@article{AtaollahiOshkourTalebiSeyedShirazietal.,
  author    = {Ataollahi Oshkour, Azim and Talebi, Hossein and Seyed Shirazi, Seyed Farid and Bayat, Mehdi and Yau, Yat Huang and Tarlochan, Faris and Abu Osman, Noor Azuan},
  title     = {Comparison of various functionally graded femoral prostheses by finite element analysis},
  series = {Scientific World Journal},
  journal   = {Scientific World Journal},
  doi       = {10.1155/2014/807621},
  url       = {http://nbn-resolving.de/urn:nbn:de:gbv:wim2-20170413-31194},
  abstract  = {This study is focused on finite element analysis of a model comprising femur into which a femoral component of a total hip replacement was implanted. The considered prosthesis is fabricated from a functionally graded material (FGM) comprising a layer of a titanium alloy bonded to a layer of hydroxyapatite. The elastic modulus of the FGM was adjusted in the radial, longitudinal, and longitudinal-radial directions by altering the volume fraction gradient exponent. Four cases were studied, involving two different methods of anchoring the prosthesis to the spongy bone and two cases of applied loading. The results revealed that the FG prostheses provoked more SED to the bone. The FG prostheses carried less stress, while more stress was induced to the bone and cement. Meanwhile, less shear interface stress was stimulated to the prosthesis-bone interface in the noncemented FG prostheses. The cement-bone interface carried more stress compared to the prosthesis-cement interface. Stair climbing induced more harmful effects to the implanted femur components compared to the normal walking by causing more stress. Therefore, stress shielding, developed stresses, and interface stresses in the THR components could be adjusted through the controlling stiffness of the FG prosthesis by managing volume fraction gradient exponent.},
  subject      = {Finite-Elemente-Methode},
  language  = {en}
}
@inproceedings{BaitschHartmann2004,
  author    = {Baitsch, Matthias and Hartmann, Dietrich},
  title     = {Object Oriented Finite Element Analysis for Structural Optimization using p-Elements},
  doi       = {10.25643/bauhaus-universitaet.108},
  url       = {http://nbn-resolving.de/urn:nbn:de:gbv:wim2-20111215-1089},
  year      = {2004},
  abstract  = {The optimization of continuous structures requires careful attention to discretization errors. Compared to ordinary low order formulation (h-elements) in conjunction with an adaptive mesh refinement in each optimization step, the use of high order finite elements (so called p-elements) has several advantages. However, compared to the h-method a higher order finite element analysis program poses higher demands from a software engineering point of view. In this article the basics of an object oriented higher order finite element system especially tailored to the use in structural optimization is presented. Besides the design of the system, aspects related to the employed implementation language Java are discussed.},
  subject      = {Konzipieren <Technik>},
  language  = {en}
}
@article{BanihaniRabczukAlmomani,
  author    = {Banihani, Suleiman and Rabczuk, Timon and Almomani, Thakir},
  title     = {POD for real-time simulation of hyperelastic soft biological tissue using the point collocation method of finite spheres},
  series = {Mathematical Problems in Engineering},
  journal   = {Mathematical Problems in Engineering},
  doi       = {10.1155/2013/386501},
  url       = {http://nbn-resolving.de/urn:nbn:de:gbv:wim2-20170413-31203},
  abstract  = {The point collocation method of finite spheres (PCMFS) is used to model the hyperelastic response of soft biological tissue in real time within the framework of virtual surgery simulation. The proper orthogonal decomposition (POD) model order reduction (MOR) technique was used to achieve reduced-order model of the problem, minimizing computational cost. The PCMFS is a physics-based meshfree numerical technique for real-time simulation of surgical procedures where the approximation functions are applied directly on the strong form of the boundary value problem without the need for integration, increasing computational efficiency. Since computational speed has a significant role in simulation of surgical procedures, the proposed technique was able to model realistic nonlinear behavior of organs in real time. Numerical results are shown to demonstrate the effectiveness of the new methodology through a comparison between full and reduced analyses for several nonlinear problems. It is shown that the proposed technique was able to achieve good agreement with the full model; moreover, the computational and data storage costs were significantly reduced.},
