@phdthesis{Chen,
  author    = {Chen, Na},
  title     = {A Balance between Ideals and Reality — Establishing and Evaluating a Resilient City Indicator System for Central Chinese Cities},
  doi       = {10.25643/bauhaus-universitaet.4030},
  url       = {http://nbn-resolving.de/urn:nbn:de:gbv:wim2-20191121-40309},
  school      = {Bauhaus-Universit{\"a}t Weimar},
  pages     = {212},
  abstract  = {Recent years have seen a gradual shift in focus of international policies from a national and regional perspective to that of cities, a shift which is closely related to the rapid urbanization of developing countries. As revealed in the 2011 Revision of the World Urbanization Prospects published by the United Nations, 51\% of the global population (approximately 3.6 billion people) lives in cities. The report predicts that by 2050, the world's urban population will increase by 2.3 billion, making up 68\% of the population. The growth of urbanization in the next few decades is expected to primarily come from developing countries, one third of which will be in China and India. With rapid urbanization and the ongoing growth of mega cities, cities must become increasingly resilient and intelligent to cope with numerous challenges and crises like droughts and floods arising from extreme climate, destruction brought by severe natural disasters, and aggregated social contradictions resulting from economic crises. All cities face the urban development dynamics and uncertainties arising from these problems. Under such circumstances, cities are considered the critical path from crisis to prosperity, so scholars and organizations have proposed the construction of "resilient cities." On the one hand, this theory emphasizes cities' defenses and buffering capacity against disasters, crises and uncertainties, as well as recovery after destruction; on the other hand, it highlights the learning capacity of urban systems, identification of opportunities amid challenges, and maintenance of development vitality. Some scholars even believe that urban resilience is a powerful supplement to sustainable development. Hence, resilience assessment has become the latest and most important perspective for evaluating the development and crisis defense capacity of cities. Rather than a general abstract concept, urban resilience is a comprehensive measurement of a city's level of development. The dynamic development of problems is reflected through quantitative indicators and appraisal systems not only from the perspective of academic research, but also governmental policy, so as to scientifically guide development, and measure and compare cities' development levels. Although international scholars have proposed quantitative methods for urban resilience assessment, they are however insufficiently systematic and regionally adaptive for China's current urban development needs. On the basis of comparative study on European and North American resilient city theories, therefore, this paper puts forwards a theoretical framework for resilient city systems consistent with China's national conditions in light of economic development pressure, natural resource depletion, pollution, and other salient development crises in China. The key factors influencing urban resilience are taken into full consideration; expert appraisal is conducted based on the Delphi Method and the analytic hierarchy process (AHP) to design an extensible and updatable resilient city evaluation system which is sufficiently systematic, geographically adaptable, and sustainable for China's current urban development needs. Finally, Changsha is taken as the main case for empirical study on comprehensive evaluation of similar cities in Central China to improve the indicator system.},
  subject      = {Stadtplanung},
  language  = {en}
}
@article{KavrakovLegatiukGuerlebecketal.,
  author    = {Kavrakov, Igor and Legatiuk, Dmitrii and G{\"u}rlebeck, Klaus and Morgenthal, Guido},
  title     = {A categorical perspective towards aerodynamic models for aeroelastic analyses of bridge decks},
  series = {Royal Society Open Science},
  journal   = {Royal Society Open Science},
  number    = {Volume 6, Issue 3},
  doi       = {/10.1098/rsos.181848},
  url       = {http://nbn-resolving.de/urn:nbn:de:gbv:wim2-20190314-38656},
  pages     = {20},
  abstract  = {Reliable modelling in structural engineering is crucial for the serviceability and safety of structures. A huge variety of aerodynamic models for aeroelastic analyses of bridges poses natural questions on their complexity and thus, quality. Moreover, a direct comparison of aerodynamic models is typically either not possible or senseless, as the models can be based on very different physical assumptions. Therefore, to address the question of principal comparability and complexity of models, a more abstract approach, accounting for the effect of basic physical assumptions, is necessary. This paper presents an application of a recently introduced category theory-based modelling approach to a diverse set of models from bridge aerodynamics. Initially, the categorical approach is extended to allow an adequate description of aerodynamic models. Complexity of the selected aerodynamic models is evaluated, based on which model comparability is established. Finally, the utility of the approach for model comparison and characterisation is demonstrated on an illustrative example from bridge aeroelasticity. The outcome of this study is intended to serve as an alternative framework for model comparison and impact future model assessment studies of mathematical models for engineering applications.},
  subject      = {Br{\"u}cke},
  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}
}
@article{SaadatfarKhosraviHassannatajJoloudarietal.,
  author    = {Saadatfar, Hamid and Khosravi, Samiyeh and Hassannataj Joloudari, Javad and Mosavi, Amir and Shamshirband, Shahaboddin},
  title     = {A New K-Nearest Neighbors Classifier for Big Data Based on Efficient Data Pruning},
  series = {Mathematics},
  volume    = {2020},
  journal   = {Mathematics},
  number    = {volume 8, issue 2, article 286},
  publisher = {MDPI},
  doi       = {10.3390/math8020286},
  url       = {http://nbn-resolving.de/urn:nbn:de:gbv:wim2-20200225-40996},
  pages     = {12},
  abstract  = {The K-nearest neighbors (KNN) machine learning algorithm is a well-known non-parametric classification method. However, like other traditional data mining methods, applying it on big data comes with computational challenges. Indeed, KNN determines the class of a new sample based on the class of its nearest neighbors; however, identifying the neighbors in a large amount of data imposes a large computational cost so that it is no longer applicable by a single computing machine. One of the proposed techniques to make classification methods applicable on large datasets is pruning. LC-KNN is an improved KNN method which first clusters the data into some smaller partitions using the K-means clustering method; and then applies the KNN for each new sample on the partition which its center is the nearest one. However, because the clusters have different shapes and densities, selection of the appropriate cluster is a challenge. In this paper, an approach has been proposed to improve the pruning phase of the LC-KNN method by taking into account these factors. The proposed approach helps to choose a more appropriate cluster of data for looking for the neighbors, thus, increasing the classification accuracy. The performance of the proposed approach is evaluated on different real datasets. The experimental results show the effectiveness of the proposed approach and its higher classification accuracy and lower time cost in comparison to other recent relevant methods.},
  subject      = {Maschinelles Lernen},
  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}
}
@article{AlkamLahmer,
  author    = {Alkam, Feras and Lahmer, Tom},
  title     = {A robust method of the status monitoring of catenary poles installed along high-speed electrified train tracks},
  series = {Results in Engineering},
  volume    = {2021},
  journal   = {Results in Engineering},
  number    = {volume 12, article 100289},
  publisher = {Elsevier},
  address   = {Amsterdam},
  doi       = {10.1016/j.rineng.2021.100289},
  url       = {http://nbn-resolving.de/urn:nbn:de:gbv:wim2-20211011-45212},
  pages     = {1 -- 8},
  abstract  = {Electric trains are considered one of the most eco-friendly and safest means of transportation. Catenary poles are used worldwide to support overhead power lines for electric trains. The performance of the catenary poles has an extensive influence on the integrity of the train systems and, consequently, the connected human services. It became a must nowadays to develop SHM systems that provide the instantaneous status of catenary poles in- service, making the decision-making processes to keep or repair the damaged poles more feasible. This study develops a data-driven, model-free approach for status monitoring of cantilever structures, focusing on pre-stressed, spun-cast ultrahigh-strength concrete catenary poles installed along high-speed train tracks. The pro-posed approach evaluates multiple damage features in an unfied damage index, which leads to straightforward interpretation and comparison of the output. Besides, it distinguishes between multiple damage scenarios of the poles, either the ones caused by material degradation of the concrete or by the cracks that can be propagated during the life span of the given structure. Moreover, using a logistic function to classify the integrity of structure avoids the expensive learning step in the existing damage detection approaches, namely, using the modern machine and deep learning methods. The findings of this study look very promising when applied to other types of cantilever structures, such as the poles that support the power transmission lines, antenna masts, chimneys, and wind turbines.},
  subject      = {Fahrleitung},
  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{Oucif,
  author    = {Oucif, Chahmi},
  title     = {Analytical Modeling of Self-Healing and Super Healing in Cementitious Materials},
  doi       = {10.25643/bauhaus-universitaet.4229},
  url       = {http://nbn-resolving.de/urn:nbn:de:gbv:wim2-20200831-42296},
  school      = {Bauhaus-Universit{\"a}t Weimar},
  pages     = {208},
  abstract  = {Self-healing materials have recently become more popular due to their capability to autonomously and autogenously repair the damage in cementitious materials. The concept of self-healing gives the damaged material the ability to recover its stiffness. This gives a difference in comparing with a material that is not subjected to healing. Once this material is damaged, it cannot sustain loading due to the stiffness degradation. Numerical modeling of self-healing materials is still in its infancy. Multiple experimental researches were conducted in literature to describe the behavior of self-healing of cementitious materials. However, few numerical investigations were undertaken. The thesis presents an analytical framework of self-healing and super healing materials based on continuum damage-healing mechanics. Through this framework, we aim to describe the recovery and strengthening of material stiffness and strength. A simple damage healing law is proposed and applied on concrete material. The proposed damage-healing law is based on a new time-dependent healing variable. The damage-healing model is applied on isotropic concrete material at the macroscale under tensile load. Both autonomous and autogenous self-healing mechanisms are simulated under different loading conditions. These two mechanisms are denoted in the present work by coupled and uncoupled self-healing mechanisms, respectively. We assume in the coupled self-healing that the healing occurs at the same time with damage evolution, while we assume in the uncoupled self-healing that the healing occurs when the material is deformed and subjected to a rest period (damage is constant). In order to describe both coupled and uncoupled healing mechanisms, a one-dimensional element is subjected to different types of loading history. In the same context, derivation of nonlinear self-healing theory is given, and comparison of linear and nonlinear damage-healing models is carried out using both coupled and uncoupled self-healing mechanisms. The nonlinear healing theory includes generalized nonlinear and quadratic healing models. The healing efficiency is studied by varying the values of the healing rest period and the parameter describing the material characteristics. In addition, theoretical formulation of different self-healing variables is presented for both isotropic and anisotropic maerials. The healing variables are defined based on the recovery in elastic modulus, shear modulus, Poisson's ratio, and bulk modulus. The evolution of the healing variable calculated based on cross-section as function of the healing variable calculated based on elastic stiffness is presented in both hypotheses of elastic strain equivalence and elastic energy equivalence. The components of the fourth-rank healing tensor are also obtained in the case of isotropic elasticity, plane stress and plane strain. Recent research revealed that self-healing presents a crucial solution also for the strengthening of the materials. This new concept has been termed ``Super Healing``. Once the stiffness of the material is recovered, further healing can result as a strengthening material. In the present thesis, new theory of super healing materials is defined in isotropic and anisotropic cases using sound mathematical and mechanical principles which are applied in linear and nonlinear super healing theories. Additionally, the link of the proposed theory with the theory of undamageable materials is outlined. In order to describe the super healing efficiency in linear and nonlinear theories, the ratio of effective stress to nominal stress is calculated as function of the super healing variable. In addition, the hypotheses of elastic strain and elastic energy equivalence are applied. In the same context, new super healing matrix in plane strain is proposed based on continuum damage-healing mechanics. In the present work, we also focus on numerical modeling of impact behavior of reinforced concrete slabs using the commercial finite element package Abaqus/Explicit. Plain and reinforced concrete slabs of unconfined compressive strength 41 MPa are simulated under impact of ogive-nosed hard projectile. The constitutive material modeling of the concrete and steel reinforcement bars is performed using the Johnson-Holmquist-2 damage and the Johnson-Cook plasticity material models, respectively. Damage diameters and residual velocities obtained by the numerical model are compared with the experimental results and effect of steel reinforcement and projectile diameter is studied.},
