@article{SchuchKaps,
  author    = {Schuch, Kai and Kaps, Christian},
  title     = {Reifungs- und Strukturbildungsprozesse bei Bindern mit w{\"a}ssrigen Alkalisilikat-L{\"o}sungen},
  doi       = {10.25643/bauhaus-universitaet.3268},
  url       = {http://nbn-resolving.de/urn:nbn:de:gbv:wim2-20170728-32682},
  pages     = {1 -- 17},
  abstract  = {Durch Reifungs- und Strukturbildungsprozesse kann es bei silikatischen und alumosilikatischen Bindern zu Rissbildung bei behinderter Verformung, Festigkeitsverlust und somit Verlust der Dauerhaftigkeit kommen. Die Bewertung dieser Prozesse erfolgt an silikatischen Materialien mit einem Ausblick auf die alumosilikatischen Binder.},
  subject      = {Alkalisilikat},
  language  = {de}
}
@article{SchuchKaps,
  author    = {Schuch, Kai and Kaps, Christian},
  title     = {Reifungs- und Strukturbildungsprozesse bei Bindern mit w{\"a}ssrigen Alkalisilikat-L{\"o}sungen},
  doi       = {10.25643/bauhaus-universitaet.3267},
  url       = {http://nbn-resolving.de/urn:nbn:de:gbv:wim2-20170718-32675},
  pages     = {1 -- 17},
  abstract  = {Durch Reifungs- und Strukturbildungsprozesse kann es bei silikatischen und alumosilikatischen Bindern zu Rissbildung bei behinderter Verformung, Festigkeitsverlust und somit Verlust der Dauerhaftigkeit kommen. Die Bewertung dieser Prozesse erfolgt an silikatischen Materialien mit einem Ausblick auf die alumosilikatischen Binder},
  subject      = {Alkalisilikat},
  language  = {de}
}
@masterthesis{Steinkrauss,
  type      = {Bachelor Thesis},
  author    = {Steinkrauß, Tobias},
  title     = {Building Information Modeling im Erdbau - eine Potentialanalyse im Spezialtiefbau},
  doi       = {10.25643/bauhaus-universitaet.2614},
  url       = {http://nbn-resolving.de/urn:nbn:de:gbv:wim2-20160623-26140},
  school      = {Bauhaus-Universit{\"a}t Weimar},
  abstract  = {Jede Baumaßnahme ist durch einen Unikatcharakter gepr{\"a}gt. Individuelle Planung, Vergabe und Bauvorg{\"a}nge stellen immer wieder aufs Neue eine große Herausforderung dar. Durch die sich teilweise sehr schnell {\"a}ndernden Randbedingungen, m{\"u}ssen erarbeitete Abl{\"a}ufe h{\"a}ufig schnell ge{\"a}ndert werden. Dies geschieht heutzutage meist auf Grundlage von Erfahrungen der am Bau Beteiligten. Auch bei bester Planung und Vorbereitung k{\"o}nnen Unw{\"a}gbarkeiten den Bauprozess aufhalten. Das k{\"o}nnen ungeeigneter Baugrund, verschiedenste Hinderungen im Baufeld, schlechte Witterungsverh{\"a}ltnisse, Ausf{\"a}lle von Maschinen, ver{\"a}nderte Zielsetzungen des Auftraggebers und vieles mehr sein. Dies f{\"u}hrt zu Bauzeitverl{\"a}ngerungen und damit zu Kostensteigerungen. Um diesen Problemen besser begegnen zu k{\"o}nnen und diesen komplexen und fehler-anf{\"a}lligen Prozess zu unterst{\"u}tzen, sind ein verbesserter Informationsfluss, genauere Boden-aufschl{\"u}sse und eine exaktere Dimensionierung des einzusetzenden Ger{\"a}tes notwendig. Aus diesen Gr{\"u}nden ist der Einsatz von Building Information Modeling (BIM) sinnvoll. BIM bietet die M{\"o}glichkeit den Informationsfluss zu verbessern, die Datengenauigkeit zu erh{\"o}hen und Abl{\"a}ufe zu optimieren. Außerdem erm{\"o}glicht die Anwendung Planungsschritte miteinander zu verkn{\"u}pfen, Kalkulationen zu vereinfachen und das Erstellen eines intelligenten Modells, das {\"u}ber den gesamten Lebenszyklus erweitert werden kann. Die Maßnahmen des Spezialtiefbaus z{\"a}hlen zu den kostenintensivsten auf einer Baustelle. Großes Ger{\"a}t und spezialisierte Firmen sind f{\"u}r eine erfolgreiche Durchf{\"u}hrung unerl{\"a}sslich. Da der Baugrund immer einen großen Unsicherheitsfaktor bildet, m{\"u}ssen geeignete, unterst{\"u}tzende Anwendungen zum Einsatz kommen. Hierf{\"u}r bildet BIM eine geeignete Plattform. Protokolle, Maschinendaten und Kontrolldaten k{\"o}nnen hier webbasiert analysiert und f{\"u}r alle zug{\"a}nglich gemacht werden, um zum einen die Transparenz zu steigern und zum anderen den {\"U}berblick, selbst bei hochkomplexen Bauvorhaben zu behalten. In dieser Arbeit soll ein {\"U}berblick {\"u}ber die aktuelle Forschungssituation im Bereich Building Information Modeling im Erdbau, speziell im Spezialtiefbau, gegeben werden. Die Ergebnisse die mit Hilfe vorhandener Publikationen und Forschungsarbeiten verschiedener Universit{\"a}ten und namhafter Forschungsgruppen zusammengetragen wurden sollen eine Grundlage f{\"u}r die weitere Forschung in diesem Bereich bilden. {\"U}ber die Aufgabenstellung hinaus wird zus{\"a}tzlich mit dem Softwareprogramm Revit 2014 ein Modell erstellt. Es wird versucht eine {\"u}berschnittene Bohrpfahlwand zu modellieren und sie mit Parametern auszustatten. Zusammenfassend wird das Programm f{\"u}r den Einsatz bewertet.},