  subject      = {Chirurgie},
  language  = {en}
}
@inproceedings{BergerGraeffWeinberg1997,
  author    = {Berger, Hans and Graeff-Weinberg, K.},
  title     = {FEM-Detailuntersuchungen an Tragwerken unter Einsatz von pNh-{\"U}bergangselementen},
  doi       = {10.25643/bauhaus-universitaet.426},
  url       = {http://nbn-resolving.de/urn:nbn:de:gbv:wim2-20111215-4267},
  year      = {1997},
  abstract  = {Detailuntersuchungen an Tragwerken f{\"u}hren bei FE-Berechnungen immer wieder auf das Problem einer geeigneten Netzgestaltung. W{\"a}hrend in weiten Bereichen ein grobes Netz ausreicht, muß an kritischen Stellen ein sehr feines Netz gew{\"a}hlt werden, um gerade dort hinreichend genaue Ergebnisse zu erhalten. Bei der Realisierung lokaler Netzverdichtungen stellt die Gestaltung des {\"U}bergangs vom groben zum feinen Netz das Hauptproblem dar. Im Beitrag wird hierzu eine Familie von FE-{\"U}bergangselementen vorgestellt, mit denen sich eine voll-kompatible Kopplung von wenigen großen Elementen mit vielen kleinen Elementen bereits {\"u}ber nur eine Stufe erzielen l{\"a}ßt. Diese neu entwickelten sogenannten pNh-Elemente erm{\"o}glichen an einer oder mehreren Seiten den Anschluß von N kleineren Elementen (Elementseiten f{\"u}r h-Verfeinerung). Das wird durch N st{\"u}ckweise definierte Ansatzfunktionen an den entsprechenden Seiten erreicht, wobei die Teilung nicht {\"a}quidistant sein braucht. Dar{\"u}ber hinaus ist es m{\"o}glich, Elemente unterschiedlichen Polynomgrades p an den Standardseiten und den Verfeinerungsseiten anzuschließen. Der praktische Einsatz der {\"U}bergangselemente setzt geeignete automatische oder halbautomatische Netzgeneratoren voraus, die diese Elemente einbeziehen. Im Rahmen einer substrukturorientierten Modellierung l{\"a}ßt sich dies besonders g{\"u}nstig realisieren. Im Beitrag wird gezeigt, wie durch Zerlegung des Gesamtmodells in Bereiche mit grobem Netz, mit {\"U}bergangsnetz und mit feinem Netz, eine effektive Generierung der Netzverdichtungen zu erreichen ist. An einem praktischen Beispiel aus dem Bauingenieurwesen werden die Vorteile des vorgestellten {\"U}bergangselementkonzeptes umfassend demonstriert.},
  subject      = {Tragwerk},
  language  = {de}
}
@inproceedings{BernsteinRichter2003,
  author    = {Bernstein, Swanhild and Richter, Matthias},
  title     = {The Use of Genetic Algorithms in Finite Element Model Identification},
  doi       = {10.25643/bauhaus-universitaet.276},
  url       = {http://nbn-resolving.de/urn:nbn:de:gbv:wim2-20111215-2769},
  year      = {2003},
  abstract  = {A realistic and reliable model is an important precondition for the simulation of revitalization tasks and the estimation of system properties of existing buildings. Thereby, the main focus lies on the parameter identification, the optimization strategies and the preparation of experiments. As usual structures are modeled by the finite element method. This as well as other techniques are based on idealizations and empiric material properties. Within one theory the parameters of the model should be approximated by gradually performed experiments and their analysis. This approximation method is performed by solving an optimization problem, which is usually non-convex, of high dimension and possesses a non-differentiable objective function. Therefore we use an optimization procedure based on genetic algorithms which was implemented by using the program package SLang...},
  subject      = {Finite-Elemente-Methode},
  language  = {en}
}
@inproceedings{BrehmMost2003,
  author    = {Brehm, Maik and Most, Thomas},
  title     = {A Four-Node Plane EAS-Element for Stochastic Nonlinear Materials},
  doi       = {10.25643/bauhaus-universitaet.282},
  url       = {http://nbn-resolving.de/urn:nbn:de:gbv:wim2-20111215-2825},
  year      = {2003},
