Refine
Document Type
- Doctoral Thesis (33)
- Article (7)
- Conference Proceeding (6)
- Master's Thesis (4)
- Book (3)
- Preprint (3)
- Bachelor Thesis (2)
- Periodical (2)
- Report (2)
- Habilitation (1)
Institute
- Institut für Strukturmechanik (ISM) (12)
- Institut für Europäische Urbanistik (6)
- Institut für Konstruktiven Ingenieurbau (IKI) (4)
- Professur Sozialwissenschaftliche Stadtforschung (4)
- Professur Modellierung und Simulation - Konstruktion (3)
- Professur Raumplanung und Raumforschung (3)
- Promotionsstudiengang Kunst und Design-Freie Kunst-Medienkunst (Ph.D) (3)
- An-Institute (2)
- Junior-Professur Organisation und vernetzte Medien (2)
- Medienkunst/Mediengestaltung (2)
Keywords
- OA-Publikationsfonds2019 (8)
- Architektur (5)
- Ingenieurwissenschaften (4)
- Stadtplanung (4)
- Denkmalpflege (3)
- Ingenieurbau (3)
- Stadtentwicklung (3)
- Structural Engineering (3)
- Städtebau (3)
- Aerodynamik (2)
- Architekturtheorie (2)
- Finite-Elemente-Methode (2)
- Gashochdruckleitungen (2)
- Geschäftsmodell (2)
- Inventarisierung (2)
- Journalismus (2)
- Korrosion (2)
- Kulturerbe (2)
- Kulturwissenschaft (2)
- Maschinelles Lernen (2)
- Medienwissenschaft (2)
- Nachkriegsarchitektur (2)
- Neue Medien (2)
- Nutzung (2)
- Optimierung (2)
- Planung (2)
- Proceedings (2)
- Sicherheit (2)
- Siedlung (2)
- Sommerkurs (2)
- Zahlungsbereitschaft (2)
- proceedings (2)
- summer school (2)
- 3D Telepresence (1)
- ANT (1)
- Acoustic Travel-Time Tomography (1)
- Actor-Network-Theory (1)
- Aerodynamic admittance (1)
- Aeroelastizität (1)
- Akustische Tomographie (1)
- Amsterdam (1)
- Amsterdamer Schule (1)
- Angewandte Informatik (1)
- Angewandte Mathematik (1)
- Anschluss (1)
- Architecture Guidebook (1)
- Architekturfotografie (1)
- Audio-Walk (1)
- Audioführung (1)
- Audiowalk (1)
- Auditory Awareness (1)
- Aufführung (1)
- Autorschaft (1)
- Bauberatung (1)
- Baugestaltung (1)
- Bauklimatik (1)
- Baukultur (1)
- Bauphysik (1)
- Bebauungsplan (1)
- Bending Stiffness of cable elements (1)
- Beton (1)
- Biegesteifigkeit (1)
- Bild-Autorenschaft (1)
- Bildanalyse (1)
- Biogas (1)
- Biogasanlage (1)
- Brazil (1)
- Bridge (1)
- Britain (1)
- Brücke (1)
- Buchgestaltung (1)
- Buffeting (1)
- Camera Calibration (1)
- Child Friendly Cities Initiative (1)
- Collective Listening (1)
- Computational fluid dynamics (1)
- Damage identification (1)
- Dams (1)
- Denkmal (1)
- Depth Camera (1)
- Design (1)
- Designing Urban National Memory (1)
- Development (1)
- Digitale Fotografie (1)
- Digitalisierung (1)
- Digitaljournalismus (1)
- Dissertation (1)
- Dissipationsenergie (1)
- Egypt (1)
- Eija-Liisa Ahtila (1)
- Eisenbahn (1)
- Elektrifizierung (1)
- Elektropolis (1)
- Energiewende (1)
- Erasmus + (1)
- Erfahrungswissen (1)
- Erinnerung (1)
- Ermüdung (1)
- Fachkonzept (1)
- Feminismus (1)
- Finite-Differenzen-Methode (1)
- Finnland (1)
- Fotografie als Handlung (1)
- Fotografisches Handlungsgefüge (1)
- Frankfurt am Main (1)
- Full waveform inversion (1)
- Funktechnik (1)
- Förderungsprogramm (1)
- Gartenstadt (1)
- Gartenvorort (1)
- Gemeinwohl (1)
- Gentrifizierung (1)
- Geoinformationssystem (1)
- Geometry Independent Field Approximation (1)
- Geschichte (1)
- Gestaltoptimierung (1)
- Gestaltungsbeirat (1)
- Gestaltungssatzung (1)
- Gleisanlage (1)
- Gleisdynamik (1)
- Globalgeschichte (1)
- Grasshopper 3D (1)
- Großbritannien (1)
- Großsiedlung (1)
- Herrschaftsarchitektur (1)
- Hochbau (1)
- Holzbau (1)
- Illustration (1)
- Illustriertes Buch (1)
- Industriekultur (1)
- Inertgas (1)
- Information Retrieval (1)
- Informationsdesign (1)
- Infrastruktur (1)