  subject      = {Schaden},
  language  = {en}
}
@inproceedings{VoellmeckeSchwendnerHoetal.,
  author    = {V{\"o}llmecke, Lars and Schwendner, Sascha and Ho, Ai Phien and Fischer, Jens and Seim, Werner},
  title     = {Assessment of nailed connections in existing structures},
  doi       = {10.25643/bauhaus-universitaet.6361},
  url       = {http://nbn-resolving.de/urn:nbn:de:gbv:wim2-20230609-63615},
  pages     = {7},
  abstract  = {This paper presents the development of an assessment scheme for a visual qualitative evaluation of nailed connections in existing structures, such as board trusses. In terms of further use and preservation, a quick visual inspection will help to evaluate the quality of a structure regarding its load-bearing capacity and deformation behaviour. Tests of old and new nailed joints in combination with a rating scheme point out the correlation between the load-bearing capacity and condition of a joint. Old joints of comparatively good condition tend to exhibit better results than those of poor condition. Moreover, aged joints are generally more load-bearing than newly assembled ones.},
  subject      = {Holzbau},
  language  = {en}
}
@misc{Alabassy,
  type      = {Master Thesis},
  author    = {Alabassy, Mohamed Said Helmy},
  title     = {Automated Approach for Building Information Modelling of Crack Damages via Image Segmentation and Image-based 3D Reconstruction},
  doi       = {10.25643/bauhaus-universitaet.6416},
  url       = {http://nbn-resolving.de/urn:nbn:de:gbv:wim2-20230818-64162},
  school      = {Bauhaus-Universit{\"a}t Weimar},
  pages     = {101},
  abstract  = {As machine vision-based inspection methods in the field of Structural Health Monitoring (SHM) continue to advance, the need for integrating resulting inspection and maintenance data into a centralised building information model for structures notably grows. Consequently, the modelling of found damages based on those images in a streamlined automated manner becomes increasingly important, not just for saving time and money spent on updating the model to include the latest information gathered through each inspection, but also to easily visualise them, provide all stakeholders involved with a comprehensive digital representation containing all the necessary information to fully understand the structure's current condition, keep track of any progressing deterioration, estimate the reduced load bearing capacity of the damaged element in the model or simulate the propagation of cracks to make well-informed decisions interactively and facilitate maintenance actions that optimally extend the service life of the structure. Though significant progress has been recently made in information modelling of damages, the current devised methods for the geometrical modelling approach are cumbersome and time consuming to implement in a full-scale model. For crack damages, an approach for a feasible automated image-based modelling is proposed utilising neural networks, classical computer vision and computational geometry techniques with the aim of creating valid shapes to be introduced into the information model, including related semantic properties and attributes from inspection data (e.g., width, depth, length, date, etc.). The creation of such models opens the door for further possible uses ranging from more accurate structural analysis possibilities to simulation of damage propagation in model elements, estimating deterioration rates and allows for better documentation, data sharing, and realistic visualisation of damages in a 3D model.},
  subject      = {Building Information Modeling},
  language  = {en}
}
@article{ChenSchwingKarlovšeketal.,
  author    = {Chen, Zhen and Schwing, Moritz and Karlovšek, Jurij and Wagner, Norman and Scheuermann, Alexander},
  title     = {Broadband Dielectric Measurement Methods for Soft Geomaterials: Coaxial Transmission Line Cell and Open-Ended Coaxial Probe},
  series = {International Journal of Engineering and Technology},
  volume    = {2014},
  journal   = {International Journal of Engineering and Technology},
  number    = {volume 6, number 5},
  doi       = {10.7763/IJET.2014.V6.728},
  url       = {http://nbn-resolving.de/urn:nbn:de:gbv:wim2-20210408-43984},
  pages     = {373 -- 380},
  abstract  = {Broadband dielectric measurement methods based on vector network analyzer coupled with coaxial transmission line cell (CC) and open-ended coaxial probe (OC) are simply reviewed, by which the dielectric behaviors in the frequency range of 1 MHz to 3 GHz of two practical geomaterials are investigated. Kaolin after modified compaction with different water contents is measured by using CC. The results are consistent with previous study on standardized compacted kaolin and suggest that the dielectric properties at frequencies below 100 MHz are not only a function of water content but also functions of other soil state parameters including dry density. The hydration process of a commercial grout is monitored in real time by using OC. It is found that the time dependent dielectric properties can accurately reveal the different stages of the hydration process. These measurement results demonstrate the practicability of the introduced methods in determining dielectric properties of soft geomaterials.},
  subject      = {Impedanzspektroskopie},
  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{AbuBakar,
  author    = {Abu Bakar, Ilyani Akmar},
  title     = {Computational Analysis of Woven Fabric Composites: Single- and Multi-Objective Optimizations and Sensitivity Analysis in Meso-scale Structures},
  issn      = {1610-7381},
  doi       = {10.25643/bauhaus-universitaet.4176},
  url       = {http://nbn-resolving.de/urn:nbn:de:gbv:wim2-20200605-41762},
  school      = {Bauhaus-Universit{\"a}t Weimar},
  pages     = {151},
  abstract  = {This study permits a reliability analysis to solve the mechanical behaviour issues existing in the current structural design of fabric structures. Purely predictive material models are highly desirable to facilitate an optimized design scheme and to significantly reduce time and cost at the design stage, such as experimental characterization. The present study examined the role of three major tasks; a) single-objective optimization, b) sensitivity analyses and c) multi-objective optimization on proposed weave structures for woven fabric composites. For single-objective optimization task, the first goal is to optimize the elastic properties of proposed complex weave structure under unit cells basis based on periodic boundary conditions. We predict the geometric characteristics towards skewness of woven fabric composites via Evolutionary Algorithm (EA) and a parametric study. We also demonstrate the effect of complex weave structures on the fray tendency in woven fabric composites via tightness evaluation. We utilize a procedure which does not require a numerical averaging process for evaluating the elastic properties of woven fabric composites. The fray tendency and skewness of woven fabrics depends upon the behaviour of the floats which is related to the factor of weave. Results of this study may suggest a broader view for further research into the effects of complex weave structures or may provide an alternative to the fray and skewness problems of current weave structure in woven fabric composites. A comprehensive study is developed on the complex weave structure model which adopts the dry woven fabric of the most potential pattern in singleobjective optimization incorporating the uncertainties parameters of woven fabric composites. The comprehensive study covers the regression-based and variance-based sensitivity analyses. The second task goal is to introduce the fabric uncertainties parameters and elaborate how they can be incorporated into finite element models on macroscopic material parameters such as elastic modulus and shear modulus of dry woven fabric subjected to uni-axial and biaxial deformations. Significant correlations in the study, would indicate the need for a thorough investigation of woven fabric composites under uncertainties parameters. The study describes here could serve as an alternative to identify effective material properties without prolonged time consumption and expensive experimental tests. The last part focuses on a hierarchical stochastic multi-scale optimization approach (fine-scale and coarse-scale optimizations) under geometrical uncertainties parameters for hybrid composites considering complex weave structure. The fine-scale optimization is to determine the best lamina pattern that maximizes its macroscopic elastic properties, conducted by EA under the following uncertain mesoscopic parameters: yarn spacing, yarn height, yarn width and misalignment of yarn angle. The coarse-scale optimization has been carried out to optimize the stacking sequences of symmetric hybrid laminated composite plate with uncertain mesoscopic parameters by employing the Ant Colony Algorithm (ACO). The objective functions of the coarse-scale optimization are to minimize the cost (C) and weight (W) of the hybrid laminated composite plate considering the fundamental frequency and the buckling load factor as the design constraints. Based on the uncertainty criteria of the design parameters, the appropriate variation required for the structural design standards can be evaluated using the reliability tool, and then an optimized design decision in consideration of cost can be subsequently determined.},
  subject      = {Verbundwerkstoff},
  language  = {en}
}
@phdthesis{Amiri,
  author    = {Amiri, Fatemeh},
  title     = {Computational modelling of fracture with local maximum entropy approximations},
  doi       = {10.25643/bauhaus-universitaet.2631},
  url       = {http://nbn-resolving.de/urn:nbn:de:gbv:wim2-20160719-26310},
  school      = {Bauhaus-Universit{\"a}t Weimar},
  pages     = {130},
  abstract  = {The key objective of this research is to study fracture with a meshfree method, local maximum entropy approximations, and model fracture in thin shell structures with complex geometry and topology. This topic is of high relevance for real-world applications, for example in the automotive industry and in aerospace engineering. The shell structure can be described efficiently by meshless methods which are capable of describing complex shapes as a collection of points instead of a structured mesh. In order to find the appropriate numerical method to achieve this goal, the first part of the work was development of a method based on local maximum entropy (LME) shape functions together with enrichment functions used in partition of unity methods to discretize problems in linear elastic fracture mechanics. We obtain improved accuracy relative to the standard extended finite element method (XFEM) at a comparable computational cost. In addition, we keep the advantages of the LME shape functions,such as smoothness and non-negativity. We show numerically that optimal convergence (same as in FEM) for energy norm and stress intensity factors can be obtained through the use of geometric (fixed area) enrichment with no special treatment of the nodes near the crack such as blending or shifting. As extension of this method to three dimensional problems and complex thin shell structures with arbitrary crack growth is cumbersome, we developed a phase field model for fracture using LME. Phase field models provide a powerful tool to tackle moving interface problems, and have been extensively used in physics and materials science. Phase methods are gaining popularity in a wide set of applications in applied science and engineering, recently a second order phase field approximation for brittle fracture has gathered significant interest in computational fracture such that sharp cracks discontinuities are modeled by a diffusive crack. By minimizing the system energy with respect to the mechanical displacements and the phase-field, subject to an irreversibility condition to avoid crack healing, this model can describe crack nucleation, propagation, branching and merging. One of the main advantages of the phase field modeling of fractures is the unified treatment of the interfacial tracking and mechanics, which potentially leads to simple, robust, scalable computer codes applicable to complex systems. In other words, this approximation reduces considerably the implementation complexity because the numerical tracking of the fracture is not needed, at the expense of a high computational cost. We present a fourth-order phase field model for fracture based on local maximum entropy (LME) approximations. The higher order continuity of the meshfree LME approximation allows to directly solve the fourth-order phase field equations without splitting the fourth-order differential equation into two second order differential equations. Notably, in contrast to previous discretizations that use at least a quadratic basis, only linear completeness is needed in the LME approximation. We show that the crack surface can be captured more accurately in the fourth-order model than the second-order model. Furthermore, less nodes are needed for the fourth-order model to resolve the crack path. Finally, we demonstrate the performance of the proposed meshfree fourth order phase-field formulation for 5 representative numerical examples. Computational results will be compared to analytical solutions within linear elastic fracture mechanics and experimental data for three-dimensional crack propagation. In the last part of this research, we present a phase-field model for fracture in Kirchoff-Love thin shells using the local maximum-entropy (LME) meshfree method. Since the crack is a natural outcome of the analysis it does not require an explicit representation and tracking, which is advantageous over techniques as the extended finite element method that requires tracking of the crack paths. The geometric description of the shell is based on statistical learning techniques that allow dealing with general point set surfaces avoiding a global parametrization, which can be applied to tackle surfaces of complex geometry and topology. We show the flexibility and robustness of the present methodology for two examples: plate in tension and a set of open connected pipes.},