  abstract  = {Iso-parametric finite elements with linear shape functions show in general a too stiff element behavior, called locking. By the investigation of structural parts under bending loading the so-called shear locking appears, because these elements can not reproduce pure bending modes. Many studies dealt with the locking problem and a number of methods to avoid the undesirable effects have been developed. Two well known methods are the >Assumed Natural Strain< (ANS) method and the >Enhanced Assumed Strain< (EAS) method. In this study the EAS method is applied to a four-node plane element with four EAS-parameters. The paper will describe the well-known linear formulation, its extension to nonlinear materials and the modeling of material uncertainties with random fields. For nonlinear material behavior the EAS parameters can not be determined directly. Here the problem is solved by using an internal iteration at the element level, which is much more efficient and stable than the determination via a global iteration. To verify the deterministic element behavior the results of common test examples are presented for linear and nonlinear materials. The modeling of material uncertainties is done by point-discretized random fields. To show the applicability of the element for stochastic finite element calculations Latin Hypercube Sampling was applied to investigate the stochastic hardening behavior of a cantilever beam with nonlinear material. The enhanced linear element can be applied as an alternative to higher-order finite elements where more nodes are necessary. The presented element formulation can be used in a similar manner to improve stochastic linear solid elements.},
  subject      = {Nichtlineare Mechanik},
  language  = {en}
}
@inproceedings{BurghardtMeissner2000,
  author    = {Burghardt, Michael and Meißner, Udo F.},
  title     = {Dreidimensionale Finite-Element-Baugrundmodelle f{\"u}r Ingeniuerprobleme},
  doi       = {10.25643/bauhaus-universitaet.575},
  url       = {http://nbn-resolving.de/urn:nbn:de:gbv:wim2-20111215-5750},
  year      = {2000},
  abstract  = {Bei komplexen Gr{\"u}ndungskonstruktionen sind Planungsfehler durch eine konsistente Modellierung vermeidbar. Manuelle Berechnungsmethoden erm{\"o}glichen im allgemeinen ein dreidimensionales Vorgehen nicht. Numerische Berechnungsmethoden, wie z.B. die Finite-Element-Methode, sind ein optimales Werkzeug zur ganzheitlichen Simulation des Problems. Die f{\"u}r die Finite-Element-Analyse notwendige Diskretisierung komplexer Bau- grundstrukturen ist manuell nicht zu bew{\"a}ltigen. Der vorliegende Beitrag zeigt wie ein Finite-Element-Modell automatisch aus einem geotechnischen Modell unter Ber{\"u}cksichtigung der spezifischen Anforderungen der Baugrund-Tragwerk-Struktur und des Bauablaufes erzeugt werden kann. Hierbei wird die Ber{\"u}cksichtigung der geometrischen und der mechanischen Besonderheiten bei der Netzgenerierung dargestellt.},
  subject      = {Baugrund},
  language  = {de}
}
@inproceedings{DaniunasKomkaWerner2000,
  author    = {Daniunas, A. and Komka, A. and Werner, F.},
  title     = {ANALYSIS AND DETERMINATION OF STRENGTH IN PLASTIC STAGE OF FREE FORM STEEL SHAPES},
  doi       = {10.25643/bauhaus-universitaet.580},
  url       = {http://nbn-resolving.de/urn:nbn:de:gbv:wim2-20111215-5803},
  year      = {2000},
  abstract  = {The steel structure design codes require to check up the member strength when evaluating plastic deformations. The model of perfectly plastic material is accepted. The strength criteria for simple cross-sections (I section, etc.) of steel members are given in design codes. The analytical strength criteria for steel cross-sections and numerical approaches based on stepwise procedure are investigated in many articles. Another way for checking the carrying capacity of cross-sections is the use of methods that are applied for defining strain-deformed state of elastic perfectly plastic systems. In this paper non-iterative methods are suggested for checking strength of cross-sections. Carrying capacity of cross section is verified according to extremum principle of plastic fail under monotonically loading and the strain-deformed state of cross-section is defined according to extremum energy principals of elastic potential of residual stresses and complementary work of residual displacements. The mathematical expressions of these principals for discrete cross-section are formulated as problems of convex mathematical programming. The cross-section of steel member using finite element method is divided into free form plane elements. The constant distribution of stresses along the finite element is accepted. The relationships of finite elements for static formulation of the problem are formed so, that kinematics formulation relationships could be obtained in a formal way using the theory of duality. Numerical examples of determination of cross-section strength, composition of interactive curves and composition of moment-curvature curves for different axial force levels are presented.},
