@phdthesis{Moosbrugger, author = {Moosbrugger, Jennifer}, title = {Design Intelligence - Human-Centered-Design for the development of industrial AI/ML agents}, doi = {10.25643/bauhaus-universitaet.6409}, url = {http://nbn-resolving.de/urn:nbn:de:gbv:wim2-20230719-64098}, school = {Bauhaus-Universit{\"a}t Weimar}, pages = {201}, abstract = {This study deals with design for AI/ML systems, more precisely in the industrial AI context based on case studies from the factory automation field. It therefore touches on core concepts from Human-Centered-Design (HCD), User Experience (UX) and Human Computer Interaction (HCI) on one hand, as well as concepts from Artificial Intelligence (AI), Machine Learning (ML) and the impact of technology on the other. The case studies the research is based on are within the industrial AI domain. However, the final outcomes, the findings, solutions, artifacts and so forth, should be transferable to a wider spectrum of domains. The study's aim is to examine the role of designers in the age of AI and the factors which are relevant, based on the hypothesis that current AI/ML development lacks the human perspective, which means that there are pitfalls and challenges that design can help resolve. The initial literature review revealed that AI/ML are perceived as a new design material that calls for a new design paradigm. Additional research based on qualitative case study research was conducted to gain an overview of the relevant issues and challenges. From this, 17 themes emerged, which together with explorative expert interviews and a structured literature review, were further analyzed to produce the relevant HCD, UX and HCI themes. It became clear that designers need new processes, methods, and tools in the age of AI/ML in combination with not only design, but also data science and business expertise, which is why the proposed solution in this PhD features process modules for design, data science and business collaboration. There are seven process modules and their related activities and dependencies that serve as guidelines for practitioners who want to design intelligence. A unified framework for collecting use case exemplars was created, based on a workshop with different practitioners and researchers from the area of AI/ML to support and enrich the process modules with concrete projects examples.}, subject = {K{\"u}nstliche Intelligenz}, language = {en} } @phdthesis{Drescher, author = {Drescher, Marcel}, title = {Open Innovation in KMU - Eine empirische Analyse der offenen Innovationsaktivit{\"a}ten im Kontext der Entrepreneurial Orientation}, doi = {10.25643/bauhaus-universitaet.4946}, url = {http://nbn-resolving.de/urn:nbn:de:gbv:wim2-20230314-49463}, school = {Bauhaus-Universit{\"a}t Weimar}, pages = {211}, abstract = {Open Innovation in kleinen und mittleren Unternehmen (KMU) hat sich stark ausdifferenziert. Dabei zeigt die Empirie, dass KMU unterschiedliche Wege in der offenen Entwicklung von Innovationen begehen. Um die bestehende Literatur zu erweitern, wurden mit dieser Dissertation die Ziele verfolgt 1) offene Innovationsaktivit{\"a}ten in KMU aus einer Prozessperspektive aufzudecken und genau zu beschreiben und 2) zu erkl{\"a}ren, warum sich die {\"O}ffnung von Innovationsprozessen in KMU unterscheidet. Daf{\"u}r wurde auf eine multiple Fallstudienanalyse zur{\"u}ckgegriffen. Untersuchungsobjekte waren kleine etablierte High-Tech Unternehmen aus den neuen Bundesl{\"a}ndern. Die Ergebnisse zeigen sechs Prozessmodelle der offenen Innovationsentwicklung, beschrieben als Open Innovation Muster. Deskriptionen dieser Muster unter Ber{\"u}cksichtigung von formenden Innovationsaktivit{\"a}ten, ausgetauschtem Wissen, beteiligten externen Akteuren und Gr{\"u}nden f{\"u}r und gegen Open Innovation vermitteln ein {\"u}ber den bisherigen Forschungsstand hinausgehendes Verst{\"a}ndnis von Open Innovation in KMU. Zudem zeigen die Ergebnisse, dass die Entrepreneurial Orientation erkl{\"a}rt, warum KMU bei der Ausgestaltung von offenen Innovationsprozessen unterschiedlich vorgehen. In der Dissertation wird detailliert dargelegt, welche Open Innovation Muster sich anhand der Entrepreneurial Orientation von KMU (nicht-entrepreneurial bis entrepreneurial) zeigen. Die Ergebnisse liefern sowohl wissenschaftliche Implikationen, als auch Handlungsempfehlungen f{\"u}r die Unternehmenspraxis.}, subject = {Open Innovation}, language = {de} } @phdthesis{Held, author = {Held, Tobias}, title = {Einblick: Gestalterische Potentiale und Perspektiven der Videotelefonie im Kontext von N{\"a}he und Distanz. Eine praxis-basierte, (re-)kontextualisierende und diskursanalytische Studie.}, doi = {10.25643/bauhaus-universitaet.4886}, url = {http://nbn-resolving.de/urn:nbn:de:gbv:wim2-20230111-48867}, school = {Bauhaus-Universit{\"a}t Weimar}, pages = {534}, abstract = {Inhaltlich besch{\"a}ftigt sich die Arbeit, die im Rahmen des Promotionsstudiengangs Kunst und Gestaltung an der Bauhaus-Universit{\"a}t entstand, mit der Erforschung sozio-interaktiver Potentiale der Videotelefonie im Kontext von N{\"a}he und Verbundenheit mit Fokus auf Eigenbild, Embodiment sowie den Rederechtswechsel. Die Videotelefonie als Kommunikationsform hat sich - und darauf deuten die Erfahrungen der Co- vid-19-Pandemie hin - im lebensweltlichen Alltag der Menschen etabliert und wird dort in naher Zukunft nicht mehr wegzudenken sein. Auf Basis ihrer M{\"o}glichkeiten und Errungenschaften ist es inzwischen Realit{\"a}t und Lebenswirklichkeit, dass die Kommunikation sowohl im privaten als auch im gesch{\"a}ftlichen Kontext mittels verschiedenster Kan{\"a}le stattfindet. Der Videotelefonie kommt hierbei als solche nicht nur eine tragende Funktion, sondern auch eine herausragende Rolle bei der vermeintlichen Reproduktion der Face-to-Face-Kommunikation im digitalen Raum zu und wird wie selbstverst{\"a}ndlich zum zwischenmenschlichen Austausch genutzt. Just an diesem Punkt kn{\"u}pft die Forschungsarbeit an. Zentral stand dabei das Vorhaben einer dezidierte Untersuchung des Forschungsgegenstandes Videotelefonie, sowohl aus Kultur- als auch Technikhistorischer, aber auch Medien-, Wahrnehmungs- wie Kommunikations- theoretischer Perspektive, indem analytische und ph{\"a}nosemiotische Perspektiven miteinander in Beziehung gesetzt werden (z.B. Wahrnehmungsbedingungen, Interaktionsmerkmale, realisierte Kommunikationsprozesse etc.). Damit verbundenes, w{\"u}nschenswertes Ziel war es, eine m{\"o}glichst zeitgem{\"a}ße wie relevante Forschungsfrage zu adressieren, die neben den kulturellen Technisierungs- und Mediatisierungstendenzen in institutionellen und privaten Milieus ebenfalls eine conditio sine qua non der pandemischen (Massen-)Kommunikation entwirft. Die Arbeit ist damit vor allem im Bereich des Produkt- und Interactiondesigns zu verorten. Dar{\"u}ber hinaus hatte sie das Ziel der Darlegung und Begr{\"u}ndung der Videotelefonie als eigenst{\"a}ndige Kommunikationsform, welche durch eigene, kommunikative Besonderheiten, die sich in ihrer jeweiligen Ingebrauchnahme sowie durch spezielle Wahrnehmungsbedingungen {\"a}ußern, und die die Videotelefonie als »Rederechtswechselmedium« avant la lettre konsolidieren, gekennzeichnet ist. Dabei sollte der Beweis erbracht werden, dass die Videotelefonie nicht als Schwundstufe einer Kommunikation Face-to-Face, sondern als ein eigenst{\"a}ndiges Mediatisierungs- und Kommunikationsereignis zu verstehen sei. Und eben nicht als eine beliebige - sich linear vom Telefon ausgehende - entwickelte Form der audio-visuellen Fernkommunikation darstellt, sondern die gestalterische (Bewegtbild-)Technizit{\"a}t ein eigenst{\"a}ndiges Funktionsmaß offeriert, welches wiederum ein innovatives Kommunikationsmilieu im Kontext einer Rederechtswechsel-Medialit{\"a}t stabilisiert.}, subject = {Videotelefonie}, language = {de} } @phdthesis{Mueller, author = {M{\"u}ller, Matthias}, title = {Salt-frost Attack on Concrete - New Findings regarding the Damage Mechanism}, doi = {10.25643/bauhaus-universitaet.4868}, url = {http://nbn-resolving.de/urn:nbn:de:gbv:wim2-20230103-48681}, school = {Bauhaus-Universit{\"a}t Weimar}, abstract = {The reduction of the cement clinker content is an important prerequisite for the improvement of the CO2-footprint of concrete. Nevertheless, the durability of such concretes must be sufficient to guarantee a satisfactory service life of structures. Salt frost scaling resistance is a critical factor in this regard, as it is often diminished at increased clinker substitution rates. Furthermore, only insufficient long-term experience for such concretes exists. A high salt frost scaling resistance thus cannot be achieved by applying only descriptive criteria, such as the concrete composition. It is therefore to be expected, that in the long term a performance based service life prediction will replace the descriptive concept. To achieve the important goal of clinker reduction for concretes also in cold and temperate climates it is important to understand the underlying mechanisms for salt frost scaling. However, conflicting damage theories dominate the current State of the Art. It was consequently derived as the goal of this thesis to evaluate existing damage theories and to examine them experimentally. It was found that only two theories have the potential to describe the salt frost attack satisfactorily - the glue spall theory and the cryogenic suction theory. The glue spall theory attributes the surface scaling to the interaction of an external ice layer with the concrete surface. Only when moderate amounts of deicing salt are present in the test solution the resulting mechanical properties of the ice can cause scaling. However, the results in this thesis indicate that severe scaling also occurs at deicing salt levels, at which the ice is much too soft to damage concrete. Thus, the inability of the glue spall theory to account for all aspects of salt frost scaling was shown. The cryogenic suction theory is based on the eutectic behavior of salt solutions, which consist of two phases - water ice and liquid brine - between the freezing point and the eutectic temperature. The liquid brine acts as an additional moisture reservoir, which facilitates the growth of ice lenses in the surface layer of the concrete. The experiments in this thesis confirmed, that the ice formation in hardened cement paste increases due to the suction of brine at sub-zero temperatures. The extent of additional ice formation was influenced mainly by the porosity and by the chloride binding capacity of the hardened cement paste. Consequently, the cryogenic suction theory plausibly describes the actual generation of scaling, but it has to be expanded by some crucial aspects to represent the salt frost scaling attack completely. The most important aspect is the intensive saturation process, which is ascribed to the so-called micro ice lens pump. Therefore a combined damage theory was proposed, which considers multiple saturation processes. Important aspects of this combined theory were confirmed experimentally. As a result, the combined damage theory constitutes a good basis to understand the salt frost scaling attack on concrete on a fundamental level. Furthermore, a new approach was identified, to account for the reduced salt frost scaling resistance of concretes with reduced clinker content.