  language  = {en}
}
@article{AlYasiriMutasharGuerlebecketal.,
  author    = {Al-Yasiri, Zainab Riyadh Shaker and Mutashar, Hayder Majid and G{\"u}rlebeck, Klaus and Lahmer, Tom},
  title     = {Damage Sensitive Signals for the Assessment of the Conditions of Wind Turbine Rotor Blades Using Electromagnetic Waves},
  series = {Infrastructures},
  volume    = {2022},
  journal   = {Infrastructures},
  number    = {Volume 7, Issue 8 (August 2022), article 104},
  editor    = {Shafiullah, GM},
  publisher = {MDPI},
  address   = {Basel},
  doi       = {10.3390/infrastructures7080104},
  url       = {http://nbn-resolving.de/urn:nbn:de:gbv:wim2-20220831-47093},
  pages     = {18},
  abstract  = {One of the most important renewable energy technologies used nowadays are wind power turbines. In this paper, we are interested in identifying the operating status of wind turbines, especially rotor blades, by means of multiphysical models. It is a state-of-the-art technology to test mechanical structures with ultrasonic-based methods. However, due to the density and the required high resolution, the testing is performed with high-frequency waves, which cannot penetrate the structure in depth. Therefore, there is a need to adopt techniques in the fields of multiphysical model-based inversion schemes or data-driven structural health monitoring. Before investing effort in the development of such approaches, further insights and approaches are necessary to make the techniques applicable to structures such as wind power plants (blades). Among the expected developments, further accelerations of the so-called "forward codes" for a more efficient implementation of the wave equation could be envisaged. Here, we employ electromagnetic waves for the early detection of cracks. Because in many practical situations, it is not possible to apply techniques from tomography (characterized by multiple sources and sensor pairs), we focus here on the question of whether the existence of cracks can be determined by using only one source for the sent waves.},
  subject      = {Windkraftwerk},
  language  = {en}
}
@phdthesis{Staeudel,
  author    = {St{\"a}udel, J{\"u}rgen},
  title     = {Development, Implementation and Operation of Integrated Sanitation Systems Based on Material-Flows - Integrated Sanitation in the City of Darkhan, Mongolia - A Practicable Example},
  doi       = {10.25643/bauhaus-universitaet.3179},
  url       = {http://nbn-resolving.de/urn:nbn:de:gbv:wim2-20170512-31794},
  school      = {Bauhaus-Universit{\"a}t Weimar},
  abstract  = {The world society faces a huge challenge to implement the human right of "access to sanitation". More and more it is accepted that the conventional approach towards providing sanitation services is not suitable to solve this problem. This dissertation examines the possibility to enhance "access to sanitation" for people who are living in areas with underdeveloped water and wastewater infrastructure systems. The idea hereby is to follow an integrated approach for sanitation, which allows for a mutual completion of existing infrastructure with resource-based sanitation systems. The notion "integrated sanitation system (iSaS)" is defined in this work and guiding principles for iSaS are formulated. Further on the implementation of iSaS is assessed at the example of a case study in the city of Darkhan in Mongolia. More than half of Mongolia's population live in settlements where yurts (tents of Nomadic people) are predominant. In these settlements (or "ger areas") sanitation systems are not existent and the hygienic situation is precarious. An iSaS has been developed for the ger areas in Darkhan and tested over more than two years. Further on a software-based model has been developed with the goal to describe and assess different variations of the iSaS. The results of the assessment of material-flows, monetary-flows and communication-flows within the iSaS are presented in this dissertation. The iSaS model is adaptable and transferable to the socio-economic conditions in other regions and climate zones.},
  subject      = {Abwasser},
  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{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{Hommel,
  author    = {Hommel, Angela},
  title     = {Diskret holomorphe Funktionen und deren Bedeutung bei der L{\"o}sung von Differenzengleichungen},
  doi       = {10.25643/bauhaus-universitaet.3784},
  url       = {http://nbn-resolving.de/urn:nbn:de:gbv:wim2-20180827-37846},
  school      = {Bauhaus-Universit{\"a}t Weimar},
  abstract  = {Auf der Grundlage diskreter Cauchy-Riemann Operatoren werden diskret holomorphe Funktionen definiert und detailliert studiert. Darauf aufbauend wird die L{\"o}sung von Differenzengleichungen mit Hilfe der diskret holomorphen Funktionen beschrieben.},
  subject      = {Differenzengleichung},
  language  = {de}
}
@phdthesis{Ren,
  author    = {Ren, Huilong},
  title     = {Dual-horizon peridynamics and Nonlocal operator method},
  doi       = {10.25643/bauhaus-universitaet.4403},
  url       = {http://nbn-resolving.de/urn:nbn:de:gbv:wim2-20210412-44039},
  school      = {Bauhaus-Universit{\"a}t Weimar},
  pages     = {223},
  abstract  = {In the last two decades, Peridynamics (PD) attracts much attention in the field of fracture mechanics. One key feature of PD is the nonlocality, which is quite different from the ideas in conventional methods such as FEM and meshless method. However, conventional PD suffers from problems such as constant horizon, explicit algorithm, hourglass mode. In this thesis, by examining the nonlocality with scrutiny, we proposed several new concepts such as dual-horizon (DH) in PD, dual-support (DS) in smoothed particle hydrodynamics (SPH), nonlocal operators and operator energy functional. The conventional PD (SPH) is incorporated in the DH-PD (DS-SPH), which can adopt an inhomogeneous discretization and inhomogeneous support domains. The DH-PD (DS-SPH) can be viewed as some fundamental improvement on the conventional PD (SPH). Dual formulation of PD and SPH allows h-adaptivity while satisfying the conservations of linear momentum, angular momentum and energy. By developing the concept of nonlocality further, we introduced the nonlocal operator method as a generalization of DH-PD. Combined with energy functional of various physical models, the nonlocal forms based on dual-support concept are derived. In addition, the variation of the energy functional allows implicit formulation of the nonlocal theory. At last, we developed the higher order nonlocal operator method which is capable of solving higher order partial differential equations on arbitrary domain in higher dimensional space. Since the concepts are developed gradually, we described our findings chronologically. In chapter 2, we developed a DH-PD formulation that includes varying horizon sizes and solves the "ghost force" issue. The concept of dual-horizon considers the unbalanced interactions between the particles with different horizon sizes. The present formulation fulfills both the balances of linear momentum and angular momentum exactly with arbitrary particle discretization. All three peridynamic formulations, namely bond based, ordinary state based and non-ordinary state based peridynamics can be implemented within the DH-PD framework. A simple adaptive refinement procedure (h-adaptivity) is proposed reducing the computational cost. Both two- and three- dimensional examples including the Kalthoff-Winkler experiment and plate with branching cracks are tested to demonstrate the capability of the method. In chapter 3, a nonlocal operator method (NOM) based on the variational principle is proposed for the solution of waveguide problem in computational electromagnetic field. Common differential operators as well as the variational forms are defined within the context of nonlocal operators. The present nonlocal formulation allows the assembling of the tangent stiffness matrix with ease, which is necessary for the eigenvalue analysis of the waveguide problem. The present formulation is applied to solve 1D Schrodinger equation, 2D electrostatic problem and the differential electromagnetic vector wave equations based on electric fields. In chapter 4, a general nonlocal operator method is proposed which is applicable for solving partial differential equations (PDEs) of mechanical problems. The nonlocal operator can be regarded as the integral form, ``equivalent'' to the differential form in the sense of a nonlocal interaction model. The variation of a nonlocal operator plays an equivalent role as the derivatives of the shape functions in the meshless methods or those of the finite element method. Based on the variational principle, the residual and the tangent stiffness matrix can be obtained with ease. The nonlocal operator method is enhanced here also with an operator energy functional to satisfy the linear consistency of the field. A highlight of the present method is the functional derived based on the nonlocal operator can convert the construction of residual and stiffness matrix into a series of matrix multiplications using the predefined nonlocal operators. The nonlocal strong forms of different functionals can be obtained easily via the concept of support and dual-support. Several numerical examples of different types of PDEs are presented. In chapter 5, we extended the NOM to higher order scheme by using a higher order Taylor series expansion of the unknown field. Such a higher order scheme improves the original NOM in chapter 3 and chapter 4, which can only achieve one-order convergence. The higher order NOM obtains all partial derivatives with specified maximal order simultaneously without resorting to shape functions. The functional based on the nonlocal operators converts the construction of residual and stiffness matrix into a series of matrix multiplication on the nonlocal operator matrix. Several numerical examples solved by strong form or weak form are presented to show the capabilities of this method. In chapter 6, the NOM proposed as a particle-based method in chapter 3,4,5, has difficulty in imposing accurately the boundary conditions of various orders. In this paper, we converted the particle-based NOM into a scheme with interpolation property. The new scheme describes partial derivatives of various orders at a point by the nodes in the support and takes advantage of the background mesh for numerical integration. The boundary conditions are enforced via the modified variational principle. The particle-based NOM can be viewed a special case of NOM with interpolation property when nodal integration is used. The scheme based on numerical integration greatly improves the stability of the method, as a consequence, the operator energy functional in particle-based NOM is not required. We demonstrated the capabilities of current method by solving the gradient solid problems and comparing the numerical results with the available exact solutions. In chapter 7, we derived the DS-SPH in solid within the framework of variational principle. The tangent stiffness matrix of SPH can be obtained with ease, and can be served as the basis for the present implicit SPH. We proposed an hourglass energy functional, which allows the direct derivation of hourglass force and hourglass tangent stiffness matrix. The dual-support is {involved} in all derivations based on variational principles and is automatically satisfied in the assembling of stiffness matrix. The implementation of stiffness matrix comprises with two steps, the nodal assembly based on deformation gradient and global assembly on all nodes. Several numerical examples are presented to validate the method.},
  subject      = {Peridynamik},
  language  = {en}
}
@phdthesis{Ashour,
  author    = {Ashour, Mohammed},
  title     = {Electromechanics and Hydrodynamics of Single Vesicles and Vesicle Doublet Using Phase-Field Isogeometric Analysis},
  doi       = {10.25643/bauhaus-universitaet.6400},
  url       = {http://nbn-resolving.de/urn:nbn:de:gbv:wim2-20230628-64003},
  school      = {Bauhaus-Universit{\"a}t Weimar},
  pages     = {175},