  subject      = {Stahlkonstruktion},
  language  = {en}
}
@inproceedings{DuckeEcksteinMontag2000,
  author    = {Ducke, M. and Eckstein, U. and Montag, U.},
  title     = {Die Eisenbahnbr{\"u}cken des Lehrter Bahnhofs in Berlin - Ein ganzheitliches FE-Berechnungskonzept},
  doi       = {10.25643/bauhaus-universitaet.581},
  url       = {http://nbn-resolving.de/urn:nbn:de:gbv:wim2-20111215-5812},
  year      = {2000},
  abstract  = {Der Komplexit{\"a}t moderner Br{\"u}ckenbauwerke scheinen die verwendeten Berechungsmodelle oft nicht angemessen. Tragwerksberechnungen basieren in vielen F{\"a}llen noch auf der Vorgehensweise, das Br{\"u}ckenbauwerk in Einzelbauteile zu zerlegen und mit unterschiedlichen Teilmodellen zu behandeln. Das erscheint, auch vor dem Hintergrund st{\"a}ndig wachsender Rechnerleistung, nicht mehr zeitgem{\"a}ß. Dies gilt zum Beispiel auch f{\"u}r die g{\"a}ngige Praxis, fl{\"a}chenhafte Br{\"u}cken{\"u}berbauten mit Balkenmodellen zu berechnen. Der vorliegende Beitrag stellt ein ganzheitliches Berech-nungskonzept vor, welches auf der Basis eines einzigen FE-Modells die Berechnung des Gesamtbauwerks erlaubt. Damit wird f{\"u}r alle Bauteile neben der Zustandsgr{\"o}ßenberechnung auch die Bemessung von Stahl- und Spannbetonbauteilen bis hin zu Nachweisen wie zur Beschr{\"a}nkung der Rissbreite gef{\"u}hrt. Die Anwendung dieses Berechnungskonzeptes wird am Beispiel der Eisenbahn{\"u}berf{\"u}hrung des neuen Lehrter Bahn-hofs in Berlin gezeigt. Das verwendete FE-Modell umfasst Baugrund, Fundamente, Stahl- bzw. Gußstahlunterkonstruktion sowie den Stahl- bzw. Spannbeton{\"u}berbau. Besonderheiten sind unter anderem die Modellierung des plattenbalkenartigen {\"U}berbaus durch exzentrische, vorspannbare Schalenelemente und das getrennte Vorhalten von tragwerks- und lastbezogenen Eingabefiles. Damit gelingt die sequentielle Erfassung unterschiedlicher Bettungsmoduli zur Simulation statischer und dynamischer Beanspruchungen, die Ber{\"u}cksichtigung des Anspannens und der Interaktion zwischen vorgespannten Stahlverb{\"a}nden zur Aufnahme von Horizontallasten sowie die Ber{\"u}cksichtigung unterschiedlicher statischer Systeme bei der Herstellung des Spannbeton{\"u}berbaus.},
  subject      = {Berlin},
  language  = {de}
}
@inproceedings{EbertBucher2000,
  author    = {Ebert, Matthias and Bucher, Christian},
  title     = {Modelling of changing of dynamic and static parameters of damaged R/C},
  doi       = {10.25643/bauhaus-universitaet.582},
  url       = {http://nbn-resolving.de/urn:nbn:de:gbv:wim2-20111215-5825},
  year      = {2000},
  abstract  = {Dynamic testing for damage assessment as non-destructive method has attracted growing in-terest for systematic inspections and maintenance of civil engineering structures. In this con-text the paper presents the Stochastic Finite Element (SFE) Modeling of the static and dy-namic results of own four point bending experiments with R/C beams. The beams are dam-aged by an increasing load. Between the load levels the dynamic properties are determined. Calculated stiffness loss factors for the displacements and the natural frequencies show differ-ent histories. A FE Model for the beams is developed with a discrete crack formulation. Cor-related random fields are used for structural parameters stiffness and tension strength. The idea is to simulate different crack evolutions. The beams have the same design parameters, but because of the stochastic material properties their undamaged state isn't yet the same. As the structure is loaded a stochastic first crack occurs on the weakest place of the structure. The further crack evolution is also stochastic. These is a great advantage compared with de-terministic formulations. To reduce the computational effort of the Monte Carlo simulation of this nonlinear problem the Latin-Hypercube sampling technique is applied. From the results functions of mean value and standard deviation of displacements and frequencies are calcu-lated. Compared with the experimental results some qualitative phenomena are good de-scribed by the model. Differences occurs especially in the dynamic behavior of the higher load levels. Aim of the investigations is to assess the possibilities of dynamic testing under consideration of effects from stochastic material properties},