- Infrastrukturgeschichte (1)
- Intangible Acoustic Heritage (1)
- Internet of Things (1)
- Inverse analysis (1)
- Isogeometrc Analysis (1)
- Jazz (1)
- Jazzforschung (1)
- Jugend (1)
- Kabel (1)
- Kairo (1)
- Kapitalisierung (1)
- Keramik (1)
- Kind (1)
- Klangkunst (1)
- Kleben (1)
- Klimaänderung (1)
- Kommunalplanung (1)
- Kommunikation (1)
- Konjugierte-Gradienten-Methode (1)
- Konstruktion (1)
- Konstruktiver Ingenieurbau (1)
- Korea (1)
- Kunst (1)
- Künstlerische Forschung (1)
- Learned Lessons (1)
- Long-span bridges (1)
- Luftzerlegung (1)
- Machine learning (1)
- Machttheorie (1)
- Maissilage (1)
- Maschinenbau (1)
- Medienbudget (1)
- Mediendesign (1)
- Medienmarkt (1)
- Medium (1)
- Mehrgitterverfahren (1)
- Mehrkriterielle Optimierung (1)
- Mensch-Maschine-Kommunikation (1)
- Migration (1)
- Mikrocomputer (1)
- Mobile Media Art (1)
- Modalanalyse (1)
- Modellierung (1)
- Multiobjective Optimization (1)
- Neues Bauen (1)
- Niederlande (1)
- Nonlinear Cable Analysis (1)
- Numerical (1)
- OA-Publikationsfonds2020 (1)
- Oberflächenanalyse (1)
- Oberflächenporosität (1)
- Operational modal analysis (1)
- Organoleptik (1)
- Oxidkeramik (1)
- Performative Fotografie (1)
- Politics (1)
- Polynomial Splines over Hierarchical T-meshes (1)
- Post-Conflict society (1)
- Praxisbasierte Forschung (1)
- Prevailing/ Competing Narratives (1)
- Probabilistik (1)
- Probailistik (1)
- Probekörpererwärmung (1)
- Psychogeographie (1)
- Qualitätskontrolle (1)
- Qualitätsmanagement (1)
- Qualitätsstandard (1)
- Quartiersmanagement (1)
- Railway (1)
- Raspberry Pi (1)
- Reading Urban National Memory (1)
- Recovery Based Error Estimator (1)
- Reliability Analysis (1)
- Rezeption (1)
- Rotterdam (1)
- Sanierungssatzung (1)
- Sauerstoff (1)
- Sauerstoffseparation (1)
- Scalarization Methods (1)
- Schottersäule (1)
- Schule (1)
- Schwingungsdämpfer (1)
- Schwingungsmessung (1)
- Selfie (1)
- Semiotik (1)
- Sensor (1)
- Sichtbeton (1)
- Simulation (1)
- Skopje 2014 (1)
- Smartphone (1)
- Smartphones (1)
- Social Media (1)
- Soziale Bewegung (1)
- Sozialwohnung (1)
- Spielleitplanung (1)
- Stadterneuerung (1)
- Stadtforschung (1)
- Stadtgeschichte (1)
- Stadtsanierung (1)
- Stadtumbau (1)
- Staudamm (1)
- Staumauer (1)
- Stereotyp (1)
- Stickstoff (1)
- Stone Columns (1)
- Structural Health Monitoring (1)
- Structural Optimization (1)
- Strukturdynamik (1)
- Strukturmechanik (1)
- Strömungsmechanik (1)
- Städtebauförderung (1)
- Subjekt (1)
- Talsperre (1)
- Technikgeschichte (1)
- Telepräsenz (1)
- Text-bild-basierte Narration (1)
- Tiefensensor (1)
- Tirana (1)
- Traditioneller Illustrationsbegriff (1)
- UN-Kinderrechtskonvention (1)
- Universitätsgeschichte (1)
- Urban studies (1)
- Valparaíso (1)
- Verbindung (1)
- Verbund (1)
- Verkehrslast (1)
- Vernetzung (1)
- Vibration measurements (1)
- Videokunst (1)
- Virtual Reality (1)
- Virtuelle Realität (1)
- Visuelle Semiotik (1)
- Vortex particle method (1)
- Wasserbau (1)
- Wave propagation (1)
- Weimar (1)
- Weltgeschichte (1)
- Wettbewerbswesen (1)
- Wind Energy (1)
- Wind Turbines (1)
- Windenergie (1)
- Windturbine (1)
- Wireless sensor network (1)
- Wirklichkeit (1)
- Wirtschaftsimperialismus (1)
- Wohnbau (1)
- Wohnen (1)
- Wohnungsmoderne (1)
- Wohnungswesen (1)
- Wärmeleitfähigkeit (1)
- Zeitgenössischer Illustrationsbegriff (1)
- Zentralchina (1)
- Zuverlässigkeitsanalyse (1)
- abstract modelling (1)
- abstraction (1)
- aerodynamic models (1)
- art in public space (1)
- artistic research (1)
- audio walk (1)
- bridge (1)
- bridge aerodynamics (1)
- bridge aeroelasticity (1)
- business model (1)