  abstract  = {Biomembranes are selectively permeable barriers that separate the internal components of the cell from its surroundings. They have remarkable mechanical behavior which is characterized by many phenomena, but most noticeably their fluid-like in-plane behavior and solid-like out-of-plane behavior. Vesicles have been studied in the context of discrete models, such as Molecular Dynamics, Monte Carlo methods, Dissipative Particle Dynamics, and Brownian Dynamics. Those methods, however, tend to have high computational costs, which limited their uses for studying atomistic details. In order to broaden the scope of this research, we resort to the continuum models, where the atomistic details of the vesicles are neglected, and the focus shifts to the overall morphological evolution. Under the umbrella of continuum models, vesicles morphology has been studied extensively. However, most of those studies were limited to the mechanical response of vesicles by considering only the bending energy and aiming for the solution by minimizing the total energy of the system. Most of the literature is divided between two geometrical representation methods; the sharp interface methods and the diffusive interface methods. Both of those methods track the boundaries and interfaces implicitly. In this research, we focus our attention on solving two non-trivial problems. In the first one, we study a constrained Willmore problem coupled with an electrical field, and in the second one, we investigate the hydrodynamics of a vesicle doublet suspended in an external viscous fluid flow. For the first problem, we solve a constrained Willmore problem coupled with an electrical field using isogeometric analysis to study the morphological evolution of vesicles subjected to static electrical fields. The model comprises two phases, the lipid bilayer, and the electrolyte. This two-phase problem is modeled using the phase-field method, which is a subclass of the diffusive interface methods mentioned earlier. The bending, flexoelectric, and dielectric energies of the model are reformulated using the phase-field parameter. A modified Augmented-Lagrangian (ALM) approach was used to satisfy the constraints while maintaining numerical stability and a relatively large time step. This approach guarantees the satisfaction of the constraints at each time step over the entire temporal domain. In the second problem, we study the hydrodynamics of vesicle doublet suspended in an external viscous fluid flow. Vesicles in this part of the research are also modeled using the phase-field model. The bending energy and energies associated with enforcing the global volume and area are considered. In addition, the local inextensibility condition is ensured by introducing an additional equation to the system. To prevent the vesicles from numerically overlapping, we deploy an interaction energy definition to maintain a short-range repulsion between the vesicles. The fluid flow is modeled using the incompressible Navier-Stokes equations and the vesicle evolution in time is modeled using two advection equations describing the process of advecting each vesicle by the fluid flow. To overcome the velocity-pressure saddle point system, we apply the Residual-Based Variational MultiScale (RBVMS) method to the Navier-Stokes equations and solve the coupled systems using isogeometric analysis. We study vesicle doublet hydrodynamics in shear flow, planar extensional flow, and parabolic flow under various configurations and boundary conditions. The results reveal several interesting points about the electrodynamics and hydrodynamics responses of single vesicles and vesicle doublets. But first, it can be seen that isogeometric analysis as a numerical tool has the ability to model and solve 4th-order PDEs in a primal variational framework at extreme efficiency and accuracy due to the abilities embedded within the NURBS functions without the need to reduce the order of the PDE by creating an intermediate environment. Refinement whether by knot insertion, order increasing or both is far easier to obtain than traditional mesh-based methods. Given the wide variety of phenomena in natural sciences and engineering that are mathematically modeled by high-order PDEs, the isogeometric analysis is among the most robust methods to address such problems as the basis functions can easily attain high global continuity. On the applicational side, we study the vesicle morphological evolution based on the electromechanical liquid-crystal model in 3D settings. This model describing the evolution of vesicles is composed of time-dependent, highly nonlinear, high-order PDEs, which are nontrivial to solve. Solving this problem requires robust numerical methods, such as isogeometric analysis. We concluded that the vesicle tends to deform under increasing magnitudes of electric fields from the original sphere shape to an oblate-like shape. This evolution is affected by many factors and requires fine-tuning of several parameters, mainly the regularization parameter which controls the thickness of the diffusive interface width. But it is most affected by the method used for enforcing the constraints. The penalty method in presence of an electrical field tends to lock on the initial phase-field and prevent any evolution while a modified version of the ALM has proven to be sufficiently stable and accurate to let the phase-field evolve while satisfying the constraints over time at each time step. We show additionally the effect of including the flexoelectric nature of the Biomembranes in the computation and how it affects the shape evolution as well as the effect of having different conductivity ratios. All the examples were solved based on a staggered scheme, which reduces the computational cost significantly. For the second part of the research, we consider vesicle doublet suspended in a shear flow, in a planar extensional flow, and in a parabolic flow. When the vesicle doublet is suspended in a shear flow, it can either slip past each other or slide on top of each other based on the value of the vertical displacement, that is the vertical distance between the center of masses between the two vesicles, and the velocity profile applied. When the vesicle doublet is suspended in a planar extensional flow in a configuration that resembles a junction, the time in which both vesicles separate depends largely on the value of the vertical displacement after displacing as much fluid from between the two vesicles. However, when the vesicles are suspended in a tubular channel with a parabolic fluid flow, they develop a parachute-like shape upon converging towards each other before exiting the computational domain from the predetermined outlets. This shape however is affected largely by the height of the tubular channel in which the vesicle is suspended. The velocity essential boundary conditions are imposed weakly and strongly. The weak implementation of the boundary conditions was used when the velocity profile was defined on the entire boundary, while the strong implementation was used when the velocity profile was defined on a part of the boundary. The strong implementation of the essential boundary conditions was done by selectively applying it to the predetermined set of elements in a parallel-based code. This allowed us to simulate vesicle hydrodynamics in a computational domain with multiple inlets and outlets. We also investigate the hydrodynamics of oblate-like shape vesicles in a parabolic flow. This work has been done in 2D configuration because of the immense computational load resulting from a large number of degrees of freedom, but we are actively seeking to expand it to 3D settings and test a broader set of parameters and geometrical configurations.},
  subject      = {Isogeometrische Analyse},
  language  = {en}
}
@article{AmirinasabShamshirbandChronopoulosetal.,
  author    = {Amirinasab, Mehdi and Shamshirband, Shahaboddin and Chronopoulos, Anthony Theodore and Mosavi, Amir and Nabipour, Narjes},
  title     = {Energy-Efficient Method for Wireless Sensor Networks Low-Power Radio Operation in Internet of Things},
  series = {electronics},
  volume    = {2020},
  journal   = {electronics},
  number    = {volume 9, issue 2, 320},
  publisher = {MDPI},
  doi       = {10.3390/electronics9020320},
  url       = {http://nbn-resolving.de/urn:nbn:de:gbv:wim2-20200213-40954},
  pages     = {20},
  abstract  = {The radio operation in wireless sensor networks (WSN) in Internet of Things (IoT)applications is the most common source for power consumption. Consequently, recognizing and controlling the factors affecting radio operation can be valuable for managing the node power consumption. Among essential factors affecting radio operation, the time spent for checking the radio is of utmost importance for monitoring power consumption. It can lead to false WakeUp or idle listening in radio duty cycles and ContikiMAC. ContikiMAC is a low-power radio duty-cycle protocol in Contiki OS used in WakeUp mode, as a clear channel assessment (CCA) for checking radio status periodically. This paper presents a detailed analysis of radio WakeUp time factors of ContikiMAC. Furthermore, we propose a lightweight CCA (LW-CCA) as an extension to ContikiMAC to reduce the Radio Duty-Cycles in false WakeUps and idle listening though using dynamic received signal strength indicator (RSSI) status check time. The simulation results in the Cooja simulator show that LW-CCA reduces about 8\% energy consumption in nodes while maintaining up to 99\% of the packet delivery rate (PDR).},
  subject      = {Internet der Dinge},
  language  = {en}
}
@phdthesis{Rost,
  author    = {Rost, Grit},
  title     = {Entwicklung eines Toolboxmodells als Planungswerkzeug f{\"u}r ein transdisziplin{\"a}res Wasserressourcenmanagement am Beispiel der Stadt Darkhan, Mongolei},
  publisher = {Rhombus},
  address   = {Berlin},
  isbn      = {978-3-941216-94-5},
  doi       = {10.25643/bauhaus-universitaet.4287},
  url       = {http://nbn-resolving.de/urn:nbn:de:gbv:wim2-20201113-42874},
  school      = {Bauhaus-Universit{\"a}t Weimar},
  pages     = {172},
  abstract  = {Im Rahmen der Dissertation wurde ein Toolboxmodell f{\"u}r transdisziplin{\"a}res Wasserressourcenmanagement entwickelt. Das Modell liefert den methodischen Rahmen Wasserressourcen nachhaltig und transdisziplin{\"a}r zu bewirtschaften. Der Begriff der Nachhaltigkeit und eine Konkretisierung der nachhaltigen Bewirtschaftung globaler Wasserressourcen scheinen un{\"u}berschaubar und suggerieren die Forderung nach einer neuen Weltformel. Die globale Bedeutung der Wasserressourcen, die f{\"u}r Regionen spezifischen Besonderheiten des nat{\"u}rlichen Wasserhaushalts und der anthropogenen Nutzung, die Zeitskala und die Kontextualisierung in alle betroffenen und benachbarten Disziplinen deuten auf die Komplexit{\"a}t der Thematik hin. Es wird eine Systematisierung des Planungsprozesses von Wasserressourcen notwendig, anhand derer eine holistische Herangehensweise mit einer Strategieentwicklung f{\"u}r Regionen spezifischer Schwerpunktprobleme erfolgt. Ziel der Arbeit ist die Erarbeitung einer Strategie zur Systematisierung nach diesen Forderungen und die Bereitstellung eines Toolboxmodelles als Planungswerkzeug f{\"u}r das transdisziplin{\"a}re Wasserressourcenmanagement. Das Toolboxmodell stellt den konzeptionellen Rahmen f{\"u}r die Bewirtschaftung von Wasserressourcen mit der Anwendung transdisziplin{\"a}rer Forschungsmethoden bereit. Wesentliche Herausforderung bei der Anwendung der transdisziplin{\"a}ren Methode sind die Implementierung verschiedener Skalenbereiche, der Umgang mit der Komplexit{\"a}t von Daten, das Bewahren von Transparenz und Objektivit{\"a}t sowie die Erm{\"o}glichung eines auf andere Regionen {\"u}bertragbaren Planungsprozesses. Die theoretischen Grundlagen naturwissenschaftlicher Forschung zur Nachhaltigkeit haben ihren Ursprung in den biologischen und geographischen Disziplinen. Das Ineinandergreifen naturr{\"a}umlicher Zusammenh{\"a}nge und der Einfluss anthropogener Nutzung und technischer Innovationen auf den Naturhaushalt sind Kern der Kausalit{\"a}t {\"u}bergreifenden Denkens und Verstehens. Mit dem Ansatz des integrierten Wasserressourcenmanagements (IWRM) erfolgt die Ber{\"u}cksichtigung wirtschaftlicher und sozio{\"o}konomischer Ziele in den Planungsprozess f{\"u}r {\"o}kologisch nachhaltige Wasserwirtschaft. Das Instrument der Wasserrahmenrichtlinie (EU-WRRL) ist auf eine Gew{\"a}sser{\"o}kologie ausgerichtete Richtlinie, welche die Integration verschiedener Interessenvertreter in den Planungsprozess vorsieht. Das Konzept der neuartigen Sanit{\"a}rsysteme basiert auf Stofffl{\"u}ssen zwischen konkurrierenden Handlungsbereichen, wie Abfall-, Ressourcen- und Landwirtschaft. Den integrierten Ans{\"a}tzen fehlt eine {\"u}bergeordnete gemeinsame Zielstrategie - eine sogenannte Phase Null. Diese Phase Null - das Lernen aller 7 Zusammenfassung 157 relevanten, konkurrierenden und harmonisierenden Handlungsfelder eines Planungshorizontes wird durch eine transdisziplin{\"a}re Perspektive erm{\"o}glicht. W{\"a}hrend bei der integralen Perspektive eine disziplinorientierte Kooperation im Vordergrund steht, verlangt die transdisziplin{\"a}re Perspektive nach einer problemorientierten Kooperation zwischen den Interessenvertretern (Werlen 2015). Die bestehenden Konzepte und Richtlinien f{\"u}r das nachhaltige Management von Wasserressourcen sind etabliert und evaluiert. Der Literatur zur Folge ist eine Weiterentwicklung nach der Perspektive der Transdisziplinarit{\"a}t erforderlich. Das Toolboxmodell f{\"u}r integrales Wasserressourcenmanagement entspricht einem Planungstool bestehend aus Werkzeugen f{\"u}r die Anwendung wissenschaftlicher Methoden. Die Zusammenstellung der Methoden/Werkzeuge erf{\"u}llt im Rahmen die Methode transdisziplin{\"a}rer Forschung. Das Werkzeug zum Aufstellen der relevanten Handlungsfelder umfasst die Charakterisierung eines Untersuchungsgebietes und Planungsrahmens, die kausale Verkn{\"u}pfung des Bewirtschaftungskonzeptes und konkurrierender sowie sich unterst{\"u}tzender Stakeholder. Mit dem Werkzeug der Kontextualisierung und Indikatorenaufstellung wird eine Methode der stufenweisen und von einer Skala unabh{\"a}ngigen Bewertung des Umweltzustandes f{\"u}r die Zielpriorisierung vorgenommen. Damit wird das Toolboxmodell dem Problem der Komplexit{\"a}t und Datenverf{\"u}gbarkeit gerecht. Anhand der eingesetzten ABC Methode, werden die Bewertungsgr{\"o}ßen differenziert strukturiert auf verschiedene Skalen und Datenressourcen (A=Ersterkennung,B=Zeigerwerte, C=Modell/Index). Die ABC-Methode erm{\"o}glicht die Planung bereits mit unsicherer und l{\"u}ckenhafter Datengrundlage, ist jederzeit erweiterbar und bietet somit eine operative Wissensgenerierung w{\"a}hrend des Gestaltungsprozesses. F{\"u}r das Werkzeug zur Bewertung und Priorisierung wird der Algorithmus der Composite Programmierung angewandt. Diese Methode der Mehrfachzielplanung erf{\"u}llt den Anspruch der permanenten Erweiterbarkeit und der transparenten und objektiven Entscheidungsfindung. Die Komplexit{\"a}t des transdisziplin{\"a}ren Wasserressourcenmanagements kann durch die Methode der Composite Programmierung systematisiert werden. Das wesentliche Ergebnis der Arbeit stellt die erfolgreiche Erarbeitung und Anwendung des Tool-boxmodells f{\"u}r das transdisziplin{\"a}re Wasserressourcenmanagement im Untersuchungsgebiet Stadt Darkhan in der Mongolei dar. Auf Grund seiner besonderen hydrologischen und strukturellen Situa-tion wird die Relevanz eines nachhaltigen Bewirtschaftungskonzeptes deutlich. Im Rahmen des Querschnittsmoduls des MoMo-Projektes wurde eine f{\"u}r das Toolboxmodell geeignete Datengrundlage erarbeitet. Planungsrelevante Handlungsfelder wurden im Rahmen eines Workshops mit verschiedenen Interessenvertretern erarbeitet. Im Ergebnis dessen wurde die Systematik eines Zielbaumes mit Hauptzielen und untergeordneten Teilzielen als Grundlage der Priorisierung nach den holistischen Anspruch der transdisziplin{\"a}ren Forschung aufgestellt. F{\"u}r die Messbarkeit, in-wieweit Teilziele erreicht sind oder Handlungsbedarf besteht, wurden Indikatoren erarbeitet. Die Indikatoren-Aufstellung erfolgte exemplarisch f{\"u}r das Handlungsfeld Siedlungswasserwirtschaft in allen Skalen des ABC-Systems. Die im BMBF-MoMo Projekt generierte umfassende Datengrundlage erm{\"o}glichte die Anwendung und Evaluierung des Toolboxmodells mit unterschiedlichem quantitativem und qualitativem Dateninput. Verschiedene Kombination von A (Ersterkennung), B (Zeigerwerte) und C (Modell/Index) als Grundlage der Priorisierung mit der Compostite Programmierung erm{\"o}glichten die Durchf{\"u}hrung und Bewertung des transdisziplin{\"a}ren Planungstools. Die er-mittelten Rangfolgen von Teilzielen mit unterschiedlichen Bewertungsvarianten ergaben {\"a}hnliche Tendenzen. Das ist ein Hinweis daf{\"u}r, dass f{\"u}r die zuk{\"u}nftige Anwendung des Toolboxmodells die operative Wissensgenerierung, d.h. das schrittweise Hinzuf{\"u}gen neu ermittelter, gesicherterer Daten, funktioniert. Eine schwierige Datenverf{\"u}gbarkeit oder eine noch im Prozess befindliche wissenschaftliche Analyse sollen keine Hindernisse f{\"u}r eine schrittweise und erweiterbare Zielpriorisierung und Maßnahmenplanung sein. Trotz der Komplexit{\"a}t des transdisziplin{\"a}ren Ansatzes wird durch die Anwendung des Toolboxmodells eine effiziente und zielorientierte Handlungspriorisierung erm{\"o}glicht. Die Effizienz wird erreicht durch ressourcenschonende und flexible, Ziel fokussierte Datenermittlung. Zeit und Kosten im Planungsprozess k{\"o}nnen eingespart werden. Die erzielte Priorisierung von letztlich Handlungsempfehlungen erfolgt individuell auf die Eigenart des Untersuchungsgebietes angepasst, was hinsichtlich seiner Wirkung als erfolgsversprechend gilt.},