  subject      = {Erdbau},
  language  = {de}
}
@masterthesis{Kratt,
  type      = {Bachelor Thesis},
  author    = {Kratt, Helen},
  title     = {Building Information Modeling im Erdbau - eine Potentialanalyse im Tiefbau},
  doi       = {10.25643/bauhaus-universitaet.2613},
  url       = {http://nbn-resolving.de/urn:nbn:de:gbv:wim2-20160623-26132},
  school      = {Bauhaus-Universit{\"a}t Weimar},
  abstract  = {Die meisten Baustellen bieten Optimierungspotential. Vor allem der Erdbau fordert durch seine hohe Dynamik und großen Unsicherheiten eine hohe Planungsleistung f{\"u}r jedes neue Projekt. Doch auch bei bester Planung und Vorbereitung kann der Bauprozess durch nicht vorhersehbare Einwirkungen aufgehalten werden. Dazu z{\"a}hlen Witterungseinfl{\"u}sse, Baumaschinenausf{\"a}lle, unvorhergesehene Bodenschichten und ver{\"a}nderte Zielsetzungen des Auftraggebers. Dies kann zu St{\"o}rungen im Bauablauf f{\"u}hren, die eine Bauzeitverz{\"o}gerung und eine Kostensteigerung nach sich ziehen. Um diese Probleme zu umgehen, sind ein verbesserter Informationsfluss, genaue Bodenaufschl{\"u}sse und eine exakte Dimensionierung des einzusetzenden Ger{\"a}tes notwendig. Hier kann Building Information Modeling (BIM) zum Einsatz kommen. Diese Anwendung bietet die M{\"o}glichkeit, die Datengenauigkeit zu erh{\"o}hen, den Informationsfluss auf der Baustelle zu verbessern, eine Informationsplattform f{\"u}r alle Beteiligten zu schaffen und die Abl{\"a}ufe transparent zu gestalten. Außerdem erm{\"o}glicht die Anwendung Planungsschritte miteinander zu verkn{\"u}pfen, Kalkulationen zu vereinfachen und das Erstellen eines intelligenten Modells, das {\"u}ber den gesamten Lebenszyklus erweitert werden kann. Die Grundlagen dieser Arbeit bilden die Begriffsdefinitionen zu Erdbau, Tiefbau und Building Information Modeling. Diese Arbeit setzt sich speziell mit Erdbauwerken und deren Sicherungsmaßnahmen auseinander. Darauf aufbauend wird im Rahmen einer Recherche der Forschungsstand im Bereich Building Information Modeling und Tiefbau zusammengefasst. Mit Hilfe einiger Forschungsbeitr{\"a}ge, -projekte, -verb{\"a}nde, Dissertationen und Anwendungsprogrammen wird ein {\"U}berblick geschaffen. Die {\"U}bersicht soll eine Grundlage f{\"u}r die weitere Forschung auf diesem Gebiet bilden. Abschließend findet eine Bewertung statt. {\"U}ber die Aufgabenstellung hinaus wird zus{\"a}tzlich mit dem Softwareprogramm Revit 2014 ein Modell erstellt, um aufzuzeigen, dass das Potential auf Erdbaustellen mit BIM-Anwendungen besser ausgesch{\"o}pft werden kann. Es wird versucht eine Gabionenwand, eine Sicherungsmaßnahme von Erdbauwerken zu modellieren und sie mit Parametern auszustatten. Zusammenfassend wird das Programm f{\"u}r den Einsatz im Tiefbau bewertet.},
  subject      = {Erdbau},
  language  = {de}
}
@phdthesis{ShaabanMohamed,
  author    = {Shaaban Mohamed, Ahmed Mostafa},
  title     = {Isogeometric boundary element analysis and structural shape optimization for Helmholtz acoustic problems},
  doi       = {10.25643/bauhaus-universitaet.4703},
  url       = {http://nbn-resolving.de/urn:nbn:de:gbv:wim2-20220816-47030},
  school      = {Bauhaus-Universit{\"a}t Weimar},
  abstract  = {In this thesis, a new approach is developed for applications of shape optimization on the time harmonic wave propagation (Helmholtz equation) for acoustic problems. This approach is introduced for different dimensional problems: 2D, 3D axi-symmetric and fully 3D problems. The boundary element method (BEM) is coupled with the isogeometric analysis (IGA) forming the so-called (IGABEM) which speeds up meshing and gives higher accuracy in comparison with standard BEM. BEM is superior for handling unbounded domains by modeling only the inner boundaries and avoiding the truncation error, present in the finite element method (FEM) since BEM solutions satisfy the Sommerfeld radiation condition automatically. Moreover, BEM reduces the space dimension by one from a volumetric three-dimensional problem to a surface two-dimensional problem, or from a surface two-dimensional problem to a perimeter one-dimensional problem. Non-uniform rational B-splines basis functions (NURBS) are used in an isogeometric setting to describe both the CAD geometries and the physical fields. IGABEM is coupled with one of the gradient-free optimization methods, the Particle Swarm Optimization (PSO) for structural shape