}, subject = {Beton}, language = {en} } @phdthesis{Mojahedin, author = {Mojahedin, Arvin}, title = {Analysis of Functionally Graded Porous Materials Using Deep Energy Method and Analytical Solution}, doi = {10.25643/bauhaus-universitaet.4867}, url = {http://nbn-resolving.de/urn:nbn:de:gbv:wim2-20221220-48674}, school = {Bauhaus-Universit{\"a}t Weimar}, abstract = {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.}, subject = {Por{\"o}ser Stoff}, language = {en} } @phdthesis{Legatiuk, author = {Legatiuk, Anastasiia}, title = {Discrete potential and function theories on a rectangular lattice and their applications}, doi = {10.25643/bauhaus-universitaet.4865}, url = {http://nbn-resolving.de/urn:nbn:de:gbv:wim2-20221220-48654}, school = {Bauhaus-Universit{\"a}t Weimar}, abstract = {The growing complexity of modern engineering problems necessitates development of advanced numerical methods. In particular, methods working directly with discrete structures, and thus, representing exactly some important properties of the solution on a lattice and not just approximating the continuous properties, become more and more popular nowadays. Among others, discrete potential theory and discrete function theory provide a variety of methods, which are discrete counterparts of the classical continuous methods for solving boundary value problems. A lot of results related to the discrete potential and function theories have been presented in recent years. However, these results are related to the discrete theories constructed on square lattices, and, thus, limiting their practical applicability and potentially leading to higher computational costs while discretising realistic domains. This thesis presents an extension of the discrete potential theory and discrete function theory to rectangular lattices. As usual in the discrete theories, construction of discrete operators is strongly influenced by a definition of discrete geometric setting. For providing consistent constructions throughout the whole thesis, a detailed discussion on the discrete geometric setting is presented in the beginning. After that, the discrete fundamental solution of the discrete Laplace operator on a rectangular lattice, which is the core of the discrete potential theory, its numerical analysis, and practical calculations are presented. By using the discrete fundamental solution of the discrete Laplace operator on a rectangular lattice, the discrete potential theory is then constructed for interior and exterior settings. Several discrete interior and exterior boundary value problems are then solved. Moreover, discrete transmission problems are introduced and several numerical examples of these problems are discussed. Finally, a discrete fundamental solution of the discrete Cauchy-Riemann operator on a rectangular lattice is constructed, and basics of the discrete function theory on a rectangular lattice are provided. This work indicates that the discrete theories provide solution methods with very good numerical properties to tackle various boundary value problems, as well as transmission problems coupling interior and exterior problems. The results presented in this thesis provide a basis for further development of discrete theories on irregular lattices.}, subject = {Diskrete Funktionentheorie}, language = {en} } @phdthesis{Hanna, author = {Hanna, John}, title = {Computational Fracture Modeling and Design of Encapsulation-Based Self-Healing Concrete Using XFEM and Cohesive Surface Technique}, doi = {10.25643/bauhaus-universitaet.4746}, url = {http://nbn-resolving.de/urn:nbn:de:gbv:wim2-20221124-47467}, school = {Bauhaus-Universit{\"a}t Weimar}, pages = {125}, abstract = {Encapsulation-based self-healing concrete (SHC) is the most promising technique for providing a self-healing mechanism to concrete. This is due to its capacity to heal fractures effectively without human interventions, extending the operational life and lowering maintenance costs. The healing mechanism is created by embedding capsules containing the healing agent inside the concrete. The healing agent will be released once the capsules are fractured and the healing occurs in the vicinity of the damaged part. The healing efficiency of the SHC is still not clear and depends on several factors; in the case of microcapsules SHC the fracture of microcapsules is the most important aspect to release the healing agents and hence heal the cracks. This study contributes to verifying the healing efficiency of SHC and the fracture mechanism of the microcapsules. Extended finite element method (XFEM) is a flexible, and powerful discrete crack method that allows crack propagation without the requirement for re-meshing and has been shown high accuracy for modeling fracture in concrete. In this thesis, a computational fracture modeling approach of Encapsulation-based SHC is proposed based on the XFEM and cohesive surface technique (CS) to study the healing efficiency and the potential of fracture and debonding of the microcapsules or the solidified healing agents from the concrete matrix as well. The concrete matrix and a microcapsule shell both are modeled by the XFEM and combined together by CS. The effects of the healed-crack length, the interfacial fracture properties, and microcapsule size on the load carrying capability and fracture pattern of the SHC have been studied. The obtained results are compared to those obtained from the zero thickness cohesive element approach to demonstrate the significant accuracy and the validity of the proposed simulation. The present fracture simulation is developed to study the influence of the capsular clustering on the fracture mechanism by varying the contact surface area of the CS between the microcapsule shell and the concrete matrix. The proposed fracture simulation is expanded to 3D simulations to validate the 2D computational simulations and to estimate the accuracy difference ratio between 2D and 3D simulations. In addition, a proposed design method is developed to design the size of the microcapsules consideration of a sufficient volume of healing agent to heal the expected crack width. This method is based on the configuration of the unit cell (UC), Representative Volume Element (RVE), Periodic Boundary Conditions (PBC), and associated them to the volume fraction (Vf) and the crack width as variables. The proposed microcapsule design is verified through computational fracture simulations.}, subject = {Beton}, language = {en} } @phdthesis{Jenabidehkordi, author = {Jenabidehkordi, Ali}, title = {An Efficient Adaptive PD Formulation for Complex Microstructures}, doi = {10.25643/bauhaus-universitaet.4742}, url = {http://nbn-resolving.de/urn:nbn:de:gbv:wim2-20221124-47422}, school = {Bauhaus-Universit{\"a}t Weimar}, pages = {118}, abstract = {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. Peridy- namic (PD) is a newly developed numerical method with nonlocal nature. Its straightforward integral form equation of motion allows simulating dy- namic 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 dis- tinguished 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.}, subject = {Peridynamik}, language = {en} } @phdthesis{Jenabidehkordi, author = {Jenabidehkordi, Ali}, title = {An efficient adaptive PD formulation for complex microstructures}, doi = {10.25643/bauhaus-universitaet.4738}, url = {http://nbn-resolving.de/urn:nbn:de:gbv:wim2-20221116-47389}, school = {Bauhaus-Universit{\"a}t Weimar}, pages = {118}, abstract = {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.}, subject = {Peridynamik}, language = {en} } @phdthesis{Zacharias, author = {Zacharias, Christin}, title = {Numerical Simulation Models for Thermoelastic Damping Effects}, doi = {10.25643/bauhaus-universitaet.4735}, url = {http://nbn-resolving.de/urn:nbn:de:gbv:wim2-20221116-47352}, school = {Bauhaus-Universit{\"a}t Weimar}, pages = {191}, abstract = {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.}, subject = {Werkstoffd{\"a}mpfung}, language = {en} } @phdthesis{Zhang, author = {Zhang, Yongzheng}, title = {A Nonlocal Operator Method for Quasi-static and Dynamic Fracture Modeling}, doi = {10.25643/bauhaus-universitaet.4732}, url = {http://nbn-resolving.de/urn:nbn:de:gbv:wim2-20221026-47321}, school = {Bauhaus-Universit{\"a}t Weimar}, abstract = {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.}, subject = {Variationsprinzip}, language = {en} } @phdthesis{OrtizAlvis, author = {Ortiz Alvis, Alfredo}, title = {Urban Agoraphobia: The pursuit of security within confined community ties. Urban-ethnographic analysis on gated housing developments of Guadalajara, Mexico.}, doi = {10.25643/bauhaus-universitaet.4723}, url = {http://nbn-resolving.de/urn:nbn:de:gbv:wim2-20221005-47234}, school = {Bauhaus-Universit{\"a}t Weimar}, pages = {436}, abstract = {The Gated Community (GC) phenomenon in Latin American cities has become an inherent element of their urban development, despite academical debate, their approach thrives within the housing market; not surprisingly, as some of the premises on which GCs are based, namely safety, control and supervision intersperse seamlessly with the insecure conditions of the contexts from which they arise. The current security crisis in Mexico, triggered in 2006 by the so-called war on drugs, has reached its peak with the highest insecurity rates in decades, representing a unique chance to study these interactions. Although the leading term of this research, Urban Agoraphobia, implies a causal dichotomy between the rise in the sense of fear amongst citizens and housing confinement as lineal consequence, I acknowledge that GCs represent a complex phenomenon, a hub of diverse factors and multidimensional processes held on four fundamental levels: global, social, individual and state-related. The focus of this dissertation is set on the individual plane and contributes, from the analysis of the GC's resident's perspective, experiences and perceptions, to a debate that has usually been limited to the scrutiny of other drivers, disregarding the role of dweller's underlying fears, motivations and concerns. Assuming that the current ruling security model in Mexico tends to empower its commodification rather than its collective quality, this research draws upon the use of a methodological triangulation, along conceptual and contextual analyses, to test the hypothesis that insecurity plays an increasingly major role, leading citizens into the belief that acquiring a household in a controlled and surveilled community represents a counterweight against the feared environment of the open city. The focus of the analysis lies on the internal hatch of community ties as potential palliative for the provision of a sense of security, aiming to transcend the unidimensional discourse of GCs as defined mainly by their defensive apparatus. Residents' perspectives acquired through ethnographical analyses may provide the chance to gain an essential view into a phenomenon that further consolidates without a critical study of its actual implications, not only for Mexican cities, but also for the Latin American and global contexts.