- capitalization (1)
- category theory (1)
- ceramics (1)
- climate change (1)
- computational planning (1)
- conjugate gradient method (1)
- crack (1)
- crack identification (1)
- dams (1)
- digital media (1)
- discrete function theory (1)
- energy demand (1)
- engineering (1)
- evidence-based design (1)
- finite difference methods (1)
- finite element method (1)
- formal approaches (1)
- genetic algorithm (1)
- grid-based (1)
- kinder- und jugendfreundliche Stadtentwicklung (1)
- low middle class (1)
- machine learning (1)
- matrix-free (1)
- media use (1)
- modal analysis (1)
- model complexity (1)
- modelling (1)
- multigrid method (1)
- neoliberal urban reconstruction (1)
- network analysis (1)
- nonlinear analysis (1)
- p-Laplace equation (1)
- passive control (1)
- planning history (1)
- power theory of value (1)
- price policy (1)
- property sector (1)
- resilient city (1)
- self-production (1)
- social accessibility (1)
- social housing (1)
- spatial analysis (1)
- strategic limitation (1)
- structural dynamics (1)
- tall buildings (1)
- thermal conductivity (1)
- town planning (1)
- trade-offs (1)
- transfer (1)
- tuned mass dampers (1)
- type theory (1)
- urban form (1)
- urban history (1)
- urban narratives (1)
- urban perception (1)
- urban planning (1)
- urbanHIST (1)
- willingness to pay (1)
- wind-induced vibration (1)
- wireless sensor networks (1)
- Ägypten (1)
- Öffentlichkeitsbeteiligung (1)
Year of publication
- 2019 (65) (remove)
This research seeks to make an exploratory study of the strategies used by the creators of monuments, memorials, and commemorative places located in the public spaces that use sound as one of the primary raw material in their design. The term acoustic monu-memorials was coined in this research to encircle these structures and places. In order to achieve the goal of this research, it was necessary to compile a number of samples, primarily after the digital recording era of captured sound around 1971 to the present. The compilation was relevant because such a compendium was not found in the literature, and to the author's knowledge, a comprehensive investigation of the strategies used in planning acoustic monu-memorials in the urban spaces does not exist.
The method used to create such compendium was to send a question to people with different background identities, such as visual and sound artists, musicians, art curators, and heritage scholars among others. This question produced a selection of 51 examples of acoustic monu-memorials located in public spaces. Subsequently, the examples were classified into four major categories according to their form and nature. Additionally, two examples from the main categories were chosen as case studies: The Sinti and Roma Memorial in Berlin, Germany and the Niche monument in Cali, Colombia. These study cases were presented, described, and analysed in detail as they represent the type of what could be defined as an acoustic monu-memorial in general.
Lynch’s (1960) five elements that help individuals build the image of the city were transferred and used as a tool to help to build this image into acoustic terms. A thorough analysis of the acquired data yielded found the strategies used by the designers to shape, modify, transform, and structure public space. These strategies are entitled Sound Spaces. Moreover, a list entitled Urban Acoustic Commemoration Code was compiled. This list of suggestions addresses urban planners, architects, artists, designers, and general public interested in the aspects involved when creating acoustic commemoration phenomena in public spaces.
