based digital humanities projects.
The presentation is structured by a conceptual research process that is introduced in Chapter 1. The process distinguishes a set of five research activities: research question generation, corpus acquisition, research question modeling, corpus annotation, and result dissemination. Each of these research activities elicits different information retrieval tasks with special challenges, for which algorithmic approaches are presented after an introduction of the core information retrieval concepts in Chapter 2.
A vital concept in many of the presented approaches is the keyquery paradigm introduced in Chapter 3, which represents an operation that returns relevant search queries in response to a given set of input documents. Keyqueries are proposed in Chapter 4 for the recommendation of related work, and in Chapter 5 for improving access to aspects hidden in the long tail of search result lists.
With pseudo-descriptions, a document expansion approach is presented in Chapter 6. The approach improves the retrieval performance for corpora where only bibliographic meta-data is originally available. In Chapter 7, the keyquery paradigm is employed to generate dynamic taxonomies for corpora in an unsupervised fashion.
Chapter 8 turns to the exploration of annotated corpora, and presents scoped facets as a conceptual extension to faceted search systems, which is particularly useful in exploratory search settings. For the purpose of highlighting the major topical differences in a sequence of sub-corpora, an algorithm called topical sequence profiling is presented in Chapter 9.
The thesis concludes with two pilot studies regarding the visualization of (re)search results for the means of successful result dissemination: a metaphoric interpretation of the information nutrition label, as well as the philosophical bodies, which are 3D-printed search results.
Multi-criteria decision analysis (MCDA) is an established methodology to support the decision-making of multi-objective problems. For conducting an MCDA, in most cases, a set of objectives (SOO) is required, which consists of a hierarchical structure comprised of objectives, criteria, and indicators. The development of an SOO is usually based on moderated development processes requiring high organizational and cognitive effort from all stakeholders involved. This article proposes elementary interactions as a key paradigm of an algorithm-driven development process for an SOO that requires little moderation efforts. Elementary interactions are self-contained information requests that may be answered with little cognitive effort. The pairwise comparison of elements in the well-known analytical hierarchical process (AHP) is an example of an elementary interaction. Each elementary interaction in the development process presented contributes to the stepwise development of an SOO. Based on the hypothesis that an SOO may be developed exclusively using elementary interactions (EIs), a concept for a multi-user platform is proposed. Essential components of the platform are a Model Aggregator, an Elementary Interaction Stream Generator, a Participant Manager, and a Discussion Forum. While the latter component serves the professional exchange of the participants, the first three components are intended to be automatable by algorithms. The platform concept proposed has been evaluated partly in an explorative validation study demonstrating the general functionality of the algorithms outlined. In summary, the platform concept suggested demonstrates the potential to ease SOO development processes as the platform concept does not restrict the application domain; it is intended to work with little administration moderation efforts, and it supports the further development of an existing SOO in the event of changes in external conditions. The algorithm-driven development of SOOs proposed in this article may ease the development of MCDA applications and, thus, may have a positive effect on the spread of MCDA applications.
Operator Calculus Approach to Comparison of Elasticity Models for Modelling of Masonry Structures
(2022)
The solution of any engineering problem starts with a modelling process aimed at formulating a mathematical model, which must describe the problem under consideration with sufficient precision. Because of heterogeneity of modern engineering applications, mathematical modelling scatters nowadays from incredibly precise micro- and even nano-modelling of materials to macro-modelling, which is more appropriate for practical engineering computations. In the field of masonry structures, a macro-model of the material can be constructed based on various elasticity theories, such as classical elasticity, micropolar elasticity and Cosserat elasticity. Evidently, a different macro-behaviour is expected depending on the specific theory used in the background. Although there have been several theoretical studies of different elasticity theories in recent years, there is still a lack of understanding of how modelling assumptions of different elasticity theories influence the modelling results of masonry structures. Therefore, a rigorous approach to comparison of different three-dimensional elasticity models based on quaternionic operator calculus is proposed in this paper. In this way, three elasticity models are described and spatial boundary value problems for these models are discussed. In particular, explicit representation formulae for their solutions are constructed. After that, by using these representation formulae, explicit estimates for the solutions obtained by different elasticity theories are obtained. Finally, several numerical examples are presented, which indicate a practical difference in the solutions.
It is widely accepted that most people spend the majority of their lives indoors. Most individuals do not realize that while indoors, roughly half of heat exchange affecting their thermal comfort is in the form of thermal infrared radiation. We show that while researchers have been aware of its thermal comfort significance over the past century, systemic error has crept into the most common evaluation techniques, preventing adequate characterization of the radiant environment. Measuring and characterizing radiant heat transfer is a critical component of both building energy efficiency and occupant thermal comfort and productivity. Globe thermometers are typically used to measure mean radiant temperature (MRT), a commonly used metric for accounting for the radiant effects of an environment at a point in space. In this paper we extend previous field work to a controlled laboratory setting to (1) rigorously demonstrate that existing correction factors used in the American Society of Heating Ventilation and Air-conditioning Engineers (ASHRAE) Standard 55 or ISO7726 for using globe thermometers to quantify MRT are not sufficient; (2) develop a correction to improve the use of globe thermometers to address problems in the current standards; and (3) show that mean radiant temperature measured with ping-pong ball-sized globe thermometers is not reliable due to a stochastic convective bias. We also provide an analysis of the maximum precision of globe sensors themselves, a piece missing from the domain in contemporary literature.
Data acquisition systems and methods to capture high-resolution images or reconstruct 3D point clouds of existing structures are an effective way to document their as-is condition. These methods enable a detailed analysis of building surfaces, providing precise 3D representations. However, for the condition assessment and documentation, damages are mainly annotated in 2D representations, such as images, orthophotos, or technical drawings, which do not allow for the application of a 3D workflow or automated comparisons of multitemporal datasets. In the available software for building heritage data management and analysis, a wide range of annotation and evaluation functions are available, but they also lack integrated post-processing methods and systematic workflows. The article presents novel methods developed to facilitate such automated 3D workflows and validates them on a small historic church building in Thuringia, Germany. Post-processing steps using photogrammetric 3D reconstruction data along with imagery were implemented, which show the possibilities of integrating 2D annotations into 3D documentations. Further, the application of voxel-based methods on the dataset enables the evaluation of geometrical changes of multitemporal annotations in different states and the assignment to elements of scans or building models. The proposed workflow also highlights the potential of these methods for condition assessment and planning of restoration work, as well as the possibility to represent the analysis results in standardised building model formats.
This dataset consists mainly of two subsets. The first subset includes measurements and simulation data conducted to validate the simulation tool ENVI-met. The measurements were conducted at the campus of the Bauhaus-University Weimar in Weimar, Germany and consisted of recording exterior air temperature, globe temperature, relative humidity, and wind velocity at 1.5 m at four points on four different days. After the measurements, the geometry of the campus was modelled and meshed; the simulations were conducted using the weather data of the measurements days with the aim of investigating the accuracy of the model.
The second data subset consists of ENVI-met simulation data of the potential of facade greening in improving the outdoor environment and the indoor air temperature during heatwaves in Central European cities. The data consist of the boundary conditions and the simulation output of two simulation models: with and without facade greening. The geometry of the models corresponded to a residential buildings district in Stuttgart, Germany. The simulation output consisted of exterior air temperature, mean radiant temperature, relative humidity, and wind velocity at 12 different probe points in the model in addition to the indoor air temperature of an exemplary building. The dataset presents both vertical profiles of the probed parameters as well as the time series output of the five-day simulation duration. Both data subsets correspond to the investigations presented in the co-submitted article [1].
The fracture of microcapsules is an important issue to release the healing agent for healing the cracks in encapsulation-based self-healing concrete. The capsular clustering generated from the concrete mixing process is considered one of the critical factors in the fracture mechanism. Since there is a lack of studies in the literature regarding this issue, the design of self-healing concrete cannot be made without an appropriate modelling strategy. In this paper, the effects of microcapsule size and clustering on the fractured microcapsules are studied computationally. A simple 2D computational modelling approach is developed based on the eXtended Finite Element Method (XFEM) and cohesive surface technique. The proposed model shows that the microcapsule size and clustering have significant roles in governing the load-carrying capacity and the crack propagation pattern and determines whether the microcapsule will be fractured or debonded from the concrete matrix. The higher the microcapsule circumferential contact length, the higher the load-carrying capacity. When it is lower than 25% of the microcapsule circumference, it will result in a greater possibility for the debonding of the microcapsule from the concrete. The greater the core/shell ratio (smaller shell thickness), the greater the likelihood of microcapsules being fractured.
Das Fahrrad ist ein Medium sozialer Veränderung. Seine vielfältigen utopischen Potenziale ergeben sich nicht zuletzt aus seinen ebenso vielfältigen und häufig übersehenen medialen Qualitäten: Es vermittelt, es verbindet, es übersetzt; es modifiziert Wahrnehmung und Organisation von Raum und Zeit, von Körpern und von Sozialität. Umgekehrt kann auch das medienwissenschaftliche Denken fahrradmedial verändert werden. Das Fahrrad ist nicht nur Medium des sozialen und ökologischen Wandels: Radfahren eröffnet Perspektiven, verändert Räume, lässt neue Relationen entstehen und teilt Handlungsmacht neu auf.
Fahrradutopien denkt vom Fahrrad aus und ergänzt dabei bestehende Ansätze zur Mobilitätsforschung um medienkulturwissenschaftliche Perspektiven. Die Beiträge verbinden Medienwissenschaften und Forschungen zu Fahrradaktivismus mit der Liebe zum Radfahren. Fokussiert werden Fahrradfilme und -vlogs, Verkehr und Infrastrukturen, Virtuelle Realität und Fahrrad, Fahrradkollektive und Fahrradfeminismus.
Im Heft zum zehnjährigen Jubiläum von sub\urban mit dem Themenschwerpunkt „sub\x: Verortungen, Entortungen" veröffentlichen wir eine Debatte, die von den bisherigen in unserer Zeitschrift in dieser Rubrik geführten textlichen Diskussionen abweicht. Im Vorfeld der Planungen für unsere Jubiläumsausgabe haben wir die aktuellen Mitglieder unseres wissenschaftlichen Beirats darum gebeten, zwei grundlegende Fragen von kritischer Stadtforschung in kurzen Beiträgen zu diskutieren: Was ist Stadt? Was ist Kritik?
Das Ziel der Arbeit ist, eine mögliche Verbesserung der Güte der Lebensdauervorhersage für Gusseisenwerkstoffe mit Kugelgraphit zu erreichen, wobei die Gießprozesse verschiedener Hersteller berücksichtigt werden.
Im ersten Schritt wurden Probenkörper aus GJS500 und GJS600 von mehreren Gusslieferanten gegossen und daraus Schwingproben erstellt.
Insgesamt wurden Schwingfestigkeitswerte der einzelnen gegossenen Proben sowie der Proben des Bauteils von verschiedenen Gussherstellern weltweit entweder durch direkte Schwingversuche oder durch eine Sammlung von Betriebsfestigkeitsversuchen bestimmt.
Dank der metallografischen Arbeit und Korrelationsanalyse konnten drei wesentliche Parameter zur Bestimmung der lokalen Dauerfestigkeit festgestellt werden: 1. statische Festigkeit, 2. Ferrit- und Perlitanteil der Mikrostrukturen und 3. Kugelgraphitanzahl pro Flächeneinheit.
Basierend auf diesen Erkenntnissen wurde ein neues Festigkeitsverhältnisdiagramm (sogenanntes Sd/Rm-SG-Diagramm) entwickelt.
Diese neue Methodik sollte vor allem ermöglichen, die Bauteildauerfestigkeit auf der Grundlage der gemessenen oder durch eine Gießsimulation vorhersagten lokalen Zugfestigkeitswerte sowie Mikrogefügenstrukturen besser zu prognostizieren.
Mithilfe der Versuche sowie der Gießsimulation ist es gelungen, unterschiedliche Methoden der Lebensdauervorhersage unter Berücksichtigung der Herstellungsprozesse weiterzuentwickeln.
The computational costs of newly developed numerical simulation play a critical role in their acceptance within both academic use and industrial employment. Normally, the refinement of a method in the area of interest reduces the computational cost. This is unfortunately not true for most nonlocal simulation, since refinement typically increases the size of the material point neighborhood. Reducing the discretization size while keep- ing the neighborhood size will often require extra consideration. Peridynamic (PD) is a newly developed numerical method with nonlocal nature. Its straightforward integral form equation of motion allows simulating dynamic problems without any extra consideration required. The formation of crack and its propagation is known as natural to peridynamic. This means that discontinuity is a result of the simulation and does not demand any post-processing. As with other nonlocal methods, PD is considered an expensive method. The refinement of the nodal spacing while keeping the neighborhood size (i.e., horizon radius) constant, emerges to several nonphysical phenomena.
This research aims to reduce the peridynamic computational and imple- mentation costs. A novel refinement approach is introduced. The pro- posed approach takes advantage of the PD flexibility in choosing the shape of the horizon by introducing multiple domains (with no intersections) to the nodes of the refinement zone. It will be shown that no ghost forces will be created when changing the horizon sizes in both subdomains. The approach is applied to both bond-based and state-based peridynamic and verified for a simple wave propagation refinement problem illustrating the efficiency of the method. Further development of the method for higher dimensions proves to have a direct relationship with the mesh sensitivity of the PD. A method for solving the mesh sensitivity of the PD is intro- duced. The application of the method will be examined by solving a crack propagation problem similar to those reported in the literature.
New software architecture is proposed considering both academic and in- dustrial use. The available simulation tools for employing PD will be collected, and their advantages and drawbacks will be addressed. The challenges of implementing any node base nonlocal methods while max- imizing the software flexibility to further development and modification will be discussed and addressed. A software named Relation-Based Sim- ulator (RBS) is developed for examining the proposed architecture. The exceptional capabilities of RBS will be explored by simulating three distinguished models. RBS is available publicly and open to further develop- ment. The industrial acceptance of the RBS will be tested by targeting its performance on one Mac and two Linux distributions.
Die Europatournee des Indischen Menaka-Balletts von 1936-38 ist der Ausgangspunkt dieser archivologischen Navigation entlang der Spuren indischer KünstlerInnen in Europa. In einer breit angelegten Archivrecherche wurden dazu Dokumente, Fundstücke, orale Erinnerungen und ethnografische Beobachtungen aus dem Kontext der Menaka-Tournee durch das nationalsozialistische Deutschland zusammengetragen.
Das Buch beschreibt den Rekonstruktionsprozess eines bedeutsamen Projekts der indischen Tanzmoderne. Es verfolgt dabei eine Methode, mit der sich die fragmentierten Dokumente des Medienereignisses als Spur lesen lassen und nutzt eine künstlerisch-forschende Involvierung in gegenwärtige Erinnerungspolitiken, in welche die verflochtenen Strukturen der künstlerischen Avantgarde zwischen Kolkata, Mumbai und Berlin hineinreichen. Die Spur des Menaka-Ballett erweist sich dabei als Teil weitreichender ideologischer, tänzerischer, musikalischer, filmischer und literarischer Strömungen, die auch in gegenwärtigen kulturellen Bestimmungen fortwirken.
Fotografien, Zeitungsberichte, Film- und Tonaufnahmen, Briefe und persönliche Erinnerungstücke erzählen davon, wie sich, vor dem Hintergrund der im antikolonialen Aufbruch befindlichen Kulturreform in Indien, und der nationsozialistisch-völkischen Kulturpolitik in Deutschland, die Tänzerinnen und Musiker der indischen Ballettgruppe und die deutsche Öffentlichkeit im gegenseitigen Spiegel betrachteten, während die Vorzeichen des kommenden Krieges immer deutlicher wurden.
Das Ziel dieser Arbeit war es, neuartige Fließmittel auf Basis von Stärke als nachwachsenden Rohstoff zu synthetisieren und die Wechselwirkung mit Portlandzement zu charakterisieren. Die Notwendigkeit, Alternativen zu synthetischen Zusatzmittel zu erforschen, ergibt sich aus der benötigten Menge zur Verarbeitung von ca. 4,1 Gt/a, wobei ca. 85 % der Zusatzmittel auf die Fließmittel entfallen.
Um Fließmittel aus Stärke zu synthetisieren, wurden drei Basisstärken unterschiedlicher Herkunft verwendet. Es wurde eine Maniokstärke mit einer niedrigen Molekularmasse und eine Weizenstärke mit einer hohen Molekularmasse verwendet. Darüber hinaus wurde eine Kartoffelstärke mit einer mittleren Molekularmasse, die ein Abfallprodukt der kartoffelverarbeitenden Industrie darstellt, genutzt. Die Stärkefließmittel wurden durch chemische Modifikation in einem zweistufigen Prozess synthetisiert. Im ersten Schritt wurde das Molekulargewicht der Weizen- und Kartoffelstärke durch säurehydrolytischen Abbau verringert. Für die kurzkettige Maniokstärke war eine Degradation der Molekularmasse nicht notwendig. Im zweiten Syntheseschritt wurden anionische Ladungen durch das Versetzen der degradierten Stärken und Maniokstärke mit Natriumvinylsulfonat in die Stärkemoleküle eingeführt.
Beurteilung der Synthesemethode zur Erzeugung von Stärkefließmitteln
In diesem Zusammenhang sollten molekulare Parameter der Stärkefließmittel gezielt eingestellt werden, um eine Fließwirkung im Portlandzement zu erhalten. Insbesondere die Molekularmasse und die Menge anionischer Ladungen sollte variiert werden, um Abhängigkeiten mit der Dispergierleistung zu identifizieren.
1. Es konnte durch GPC-Messungen gezeigt werden, dass die Molekularmasse der langkettigen Weizenstärke durch die gewählten Modifizierungsbedingungen zum säurehydrolytischen Abbau verringert werden konnte. Durch Variation der säurehydrolytischen Bedingungen wurden 4 degradierte Weizenstärken erzeugt, die eine Reduzierung der Molekularmasse um 27,5 – 43 % aufwiesen. Die Molekularmasse der Kartoffelstärke konnte durch säurehydrolytischen Abbau um ca. 26 % verringert werden.
2. Durch PCD-Messungen wurde gezeigt, dass anionische Ladungen durch Sulfoethylierung der freien Hydroxylgruppen in die degradierten Stärken eingeführt werden konnten. Durch Variation der Dauer der Sulfoethylierung konnte die Menge der anionischen Ladungen gesteuert und gezielt variiert werden, so dass Stärkefließmittel mit steigender Ladungsmenge in folgender Reihenfolge synthetisiert wurden:
W-3 < W-2 < K-1 < W¬-4 < W¬1 < M-1
Im Ergebnis der chemischen Modifizierung konnten 6 Stärkefließmittel mit variierten Molekularmassen und anionischen Ladungen erzeugt werden. Es konnte gezeigt werden, dass die Herkunft der Stärke für die chemische Modifizierung unerheblich ist. Die Fließmittel lagen synthesebedingt als basische, wässrige Suspensionen mit Wirkstoffgehalten im Bereich von 23,5 – 50 % vor.