}, subject = {Agoraphobie}, language = {en} } @phdthesis{Yousefi, author = {Yousefi, Hassan}, title = {Discontinuous propagating fronts: linear and nonlinear systems}, doi = {10.25643/bauhaus-universitaet.4717}, url = {http://nbn-resolving.de/urn:nbn:de:gbv:wim2-20220922-47178}, school = {Bauhaus-Universit{\"a}t Weimar}, pages = {356}, abstract = {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.}, subject = {Partielle Differentialgleichung}, language = {en} } @phdthesis{CarvajalBermudez, author = {Carvajal Berm{\´u}dez, Juan Carlos}, title = {New methods of citizen participation based on digital technologies}, doi = {10.25643/bauhaus-universitaet.4712}, url = {http://nbn-resolving.de/urn:nbn:de:gbv:wim2-20220906-47124}, school = {Bauhaus-Universit{\"a}t Weimar}, abstract = {The current thesis presents research about new methods of citizen participation based on digital technologies. The focus on the research lies on decentralized methods of participation where citizens take the role of co-creators. The research project first conducted a review of the literature on citizen participation, its origins and the different paradigms that have emerged over the years. The literature review also looked at the influence of technologies on participation processes and the theoretical frameworks that have emerged to understand the introduction of technologies in the context of urban development. The literature review generated the conceptual basis for the further development of the thesis. The research begins with a survey of technology enabled participation applications that examined the roles and structures emerging due to the introduction of technology. The results showed that cities use technology mostly to control and monitor urban infrastructure and are rather reluctant to give citizens the role of co-creators. Based on these findings, three case studies were developed. Digital tools for citizen participation were conceived and introduced for each case study. The adoption and reaction of the citizens were observed using three data collection methods. The results of the case studies showed consistently that previous participation and engagement with informal citizen participation are a determinining factor in the potential adoption of digital tools for decentralized engagement. Based on these results, the case studies proposed methods and frameworks that can be used for the conception and introduction of technologies for decentralized citizen participation.}, subject = {Partizipation}, language = {en} } @phdthesis{LopezZermeno, author = {L{\´o}pez Zerme{\~n}o, Jorge Alberto}, title = {Isogeometric and CAD-based methods for shape and topology optimization: Sensitivity analysis, B{\´e}zier elements and phase-field approaches}, doi = {10.25643/bauhaus-universitaet.4710}, url = {http://nbn-resolving.de/urn:nbn:de:gbv:wim2-20220831-47102}, school = {Bauhaus-Universit{\"a}t Weimar}, abstract = {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 B{\´e}zier 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 B{\´e}zier 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 B{\´e}zier 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 B{\´e}zier 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.}, subject = {CAD}, language = {en} } @phdthesis{Riechert, author = {Riechert, Christin}, title = {Hydratation und Eigenschaften von Gips-Zement-Puzzolan-Bindemitteln mit alumosilikatischen Puzzolanen}, isbn = {978-3-00-073003-0}, doi = {10.25643/bauhaus-universitaet.4707}, url = {http://nbn-resolving.de/urn:nbn:de:gbv:wim2-20220825-47076}, school = {Bauhaus-Universit{\"a}t Weimar}, pages = {148}, abstract = {Reine Calciumsulfatbindemittel weisen eine hohe L{\"o}slichkeit auf. Feuchteinwirkung f{\"u}hrt zudem zu starken Festigkeitsverlusten. Aus diesem Grund werden diese Bindemittel ausschließlich f{\"u}r Baustoffe und -produkte im Innenbereich ohne permanenten Feuchtebeanspruchung eingesetzt. Eine M{\"o}glichkeit, die Feuchtebest{\"a}ndigkeit zu erh{\"o}hen, ist die Beimischung puzzolanischer und zement{\"a}rer Komponenten. Diese Mischsysteme werden Gips-Zement-Puzzolan-Bindemittel (kurz: GZPB) genannt. Mischungen aus Calciumsulfaten und Portlandzementen allein sind aufgrund der treibenden Ettringitbildung nicht raumbest{\"a}ndig. Durch die Zugabe von puzzolanischen Stoffen k{\"o}nnen aber Bedingungen im hydratisierenden System geschaffen werden, welche eine rissfreie Erh{\"a}rtung erm{\"o}glichen. Hierf{\"u}r ist eine exakte Rezeptierung der GZPB notwendig, um die GZPB-typischen, ettringitbedingten Dehnungen zeitlich zu begrenzen. Insbesondere bei alumosilikatischen Puzzolanen treten w{\"a}hrend der Hydratation gegen{\"u}ber rein silikatischen Puzzolanen deutlich h{\"o}here Expansionen auf, wodurch die Gefahr einer potenziellen Rissbildung steigt. F{\"u}r die Erstellung geeigneter GZPB-Zusammensetzungen bedarf es daher einer Methodik, um raumbest{\"a}ndig erh{\"a}rtende Systeme sicher von destruktiven Mischungen unterscheiden zu k{\"o}nnen. Sowohl f{\"u}r die Rezeptierung als auch f{\"u}r die Anwendung der GZPB existieren in Deutschland keinerlei Normen. Dar{\"u}ber hinaus sind die Hydratationsvorg{\"a}nge sowie die entstehenden Produkte nicht konsistent beschrieben. Auch auf die Besonderheiten der GZPB mit alumosilikatischen Puzzolanen wird in der Literatur nur unzureichend eingegangen. Ziel war es daher, ein grundlegendes Verst{\"a}ndnis der Hydratation sowie eine sichere Methodik zur Rezeptierung raumbest{\"a}ndig und rissfrei erh{\"a}rtender GZPB, insbesondere in Hinblick auf die Verwendung alumosilikatischer Puzzolane, zu erarbeiten. Dar{\"u}ber hinaus sollte systematisch der Einfluss der Einzelkomponenten auf Hydratation und Eigenschaften dieser Bindemittelsysteme untersucht werden. Dies soll erm{\"o}glichen, die GZPB f{\"u}r ein breites Anwendungsspektrum als Bindemittel zu etablieren, und somit vorteilhafte Eigenschaften der Calciumsulfate (geringe Schwindneigung, geringe CO2-Emission etc.) mit der Leistungs-f{\"a}higkeit von Zementen (Wasserbest{\"a}ndigkeit, Festigkeit, Dauerhaftigkeit etc.) zu verbinden. Als Ausgangsstoffe der Untersuchungen zu den GZPB wurden Stuckgips und Alpha-Halbhydrat als Calciumsulfatbindemittel in unterschiedlichen Anteilen im GZPB verwendet. Die Puzzolan-Zement-Verh{\"a}ltnisse wurden ebenfalls variiert. Als Puzzolan kam f{\"u}r den Großteil der Untersuchungen ein alumosilikatisches Metakaolin zum Einsatz. Als kalkspendende Komponente diente ein reiner Portlandzement. Das Untersuchungsprogramm gliederte sich in 4 Teile. Zuerst wurde anhand von CaO- und pH-Wert-Messungen in Suspensionen sowie dem L{\"a}ngen{\"a}nderungsverhalten von Bindemittelleimen verschiedener Zusammensetzungen eine Vorauswahl geeigneter GZPB-Rezepturen ermittelt. Danach erfolgten, ebenfalls an Bindemittelleimen, Untersuchungen zu den Eigenschaften der als geeignet eingesch{\"a}tzten GZPB-Mischungen. Hierzu z{\"a}hlten Langzeitbetrachtungen zur rissfreien Erh{\"a}rtung bei unterschiedlichen Umgebungsbedingungen sowie die Festigkeitsentwicklung im trockenen und feuchten Zustand. Im n{\"a}chsten Schritt wurde anhand zweier exemplarischer GZPB-Zusammensetzungen (mit silikatischen und alumosilikatischen Puzzolan) die prinzipiell m{\"o}gliche Phasenzusammensetzung unter Variation des Puzzolan-Zement-Verh{\"a}ltnisses (P/Z-Verh{\"a}ltnis) und des Calciumsulfatanteils im thermodynamischen Gleichgewichtszustand berechnet. Hier wurde im Besonderen auf Unterschiede der silikatischen und alumosilikatischen Puzzolane eingegangen. Im letzten Teil der Untersuchungen wurden die Hydratationskinetik der GZPB sowie die Gef{\"u}geentwicklung n{\"a}her betrachtet. Hierf{\"u}r wurden die Porenl{\"o}sungen chemisch analysiert und S{\"a}ttigungsindizes berechnet, sowie elektronenmikropische, porosimetrische und r{\"o}ntgenografische Untersuchungen durchgef{\"u}hrt. Abschließend wurden die Ergebnisse gesamtheitlich interpretiert, da die Ergebnisse der einzelnen Untersuchungsprogramme miteinander in Wechselwirkung stehen. Als haupts{\"a}chliche Hydratationsprodukte wurden Calciumsulfat-Dihydrat, Ettringit und C-(A)-S-H-Phasen ermittelt, deren Anteile im GZPB neben dem Calciumsulfatanteil und dem Puzzolan-Zement-Verh{\"a}ltnis auch deutlich vom Wasserangebot und der Gef{\"u}geentwicklung abh{\"a}ngen. Bei Verwendung von alumosilikatischen Puzzolans kommt es wahrscheinlich zur teilweisen Substitution des Siliciums durch Aluminium in den C-S-H-Phasen. Dies erscheint aufgrund des Nachweises der f{\"u}r diese Phasen typischen, folienartigen Morphologie wahrscheinlich. Portlandit wurde in raumbest{\"a}ndigen GZPB-Systemen nur zu sehr fr{\"u}hen Zeitpunkten in geringen Mengen gefunden. In den Untersuchungen konnte ein Teil der in der Literatur beschriebenen, prinzipiellen Hydratationsabl{\"a}ufe best{\"a}tigt werden. Bei Verwendung von Halbhydrat als Calciumsulfatkomponente entsteht zuerst Dihydrat und bildet die Prim{\"a}rstruktur der GZPB. In dieses existierende Grundgef{\"u}ge kristallisieren dann das Ettringit und die C-(A)-S-H-Phasen. In den GZPB sorgen entgegen der Beschreibungen in der Literatur nicht ausschließlich die C-(A)-S-H-Phasen zur Verbesserung der Feuchtebest{\"a}ndigkeit und der Erh{\"o}hung des Festigkeitsniveaus, sondern auch das Ettringit. Beide Phasen {\"u}berwachsen im zeitlichen Verlauf der Hydratation die Dihydratkristalle in der Matrix und h{\"u}llen diese - je nach Calciumsulfatanteil im GZPB - teilweise oder vollst{\"a}ndig ein. Diese Umh{\"u}llung sowie die starke Gef{\"u}geverdichtung durch die C-(A)-S-H-Phasen und das Ettringit bedingen, dass ein l{\"o}sender Angriff durch Wasser erschwert oder gar verhindert wird. Gleichzeitig wird die Gleitf{\"a}higkeit an den Kontaktstellen der Dihydratkristalle verringert. Eine rissfreie und raumbest{\"a}ndige Erh{\"a}rtung ist f{\"u}r die gefahrlose Anwendung eines GZPB-Systems essentiell. Hierf{\"u}r ist die Kinetik der Ettringitbildung von elementarer Bedeutung. Die gebildete Ettringitmenge spielt nur eine untergeordnete Rolle. Selbst ausgepr{\"a}gte, ettringitbedingte Dehnungen und hohe sich bildende Mengen f{\"u}hren zu fr{\"u}hen Zeitpunkten, wenn die Dihydratkristalle noch leicht gegeneinander verschiebbar sind, zu keinen Sch{\"a}den. Bleibt die {\"U}bers{\"a}ttigung bez{\"u}glich Ettringit und somit auch der Kristallisationsdruck allerdings {\"u}ber einen langen Zeitraum hoch, gen{\"u}gen bereits geringe Ettringitmengen, um das sich stetig verfestigende Gef{\"u}ge stark zu sch{\"a}digen. Die f{\"u}r die raumbest{\"a}ndige Erh{\"a}rtung der GZPB notwendige, schnelle Abnahme der Ettringit{\"u}bers{\"a}ttigung wird haupts{\"a}chlich durch die Reaktivit{\"a}t des Puzzolans beeinflusst. Die puzzolanische Reaktion f{\"u}hrt zur Bindung des aus dem Zement stammenden Calciumhydroxid durch die Bildung von C-(A)-S-H-Phasen und Ettringit. Hierdurch sinkt die Calcium- und Hydroxidionenkonzentration in der Porenl{\"o}sung im Verlauf der Hydratation, wodurch auch die {\"U}bers{\"a}ttigung bez{\"u}glich Ettringit abnimmt. Je h{\"o}her die Reaktivit{\"a}t des Puzzolans ist, desto schneller sinkt der S{\"a}ttigungsindex des Ettringits und somit auch der Kristallisationsdruck. Nach Unterschreiten