Am Beispiel der Elektrifizierung zweier Großstädte an der Westküste Südamerikas zeigt die Arbeit den globalen Einfluss deutscher Industrie- und Finanzakteure auf technische, städtebauliche und gesellschaftlich-kulturelle Entwicklungen zur Blütezeit des europäischen Imperialismus auf. Damit werden die Regionalgeschichten der chilenischen Hauptstadtregion und der Elektropolis Berlin zu einer Globalgeschichte miteinander verknüpft. Ein Hauptaugenmerk der Analyse liegt dabei auf den weltweiten Akteursnetzwerken und Machtverhältnissen sowie dem kulturellen Erbe und seiner gegenwärtigen Interpretation.
Wireless sensor networks have attracted great attention for applications in structural health monitoring due to their ease of use, flexibility of deployment, and cost-effectiveness. This paper presents a software framework for WiFi-based wireless sensor networks composed of low-cost mass market single-board computers. A number of specific system-level software components were developed to enable robust data acquisition, data processing, sensor network communication, and timing with a focus on structural health monitoring (SHM) applications. The framework was validated on Raspberry Pi computers, and its performance was studied in detail. The paper presents several characteristics of the measurement quality such as sampling accuracy and time synchronization and discusses the specific limitations of the system. The implementation includes a complementary smartphone application that is utilized for data acquisition, visualization, and analysis. A prototypical implementation further demonstrates the feasibility of integrating smartphones as data acquisition nodes into the network, utilizing their internal sensors. The measurement system was employed in several monitoring campaigns, three of which are documented in detail. The suitability of the system is evaluated based on comparisons of target quantities with reference measurements. The results indicate that the presented system can robustly achieve a measurement performance commensurate with that required in many typical SHM tasks such as modal identification. As such, it represents a cost-effective alternative to more traditional monitoring solutions.
The p-Laplace equation is a nonlinear generalization of the well-known Laplace equation. It is often used as a model problem for special types of nonlinearities, and therefore it can be seen as a bridge between very general nonlinear equations and the linear Laplace equation, too. It appears in many problems for instance in the theory of non-Newtonian fluids and fluid dynamics or in rockfill dam problems, as well as in special problems of image restoration and image processing.
The aim of this thesis is to solve the p-Laplace equation for 1 < p < 2, as well as for 2 < p < 3 and to find strong solutions in the framework of Clifford analysis. The idea is to apply a hypercomplex integral operator and special function theoretic methods to transform the p-Laplace equation into a p-Dirac equation. We consider boundary value problems for the p-Laplace equation and transfer them to boundary value problems for a p-Dirac equation. These equations will be solved iteratively by applying Banach’s fixed-point principle. Applying operator-theoretical methods for the p-Dirac equation, the existence and uniqueness of solutions in certain Sobolev spaces will be proved.
In addition, using a finite difference approach on a uniform lattice in the plane, the fundamental solution of the Cauchy-Riemann operator and its adjoint based on the fundamental solution of the Laplacian will be calculated. Besides, we define gener- alized discrete Teodorescu transform operators, which are right-inverse to the discrete Cauchy-Riemann operator and its adjoint in the plane. Furthermore, a new formula for generalized discrete boundary operators (analogues of the Cauchy integral operator) will be considered. Based on these operators a new version of discrete Borel-Pompeiu formula is formulated and proved.
This is the basis for an operator calculus that will be applied to the numerical solution of the p-Dirac equation. Finally, numerical results will be presented showing advantages and problems of this approach.
Brazilian battlers’ housing discusses the self-production of dwellings in the circumstances of the socioeconomic rise of the so-called Brazilian new middle class, occurred on the first decade of the years 2000. Battlers are a precarious working class of about 100 million people, who have used their recently increased purchase power to informally solve their private housing demands, planning, building and renovating their homes themselves, with limited technical knowledge and almost no access to formal technicians as for example architects. The result is a mode of housing production, which spreads over the territory in micro-local self-initiatives and informal social practices of construction and management. With the support of a controversial manpower, this practice presents all sorts of technical complications, but at the same time expedient ways of affordability and creative spatial solutions for ordinary constructive problems. Such initiatives have consolidated Brazilian informal settlements and peripheral subdivisions, attending a demand poorly responded by the government. This research recognises the benefits of the self-production, but questions the conditions under which it happens and asks if it really collaborates for a true social rise of those who are engaged in it. With an empirical and qualitative approach and taking dwelling construction processes leaded by battlers as main information sources, the academic work responds if and how the socioeconomic rise of the Brazilian battlers has exactly affected the self-production of dwellings. For that, battlers’ self-production of dwellings is analysed and discussed in five main aspects: 1) acquisition of land and real state, 2) building overtime, 3) space and creative power, 4) technical complications and building materials and 5) manpower and know-how.