  subject      = {Wasserreserve},
  language  = {de}
}
@masterthesis{Kuehnert2011,
  type      = {Bachelor Thesis},
  author    = {K{\"u}hnert, Christin},
  title     = {Entwicklung von Spielmechaniken f{\"u}r ein bauphysikalisches Social Game},
  doi       = {10.25643/bauhaus-universitaet.1522},
  url       = {http://nbn-resolving.de/urn:nbn:de:gbv:wim2-20120117-15227},
  school      = {Bauhaus-Universit{\"a}t Weimar},
  year      = {2011},
  abstract  = {Eine der j{\"u}ngsten Entwicklungen in der Games Branche sind sogenannte Social Games. Hierbei handelt es sich um digitale Spiele, die innerhalb von sozialen Netzwerken, wie z.B. Facebook und Myspace, gespielt werden. Studien zeigen, dass kommerzielle digitale Spiele mehr als nur ein Zeitvertreib sind. Sie f{\"o}rdern sowohl kognitive, als auch affektive und psychomotorische Kompetenzen. Aus diesem Grund werden seit Jahrzehnten digitale Spiele in der P{\"a}dagogik eingesetzt, um ihre Motivationskraft zu nutzen, um Lerneffekte zu erzielen. Ziel dieser Arbeit ist es Spielmechaniken f{\"u}r ein bauphysikalisches Social Game zu entwickeln. Ausgehend von der Identifikation von Spielmechaniken, basierend auf einer Analyse der Funktionsweisen existierender popul{\"a}rer Social Games, und einem grundlegenden p{\"a}dagogischen Verst{\"a}ndnis bez{\"u}glich Digital Game Based Learning (DGBL), werden Spielmechaniken entwickelt, mit deren Hilfe bauphysikalische Fachkompetenzen vermittelt werden k{\"o}nnen.},
  subject      = {Computerunterst{\"u}tztes Lernen},
  language  = {de}
}
@masterthesis{Mueller,
  type      = {Bachelor Thesis},
  author    = {M{\"u}ller, Naira},
  title     = {Erweiterung von Fliplife mit bauphysikalischen Inhalten},
  doi       = {10.25643/bauhaus-universitaet.1676},
  url       = {http://nbn-resolving.de/urn:nbn:de:gbv:wim2-20120704-16763},
  school      = {Bauhaus-Universit{\"a}t Weimar},
  pages     = {105},
  abstract  = {In dieser Arbeit wurde ein Konzept erstellt, das Fliplife um einen bauphysikalischen Karriereweg erweitert. In das Spiel wurden beispielhaft bauphysikalische Inhalte sowie spielkonzept-kompatible und wissensvermittelnde Spielmechaniken implementiert.},
  subject      = {Social Game},
  language  = {de}
}
@article{Lahmer,
  author    = {Lahmer, Tom},
  title     = {FEM-Based determination of real and complex elastic, dielectric, and piezoelectric moduli in piezoceramic materials},
  series = {IEEE Transactions on Ultrasonics, Ferroelectrics, and Frequency Control},
  journal   = {IEEE Transactions on Ultrasonics, Ferroelectrics, and Frequency Control},
  doi       = {10.25643/bauhaus-universitaet.3608},
  url       = {http://nbn-resolving.de/urn:nbn:de:gbv:wim2-20171030-36083},
  abstract  = {We propose an enhanced iterative scheme for the precise reconstruction of piezoelectric material parameters from electric impedance and mechanical displacement measurements. It is based on finite-element simulations of the full three-dimensional piezoelectric equations, combined with an inexact Newton or nonlinear Landweber iterative inversion scheme. We apply our method to two piezoelectric materials and test its performance. For the first material, the manufacturer provides a full data set; for the second one, no material data set is available. For both cases, our inverse scheme, using electric impedance measurements as input data, performs well.},
  subject      = {Finite-Elemente-Methode},
  language  = {en}
}
@masterthesis{Nguyen,
  type      = {Bachelor Thesis},
  author    = {Nguyen, Thai Cuong},
  title     = {Fl{\"a}chen zweiter Ordnung - D{\"a}cher m{\"u}ssen nicht eben sein},
  doi       = {10.25643/bauhaus-universitaet.3749},
  url       = {http://nbn-resolving.de/urn:nbn:de:gbv:wim2-20181024-37496},
  school      = {Bauhaus-Universit{\"a}t Weimar},
  pages     = {47},
  abstract  = {In dieser Arbeit geht es um die Quadriken in der Ebene und im Raum. Dabei werden die Transformation in die Normalform und die Klassifikation untersucht. Aus den geometrischen Eigenschaften werden einige Anwendungsbeispiele der Quadriken in der Technik und dem allt{\"a}glichen Leben vorgestellt.},
  subject      = {Quadrik},
  language  = {de}
}
@phdthesis{Ruhland,
  author    = {Ruhland, Grit},
  title     = {FOLGELANDSCHAFT. Eine Untersuchung der Auswirkungen des Uranbergbaus auf die Landschaft um Gera/Ronneburg.},
  doi       = {10.25643/bauhaus-universitaet.4495},
  url       = {http://nbn-resolving.de/urn:nbn:de:gbv:wim2-20210906-44953},
  school      = {Bauhaus-Universit{\"a}t Weimar},
  pages     = {357},
  abstract  = {Das Kernthema dieser Arbeit ist die Besch{\"a}ftigung mit den Folgen des Uranbergbaus in dem Gebiet um die ehemalige Abbauregion der Wismut SAG/SDAG in Ronneburg (Ostth{\"u}ringen). Dieses Thema wird unter historischen, sozialen, kulturanthropologischen und k{\"u}nstlerischen Aspekten betrachtet und in den Zusammenhang mit den weltweiten Voraussetzungen der Nuklearindustrie und Auswirkungen des Uranbergbaus und seiner Folgen gestellt. Die Arbeit legt dar, wie eine Uranbergbaufolgelandschaft entsteht und welches Wissen ist f{\"u}r ein angemessenes Verst{\"a}ndnis des Ph{\"a}nomens wichtig ist. Es wird untersucht, ob Kunst bez{\"u}glich der Uranbergbaufolgelandschaft einen relevanten Beitrag leisten kann bzw. in welcher Form dies versucht wurde, bzw. stellte Arbeiten vor, die verwandete Themen bearbeitet haben. In Kombination dieser beiden Hauptaspekte geht die Arbeit der Frage nach, welche Faktoren die Uranbergbaufolgelandschaft pr{\"a}gen und ob es sinnvolle Beteiligungsfelder f{\"u}r k{\"u}nstlerisches Forschen oder Handeln gibt sowie welche Bedingungen hierf{\"u}r erf{\"u}llt werdenm{\"u}ssten. Die Kernthese der Arbeit ist, dass k{\"u}nstlerische Arbeiten im Themenfeld des Uranbergbaus unter bestimmten Bedingungen relevante Beitr{\"a}ge leisten k{\"o}nnen.},
  subject      = {Uranbergbau},
  language  = {de}
}
@misc{Loesel,
  author    = {L{\"o}sel, Joy-Fabienne},
  title     = {Fungal Future - Der Zukunft gewachsen},
  volume    = {2021},
  publisher = {Lucia Verlag},
  address   = {Weimar},
  doi       = {10.25643/bauhaus-universitaet.4440},
  url       = {http://nbn-resolving.de/urn:nbn:de:gbv:wim2-20210603-44408},
  pages     = {134},
  abstract  = {Die Auswirkungen der durch den Kapitalismus befeuerten Umweltzerst{\"o}rung werden immer deutlicher erkennbar. Unsere Gesellschaft ist nun damit konfrontiert, dass ihre kulturelle Identit{\"a}t, aber auch ihr Wohlstand sowohl eng mit Konsum und Wirtschaftswachstum als auch mit der Gesundheit der Natur verbunden sind. Es scheint ein geeigneter Moment, um die Perspektive zu wechseln und einer neuen Form des Wachstums eine Chance zu geben. Pilze sind eine von der Region unabh{\"a}ngige, nat{\"u}rlich vorkommende Ressource, die lokal angebaut und verarbeitet werden kann, ohne die Umwelt zu belasten. Pilze sind klimafreundlich, m{\"u}llvermeidend und in bestehende nat{\"u}rliche Kreisl{\"a}ufe inkludierbar. Kurzum, Pilze sind cool, doch das wissen nicht Viele. Das sollte sich {\"a}ndern. Mit Myzelwachstum gegen das Wachstumsparadigma.},
  subject      = {Pilze},
  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}
}
@masterthesis{Hoinkis,
  type      = {Bachelor Thesis},
  author    = {Hoinkis, Jule Hannah},
  title     = {Hitze in der Stadt Jena},
  doi       = {10.25643/bauhaus-universitaet.4632},
  url       = {http://nbn-resolving.de/urn:nbn:de:gbv:wim2-20220414-46323},
  school      = {Bauhaus-Universit{\"a}t Weimar},
  abstract  = {Die vorliegende Arbeit befasst sich mit den spezifischen Faktoren und Wechselwirkungen des st{\"a}dtischen Klimas und Strategien zur Pr{\"a}vention und Kompensation lokaler Klimaver{\"a}nderungen. Problematische Merkmale des Stadtklimas werden sich infolge des Klimawandels st{\"a}rker auspr{\"a}gen. Insbesondere die Hitzebelastung wird zunehmen und die Lebensbedingungen in der Stadt negativ beeinflussen. Infolge h{\"o}herer Temperaturen in St{\"a}dten und einer h{\"o}heren Temperaturdifferenz zum Umland ver{\"a}ndern sich Windstr{\"o}me und die Wasserbilanz. Es sind Strategien notwendig, um den Schadstoffausstoß, die Fl{\"a}cheninanspruchnahme, die Abfallproduktion und den Wasser-, Energie- und Ressourcenverbrauch zu verringern, um sowohl langfristig den Klimawandel als auch dessen bereits unvermeidbaren Auswirkungen auf St{\"a}dte zu begrenzen. Beispielhaft untersucht die Arbeit das Stadtklima, dessen zuk{\"u}nftige Ver{\"a}nderungen infolge des Klimawandels, bauliche Maßnahmen und Anpassungsstrategien der Stadt Jena. Jena ist die zweitgr{\"o}ßte Stadt im Bundesland Th{\"u}ringen und geh{\"o}rt heute zu den w{\"a}rmsten und trockensten Großst{\"a}dten Deutschlands. Die Ergebnisse der Arbeit werden anschließend anhand eines st{\"a}dtebaulichen Konzepts und Entwurfs angewendet. Das Bachstraßenareal liegt in der Innenstadt, dem am st{\"a}rksten von Hitze betroffenen Stadtteil. Als ehemaliger Hauptstandort des Jenaer Universit{\"a}tsklinikums, soll es zu einem nachhaltigen Wissenschaftscampus der Lebenswissenschaften umgebaut werden, wobei ein Großteil der denkmalgesch{\"u}tzten, ehemaligen Klinikgeb{\"a}ude erhalten bleibt. Der Fokus liegt dabei auf der Umsetzung der zuvor formulierten, nachhaltigen Strategien zur Verbesserung des lokalen Stadtklimas und einer Abschw{\"a}chung der Auswirkungen des Klimawandels auf den besonders stark betroffenen Innenstadtbereich Jenas.},
  subject      = {Hitze},
  language  = {de}
}
@phdthesis{Schrader,
  author    = {Schrader, Kai},
  title     = {Hybrid 3D simulation methods for the damage analysis of multiphase composites},
  doi       = {10.25643/bauhaus-universitaet.2059},
  url       = {http://nbn-resolving.de/urn:nbn:de:gbv:wim2-20131021-20595},
  school      = {Bauhaus-Universit{\"a}t Weimar},
  pages     = {174},
  abstract  = {Modern digital material approaches for the visualization and simulation of heterogeneous materials allow to investigate the behavior of complex multiphase materials with their physical nonlinear material response at various scales. However, these computational techniques require extensive hardware resources with respect to computing power and main memory to solve numerically large-scale discretized models in 3D. Due to a very high number of degrees of freedom, which may rapidly be increased to the two-digit million range, the limited hardware ressources are to be utilized in a most efficient way to enable an execution of the numerical algorithms in minimal computation time. Hence, in the field of computational mechanics, various methods and algorithms can lead to an optimized runtime behavior of nonlinear simulation models, where several approaches are proposed and investigated in this thesis. Today, the numerical simulation of damage effects in heterogeneous materials is performed by the adaption of multiscale methods. A consistent modeling in the three-dimensional space with an appropriate discretization resolution on each scale (based on a hierarchical or concurrent multiscale model), however, still contains computational challenges in respect to the convergence behavior, the scale transition or the solver performance of the weak coupled problems. The computational efficiency and the distribution among available hardware resources (often based on a parallel hardware architecture) can significantly be improved. In the past years, high-performance computing (HPC) and graphics processing unit (GPU) based computation techniques were established for the investigationof scientific objectives. Their application results in the modification of existing and the development of new computational methods for the numerical implementation, which enables to take advantage of massively clustered computer hardware resources. In the field of numerical simulation in material science, e.g. within the investigation of damage effects in multiphase composites, the suitability of such models is often restricted by the number of degrees of freedom (d.o.f.s) in the three-dimensional spatial discretization. This proves to be difficult for the type of implementation method used for the nonlinear simulation procedure and, simultaneously has a great influence on memory demand and computational time. In this thesis, a hybrid discretization technique has been developed for the three-dimensional discretization of a three-phase material, which is respecting the numerical efficiency of nonlinear (damage) simulations of these materials. The increase of the computational efficiency is enabled by the improved scalability of the numerical algorithms. Consequently, substructuring methods for partitioning the hybrid mesh were implemented, tested and adapted to the HPC computing framework using several hundred CPU (central processing units) nodes for building the finite element assembly. A memory-efficient iterative and parallelized equation solver combined with a special preconditioning technique for solving the underlying equation system was modified and adapted to enable combined CPU and GPU based computations. Hence, it is recommended by the author to apply the substructuring method for hybrid meshes, which respects different material phases and their mechanical behavior and which enables to split the structure in elastic and inelastic parts. However, the consideration of the nonlinear material behavior, specified for the corresponding phase, is limited to the inelastic domains only, and by that causes a decreased computing time for the nonlinear procedure. Due to the high numerical effort for such simulations, an alternative approach for the nonlinear finite element analysis, based on the sequential linear analysis, was implemented in respect to scalable HPC. The incremental-iterative procedure in finite element analysis (FEA) during the nonlinear step was then replaced by a sequence of linear FE analysis when damage in critical regions occured, known in literature as saw-tooth approach. As a result, qualitative (smeared) crack initiation in 3D multiphase specimens has efficiently been simulated.},