eines noch n{\"a}her zu kl{\"a}rendem Grenzwert der {\"U}bers{\"a}ttigung stagnieren die Dehnungen. Das Ettringit kristallisiert bzw. w{\"a}chst nun bevorzugt in den Poren ohne eine weitere, {\"a}ußere Volumenzunahme zu verursachen. Um eine schadensfreie Erh{\"a}rtung des GZPB zu gew{\"a}hrleisten, muss gerade in der fr{\"u}hen Phase der Hydratation ein ausreichendes Wasserangebot gew{\"a}hrleistet werden, so dass die Ettringitbildung m{\"o}glichst vollst{\"a}ndig ablaufen kann. Andernfalls kann es bei einer Wiederbefeuchtung zur Reaktivierung der Ettringitbildung kommen, was im eingebauten Zustand Sch{\"a}den verursachen kann. Die Gew{\"a}hrleistung eines ausreichenden Wasserangebots ist im GZPB-System nicht unproblematisch. In Abh{\"a}ngigkeit der GZPB-Zusammensetzung k{\"o}nnen sich große Ettringitmengen bilden, die einen sehr hohen Wasserbedarf aufweisen. Deshalb kann es, je nach verwendeten Wasser-Bindemittel-Wert, im Bindemittelleim zu einem Wassermangel kommen, welcher die weitere Hydratation verlangsamt bzw. komplett verhindert. Zudem k{\"o}nnen GZPB-Systeme teils sehr dichte Gef{\"u}ge ausbilden, wodurch der Wassertransport zum Reaktionsort des Ettringits zus{\"a}tzlich behindert wird. Die Konzeption raumbest{\"a}ndiger GZPB-Systeme muss anhand mehrerer aufeinander aufbauender Untersuchungen erfolgen. Zur Vorauswahl geeigneter Puzzolan-Zementverh{\"a}ltnisse eignen sich die Messungen der CaO-Konzentration und des pH-Wertes in Suspensionen. Als alleinige Beurteilungsgrundlage reicht dies allerdings nicht aus. Zus{\"a}tzlich muss das L{\"a}ngen{\"a}nderungs-verhalten beurteilt werden. Raumbest{\"a}ndige Mischungen mit alumosilikatischen Puzzolanen zeigen zu fr{\"u}hen Zeitpunkten starke Dehnungen, welche dann abrupt stagnieren. Stetige - auch geringe - Dehnungen weisen auf eine destruktive Zusammensetzung hin. Mit diesem mehrstufigen Vorgehen k{\"o}nnen raumbest{\"a}ndige, stabile GZPB-Systeme konzipiert werden, so dass die Zielstellung der Arbeit erreicht wurde und ein sicherer praktischer Einsatz dieser Bindemittelart gew{\"a}hrleistet werden kann.  }, subject = {Gips}, language = {de} } @phdthesis{Schlaffke, author = {Schlaffke, Markus}, title = {Die Rekonstruktion des Menaka-Archivs: Navigationen durch die Tanz-Moderne zwischen Kolkata, Mumbai und Berlin 1936-38}, doi = {10.25643/bauhaus-universitaet.4706}, url = {http://nbn-resolving.de/urn:nbn:de:gbv:wim2-20220823-47069}, school = {Bauhaus-Universit{\"a}t Weimar}, abstract = {Die Europatournee des Indischen Menaka-Balletts von 1936-38 ist der Ausgangspunkt dieser archivologischen Navigation entlang der Spuren indischer K{\"u}nstlerInnen in Europa. In einer breit angelegten Archivrecherche wurden dazu Dokumente, Fundst{\"u}cke, 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 k{\"u}nstlerisch-forschende Involvierung in gegenw{\"a}rtige Erinnerungspolitiken, in welche die verflochtenen Strukturen der k{\"u}nstlerischen Avantgarde zwischen Kolkata, Mumbai und Berlin hineinreichen. Die Spur des Menaka-Ballett erweist sich dabei als Teil weitreichender ideologischer, t{\"a}nzerischer, musikalischer, filmischer und literarischer Str{\"o}mungen, die auch in gegenw{\"a}rtigen kulturellen Bestimmungen fortwirken. Fotografien, Zeitungsberichte, Film- und Tonaufnahmen, Briefe und pers{\"o}nliche Erinnerungst{\"u}cke erz{\"a}hlen davon, wie sich, vor dem Hintergrund der im antikolonialen Aufbruch befindlichen Kulturreform in Indien, und der nationsozialistisch-v{\"o}lkischen Kulturpolitik in Deutschland, die T{\"a}nzerinnen und Musiker der indischen Ballettgruppe und die deutsche {\"O}ffentlichkeit im gegenseitigen Spiegel betrachteten, w{\"a}hrend die Vorzeichen des kommenden Krieges immer deutlicher wurden.}, subject = {Menaka }, language = {de} } @phdthesis{ShaabanMohamed, author = {Shaaban Mohamed, Ahmed Mostafa}, title = {Isogeometric boundary element analysis and structural shape optimization for Helmholtz acoustic problems}, doi = {10.25643/bauhaus-universitaet.4703}, url = {http://nbn-resolving.de/urn:nbn:de:gbv:wim2-20220816-47030}, school = {Bauhaus-Universit{\"a}t Weimar}, abstract = {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.}, subject = {Randelemente-Methode}, language = {en} } @phdthesis{Arganaraz, author = {Arga{\~n}araz, Cecilia Magdalena}, title = {Tiempos imaginados y espacios {\´a}ridos: controversias en torno al agua en el Valle de Catamarca (siglos XIX-XX)}, doi = {10.25643/bauhaus-universitaet.4681}, url = {http://nbn-resolving.de/urn:nbn:de:gbv:wim2-20220803-46817}, school = {Bauhaus-Universit{\"a}t Weimar}, abstract = {The thesis addresses journalistic, administrative and judicial historical documentation to analyze the links between aridity and geographical imaginaries in the province of Catamarca (Argentina), from a historical point of view. The research aims to contribute to the understanding of the "non-hegemonic" versions of Modernity, its territoriality and the productions of geographic imaginaries that they involve. To provide a broad purpose, it raises as an object of study the ways in which "modern" practices, actors, links, discourses and expectations about the territory are mobilized when they are located in a space in "other" water conditions. those that are intended to "civilize" it. The general objective of the research is to analyze time-space controversies around water in the city and valley of Catamarca towards 19th and 20th centuries. The specific objectives derived are a) analyzing how various actors are related to waters behavior - in other words, the local water regime - in Catamarca and the meanings built around it. b) to analyze the controversies about the place of Catamarca and its water regime in the local and national geographic imaginary. c) analyze controversies in which the relationships between actors and materialities involved in modernization projects are put into discussion. These concerns by the experience of the actors and by the historical-spatial imagination of the territory, combined, led to the construction of an interdisciplinary methodology based on tools from anthropology, sociology, geography and history.}, subject = {Anthologie}, language = {es} } @phdthesis{Torres, author = {Torres, C{\´e}sar}, title = {El paisaje de la Cuenca Lechera Central Argentina: la huella de la producci{\´o}n sobre el territorio}, doi = {10.25643/bauhaus-universitaet.4683}, url = {http://nbn-resolving.de/urn:nbn:de:gbv:wim2-20220803-46835}, school = {Bauhaus-Universit{\"a}t Weimar}, pages = {427}, abstract = {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.}, subject = {Landschaft}, language = {es} } @phdthesis{Cicek, author = {Cicek, Burhan}, title = {Revisiting vernacular technique: Engineering a low environmental impact earth stabilisation method}, doi = {10.25643/bauhaus-universitaet.4698}, url = {http://nbn-resolving.de/urn:nbn:de:gbv:wim2-20220803-46989}, school = {Bauhaus-Universit{\"a}t Weimar}, pages = {195}, abstract = {The major drawbacks of earth as a construction material — such as its low water stability and moderate strength — have led mankind to stabilize earth. Different civilizations developed vernacular techniques mainly focussing on lime, pozzolan or gypsum stabilization. Recently, cement has become the most commonly used additive in earth stabilization as it improves the strength and durability of plain earth. Also, it is a familiar and globally available construction material. However, using cement as an additive reduces the environmental advantages of earth and run counter to global targets regarding the reduction of CO2 emissions. Alternatives to cement stabilization are currently neither efficient enough to reduce its environmental impact nor allow the possibility of obtaining better results than those of cement. As such, this thesis deals with the rediscovery of a reverse engineering approach for a low environmental impact earth stabilization technique, aiming to replace cement in earth stabilization. The first step in the method consists in a comprehensive review of earth stabilization with regards to earthen building standards and soil classification, which allows us to identify the research gap. The review showed that there is great potential in using other additives which result in similar improvements as those achieved by cement. However, the studies that have been conducted so far either use expansive soils, which are not suitable for earth constructions or artificial pozzolans that indirectly contribute to CO2 emissions. This is the main research gap. The key concept for the development in the second step of the method is to combine vernacular additives to both improve the strength and durability of plain earth and to reduce the CO2 emissions. Various earth-mixtures were prepared and both development and performance tests were done to investigate the performance of this technique. The laboratory analyses on mix-design have proven a high durability and the results show a remarkable increase in strength performance. Furthermore, a significant reduction in CO2 emissions in comparison to cement stabilization could be shown. The third step of the method discusses the results drawn from the experimental programme. In addition, the potential of the new earth mixture with regards to its usability in the field of building construction and architectural design is further elaborated on. The method used in this study is the first of its kind that allows investors to avoid the very time-consuming processes such as finding a suitable source for soil excavation and soil classification. The developed mixture has significant workability and suitability for production of stabilized earthen panels — the very first of its kind. Such a panel is practically feasible, reasonable, and could be integrated into earthen building standards in general and in particular to DIN 18948, which is related to earthen boards and published in 2018.}, subject = {Lehm}, language = {en} } @phdthesis{Gollub, author = {Gollub, Tim}, title = {Information Retrieval for the Digital Humanities}, doi = {10.25643/bauhaus-universitaet.4673}, url = {http://nbn-resolving.de/urn:nbn:de:gbv:wim2-20220801-46738}, school = {Bauhaus-Universit{\"a}t Weimar}, pages = {177}, abstract = {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.}, subject = {Information Retrieval}, language = {en} } @phdthesis{Nouri, author = {Nouri, Hamidreza}, title = {Mechanical Behavior of two dimensional sheets and polymer compounds based on molecular dynamics and continuum mechanics approach}, doi = {10.25643/bauhaus-universitaet.4670}, url = {http://nbn-resolving.de/urn:nbn:de:gbv:wim2-20220713-46700}, school = {Bauhaus-Universit{\"a}t Weimar}, pages = {152}, abstract = {Compactly, this thesis encompasses two major parts to examine mechanical responses of polymer compounds and two dimensional materials: 1- Molecular dynamics approach is investigated to study transverse impact behavior of polymers, polymer compounds and two dimensional materials. 