Acoustic travel-time tomography (ATOM) determines the distribution of the temperature in a propagation medium by measuring the travel-time of acoustic signals between transmitters and receivers. To employ ATOM for indoor climate measurements, the impulse responses have been measured in the climate chamber lab of the Bauhaus-University Weimar and compared with the theoretical results of its image source model (ISM). A challenging task is distinguishing the reflections of interest in the reflectogram when the sound rays have similar travel-times. This paper presents a numerical method to address this problem by finding optimal positions of transmitter and receiver, since they have a direct impact on the distribution of travel times. These optimal positions have the minimum number of simultaneous arrival time within a threshold level. Moreover, for the tomographic reconstruction, when some of the voxels remain empty of sound-rays, it leads to inaccurate determination of the air temperature within those voxels. Based on the presented numerical method, the number of empty tomographic voxels are minimized to ensure the best sound-ray coverage of the room. Subsequently, a spatial temperature distribution is estimated by simultaneous iterative reconstruction technique (SIRT). The experimental set-up in the climate chamber verifies the simulation results.
Urban planners are often challenged with the task of developing design solutions which must meet multiple, and often contradictory, criteria. In this paper, we investigated the trade-offs between social, psychological, and energy potential of the fundamental elements of urban form: the street network and the building massing. Since formal mehods to evaluate urban form from the psychological and social point of view are not readily available, we developed a methodological framework to quantify these criteria as the first contribution in this paper. To evaluate the psychological potential, we conducted a three-tiered empirical study starting from real world environments and then abstracting them to virtual environments. In each context, the implicit (physiological) response and explicit (subjective) response of pedestrians were measured. To quantify the social potential, we developed a street network centrality-based measure of social accessibility.
For the energy potential, we created an energy model to analyze the impact of pure geometric form on the energy demand of the building stock. The second contribution of this work is a method to identify distinct clusters of urban form and, for each, explore the trade-offs between the select design criteria. We applied this method to two case studies identifying nine types of urban form and their respective potential trade-offs, which are directly applicable for the assessment of strategic decisions regarding urban form during the early planning stages.
A categorical perspective towards aerodynamic models for aeroelastic analyses of bridge decks
(2019)
Reliable modelling in structural engineering is crucial for the serviceability and safety of structures. A huge variety of aerodynamic models for aeroelastic analyses of bridges poses natural questions on their complexity and thus, quality. Moreover, a direct comparison of aerodynamic models is typically either not possible or senseless, as the models can be based on very different physical assumptions. Therefore, to address the question of principal comparability and complexity of models, a more abstract approach, accounting for the effect of basic physical assumptions, is necessary.
This paper presents an application of a recently introduced category theory-based modelling approach to a diverse set of models from bridge aerodynamics. Initially, the categorical approach is extended to allow an adequate description of aerodynamic models. Complexity of the selected aerodynamic models is evaluated, based on which model comparability is established. Finally, the utility of the approach for model comparison and characterisation is demonstrated on an illustrative example from bridge aeroelasticity. The outcome of this study is intended to serve as an alternative framework for model comparison and impact future model assessment studies of mathematical models for engineering applications.
The vibration control of the tall building during earthquake excitations is a challenging task due to their complex seismic behavior. This paper investigates the optimum placement and properties of the Tuned Mass Dampers (TMDs) in tall buildings, which are employed to control the vibrations during earthquakes. An algorithm was developed to spend a limited mass either in a single TMD or in multiple TMDs and distribute them optimally over the height of the building. The Non-dominated Sorting Genetic Algorithm (NSGA – II) method was improved by adding multi-variant genetic operators and utilized to simultaneously study the optimum design parameters of the TMDs and the optimum placement. The results showed that under earthquake excitations with noticeable amplitude in higher modes, distributing TMDs over the height of the building is more effective in mitigating the vibrations compared to the use of a single TMD system. From the optimization, it was observed that the locations of the TMDs were related to the stories corresponding to the maximum modal displacements in the lower modes and the stories corresponding to the maximum modal displacements in the modes which were highly activated by the earthquake excitations. It was also noted that the frequency content of the earthquake has significant influence on the optimum location of the TMDs.