  subject      = {Stahlbetonbauteil},
  language  = {en}
}
@phdthesis{Eckardt2009,
  author    = {Eckardt, Stefan},
  title     = {Adaptive heterogeneous multiscale models for the nonlinear simulation of concrete},
  doi       = {10.25643/bauhaus-universitaet.1416},
  url       = {http://nbn-resolving.de/urn:nbn:de:gbv:wim2-20100317-15023},
  school      = {Bauhaus-Universit{\"a}t Weimar},
  year      = {2009},
  abstract  = {The nonlinear behavior of concrete can be attributed to the propagation of microcracks within the heterogeneous internal material structure. In this thesis, a mesoscale model is developed which allows for the explicit simulation of these microcracks. Consequently, the actual physical phenomena causing the complex nonlinear macroscopic behavior of concrete can be represented using rather simple material formulations. On the mesoscale, the numerical model explicitly resolves the components of the internal material structure. For concrete, a three-phase model consisting of aggregates, mortar matrix and interfacial transition zone is proposed. Based on prescribed grading curves, an efficient algorithm for the generation of three-dimensional aggregate distributions using ellipsoids is presented. In the numerical model, tensile failure of the mortar matrix is described using a continuum damage approach. In order to reduce spurious mesh sensitivities, introduced by the softening behavior of the matrix material, nonlocal integral-type material formulations are applied. The propagation of cracks at the interface between aggregates and mortar matrix is represented in a discrete way using a cohesive crack approach. The iterative solution procedure is stabilized using a new path following constraint within the framework of load-displacement-constraint methods which allows for an efficient representation of snap-back phenomena. In several examples, the influence of the randomly generated heterogeneous material structure on the stochastic scatter of the results is analyzed. Furthermore, the ability of mesoscale models to represent size effects is investigated. Mesoscale simulations require the discretization of the internal material structure. Compared to simulations on the macroscale, the numerical effort and the memory demand increases dramatically. Due to the complexity of the numerical model, mesoscale simulations are, in general, limited to small specimens. In this thesis, an adaptive heterogeneous multiscale approach is presented which allows for the incorporation of mesoscale models within nonlinear simulations of concrete structures. In heterogeneous multiscale models, only critical regions, i.e. regions in which damage develops, are resolved on the mesoscale, whereas undamaged or sparsely damage regions are modeled on the macroscale. A crucial point in simulations with heterogeneous multiscale models is the coupling of sub-domains discretized on different length scales. The sub-domains differ not only in the size of the finite elements but also in the constitutive description. In this thesis, different methods for the coupling of non-matching discretizations - constraint equations, the mortar method and the arlequin method - are investigated and the application to heterogeneous multiscale models is presented. Another important point is the detection of critical regions. An adaptive solution procedure allowing the transfer of macroscale sub-domains to the mesoscale is proposed. In this context, several indicators which trigger the model adaptation are introduced. Finally, the application of the proposed adaptive heterogeneous multiscale approach in nonlinear simulations of concrete structures is presented.},
  subject      = {Beton},
  language  = {en}
}
@inproceedings{GabbertGrochlaKoeppe1997,
  author    = {Gabbert, U. and Grochla, J. and K{\"o}ppe, H.},
  title     = {Dynamic-explicit finite element simulation of complex problems in civil engineering by parallel computing},