2- Large deflection of circular and rectangular membranes is examined by employing continuum mechanics approach. Two dimensional materials (2D), including, Graphene and molybdenum disulfide (MoS2), exhibited new and promising physical and chemical properties, opening new opportunities to be utilized alone or to enhance the performance of conventional materials. These 2D materials have attracted tremendous attention owing to their outstanding physical properties, especially concerning transverse impact loading. Polymers, with the backbone of carbon (organic polymers) or do not include carbon atoms in the backbone (inorganic polymers) like polydimethylsiloxane (PDMS), have extraordinary characteristics particularly their flexibility leads to various easy ways of forming and casting. These simple shape processing label polymers as an excellent material often used as a matrix in composites (polymer compounds). In this PhD work, Classical Molecular Dynamics (MD) is implemented to calculate transverse impact loading of 2D materials as well as polymer compounds reinforced with graphene sheets. In particular, MD was adopted to investigate perforation of the target and impact resistance force . By employing MD approach, the minimum velocity of the projectile that could create perforation and passes through the target is obtained. The largest investigation was focused on how graphene could enhance the impact properties of the compound. Also the purpose of this work was to discover the effect of the atomic arrangement of 2D materials on the impact problem. To this aim, the impact properties of two different 2D materials, graphene and MoS2, are studied. The simulation of chemical functionalization was carried out systematically, either with covalently bonded molecules or with non-bonded ones, focusing the following efforts on the covalently bounded species, revealed as the most efficient linkers. To study transverse impact behavior by using classical MD approach , Large-scale Atomic/Molecular Massively Parallel Simulator (LAMMPS) software, that is well-known among most researchers, is employed. The simulation is done through predefined commands in LAMMPS. Generally these commands (atom style, pair style, angle style, dihedral style, improper style, kspace style, read data, fix, run, compute and so on) are used to simulate and run the model for the desired outputs. Depends on the particles and model types, suitable inter-atomic potentials (force fields) are considered. The ensembles, constraints and boundary conditions are applied depends upon the problem definition. To do so, atomic creation is needed. Python codes are developed to generate particles which explain atomic arrangement of each model. Each atomic arrangement introduced separately to LAMMPS for simulation. After applying constraints and boundary conditions, LAMMPS also include integrators like velocity-Verlet integrator or Brownian dynamics or other types of integrator to run the simulation and finally the outputs are emerged. The outputs are inspected carefully to appreciate the natural behavior of the problem. Appreciation of natural properties of the materials assist us to design new applicable materials. In investigation on the large deflection of circular and rectangular membranes, which is related to the second part of this thesis, continuum mechanics approach is implemented. Nonlinear F{\"o}ppl membrane theory, which carefully release nonlinear governing equations of motion, is considered to establish the non-linear partial differential equilibrium equations of the membranes under distributed and centric point loads. The Galerkin and energy methods are utilized to solve non-linear partial differential equilibrium equations of circular and rectangular plates respectively. Maximum deflection as well as stress through the film region, which are kinds of issue in many industrial applications, are obtained.}, subject = {Molekulardynamik}, language = {en} } @phdthesis{Kiesel2022, author = {Kiesel, Johannes}, title = {Harnessing Web Archives to Tackle Selected Societal Challenges}, doi = {10.25643/bauhaus-universitaet.4660}, url = {http://nbn-resolving.de/urn:nbn:de:gbv:wim2-20220622-46602}, school = {Bauhaus-Universit{\"a}t Weimar}, year = {2022}, abstract = {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.}, subject = {Informatik}, language = {en} } @phdthesis{Partschefeld, author = {Partschefeld, Stephan}, title = {Synthese von Fließmitteln aus St{\"a}rke und Untersuchung der Wechselwirkung mit Portlandzement}, doi = {10.25643/bauhaus-universitaet.4640}, url = {http://nbn-resolving.de/urn:nbn:de:gbv:wim2-20220505-46402}, school = {Bauhaus-Universit{\"a}t Weimar}, pages = {145}, abstract = {Das Ziel dieser Arbeit war es, neuartige Fließmittel auf Basis von St{\"a}rke als nachwachsenden Rohstoff zu synthetisieren und die Wechselwirkung mit Portlandzement zu charakterisieren. Die Notwendigkeit, Alternativen zu synthetischen Zusatzmittel zu erforschen, ergibt sich aus der ben{\"o}tigten Menge zur Verarbeitung von ca. 4,1 Gt/a, wobei ca. 85 \% der Zusatzmittel auf die Fließmittel entfallen. Um Fließmittel aus St{\"a}rke zu synthetisieren, wurden drei Basisst{\"a}rken unterschiedlicher Herkunft verwendet. Es wurde eine Maniokst{\"a}rke mit einer niedrigen Molekularmasse und eine Weizenst{\"a}rke mit einer hohen Molekularmasse verwendet. Dar{\"u}ber hinaus wurde eine Kartoffelst{\"a}rke mit einer mittleren Molekularmasse, die ein Abfallprodukt der kartoffelverarbeitenden Industrie darstellt, genutzt. Die St{\"a}rkefließmittel wurden durch chemische Modifikation in einem zweistufigen Prozess synthetisiert. Im ersten Schritt wurde das Molekulargewicht der Weizen- und Kartoffelst{\"a}rke durch s{\"a}urehydrolytischen Abbau verringert. F{\"u}r die kurzkettige Maniokst{\"a}rke war eine Degradation der Molekularmasse nicht notwendig. Im zweiten Syntheseschritt wurden anionische Ladungen durch das Versetzen der degradierten St{\"a}rken und Maniokst{\"a}rke mit Natriumvinylsulfonat in die St{\"a}rkemolek{\"u}le eingef{\"u}hrt. Beurteilung der Synthesemethode zur Erzeugung von St{\"a}rkefließmitteln In diesem Zusammenhang sollten molekulare Parameter der St{\"a}rkefließmittel gezielt eingestellt werden, um eine Fließwirkung im Portlandzement zu erhalten. Insbesondere die Molekularmasse und die Menge anionischer Ladungen sollte variiert werden, um Abh{\"a}ngigkeiten mit der Dispergierleistung zu identifizieren. 1. Es konnte durch GPC-Messungen gezeigt werden, dass die Molekularmasse der langkettigen Weizenst{\"a}rke durch die gew{\"a}hlten Modifizierungsbedingungen zum s{\"a}urehydrolytischen Abbau verringert werden konnte. Durch Variation der s{\"a}urehydrolytischen Bedingungen wurden 4 degradierte Weizenst{\"a}rken erzeugt, die eine Reduzierung der Molekularmasse um 27,5 - 43 \% aufwiesen. Die Molekularmasse der Kartoffelst{\"a}rke konnte durch s{\"a}urehydrolytischen Abbau um ca. 26 \% verringert werden. 2. Durch PCD-Messungen wurde gezeigt, dass anionische Ladungen durch Sulfoethylierung der freien Hydroxylgruppen in die degradierten St{\"a}rken eingef{\"u}hrt werden konnten. Durch Variation der Dauer der Sulfoethylierung konnte die Menge der anionischen Ladungen gesteuert und gezielt variiert werden, so dass St{\"a}rkefließmittel 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 St{\"a}rkefließmittel mit variierten Molekularmassen und anionischen Ladungen erzeugt werden. Es konnte gezeigt werden, dass die Herkunft der St{\"a}rke f{\"u}r die chemische Modifizierung unerheblich ist. Die Fließmittel lagen synthesebedingt als basische, w{\"a}ssrige Suspensionen mit Wirkstoffgehalten im Bereich von 23,5 - 50 \% vor. Beurteilung der Dispergierleistung der synthetisierten St{\"a}rkefließmittel Die Dispergierperformance wurde durch rheologische Experimente mit einem Rotationsviskosimeter erfasst. Dabei wurden der Einfluss auf die Fließkurven und die Viskosit{\"a}tskurven 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 St{\"a}rkefließmittel eine vergleichbar hohe Dispergierleistung aufweisen, wie das zum Vergleich herangezogen PCE-Fließmittel. Dar{\"u}ber hinaus zeigte sich, dass die Fließwirkung der 6 St{\"a}rkefließmittel gegen{\"u}ber dem Polykondensatfließmittel deutlich h{\"o}her ist. Das aus der Literatur bekannte Einbrechen der Dispergierleistung der Polykondensat-fließmittel bei w/z-Werten < 0,4 konnte best{\"a}tigt werden. 4. Alle 6 St{\"a}rkefließmittel f{\"u}hrten zu einer Verringerung der Fließgrenze und der dynamischen Viskosit{\"a}t des Zementleimes bei einem w/z-Wert von 0,35. 5. Der Vergleich der Dispergierleistung der St{\"a}rkefließmittel untereinander zeigte, dass die anionische Ladungsmenge einen Schl{\"u}sselparameter darstellt. Die St{\"a}rkefließmittel M-1, K-1, W-1 und W-4 mit anionischen Ladungsmengen > 6 C/g zeigten die h{\"o}chste 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 f{\"u}r die Dispergierleistung zun{\"a}chst unerheblich zu sein. Aus diesem Grund wurde die Basisweizenst{\"a}rke erneut chemisch modifiziert, indem anionische Ladungen eingef{\"u}hrt wurden, ohne die Molekularmasse jedoch zu verringern. Das St{\"a}rkederivat 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 St{\"a}rke zu erzeugen. Des Weiteren zeigen die Ergebnisse, dass durch die chemische Modifizierung sowohl Fließmittel als auch Verdicker aus St{\"a}rke erzeugt werden k{\"o}nnen. Beurteilung der Beeinflussung der Hydratation und der Porenl{\"o}sung des Portlandzementes Aus der Literatur ist bekannt, dass Fließmittel die Hydratation von Portlandzement maßgeblich beeinflussen k{\"o}nnen. Aus diesem Grund wurden kalorimetrische und konduktometrische Untersuchungen an Zementsuspensionen, die mit den synthetisierten St{\"a}rkefließmitteln versetzt wurden, durchgef{\"u}hrt. Erg{\"a}nzt wurden die Untersuchungen durch Porenl{\"o}sungsanalysen zu verschiedenen Zeitpunkten der Hydratation. 6. Die kalorimetrischen Untersuchungen zur Beeinflussung der Hydratation des Portlandzementes zeigten, dass die dormante Periode durch die Zugabe der St{\"a}rkefließmittel z.T. erheblich verl{\"a}ngert wird. Es konnte gezeigt werden, dass, je h{\"o}her die anionische Ladungsmenge der St{\"a}rkefließmittel ist, desto l{\"a}nger dauert die dormante Periode andauert. Dar{\"u}ber hinaus zeigte sich, dass eine niedrige Molekularmasse der St{\"a}rkefließmittel die Verl{\"a}ngerung der dormanten Periode beg{\"u}nstigt. 