Modern immersive telepresence systems enable people at different locations to meet in virtual environments using realistic three-dimensional representations of their bodies. For the realization of such a three-dimensional version of a video conferencing system, each user is continuously recorded in 3D. These 3D recordings are exchanged over the network between remote sites. At each site, the remote recordings of the users, referred to as 3D video avatars, are seamlessly integrated into a shared virtual scenery and displayed in stereoscopic 3D for each user from his or her perspective.
This thesis reports on algorithmic and technical contributions to modern immersive telepresence systems and presents the design, implementation and evaluation of the first immersive group-to-group telepresence system in which each user is represented as realistic life-size 3D video avatar. The system enabled two remote user groups to meet and collaborate in a consistent shared virtual environment. The system relied on novel methods for the precise calibration and registration of color- and depth- sensors (RGBD) into the coordinate system of the application as well as an advanced distributed processing pipeline that reconstructs realistic 3D video avatars in real-time. During the course of this thesis, the calibration of 3D capturing systems was greatly improved. While the first development focused on precisely calibrating individual RGBD-sensors, the second stage presents a new method for calibrating and registering multiple color and depth sensors at a very high precision throughout a large 3D capturing volume. This method was further refined by a novel automatic optimization process that significantly speeds up the manual operation and yields similarly high accuracy. A core benefit of the new calibration method is its high runtime efficiency by directly mapping from raw depth sensor measurements into an application coordinate system and to the coordinates of its associated color sensor. As a result, the calibration method is an efficient solution in terms of precision and applicability in virtual reality and immersive telepresence applications. In addition to the core contributions, the results of two case studies which address 3D reconstruction and data streaming lead to the final conclusion of this thesis and to directions of future work in the rapidly advancing field of immersive telepresence research.
Landwirtschaftliche Biogasanlagen leisten mit ca. 9.300 Anlagen und einem Anteil von 5,3% an der Stromerzeugung, einen Beitrag zur Erzeugung Erneuer-barer Energien in Deutschland. Die Optimierung dieser Anlagen fördert die nachhaltige Bereitstellung von Strom, Wärme und BioErdgas.
Das Ergebnis dieser Forschungsarbeit ist die Entwicklung eines mehrmethodi-schen Bewertungsansatzes zur Beschreibung der Qualität der Eingangs-substrate als Teil einer ganzheitlichen Prozessoptimierung. Dies gelingt durch die kombinierte Nutzung klassischer Analysesätze, der Nutzung organolepti-scher Parameter – der humansensorischen Sinnenprüfung – und der Integration von prozess- und substratspezifischem Erfahrungswissen. Anhand von halbtechnischen Versuchen werden Korrelationen und Kausalitäten zwi-schen chemisch-physikalischen, biologischen, organoleptischen und erfahrungsbezogenen Parametern erforscht. Die Entwicklung einer Fallbasis mit Hilfe des Fallbasierten Schließens, einer Form Künstlicher Intelligenz, zeigt das Entwicklungs- und Integrationspotenzial der Automatisierung auf, insbesondere auch im Hinblick auf neue Ansätze z.B. Industrie 4.0. Erste Lösungen zur Bewältigung der identifizierten Herausforderungen der mehrmethodischen Prozessbewertung werden vorgestellt.
Abschließend wird ein Ausblick auf den weiteren Forschungsbedarf gegeben und die Übertragbarkeit des mehrmethodischen Bewertungsansatzes auf andere Anwendungsfelder z.B. Bioabfallbehandlung, Kläranlagen angeregt.
Identification of flaws in structures is a critical element in the management of maintenance and quality assurance processes in engineering. Nondestructive testing (NDT) techniques based on a wide range of physical principles have been developed and are used in common practice for structural health monitoring. However, basic NDT techniques are usually limited in their ability to provide the accurate information on locations, dimensions and shapes of flaws. One alternative to extract additional information from the results of NDT is to append it with a computational model that provides detailed analysis of the physical process involved and enables the accurate identification of the flaw parameters. The aim here is to develop the strategies to uniquely identify cracks in two-dimensional 2D) structures under dynamic loadings.