  subject      = {high-performance computing},
  language  = {en}
}
@phdthesis{Schoeler,
  author    = {Sch{\"o}ler, Axel},
  title     = {Hydration of multi-component cements containing clinker, slag, type-V fly ash and limestone},
  doi       = {10.25643/bauhaus-universitaet.2622},
  url       = {http://nbn-resolving.de/urn:nbn:de:gbv:wim2-20160705-26221},
  school      = {Bauhaus-Universit{\"a}t Weimar},
  pages     = {189},
  abstract  = {Problemstellung und Zielsetzung 1. Die Herstellung von Portlandzementklinker tr{\"a}gt zu etwa 5 bis 8 \% zur j{\"a}hrlichen Emissionsmenge an menschlich generiertem CO2 bei. Dies ist begr{\"u}ndet in der Verwendung von fossilen Brennstoffen (ca. 40 \% des gesamten CO2) und in der Ents{\"a}uerung des stark kalksteinhaltigen Rohmehls (ca. 60 \% des gesamten CO2). 2. Verschiedene Strategien zur Verringerung des Ausstoßes an CO2 werden angewandt. Dies sind insbesondere die Optimierung der Prozessf{\"u}hrung bei der Klinkerherstellung, die Verwendung alternativer Brennstoffe und die teilweise Substitution des Klinkeranteils in Zementen mit mehreren Hauptbestandteilen durch Zementersatzstoffe, sogenannte SCM (supplementary cementitious materials), wobei H{\"u}ttensand, Flugasche und Kalksteinmehl die meist verwendeten Materialien darstellen. 3. Durch die Reduktion des Klinkeranteils k{\"o}nnen quatern{\"a}re Systeme nicht nur einen Beitrag zur Reduzierung von CO2-Emissionen leisten. Ebenfalls ist es mit derartigen Systemen m{\"o}glich H{\"u}ttensande und Flugaschen m{\"o}glichst {\"o}konomisch einzusetzen und gegebenenfalls auf Engp{\"a}sse bei deren Verf{\"u}gbarkeit zu reagieren. 4. H{\"u}ttensande und Flugaschen zeigen {\"A}hnlichkeiten in ihrer prinzipiellen chemischen Zusammensetzung, so dass {\"a}hnliche Hydratphasen w{\"a}hrend ihrer Reaktion in Anwesenheit von Portlandzement gebildet werden k{\"o}nnen. Im Vergleich zu tern{\"a}ren Systemen, die neben Kalkstein auch H{\"u}ttensand oder Flugasche enthalten, kann bei quatern{\"a}ren Zementen, die neben Kalkstein sowohl H{\"u}ttensand als auch Flugasche enthalten, eine {\"a}hnliche Phasenentwicklung und damit auch {\"a}hnliche Festigkeitsentwicklung erwartet werden. 5. Die Verwendung von SCM als Zementersatzstoff ist durch die im Vergleich zu Portlandzement deutlich langsamere Reaktion und die dadurch bedingte ebenfalls langsamere Festigkeitsentwicklung begrenzt. Dies betrifft insbesondere die Entwicklung innerhalb der ersten 28 Tage. Dementsprechend ist es unerl{\"a}sslich die Reaktivit{\"a}t von SCM wie H{\"u}ttensanden und Flugaschen eingehend zu untersuchen um die Reaktionsf{\"a}higkeit- und Geschwindigkeit und somit die Festigkeitsentwicklung zu steigern. 6. Die fr{\"u}he Reaktion der Hauptklinkerphasen ist weitgehend untersucht und beschrieben, wobei entsprechende Studien meist hochverd{\"u}nnte Modellsysteme betrachten. Jedoch gibt es kaum Hinweise inwiefern diese Erkenntnisse auf konzentrierte Systeme bei realistischen Wasser-Feststoff Verh{\"a}ltnissen {\"u}bertragen werden k{\"o}nnen. Entsprechende Untersuchungen sind n{\"o}tig um die Wechselwirkungen von Portlandzement und SCM in der Fr{\"u}hphase der Reaktion zu beschreiben. Stand der Wissenschaft 7. In verd{\"u}nnten Systemen f{\"u}hrt steigender Ca-Gehalt zu einer niedrigeren Aufl{\"o}sungsrate von C3S und C2S. 8. Bestimmende Faktoren der Aufl{\"o}sung von C3S sind sowohl die Unters{\"a}ttigung bez{\"u}glich C3S als auch die {\"U}bers{\"a}ttigung in Bezug auf C-S-H. 9. Erh{\"o}hte Al-Konzentrationen f{\"u}hren zur Verz{\"o}gerung der Hydratation von C3S. Dies kann begr{\"u}ndet sein durch die Einbindung von Al in C-S-H und eine dadurch bedingte deutlich langsamere Wachstumsrate von C-(A)-S-H. Ebenfalls scheint ein verz{\"o}gernder Effekt von Al auf die Aufl{\"o}sung von C3S m{\"o}glich. 10. Die Oberfl{\"a}che von Kalkstein bietet besonders gute Bedingungen f{\"u}r die Keimbildung von C-S-H, so dass im Vergleich zu anderen SCM in Anwesenheit von Kalkstein deutlich mehr C-S-H Keime gebildet werden. 11. Die Reaktivit{\"a}t von H{\"u}ttensand und Flugasche wird einerseits durch die Korngr{\"o}sse, andererseits jedoch auch durch die intrinsische Reaktivit{\"a}t des amorphen Anteils selbst bestimmt. 12. In amorphen (Calcium)Aluminosilikaten f{\"u}hrt ein steigender Gehalt an Netzwerkmodifizierern, wie z.B. CaO, zu einem st{\"a}rker depolymerisierten Glasnetzwerk und damit zu steigender Reaktivit{\"a}t. Die Wirkung von amphoteren Oxiden (Al2O3, Fe2O3) die sowohl als Netzwerkmodifizierer als auch als Netzwerkbildner auftreten k{\"o}nnen ist nicht vollst{\"a}ndig gekl{\"a}rt. 13. CO2 haltige Monophasen besitzen im Vergleich zu Monosulfoaluminat eine h{\"o}here thermodynamische Stabilit{\"a}t, wodurch Ettringit stabilisiert wird. Durch das hohe spezifische Volumen von Ettringit wird ein Maximum an Raumausf{\"u}llung, dadurch eine geringere Porosit{\"a}t und in Folge ein Maximum an Festigkeit erreicht. 14. Kalkstein reagiert nur in geringem Ausmaß entsprechend dem zur Reaktion vorhandenen Al2O3, wobei sich zun{\"a}chst Hemicarboaluminat, sp{\"a}ter Monocarboaluminat bildet. Dabei wird Al2O3 nicht nur durch den Portlandzement selbst, sondern auch durch die Aufl{\"o}sung von SCM, insbesondere von Flugasche, zur Verf{\"u}gung gestellt. Methodik 15. Der Einfluss von SCM auf die fr{\"u}he Hydratation von Portlandzement in bin{\"a}ren (d.h. H{\"u}ttensand oder Flugasche oder Quarz) und tern{\"a}ren (d.h. Flugasche und Kalkstein) Systemen wurde mittels isothermer Kalorimetrie und Porenl{\"o}sungsanalysen untersucht. {\"U}ber die chemische Zusammensetzung der Porenl{\"o}sung ermittelte S{\"a}ttigungsindices und L{\"o}slichkeitsprodukte wurden in Bezug zur W{\"a}rmeentwicklung gesetzt. Basierend auf den ermittelten Daten wurde evaluiert, inwiefern Mechanismen die die Hydratation von reinen Klinkerphasen in verd{\"u}nnten Systemen bestimmen ebenfalls in Zementpasten unter realistischen Bedingungen maßgebend sind. 16. Der Einfluss der chemischen Zusammensetzung auf die Reaktivit{\"a}t von Gl{\"a}sern bei hohem pH (>13) wurde mittels Ionenchromatographie in hoch verd{\"u}nnten Systemen untersucht. Puzzolanit{\"a}tstests wurden an vereinfachten Modellsystemen sowie an Portlandzement-Glass-Systemen durchgef{\"u}hrt. Das Reaktionsverhalten der Gl{\"a}ser wurde {\"u}ber isotherme Kalorimetrie und thermogravimetrische Experimente untersucht. {\"U}ber Massenbilanzkalkulationen kann der Gehalt an gebundenem Wasser in Funktion der Menge an reagiertem Glas berechnet werden. Ein Abgleich mit gebundenem Wasser bestimmt {\"u}ber thermogravimetrische Untersuchungen erlaubt es, den Reaktionsgrad der Gl{\"a}ser abzusch{\"a}tzen. Zus{\"a}tzliche Experimente mittels selektiver L{\"o}sung wurden zu Vergleichszwecken durchgef{\"u}hrt. 17. Die Reaktionskinetik von quatern{\"a}ren Pasten die sowohl Kalksteinmehl als auch H{\"u}ttensand und Flugasche enthalten wurden bis zum Alter von 28 Tagen mittels isothermer Kalorimetrie und Experimenten zum chemischen Schwinden untersucht. Erg{\"a}nzend wurden Festigkeitspr{\"u}fungen an M{\"o}rtelprismen durchgef{\"u}hrt. 18. Quatern{\"a}re Pasten wurden ebenfalls hinsichtlich der gebildeten Hydratphasen bis zu einem Alter von 182 Tagen untersucht. Hierzu wurden basierend auf thermodynamischen Modellierungen volumetrische Berechnungen zum gesamten Phasenvolumen als Funktion des Kalkstein- und des Flugaschen- bzw. H{\"u}ttensandgehalts durchgef{\"u}hrt. Erg{\"a}nzt durch thermogravimetrische Ermittlung des Gehalts an gebundenem Wasser und Portlandit, sowie mittels qualitativen r{\"o}ntgendiffraktometrischen Untersuchungen wurden die Ergebnisse der thermodynamischen Berechnungen mit der Festigkeitsentwicklung von M{\"o}rtelprismen abgeglichen. 19. Porenl{\"o}sungen von quatern{\"a}ren Systemen wurden bis zu einem Alter von 728 Tagen mittels Ionenchromatographie und pH-Bestimmung analysiert. {\"U}ber die ermittelten Konzentrationen wurden S{\"a}ttigungsindices f{\"u}r relevante Phasen ermittelt. Im Hinblick auf den Einfluss des H{\"u}ttensandes wurden Porenl{\"o}sungen f{\"u}r ausgew{\"a}hlte Systeme bei verschiedenen H{\"u}ttensandgehalten (20 und 30 M.\%) bei 91 Tagen, sowie f{\"u}r die gesamten Matrix bis zu 91 Tagen, auf verschiedene Schwefelspecies untersucht. Im Wesentlichen erzielte Ergebnisse 20. Untersuchungen zur fr{\"u}hen Reaktionskinetik von bin{\"a}ren Systemen zeigten einen st{\"a}rkeren W{\"a}rmefluss in Anwesenheit von SCM, bedingt durch erh{\"o}hte f{\"u}r die Keimbildung zur Verf{\"u}gung stehende Oberfl{\"a}che sowie eine geringere ({\"U}ber)S{\"a}ttigung bez{\"u}glich C-S-H. Erh{\"o}hte Ca-Konzentrationen f{\"u}hrten nicht zu langsamerer Aufl{\"o}sung von C3S, wie dies f{\"u}r reine Phasen bei hoher Verd{\"u}nnung beobachtet wurde. Im Gegensatz zu Untersuchungen in Reinstsystemen f{\"u}hrten h{\"o}here Ca-Konzentrationen nicht zu geringeren Reaktionsraten von C3S. Die schnellste Reaktion wurde bei Anwesenheit von Kalkstein, d.h. den h{\"o}chsten Ca-Konzentrationen, beobachtet. Die grunds{\"a}tzliche Reaktionscharakteristik zeigt einen inversen Bezug zur Unters{\"a}ttigung bez{\"u}glich C3S, wobei h{\"o}here Unters{\"a}ttigung zu schnellerer Reaktion f{\"u}hrt. Wie ebenfalls in Reinstsystemen bei hoher Verd{\"u}nnung beobachtet, f{\"u}hrt die Anwesenheit von Aluminium zur Verz{\"o}gerung der Reaktion. H{\"o}here SO42--Konzentrationen wurden in Anwesenheit von Flugasche beobachtet was die Ettringitausf{\"a}llung verhinderte und zu h{\"o}heren Al-Konzentrationen f{\"u}hrt. Dieser Mechanismus f{\"u}hrt zu h{\"o}heren Al-Konzentrationen in Gegenwart von Quarz, H{\"u}ttensand und Kalkstein im Gegensatz zu Anwesenheit von Flugasche. 21. Die fr{\"u}he Hydratation von quatern{\"a}ren Systemen wird in Anwesenheit von Kalkstein deutlich beschleunigt, w{\"a}hrend Flugasche zu einer Verz{\"o}gerung f{\"u}hrt. Im Gegensatz zu einem Referenzsystem mit inertem Quarz konnte mittels isothermer Kalorimetrie und chemischem Schwinden eine Reaktionsbeschleunigung in Anwesenheit von H{\"u}ttensand nachgewiesen werden. Weitere Zugaben an Flugasche, Kalkstein oder Mischungen von beiden f{\"u}hrten zu einer weiteren Beschleunigung, wobei die Unterschiede zwischen diesen Materialien zu gering sind um eine klare Unterscheidung zu erm{\"o}glichen. 22. Bei allen zur Glasaufl{\"o}sung- bzw. Reaktivit{\"a}t durchgef{\"u}hrten Experimenten zeigten sich identische Trends, d.h. steigende Reaktivit{\"a}t und Aufl{\"o}sungsgeschwindigkeit mit steigendem Anteil an Netzwerkmodifizierern innerhalb der Glasstruktur. Die Ergebnisse weisen darauf hin, dass Al2O3 in s{\"a}mtlichen betrachteten Glaszusammensetzungen vorwiegend als Netzwerkmodifizierer vorliegt. Die thermogravimetrische Bestimmung von gebundenem Wasser bei den Modellsystemen und den glashaltigen Zementen kann {\"u}ber Massenbilanzberechnungen als Funktion des Anteils an reagiertem Glas zur Absch{\"a}tzung des Glasreaktionsgrades verwendet werden. 23. Zu fr{\"u}hen Zeiten von bis zu 7 Tagen hat der Anteil an H{\"u}ttensand, Flugasche oder Kalkstein keinen wesentlichen Einfluss auf die Festigkeitsentwicklung. Zu sp{\"a}teren Zeiten wurde {\"u}ber thermodynamische Berechnungen ein Reaktionsgrad des enthaltenen CaCO3 (Calcit) von 2 bis 5 M.\% ermittelt. Dies f{\"u}hrt zur Bildung von Hemicarboaluminat und Monocarboaluminat wodurch Ettringit indirekt stabilisiert wird. In Folge ergibt sich ein h{\"o}heres absolutes Volumen der gebildeten Hydratphasen und damit h{\"o}here Festigkeiten wie Festigkeitsuntersuchungen an M{\"o}rtelprismen zeigen. Dabei h{\"a}ngt der Reaktionsgrad des CaCO3 vom verf{\"u}gbaren Al2O3 ab, welches neben dem Portlandzement selbst auch durch die Reaktion von H{\"u}ttensand, im Besonderen aber durch die Aufl{\"o}sung der Flugasche zur Verf{\"u}gung steht. 24. Allgemein hat die Anwesenheit von H{\"u}ttensand und Flugasche in Gegenwart von Kalkstein wenig Einfluss auf die gebildeten Hydratphasen. Die sukzessive Substitution von H{\"u}ttensand durch Flugasche f{\"u}hrt zu einer geringen Abnahme von Portlandit und C-S-H und beg{\"u}nstigt die Bildung von mehr Monocarboaluminat und Hemicarboaluminat. Portlandit reagiert puzzolanisch mit der Flugasche wobei sich C-S-H bildet. Dennoch f{\"u}hrt die geringe Reaktivit{\"a}t der Flugasche zu geringerem Gehalt an C-S-H was wiederrum sinkendes gesamtes Hydratphasenvolumen und damit niedrigere Festigkeitswerte generiert. Allerdings ist der Einfluss gering und alle untersuchten Systeme erreichen die Festigkeitsklasse 42.5 N entsprechend EN 196-1. 25. Analog zur Hydratphasenbildung zeigten Untersuchungen der Porenl{\"o}sungschemie von quatern{\"a}ren Systemen durchweg {\"a}hnliche Ergebnisse. Entsprechend dem Gehalt an Flugasche sind die st{\"a}rksten Variationen in den Al-Konzentrationen zu verzeichnen, welche mit steigendem Gehalt an Flugasche und mit fortschreitender Hydratation ansteigen. Weiterhin ist zu sp{\"a}teren Zeiten Portlandit bei hohen Gehalten an Flugasche zusehends unters{\"a}ttigt, w{\"a}hrend die Unters{\"a}ttigung bez{\"u}glich Str{\"a}tlingit abnimmt, was auf die Aufl{\"o}sung von Portlandit hinweist. 26. Der absolute Gehalt an SO3 in der Porenl{\"o}sung wird dominiert von Sulfat (SO42-), w{\"a}hrend die Konzentrationen von Sulfit (SO32-) und Thiosulfat (S2O32-) sehr niedrig waren. Nach 2 Tagen lagen ca. 90 \% des gesamten Schwefels in Form von SO42- vor. Nach 91 Tagen waren dies ca. 36 \% w{\"a}hrend ca. 28 \% als S2O32- vorlagen. Bei h{\"o}heren Gehalten an H{\"u}ttensand sind dabei nach 7 Tagen h{\"o}here Konzentrationen an SO32- und S2O32- feststellbar.},