Beurteilung der Dispergierleistung der synthetisierten Stärkefließmittel
Die Dispergierperformance wurde durch rheologische Experimente mit einem Rotationsviskosimeter erfasst. Dabei wurden der Einfluss auf die Fließkurven und die Viskositätskurven betrachtet. Durch Vergleich der Dispergierleistung mit einem Polykondensat- und einem PCE-Fließmittel konnte eine Einordnung und Bewertung der Fließmittel vorgenommen werden.
3. Die rheologische Experimente haben gezeigt, dass die Stärkefließmittel eine vergleichbar hohe Dispergierleistung aufweisen, wie das zum Vergleich herangezogen PCE-Fließmittel. Darüber hinaus zeigte sich, dass die Fließwirkung der 6 Stärkefließmittel gegenüber dem Polykondensatfließmittel deutlich höher ist. Das aus der Literatur bekannte Einbrechen der Dispergierleistung der Polykondensat-fließmittel bei w/z-Werten < 0,4 konnte bestätigt werden.
4. Alle 6 Stärkefließmittel führten zu einer Verringerung der Fließgrenze und der dynamischen Viskosität des Zementleimes bei einem w/z-Wert von 0,35.
5. Der Vergleich der Dispergierleistung der Stärkefließmittel untereinander zeigte, dass die anionische Ladungsmenge einen Schlüsselparameter darstellt. Die Stärkefließmittel M-1, K-1, W-1 und W-4 mit anionischen Ladungsmengen > 6 C/g zeigten die höchste Dispergier¬performance. Die vergleichend herangezogenen klassischen Fließmittel wiesen anionische Ladungsmengen im Bereich von 1,2 C/g (Polycondensat) und 1,6 C/g (PCE) auf. Die Molekularmasse schien für die Dispergierleistung zunächst unerheblich zu sein. Aus diesem Grund wurde die Basisweizenstärke erneut chemisch modifiziert, indem anionische Ladungen eingeführt wurden, ohne die Molekularmasse jedoch zu verringern. Das Stärkederivat wies verdickende Eigenschaften im Zementleim auf. Daraus konnte geschlussfolgert werden, dass eine definierte Grenzmolekularmasse (150.000 Da) existiert, die unterschritten werden muss, um Fließmittel aus Stärke zu erzeugen. Des Weiteren zeigen die Ergebnisse, dass durch die chemische Modifizierung sowohl Fließmittel als auch Verdicker aus Stärke erzeugt werden können.
Beurteilung der Beeinflussung der Hydratation und der Porenlösung des Portlandzementes
Aus der Literatur ist bekannt, dass Fließmittel die Hydratation von Portlandzement maßgeblich beeinflussen können. Aus diesem Grund wurden kalorimetrische und konduktometrische Untersuchungen an Zementsuspensionen, die mit den synthetisierten Stärkefließmitteln versetzt wurden, durchgeführt. Ergänzt wurden die Untersuchungen durch Porenlösungsanalysen zu verschiedenen Zeitpunkten der Hydratation.
6. Die kalorimetrischen Untersuchungen zur Beeinflussung der Hydratation des Portlandzementes zeigten, dass die dormante Periode durch die Zugabe der Stärkefließmittel z.T. erheblich verlängert wird. Es konnte gezeigt werden, dass, je höher die anionische Ladungsmenge der Stärkefließmittel ist, desto länger dauert die dormante Periode andauert. Darüber hinaus zeigte sich, dass eine niedrige Molekularmasse der Stärkefließmittel die Verlängerung der dormanten Periode begünstigt.
7. Durch die konduktometrischen Untersuchungen konnte gezeigt werden, dass alle Stärkefließmittel die Dauer des freien- und diffusionskontrollierten CSH-Phasenwachstums verlangsamen. Insbesondere die Ausfällung des Portlandits, welches mit dem Erstarrungsbeginn korreliert, erfolgt zu deutlich späteren Zeitpunkten. Des Weiteren korrelierten die konduktometrischen Untersuchungen mit der zeitlichen Entwicklung der Calciumkonzentration der Porenlösungen. Der Vergleich der Stärkefließmittel untereinander zeigte, dass die Molekularmasse ein Schlüsselparameter ist. Das Stärkefließmittel M-1 mit der geringsten Molekularmasse, welches geringe Mengen kurzkettiger Anhydroglucoseeinheiten aufweist, verzögert die Hydratphasenbildung am stärksten. Diese Wirkung ist vergleichbar mit der von Zuckern. Darüber hinaus deuteten die Ergebnisse daraufhin, dass die Stärkefließmittel auf den ersten Hydratationsprodukten adsorbieren, wodurch die Hydratphasenbildung verlangsamt wird.
Die kalorimetrischen und konduktometrischen Daten sowie die Ergebnisse der Porenlösungsanalytik des Zementes, erforderten eine genauere Betrachtung der Beeinflussung der Hydratation der Klinkerphasen C3A und C3S, durch die Stärkefließmittel. Demzufolge wurden die Untersuchungen mit den Klinkerphasen C3A und C3S in Analogie zum Portlandzement durchgeführt.
Beurteilung der Beeinflussung der Hydratation und der Porenlösung des C3A
Während die kalorimetrischen Untersuchungen zur C3A-Hydratation eine Tendenz zur verlangsamten Hydratphasenbildung durch die Stärkefließmittel aufzeigten, lieferten die konduktometrischen Ergebnisse grundlegende Erkenntnisse zur Beeinflussung der C3A-Hydratation. Das Stadium I der C3A-Hydratation ist durch einen Abfall der elektrischen Leitfähigkeit geprägt. Dies korreliert mit dem Absinken der Calciumionenkonzentration und dem Anstieg der Aluminiumionenkonzentration in der Porenlösung der C3A-Suspensionen. Im Anschluss an das Stadium I bildet sich ein Plateau in den elektrischen Leitfähigkeitskurven aus.
8. Es konnte gezeigt werden, dass die Stärkefließmittel das Stadium I der C3A-Hydratation, d.h. die Auflösung und Bildung erster Calciumaluminathydrate verlangsamen. Insbesondere die Stärkefließmittel mit höherer Molekularmasse erhöhten die Dauer des Stadium I. Das Stadium II wird durch die Stärkefließmittel in folgender Reihenfolge am stärksten verlängert: M-1 > W-3 > K-1 > W-2 ≥ W-4 und verdeutlicht, dass keine Abhängigkeit von der anionischen Ladungsmenge identifiziert werden konnte. Die Ergebnisse zeigten, dass speziell die kurzkettige Stärke M-1, das Stadium II länger aufrechterhalten.
9. Das Stadium III und IV der C3A-Hydratation wird insbesondere durch die Stärkefließmittel mit höherer Molekularmasse verlängert.
Die Ergebnisse der Porenlösungsanalytik korrelieren mit den Ergebnissen der elektrischen Leitfähigkeit. Speziell die zeitlichen Verläufe der Calciumionenkonzentration bildeten die Verläufe der Konduktivitätskurven der C3A-Hydratation mit großer Übereinstimmung ab.
Beurteilung der Beeinflussung der Hydratation und der Porenlösung des C3S
Die Ergebnisse der kalorimetrischen Untersuchungen zur Beeinflussung der C3S-Hydratation durch die Stärkefließmittel zeigen, dass diese maßgeblich verlangsamt wird. Das Maximum des Haupthydratationspeaks wird zu späteren Zeiten verschoben und auch die Höhe des Maximums wird deutlich verringert. Durch die konduktometrischen Experimente wurde aufgeklärt, welche Stadien der C3S-Hydrataion beeinflusst wurden.
10. Es konnte gezeigt werden, dass sowohl die Menge der eingebrachten anionischen Ladungen als auch das Vorhandensein sehr kleiner Stärkefließmittelmoleküle (Zucker), Schlüsselparameter der verzögerten Hydratationskinetik des C3S sind. Der grundlegende Mechanismus der Hydratationsverzögerung beruht auf einer Kombination aus verminderter CSH-Keimbildung und Adsorptionsprozessen auf den ersten gebildeten CSH-Phasen der C3S-Partikel.
Beurteilung des Adsorptionsverhaltens am Zement, C3A und C3S
Die Bestimmung des Adsorptionsverhaltens der Stärkefließmittel erfolgte mit der Phenol-Schwefelsäure-Methode an Zement,- C3A- und C3S-Suspensionen. Durch den Vergleich der Adsorptionsraten und Adsorptionsmengen in Abhängigkeit von den molekularen Parametern der Stärkefließmittel wurde ein Wechselwirkungsmodell identifiziert.
11. Die Ursache für die hohe Dispergierleistung der Stärkefließmittel liegt in Adsorptionsprozessen an den ersten gebildeten Hydratphasen des Zementes begründet. Die Molekularmasse der Stärkefließmittel ist ein Schlüsselparameter der entscheidend für den Mechanismus der Adsorption ist. Während anionische, langkettige Stärken an mehreren Zementpartikeln gleichzeitig adsorbieren und für eine Vernetzung der Zementpartikel untereinander sorgen (Verdickerwirkung), adsorbieren kurzkettige anionische Stärken lediglich an den ersten gebildeten Hydratphasen der einzelnen Zementpartikel und führen zu elektrostatischer Abstoßung (Fließmittelwirkung).
12. Es konnte gezeigt werden, dass die Stärkefließmittel mit geringerem Molekulargewicht bei höheren Konzentrationen an den Hydratphasen des Zementes adsorbieren. Die Stärkefließmittel mit höherer Molekularmasse erreichen bei einer Zugabemenge von 0,7 % ein Plateau. Daraus wird geschlussfolgert, dass die größeren Fließmittelmoleküle einen erhöhten Platzbedarf erfordern und zur Absättigung der hydratisierenden Oberflächen bei geringeren Zugabemengen führen. Darüber hinaus konnte gezeigt werden, dass die Stärkefließmittel mit höherer anionischer Ladungsmenge zu höheren Adsorptionsmengen auf den Zement-, C3A- und C3S-Partikeln führen.
13. Die Adsorptionsprozesse finden an den ersten gebildeten Hydratphasen der C3A-Partikel statt, wodurch sowohl die Auflösung des C3A als auch die Bildung der Calciumhydroaluminate verlangsamt wird. Darüber hinaus wurde festgestellt, dass die Verlangsamung des freien- und diffusionskontrollierten Hydratphasenwachstums des C3S, durch die Adsorption der Stärkefließmittel auf den ersten gebildeten CSH-Phasen hervorgerufen wird. Des Weiteren wurde festgestellt, dass sehr kleine zuckerähnliche Moleküle in der kurzkettigen Maniokstärke in der Lage sind, die Bildung der ersten CSH-Keime zu unterdrücken. Dadurch kann die langanhaltende Plateauphase der elektrischen Leitfähigkeit der C3S-Hydratation erklärt werden.
Beurteilung der Porenstruktur- und Festigkeitsausbildung
Die Beurteilung der Qualität der Mikrostruktur erfolgte durch die Bestimmung der Rohdichte und der Porenradienverteilung mit Hilfe der Quecksilberhochdruckporosimetrie. Durch das Versetzen der Zementleime mit den Stärkefließmitteln konnten bei gleichbleibender Verarbeitbarkeit Zementsteinprobekörper mit einem um 17,5 % geringeren w/z-Wert von 0,35 hergestellt werden. Die Absenkung des w/z-Wertes führt zu einem Anstieg der Rohdichte des Zementsteins.
14. Durch die Zugabe der Stärkefließmittel und den verringerten w/z-Wert wird die Porenstruktur der Zementsteinproben im Vergleich zum Referenzzementstein verfeinert, da die Gesamtporosität sinkt. Insbesondere der Kapillarporenanteil wird verringert und der Gelporenanteil erhöht. Im Unterschied zu den PCE-Fließmitteln führt die Zugabe der Stärkefließmittel zu keinem erhöhten Eintrag von Luftporen. Dies wiederum hat zur Folge, dass bei der Verwendung der Stärkefließmittel auf Entschäumer verzichtet werden kann.
15. Entsprechend der dichteren Zementsteinmatrix wurden für die Zementsteine mit den Stärkefließmitteln nach 7 d und 28 d, erhöhte Biegezug- und Druckfestigkeiten ermittelt. Insbesondere die 28 d Druckfestigkeit wurde durch den verringerten w/z-Wert um die Faktoren 3,5 - 6,6 erhöht.
Multi-criteria decision analysis (MCDA) is an established methodology to support the decision-making of multi-objective problems. For conducting an MCDA, in most cases, a set of objectives (SOO) is required, which consists of a hierarchical structure comprised of objectives, criteria, and indicators. The development of an SOO is usually based on moderated development processes requiring high organizational and cognitive effort from all stakeholders involved. This article proposes elementary interactions as a key paradigm of an algorithm-driven development process for an SOO that requires little moderation efforts. Elementary interactions are self-contained information requests that may be answered with little cognitive effort. The pairwise comparison of elements in the well-known analytical hierarchical process (AHP) is an example of an elementary interaction. Each elementary interaction in the development process presented contributes to the stepwise development of an SOO. Based on the hypothesis that an SOO may be developed exclusively using elementary interactions (EIs), a concept for a multi-user platform is proposed. Essential components of the platform are a Model Aggregator, an Elementary Interaction Stream Generator, a Participant Manager, and a Discussion Forum. While the latter component serves the professional exchange of the participants, the first three components are intended to be automatable by algorithms. The platform concept proposed has been evaluated partly in an explorative validation study demonstrating the general functionality of the algorithms outlined. In summary, the platform concept suggested demonstrates the potential to ease SOO development processes as the platform concept does not restrict the application domain; it is intended to work with little administration moderation efforts, and it supports the further development of an existing SOO in the event of changes in external conditions. The algorithm-driven development of SOOs proposed in this article may ease the development of MCDA applications and, thus, may have a positive effect on the spread of MCDA applications.
The aim of this study is controlling of spurious oscillations developing around discontinuous solutions of both linear and non-linear wave equations or hyperbolic partial differential equations (PDEs). The equations include both first-order and second-order (wave) hyperbolic systems. In these systems even smooth initial conditions, or smoothly varying source (load) terms could lead to discontinuous propagating solutions (fronts). For the first order hyperbolic PDEs, the concept of central high resolution schemes is integrated with the multiresolution-based adaptation to capture properly both discontinuous propagating fronts and effects of fine-scale responses on those of larger scales in the multiscale manner. This integration leads to using central high resolution schemes on non-uniform grids; however, such simulation is unstable, as the central schemes are originally developed to work properly on uniform cells/grids. Hence, the main concern is stable collaboration of central schemes and multiresoltion-based cell adapters. Regarding central schemes, the considered approaches are: 1) Second order central and central-upwind schemes; 2) Third order central schemes; 3) Third and fourth order central weighted non-oscillatory schemes (central-WENO or CWENO); 4) Piece-wise parabolic methods (PPMs) obtained with two different local stencils. For these methods, corresponding (nonlinear) stability conditions are studied and modified, as well. Based on these stability conditions several limiters are modified/developed as follows: 1) Several second-order limiters with total variation diminishing (TVD) feature, 2) Second-order uniformly high order accurate non-oscillatory (UNO) limiters, 3) Two third-order nonlinear scaling limiters, 4) Two new limiters for PPMs. Numerical results show that adaptive solvers lead to cost-effective computations (e.g., in some 1-D problems, number of adapted grid points are less than 200 points during simulations, while in the uniform-grid case, to have the same accuracy, using of 2049 points is essential). Also, in some cases, it is confirmed that fine scale responses have considerable effects on higher scales.
In numerical simulation of nonlinear first order hyperbolic systems, the two main concerns are: convergence and uniqueness. The former is important due to developing of the spurious oscillations, the numerical dispersion and the numerical dissipation. Convergence in a numerical solution does not guarantee that it is the physical/real one (the uniqueness feature). Indeed, a nonlinear systems can converge to several numerical results (which mathematically all of them are true). In this work, the convergence and uniqueness are directly studied on non-uniform grids/cells by the concepts of local numerical truncation error and numerical entropy production, respectively. Also, both of these concepts have been used for cell/grid adaptations. So, the performance of these concepts is also compared by the multiresolution-based method. Several 1-D and 2-D numerical examples are examined to confirm the efficiency of the adaptive solver. Examples involve problems with convex and non-convex fluxes. In the latter case, due to developing of complex waves, proper capturing of real answers needs more attention. For this purpose, using of method-adaptation seems to be essential (in parallel to the cell/grid adaptation). This new type of adaptation is also performed in the framework of the multiresolution analysis.
Regarding second order hyperbolic PDEs (mechanical waves), the regularization concept is used to cure artificial (numerical) oscillation effects, especially for high-gradient or discontinuous solutions. There, oscillations are removed by the regularization concept acting as a post-processor. Simulations will be performed directly on the second-order form of wave equations. It should be mentioned that it is possible to rewrite second order wave equations as a system of first-order waves, and then simulated the new system by high resolution schemes. However, this approach ends to increasing of variable numbers (especially for 3D problems).
The numerical discretization is performed by the compact finite difference (FD) formulation with desire feature; e.g., methods with spectral-like or optimized-error properties. These FD methods are developed to handle high frequency waves (such as waves near earthquake sources). The performance of several regularization approaches is studied (both theoretically and numerically); at last, a proper regularization approach controlling the Gibbs phenomenon is recommended.
At the end, some numerical results are provided to confirm efficiency of numerical solvers enhanced by the regularization concept. In this part, shock-like responses due to local and abrupt changing of physical properties, and also stress wave propagation in stochastic-like domains are studied.
Diese Dissertation untersucht Handlungsressourcen von zivilgesellschaftlichen Akteuren in Planungsprozessen um innerstädtische Planungsverfahren. Den theoretischen Rahmen bilden die Kapitalarten von Pierre Bourdieu, die zusammen mit dem Matrixraum von Dieter Läpple zu einem neuen Feldbegriff des ‚Raumfeldes‘ zusammengeführt und operationalisiert wurden. Es handelt sich um eine qualitative Arbeit, die zwischen Stadtsoziologie und Urbanistik zu verorten ist. Als Fallbeispiele wurde die Erweiterung des Berliner Mauerparks sowie das Baugebiet „So! Berlin“ in Berlin gewählt.
El paisaje de la Cuenca Lechera Central Argentina: la huella de la producción sobre el territorio
(2022)
In recent times, the study of landscape heritage acquires value by virtue of becoming an alternative to rethink regional development, especially from the point of view of territorial planning. In this sense, the Central Argentine Dairy Basin (CADB) is presented as a space where the traces of different human projects have accumulated over centuries of occupation, which can be read as heritage. The impact of dairy farming and other productive activities has shaped the configuration of its landscape. The main hypothesis assumed that a cultural landscape would have been formed in the CADB, whose configuration would have depended to a great extent on the history of productive activities and their deployment over the territory, and this same history would hide the keys to its alternative.