7. Durch die konduktometrischen Untersuchungen konnte gezeigt werden, dass alle St{\"a}rkefließmittel die Dauer des freien- und diffusionskontrollierten CSH-Phasenwachstums verlangsamen. Insbesondere die Ausf{\"a}llung des Portlandits, welches mit dem Erstarrungsbeginn korreliert, erfolgt zu deutlich sp{\"a}teren Zeitpunkten. Des Weiteren korrelierten die konduktometrischen Untersuchungen mit der zeitlichen Entwicklung der Calciumkonzentration der Porenl{\"o}sungen. Der Vergleich der St{\"a}rkefließmittel untereinander zeigte, dass die Molekularmasse ein Schl{\"u}sselparameter ist. Das St{\"a}rkefließmittel M-1 mit der geringsten Molekularmasse, welches geringe Mengen kurzkettiger Anhydroglucoseeinheiten aufweist, verz{\"o}gert die Hydratphasenbildung am st{\"a}rksten. Diese Wirkung ist vergleichbar mit der von Zuckern. Dar{\"u}ber hinaus deuteten die Ergebnisse daraufhin, dass die St{\"a}rkefließmittel auf den ersten Hydratationsprodukten adsorbieren, wodurch die Hydratphasenbildung verlangsamt wird. Die kalorimetrischen und konduktometrischen Daten sowie die Ergebnisse der Porenl{\"o}sungsanalytik des Zementes, erforderten eine genauere Betrachtung der Beeinflussung der Hydratation der Klinkerphasen C3A und C3S, durch die St{\"a}rkefließmittel. Demzufolge wurden die Untersuchungen mit den Klinkerphasen C3A und C3S in Analogie zum Portlandzement durchgef{\"u}hrt. Beurteilung der Beeinflussung der Hydratation und der Porenl{\"o}sung des C3A W{\"a}hrend die kalorimetrischen Untersuchungen zur C3A-Hydratation eine Tendenz zur verlangsamten Hydratphasenbildung durch die St{\"a}rkefließmittel aufzeigten, lieferten die konduktometrischen Ergebnisse grundlegende Erkenntnisse zur Beeinflussung der C3A-Hydratation. Das Stadium I der C3A-Hydratation ist durch einen Abfall der elektrischen Leitf{\"a}higkeit gepr{\"a}gt. Dies korreliert mit dem Absinken der Calciumionenkonzentration und dem Anstieg der Aluminiumionenkonzentration in der Porenl{\"o}sung der C3A-Suspensionen. Im Anschluss an das Stadium I bildet sich ein Plateau in den elektrischen Leitf{\"a}higkeitskurven aus. 8. Es konnte gezeigt werden, dass die St{\"a}rkefließmittel das Stadium I der C3A-Hydratation, d.h. die Aufl{\"o}sung und Bildung erster Calciumaluminathydrate verlangsamen. Insbesondere die St{\"a}rkefließmittel mit h{\"o}herer Molekularmasse erh{\"o}hten die Dauer des Stadium I. Das Stadium II wird durch die St{\"a}rkefließmittel in folgender Reihenfolge am st{\"a}rksten verl{\"a}ngert: M-1 > W-3 > K-1 > W-2 ≥ W-4 und verdeutlicht, dass keine Abh{\"a}ngigkeit von der anionischen Ladungsmenge identifiziert werden konnte. Die Ergebnisse zeigten, dass speziell die kurzkettige St{\"a}rke M-1, das Stadium II l{\"a}nger aufrechterhalten. 9. Das Stadium III und IV der C3A-Hydratation wird insbesondere durch die St{\"a}rkefließmittel mit h{\"o}herer Molekularmasse verl{\"a}ngert. Die Ergebnisse der Porenl{\"o}sungsanalytik korrelieren mit den Ergebnissen der elektrischen Leitf{\"a}higkeit. Speziell die zeitlichen Verl{\"a}ufe der Calciumionenkonzentration bildeten die Verl{\"a}ufe der Konduktivit{\"a}tskurven der C3A-Hydratation mit großer {\"U}bereinstimmung ab. Beurteilung der Beeinflussung der Hydratation und der Porenl{\"o}sung des C3S Die Ergebnisse der kalorimetrischen Untersuchungen zur Beeinflussung der C3S-Hydratation durch die St{\"a}rkefließmittel zeigen, dass diese maßgeblich verlangsamt wird. Das Maximum des Haupthydratationspeaks wird zu sp{\"a}teren Zeiten verschoben und auch die H{\"o}he des Maximums wird deutlich verringert. Durch die konduktometrischen Experimente wurde aufgekl{\"a}rt, 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 St{\"a}rkefließmittelmolek{\"u}le (Zucker), Schl{\"u}sselparameter der verz{\"o}gerten Hydratationskinetik des C3S sind. Der grundlegende Mechanismus der Hydratationsverz{\"o}gerung 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 St{\"a}rkefließmittel erfolgte mit der Phenol-Schwefels{\"a}ure-Methode an Zement,- C3A- und C3S-Suspensionen. Durch den Vergleich der Adsorptionsraten und Adsorptionsmengen in Abh{\"a}ngigkeit von den molekularen Parametern der St{\"a}rkefließmittel wurde ein Wechselwirkungsmodell identifiziert. 11. Die Ursache f{\"u}r die hohe Dispergierleistung der St{\"a}rkefließmittel liegt in Adsorptionsprozessen an den ersten gebildeten Hydratphasen des Zementes begr{\"u}ndet. Die Molekularmasse der St{\"a}rkefließmittel ist ein Schl{\"u}sselparameter der entscheidend f{\"u}r den Mechanismus der Adsorption ist. W{\"a}hrend anionische, langkettige St{\"a}rken an mehreren Zementpartikeln gleichzeitig adsorbieren und f{\"u}r eine Vernetzung der Zementpartikel untereinander sorgen (Verdickerwirkung), adsorbieren kurzkettige anionische St{\"a}rken lediglich an den ersten gebildeten Hydratphasen der einzelnen Zementpartikel und f{\"u}hren zu elektrostatischer Abstoßung (Fließmittelwirkung). 12. Es konnte gezeigt werden, dass die St{\"a}rkefließmittel mit geringerem Molekulargewicht bei h{\"o}heren Konzentrationen an den Hydratphasen des Zementes adsorbieren. Die St{\"a}rkefließmittel mit h{\"o}herer Molekularmasse erreichen bei einer Zugabemenge von 0,7 \% ein Plateau. Daraus wird geschlussfolgert, dass die gr{\"o}ßeren Fließmittelmolek{\"u}le einen erh{\"o}hten Platzbedarf erfordern und zur Abs{\"a}ttigung der hydratisierenden Oberfl{\"a}chen bei geringeren Zugabemengen f{\"u}hren. Dar{\"u}ber hinaus konnte gezeigt werden, dass die St{\"a}rkefließmittel mit h{\"o}herer anionischer Ladungsmenge zu h{\"o}heren Adsorptionsmengen auf den Zement-, C3A- und C3S-Partikeln f{\"u}hren. 13. Die Adsorptionsprozesse finden an den ersten gebildeten Hydratphasen der C3A-Partikel statt, wodurch sowohl die Aufl{\"o}sung des C3A als auch die Bildung der Calciumhydroaluminate verlangsamt wird. Dar{\"u}ber hinaus wurde festgestellt, dass die Verlangsamung des freien- und diffusionskontrollierten Hydratphasenwachstums des C3S, durch die Adsorption der St{\"a}rkefließmittel auf den ersten gebildeten CSH-Phasen hervorgerufen wird. Des Weiteren wurde festgestellt, dass sehr kleine zucker{\"a}hnliche Molek{\"u}le in der kurzkettigen Maniokst{\"a}rke in der Lage sind, die Bildung der ersten CSH-Keime zu unterdr{\"u}cken. Dadurch kann die langanhaltende Plateauphase der elektrischen Leitf{\"a}higkeit der C3S-Hydratation erkl{\"a}rt werden. Beurteilung der Porenstruktur- und Festigkeitsausbildung Die Beurteilung der Qualit{\"a}t der Mikrostruktur erfolgte durch die Bestimmung der Rohdichte und der Porenradienverteilung mit Hilfe der Quecksilberhochdruckporosimetrie. Durch das Versetzen der Zementleime mit den St{\"a}rkefließmitteln konnten bei gleichbleibender Verarbeitbarkeit Zementsteinprobek{\"o}rper mit einem um 17,5 \% geringeren w/z-Wert von 0,35 hergestellt werden. Die Absenkung des w/z-Wertes f{\"u}hrt zu einem Anstieg der Rohdichte des Zementsteins. 14. Durch die Zugabe der St{\"a}rkefließmittel und den verringerten w/z-Wert wird die Porenstruktur der Zementsteinproben im Vergleich zum Referenzzementstein verfeinert, da die Gesamtporosit{\"a}t sinkt. Insbesondere der Kapillarporenanteil wird verringert und der Gelporenanteil erh{\"o}ht. Im Unterschied zu den PCE-Fließmitteln f{\"u}hrt die Zugabe der St{\"a}rkefließmittel zu keinem erh{\"o}hten Eintrag von Luftporen. Dies wiederum hat zur Folge, dass bei der Verwendung der St{\"a}rkefließmittel auf Entsch{\"a}umer verzichtet werden kann. 15. Entsprechend der dichteren Zementsteinmatrix wurden f{\"u}r die Zementsteine mit den St{\"a}rkefließmitteln nach 7 d und 28 d, erh{\"o}hte Biegezug- und Druckfestigkeiten ermittelt. Insbesondere die 28 d Druckfestigkeit wurde durch den verringerten w/z-Wert um die Faktoren 3,5 - 6,6 erh{\"o}ht.}, subject = {Bauchemie}, language = {de} } @phdthesis{Schnoes, author = {Schn{\"o}s, Christian Emanuel}, title = {Handlungsressourcen von zivilgesellschaftlichen Akteuren in Planungsprozessen}, doi = {10.25643/bauhaus-universitaet.4634}, url = {http://nbn-resolving.de/urn:nbn:de:gbv:wim2-20220505-46346}, school = {Bauhaus-Universit{\"a}t Weimar}, pages = {273}, abstract = {Diese Dissertation untersucht Handlungsressourcen von zivilgesellschaftlichen Akteuren in Planungsprozessen um innerst{\"a}dtische Planungsverfahren. Den theoretischen Rahmen bilden die Kapitalarten von Pierre Bourdieu, die zusammen mit dem Matrixraum von Dieter L{\"a}pple zu einem neuen Feldbegriff des ‚Raumfeldes' zusammengef{\"u}hrt 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 gew{\"a}hlt.}, subject = {Zivilgesellschaft}, language = {de} } @phdthesis{Liu, author = {Liu, Bokai}, title = {Stochastic multiscale modeling of polymeric nanocomposites using Data-driven techniques}, doi = {10.25643/bauhaus-universitaet.4637}, url = {http://nbn-resolving.de/urn:nbn:de:gbv:wim2-20220503-46379}, school = {Bauhaus-Universit{\"a}t Weimar}, pages = {134}, abstract = {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.}, subject = {Polymere}, language = {en} } @phdthesis{Damir, author = {Damir, Mirhan}, title = {Recalling the Omitted: Exploring the Spatial Development of the Modern Industrial Legacies in Egypt. The Case of Alexandria.}, doi = {10.25643/bauhaus-universitaet.4619}, url = {http://nbn-resolving.de/urn:nbn:de:gbv:wim2-20220329-46196}, school = {Bauhaus-Universit{\"a}t Weimar}, pages = {237}, abstract = {The modern industries of the 19th and 20th centuries had multiple effects on the spatial transformation of cities and regions. The past decade has witnessed increasing scholarly and governmental attempts toward conserving modern industrial heritage in the so-called Global North, with the goal, among others, of leveraging this heritage as a driver for urban economic development. In Egypt, the process continues to lag behind; on the one hand, this is due to the perplexing official recognition of the (in)tangible witnesses of modern industries. On the other hand, the official recognition and previous publications focus predominantly on weighing the significance of industrial structures based on their monumental architectural aesthetics. Their historical urban role and spatial attributes as part of urban heritage have yet to be seriously acknowledged. Accordingly, this hinders the integration of the extant industrial sites into the broader debate surrounding urban conservation, leaving them vulnerable to decay and destruction. This dissertation steers away from the singular investigation of selective modern industrial sites to recall their historical spatial development on a city scale. This is effected by investigating a case study - the Egyptian port city of Alexandria. With the limited secondary data available on modern industries in Alexandria, this dissertation relied predominantly on primary sources. The author collected and leveraged both quantitative and qualitative data to recontextualize modern industries in terms of their spatial dynamics, order, and rationale within cities' transformation. By recalling historical spatial development in Alexandria, the contribution of this dissertation lies in highlighting what the author refers to as the Omitted Heritage. This is defined by the modern industries in Egypt that are intentionally, unintentionally, and forgetfully excluded in terms of physical documentation, evaluation, appreciation, and integration within urban development plans. The method used excavated the richness of the established modern industries in Alexandria in terms of their quantity and diversity, which would have otherwise remained largely forgotten. The contextualization of modern industries unveiled spatial periodization, spatial dynamics, and conceptual development. The study draws on important analytical aspects that transcend the sites' boundaries, elevating their significance to the municipal, regional, national, and even global levels. Its recommendations for further research are also divided into those levels.