optimization problems. PSO is a straightforward method since it does not require any sensitivity analysis but it has some trade-offs with regard to the computational cost. Coupling IGA with optimization problems enables the NURBS basis functions to represent the three models: shape design, analysis and optimization models, by a definition of a set of control points to be the control variables and the optimization parameters as well which enables an easy transition between the three models. Acoustic shape optimization for various frequencies in different mediums is performed with PSO and the results are compared with the benchmark solutions from the literature for different dimensional problems proving the efficiency of the proposed approach with the following remarks: - In 2D problems, two BEM methods are used: the conventional isogeometric boundary element method (IGABEM) and the eXtended IGABEM (XIBEM) enriched with the partition-of-unity expansion using a set of plane waves, where the results are generally in good agreement with the linterature with some computation advantage to XIBEM which allows coarser meshes. -In 3D axi-symmetric problems, the three-dimensional problem is simplified in BEM from a surface integral to a combination of two 1D integrals. The first is the line integral similar to a two-dimensional BEM problem. The second integral is performed over the angle of revolution. The discretization is applied only to the former integration. This leads to significant computational savings and, consequently, better treatment for higher frequencies over the full three-dimensional models. - In fully 3D problems, a detailed comparison between two BEM methods: the conventional boundary integral equation (CBIE) and Burton-Miller (BM) is provided including the computational cost. The proposed models are enhanced with a modified collocation scheme with offsets to Greville abscissae to avoid placing collocation points at the corners. Placing collocation points on smooth surface enables accurate evaluation of normals for BM formulation in addition to straightforward prediction of jump-terms and avoids singularities in \$\mathcal{O} (1/r)\$ integrals eliminating the need for polar integration. Furthermore, no additional special treatment is required for the hyper-singular integral while collocating on highly distorted elements, such as those containing sphere poles. The obtained results indicate that, CBIE with PSO is a feasible alternative (except for a small number of fictitious frequencies) which is easier to implement. Furthermore, BM presents an outstanding treatment of the complicated geometry of mufflers with internal extended inlet/outlet tube as an interior 3D Helmholtz acoustic problem instead of using mixed or dual BEM.},
  subject      = {Randelemente-Methode},
  language  = {en}
}
@phdthesis{Mai,
  author    = {Mai, Luu},
  title     = {Structural Control Systems in High-speed Railway Bridges},
  issn      = {1610-7381},
  doi       = {10.25643/bauhaus-universitaet.2339},
  url       = {http://nbn-resolving.de/urn:nbn:de:gbv:wim2-20141223-23391},
  school      = {Bauhaus-Universit{\"a}t Weimar},
  pages     = {147},
  abstract  = {Structural vibration control of high-speed railway bridges using tuned mass dampers, semi-active tuned mass dampers, fluid viscous dampers and magnetorheological dampers to reduce resonant structural vibrations is studied. In this work, the addressed main issues include modeling of the dynamic interaction of the structures, optimization of the parameters of the dampers and comparison of their efficiency. A new approach to optimize multiple tuned mass damper systems on an uncertain model is proposed based on the H-infinity optimization criteria and the DK iteration procedure with norm-bounded uncertainties in frequency domain. The parameters of tuned mass dampers are optimized directly and simultaneously on different modes contributing significantly to the multi-resonant peaks to explore the different possible combinations of parameters. The effectiveness of the present method is also evaluated through comparison with a previous method. In the case of semi-active tuned mass dampers, an optimization algorithm is derived to control the magnetorheological damper in these semi-active damping systems. The use of the proposed algorithm can generate various combinations of control gains and state variables. This can lead to the improvement of the ability of MR dampers to track the desired control forces. An uncertain model to reduce detuning effects is also