The thesis approached the object of study from descriptive and cartographic methods that placed the narration of the history of territory and the resources of the landscape as a discursive axis. A series of intentional readings of the territory and its constituent parts pondered the layers of data that have accumulated on it in the form of landscape traces, with the help of an approach from complementary dimensions (natural, sociocultural, productive, planning). Furthermore, the intersection of historical sources was used in order to allow the construction of the territorial story and the detection of the origin of the landscape components. A meticulous cartographic work also helped to spatialise the set of phenomena and elements studied, and was reflected in a multiscalar scanning.
Teilhabe an Gesundheitsversorgung von aufenthaltsrechtlich illegalisierten Menschen in Deutschland
(2022)
Die Gesundheitsversorgung in Deutschland ist seit den Bismarckschen Sozialreformen ein zunehmend institutionalisierter Teil der staatlichen Daseinsvorsorge im wohlfahrtsstaatlichen Gefüge. Institutionalisiert ist die Gesundheitsversorgung in korporatistischer Logik, das heißt in kooperativen Beziehungen zum privatwirtschaftlichen und zivilgesellschaftlichen Sektor und mit Befugnissen der Selbstverwaltung. Zudem fußt das Gesundheitssystem auf einem Versicherungssystem mit lohnabhängigen Abgaben. Institutionalisiert ist die staatliche Daseinsvorsorge jedoch auch in seinen Ausschlüssen. So werden Menschen ohne Bürgerrechte von vielen sozialen Rechten, wie von der Gesundheitsversorgung, ausgeschlossen, obwohl dieser Ausschluss im Widerspruch zu anderen konstitutiven Elementen des Nationalstaats steht.
In diesem Working Paper werden die grundlegende Strukturen des deutschen Gesundheitssystems und darin innewohnende Funktionslogiken der Produktion von Teilhabe dargestellt. Abschließend werden in Anlehnung an Kronauer die verschiedenen Dimensionen von Teilhabe an Gesundheitsversorgung in ihrer Produktions- und Ausschlusslogik im Wohlfahrtsregime dargelegt dabei auf die Gruppe der aufenthaltsrechtlich Illegalisierten fokussiert, denen gesellschaftliche Teilhabe in vielen Lebensbereichen, wie auch stark im Gesundheitsbereich, untersagt wird. Gleichzeitig soll dargestellt werden, wie zivilgesellschaftliche Akteur*innen auch gegen staatliche Vorgaben oder Anreize, Teilhabe (wieder-)herstellen.
Ernährung bestimmt unser tägliches Leben. Sie erfüllt in erster Linie die physiologische Notwendigkeit unseren Körper am Leben zu halten und ist gleichzeitig Alltagspraxis, durch welche gesamtgesellschaftliche Strukturen sichtbar werden. Innerhalb dieser Alltagspraxen erfüllt Ernährung vor allem eine wichtige Funktion in der Herstellung gesellschaftlicher Teilhabe oder kann strukturelle Ausschlüsse und soziale Ungleichheit bedingen. Dem Wohlfahrtsregime kommt somit eine wichtige Aufgabe in der Grundversorgung der Bevölkerung zu und muss innerhalb der Daseinsvorsorge auf Ausschlüsse von ernährungsbezogener Teilhabe einzelner Bevölkerungsschichten eingehen und sozialer Ungleichheit entgegenwirken. In diesem Working Paper soll der Fragestellung nachgegangen werden, inwiefern Teilhabe bzw. strukturelle Ausschlüsse von Ernährung innerhalb des bundesdeutschen Wohlfahrtsregimes hergestellt werden und durch welche politischen Praktiken und Forderungen aus der Zivilgesellschaft bzw. sozialen Bewegungen ernährungsvermittelte Teilhabe (wieder) hergestellt wird.
Hitze in der Stadt Jena
(2022)
Die vorliegende Arbeit befasst sich mit den spezifischen Faktoren und Wechselwirkungen des städtischen Klimas und Strategien zur Prävention und Kompensation lokaler Klimaveränderungen. Problematische Merkmale des Stadtklimas werden sich infolge des Klimawandels stärker ausprägen. Insbesondere die Hitzebelastung wird zunehmen und die Lebensbedingungen in der Stadt negativ beeinflussen. Infolge höherer Temperaturen in Städten und einer höheren Temperaturdifferenz zum Umland verändern sich Windströme und die Wasserbilanz. Es sind Strategien notwendig, um den Schadstoffausstoß, die Flächeninanspruchnahme, die Abfallproduktion und den Wasser-, Energie- und Ressourcenverbrauch zu verringern, um sowohl langfristig den Klimawandel als auch dessen bereits unvermeidbaren Auswirkungen auf Städte zu begrenzen.
Beispielhaft untersucht die Arbeit das Stadtklima, dessen zukünftige Veränderungen infolge des Klimawandels, bauliche Maßnahmen und Anpassungsstrategien der Stadt Jena. Jena ist die zweitgrößte Stadt im Bundesland Thüringen und gehört heute zu den wärmsten und trockensten Großstädten Deutschlands.
Die Ergebnisse der Arbeit werden anschließend anhand eines städtebaulichen Konzepts und Entwurfs angewendet. Das Bachstraßenareal liegt in der Innenstadt, dem am stärksten von Hitze betroffenen Stadtteil. Als ehemaliger Hauptstandort des Jenaer Universitätsklinikums, soll es zu einem nachhaltigen Wissenschaftscampus der Lebenswissenschaften umgebaut werden, wobei ein Großteil der denkmalgeschützten, ehemaligen Klinikgebäude erhalten bleibt. Der Fokus liegt dabei auf der Umsetzung der zuvor formulierten, nachhaltigen Strategien zur Verbesserung des lokalen Stadtklimas und einer Abschwächung der Auswirkungen des Klimawandels auf den besonders stark betroffenen Innenstadtbereich Jenas.
Warum werden in aktuellen Diskussionen Wohnungsgenossenschaften immer wieder als zentrale Akteure einer gemeinwohlorientierten Wohnraumversorgung benannt – obwohl sie kaum zur Schaffung neuen bezahlbaren Wohnraums beitragen? Warum wehrt sich die Mehrzahl der Wohnungsgenossenschaften mit Händen und Füßen gegen die Wiedereinführung eines Gesetzes zur Wohnungsgemeinnützigkeit, obwohl es doch gerade dieses Gesetz war, dass sie im 20. Jahrhundert zu im internationalen Vergleich großen Unternehmen wachsen ließ? Sind Wohnungsgenossenschaften nun klientilistische, wenig demokratische und nur halb dekommodifizierte Marktteilnehmer oder wichtiger Teil der Wohnungsversorgung der unteren Mittelschicht? Wer Antworten auf diese und andere Fragen sucht und Differenziertheit in ihrer Beantwortung aushält, lese Joscha Metzers Dissertation „Genossenschaften und die Wohnungsfrage.
Plastic structural analysis may be applied without any difficulty and with little effort for structural member verifications with regard to lateral torsional buckling of doubly symmetric rolled I sections. Suchlike analyses can be performed based on the plastic zone theory, specifically using finite beam elements with seven degrees of freedom and 2nd order theory considering material nonlinearity. The existing Eurocode enables these approaches and the coming-up generation will provide corresponding regulations in EN 1993-1-14. The investigations allow the determination of computationally accurate limit loads, which are determined in the present paper for selected structural systems with different sets of parameters, such as length, steel grade and cross section types. The results are compared to approximations gained by more sophisticated FEM analyses (commercial software Ansys Workbench applying solid elements) for reasons of verification/validation. In this course, differences in the results of the numerical models are addressed and discussed. In addition, results are compared to resistances obtained by common design regulations based on reduction factors χlt including regulations of EN 1993-1-1 (including German National Annex) as well as prEN 1993-1-1: 2020-08 (proposed new Eurocode generation). Concluding, correlations of results and their advantages as well as disadvantages are discussed.
Vertical green system for gray water treatment: Analysis of the VertiKKA-module in a field test
(2022)
This work presents a modular Vertical Green System (VGS) for gray water treatment, developed at the Bauhaus-Universität Weimar. The concept was transformed into a field study with four modules built and tested with synthetic gray water. Each module set contains a small and larger module with the same treatment substrate and was fed hourly. A combination of lightweight structural material and biochar of agricultural residues and wood chips was used as the treatment substrate. In this article, we present the first 18 weeks of operation. Regarding the treatment efficiency, the parameters chemical oxygen demand (COD), total phosphorous (TP), ortho-phosphate (ortho-P), total bound nitrogen (TNb), ammonium nitrogen (NH4-N), and nitrate nitrogen (NO3-N) were analyzed and are presented in this work. The results of the modules with agricultural residues are promising. Up to 92% COD reduction is stated in the data. The phosphate and nitrogen fractions are reduced significantly in these modules. By contrast, the modules with wood chips reduce only 67% of the incoming COD and respectively less regarding phosphates and the nitrogen fraction.
Material failure can be tackled by so-called nonlocal models, which introduce an intrinsic length scale into the formulation and, in the case of material failure, restore the well-posedness of the underlying boundary value problem or initial boundary value problem. Among nonlocal models, peridynamics (PD) has attracted a lot of attention as it allows the natural transition from continuum to discontinue and thus allows modeling of discrete cracks without the need to describe and track the crack topology, which has been a major obstacle in traditional discrete crack approaches. This is achieved by replacing the divergence of the Cauchy stress tensor through an integral over so-called bond forces, which account for the interaction of particles. A quasi-continuum approach is then used to calibrate the material parameters of the bond forces, i.e., equating the PD energy with the energy of a continuum. One major issue for the application of PD to general complex problems is that they are limited to fairly simple material behavior and pure mechanical problems based on explicit time integration. PD has been extended to other applications but losing simultaneously its simplicity and ease in modeling material failure. Furthermore, conventional PD suffers from instability and hourglass modes that require stabilization. It also requires the use of constant horizon sizes, which drastically reduces its computational efficiency. The latter issue was resolved by the so-called dual-horizon peridynamics (DH-PD) formulation and the introduction of the duality of horizons.
Within the nonlocal operator method (NOM), the concept of nonlocality is further extended and can be considered a generalization of DH-PD. Combined with the energy functionals of various physical models, the nonlocal forms based on the dual-support concept can be derived. In addition, the variation of the energy functional allows implicit formulations of the nonlocal theory. While traditional integral equations are formulated in an integral domain, the dual-support approaches are based on dual integral domains. One prominent feature of NOM is its compatibility with variational and weighted residual methods. The NOM yields a direct numerical implementation based on the weighted residual method for many physical problems without the need for shape functions. Only the definition of the energy or boundary value problem is needed to drastically facilitate the implementation. The nonlocal operator plays an equivalent role to the derivatives of the shape functions in meshless methods and finite element methods (FEM). Based on the variational principle, the residual and the tangent stiffness matrix can be obtained with ease by a series of matrix multiplications. In addition, NOM can be used to derive many nonlocal models in strong form.
The principal contributions of this dissertation are the implementation and application of NOM, and also the development of approaches for dealing with fractures within the NOM, mostly for dynamic fractures. The primary coverage and results of the dissertation are as follows:
-The first/higher-order implicit NOM and explicit NOM, including a detailed description of the implementation, are presented. The NOM is based on so-called support, dual-support, nonlocal operators, and an operate energy functional ensuring stability. The nonlocal operator is a generalization of the conventional differential operators. Combining with the method of weighted residuals and variational principles, NOM establishes the residual and tangent stiffness matrix of operate energy functional through some simple matrix without the need of shape functions as in other classical computational methods such as FEM. NOM only requires the definition of the energy drastically simplifying its implementation. For the sake of conciseness, the implementation in this chapter is focused on linear elastic solids only, though the NOM can handle more complex nonlinear problems. An explicit nonlocal operator method for the dynamic analysis of elasticity solid problems is also presented. The explicit NOM avoids the calculation of the tangent stiffness matrix as in the implicit NOM model. The explicit scheme comprises the Verlet-velocity algorithm. The NOM can be very flexible and efficient for solving partial differential equations (PDEs). It's also quite easy for readers to use the NOM and extend it to solve other complicated physical phenomena described by one or a set of PDEs. Several numerical examples are presented to show the capabilities of this method.
-A nonlocal operator method for the dynamic analysis of (thin) Kirchhoff plates is proposed. The nonlocal Hessian operator is derived from a second-order Taylor series expansion. NOM is higher-order continuous, which is exploited for thin plate analysis that requires $C^1$ continuity. The nonlocal dynamic governing formulation and operator energy functional for Kirchhoff plates are derived from a variational principle. The Verlet-velocity algorithm is used for time discretization. After confirming the accuracy of the nonlocal Hessian operator, several numerical examples are simulated by the nonlocal dynamic Kirchhoff plate formulation.
-A nonlocal fracture modeling is developed and applied to the simulation of quasi-static and dynamic fractures using the NOM. The phase field's nonlocal weak and associated strong forms are derived from a variational principle. The NOM requires only the definition of energy. We present both a nonlocal implicit phase field model and a nonlocal explicit phase field model for fracture; the first approach is better suited for quasi-static fracture problems, while the key application of the latter one is dynamic fracture. To demonstrate the performance of the underlying approach, several benchmark examples for quasi-static and dynamic fracture are solved.
Analysis of Functionally Graded Porous Materials Using Deep Energy Method and Analytical Solution
(2022)
Porous materials are an emerging branch of engineering materials that are composed of two elements: One element is a solid (matrix), and the other element is either liquid or gas. Pores can be distributed within the solid matrix of porous materials with different shapes and sizes. In addition, porous materials are lightweight, and flexible, and have higher resistance to crack propagation and specific thermal, mechanical, and magnetic properties. These properties are necessary for manufacturing engineering structures such as beams and other engineering structures. These materials are widely used in solid mechanics and are considered a good replacement for classical materials by many researchers recently. Producing lightweight materials has been developed because of the possibility of exploiting the properties of these materials. Various types of porous material are generated naturally or artificially for a specific application such as bones and foams. Like functionally graded materials, pore distribution patterns can be uniform or non-uniform. Biot’s theory is a well-developed theory to study the behavior of poroelastic materials which investigates the interaction between fluid and solid phases of a fluid-saturated porous medium.
Functionally graded porous materials (FGPM) are widely used in modern industries, such as aerospace, automotive, and biomechanics. These advanced materials have some specific properties compared to materials with a classic structure. They are extremely light, while they have specific strength in mechanical and high-temperature environments. FGPMs are characterized by a gradual variation of material parameters over the volume. Although these materials can be made naturally, it is possible to design and manufacture them for a specific application. Therefore, many studies have been done to analyze the mechanical and thermal properties of FGPM structures, especially beams.
Biot was the pioneer in formulating the linear elasticity and thermoelasticity equations of porous material. Since then, Biot's formulation has been developed in continuum mechanics which is named poroelasticity. There are obstacles to analyzing the behavior of these materials accurately like the shape of the pores, the distribution of pores in the material, and the behavior of the fluid (or gas) that saturated pores. Indeed, most of the engineering structures made of FGPM have nonlinear governing equations. Therefore, it is difficult to study engineering structures by solving these complicated equations.
The main purpose of this dissertation is to analyze porous materials in engineering structures. For this purpose, the complex equations of porous materials have been simplified and applied to engineering problems so that the effect of all parameters of porous materials on the behavior of engineering structure has been investigated.
The effect of important parameters of porous materials on beam behavior including pores compressibility, porosity distribution, thermal expansion of fluid within pores, the interaction of stresses between pores and material matrix due to temperature increase, effects of pore size, material thickness, and saturated pores with fluid and unsaturated conditions are investigated.
Two methods, the deep energy method, and the exact solution have been used to reduce the problem hypotheses, increase accuracy, increase processing speed, and apply these in engineering structures. In both methods, they are analyzed nonlinear and complex equations of porous materials.
To increase the accuracy of analysis and study of the effect of shear forces, Timoshenko and Reddy's beam theories have been used. Also, neural networks such as residual and fully connected networks are designed to have high accuracy and less processing time than other computational methods.
Atlas der Datenkörper. Körperbilder in Kunst, Design und Wissenschaft im Zeitalter digitaler Medien
(2022)
Digitale Technologien und soziale Medien verändern die Selbst- und Körperwahrnehmung und verzerren, verstärken oder produzieren dabei spezifische Körperbilder. Die Beiträger*innen kartographieren diese Phänomene, fragen nach ihrer medialen Existenzweise sowie nach den Möglichkeiten ihrer Kritik. Dabei begegnen sie ihrer Neuartigkeit mit einer transdisziplinären Herangehensweise. Aus sowohl der Perspektive künstlerischer und gestalterischer Forschung als auch der Kunst-, Kultur- und Medienwissenschaft sowie der Psychologie und Neurowissenschaft wird die Landschaft rezenter Körperbilder und Techniken einer digitalen Körperlichkeit untersucht.
Zugang zu gesunder und nachhaltiger Ernährung ist in Berlin nicht für alle Menschen eine Selbstverständlichkeit. Um Ernährung für alle gewährleisten zu können, braucht es einen Wandel des Ernährungssystems in Berlin, der eine ökologische, klima- und sozialgerechte Nahrungsproduktion und Verteilung für alle Menschen in der Stadt ermöglicht.
Einen Beitrag um die Ernährung in der Stadt gerechter und nachhaltiger zu gestalten kann ein sogenannter LebensMittelPunkt (LMP) leisten.
LebensMittelPunkte entstehen meist aus ehrenamtlichen Initiativen, können aber auch in Zusammenarbeit mit städtischen Verwaltungen etabliert werden. Eine Zusammenarbeit zwischen zivilgesellschaftlichen Organisationen und Verwaltungen kann dabei Potenziale und Ressourcen freisetzen.
Dieser Leitfaden soll ernährungspolitischen Initiativen und Vereinen aus der Zivilgesellschaft sowie kommunalen oder bezirklichen Verwaltungen in Berlin – und darüber hinaus – Empfehlungen geben, wie ein LebensMittelPunkt in einer gemeinsamen Kooperation aufgebaut werden kann.
Städten kam bei demokratischen Innovationsprozessen immer eine zentrale Rolle zu. Die öffentlichen Verwaltungen der großen Städte stellten Regeln für die Einführung und Ausweitung der bürgerschaftlichen Partizipation auf und reagierten damit auf Erfahrungen und Forderungen, die von der schöpferischen politischen Kraft der sozialen und urbanen Bewegungen getragen wurden. Die Geschichte Barcelonas ist dafür ein typisches Beispiel.