}, subject = {{\"A}gypten}, language = {en} } @phdthesis{Malik, author = {Malik, Irfan}, title = {An adaptive contact formulation for Isogeometric Finite Element Analysis}, doi = {10.25643/bauhaus-universitaet.4612}, url = {http://nbn-resolving.de/urn:nbn:de:gbv:wim2-20220324-46129}, school = {Bauhaus-Universit{\"a}t Weimar}, pages = {124}, abstract = {Numerical simulation of physical phenomena, like electro-magnetics, structural and fluid mechanics is essential for the cost- and time-efficient development of mechanical products at high quality. It allows to investigate the behavior of a product or a system far before the first prototype of a product is manufactured. This thesis addresses the simulation of contact mechanics. Mechanical contacts appear in nearly every product of mechanical engineering. Gearboxes, roller bearings, valves and pumps are only some examples. Simulating these systems not only for the maximal/minimal stresses and strains but for the stress-distribution in case of tribo-contacts is a challenging task from a numerical point of view. Classical procedures like the Finite Element Method suffer from the nonsmooth representation of contact surfaces with discrete Lagrange elements. On the one hand, an error due to the approximate description of the surface is introduced. On the other hand it is difficult to attain a robust contact search because surface normals can not be described in a unique form at element edges. This thesis introduces therefore a novel approach, the adaptive isogeometric contact formulation based on polynomial Splines over hierarchical T-meshes (PHT-Splines), for the approximate solution of the non-linear contact problem. It provides a more accurate, robust and efficient solution compared to conventional methods. During the development of this method the focus was laid on the solution of static contact problems without friction in 2D and 3D in which the structures undergo small deformations. The mathematical description of the problem entails a system of partial differential equations and boundary conditions which model the linear elastic behaviour of continua. Additionally, it comprises side conditions, the Karush-Kuhn-Tuckerconditions, to prevent the contacting structures from non-physical penetration. The mathematical model must be transformed into its integral form for approximation of the solution. Employing a penalty method, contact constraints are incorporated by adding the resulting equations in weak form to the overall set of equations. For an efficient space discretization of the bulk and especially the contact boundary of the structures, the principle of Isogeometric Analysis (IGA) is applied. Isogeometric Finite Element Methods provide several advantages over conventional Finite Element discretization. Surface approximation with Non-Uniform Rational B-Splines (NURBS) allow a robust numerical solution of the contact problem with high accuracy in terms of an exact geometry description including the surface smoothness. The numerical evaluation of the contact integral is challenging due to generally non-conforming meshes of the contacting structures. In this work the highly accurate Mortar Method is applied in the isogeometric setting for the evaluation of contact contributions. This leads to an algebraic system of equations that is linearized and solved in sequential steps. This procedure is known as the Newton Raphson Method. Based on numerical examples, the advantages of the isogeometric approach with classical refinement strategies, like the p- and h-refinement, are shown and the influence of relevant algorithmic parameters on the approximate solution of the contact problem is verified. One drawback of the Spline approximations of stresses though is that they lack accuracy at the contact edge where the structures change their boundary from contact to no contact and where the solution features a kink. The approximation with smooth Spline functions yields numerical artefacts in the form of non-physical oscillations. This property of the numerical solution is not only a drawback for the simulation of e.g. tribological contacts, it also influences the convergence properties of iterative solution procedures negatively. Hence, the NURBS discretized geometries are transformed to Polynomial Splines over Hierarchical T-meshes (PHT-Splines), for the local refinement along contact edges to reduce the artefact of pressure oscillations. NURBS have a tensor product structure which does not allow to refine only certain parts of the geometrical domain while leaving other parts unchanged. Due to the B{\´e}zier Extraction, lying behind the transformation from NURBS to PHT-Splines, the connected mesh structure is broken up into separate elements. This allows an efficient local refinement along the contact edge. Before single elements are refined in a hierarchical form with cross-insertion, existing basis functions must be modified or eliminated. This process of truncation assures local and global linear independence of the refined basis which is needed for a unique approximate solution. The contact boundary is a priori unknown. Local refinement along the contact edge, especially for 3D problems, is for this reason not straight forward. In this work the use of an a posteriori error estimation procedure, the Super Convergent Recovery Solution Based Error Estimation Scheme, together with the D{\"o}rfler Marking Method is suggested for the spatial search of the contact edge. Numerical examples show that the developed method improves the quality of solutions along the contact edge significantly compared to NURBS based approximate solutions. Also, the error in maximum contact pressures, which correlates with the pressure artefacts, is minimized by the adaptive local refinement. In a final step the practicability of the developed solution algorithm is verified by an industrial application: The highly loaded mechanical contact between roller and cam in the drive train of a high-pressure fuel pump is considered.}, subject = {Isogeometrische Analyse}, language = {en} } @phdthesis{Vogler, author = {Vogler, Verena}, title = {A framework for artificial coral reef design: Integrating computational modelling and high precision monitoring strategies for artificial coral reefs - an Ecosystem-aware design approach in times of climate change}, isbn = {978-3-00-074495-2}, doi = {10.25643/bauhaus-universitaet.4611}, url = {http://nbn-resolving.de/urn:nbn:de:gbv:wim2-20220322-46115}, school = {Bauhaus-Universit{\"a}t Weimar}, pages = {243}, abstract = {Tropical coral reefs, one of the world's oldest ecosystems which support some of the highest levels of biodiversity on the planet, are currently facing an unprecedented ecological crisis during this massive human-activity-induced period of extinction. Hence, tropical reefs symbolically stand for the destructive effects of human activities on nature [4], [5]. Artificial reefs are excellent examples of how architectural design can be combined with ecosystem regeneration [6], [7], [8]. However, to work at the interface between the artificial and the complex and temporal nature of natural systems presents a challenge, i.a. in respect to the B-rep modelling legacy of computational modelling. The presented doctorate investigates strategies on how to apply digital practice to realise what is an essential bulwark to retain reefs in impossibly challenging times. Beyond the main question of integrating computational modelling and high precision monitoring strategies in artificial coral reef design, this doctorate explores techniques, methods, and linking frameworks to support future research and practice in ecology led design contexts. Considering the many existing approaches for artificial coral reefs design, one finds they often fall short in precisely understanding the relationships between architectural and ecological aspects (e.g. how a surface design and material composition can foster coral larvae settlement, or structural three-dimensionality enhance biodiversity) and lack an integrated underwater (UW) monitoring process. Such a process is necessary in order to gather knowledge about the ecosystem and make it available for design, and to learn whether artificial structures contribute to reef regeneration or rather harm the coral reef ecosystem. For the research, empirical experimental methods were applied: Algorithmic coral reef design, high precision UW monitoring, computational modelling and simulation, and validated through parallel real-world physical experimentation - two Artificial Reef Prototypes (ARPs) in Gili Trawangan, Indonesia (2012-today). Multiple discrete methods and sub techniques were developed in seventeen computational experiments and applied in a way in which many are cross valid and integrated in an overall framework that is offered as a significant contribution to the field. Other main contributions include the Ecosystem-aware design approach, Key Performance Indicators (KPIs) for coral reef design, algorithmic design and fabrication of Biorock cathodes, new high precision UW monitoring strategies, long-term real-world constructed experiments, new digital analysis methods and two new front-end web-based tools for reef design and monitoring reefs. The methodological framework is a finding of the research that has many technical components that were tested and combined in this way for the very first time. In summary, the thesis responds to the urgency and relevance in preserving marine species in tropical reefs during this massive extinction period by offering a differentiated approach towards artificial coral reefs - demonstrating the feasibility of digitally designing such 'living architecture' according to multiple context and performance parameters. It also provides an in-depth critical discussion of computational design and architecture in the context of ecosystem regeneration and Planetary Thinking. In that respect, the thesis functions as both theoretical and practical background for computational design, ecology and marine conservation - not only to foster the design of artificial coral reefs technically but also to provide essential criteria and techniques for conceiving them. Keywords: Artificial coral reefs, computational modelling, high precision underwater monitoring, ecology in design.