A local NDT technique combined eXtended Finite Element Method (XFEM) with dynamic loading in order to identify the cracks in the structures quickly and accurately is developed in this dissertation. The Newmark-b time integration method with Rayleigh damping is used for the time integration. We apply Nelder-Mead (NM)and Quasi-Newton (QN) methods for identifying the crack tip in plate. The inverse problem is solved iteratively, in which XFEM is used for solving the forward problem in each iteration. For a timeharmonic excitation with a single frequency and a short-duration signal measured along part of the external boundary, the crack is detected through the solution of an inverse time-dependent problem. Compared to the static load, we show that the dynamic loads are more effective for crack detection problems. Moreover, we tested different dynamic loads and find that NM method works more efficient under the harmonic load than the pounding load while the QN method achieves almost the same results for both load types.
A global strategy, Multilevel Coordinate Search (MCS) with XFEM (XFEM-MCS) methodology under the dynamic electric load, to detect multiple cracks in 2D piezoelectric plates is proposed in this dissertation. The Newmark-b method is employed for the time integration and in each iteration the forward problem is solved by XFEM for various cracks. The objective functional is minimized by using a global search algorithm MCS. The test problems show that the XFEM-MCS algorithm under the dynamic electric load can be effectively employed for multiple cracks detection in piezoelectric materials, and it proves to be robust in identifying defects in piezoelectric structures. Fiber-reinforced composites (FRCs) are extensively applied in practical engineering since they have high stiffness and strength. Experiments reveal a so-called interphase zone, i.e. the space between the outside interface of the fiber and the inside interface of the matrix. The interphase strength between the fiber and the matrix strongly affects the mechanical properties as a result of the large ratio of interface/volume. For the purpose of understanding the mechanical properties of FRCs with functionally graded interphase (FGI), a closed-form expression of the interface strength between a fiber and a matrix is obtained in this dissertation using a continuum modeling approach according to the ver derWaals (vdW) forces. Based on the interatomic potential, we develop a new modified nonlinear cohesive law, which is applied to study the interface delamination of FRCs with FGI under different loadings. The analytical solutions show that the delamination behavior strongly depends on the interphase thickness, the fiber radius, the Young’s moduli and Poisson’s ratios of the fiber and the matrix. Thermal conductivity is the property of a material to conduct heat. With the development and deep research of 2D materials, especially graphene and molybdenum disulfide (MoS2), the thermal conductivity of 2D materials attracts wide attentions. The thermal conductivity of graphene nanoribbons (GNRs) is found to appear a tendency of decreasing under tensile strain by classical molecular dynamics (MD) simulations. Hence, the strain effects of graphene can play a key role in the continuous tunability and applicability of its thermal conductivity property at nanoscale, and the dissipation of thermal conductivity is an obstacle for the applications of thermal management. Up to now, the thermal conductivity of graphene under shear deformation has not been investigated yet. From a practical point of view, good thermal managements of GNRs have significantly potential applications of future GNR-based thermal nanodevices, which can greatly improve performances of the nanosized devices due to heat dissipations. Meanwhile, graphene is a thin membrane structure, it is also important to understand the wrinkling behavior under shear deformation. MoS2 exists in the stable semiconducting 1H phase (1H-MoS2) while the metallic 1T phase (1T-MoS2) is unstable at ambient conditions. As it’s well known that much attention has been focused on studying the nonlinear optical properties of the 1H-MoS2. In a very recent research, the 1T-type monolayer crystals of TMDCs, MX2 (MoS2, WS2 ...) was reported having an intrinsic in-plane negative Poisson’s ratio. Luckily, nearly at the same time, unprecedented long-term (>3months) air stability of the 1T-MoS2 can be achieved by using the donor lithium hydride (LiH). Therefore, it’s very important to study the thermal conductivity of 1T-MoS2.
The thermal conductivity of graphene under shear strain is systematically studied in this dissertation by MD simulations. The results show that, in contrast to the dramatic decrease of thermal conductivity of graphene under uniaxial tensile, the thermal conductivity of graphene is not sensitive to the shear strain, and the thermal conductivity decreases only 12-16%. The wrinkle evolves when the shear strain is around 5%-10%, but the thermal conductivity barely changes.