Dank dieser sozialen Errungenschaften können wir von einer Reihe von Gütern und Dienstleistungen profitieren, die lokale Wohlfahrtssysteme ausmachen. Die Stadtverwal-tungen übernehmen die Aufgabe, Ressourcen und Dienstleistungen bereitzustellen, die nicht nur mit Wohlfahrt und Gesundheit in Verbindung stehen, sondern auch mit der Sorge um Umfeld und Umwelt, mit der Förderung von Maßnahmen in Bereichen wie Bildung, Kultur, Kunst oder Sport sowie mit der Dynamisierung von Wirtschaft und Gesellschaft. Ob zuständig oder nicht, die Kommunen müssen auf die Forderungen der Bürger*innen reagieren, sind sie doch die Verwaltungen, die den alltäglichen Problemen und Bedürfnissen am nächsten stehen. Daher liegt es weniger im Belieben der Stadtverwaltungen, ob sie notwendige Innova¬tionen anstoßen, sondern diese sind vielmehr Teil ihres Aufgabenbereichs.
Um den Bedürfnissen der Bürger*innen seitens der öffentlichen Verwaltung gerecht zu werden, kam in den meisten Fällen eine von zwei Methoden zur Anwendung: die direkte Verwaltung durch die Behörden oder die indirekte Verwaltung mit dem privaten Sektor. Mit dem Anbruch einer neuen Zeit, in der alternative Methoden an Bedeutung gewonnen haben, wächst das Interesse an Modellen öffentlich-zivilgesellschaftlicher Zusammenarbeit. Hauptziel dieser Modelle ist es, Verwaltungen und Bürgerschaft eine Zusammenarbeit im gemeinsamen und allgemeinen Interesse zu ermöglichen, indem Projekte unterstützt werden, die Zugang, Nähe und Partizipation in sich vereinen. Vor diesem Hintergrund bietet die Verwaltung öffent¬licher Ressourcen Möglichkeiten zur Entwicklung neuer Formen kollektiver Intelligenz, mit ge¬meinsamer Verantwortung und Synergie zwischen Institution und Bürgerschaft, sodass die Städte zu wahrhaft kooperativen Plattformen für öffentliche Innovationen werden.
The Finite Element Method (FEM) is widely used in engineering for solving Partial Differential Equations (PDEs) over complex geometries. To this end, it is required to provide the FEM software with a geometric model that is typically constructed in a Computer-Aided Design (CAD) software. However, FEM and CAD use different approaches for the mathematical description of the geometry. Thus, it is required to generate a mesh, which is suitable for FEM, based on the CAD model. Nonetheless, this procedure is not a trivial task and it can be time consuming. This issue becomes more significant for solving shape and topology optimization problems, which consist in evolving the geometry iteratively. Therefore, the computational cost associated to the mesh generation process is increased exponentially for this type of applications.
The main goal of this work is to investigate the integration of CAD and CAE in shape and topology optimization. To this end, numerical tools that close the gap between design and analysis are presented. The specific objectives of this work are listed below:
• Automatize the sensitivity analysis in an isogeometric framework for applications in shape optimization. Applications for linear elasticity are considered.
• A methodology is developed for providing a direct link between the CAD model and the analysis mesh. In consequence, the sensitivity analysis can be performed in terms of the design variables located in the design model.
• The last objective is to develop an isogeometric method for shape and topological optimization. This method should take advantage of using Non-Uniform Rational B-Splines (NURBS) with higher continuity as basis functions.
Isogeometric Analysis (IGA) is a framework designed to integrate the design and analysis in engineering problems. The fundamental idea of IGA is to use the same basis functions for modeling the geometry, usually NURBS, for the approximation of the solution fields. The advantage of integrating design and analysis is two-fold. First, the analysis stage is more accurate since the system of PDEs is not solved using an approximated geometry, but the exact CAD model. Moreover, providing a direct link between the design and analysis discretizations makes possible the implementation of efficient sensitivity analysis methods. Second, the computational time is significantly reduced because the mesh generation process can be avoided.
Sensitivity analysis is essential for solving optimization problems when gradient-based optimization algorithms are employed. Automatic differentiation can compute exact gradients, automatically by tracking the algebraic operations performed on the design variables. For the automation of the sensitivity analysis, an isogeometric framework is used. Here, the analysis mesh is obtained after carrying out successive refinements, while retaining the coarse geometry for the domain design. An automatic differentiation (AD) toolbox is used to perform the sensitivity analysis. The AD toolbox takes the code for computing the objective and constraint functions as input. Then, using a source code transformation approach, it outputs a code for computing the objective and constraint functions, and their sensitivities as well. The sensitivities obtained from the sensitivity propagation method are compared with analytical sensitivities, which are computed using a full isogeometric approach.
The computational efficiency of AD is comparable to that of analytical sensitivities. However, the memory requirements are larger for AD. Therefore, AD is preferable if the memory requirements are satisfied. Automatic sensitivity analysis demonstrates its practicality since it simplifies the work of engineers and designers.
Complex geometries with sharp edges and/or holes cannot easily be described with NURBS. One solution is the use of unstructured meshes. Simplex-elements (triangles and tetrahedra for two and three dimensions respectively) are particularly useful since they can automatically parameterize a wide variety of domains. In this regard, unstructured Bézier elements, commonly used in CAD, can be employed for the exact modelling of CAD boundary representations. In two dimensions, the domain enclosed by NURBS curves is parameterized with Bézier triangles. To describe exactly the boundary of a two-dimensional CAD model, the continuity of a NURBS boundary representation is reduced to C^0. Then, the control points are used to generate a triangulation such that the boundary of the domain is identical to the initial CAD boundary representation. Thus, a direct link between the design and analysis discretizations is provided and the sensitivities can be propagated to the design domain.
In three dimensions, the initial CAD boundary representation is given as a collection of NURBS surfaces that enclose a volume. Using a mesh generator (Gmsh), a tetrahedral mesh is obtained. The original surface is reconstructed by modifying the location of the control points of the tetrahedral mesh using Bézier tetrahedral elements and a point inversion algorithm. This method offers the possibility of computing the sensitivity analysis using the analysis mesh. Then, the sensitivities can be propagated into the design discretization. To reuse the mesh originally generated, a moving Bézier tetrahedral mesh approach was implemented.
A gradient-based optimization algorithm is employed together with a sensitivity propagation procedure for the shape optimization cases. The proposed shape optimization approaches are used to solve some standard benchmark problems in structural mechanics. The results obtained show that the proposed approach can compute accurate gradients and evolve the geometry towards optimal solutions. In three dimensions, the moving mesh approach results in faster convergence in terms of computational time and avoids remeshing at each optimization step.
For considering topological changes in a CAD-based framework, an isogeometric phase-field based shape and topology optimization is developed. In this case, the diffuse interface of a phase-field variable over a design domain implicitly describes the boundaries of the geometry. The design variables are the local values of the phase-field variable. The descent direction to minimize the objective function is found by using the sensitivities of the objective function with respect to the design variables. The evolution of the phase-field is determined by solving the time dependent Allen-Cahn equation.
Especially for topology optimization problems that require C^1 continuity, such as for flexoelectric structures, the isogeometric phase field method is of great advantage. NURBS can achieve the desired continuity more efficiently than the traditional employed functions. The robustness of the method is demonstrated when applied to different geometries, boundary conditions, and material configurations. The applications illustrate that compared to piezoelectricity, the electrical performance of flexoelectric microbeams is larger under bending. In contrast, the electrical power for a structure under compression becomes larger with piezoelectricity.
Finite Element Simulations of dynamically excited structures are mainly influenced by the mass, stiffness, and damping properties of the system, as well as external loads. The prediction quality of dynamic simulations of vibration-sensitive components depends significantly on the use of appropriate damping models. Damping phenomena have a decisive influence on the vibration amplitude and the frequencies of the vibrating structure. However, developing realistic damping models is challenging due to the multiple sources that cause energy dissipation, such as material damping, different types of friction, or various interactions with the environment.
This thesis focuses on thermoelastic damping, which is the main cause of material damping in homogeneous materials. The effect is caused by temperature changes due to mechanical strains. In vibrating structures, temperature gradients arise in adjacent tension and compression areas. Depending on the vibration frequency, they result in heat flows, leading to increased entropy and the irreversible transformation of mechanical energy into thermal energy.
The central objective of this thesis is the development of efficient simulation methods to incorporate thermoelastic damping in finite element analyses based on modal superposition. The thermoelastic loss factor is derived from the structure's mechanical mode shapes and eigenfrequencies. In subsequent analyses that are performed in the time and frequency domain, it is applied as modal damping.
Two approaches are developed to determine the thermoelastic loss in thin-walled plate structures, as well as three-dimensional solid structures. The realistic representation of the dissipation effects is verified by comparing the simulation results with experimentally determined data. Therefore, an experimental setup is developed to measure material damping, excluding other sources of energy dissipation.
The three-dimensional solid approach is based on the determination of the generated entropy and therefore the generated heat per vibration cycle, which is a measure for thermoelastic loss in relation to the total strain energy. For thin plate structures, the amount of bending energy in a modal deformation is calculated and summarized in the so-called Modal Bending Factor (MBF). The highest amount of thermoelastic loss occurs in the state of pure bending. Therefore, the MBF enables a quantitative classification of the mode shapes concerning the thermoelastic damping potential.
The results of the developed simulations are in good agreement with the experimental results and are appropriate to predict thermoelastic loss factors. Both approaches are based on modal superposition with the advantage of a high computational efficiency. Overall, the modeling of thermoelastic damping represents an important component in a comprehensive damping model, which is necessary to perform realistic simulations of vibration processes.
In recent years, lightweight materials, such as polymer composite materials (PNCs) have been studied and developed due to their excellent physical and chemical properties. Structures composed of these composite materials are widely used in aerospace engineering structures, automotive components, and electrical devices. The excellent and outstanding mechanical, thermal, and electrical properties of Carbon nanotube (CNT) make it an ideal filler to strengthen polymer materials’ comparable properties. The heat transfer of composite materials has very promising engineering applications in many fields, especially in electronic devices and energy storage equipment. It is essential in high-energy density systems since electronic components need heat dissipation functionality. Or in other words, in electronic devices the generated heat should ideally be dissipated by light and small heat sinks.
Polymeric composites consist of fillers embedded in a polymer matrix, the first ones will significantly affect the overall (macroscopic) performance of the material. There are many common carbon-based fillers such as single-walled carbon nanotubes (SWCNT), multi-walled carbon nanotubes (MWCNT), carbon nanobuds (CNB), fullerene, and graphene. Additives inside the matrix have become a popular subject for researchers. Some extraordinary characters, such as high-performance load, lightweight design, excellent chemical resistance, easy processing, and heat transfer, make the design of polymeric nanotube composites (PNCs) flexible. Due to the reinforcing effects with different fillers on composite materials, it has a higher degree of freedom and can be designed for the structure according to specific applications’ needs. As already stated, our research focus will be on SWCNT enhanced PNCs. Since experiments are timeconsuming, sometimes expensive and cannot shed light into phenomena taking place for instance at the interfaces/interphases of composites, they are often complemented through theoretical and computational analysis.
While most studies are based on deterministic approaches, there is a comparatively lower number of stochastic methods accounting for uncertainties in the input parameters. In deterministic models, the output of the model is fully determined by the parameter values and the initial conditions. However, uncertainties in the input parameters such as aspect ratio, volume fraction, thermal properties of fiber and matrix need to be taken into account for reliable predictions. In this research, a stochastic multiscale method is provided to study the influence of numerous uncertain input parameters on the thermal conductivity of the composite. Therefore, a hierarchical multi-scale method based on computational homogenization is presented in to predict the macroscopic thermal conductivity based on the fine-scale structure. In order to study the inner mechanism, we use the finite element method and employ surrogate models to conduct a Global Sensitivity Analysis (GSA). The SA is performed in order to quantify the influence of the conductivity of the fiber, matrix, Kapitza resistance, volume fraction and aspect ratio on the macroscopic conductivity. Therefore, we compute first-order and total-effect sensitivity indices with different surrogate models.
As stochastic multiscale models are computational expensive, surrogate approaches are commonly exploited. With the emergence of high performance computing and artificial intelligence, machine learning has become a popular modeling tool for numerous applications. Machine learning (ML) is commonly used in regression and maps data through specific rules with algorithms to build input and output models. They are particularly useful for nonlinear input-output relationships when sufficient data is available. ML has also been used in the design of new materials and multiscale analysis. For instance, Artificial neural networks and integrated learning seem to be ideally for such a task. They can theoretically simulate any non-linear relationship through the connection of neurons. Mapping relationships are employed to carry out data-driven simulations of inputs and outputs in stochastic modeling.
This research aims to develop a stochastic multi-scale computational models of PNCs in heat transfer. Multi-scale stochastic modeling with uncertainty analysis and machine learning methods consist of the following components:
-Uncertainty Analysis. A surrogate based global sensitivity analysis is coupled with a hierarchical multi-scale method employing computational homogenization. The effect of the conductivity of the fibers and the matrix, the Kapitza resistance, volume fraction and aspect ratio on the ’macroscopic’ conductivity of the composite is systematically studied. All selected surrogate models yield consistently the conclusions that the most influential input parameters are the aspect ratio followed by the volume fraction. The Kapitza Resistance has no significant effect on the thermal conductivity of the PNCs. The most accurate surrogate model in terms of the R2 value is the moving least square (MLS).
-Hybrid Machine Learning Algorithms. A combination of artificial neural network (ANN) and particle swarm optimization (PSO) is applied to estimate the relationship between variable input and output parameters. The ANN is used for modeling the composite while PSO improves the prediction performance through an optimized global minimum search. The thermal conductivity of the fibers and the matrix, the kapitza resistance, volume fraction and aspect ratio are selected as input parameters. The output is the macroscopic (homogenized) thermal conductivity of the composite. The results show that the PSO significantly improves the predictive ability of this hybrid intelligent algorithm, which outperforms traditional neural networks.
-Stochastic Integrated Machine Learning. A stochastic integrated machine learning based multiscale approach for the prediction of the macroscopic thermal conductivity in PNCs is developed. Seven types of machine learning models are exploited in this research, namely Multivariate Adaptive Regression Splines (MARS), Support Vector Machine (SVM), Regression Tree (RT), Bagging Tree (Bag), Random Forest (RF), Gradient Boosting Machine (GBM) and Cubist. They are used as components of stochastic modeling to construct the relationship between the variable of the inputs’ uncertainty and the macroscopic thermal conductivity of PNCs. Particle Swarm Optimization (PSO) is used for hyper-parameter tuning to find the global optimal values leading to a significant reduction in the computational cost. The advantages and disadvantages of various methods are also analyzed in terms of computing time and model complexity to finally give a recommendation for the applicability of different models.
The detailed structural analysis of thin-walled circular pipe members often requires the use of a shell or solid-based finite element method. Although these methods provide a very good approximation of the deformations, they require a higher degree of discretization which causes high computational costs. On the other hand, the analysis of thin-walled circular pipe members based on classical beam theories is easy to implement and needs much less computation time, however, they are limited in their ability to approximate the deformations as they cannot consider the deformation of the cross-section.
This dissertation focuses on the study of the Generalized Beam Theory (GBT) which is both accurate and efficient in analyzing thin-walled members. This theory is based on the separation of variables in which the displacement field is expressed as a combination of predetermined deformation modes related to the cross-section, and unknown amplitude functions defined on the beam's longitudinal axis. Although the GBT was initially developed for long straight members, through the consideration of complementary deformation modes, which amend the null transverse and shear membrane strain assumptions of the classical GBT, problems involving short members, pipe bends, and geometrical nonlinearity can also be analyzed using GBT. In this dissertation, the GBT formulation for the analysis of these problems is developed and the application and capabilities of the method are illustrated using several numerical examples. Furthermore, the displacement and stress field results of these examples are verified using an equivalent refined shell-based finite element model.
The developed static and dynamic GBT formulations for curved thin-walled circular pipes are based on the linear kinematic description of the curved shell theory. In these formulations, the complex problem in pipe bends due to the strong coupling effect of the longitudinal bending, warping and the cross-sectional ovalization is handled precisely through the derivation of the coupling tensors between the considered GBT deformation modes. Similarly, the geometrically nonlinear GBT analysis is formulated for thin-walled circular pipes based on the nonlinear membrane kinematic equations. Here, the initial linear and quadratic stress and displacement tangent stiffness matrices are built using the third and fourth-order GBT deformation mode coupling tensors.
Longitudinally, the formulation of the coupled GBT element stiffness and mass matrices are presented using a beam-based finite element formulation. Furthermore, the formulated GBT elements are tested for shear and membrane locking problems and the limitations of the formulations regarding the membrane locking problem are discussed.
Isogeometric analysis (IGA) is a numerical method for solving partial differential equations (PDEs), which was introduced with the aim of integrating finite element analysis with computer-aided design systems. The main idea of the method is to use the same spline basis functions which describe the geometry in CAD systems for the approximation of solution fields in the finite element method (FEM). Originally, NURBS which is a standard technology employed in CAD systems was adopted as basis functions in IGA but there were several variants of IGA using other technologies such as T-splines, PHT splines, and subdivision surfaces as basis functions. In general, IGA offers two key advantages over classical FEM: (i) by describing the CAD geometry exactly using smooth, high-order spline functions, the mesh generation process is simplified and the interoperability between CAD and FEM is improved, (ii) IGA can be viewed as a high-order finite element method which offers basis functions with high inter-element continuity and therefore can provide a primal variational formulation of high-order PDEs in a straightforward fashion. The main goal of this thesis is to further advance isogeometric analysis by exploiting these major advantages, namely precise geometric modeling and the use of smooth high-order splines as basis functions, and develop robust computational methods for problems with complex geometry and/or complex multi-physics.
As the first contribution of this thesis, we leverage the precise geometric modeling of isogeometric analysis and propose a new method for its coupling with meshfree discretizations. We exploit the strengths of both methods by using IGA to provide a smooth, geometrically-exact surface discretization of the problem domain boundary, while the Reproducing Kernel Particle Method (RKPM) discretization is used to provide the volumetric discretization of the domain interior. The coupling strategy is based upon the higher-order consistency or reproducing conditions that are directly imposed in the physical domain. The resulting coupled method enjoys several favorable features: (i) it preserves the geometric exactness of IGA, (ii) it circumvents the need for global volumetric parameterization of the problem domain, (iii) it achieves arbitrary-order approximation accuracy while preserving higher-order smoothness of the discretization. Several numerical examples are solved to show the optimal convergence properties of the coupled IGA–RKPM formulation, and to demonstrate its effectiveness in constructing volumetric discretizations for complex-geometry objects.
As for the next contribution, we exploit the use of smooth, high-order spline basis functions in IGA to solve high-order surface PDEs governing the morphological evolution of vesicles. These governing equations are often consisted of geometric PDEs, high-order PDEs on stationary or evolving surfaces, or a combination of them. We propose an isogeometric formulation for solving these PDEs. In the context of geometric PDEs, we consider phase-field approximations of mean curvature flow and Willmore flow problems and numerically study the convergence behavior of isogeometric analysis for these problems. As a model problem for high-order PDEs on stationary surfaces, we consider the Cahn–Hilliard equation on a sphere, where the surface is modeled using a phase-field approach. As for the high-order PDEs on evolving surfaces, a phase-field model of a deforming multi-component vesicle, which consists of two fourth-order nonlinear PDEs, is solved using the isogeometric analysis in a primal variational framework. Through several numerical examples in 2D, 3D and axisymmetric 3D settings, we show the robustness of IGA for solving the considered phase-field models.