}, subject = {Korallenriff}, language = {en} } @phdthesis{Tatarin, author = {Tatarin, Ren{\´e}}, title = {Charakterisieren struktureller Ver{\"a}nderungen in zementgebundenen Baustoffen durch akustische zerst{\"o}rungsfreie Pr{\"u}fverfahren}, publisher = {Cuvillier Verlag}, address = {G{\"o}ttingen}, isbn = {978-3-7369-7575-0}, doi = {10.25643/bauhaus-universitaet.4592}, url = {http://nbn-resolving.de/urn:nbn:de:gbv:wim2-20220215-45920}, school = {Bauhaus-Universit{\"a}t Weimar}, pages = {293}, abstract = {Im Rahmen dieser Arbeit wird das Charakterisieren struktureller Ver{\"a}nderungen zementgebundener Baustoffe durch zwei auf dem Ultraschall-Transmissionsverfahren beruhenden Methoden der zerst{\"o}rungsfreien Pr{\"u}fung (ZfP) mit mechanischen Wellen vorgenommen. Zur kontinuierlichen Charakterisierung der Erstarrung und Erh{\"a}rtung frischer zementgebundener Systeme wird ein auf Ultraschallsensoren f{\"u}r Longitudinal- und Scherwellen basierendes Messsystem in Kombination mit zugeh{\"o}rigen Verfahrensweisen zur Datenauswertung konzipiert, charakterisiert und angewandt. Gegen{\"u}ber der bislang {\"u}blichen alleinigen Bewertung der Verfestigung anhand indirekter Ultraschallparameter wie Ausbreitungsgeschwindigkeit, Signalenergie oder Frequenzgehalt der Longitudinalwelle l{\"a}sst sich damit eine direkte, sensible Erfassung der sich w{\"a}hrend der Strukturbildung entwickelnden dynamischen elastischen Eigenschaften auf der Basis prim{\"a}rer physikalischer Werkstoffparameter erreichen. Insbesondere Scherwellen und der dynamische Schubmodul sind geeignet, den graduellen {\"U}bergang zum Festk{\"o}rper mit {\"U}berschreiten der Perkolationsschwelle sensibel und unabh{\"a}ngig vom Luftgehalt zu erfassen. Die zeitliche Entwicklung der dynamischen elastischen Eigenschaften, die Strukturbildungsraten sowie die daraus extrahierten diskreten Ergebnisparameter erm{\"o}glichen eine vergleichende quantitative Charakterisierung der Strukturbildung zementgebundener Baustoffe aus mechanischer Sicht. Dabei lassen sich typische, oft unvermeidbare Unterschiede in der Zusammensetzung der Versuchsmischungen ber{\"u}cksichtigen. Der Einsatz laserbasierter Methoden zur Anregung und Erfassung von mechanischen Wellen und deren Kombination zu Laser-Ultraschall zielt darauf ab, die mit der Anwendung des konventionellen Ultraschall-Transmissionsverfahrens verbundenen Nachteile zu eliminieren. Diese resultieren aus der Sensorgeometrie, der mechanischen Ankopplung und bei einer Vielzahl von Oberfl{\"a}chenpunkten aus einem hohen pr{\"u}ftechnischen Aufwand. Die laserbasierte, interferometrische Erfassung mechanischer Wellen ist gegen{\"u}ber Ultraschallsensoren rauschbehaftet und vergleichsweise unsensibel. Als wesentliche Voraussetzung der scannenden Anwendung von Laser-Ultraschall auf zementgebundene Baustoffe erfolgen systematische experimentelle Untersuchungen zur laserinduzierten ablativen Anregung. Diese sollen zum Verst{\"a}ndnis des Anregungsmechanismus unmittelbar auf den Oberfl{\"a}chen von zementgebundenen Baustoffen, Gesteinsk{\"o}rnungen und metallischen Werkstoffen beitragen, relevante Einflussfaktoren aus den charakteristischen Materialeigenschaften identifizieren, geeignete Prozessparameter gewinnen und die Verfahrensgrenzen aufzeigen. Unter Einsatz von Longitudinalwellen erfolgt die Anwendung von Laser-Ultraschall zur zeit- und ortsaufgel{\"o}sten Charakterisierung der Strukturbildung und Homogenit{\"a}t frischer sowie erh{\"a}rteter Proben zementgebundener Baustoffe. W{\"a}hrend der Strukturbildung wird erstmals eine simultane ber{\"u}hrungslose Erfassung von Longitudinal- und Scherwellen vorgenommen. Unter Anwendung von tomographischen Methoden (2D-Laufzeit¬tomo¬graphie) werden {\"u}berlagerungsfreie Informationen zur r{\"a}umlichen Verteilung struktureller Gef{\"u}gever{\"a}nderungen anhand der longitudinalen Ausbreitungsgeschwindigkeit bzw. des relativen dynamischen Elastizit{\"a}tsmoduls innerhalb von virtuellen Schnittebenen gesch{\"a}digter Probek{\"o}rper gewonnen. Als beton-sch{\"a}digende Mechanismen werden exemplarisch der kombinierte Frost-Tausalz-Angriff sowie die Alkali-Kiesels{\"a}ure-Reaktion (AKR) herangezogen. Die im Rahmen dieser Arbeit entwickelten Verfahren der zerst{\"o}rungsfreien Pr{\"u}fung bieten erweiterte M{\"o}glichkeiten zur Charakterisierung zementgebundener Baustoffe und deren strukturellen Ver{\"a}nderungen und lassen sich zielgerichtet in der Werkstoffentwicklung, bei der Qualit{\"a}tssicherung sowie zur Analyse von Schadensprozessen und -ursachen einsetzen.}, subject = {Beton}, language = {de} } @phdthesis{Hartmann, author = {Hartmann, Veronika}, title = {Methoden zur Quantifizierung und Optimierung der Robustheit von Bauablaufpl{\"a}nen}, doi = {10.25643/bauhaus-universitaet.4579}, url = {http://nbn-resolving.de/urn:nbn:de:gbv:wim2-20220204-45798}, school = {Bauhaus-Universit{\"a}t Weimar}, abstract = {Bauablaufpl{\"a}nen kommt bei der Realisierung von Bauprojekten eine zentrale Rolle zu. Sie dienen der Koordination von Schnittstellen und bilden f{\"u}r die am Projekt Beteiligten die Grundlage f{\"u}r ihre individuelle Planung. Eine verl{\"a}ssliche Terminplanung ist daher von großer Bedeutung, tats{\"a}chlich sind aber gerade Bauablaufpl{\"a}ne f{\"u}r ihre Unzuverl{\"a}ssigkeit bekannt. Aufgrund der langen Vorlaufzeiten bei der Planung von Bauprojekten sind zum Zeitpunkt der Planung viele Informationen nur als Sch{\"a}tzwerte bekannt. Auf der Grundlage dieser gesch{\"a}tzten und damit mit Unsicherheiten behafteten Daten werden im Bauwesen deterministische Terminpl{\"a}ne erstellt. Kommt es w{\"a}hrend der Realisierung zu Diskrepanzen zwischen Sch{\"a}tzungen und Realit{\"a}t, erfordert dies die Anpassung der Pl{\"a}ne. Aufgrund zahlreicher Abh{\"a}ngigkeiten zwischen den geplanten Aktivit{\"a}ten k{\"o}nnen einzelne Plan{\"a}nderungen vielf{\"a}ltige weitere {\"A}nderungen und Anpassungen nach sich ziehen und damit einen reibungslosen Projektablauf gef{\"a}hrden. In dieser Arbeit wird ein Vorgehen entwickelt, welches Bauablaufpl{\"a}ne erzeugt, die im Rahmen der durch das Projekt definierten Abh{\"a}ngigkeiten und Randbedingungen in der Lage sind, {\"A}nderungen m{\"o}glichst gut zu absorbieren. Solche Pl{\"a}ne, die bei auftretenden {\"A}nderungen vergleichsweise geringe Anpassungen des Terminplans erfordern, werden hier als robust bezeichnet. Ausgehend von Verfahren der Projektplanung und Methoden zur Ber{\"u}cksichtigung von Unsicherheiten werden deterministische Terminpl{\"a}ne bez{\"u}glich ihres Verhaltens bei eintretenden {\"A}nderungen betrachtet. Hierf{\"u}r werden zun{\"a}chst m{\"o}gliche Unsicherheiten als Ursachen f{\"u}r {\"A}nderungen benannt und mathematisch abgebildet. Damit kann das Verhalten von Abl{\"a}ufen f{\"u}r m{\"o}gliche {\"A}nderungen betrachtet werden, indem die durch {\"A}nderungen erzwungenen angepassten Terminpl{\"a}ne simuliert werden. F{\"u}r diese Monte-Carlo-Simulationen der angepassten Terminpl{\"a}ne wird sichergestellt, dass die angepassten Terminpl{\"a}ne logische Weiterentwicklungen des deterministischen Terminplans darstellen. Auf der Grundlage dieser Untersuchungen wird ein stochastisches Maß zur Quantifizierung der Robustheit erarbeitet, welches die F{\"a}higkeit eines Planes, {\"A}nderungen zu absorbieren, beschreibt. Damit ist es m{\"o}glich, Terminpl{\"a}ne bez{\"u}glich ihrer Robustheit zu vergleichen. Das entwickelte Verfahren zur Quantifizierung der Robustheit wird in einem Optimierungsverfahren auf Basis Genetischer Algorithmen angewendet, um gezielt robuste Terminpl{\"a}ne zu erzeugen. An Beispielen werden die Methoden demonstriert und ihre Wirksamkeit nachgewiesen.}, subject = {Bauablaufplanung}, language = {de} } @phdthesis{Danckwerth, author = {Danckwerth, Julia}, title = {Strategien der Sichtbarkeit und Sichtbarmachung von ‚Wearable Enhancement' im Bereich Smart Health}, doi = {10.25643/bauhaus-universitaet.4576}, url = {http://nbn-resolving.de/urn:nbn:de:gbv:wim2-20220202-45768}, school = {Bauhaus-Universit{\"a}t Weimar}, abstract = {Die vorliegende Forschungsarbeit befasst sich mit der Entwicklung und Gestaltung von k{\"o}rpernahen, tragbaren Artefakten f{\"u}r den digitalisierten Gesundheitsbereich. Unter dem entwickelten Begriff des Wearable Enhancements werden die verschiedenen Termini aus smarten Textilien, Fashion Technologies, Wearable Technologies sowie elektronischen Textilien zusammengefasst und zwei zentrale Forschungsfragen untersucht. Wie kann Wearable Enhancement im Bereich Smart Health ethisch, sozial und ökologisch entwickelt und gestaltet werden? Inwiefern können textile Schnittstellen die Wahrnehmung und die Wahrnehmbarkeit des Körpers verändern? Mit der ersten Forschungsfrage sollen vorrangig Ansätze und Strategien der Sichtbarkeit f{\"u}r die Entwicklung und Gestaltung diskutiert werden, welche Aussagen f{\"u}r die Designpraxis, den Gestaltungs- und Designforschungsprozess sowie die Designlösungen selbst generieren sollen. Die zweite Forschungsfrage zielt darauf, Formen der Sichtbarmachung von sowie f{\"u}r Wearable Enhancement zu untersuchen. Anhand von drei konkreten Fallstudien werden wesentliche Aspekte der Rezeption, Perzeption, Konstruktion, Konfiguration und Konzeption von soziotechnischen Artefakten zur Funktionssteigerung des menschlichen K{\"o}rpers untersucht und verschiedene Formen der Sichtbarkeit und Sichtbarmachung entwickelt. In der Arbeit wird ein dual-angelegter transdisziplin{\"a}rer Designforschungsansatz entwickelt und praktiziert, welcher sowohl die menschlichen Bed{\"u}rfnisse der Nutzer*innen als auch die Weiterentwicklung von Technologien ber{\"u}cksichtigt. Auf dieser Grundlage wird versucht Anregungen f{\"u}r ein zukunftsf{\"a}higes und zugleich verantwortungsorientiertes Design zu geben.}, subject = {Design}, language = {de} } @phdthesis{Habtemariam, author = {Habtemariam, Abinet Kifle}, title = {Generalized Beam Theory for the analysis of thin-walled circular pipe members}, doi = {10.25643/bauhaus-universitaet.4572}, url = {http://nbn-resolving.de/urn:nbn:de:gbv:wim2-20220127-45723}, school = {Bauhaus-Universit{\"a}t Weimar}, pages = {188}, abstract = {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.}, subject = {Finite-Elemente-Methode}, language = {en} } @phdthesis{ManzanoGomez, author = {Manzano G{\´o}mez, Noel A.}, title = {The reverse of urban planning. Towards a 20th century history of informal urbanization in Europe and its origins in Madrid and Paris (1850-1940)}, doi = {10.25643/bauhaus-universitaet.4569}, url = {http://nbn-resolving.de/urn:nbn:de:gbv:wim2-20220119-45693}, school = {Bauhaus-Universit{\"a}t Weimar}, pages = {350}, abstract = {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.}, subject = {Stadtplanung}, language = {en} } @phdthesis{Valizadeh, author = {Valizadeh, Navid}, title = {Developments in Isogeometric Analysis and Application to High-Order Phase-Field Models of Biomembranes}, doi = {10.25643/bauhaus-universitaet.4565}, url = {http://nbn-resolving.de/urn:nbn:de:gbv:wim2-20220114-45658}, school = {Bauhaus-Universit{\"a}t Weimar}, abstract = {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.}, subject = {Phasenfeldmodell}, language = {en} } @phdthesis{Wang, author = {Wang, Jiasheng}, title = {Lebensdauerabsch{\"a}tzung von Bauteilen aus globularem Grauguss auf der Grundlage der lokalen gießprozessabh{\"a}ngigen Werkstoffzust{\"a}nde}, doi = {10.25643/bauhaus-universitaet.4554}, url = {http://nbn-resolving.de/urn:nbn:de:gbv:wim2-20220111-45542}, school = {Bauhaus-Universit{\"a}t Weimar}, pages = {165}, abstract = {Das Ziel der Arbeit ist, eine m{\"o}gliche Verbesserung der G{\"u}te der Lebensdauervorhersage f{\"u}r Gusseisenwerkstoffe mit Kugelgraphit zu erreichen, wobei die Gießprozesse verschiedener Hersteller ber{\"u}cksichtigt werden. Im ersten Schritt wurden Probenk{\"o}rper 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 Fl{\"a}cheneinheit. Basierend auf diesen Erkenntnissen wurde ein neues Festigkeitsverh{\"a}ltnisdiagramm (sogenanntes Sd/Rm-SG-Diagramm) entwickelt. Diese neue Methodik sollte vor allem erm{\"o}glichen, die Bauteildauerfestigkeit auf der Grundlage der gemessenen oder durch eine Gießsimulation vorhersagten lokalen Zugfestigkeitswerte sowie Mikrogef{\"u}genstrukturen besser zu prognostizieren. Mithilfe der Versuche sowie der Gießsimulation ist es gelungen, unterschiedliche Methoden der Lebensdauervorhersage unter Ber{\"u}cksichtigung der Herstellungsprozesse weiterzuentwickeln.}, subject = {Grauguss}, language = {de} }