  doi       = {10.25643/bauhaus-universitaet.425},
  url       = {http://nbn-resolving.de/urn:nbn:de:gbv:wim2-20111215-4259},
  year      = {1997},
  abstract  = {The paper deals with the simulation of the non-linear and time dependent behaviour of complex structures in engineering. Such simulations have to provide high accuracy in the prediction of deformations and stability, by taking into account the long term influences of the non-linear behaviour of the material as well as the large deformation and contact conditions. The limiting factors of the computer simulation are the computer run time and the memory requirement during solving large scale problems. To overcome these problems we use a dynamic-explicit time integration procedure for the solution of the semi-discrete equations of motion, which is very suited for parallel processing. In the paper at first we give a brief review of the theoretical background of the mechanical modelling and the dynamic-explicit technique for the solution of the semi-discrete equations of motion. Then the concept of parallel processing will be discussed . A test example concludes the paper.},
  subject      = {Tragwerk},
  language  = {en}
}
@article{GalffyWellmannJelicHartmann2004,
  author    = {Galffy, Mozes and Wellmann Jelic, Andres and Hartmann, Dietrich},
  title     = {Lifetime-oriented modelling of vortex-induced across-wind vibrations on bridge tie rods},
  doi       = {10.25643/bauhaus-universitaet.253},
  url       = {http://nbn-resolving.de/urn:nbn:de:gbv:wim2-20111215-2536},
  year      = {2004},
  abstract  = {The influence of vortex-induces vibrations on vertical tie rods has been proved as a determinant load factor in the lifetime-oriented dimensioning of arched steel bridges. Particularly, the welded connection plates between the suspenders and the arches often exhibit cracks induced primarily rods. In this context, the synchronization of the vortex-shedding to the rod motion in a critical wind velocity range, the so-called lock-in effect, is of essential interest.},
  subject      = {Finite-Elemente-Methode},
  language  = {en}
}
@article{GanevMarinov1997,
  author    = {Ganev, T. and Marinov, M.},
  title     = {Towards Optimal Designing of thin elastic Plates with a specific free Oscillations Frequency},
  doi       = {10.25643/bauhaus-universitaet.537},
  url       = {http://nbn-resolving.de/urn:nbn:de:gbv:wim2-20111215-5375},
  year      = {1997},
  abstract  = {Thin elastic plates are the basic constructional elements and are very often subjected to dynamic effects especially in the machine-building structures. Their saving design of resonance conditions of operation is an extremely complicated task which cannot be solved analytically. In the present report an efficient and sufficiently general method for optimal design of thin plates is worked out on the basis of energy resonance method of Wilder, the method of the finite elements for dynamic research and the methods of parameter optimization. By means of these methods various limitations and requirements put by the designer to the plates can be taken into account. A programme module for numerical investigation of the weight variation of the plate depending on the taken variable of the designed thickness at different supporting conditions is developed. The reasons for the considerable quantity and quality difference between the obtained optimal designs are also analysed.},
  subject      = {Platte},
  language  = {en}
}
@phdthesis{Ghasemi,
  author    = {Ghasemi, Hamid},
  title     = {Stochastic optimization of fiber reinforced composites considering uncertainties},
  doi       = {10.25643/bauhaus-universitaet.2704},
  url       = {http://nbn-resolving.de/urn:nbn:de:gbv:wim2-20161117-27042},
  school      = {Bauhaus-Universit{\"a}t Weimar},
  pages     = {140},