Finally, we present a monolithic, implicit formulation based on isogeometric analysis and generalized-alpha time integration for simulating hydrodynamics of vesicles according to a phase-field model. Compared to earlier works, the number of equations of the phase-field model which need to be solved is reduced by leveraging high continuity of NURBS functions, and the algorithm is extended to 3D settings. We use residual-based variational multi-scale method (RBVMS) for solving Navier–Stokes equations, while the rest of PDEs in the phase-field model are treated using a standard Galerkin-based IGA. We introduce the resistive immersed surface (RIS) method into the formulation which can be employed for an implicit description of complex geometries using a diffuse-interface approach. The implementation highlights the robustness of the RBVMS method for Navier–Stokes equations of incompressible flows with non-trivial localized forcing terms including bending and tension forces of the vesicle. The potential of the phase-field model and isogeometric analysis for accurate simulation of a variety of fluid-vesicle interaction problems in 2D and 3D is demonstrated.
In this thesis, a new approach is developed for applications of shape optimization on the time harmonic wave propagation (Helmholtz equation) for acoustic problems. This approach is introduced for different dimensional problems: 2D, 3D axi-symmetric and fully 3D problems. The boundary element method (BEM) is coupled with the isogeometric analysis (IGA) forming the so-called (IGABEM) which speeds up meshing and gives higher accuracy in comparison with standard BEM. BEM is superior for handling unbounded domains by modeling only the inner boundaries and avoiding the truncation error, present in the finite element method (FEM) since BEM solutions satisfy the Sommerfeld radiation condition automatically. Moreover, BEM reduces the space dimension by one from a volumetric three-dimensional problem to a surface two-dimensional problem, or from a surface two-dimensional problem to a perimeter one-dimensional problem. Non-uniform rational B-splines basis functions (NURBS) are used in an isogeometric setting to describe both the CAD geometries and the physical fields.
IGABEM is coupled with one of the gradient-free optimization methods, the Particle Swarm Optimization (PSO) for structural shape optimization problems. PSO is a straightforward method since it does not require any sensitivity analysis but it has some trade-offs with regard to the computational cost. Coupling IGA with optimization problems enables the NURBS basis functions to represent the three models: shape design, analysis and optimization models, by a definition of a set of control points to be the control variables and the optimization parameters as well which enables an easy transition between the three models.
Acoustic shape optimization for various frequencies in different mediums is performed with PSO and the results are compared with the benchmark solutions from the literature for different dimensional problems proving the efficiency of the proposed approach with the following remarks:
- In 2D problems, two BEM methods are used: the conventional isogeometric boundary element method (IGABEM) and the eXtended IGABEM (XIBEM) enriched with the partition-of-unity expansion using a set of plane waves, where the results are generally in good agreement with the linterature with some computation advantage to XIBEM which allows coarser meshes.
-In 3D axi-symmetric problems, the three-dimensional problem is simplified in BEM from a surface integral to a combination of two 1D integrals. The first is the line integral similar to a two-dimensional BEM problem. The second integral is performed over the angle of revolution. The discretization is applied only to the former integration. This leads to significant computational savings and, consequently, better treatment for higher frequencies over the full three-dimensional models.
- In fully 3D problems, a detailed comparison between two BEM methods: the conventional boundary integral equation (CBIE) and Burton-Miller (BM) is provided including the computational cost. The proposed models are enhanced with a modified collocation scheme with offsets to Greville abscissae to avoid placing collocation points at the corners. Placing collocation points on smooth surface enables accurate evaluation of normals for BM formulation in addition to straightforward prediction of jump-terms and avoids singularities in $\mathcal{O} (1/r)$ integrals eliminating the need for polar integration. Furthermore, no additional special treatment is required for the hyper-singular integral while collocating on highly distorted elements, such as those containing sphere poles. The obtained results indicate that, CBIE with PSO is a feasible alternative (except for a small number of fictitious frequencies) which is easier to implement. Furthermore, BM presents an outstanding treatment of the complicated geometry of mufflers with internal extended inlet/outlet tube as an interior 3D Helmholtz acoustic problem instead of using mixed or dual BEM.
Der vorliegende Handlungsleitfaden hilft zivilgesellschaftlichen Organisationen und staatlichen Einrichtungen bei der Installation eines anonymen Behandlungs- oder Krankenschein für Menschen ohne Krankenversicherung. Dabei bündelt sich hier der Erfahrungsschatz verschiedener Initiativen aus dem gesamten Bundesgebiet.
Carrier-bound titanium dioxide catalysts were used in a photocatalytic ozonation reactor for the degradation of micro-pollutants in real wastewater. A photocatalytic immersion rotary body reactor with a 36-cm disk diameter was used, and was irradiated using UV-A light-emitting diodes. The rotating disks were covered with catalysts based on stainless steel grids coated with titanium dioxide. The dosing of ozone was carried out through the liquid phase via an external enrichment and a supply system transverse to the flow direction. The influence of irradiation power and ozone dose on the degradation rate for photocatalytic ozonation was investigated. In addition, the performance of the individual processes photocatalysis and ozonation were studied. The degradation kinetics of the parent compounds were determined using liquid chromatography tandem mass spectrometry. First-order kinetics were determined for photocatalysis and photocatalytic ozonation. A maximum reaction rate of the reactor was determined, which could be achieved by both photocatalysis and photocatalytic ozonation. At a dosage of 0.4 mg /mg DOC, the maximum reaction rate could be achieved using 75% of the irradiation power used for sole photocatalysis, allowing increases in the energetic efficiency of photocatalytic wastewater treatment processes. The process of photocatalytic ozonation is suitable to remove a wide spectrum of micro-pollutants from wastewater.
Although it is impractical to avert subsequent natural disasters, advances in simulation science and seismological studies make it possible to lessen the catastrophic damage. There currently exists in many urban areas a large number of structures, which are prone to damage by earthquakes. These were constructed without the guidance of a national seismic code, either before it existed or before it was enforced. For instance, in Istanbul, Turkey, as a high seismic area, around 90% of buildings are substandard, which can be generalized into other earthquakeprone regions in Turkey. The reliability of this building stock resulting from earthquake-induced collapse is currently uncertain. Nonetheless, it is also not feasible to perform a detailed seismic vulnerability analysis on each building as a solution to the scenario, as it will be too complicated and expensive. This indicates the necessity of a reliable, rapid, and computationally easy method for seismic vulnerability assessment, commonly known as Rapid Visual Screening (RVS). In RVS methodology, an observational survey of buildings is performed, and according to the data collected during the visual inspection, a structural score is calculated without performing any structural calculations to determine the expected damage of a building and whether the building needs detailed assessment. Although this method might save time and resources due to the subjective/qualitative judgments of experts who performed the inspection, the evaluation process is dominated by vagueness and uncertainties, where the vagueness can be handled adequately through the fuzzy set theory but do not cover all sort of uncertainties due to its crisp membership functions. In this study, a novel method of rapid visual hazard safety assessment of buildings against earthquake is introduced in which an interval type-2 fuzzy logic system (IT2FLS) is used to cover uncertainties. In addition, the proposed method provides the possibility to evaluate the earthquake risk of the building by considering factors related to the building importance and exposure. A smartphone app prototype of the method has been introduced. For validation of the proposed method, two case studies have been selected, and the result of the analysis presents the robust efficiency of the proposed method.
A vast number of existing buildings were constructed before the development and enforcement of seismic design codes, which run into the risk of being severely damaged under the action of seismic excitations. This poses not only a threat to the life of people but also affects the socio-economic stability in the affected area. Therefore, it is necessary to assess such buildings’ present vulnerability to make an educated decision regarding risk mitigation by seismic strengthening techniques such as retrofitting. However, it is economically and timely manner not feasible to inspect, repair, and augment every old building on an urban scale. As a result, a reliable rapid screening methods, namely Rapid Visual Screening (RVS), have garnered increasing interest among researchers and decision-makers alike. In this study, the effectiveness of five different Machine Learning (ML) techniques in vulnerability prediction applications have been investigated. The damage data of four different earthquakes from Ecuador, Haiti, Nepal, and South Korea, have been utilized to train and test the developed models. Eight performance modifiers have been implemented as variables with a supervised ML. The investigations on this paper illustrate that the assessed vulnerability classes by ML techniques were very close to the actual damage levels observed in the buildings.
The growing complexity of modern practical problems puts high demand on mathematical modelling. Given that various models can be used for modelling one physical phenomenon, the role of model comparison and model choice is becoming particularly important. Methods for model comparison and model choice typically used in practical applications nowadays are computationbased, and thus time consuming and computationally costly. Therefore, it is necessary to develop other approaches to working abstractly, i.e., without computations, with mathematical models. An abstract description of mathematical models can be achieved by the help of abstract mathematics, implying formalisation of models and relations between them. In this paper, a category theory-based approach to mathematical modelling is proposed. In this way, mathematical models are formalised in the language of categories, relations between the models are formally defined and several practically relevant properties are introduced on the level of categories. Finally, an illustrative example is presented, underlying how the category-theory based approach can be used in practice. Further, all constructions presented in this paper are also discussed from a modelling point of view by making explicit the link to concrete modelling scenarios.
Modern cryptography has become an often ubiquitous but essential part of our daily lives. Protocols for secure authentication and encryption protect our communication with various digital services, from private messaging, online shopping, to bank transactions or exchanging sensitive information. Those high-level protocols can naturally be only as secure as the authentication or encryption schemes underneath. Moreover, on a more detailed level, those schemes can also at best inherit the security of their underlying primitives. While widespread standards in modern symmetric-key cryptography, such as the Advanced Encryption Standard (AES), have shown to resist analysis until now, closer analysis and design of related primitives can deepen our understanding.
The present thesis consists of two parts that portray six contributions: The first part considers block-cipher cryptanalysis of the round-reduced AES, the AES-based tweakable block cipher Kiasu-BC, and TNT. The second part studies the design, analysis, and implementation of provably secure authenticated encryption schemes.
In general, cryptanalysis aims at finding distinguishable properties in the output distribution. Block ciphers are a core primitive of symmetric-key cryptography which are useful for the construction of various higher-level schemes, ranging from authentication, encryption, authenticated encryption up to integrity protection. Therefore, their analysis is crucial to secure cryptographic schemes at their lowest level. With rare exceptions, block-cipher cryptanalysis employs a systematic strategy of investigating known attack techniques. Modern proposals are expected to be evaluated against these techniques. The considerable effort for evaluation, however, demands efforts not only from the designers but also from external sources.
The Advanced Encryption Standard (AES) is one of the most widespread block ciphers nowadays. Therefore, it is naturally an interesting target for further analysis. Tweakable block ciphers augment the usual inputs of a secret key and a public plaintext by an additional public input called tweak. Among various proposals through the previous decade, this thesis identifies Kiasu-BC as a noteworthy attempt to construct a tweakable block cipher that is very close to the AES. Hence, its analysis intertwines closely with that of the AES and illustrates the impact of the tweak on its security best. Moreover, it revisits a generic tweakable block cipher Tweak-and-Tweak (TNT) and its instantiation based on the round-reduced AES.
The first part investigates the security of the AES against several forms of differential cryptanalysis, developing distinguishers on four to six (out of ten) rounds of AES. For Kiasu-BC, it exploits the additional freedom in the tweak to develop two forms of differential-based attacks: rectangles and impossible differentials. The results on Kiasu-BC consider an additional round compared to attacks on the (untweaked) AES. The authors of TNT had provided an initial security analysis that still left a gap between provable guarantees and attacks. Our analysis conducts a considerable step towards closing this gap. For TNT-AES - an instantiation of TNT built upon the AES round function - this thesis further shows how to transform our distinguisher into a key-recovery attack.
Many applications require the simultaneous authentication and encryption of transmitted data. Authenticated encryption (AE) schemes provide both properties. Modern AE schemes usually demand a unique public input called nonce that must not repeat. Though, this requirement cannot always be guaranteed in practice. As part of a remedy, misuse-resistant and robust AE tries to reduce the impact of occasional misuses. However, robust AE considers not only the potential reuse of nonces. Common authenticated encryption also demanded that the entire ciphertext would have to be buffered until the authentication tag has been successfully verified. In practice, this approach is difficult to ensure since the setting may lack the resources for buffering the messages. Moreover, robustness guarantees in the case of misuse are valuable features.
The second part of this thesis proposes three authenticated encryption schemes: RIV, SIV-x, and DCT. RIV is robust against nonce misuse and the release of unverified plaintexts. Both SIV-x and DCT provide high security independent from nonce repetitions. As the core under SIV-x, this thesis revisits the proof of a highly secure parallel MAC, PMAC-x, revises its details, and proposes SIV-x as a highly secure authenticated encryption scheme. Finally, DCT is a generic approach to have n-bit secure deterministic AE but without the need of expanding the ciphertext-tag string by more than n bits more than the plaintext.
From its first part, this thesis aims to extend the understanding of the (1) cryptanalysis of round-reduced AES, as well as the understanding of (2) AES-like tweakable block ciphers. From its second part, it demonstrates how to simply extend known approaches for (3) robust nonce-based as well as (4) highly secure deterministic authenticated encryption.
The derivation of nonlocal strong forms for many physical problems remains cumbersome in traditional methods. In this paper, we apply the variational principle/weighted residual method based on nonlocal operator method for the derivation of nonlocal forms for elasticity, thin plate, gradient elasticity, electro-magneto-elasticity and phase-field fracture method. The nonlocal governing equations are expressed as an integral form on support and dual-support. The first example shows that the nonlocal elasticity has the same form as dual-horizon non-ordinary state-based peridynamics. The derivation is simple and general and it can convert efficiently many local physical models into their corresponding nonlocal forms. In addition, a criterion based on the instability of the nonlocal gradient is proposed for the fracture modelling in linear elasticity. Several numerical examples are presented to validate nonlocal elasticity and the nonlocal thin plate.
Personalized ventilation (PV) is a mean of delivering conditioned outdoor air into the breathing zone of the occupants. This study aims to qualitatively investigate the personalized flows using two methods of visualization: (1) schlieren imaging using a large schlieren mirror and (2) thermography using an infrared camera. While the schlieren imaging was used to render the velocity and mass transport of the supplied flow, thermography was implemented to visualize the air temperature distribution induced by the PV. Both studies were conducted using a thermal manikin to simulate an occupant facing a PV outlet. As a reference, the flow supplied by an axial fan and a cased axial fan was visualized with the schlieren system as well and compared to the flow supplied by PV. Schlieren visualization results indicate that the steady, low-turbulence flow supplied by PV was able to penetrate the thermal convective boundary layer encasing the manikin's body, providing clean air for inhalation. Contrarily, the axial fan diffused the supplied air over a large target area with high turbulence intensity; it only disturbed the convective boundary layer rather than destroying it. The cased fan supplied a flow with a reduced target area which allowed supplying more air into the breathing zone compared to the fan. The results of thermography visualization showed that the supplied cool air from PV penetrated the corona-shaped thermal boundary layer. Furthermore, the supplied air cooled the surface temperature of the face, which indicates the large impact of PV on local thermal sensation and comfort.
Multi-user virtual reality systems enable collocated as well as distributed users to perform collaborative activities in immersive virtual environments. A common activity in this context is to move from one location to the next as a group to explore the environment together. The simplest solution to realize these multi-user navigation processes is to provide each participant with a technique for individual navigation. However, this approach entails some potentially undesirable consequences such as the execution of a similar navigation sequence by each participant, a regular need for coordination within the group, and, related to this, the risk of losing each other during the navigation process.
To overcome these issues, this thesis performs research on group navigation techniques that move group members together through a virtual environment. The presented work was guided by four overarching research questions that address the quality requirements for group navigation techniques, the differences between collocated and distributed settings, the scalability of group navigation, and the suitability of individual and group navigation for various scenarios. This thesis approaches these questions by introducing a general conceptual framework as well as the specification of central requirements for the design of group navigation techniques. The design, implementation, and evaluation of corresponding group navigation techniques demonstrate the applicability of the proposed framework.
As a first step, this thesis presents ideas for the extension of the short-range teleportation metaphor, also termed jumping, for multiple users. It derives general quality requirements for the comprehensibility of the group jumping process and introduces a corresponding technique for two collocated users. The results of two user studies indicate that sickness symptoms are not affected by user roles during group jumping and confirm improved planning accuracy for the navigator, increased spatial awareness for the passenger, and reduced cognitive load for both user roles.
Next, this thesis explores the design space of group navigation techniques in distributed virtual environments. It presents a conceptual framework to systematize the design decisions for group navigation techniques based on Tuckman's model of small-group development and introduces the idea of virtual formation adjustments as part of the navigation process. A quantitative user study demonstrates that the corresponding extension of Multi-Ray Jumping for distributed dyads leads to more efficient travel sequences and reduced workload. The results of a qualitative expert review confirm these findings and provide further insights regarding the complementarity of individual and group navigation in distributed virtual environments.
Then, this thesis investigates the navigation of larger groups of distributed users in the context of guided museum tours and establishes three central requirements for (scalable) group navigation techniques. These should foster the awareness of ongoing navigation activities as well as facilitate the predictability of their consequences for all group members (Comprehensibility), assist the group with avoiding collisions in the virtual environment (Obstacle Avoidance), and support placing the group in a meaningful spatial formation for the joint observation and discussion of objects (View Optimization). The work suggests a new technique to address these requirements and reports on its evaluation in an initial usability study with groups of five to ten (partially simulated) users. The results indicate easy learnability for navigators and high comprehensibility for passengers. Moreover, they also provide valuable insights for the development of group navigation techniques for even larger groups.
Finally, this thesis embeds the previous contributions in a comprehensive literature overview and emphasizes the need to study larger, more heterogeneous, and more diverse group compositions including the related social factors that affect group dynamics.
In summary, the four major research contributions of this thesis are as follows:
- the framing of group navigation as a specific instance of Tuckman's model of small-group development
- the derivation of central requirements for effective group navigation techniques beyond common quality factors known from single-user navigation
- the introduction of virtual formation adjustments during group navigation and their integration into concrete group navigation techniques
- evidence that appropriate pre-travel information and virtual formation adjustments lead to more efficient travel sequences for groups and lower workloads for both navigators and passengers
Overall, the research of this thesis confirms that group navigation techniques are a valuable addition to the portfolio of interaction techniques in multi-user virtual reality systems. The conceptual framework, the derived quality requirements, and the development of novel group navigation techniques provide effective guidance for application developers and inform future research in this area.