considered in this work. Next, for fluid viscous dampers, in order to tune the optimal parameters of fluid viscous dampers to the vicinity of the exact values, analytical formulae which can include structural damping are developed based on the perturbation method. The proposed formulae can also be considered as an improvement of the previous analytical formulae, especially for bridge beams with large structural damping. Finally, a new combination of magnetorheological dampers and a double-beam system to improve the performance of the primary structure vibration is proposed. An algorithm to control magnetorheological dampers in this system is developed by using standard linear matrix inequality techniques. Weight functions as a loop shaping procedure are also introduced in the feedback controllers to improve the tracking ability of magnetorheological damping forces. To this end, the effectiveness of magnetorheological dampers controlled by the proposed scheme, along with the effects of the uncertain and time-delay parameters on the models, are evaluated through numerical simulations. Additionally, a comparison of the dampers based on their performance is also considered in this work.},
  subject      = {High-speed railway bridge},
  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{UrbinaCazenave,
  author    = {Urbina Cazenave, Mario Humberto},
  title     = {Gaze Controlled Applications and Optical-See-Through Displays - General Conditions for Gaze Driven Companion Technologies},
  doi       = {10.25643/bauhaus-universitaet.1749},
  url       = {http://nbn-resolving.de/urn:nbn:de:gbv:wim2-20121107-17492},
  school      = {Bauhaus-Universit{\"a}t Weimar},
  pages     = {106},
  abstract  = {Gaze based human-computer-interaction has been a research topic for over a quarter century. Since then, the main scenario for gaze interaction has been helping handicapped people to communicate an interact with their environment. With the rapid development of mobile and wearable display technologies, a new application field for gaze interaction has appeared, opening new research questions. This thesis investigates the feasibility of mobile gaze based interaction, studying deeply the use of pie menus as a generic and robust widget for gaze interaction as well as visual and perceptual issues on head mounted (wearable) optical see-through displays. It reviews conventional gaze-based selection methods and investigates in detail the use of pie menus for gaze control. It studies and discusses layout issues, selection methods and applications. Results show that pie menus can allocate up to six items in width and multiple depth layers, allowing a fast and accurate navigation through hierarchical levels by using or combining multiple selection methods. Based on these results, several text entry methods based on pie menus are proposed. Character-by-character text entry, text entry with bigrams and with text entry with bigrams derived by word prediction, as well as possible selection methods, are examined in a longitudinal study. Data showed large advantages of the bigram entry methods over single character text entry in speed and accuracy. Participants preferred the novel selection method based on saccades (selecting by borders) over the conventional and well established dwell time method. On the one hand, pie menus showed to be a feasible and robust widget, which may enable the efficient use of mobile eye tracking systems that may not be accurate enough for controlling elements on conventional interface. On the other hand, visual perception on mobile displays technologies need to be examined in order to deduce if the mentioned results can be transported to mobile devices. Optical see-through devices enable observers to see additional information embedded in real environments. There is already some evidence of increasing visual load on the respective systems. We investigated visual performance on participants with a visual search tasks and dual tasks presenting visual stimuli on the optical see-through device, only on a computer screen, and simultaneously on both devices. Results showed that switching between the presentation devices (i.e. perceiving information simultaneously from both devices) produced costs in visual performance. The implications of these costs and of further perceptual and technical factors for mobile gaze-based interaction are discussed and solutions are proposed.},
  subject      = {Eye tracking movement},
  language  = {en}
}
@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}
}