  abstract  = {Briefly, the two basic questions that this research is supposed to answer are: 1. Howmuch fiber is needed and how fibers should be distributed through a fiber reinforced composite (FRC) structure in order to obtain the optimal and reliable structural response? 2. How do uncertainties influence the optimization results and reliability of the structure? Giving answer to the above questions a double stage sequential optimization algorithm for finding the optimal content of short fiber reinforcements and their distribution in the composite structure, considering uncertain design parameters, is presented. In the first stage, the optimal amount of short fibers in a FRC structure with uniformly distributed fibers is conducted in the framework of a Reliability Based Design Optimization (RBDO) problem. Presented model considers material, structural and modeling uncertainties. In the second stage, the fiber distribution optimization (with the aim to further increase in structural reliability) is performed by defining a fiber distribution function through a Non-Uniform Rational BSpline (NURBS) surface. The advantages of using the NURBS surface as a fiber distribution function include: using the same data set for the optimization and analysis; high convergence rate due to the smoothness of the NURBS; mesh independency of the optimal layout; no need for any post processing technique and its non-heuristic nature. The output of stage 1 (the optimal fiber content for homogeneously distributed fibers) is considered as the input of stage 2. The output of stage 2 is the Reliability Index (b ) of the structure with the optimal fiber content and distribution. First order reliability method (in order to approximate the limit state function) as well as different material models including Rule of Mixtures, Mori-Tanaka, energy-based approach and stochastic multi-scales are implemented in different examples. The proposed combined model is able to capture the role of available uncertainties in FRC structures through a computationally efficient algorithm using all sequential, NURBS and sensitivity based techniques. The methodology is successfully implemented for interfacial shear stress optimization in sandwich beams and also for optimization of the internal cooling channels in a ceramic matrix composite. Finally, after some changes and modifications by combining Isogeometric Analysis, level set and point wise density mapping techniques, the computational framework is extended for topology optimization of piezoelectric / flexoelectric materials.},
  subject      = {Finite-Elemente-Methode},
  language  = {en}
}
@misc{Gundermann2005,
  type      = {Master Thesis},
  author    = {Gundermann, Ralf},
  title     = {3D-Simulation des Temperaturfeldes und der Gef{\"u}geumwandlung bei einer Laserstrahlschweißung},
  doi       = {10.25643/bauhaus-universitaet.668},
  url       = {http://nbn-resolving.de/urn:nbn:de:gbv:wim2-20111215-6680},
  school      = {Bauhaus-Universit{\"a}t Weimar},
  year      = {2005},
  abstract  = {Das FEM-Programmsystem „SYSWELD" kommt f{\"u}r die Berechnung des Temperaturfeldes bei einer Laserstrahlschweißung zum Einsatz. Insbesondere sollen der Einfluss des Energieeintrages und die damit verbundene Gef{\"u}geumwandlung eines Feinkornbaustahles untersucht und Aussagen zur notwendigen Modellierungsgenauigkeit der Nahtgeometrie bzw. Netzverfeinerung getroffen werden. Im Einzelnen sind folgende Teilaufgaben zu l{\"o}sen: - ausf{\"u}hrliche Literaturrecherche zur numerischen Analyse von Schweißverbindungen insbesondere zu temperaturabh{\"a}ngigen Materialeigenschaften von Feinkornbaust{\"a}hlen, - Darstellung der W{\"a}rmequelle f{\"u}r das Laserstrahlschweißen, - Erprobung unterschiedlicher Netzvarianten f{\"u}r die FE-Analyse von instation{\"a}ren Temperaturfeldern, - Untersuchung zur Modellierungsgenauigkeit der Nahtgeometrie, - Parameterstudien zum Einfluss der Materialkennwerte und Gef{\"u}gekinetik auf das Temperaturfeld sowie das Gef{\"u}ge.},
  subject      = {Laserschweißen},
  language  = {de}
}
@inproceedings{GurtovyPiskunov2000,
  author    = {Gurtovy, O. G. and Piskunov, V. G.},
  title     = {HIGH-PRECISION MODELING AND FINITE-ELEMENT INVESTIGATION OF ELASTOPLASTIC DEFORMATION OF NON-ISOTROPIC THICK SANDWICH PLATES AND SHELLS},
  doi       = {10.25643/bauhaus-universitaet.584},
  url       = {http://nbn-resolving.de/urn:nbn:de:gbv:wim2-20111215-5848},
  year      = {2000},