Mitigating Risks of Corruption in Construction: A theoretical rationale for BIM adoption in Ethiopia
(2021)
This PhD thesis sets out to investigate the potentials of Building Information Modeling (BIM) to mitigate risks of corruption in the Ethiopian public construction sector. The wide-ranging capabilities and promises of BIM have led to the strong perception among researchers and practitioners that it is an indispensable technology. Consequently, it has become the frequent subject of science and research. Meanwhile, many countries, especially the developed ones, have committed themselves to applying the technology extensively. Increasing productivity is the most common and frequently cited reason for that.
However, both technology developers and adopters are oblivious to the potentials of BIM in addressing critical challenges in the construction sector, such as corruption. This particularly would be significant in developing countries like Ethiopia, where its problems and effects are acute. Studies reveal that bribery and corruption have long pervaded the construction industry worldwide. The complex and fragmented nature of the sector provides an environment for corruption. The Ethiopian construction sector is not immune from this epidemic reality. In fact, it is regarded as one of the most vulnerable sectors owing to varying socio-economic and political factors. Since 2015, Ethiopia has started adopting BIM, yet without clear goals and strategies. As a result, the potential of BIM for combating concrete problems of the sector remains untapped. To this end, this dissertation does pioneering work by showing how collaboration and coordination features of the technology contribute to minimizing the opportunities for corruption. Tracing loopholes, otherwise, would remain complex and ineffective in the traditional documentation processes.
Proceeding from this anticipation, this thesis brings up two primary questions: what are areas and risks of corruption in case of the Ethiopian public construction projects; and how could BIM be leveraged to mitigate these risks? To tackle these and other secondary questions, the research employs a mixed-method approach. The selected main research strategies are Survey, Grounded Theory (GT) and Archival Study. First, the author disseminates an online questionnaire among Ethiopian construction engineering professionals to pinpoint areas of vulnerability to corruption. 155 responses are compiled and scrutinized quantitatively. Then, a semi-structured in-depth interview is conducted with 20 senior professionals, primarily to comprehend opportunities for and risks of corruption in those identified highly vulnerable project stages and decision points. At the same time, open interviews (consultations) are held with 14 informants to be aware of state of the construction documentation, BIM and loopholes for corruption in the country. Consequently, these qualitative data are analyzed utilizing the principles of GT, heat/risk mapping and Social Network Analysis (SNA). The risk mapping assists the researcher in the course of prioritizing corruption risks; whilst through SNA, methodically, it is feasible to identify key actors/stakeholders in the corruption venture. Based on the generated research data, the author constructs a [substantive] grounded theory around the elements of corruption in the Ethiopian public construction sector. This theory, later, guides the subsequent strategic proposition of BIM. Finally, 85 public construction related cases are also analyzed systematically to substantiate and confirm previous findings.
By ways of these multiple research endeavors that is based, first and foremost, on the triangulation of qualitative and quantitative data analysis, the author conveys a number of key findings. First, estimations, tender document preparation and evaluation, construction material as well as quality control and additional work orders are found to be the most vulnerable stages in the design, tendering and construction phases respectively. Second, middle management personnel of contractors and clients, aided by brokers, play most critical roles in corrupt transactions within the prevalent corruption network. Third, grand corruption persists in the sector, attributed to the fact that top management and higher officials entertain their overriding power, supported by the lack of project audits and accountability. Contrarily, individuals at operation level utilize intentional and unintentional 'errors’ as an opportunity for corruption.
In light of these findings, two conceptual BIM-based risk mitigation strategies are prescribed: active and passive automation of project audits; and the monitoring of project information throughout projects’ value chain. These propositions are made in reliance on BIM’s present dimensional capabilities and the promises of Integrated Project Delivery (IPD). Moreover, BIM’s synchronous potentials with other technologies such as Information and Communication Technology (ICT), and Radio Frequency technologies are topics which received a treatment. All these arguments form the basis for the main thesis of this dissertation, that BIM is able to mitigate corruption risks in the Ethiopian public construction sector. The discourse on the skepticisms about BIM that would stem from the complex nature of corruption and strategic as well as technological limitations of BIM is also illuminated and complemented by this work. Thus, the thesis uncovers possible research gaps and lays the foundation for further studies.
Electric trains are considered one of the most eco-friendly and safest means of transportation. Catenary poles are used worldwide to support overhead power lines for electric trains. The performance of the catenary poles has an extensive influence on the integrity of the train systems and, consequently, the connected human services. It became a must nowadays to develop SHM systems that provide the instantaneous status of catenary poles in- service, making the decision-making processes to keep or repair the damaged poles more feasible. This study develops a data-driven, model-free approach for status monitoring of cantilever structures, focusing on pre-stressed, spun-cast ultrahigh-strength concrete catenary poles installed along high-speed train tracks. The pro-posed approach evaluates multiple damage features in an unfied damage index, which leads to straightforward interpretation and comparison of the output. Besides, it distinguishes between multiple damage scenarios of the poles, either the ones caused by material degradation of the concrete or by the cracks that can be propagated during the life span of the given structure. Moreover, using a logistic function to classify the integrity of structure avoids the expensive learning step in the existing damage detection approaches, namely, using the modern machine and deep learning methods. The findings of this study look very promising when applied to other types of cantilever structures, such as the poles that support the power transmission lines, antenna masts, chimneys, and wind turbines.
Encapsulation-based self-healing concrete has received a lot of attention nowadays in civil engineering field. These capsules are embedded in the cementitious matrix during concrete mixing. When the cracks appear, the embedded capsules which are placed along the path of incoming crack are fractured and then release of healing agents in the vicinity of damage. The materials of capsules need to be designed in a way that they should be able to break with small deformation, so the internal fluid can be released to seal the crack. This study focuses on computational modeling of fracture in encapsulation-based selfhealing concrete. The numerical model of 2D and 3D with randomly packed aggreates and capsules have been developed to analyze fracture mechanism that plays a significant role in the fracture probability of capsules and consequently the self-healing process. The capsules are assumed to be made of Poly Methyl Methacrylate (PMMA) and the potential cracks are represented by pre-inserted cohesive elements with tension and shear softening laws along the element boundaries of the mortar matrix, aggregates, capsules, and at the interfaces between these phases. The effects of volume fraction, core-wall thickness ratio, and mismatch fracture properties of capsules on the load carrying capacity of self-healing concrete and fracture probability of the capsules are investigated. The output of this study will become valuable tool to assist not only the experimentalists but also the manufacturers in designing an appropriate capsule material for self-healing concrete.
Die vorliegende Arbeit richtet sich an Ingenieur*innen und Wissenschaftler*innen der technischen Gebäudeausrüstung. Sie greift einen sich abzeichnenden Änderungsbedarf in der Umwelt- und Nachhaltigkeitsbewertung von Gebäuden und wärmetechnischen Anlagen auf. Der aktuell genutzte nicht erneuerbare Primärenergiebedarf wird insbesondere hinsichtlich künftiger politischer Klima- und Umweltschutzziele als alleinige Bewertungsgröße nicht ausreichend sein. Die mit dieser Arbeit vorgestellte Ökoeffizienzbewertungsmethode kann als geeignetes Instrument zur Lösung der Probleme beitragen. Sie ermöglicht systematische, ganzheitliche Bewertungen und reproduzierbare Vergleiche wärmetechnischer Anlagen bezüglich ihrer ökologischen und ökonomischen Nachhaltigkeit. Die wesentlichsten Neuentwicklungen sind die spezifische Umweltleistung, in Erweiterung zum genutzten Primärenergiefaktor, und der Ökoeffizienzindikator UWI.
In this article, I show why it is necessary to abolish the use of predictive algorithms in the US criminal justice system at sentencing. After presenting the functioning of these algorithms in their context of emergence, I offer three arguments to demonstrate why their abolition is imperative. First, I show that sentencing based on predictive algorithms induces a process of rewriting the temporality of the judged individual, flattening their life into a present inescapably doomed by its past. Second, I demonstrate that recursive processes, comprising predictive algorithms and the decisions based on their predictions, systematically suppress outliers and progressively transform reality to match predictions. In my third and final argument, I show that decisions made on the basis of predictive algorithms actively perform a biopolitical understanding of justice as management and modulation of risks. In such a framework, justice becomes a means to maintain a perverse social homeostasis that systematically exposes disenfranchised Black and Brown populations to risk.
Scaling of concrete due to salt frost attack is an important durability issue in moderate and cold climates. The actual damage mechanism is still not completely understood. Two recent damage theories—the glue spall theory and the cryogenic suction theory—offer plausible, but conflicting explanations for the salt frost scaling mechanism. The present study deals with the cryogenic suction theory, which assumes that freezing concrete can take up unfrozen brine from a partly frozen deicing solution during salt frost attack. According to the model hypothesis, the resulting saturation of the concrete surface layer intensifies the ice formation in this layer and causes salt frost scaling. In this study an experimental technique was developed that makes it possible to quantify to which extent brine uptake can increase ice formation in hardened cement paste (used as a model material for concrete). The experiments were carried out with low temperature differential scanning calorimetry, where specimens were subjected to freeze–thaw cycles while being in contact with NaCl brine. Results showed that the ice content in the specimens increased with subsequent freeze–thaw cycles due to the brine uptake at temperatures below 0 °C. The ability of the hardened cement paste to bind chlorides from the absorbed brine at the same time affected the freezing/melting behavior of the pore solution and the magnitude of the ice content.
Marine macroalgae such as Ulva intestinalis have promising properties as feedstock for cosmetics and pharmaceuticals. However, since the quantity and quality of naturally grown algae vary widely, their exploitability is reduced – especially for producers in high-priced markets. Moreover, the expansion of marine or shore-based cultivation systems is unlikely in Europe, since promising sites either lie in fishing zones, recreational areas, or natural reserves. The aim was therefore to develop a closed photobioreactor system enabling full control of abiotic environmental parameters and an effective reconditioning of the cultivation medium in order to produce marine macroalgae at sites distant from the shore. To assess the feasibility and functionality of the chosen technological concept, a prototypal plant has been implemented in central Germany – a site distant from the sea. Using a newly developed, submersible LED light source, cultivation experiments with Ulva intestinalis led to growth rates of 7.72 ± 0.04 % day−1 in a cultivation cycle of 28 days. Based on the space demand of the production system, this results in fresh mass productivity of 3.0 kg m−2, respectively, of 1.1 kg m−2 per year. Also considering the ratio of biomass to energy input amounting to 2.76 g kWh−1, significant future improvements of the developed photobioreactor system should include the optimization of growth parameters, and the reduction of the system’s overall energy demand.
Cultural Heritage on Mobile Devices: Building Guidelines for UNESCO World Heritage Sites' Apps
(2021)
Technological improvements and access provide a fertile scenario for creating and developing mobile applications (apps). This scenario results in a myriad of Apps providing information regarding touristic destinations, including those with a cultural profile, such as those dedicated to UNESCO World Heritage Sites (WHS). However, not all of the Apps have the same efficiency. In order to have a successful app, its development must consider usability aspects and features aligned with reliable content. Despite the guidelines for mobile usability being broadly available, they are generic, and none of them concentrates specifically into cultural heritage places, especially on those placed in an open-air scenario. This research aims to fulfil this literature gap and discusses how to adequate and develop specific guidelines for a better outdoor WHS experience. It uses an empirical approach applied to an open-air WHS city: Weimar and its Bauhaus and Classical Weimar sites. In order to build a new set of guidelines applied for open-air WHS, this research used a systematic approach to compare literature-based guidelines to industry-based ones (based on affordances), extracted from the available Apps dedicated to WHS set in Germany. The instructions compiled from both sources have been comparatively tested by using two built prototypes from the distinctive guidelines, creating a set of recommendations collecting the best approach from both sources, plus suggesting new ones the evaluation.
Knapp 30.000 Windenergieanlagen zwischen Nordsee und Alpen lassen unübersehbar erkennen, dass sich unser Energiesystem in einer umfassenden Transformation befindet. Allenthalben erfährt diese Entwicklung eine breite und kontroverse Rezeption und auch in der Denkmalpflege werden Windenergieanlagen aufgrund ihrer mitunter erheblichen Auswirkungen auf die Landschaft noch überwiegend als Störung wahrgenommen. Diese Arbeit nimmt dagegen die historische Entwicklung in den Blick und plädiert dafür, Windenergieanlagen als bedeutendes Kulturerbe zu verstehen. Angesichts des Voranschreitens der Energiewende wird angenommen, dass gerade älteren Modellen als baulichen Zeugnissen umfangreicher energiepolitischer Veränderungen seit den 1970er Jahren eine hohe Bedeutung zugeschrieben werden kann. Daher besteht das Ziel darin, Windenergieanlagen herauszuarbeiten, welche als hervorragende Zeugnisse der Entwicklung der Windenergienutzung in Deutschland zu bewerten sind.
Zur Annäherung werden diese zunächst als Untersuchungsgegenstand typologisch abgegrenzt. Eine wesentliche Besonderheit von Windenergieanlagen besteht darin, dass sie im Verhältnis zur eigentlichen Flächenversiegelung durch ihre vertikale Struktur erhebliche visuelle Auswirkungen auf die Landschaft haben. Anschließend wird die Entwicklung der Windenergienutzung seit den 1970er Jahren genauer betrachtet, welche insgesamt nicht linear verlief und von vielen Konflikten gekennzeichnet ist. Diese muss im Kontext eines wachsenden Umweltbewusstseins verstanden werden, das umfangreiche energiepolitische Veränderungen zur Folge hatte. Auf dieser Grundlage werden schließlich in einer denkmalkundlichen Reihenuntersuchung Windenergieanlagen herausgearbeitet, welche in hervorragender Weise von der Entwicklung zeugen. Die Auswahl bleibt allerdings mit sechs Objekten im Verhältnis zum Gesamtbestand von knapp 30.000 Anlagen relativ beschränkt, weil das auf die Abgrenzung von Besonderheiten ausgelegte etablierte Denkmalverständnis bei einem zeitlich so dichten Bestand gleichartiger Bauwerke an eine Grenze kommt.
Abschließend werden mögliche Erhaltungsperspektiven sowie denkmaltheoretische und -praktische Schlussfolgerungen diskutiert. Dabei ist unbedingt ein Erhalt am Ursprungsstandort anzustreben, wobei im Einzelfall entschieden werden muss, ob Belange des Funktions- oder Substanzerhaltes höher zu gewichten sind. Die skizzierten Auswahlprobleme regen darüber hinaus zur Diskussion zusätzlicher denkbarer Bewertungskategorien an, wobei sich insbesondere die gesellschaftliche Wahrnehmung und ökologische Werte aufdrängen. Zudem kann für die stärkere Berücksichtigung von Funktionszusammenhängen bei der Betrachtung technischer Infrastruktur in der Denkmalpflege plädiert werden. Insgesamt führt die denkmalkundliche Auseinandersetzung mit Windenergieanlagen damit weit über die Herausarbeitung einzelner Objekte hinaus und macht eindrücklich auf aktuelle Herausforderungen der Denkmalpflege und darüber hinaus aufmerksam.
Antimicrobial resistance (AMR) is identified by the World Health Organization (WHO) as one of the top ten threats to public health worldwide. In addition to public health, AMR also poses a major threat to food security and economic development. Current sanitation systems contribute to the emergence and spread of AMR and lack effective AMR mitigation measures. This study assesses source separation of blackwater as a mitigation measure against AMR. A source-separation-modified combined sanitation system with separate collection of blackwater and graywater is conceptually described. Measures taken at the source, such as the separate collection and discharge of material flows, were not considered so far on a load balance basis, i.e., they have not yet been evaluated for their effectiveness. The sanitation system described is compared with a combined system and a separate system regarding AMR emissions by means of simulation. AMR is represented in the simulation model by one proxy parameter each for antibiotics (sulfamethoxa-zole), antibiotic-resistant bacteria (extended-spectrum beta-lactamase E. Coli), and antibiotic re-sistance genes (blaTEM). The simulation results suggest that the source-separation-based sanitation system reduces emissions of antibiotic-resistant bacteria and antibiotic resistance genes into the aquatic environment by more than six logarithm steps compared to combined systems. Sulfa-methoxazole emissions can be reduced by 75.5% by keeping blackwater separate from graywater and treating it sufficiently. In summary, sanitation systems incorporating source separation are, to date, among the most effective means of preventing the emission of AMR into the aquatic envi-ronment.
Bolted connections are commonly used in steel construction. The load-bearing behavior of bolt fittings has extensively been studied in various research activities and the bearing capacity of bolted connections can be assessed well by standard regulations for practical applications. With regard to tensile loading, the nut does not have strong influence on resistances, since the failure occurs in the bolts due to higher material strengths of the nuts. In some applications, so-called “blind holes” are used to connect plated components. In a manner of speaking, the nut is replaced by the “outer” plate with a prefabricated hole and thread, in which the bolt can be screwed and tightened. In such connections, the limit load capacity cannot solely be assessed by the bolt resistance, since the threaded hole in the base material has strong influence on the structural behavior. In this context, the available screw-in depth of the blind hole is of fundamental importance. The German National Annex of EN 1993-1-8 provides information on a necessary depth in order to transfer the full tensile capacity of the bolt. However, some connections do not allow to fabricate such depths. In these cases, the capacity of the connection is unclear and not specified. In this paper, first experiments on corresponding connections with different screw-in depths are presented and compared to limit load capacities according to the standard.
In the last two decades, Peridynamics (PD) attracts much attention in the field of fracture mechanics. One key feature of PD is the nonlocality, which is quite different from the ideas in conventional methods such as FEM and meshless method. However, conventional PD suffers from problems such as constant horizon, explicit algorithm, hourglass mode. In this thesis, by examining the nonlocality with scrutiny, we proposed several new concepts such as dual-horizon (DH) in PD, dual-support (DS) in smoothed particle hydrodynamics (SPH), nonlocal operators and operator energy functional. The conventional PD (SPH) is incorporated in the DH-PD (DS-SPH), which can adopt an inhomogeneous discretization and inhomogeneous support domains. The DH-PD (DS-SPH) can be viewed as some fundamental improvement on the conventional PD (SPH). Dual formulation of PD and SPH allows h-adaptivity while satisfying the conservations of linear momentum, angular momentum and energy. By developing the concept of nonlocality further, we introduced the nonlocal operator method as a generalization of DH-PD. Combined with energy functional of various physical models, the nonlocal forms based on dual-support concept are derived. In addition, the variation of the energy functional allows implicit formulation of the nonlocal theory. At last, we developed the higher order nonlocal operator method which is capable of solving higher order partial differential equations on arbitrary domain in higher dimensional space. Since the concepts are developed gradually, we described our findings chronologically.