The thermal conductivities of single-layer 1H-MoS2(1H-SLMoS2) and single-layer 1T-MoS2 (1T-SLMoS2) with different sample sizes, temperatures and strain rates have been studied systematically in this dissertation. We find that the thermal conductivities of 1H-SLMoS2 and 1T-SLMoS2 in both the armchair and the zigzag directions increase with the increasing of the sample length, while the increase of the width of the sample has minor effect on the thermal conductions of these two structures. The thermal conductivity of 1HSLMoS2 is smaller than that of 1T-SLMoS2 under size effect. Furthermore, the temperature effect results show that the thermal conductivities of both 1H-SLMoS2 and 1T-SLMoS2 decrease with the increasing of the temperature. The thermal conductivities of 1HSLMoS2 and 1T-SLMoS2 are nearly the same (difference <6%) in both of the chiral orientations under corresponding temperatures, especially in the armchair direction (difference <2.8%). Moreover, we find that the strain effects on the thermal conductivity of 1HSLMoS2 and 1T-SLMoS2 are different. More specifically, the thermal conductivity decreases with the increasing tensile strain rate for
1T-SLMoS2, while fluctuates with the growth of the strain for 1HSLMoS2. Finally, we find that the thermal conductivity of same sized 1H-SLMoS2 is similar with that of the strained 1H-SLMoS2 structure.
Matrix-free voxel-based finite element method for materials with heterogeneous microstructures
(2019)
Modern image detection techniques such as micro computer tomography
(μCT), magnetic resonance imaging (MRI) and scanning electron microscopy (SEM) provide us with high resolution images of the microstructure of materials in a non-invasive and convenient way. They form the basis for the geometrical models of high-resolution analysis, so called image-based analysis.
However especially in 3D, discretizations of these models reach easily the size of 100 Mill. degrees of freedoms and require extensive hardware resources in terms of main memory and computing power to solve the numerical model. Consequently, the focus of this work is to combine and adapt numerical solution methods to reduce the memory demand first and then the computation time and therewith enable an execution of the image-based analysis on modern computer desktops. Hence, the numerical model is a straightforward grid discretization of the voxel-based (pixels with a third dimension) geometry which omits the boundary detection algorithms and allows reduced storage of the finite element data structure and a matrix-free solution algorithm.
This in turn reduce the effort of almost all applied grid-based solution techniques and results in memory efficient and numerically stable algorithms for the microstructural models. Two variants of the matrix-free algorithm are presented. The efficient iterative solution method of conjugate gradients is used with matrix-free applicable preconditioners such as the Jacobi and the especially suited multigrid method. The jagged material boundaries of the voxel-based mesh are smoothed through embedded boundary elements which contain different material information at the integration point and are integrated sub-cell wise though without additional boundary detection. The efficiency of the matrix-free methods can be retained.
The capitalization of ‘certified’ sustainable building sector will be investigated over the power theory of value approach of Jonathan Nitzan and Shimshon Bichler. The study will be initiated by questioning why the environment problems are one of the first items on the agenda and by sharing the ideas of scholars who approaches the subject skeptically, because the predominant literature underlying the necessity and prominence of the topic is already well-known and adapted by the majority. Over the theory developed by Nitzan and Bichler, the concepts of capitalization, strategic sabotage, power, legitimacy, and obedience will be discussed. The hypothesis of “the absentee owners of the construction sector, holding the whip hand and capitalizing the ecology, control the growth and the creativity of green building production and make it carbon-dependent, in order to increase their profit margin” will be questioned. To strengthen the arguments in the hypothesis, the factors, the institutional arrangements, value measurement methods, which affect directly the net present value, will be investigated both in corporation and in building scale in detail, because net present value/ capitalization is asserted as the most important criteria by Nitzan and Bichler to make the investment decisions in the capitalist economic system. To trace the implications of power and the strategic sabotage that power caused, as the empirical dimension of this dissertation, an interface exploring the correlational ties between the climate responsive architecture and the ever changing political, economical, and social contexts and building economics praxis by decades will be developed and the expert interviews will be conducted with the design teams and the appraisers.
In der vorliegenden Arbeit wird die Bedeutung und Funktion des fotografischen Bildes und im Besonderen der Handyfotografie im Kontext von Internet und sozialen Onlinenetzwerken beschrieben, untersucht und diskutiert.
Im Spannungsfeld zwischen sozialwissenschaftlichen Theorien, foto- und medientheoretischem Diskurs sowie ästhetisch künstlerischen Perspektiven wird ausgelotet, welche konkreten visuellen und sozialen Formen die gegenwärtige mobile digitale Bildpraxis angenommen hat, wie sich ihre Gebrauchsweise innerhalb des globalen gesellschaftlichen Alltags darstellt, und in welcher Weise ihr spezielles Zusammenspiel aus „shooting“, „uploading“, „sharing“ zu neuen menschlichen Handlungsmustern und zur Schaffung neuer kultureller Realitäten beiträgt.