  subject      = {Hydrauliche Bindemittel},
  language  = {en}
}
@phdthesis{Abeltshauser,
  author    = {Abeltshauser, Rainer},
  title     = {Identification and separation of physical effects of coupled systems by using defined model abstractions},
  doi       = {10.25643/bauhaus-universitaet.2860},
  url       = {http://nbn-resolving.de/urn:nbn:de:gbv:wim2-20170314-28600},
  school      = {Bauhaus-Universit{\"a}t Weimar},
  abstract  = {The thesis investigates at the computer aided simulation process for operational vibration analysis of complex coupled systems. As part of the internal methods project "Absolute Values" of the BMW Group, the thesis deals with the analysis of the structural dynamic interactions and excitation interactions. The overarching aim of the methods project is to predict the operational vibrations of engines. Simulations are usually used to analyze technical aspects (e. g. operational vibrations, strength, ...) of single components in the industrial development. The boundary conditions of submodels are mostly based on experiences. So the interactions with neighboring components and systems are neglected. To get physically more realistic results but still efficient simulations, this work wants to support the engineer during the preprocessing phase by useful criteria. At first suitable abstraction levels based on the existing literature are defined to identify structural dynamic interactions and excitation interactions of coupled systems. So it is possible to separate different effects of the coupled subsystems. On this basis, criteria are derived to assess the influence of interactions between the considered systems. These criteria can be used during the preprocessing phase and help the engineer to build up efficient models with respect to the interactions with neighboring systems. The method was developed by using several models with different complexity levels. Furthermore, the method is proved for the application in the industrial environment by using the example of a current combustion engine.},
  subject      = {Strukturdynamik},
  language  = {en}
}
@phdthesis{Nanthakumar,
  author    = {Nanthakumar, S.S.},
  title     = {Inverse and optimization problems in piezoelectric materials using Extended Finite Element Method and Level sets},
  doi       = {10.25643/bauhaus-universitaet.2709},
  url       = {http://nbn-resolving.de/urn:nbn:de:gbv:wim2-20161128-27095},
  school      = {Bauhaus-Universit{\"a}t Weimar},
  abstract  = {Piezoelectric materials are used in several applications as sensors and actuators where they experience high stress and electric field concentrations as a result of which they may fail due to fracture. Though there are many analytical and experimental works on piezoelectric fracture mechanics. There are very few studies about damage detection, which is an interesting way to prevent the failure of these ceramics. An iterative method to treat the inverse problem of detecting cracks and voids in piezoelectric structures is proposed. Extended finite element method (XFEM) is employed for solving the inverse problem as it allows the use of a single regular mesh for large number of iterations with different flaw geometries. Firstly, minimization of cost function is performed by Multilevel Coordinate Search (MCS) method. The XFEM-MCS methodology is applied to two dimensional electromechanical problems where flaws considered are straight cracks and elliptical voids. Then a numerical method based on combination of classical shape derivative and level set method for front propagation used in structural optimization is utilized to minimize the cost function. The results obtained show that the XFEM-level set methodology is effectively able to determine the number of voids in a piezoelectric structure and its corresponding locations. The XFEM-level set methodology is improved to solve the inverse problem of detecting inclusion interfaces in a piezoelectric structure. The material interfaces are implicitly represented by level sets which are identified by applying regularisation using total variation penalty terms. The formulation is presented for three dimensional structures and inclusions made of different materials are detected by using multiple level sets. The results obtained prove that the iterative procedure proposed can determine the location and approximate shape of material subdomains in the presence of higher noise levels. Piezoelectric nanostructures exhibit size dependent properties because of surface elasticity and surface piezoelectricity. Initially a study to understand the influence of surface elasticity on optimization of nano elastic beams is performed. The boundary of the nano structure is implicitly represented by a level set function, which is considered as the design variable in the optimization process. Two objective functions, minimizing the total potential energy of a nanostructure subjected to a material volume constraint and minimizing the least square error compared to a target displacement, are chosen for the numerical examples. The numerical examples demonstrate the importance of size and aspect ratio in determining how surface effects impact the optimized topology of nanobeams. Finally a conventional cantilever energy harvester with a piezoelectric nano layer is analysed. The presence of surface piezoelectricity in nano beams and nano plates leads to increase in electromechanical coupling coefficient. Topology optimization of these piezoelectric structures in an energy harvesting device to further increase energy conversion using appropriately modified XFEM-level set algorithm is performed .},
  subject      = {Finite-Elemente-Methode},
  language  = {de}
}
@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{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}
}
@misc{Piethe,
  type      = {Master Thesis},
  author    = {Piethe, Vivienne},
  title     = {Konfektionierung eines Calciumsulfat-Bindemittelsystems zur Herstellung volumenstabiler Fließestrichm{\"o}rtel},
  doi       = {10.25643/bauhaus-universitaet.3944},
  url       = {http://nbn-resolving.de/urn:nbn:de:gbv:wim2-20190902-39445},
  school      = {Bauhaus-Universit{\"a}t Weimar},
  pages     = {107},
  abstract  = {Bei einem markt{\"u}blichen Calciumsulfat-Fließestrich wurden in der Praxis sch{\"a}digende Volu-menexpansionen festgestellt. Diese sind ein Resultat aus dem Zusammenwirken des einge-setzten Bindemittel-Compounds und einer kritischen Gesteinsk{\"o}rnung. Das Ziel dieser Arbeit ist es, ein Calciumsulfat-Bindemittelsystem zu konfektionieren, welches in der Lage ist, die im M{\"o}rtel festgestellten Volumenexpansionen zu unterbinden. Es sollen verschiedene Bindemittel- und Additivzusammensetzungen untersucht werden, welche in Verbindung mit der kritischen Gesteinsk{\"o}rnung die Herstellung eines volumenstabilen Fließestrichs erm{\"o}glichen. Dazu soll folgende Fragestellung beantwortet werden: Welche Ursachen hat die Volumenzunahme und wie ist diese zu minimieren bzw. unterbinden? Dabei werden unterschiedliche Bindemittelrezepturen aus α-Halbhydrat, Thermoanhydrit und Naturanhydrit, sowie verschiedene Additivzusammensetzungen hergestellt und untersucht. Durch L{\"a}ngen{\"a}nderungsmessungen in der Schwindrinne werden die Einfl{\"u}sse der Binde-mittel, der Additivzusammensetzungen und der Wasser/Bindemittel-Werte auf das L{\"a}n-gen{\"a}nderungsverhalten untersucht. Mittels Variation der einzelnen Compound-Bestandteile kann festgestellt werden, dass der Stabilisierer die L{\"a}ngen{\"a}nderung negativ beeinflusst. Dieser bindet freies Wasser, welches f{\"u}r eine Reaktion zwischen Bindemittel und Gesteins-k{\"o}rnung im plastischen Zustand nicht mehr zur Verf{\"u}gung steht. Diese Reaktion kann folglich erst im erh{\"a}rteten Zustand ablaufen und verursacht die sch{\"a}digende Volumenexpansion. Abschließend wurde ein Bindemittel-Compound konfektioniert, welcher ohne Zusatz von Stabilisierern in Zusammenhang mit der kritischen Gesteinsk{\"o}rnung volumenstabil ist und keine Sch{\"a}den ausl{\"o}st.},
  subject      = {Calciumsulfat},
  language  = {de}
}
@misc{CicekCancino,
  type      = {Master Thesis},
  author    = {Cicek, Burhan and Cancino, Pamela},
  title     = {K{\"u}reken 2013. Entwerfen eines Dorfes aus Lehm},
  doi       = {10.25643/bauhaus-universitaet.6356},
  url       = {http://nbn-resolving.de/urn:nbn:de:gbv:wim2-20240507-63568},
  school      = {Bauhaus-Universit{\"a}t Weimar},
  pages     = {107},
  abstract  = {Die Diskussionen in der Politik und in der Gesellschaft {\"u}ber Klimawandel, globale Erw{\"a}rmung oder Nachhaltigkeit, die schon noch l{\"a}nger anh{\"a}lt, werden nie ein Ende finden, solange die Probleme, auf denen sie basiert, unl{\"o}sbar bleiben. Vorgeschlagene L{\"o}sungen werden meist nicht richtig umgesetzt. Im Zusammenhang mit dieser Problematik steigt aber das Verantwortungsgef{\"u}hl f{\"u}r bessere Zukunftsstrategien immer mehr. Die in den letzten Jahren vorgekommenen Umweltkatastrophen, wie im Golf von Mexiko (April 2010) oder im Fukushima (M{\"a}rz 2011) die noch aktuell sind, zeigen, dass der Prim{\"a}renergieeinsatz oder die Transportproblematik nicht mehr nur die Sorge der Entwicklungsl{\"a}nder, sondern auch der Industriel{\"a}nder ist. Die Bauwelt mit ihrem erheblichen Energiebedarf spielt bei der Festlegung der Zukunftsstrategien eine große Rolle. Vor allem sind die Forschungen nach umweltfreundlichen Materialien, der Recyclebarkeit der eingesetzten Baumaterialien oder dem vern{\"u}nftigen Nutzen der Naturressourcen die wichtigsten Schwerpunkte. In dieser Hinsicht bringt Lehm als Baumaterial viele Vorteile mit sich. Bei einem Artikel sagt der Lehmbauexperte Martin Rauch: "In heutiger Zeit und einem Kulturkreis, in dem Baugrund und Arbeitszeit unsere großen Kosten verursachen, findet der tradierte Lehmbau mit dem verbundenen großen Aufwand an menschlicher Arbeitszeit nur schwer seinen Platz. {\"U}ber die Art der Bauweise wird auch die Entscheidung gef{\"a}llt, wie und wo die Wertsch{\"o}pfung erfolgt und ob der Einsatz des Budgets einen gesellschaftlichen Nutzen mit sich bringt. Im Vergleich zu einem Sichtbetonhaus k{\"o}nnen bei einem Stampflehmhaus 40\% der Prim{\"a}renergie ein gespart und daf{\"u}r mehr lokale Arbeitsressourcen gebunden werden. Davon profitieren vor allem die lokalen Handwerker und mittelst{\"a}ndischen Betriebe" Anatolien ist der Ort, wo man immer noch die tiefsten Wurzeln der Baukultur menschlicher Geschichte findet. Diese Baukultur, die in den vergangenen Jahrzehnten fast verlorengegangen ist, ist die Lehmbaukultur. In dieser Hinsicht beabsichtigt dieser Entwurf die W{\"u}rde des Lehms in Anatolien wieder herzustellen und dadurch dessen Glaubw{\"u}rdigkeit zur{\"u}ckzubringen.},
  subject      = {Lehm},
  language  = {de}
}
@article{Legatiuk,
  author    = {Legatiuk, Dmitrii},
  title     = {Mathematical Modelling by Help of Category Theory: Models and Relations between Them},
  series = {mathematics},
  volume    = {2021},
  journal   = {mathematics},
  number    = {volume 9, issue 16, article 1946},
  publisher = {MDPI},
  address   = {Basel},
  doi       = {10.3390/math9161946},
  url       = {http://nbn-resolving.de/urn:nbn:de:gbv:wim2-20210817-44844},
  pages     = {17},
  abstract  = {The growing complexity of modern practical problems puts high demand on mathematical modelling. Given that various models can be used for modelling one physical phenomenon, the role of model comparison and model choice is becoming particularly important. Methods for model comparison and model choice typically used in practical applications nowadays are computationbased, and thus time consuming and computationally costly. Therefore, it is necessary to develop other approaches to working abstractly, i.e., without computations, with mathematical models. An abstract description of mathematical models can be achieved by the help of abstract mathematics, implying formalisation of models and relations between them. In this paper, a category theory-based approach to mathematical modelling is proposed. In this way, mathematical models are formalised in the language of categories, relations between the models are formally defined and several practically relevant properties are introduced on the level of categories. Finally, an illustrative example is presented, underlying how the category-theory based approach can be used in practice. Further, all constructions presented in this paper are also discussed from a modelling point of view by making explicit the link to concrete modelling scenarios.},
  subject      = {Kategorientheorie},
  language  = {en}
}
@article{SchuchKaps,
  author    = {Schuch, Kai and Kaps, Christian},
  title     = {Maturation and Structure Formation Processes in Binders with Aqueous Alkali-Silicate Solutions},
  doi       = {10.25643/bauhaus-universitaet.3597},
  url       = {http://nbn-resolving.de/urn:nbn:de:gbv:wim2-20170907-35979},
  pages     = {1 -- 16},
  abstract  = {Maturation and structure formation processes can lead to crack formation in silicate and aluminosilicate binders (e.g. for coating materials...) through restricted deformation, loss of strength and thus to loss of durability. These processes are evaluated with silicate materials with an outlook on aluminosilicate binders.},