In chapter 2, we developed a DH-PD formulation that includes varying horizon sizes and solves the "ghost force" issue. The concept of dual-horizon considers the unbalanced interactions between the particles with different horizon sizes. The present formulation fulfills both the balances of linear momentum and angular momentum exactly with arbitrary particle discretization. All three peridynamic formulations, namely bond based, ordinary state based and non-ordinary state based peridynamics can be implemented within the DH-PD framework. A simple adaptive refinement procedure (h-adaptivity) is proposed reducing the computational cost. Both two- and three- dimensional examples including the Kalthoff-Winkler experiment and plate with branching cracks are tested to demonstrate the capability of the method.
In chapter 3, a nonlocal operator method (NOM) based on the variational principle is proposed for the solution of waveguide problem in computational electromagnetic field. Common differential operators as well as the variational forms are defined within the context of nonlocal operators. The present nonlocal formulation allows the assembling of the tangent stiffness matrix with ease, which is necessary for the eigenvalue analysis of the waveguide problem. The present formulation is applied to solve 1D Schrodinger equation, 2D electrostatic problem and the differential electromagnetic vector wave equations based on electric fields.
In chapter 4, a general nonlocal operator method is proposed which is applicable for solving partial differential equations (PDEs) of mechanical problems. The nonlocal operator can be regarded as the integral form, ``equivalent'' to the differential form in the sense of a nonlocal interaction model. The variation of a nonlocal operator plays an equivalent role as the derivatives of the shape functions in the meshless methods or those of the finite element method. Based on the variational principle, the residual and the tangent stiffness matrix can be obtained with ease. The nonlocal operator method is enhanced here also with an operator energy functional to satisfy the linear consistency of the field. A highlight of the present method is the functional derived based on the nonlocal operator can convert the construction of residual and stiffness matrix into a series of matrix multiplications using the predefined nonlocal operators. The nonlocal strong forms of different functionals can be obtained easily via the concept of support and dual-support. Several numerical examples of different types of PDEs are presented.
In chapter 5, we extended the NOM to higher order scheme by using a higher order Taylor series expansion of the unknown field. Such a higher order scheme improves the original NOM in chapter 3 and chapter 4, which can only achieve one-order convergence. The higher order NOM obtains all partial derivatives with specified maximal order simultaneously without resorting to shape functions. The functional based on the nonlocal operators converts the construction of residual and stiffness matrix into a series of matrix multiplication on the nonlocal operator matrix. Several numerical examples solved by strong form or weak form are presented to show the capabilities of this method.
In chapter 6, the NOM proposed as a particle-based method in chapter 3,4,5, has difficulty in imposing accurately the boundary conditions of various orders. In this paper, we converted the particle-based NOM into a scheme with interpolation property. The new scheme describes partial derivatives of various orders at a point by the nodes in the support and takes advantage of the background mesh for numerical integration. The boundary conditions are enforced via the modified variational principle. The particle-based NOM can be viewed a special case of NOM with interpolation property when nodal integration is used. The scheme based on numerical integration greatly improves the stability of the method, as a consequence, the operator energy functional in particle-based NOM is not required. We demonstrated the capabilities of current method by solving the gradient solid problems and comparing the numerical results with the available exact solutions.
In chapter 7, we derived the DS-SPH in solid within the framework of variational principle. The tangent stiffness matrix of SPH can be obtained with ease, and can be served as the basis for the present implicit SPH. We proposed an hourglass energy functional, which allows the direct derivation of hourglass force and hourglass tangent stiffness matrix. The dual-support is {involved} in all derivations based on variational principles and is automatically satisfied in the assembling of stiffness matrix. The implementation of stiffness matrix comprises with two steps, the nodal assembly based on deformation gradient and global assembly on all nodes. Several numerical examples are presented to validate the method.
Für die Verminderung der betonspezifischen CO2-Emissionen wird ein verstärkter Einsatz klinkerreduzierter Zemente bzw. Betone angestrebt. Die Reduzierung des Klinkergehaltes darf jedoch nicht zu einer lebensdauerrelevanten Beeinträchtigung der Betondauerhaftigkeit führen. In diesem Zusammenhang stellt der Frost-Tausalz-Widerstand eine kritische Größe dar, da er bei höheren Klinkersubstitutionsraten häufig negativ beeinflusst wird. Erschwerend kommt hinzu, dass für klinkerreduzierte Betone nur ein unzureichender Erfahrungsschatz vorliegt. Ein hoher Frost-Tausalz-Widerstand kann daher nicht ausschließlich anhand deskriptiver Vorgaben gewährleistet werden. Demgemäß sollte perspektivisch auch für frost-tausalzbeanspruchte Bauteile eine performancebasierte Lebensdauerbetrachtung erfolgen.
Eine unverzichtbare Grundlage für das Erreichen dieser Ziele ist ein Verständnis für die Schadensvorgänge beim Frost-Tausalz-Angriff. Der Forschungsstand ist jedoch geprägt von widersprüchlichen Schadenstheorien. Somit wurde als Zielstellung für diese Arbeit abgeleitet, die existierenden Schadenstheorien unter Berücksichtigung des aktuellen Wissensstandes zu bewerten und mit eigenen Untersuchungen zu prüfen und einzuordnen. Die Sichtung des Forschungsstandes zeigte, dass nur zwei Theorien das Potential haben, den Frost-Tausalz-Angriff umfassend abzubilden – die Glue Spall Theorie und die Cryogenic Suction Theorie.
Die Glue Spall Theorie führt die Entstehung von Abwitterungen auf die mechanische Schädigung der Betonoberfläche durch eine anhaftende Eisschicht zurück. Dabei sollen nur bei moderaten Tausalzkonzentrationen in der einwirkenden Lösung kritische Spannungszustände in der Eisschicht auftreten, die eine Schädigung der Betonoberfläche hervorrufen können. In dieser Arbeit konnte jedoch nachgewiesen werden, dass starke Abwitterungen auch bei Tausalz¬konzentrationen auftreten, bei denen eine mechanische Schädigung des Betons durch das Eis auszuschließen ist. Damit wurde die fehlende Eignung der Glue Spall Theorie aufgezeigt.
Die Cryogenic Suction Theorie fußt auf den eutektischen Eigenschaften von Tausalz-lösungen, die im gefrorenen Zustand immer als Mischung auf festem Wassereis und flüssiger, hochkonzentrierter Salzlösung bestehen, solange ihre Eutektikumstemperatur nicht unter¬schritten wird. Die flüssige Phase im salzhaltigen Eis stellt für gefrorenen Beton ein bisher nicht berücksichtigtes Flüssigkeitsreservoir dar, welches trotz der hohen Salzkonzentration die Eisbildung in der Betonrandzone verstärken und so die Entstehung von Abwitterungen verursachen soll. In dieser Arbeit wurde bestätigt, dass die Eisbildung im Zementstein beim Gefrieren in hochkonzentrierter Tausalzlösung tatsächlich verstärkt wird. Das Ausmaß der zusätzlichen Eisbildung wurde dabei auch von der Fähigkeit des Zementsteins zur Bindung von Chloridionen aus der Tausalzlösung beeinflusst.
Zusammenfassend wurde festgestellt, dass die Cryogenic Suction Theorie eine gute Beschreibung des Frost-Tausalz-Angriffes darstellt, aber um weitere Aspekte ergänzt werden muss. Die Berücksichtigung der intensiven Sättigung von Beton durch den Prozess der Mikroeislinsenpumpe stellt hier die wichtigste Erweiterung dar. Basierend auf dieser Überlegung wurde eine kombinierte Schadenstheorie aufgestellt. Wichtige Annahmen dieser Theorie konnten experimentell bestätigt werden. Im Ergebnis wurde so die Grundlage für ein tiefergehendes Verständnis des Frost-Tausalz-Angriffes geschaffen. Zudem wurde ein neuer Ansatz identifiziert, um die (potentielle) Verringerung des Frost-Tausalz-Widerstandes klinkerreduzierter Betone zu erklären.
Die Auseinandersetzung mit der Digitalisierung ist in den letzten Jahren in den Medien, auf Konferenzen und in Ausschüssen der Bau- und Immobilienbranche angekommen. Während manche Bereiche Neuerungen hervorbringen und einige Akteure als Pioniere zu bezeichnen sind, weisen andere Themen noch Defizite hinsichtlich der digitalen Transformation auf. Zu dieser Kategorie kann auch das Baugenehmigungsverfahren gezählt werden. Unabhängig davon, wie Architekten und Ingenieure in den Planungsbüros auf innovative Methoden setzen, bleiben die Bauvorlagen bisher zuhauf in Papierform oder werden nach der elektronischen Einreichung in der Behörde ausgedruckt. Vorhandene Ressourcen, beispielsweise in Form eines Bauwerksinformationsmodells, die Unterstützung bei der Baugenehmigungsfeststellung bieten können, werden nicht ausgeschöpft. Um mit digitalen Werkzeugen eine Entscheidungshilfe für die Baugenehmigungsbehörden zu erarbeiten, ist es notwendig, den Ist-Zustand zu verstehen und Gegebenheiten zu hinterfragen, bevor eine Gesamtautomatisierung der innerbehördlichen Vorgänge als alleinige Lösung zu verfolgen ist.
Mit einer inhaltlich-organisatorischen Betrachtung der relevanten Bereiche, die Einfluss auf die Baugenehmigungsfeststellung nehmen, wird eine Optimierung des Baugenehmigungsverfahrens in den
Behörden angestrebt. Es werden die komplexen Bereiche, wie die Gesetzeslage, der Einsatz von Technologie aber auch die subjektiven Handlungsalternativen, ermittelt und strukturiert. Mit der Entwicklung eines Modells zur Feststellung der Baugenehmigungsfähigkeit wird sowohl ein Verständnis für Einflussfaktoren vermittelt als auch eine Transparenzsteigerung für alle Beteiligten geschaffen.
Neben einer internationalen Literaturrecherche diente eine empirische Studie als Untersuchungsmethode. Die empirische Studie wurde in Form von qualitativen Experteninterviews durchgeführt, um den Ist-Zustand im Bereich der Baugenehmigungsverfahren festzustellen. Das erhobene Datenmaterial wurde aufbereitet und anschließend einer softwaregestützten Inhaltsanalyse unterzogen. Die Ergebnisse wurden in Kombination mit den Erkenntnissen der Literaturrecherche in verschiedenen Analysen als Modellgrundlage aufgearbeitet.
Ergebnis der Untersuchung stellt ein Entscheidungsmodell dar, welches eine Lücke zwischen den gegenwärtigen
Abläufen in den Baubehörden und einer Gesamtautomatisierung der Baugenehmigungsprüfung schließt. Die prozessorientierte Strukturierung entscheidungsrelevanter Sachverhalte im Modell ermöglicht eine Unterstützung bei der Baugenehmigungsfeststellung für Prüfer und Antragsteller. Das theoretische Modell konnte in Form einer Webanwendung in die Praxis übertragen werden.
Besides their multiple known benefits regarding urban microclimate, living walls can be used as decentralized stand-alone systems to treat greywater locally at the buildings. While this offers numerous environmental advantages, it can have a considerable impact on the hygrothermal performance of the facade as such systems involve bringing large quantities of water onto the facade. As it is difficult to represent complex entities such as plants in the typical simulation tools used for heat and moisture transport, this study suggests a new approach to tackle this challenge by coupling two tools: ENVI-Met and Delphin. ENVI-Met was used to simulate the impact of the plants to determine the local environmental parameters at the living wall. Delphin, on the other hand, was used to conduct the hygrothermal simulations using the local parameters calculated by ENVI-Met. Four wall constructions were investigated in this study: an uninsulated brick wall, a precast concrete plate, a sandy limestone wall, and a double-shell wall. The results showed that the living wall improved the U-value, the exterior surface temperature, and the heat flux through the wall. Moreover, the living wall did not increase the risk of moisture in the wall during winter and eliminated the risk of condensation.
In den letzten Jahrzehnten unterlag der Straßenbetriebsdienst tiefgreifenden Veränderungen. Diese Veränderungen schließt auch die betriebliche Steuerungsphilosophie ein, um eine planungsrationale und ökonomische Gestaltung des Straßenbetriebsdienstes zu unterstützen. Dabei erfolgt eine verbindliche Vorgabe der Leistungsinhalte und -umfänge und ermöglicht eine Budgetierung für das vorgesehene Jahresarbeitsprogramm.
Ziel der Untersuchung ist die Entwicklung eines Modells für die Ermittlung von leistungsbezogenen Musterjahresganglinien zur Unterstützung der Jahresarbeitsplanung. Dafür lagen für jede Leistung des Leistungsbereiches „Grünpflege“ jeweils 260 einzelne Jahresganglinien vor.
Im Ergebnis der Untersuchung wird die leistungsbezogene Musterjahresganglinie in vier Schritten ermittelt. Im ersten Schritt erfolgt die Prüfung der Datenqualität; im zweiten Schritt eine Korrelationsanalyse; im dritten Schritt die fachliche Überprüfung der Leistungsausprägung und im vierten Schritt die Ermittlung der leistungsbezogenen Musterjahresganglinie aus den verbliebenen leistungsbezogenen Jahresganglinien.
Few studies have investigated how search behavior affects complex writing tasks. We analyze a dataset of 150 long essays whose authors searched the ClueWeb09 corpus for source material, while all querying, clicking, and writing activity was meticulously recorded. We model the effect of search and writing behavior on essay quality using path analysis. Since the boil-down and build-up writing strategies identified in previous research have been found to affect search behavior, we model each writing strategy separately. Our analysis shows that the search process contributes significantly to essay quality through both direct and mediated effects, while the author's writing strategy moderates this relationship. Our models explain 25–35% of the variation in essay quality through rather simple search and writing process characteristics alone, a fact that has implications on how search engines could personalize result pages for writing tasks. Authors' writing strategies and associated searching patterns differ, producing differences in essay quality. In a nutshell: essay quality improves if search and writing strategies harmonize—build-up writers benefit from focused, in-depth querying, while boil-down writers fare better with a broader and shallower querying strategy.
In this paper we present a theoretical background for a coupled analytical–numerical approach to model a crack propagation process in two-dimensional bounded domains. The goal of the coupled analytical–numerical approach is to obtain the correct solution behaviour near the crack tip by help of the analytical solution constructed by using tools of complex function theory and couple it continuously with the finite element solution in the region far from the singularity. In this way, crack propagation could be modelled without using remeshing. Possible directions of crack growth can be calculated through the minimization of the total energy composed of the potential energy and the dissipated energy based on the energy release rate. Within this setting, an analytical solution of a mixed boundary value problem based on complex analysis and conformal mapping techniques is presented in a circular region containing an arbitrary crack path. More precisely, the linear elastic problem is transformed into a Riemann–Hilbert problem in the unit disk for holomorphic functions. Utilising advantages of the analytical solution in the region near the crack tip, the total energy could be evaluated within short computation times for various crack kink angles and lengths leading to a potentially efficient way of computing the minimization procedure. To this end, the paper presents a general strategy of the new coupled approach for crack propagation modelling. Additionally, we also discuss obstacles in the way of practical realisation of this strategy.
In this work, extensive reactive molecular dynamics simulations are conducted to analyze the nanopore creation by nano-particles impact over single-layer molybdenum disulfide (MoS2) with 1T and 2H phases. We also compare the results with graphene monolayer. In our simulations, nanosheets are exposed to a spherical rigid carbon projectile with high initial velocities ranging from 2 to 23 km/s. Results for three different structures are compared to examine the most critical factors in the perforation and resistance force during the impact. To analyze the perforation and impact resistance, kinetic energy and displacement time history of the projectile as well as perforation resistance force of the projectile are investigated.
Interestingly, although the elasticity module and tensile strength of the graphene are by almost five times higher than those of MoS2, the results demonstrate that 1T and 2H-MoS2 phases are more resistive to the impact loading and perforation than graphene. For the MoS2nanosheets, we realize that the 2H phase is more resistant to impact loading than the 1T counterpart.
Our reactive molecular dynamics results highlight that in addition to the strength and toughness, atomic structure is another crucial factor that can contribute substantially to impact resistance of 2D materials. The obtained results can be useful to guide the experimental setups for the nanopore creation in MoS2or other 2D lattices.
Durch internationale Fluchtbewegungen über die sogenannte Balkanroute bildete sich in Serbiens Hauptstadt Belgrad in den letzten Jahren ein sogenannter Refugee District heraus. Im Kontext von Migration und Flucht werden dabei zahlreiche Spannungsfelder auf unterschiedlichen räumlichen und politischen Ebenen sichtbar. Für Flüchtende kreieren diese eine Situation, die von Stillstand, Ausweglosigkeit, Kontrolle, Gefahr und Verdrängung geprägt ist. Allerdings führen die Vielschichtigkeit und die Diversität unterschiedlicher Akteur*innen, die bezüglich der Situation von Flüchtenden auf der Balkanroute wirkmächtig sind, auch zu Nischen, Widerständigkeiten und der Möglichkeit (neuer) Allianzen. Auf diese Weise entsteht eine kollektive Praktik der Nicht-Bewegung im Widerstand gegen die Unterdrückung und für globale Bewegungsfreiheit.
Das Kernthema dieser Arbeit ist die Beschäftigung mit den Folgen des Uranbergbaus in dem Gebiet um die ehemalige Abbauregion der Wismut SAG/SDAG in Ronneburg (Ostthüringen). Dieses Thema wird unter historischen, sozialen, kulturanthropologischen und künstlerischen Aspekten betrachtet und in den Zusammenhang mit den weltweiten Voraussetzungen der Nuklearindustrie und Auswirkungen des Uranbergbaus und seiner Folgen gestellt. Die Arbeit legt dar, wie eine Uranbergbaufolgelandschaft entsteht und welches Wissen ist für ein angemessenes Verständnis des Phänomens wichtig ist. Es wird untersucht, ob Kunst bezüglich der Uranbergbaufolgelandschaft einen relevanten Beitrag leisten kann bzw. in welcher Form dies versucht wurde, bzw. stellte Arbeiten vor, die verwandete Themen bearbeitet haben. In Kombination dieser beiden Hauptaspekte geht die Arbeit der Frage nach, welche Faktoren die Uranbergbaufolgelandschaft prägen und ob es sinnvolle Beteiligungsfelder für künstlerisches Forschen oder Handeln gibt sowie welche Bedingungen hierfür erfüllt werdenmüssten. Die Kernthese der Arbeit ist, dass künstlerische Arbeiten im Themenfeld des Uranbergbaus unter bestimmten Bedingungen relevante Beiträge leisten können.
What is Afghan music and what is its contemporary state? This question seems important to ask, considering the conflictual recent past of the country that particularly affected cultural expressions such as music. In these four articles diverse perspectives on Afghan music are explored. From traditional music of the Afghan rubab and its masters up to popular music of the Afghan-German hiphop producer “Farhot”, various insights are given into phenomena yet barely covered in academic works. This collection provides glimpses into the variety of the music of Afghanistan and the Afghan diaspora and help to shape the Western views on the music of the country into more diverse perspectives. We move further away from the bias of the majority of media representations predominantly showing the conflictual sides of Afghanistan, at the same time avoiding a limiting and narrow view on Afghanistan with solely a musical tradition located in the past. These essays go beyond and outline that apart from a rich tradition, there are present forms of musical expression. We move from “Tradition to Television” and beyond, exploring views on the future of music connected to Afghanistan.
According to Eurocode, the computation of bending strength for steel cantilever beams is a straightforward process. The approach is based on an Ayrton-Perry formula adaptation of buckling curves for steel members in compression, which involves the computation of an elastic critical buckling load for considering the instability. NCCI documents offer a simplified formula to determine the critical bending moment for cantilevers beams with symmetric cross-section. Besides the NCCI recommendations, other approaches, e.g. research literature or Finite-Element-Analysis, may be employed to determine critical buckling loads. However, in certain cases they render different results. Present paper summarizes and compares the abovementioned analytical and numerical approaches for determining critical loads and it exemplarily analyses corresponding cantilever beam capacities using numerical approaches based on plastic zones theory (GMNIA).
This study investigates the flow supplied by personalized ventilation (PV) by means of anemometer measurements and schlieren visualization. The study was conducted using a thermal manikin to simulate a seated occupant facing a PV outlet. Air velocity was measured at multiple points in the flow field; the collected velocity values were used to calculate the turbulence intensity. Results indicated that PV was supplying air with low turbulence intensity that was able to penetrate the convective boundary layer of the manikin to supply clean air for inhalation. The convective boundary layer, however, obstructed the supplied flow and reduced its velocity by a total of 0.26 m/s. The PV flow preserved its value until about 10 cm from the face where velocity started to drop. Further investigations were conducted to test a PV diffuser with a relatively large outlet diameter (18 cm). This diffuser was developed using 3d-modelling and 3d-printing. The diffuser successfully distributed the flow over the larger outlet area. However, the supplied velocity and turbulence fields were not uniform across the section.
Reconstruction of the indoor air temperature distribution using acoustic travel-time tomography
(2021)
Acoustic travel-time tomography (ATOM) is being increasingly considered recently as a remote sensing methodology to determine the indoor air temperatures distribution. It employs the relationship between the sound velocities along sound-paths and their related travel-times through measured room-impulse-response (RIR). Thus, the precise travel-time estimation is of critical importance which can be performed by applying an analysis time-window method. In this study, multiple analysis time-windows with different lengths are proposed to overcome the challenge of accurate detection of the travel-times at RIR. Hence, the ATOM-temperatures distribution has been measured at the climate chamber lab of the Bauhaus-University Weimar. As a benchmark, the temperatures of NTC thermistors are compared to the reconstructed temperatures derived from the ATOM technique illustrating this technique can be a reliable substitute for traditional thermal sensors. The numerical results indicate that the selection of an appropriate analysis time-window significantly enhances the accuracy of the reconstructed temperatures distribution.
El presente trabajo se inscribe en el campo de los estudios urbanos y plantea como ejes estructurantes la intersección entre las políticas públicas, el barrio y las prácticas del habitar (de Certeau, 1996, 1999; Gravano, 2003) en el marco de las transformaciones del espacio urbano en los barrios pericentrales, también denominados tradicionales de la ciudad de Córdoba, particularmente lo acontecido en Barrio Güemes, durante el periodo 2010-2016.
El propósito del abordaje se inscribe en conocer y realizar aportes generalizables a la comprensión de las prácticas del habitar como unidad de análisis. En ese marco, el problema de investigación se formula en el siguiente interrogante: ¿cómo se modifican las prácticas del habitar en el marco de las transformaciones urbanas, en un modo de producción capitalista? Se entiende a las prácticas como acciones elementales de las “artes de hacer” que las personas ordinarias ponen en marcha en su vida cotidiana: para circular, cocinar, trabajar, vincularse. También, a través de las mismas resignifican los espacios, les otorgan una valoración (positiva o negativa), se identifican como parte de la identidad y a su vez se reconocen lugares de (des)encuentro y vías de circulación.
Para su abordaje se toma como unidad de estudio el caso de barrio Güemes. El recorte espacial (o físico) del trabajo empírico está localizado en la ciudad de Córdoba, y se sitúa en la periferia del área central. Esta localización permite comprender el surgimiento de las primeras expansiones urbanas como consecuencia del crecimiento demográfico y cómo estas, se transformaron en los primeros barrios. El recorte temporal se encuentra delimitado entre los años 2000 y 2016, respaldado intencionalmente por dos acontecimientos significativos: el censo de población (2001) y la celebración del Bicentenario de la Independencia en Argentina.
Los cambios materializados en ciertos espacios urbanos, tanto en ciudades latinoamericanas (Buenos Aires, Salvador de Bahía en Brasil, México Distrito Federal, etc.) como en otras partes del mundo (New Orleans en los Estados Unidos, el distrito de Kreuzberg- Friedrichshain en Berlín, el puerto de Hamburgo en Alemania, etc.) demuestran cómo estos espacios se van transformado acorde al modo de reproducción capitalista. Pues, se trataba de espacios que en algún momento cumplieron funciones económicas-sociales jerarquizadas y luego por la dinámica misma del capitalismo, la sobreacumulación, dejan de ser rentables y pasan a ser espacios “obsoletos”. En ese sentido, la omisión de acciones públicas y/o privadas, la desatención y el crecimiento de situaciones sociales conflictivas (delitos, inseguridad, degradación) en estos espacios, funciona como argumento para que los gobiernos locales comiencen a planear el futuro y modernizarlos.
De esta manera, se plantean políticas urbanas con el objetivo de impulsar acciones de renovación o rehabilitación para dinamizar económicamente determinados sectores. Dos elementos discursivos aparecen como posibilitadores del proceso de renovación urbana: el turismo y el patrimonio. En ese sentido, bajo la recuperación patrimonial de ciertos lugares se dinamizan los territorios, por lo que el turismo se vuelve una herramienta económica que produce un excedente de plusvalía. La puesta en valor de bienes tangibles e intangibles atrae la afluencia de visitantes y, a la vez, es rentable económicamente. Ahora bien, muchas veces los proyectos tienen en cuenta las variables morfológicas y físicas, dejando en un segundo plano el impacto en el espacio próximo y las relaciones entre los habitantes con su territorio. Actualmente los espacios elegidos por los municipios para la intervención pública y/o privada son los barrios, puesto que son espacios cercanos al centro y considerados estratégicos. Por lo general, el argumento es la necesidad de rehabilitar/renovar zonas poco aprovechadas o degradadas con el objetivo de mejorar la calidad de vida de la población y dinamizar el sector (Brites, 2017; Guevara, 2012). Desde los 2000 el barrio Güemes asiste a un proceso de crecimiento inusitado. La cantidad de artesanos se disparó y variedad de productos ofrecidos, emergieron los comercios que forman parte de la oferta comercial, gastronómica y cultural del barrio. Hace varios años, presenta nuevos actores económicos que se pueden observar en la apertura de galerías comerciales; ubicadas sobre el eje de las calles Belgrano, Achával Rodríguez, Fructuoso Rivera y la creciente aparición de edificaciones alrededor de la feria artesanal histórica; con la venta y exposición de piezas del arte plástico, gastronomía, negocios de diseñadores cordobeses y hasta la inclusión de la idea del del “desarrollo sustentable” en los techos de las galerías.
La modificación del corpus normativo, la aparición de edificación en altura y el boom económico tuvieron como resultado, la valorización del suelo urbano, la retroalimentación en el espacio con el emplazamiento de nuevas actividades comerciales y servicios culturales. A la par, en el espacio barrial se presentan nuevos residentes con otros hábitos y prácticas que ponen en disputa los modos de habitar en el espacio.
A riesgo de simplificar, estas transformaciones fueron producto de los cambios políticoideológicos, de los modelos e instrumentos de gestión urbana puestos en juego en los diversos momentos históricos y de las propias prácticas sociales y culturales de los habitantes. De esta manera, se centrará la mirada analítica en las transformaciones de las prácticas del habitar de los pobladores de los Barrios Güemes, en el marco de la metamorfosis del espacio urbano (atravesado por tendencias de mediatización y mercantilización de la experiencia) que conjugó un proceso de intersección y asociatividad entre políticas públicas y expansión inmobiliaria.
In recent years, the discussion of digitalization has arrived in the media, at conferences, and in committees of the construction and real estate industry. While some areas are producing innovations and some contributors can be described as pioneers, other topics still show deficits with regard to digital transformation. The building permit process can also be counted in this category. Regardless of how architects and engineers in planning offices rely on innovative methods, building documents have so far remained in paper form in too many cases, or are printed out after electronic submission to the authority. Existing resources – for example in the form of a building information model, which could provide support in the building permit process – are not being taken advantage of. In order to use digital tools to support decision-making by the building permit authorities, it is necessary to understand the current situation and to question conditions before pursuing the overall automation of internal authority processes as the sole solution.
With a substantive-organizational consideration of the relevant areas that influence building permit determination, an improvement of the building permit procedure within authorities is proposed. Complex areas – such as legal situations, the use of technology, as well as the subjective alternative action – are determined and structured. With the development of a model for the determination of building permitability, both an understanding of influencing factors is conveyed and an increase in transparency for all parties involved is created.
In addition to an international literature review, an empirical study served as the research method. The empirical study was conducted in the form of qualitative expert interviews in order to determine the current state in the field of building permit procedures. The collected data material was processed and subsequently subjected to a software-supported content analysis. The results were processed, in combination with findings from the literature review, in various analyses to form the basis for a proposed model.
The result of the study is a decision model that closes the gap between the current processes within the building authorities and an overall automation of the building permit review process. The model offers support to examiners and applicants in determining building permit eligibility, through its process-oriented structuring of decision-relevant facts. The theoretical model could be transferred into practice in the form of a web application.
The spread of breathing air when playing wind instruments and singing was investigated and visualized using two methods: (1) schlieren imaging with a schlieren mirror and (2) background-oriented schlieren (BOS). These methods visualize airflow by visualizing density gradients in transparent media. The playing of professional woodwind and brass instrument players, as well as professional classical trained singers were investigated to estimate the spread distances of the breathing air. For a better comparison and consistent measurement series, a single high note, a single low note, and an extract of a musical piece were investigated. Additionally, anemometry was used to determine the velocity of the spreading breathing air and the extent to which it was quantifiable. The results showed that the ejected airflow from the examined instruments and singers did not exceed a spreading range of 1.2 m into the room. However, differences in the various instruments have to be considered to assess properly the spread of the breathing air. The findings discussed below help to estimate the risk of cross-infection for wind instrument players and singers and to develop efficacious safety precautions, which is essential during critical health periods such as the current COVID-19 pandemic.
This paper presents numerical analysis of the discrete fundamental solution of the discrete Laplace operator on a rectangular lattice. Additionally, to provide estimates in interior and exterior domains, two different regularisations of the discrete fundamental solution are considered. Estimates for the absolute difference and lp-estimates are constructed for both regularisations. Thus, this work extends the classical results in the discrete potential theory to the case of a rectangular lattice and serves as a basis for future convergence analysis of the method of discrete potentials on rectangular lattices.
Structures under wind action can exhibit various aeroelastic interaction phenomena, which can lead to destructive and catastrophic events. Such unstable interaction can be beneficially used for small-scale aeroelastic energy harvesting. Proper understanding and prediction of fluid−structure interactions (FSI) phenomena are therefore crucial in many engineering fields. This research intends to develop coupled FSI models to extend the applicability of Vortex Particle Methods (VPM) for numerically analysing the complex FSI of thin-walled flexible structures under steady and fluctuating incoming flows. In this context, the flow around deforming thin bodies is analysed using the two-dimensional and pseudo-three-dimensional implementations of VPM. The structural behaviour is modelled and analysed using the Finite Element Method. The partitioned coupling approach is considered because of the flexibility of using different mathematical procedures for solving fluid and solid mechanics. The developed coupled models are validated with several benchmark FSI problems in the literature. Finally, the models are applied to several fundamental and application field of FSI problems of different thin-walled flexible structures irrespective of their size.
Global structural analyses in civil engineering are usually performed considering linear-elastic material behavior. However, for steel structures, a certain degree of plasticization depending on the member classification may be considered. Corresponding plastic analyses taking material nonlinearities into account are effectively realized using numerical methods. Frequently applied finite elements of two and three-dimensional models evaluate the plasticity at defined nodes using a yield surface, i.e. by a yield condition, hardening rule, and flow rule. Corresponding calculations are connected to a large numerical as well as time-consuming effort and they do not rely on the theoretical background of beam theory, to which the regulations of standards mainly correspond. For that reason, methods using beam elements (one-dimensional) combined with cross-sectional analyses are commonly applied for steel members in terms of plastic zones theories. In these approaches, plasticization is in general assessed by means of axial stress only. In this paper, more precise numerical representation of the combined stress states, i.e. axial and shear stresses, is presented and results of the proposed approach are validated and discussed.
Polylactic acid (PLA) is a highly applicable material that is used in 3D printers due to some significant features such as its deformation property and affordable cost. For improvement of the end-use quality, it is of significant importance to enhance the quality of fused filament fabrication (FFF)-printed objects in PLA. The purpose of this investigation was to boost toughness and to reduce the production cost of the FFF-printed tensile test samples with the desired part thickness. To remove the need for numerous and idle printing samples, the response surface method (RSM) was used. Statistical analysis was performed to deal with this concern by considering extruder temperature (ET), infill percentage (IP), and layer thickness (LT) as controlled factors. The artificial intelligence method of artificial neural network (ANN) and ANN-genetic algorithm (ANN-GA) were further developed to estimate the toughness, part thickness, and production-cost-dependent variables. Results were evaluated by correlation coefficient and RMSE values. According to the modeling results, ANN-GA as a hybrid machine learning (ML) technique could enhance the accuracy of modeling by about 7.5, 11.5, and 4.5% for toughness, part thickness, and production cost, respectively, in comparison with those for the single ANN method. On the other hand, the optimization results confirm that the optimized specimen is cost-effective and able to comparatively undergo deformation, which enables the usability of printed PLA objects.
Burning of clinker is the most influencing step of cement quality during the production process. Appropriate characterisation for quality control and decision-making is therefore the critical point to maintain a stable production but also for the development of alternative cements. Scanning electron microscopy (SEM) in combination with energy dispersive X-ray spectroscopy (EDX) delivers spatially resolved phase and chemical information for cement clinker. This data can be used to quantify phase fractions and chemical composition of identified phases.
The contribution aims to provide an overview of phase fraction quantification by semi-automatic phase segmentation using high-resolution backscattered electron (BSE) images and lower-resolved EDX element maps. Therefore, a tool for image analysis was developed that uses state-of-the-art algorithms for pixel-wise image segmentation and labelling in combination with a decision tree that allows searching for specific clinker phases. Results show that this tool can be applied to segment sub-micron scale clinker phases and to get a quantification of all phase fractions. In addition, statistical evaluation of the data is implemented within the tool to reveal whether the imaged area is representative for all clinker phases.
This study demonstrates the application and combination of multiple imaging techniques [light microscopy, micro-X-ray computer tomography (μ-CT), scanning electron microscopy (SEM) and focussed ion beam – nano-tomography (FIB-nT)] to the analysis of the microstructure of hydrated alite across multiple scales. However, by comparing findings with mercury intrusion porosimetry (MIP), it becomes obvious that the imaged 3D volumes and 2D images do not sufficiently overlap at certain scales to allow a continuous quantification of the pore size distribution (PSD). This can be overcome by improving the resolution and increasing the measured volume. Furthermore, results show that the fibrous morphology of calcium-silicate-hydrates (C-S-H) phases is preserved during FIB-nT. This is a requirement for characterisation of nano-scale porosity. Finally, it was proven that the combination of FIB-nT with energy-dispersive X-ray spectroscopy (EDX) data facilitates the phase segmentation of a 11 × 11 × 7.7 μm3 volume of hydrated alite.
Within the scope of literature, the influence of openings within the infill walls that are bounded by a reinforced concrete frame and excited by seismic drift forces in both in- and out-of-plane direction is still uncharted. Therefore, a 3D micromodel was developed and calibrated thereafter, to gain more insight in the topic. The micromodels were calibrated against their equivalent physical test specimens of in-plane, out-of-plane drift driven tests on frames with and without infill walls and openings, as well as out-of-plane bend test of masonry walls. Micromodels were rectified based on their behavior and damage states. As a result of the calibration process, it was found that micromodels were sensitive and insensitive to various parameters, regarding the model’s behavior and computational stability. It was found that, even within the same material model, some parameters had more effects when attributed to concrete rather than on masonry. Generally, the in-plane behavior of infilled frames was found to be largely governed by the interface material model. The out-of-plane masonry wall simulations were governed by the tensile strength of both the interface and masonry material model. Yet, the out-of-plane drift driven test was governed by the concrete material properties.
Realistic uncertainty description incorporating aleatoric and epistemic uncertainties can be described within the framework of polymorphic uncertainty, which is computationally demanding. Utilizing a domain decomposition approach for random field based uncertainty models the proposed level-based sampling method can reduce these computational costs significantly and shows good agreement with a standard sampling technique. While 2-level configurations tend to get unstable with decreasing sampling density 3-level setups show encouraging results for the investigated reliability analysis of a structural unit square.
Bauhaus-Gastprofessorin Mirjam Wenzel referierte am 30. Juni 2021 im Audimax der Bauhaus-Universität Weimar zur Entstehungsgeschichte und Konzeption Jüdischer Museen. Dabei ging sie darauf ein, inwiefern diese Museen besonders relevant für aktuelle gesellschaftliche und politische Fragestellungen sind. Prof. Wenzels zweiter öffentlicher Vortrag an der Bauhaus-Universität Weimar skizzierte die Potentiale von Kultureinrichtungen in Zeiten gesellschaftspolitischer Veränderungen im Allgemeinen und die Bedeutung Jüdischer Museen angesichts verbaler und tätlicher Gewalt gegen Jüdinnen und Juden im Besonderen.
Compiling and disseminating information about incidents and disasters are key to disaster management and relief. But due to inherent limitations of the acquisition process, the required information is often incomplete or missing altogether. To fill these gaps, citizen observations spread through social media are widely considered to be a promising source of relevant information, and many studies propose new methods to tap this resource. Yet, the overarching question of whether and under which circumstances social media can supply relevant information (both qualitatively and quantitatively) still remains unanswered. To shed some light on this question, we review 37 disaster and incident databases covering 27 incident types, compile a unified overview of the contained data and their collection processes, and identify the missing or incomplete information. The resulting data collection reveals six major use cases for social media analysis in incident data collection: (1) impact assessment and verification of model predictions, (2) narrative generation, (3) recruiting citizen volunteers, (4) supporting weakly institutionalized areas, (5) narrowing surveillance areas, and (6) reporting triggers for periodical surveillance. Furthermore, we discuss the benefits and shortcomings of using social media data for closing information gaps related to incidents and disasters.