  subject      = {Waterglass},
  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{Stang,
  author    = {Stang, Ren{\´e}},
  title     = {Methode zur {\"O}koeffizienzbewertung w{\"a}rmetechnischer Anlagen in Geb{\"a}uden},
  publisher = {VDI Verlag},
  address   = {D{\"u}sseldorf},
  isbn      = {978-3-18-300623-6 (print)},
  doi       = {10.25643/bauhaus-universitaet.4528},
  url       = {http://nbn-resolving.de/urn:nbn:de:gbv:wim2-20211119-45280},
  school      = {Bauhaus-Universit{\"a}t Weimar},
  pages     = {222},
  abstract  = {Die vorliegende Arbeit richtet sich an Ingenieur*innen und Wissenschaftler*innen der technischen Geb{\"a}udeausr{\"u}stung. Sie greift einen sich abzeichnenden {\"A}nderungsbedarf in der Umwelt- und Nachhaltigkeitsbewertung von Geb{\"a}uden und w{\"a}rmetechnischen Anlagen auf. Der aktuell genutzte nicht erneuerbare Prim{\"a}renergiebedarf wird insbesondere hinsichtlich k{\"u}nftiger politischer Klima- und Umweltschutzziele als alleinige Bewertungsgr{\"o}ße nicht ausreichend sein. Die mit dieser Arbeit vorgestellte {\"O}koeffizienzbewertungsmethode kann als geeignetes Instrument zur L{\"o}sung der Probleme beitragen. Sie erm{\"o}glicht systematische, ganzheitliche Bewertungen und reproduzierbare Vergleiche w{\"a}rmetechnischer Anlagen bez{\"u}glich ihrer {\"o}kologischen und {\"o}konomischen Nachhaltigkeit. Die wesentlichsten Neuentwicklungen sind die spezifische Umweltleistung, in Erweiterung zum genutzten Prim{\"a}renergiefaktor, und der {\"O}koeffizienzindikator UWI.},
  subject      = {Energiewirtschaft},
  language  = {de}
}
@phdthesis{Salavati,
  author    = {Salavati, Mohammad},
  title     = {Multi-Scale Modeling of Mechanical and Electrochemical Properties of 1D and 2D Nanomaterials, Application in Battery Energy Storage Systems},
  doi       = {10.25643/bauhaus-universitaet.4183},
  url       = {http://nbn-resolving.de/urn:nbn:de:gbv:wim2-20200623-41830},
  school      = {Bauhaus-Universit{\"a}t Weimar},
  pages     = {166},
  abstract  = {Material properties play a critical role in durable products manufacturing. Estimation of the precise characteristics in different scales requires complex and expensive experimental measurements. Potentially, computational methods can provide a platform to determine the fundamental properties before the final experiment. Multi-scale computational modeling leads to the modeling of the various time, and length scales include nano, micro, meso, and macro scales. These scales can be modeled separately or in correlation with coarser scales. Depend on the interested scales modeling, the right selection of multi-scale methods leads to reliable results and affordable computational cost. The present dissertation deals with the problems in various length and time scales using computational methods include density functional theory (DFT), molecular mechanics (MM), molecular dynamics (MD), and finite element (FE) methods. Physical and chemical interactions in lower scales determine the coarser scale properties. Particles interaction modeling and exploring fundamental properties are significant challenges of computational science. Downscale modelings need more computational effort due to a large number of interacted atoms/particles. To deal with this problem and bring up a fine-scale (nano) as a coarse-scale (macro) problem, we extended an atomic-continuum framework. The discrete atomic models solve as a continuum problem using the computationally efficient FE method. MM or force field method based on a set of assumptions approximates a solution on the atomic scale. In this method, atoms and bonds model as a harmonic oscillator with a system of mass and springs. The negative gradient of the potential energy equal to the forces on each atom. In this way, each bond's total potential energy includes bonded, and non-bonded energies are simulated as equivalent structural strain energies. Finally, the chemical nature of the atomic bond is modeled as a piezoelectric beam element that solves by the FE method. Exploring novel materials with unique properties is a demand for various industrial applications. During the last decade, many two-dimensional (2D) materials have been synthesized and shown outstanding properties. Investigation of the probable defects during the formation/fabrication process and studying their strength under severe service life are the critical tasks to explore performance prospects. We studied various defects include nano crack, notch, and point vacancy (Stone-Wales defect) defects employing MD analysis. Classical MD has been used to simulate a considerable amount of molecules at micro-, and meso- scales. Pristine and defective nanosheet structures considered under the uniaxial tensile loading at various temperatures using open-source LAMMPS codes. The results were visualized with the open-source software of OVITO and VMD. Quantum based first principle calculations have been conducting at electronic scales and known as the most accurate Ab initio methods. However, they are computationally expensive to apply for large systems. We used density functional theory (DFT) to estimate the mechanical and electrochemical response of the 2D materials. Many-body Schr{\"o}dinger's equation describes the motion and interactions of the solid-state particles. Solid describes as a system of positive nuclei and negative electrons, all electromagnetically interacting with each other, where the wave function theory describes the quantum state of the set of particles. However, dealing with the 3N coordinates of the electrons, nuclei, and N coordinates of the electrons spin components makes the governing equation unsolvable for just a few interacted atoms. Some assumptions and theories like Born Oppenheimer and Hartree-Fock mean-field and Hohenberg-Kohn theories are needed to treat with this equation. First, Born Oppenheimer approximation reduces it to the only electronic coordinates. Then Kohn and Sham, based on Hartree-Fock and Hohenberg-Kohn theories, assumed an equivalent fictitious non-interacting electrons system as an electron density functional such that their ground state energies are equal to a set of interacting electrons. Exchange-correlation energy functionals are responsible for satisfying the equivalency between both systems. The exact form of the exchange-correlation functional is not known. However, there are widely used methods to derive functionals like local density approximation (LDA), Generalized gradient approximation (GGA), and hybrid functionals (e.g., B3LYP). In our study, DFT performed using VASP codes within the GGA/PBE approximation, and visualization/post-processing of the results realized via open-source software of VESTA. The extensive DFT calculations are conducted 2D nanomaterials prospects as anode/cathode electrode materials for batteries. Metal-ion batteries' performance strongly depends on the design of novel electrode material. Two-dimensional (2D) materials have developed a remarkable interest in using as an electrode in battery cells due to their excellent properties. Desirable battery energy storage systems (BESS) must satisfy the high energy density, safe operation, and efficient production costs. Batteries have been using in electronic devices and provide a solution to the environmental issues and store the discontinuous energies generated from renewable wind or solar power plants. Therefore, exploring optimal electrode materials can improve storage capacity and charging/discharging rates, leading to the design of advanced batteries. Our results in multiple scales highlight not only the proposed and employed methods' efficiencies but also promising prospect of recently synthesized nanomaterials and their applications as an anode material. In this way, first, a novel approach developed for the modeling of the 1D nanotube as a continuum piezoelectric beam element. The results converged and matched closely with those from experiments and other more complex models. Then mechanical properties of nanosheets estimated and the failure mechanisms results provide a useful guide for further use in prospect applications. Our results indicated a comprehensive and useful vision concerning the mechanical properties of nanosheets with/without defects. Finally, mechanical and electrochemical properties of the several 2D nanomaterials are explored for the first time—their application performance as an anode material illustrates high potentials in manufacturing super-stretchable and ultrahigh-capacity battery energy storage systems (BESS). Our results exhibited better performance in comparison to the available commercial anode materials.},
  subject      = {Batterie},
  language  = {en}
}
@article{Zhang,
  author    = {Zhang, Yongzheng},
  title     = {Nonlocal dynamic Kirchhoff plate formulation based on nonlocal operator method},
  series = {Engineering with Computers},
  volume    = {2022},
  journal   = {Engineering with Computers},
  publisher = {Springer},
  address   = {London},
  doi       = {10.1007/s00366-021-01587-1},
  url       = {http://nbn-resolving.de/urn:nbn:de:gbv:wim2-20220209-45849},
  pages     = {1 -- 35},
  abstract  = {In this study, we propose a nonlocal operator method (NOM) for the dynamic analysis of (thin) Kirchhoff plates. The nonlocal Hessian operator is derived based on a second-order Taylor series expansion. The NOM does not require any shape functions and associated derivatives as 'classical' approaches such as FEM, drastically facilitating the implementation. Furthermore, NOM is higher order continuous, which is exploited for thin plate analysis that requires C1 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 the time discretization. After confirming the accuracy of the nonlocal Hessian operator, several numerical examples are simulated by the nonlocal dynamic Kirchhoff plate formulation.},
  subject      = {Angewandte Mathematik},
  language  = {en}
}
@misc{Habtemariam,
  type      = {Master Thesis},
  author    = {Habtemariam, Abinet Kifle},
  title     = {Numerical Demolition Analysis of a Slender Guyed Antenna Mast},
  doi       = {10.25643/bauhaus-universitaet.4460},
  url       = {http://nbn-resolving.de/urn:nbn:de:gbv:wim2-20210723-44609},
  school      = {Bauhaus-Universit{\"a}t Weimar},
  pages     = {75},
  abstract  = {The main purpose of the thesis is to ensure the safe demolition of old guyed antenna masts that are located in different parts of Germany. The major problem in demolition of this masts is the falling down of the masts in unexpected direction because of buckling problem. The objective of this thesis is development of a numerical models using finite element method (FEM) and assuring a controlled collapse by coming up with different time setups for the detonation of explosives which are responsible for cutting down the cables. The result of this thesis will avoid unexpected outcomes during the demolition processes and prevent risk of collapsing of the mast over near by structures.},
  subject      = {Abbruch},
  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{Hatahet,
  author    = {Hatahet, Tareq},
  title     = {On the Analysis of the Disproportionate Structural Collapse in RC Buildings},
  doi       = {10.25643/bauhaus-universitaet.3740},
  url       = {http://nbn-resolving.de/urn:nbn:de:gbv:wim2-20180329-37405},
  school      = {Bauhaus-Universit{\"a}t Weimar},
  pages     = {243},
  abstract  = {Increasing structural robustness is the goal which is of interest for structural engineering community. The partial collapse of RC buildings is subject of this dissertation. Understanding the robustness of RC buildings will guide the development of safer structures against abnormal loading scenarios such as; explosions, earthquakes, fine, and/or long-term accumulation effects leading to deterioration or fatigue. Any of these may result in local immediate structural damage, that can propagate to the rest of the structure causing what is known by the disproportionate collapse. This work handels collapse propagation through various analytical approaches which simplifies the mechanical description of damaged reinfoced concrete structures due to extreme acidental event.},
  subject      = {Beton},
  language  = {en}
}
@article{Kleiner,
  author    = {Kleiner, Florian},
  title     = {Optimization and semi-automatic evaluation of a frosting process for a soda lime silicate glass based on phosphoric acid},
  series = {International Journal of Applied Glass Science},
  journal   = {International Journal of Applied Glass Science},
  publisher = {John Wiley \& Sons},
  doi       = {10.1111/ijag.15866},
  url       = {http://nbn-resolving.de/urn:nbn:de:gbv:wim2-20210701-44548},
  pages     = {1 -- 8},
  abstract  = {Chemical glass frosting processes are widely used to create visual attractive glass surfaces. A commonly used frosting bath mainly contains ammonium bifluoride (NH4HF2) mixed with hydrochloric acid (HCl). The frosting process consists of several baths. Firstly, the preliminary bath to clean the object. Secondly, the frosting bath which etches the rough light scattering structure into the glass surface. Finally, the washing baths to clean the frosted object. This is where the constituents of the preceding steps accumulate and have to be filtered from the sewage. In the present contribution, phosphoric acid (H3PO4) was used as a substitute for HCl to reduce the amount of ammonium (NH4+) and chloride (Cl-) dissolved in the waste water. In combination with magnesium carbonate (MgCO3), it allows the precipitation of ammonium within the sewage as ammonium magnesium phosphate (MgNH4PO4). However, a trivial replacement of HCl by H3PO4 within the frosting process causes extensive frosting errors, such as inhomogeneous size distributions of the structures or domains that are not fully covered by these structures. By modifying the preliminary bath composition, it was possible to improve the frosting result considerably. To determine the optimal composition of the preliminary bath, a semi-automatic evaluation method has been developed. This method renders the objective comparison of the resulting surface quality possible.},
  subject      = {Silicatglas},
  language  = {en}
}