  abstract  = {There was suggested a phenomenological modified quadratic condition of the beginning of plasticity for plastic and quasifragile orthotropic materials. Limiting surface in the shape of a paraboloid with an axis bend over hydrostatic axis corresponds to the condition. The equations of theory of current with the isotropic and anisotropic hardenings, associated with the suggested yield condition, modified into the version of determining equations of strain theory of plasticity are received. These defining equations formed the basis of highlyprecise non-classic continual (along thickness) theory of non-linear deformation of thick sandwich plates and sloping shells. In the approximations along the cross coordinate the specificity of flexural and non-flexural deformations is taken into account. The necessity of introducing the approximations of higher order, as well as accounting for the cross compression while decreasing of the relatively cross normal and shear layer rigidness is shown. The specifications, obtained in comparison with the known physically nonlinear specified model of the bending of plates with orthotropic layers are distinguished. An effective procedure of linearization of the solving equations and getting the solutions in frames of the discrete-continual scheme of the finite-element method is suggested. The approximations of higher order let to model the appearance of the cracs of layers being split by the introducing of slightly hard thin layers into the finite element, not violating the idea of continuality of theory. Calculation of a threelayer plate with rigid face diaphragms on the contour is considered},
  subject      = {Platte},
  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}
}
@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{Hanna,
  author    = {Hanna, John},
  title     = {Computational Fracture Modeling and Design of Encapsulation-Based Self-Healing Concrete Using XFEM and Cohesive Surface Technique},
  doi       = {10.25643/bauhaus-universitaet.4746},
  url       = {http://nbn-resolving.de/urn:nbn:de:gbv:wim2-20221124-47467},
  school      = {Bauhaus-Universit{\"a}t Weimar},
  pages     = {125},
  abstract  = {Encapsulation-based self-healing concrete (SHC) is the most promising technique for providing a self-healing mechanism to concrete. This is due to its capacity to heal fractures effectively without human interventions, extending the operational life and lowering maintenance costs. The healing mechanism is created by embedding capsules containing the healing agent inside the concrete. The healing agent will be released once the capsules are fractured and the healing occurs in the vicinity of the damaged part. The healing efficiency of the SHC is still not clear and depends on several factors; in the case of microcapsules SHC the fracture of microcapsules is the most important aspect to release the healing agents and hence heal the cracks. This study contributes to verifying the healing efficiency of SHC and the fracture mechanism of the microcapsules. Extended finite element method (XFEM) is a flexible, and powerful discrete crack method that allows crack propagation without the requirement for re-meshing and has been shown high accuracy for modeling fracture in concrete. In this thesis, a computational fracture modeling approach of Encapsulation-based SHC is proposed based on the XFEM and cohesive surface technique (CS) to study the healing efficiency and the potential of fracture and debonding of the microcapsules or the solidified healing agents from the concrete matrix as well. The concrete matrix and a microcapsule shell both are modeled by the XFEM and combined together by CS. The effects of the healed-crack length, the interfacial fracture properties, and microcapsule size on the load carrying capability and fracture pattern of the SHC have been studied. The obtained results are compared to those obtained from the zero thickness cohesive element approach to demonstrate the significant accuracy and the validity of the proposed simulation. The present fracture simulation is developed to study the influence of the capsular clustering on the fracture mechanism by varying the contact surface area of the CS between the microcapsule shell and the concrete matrix. The proposed fracture simulation is expanded to 3D simulations to validate the 2D computational simulations and to estimate the accuracy difference ratio between 2D and 3D simulations. In addition, a proposed design method is developed to design the size of the microcapsules consideration of a sufficient volume of healing agent to heal the expected crack width. This method is based on the configuration of the unit cell (UC), Representative Volume Element (RVE), Periodic Boundary Conditions (PBC), and associated them to the volume fraction (Vf) and the crack width as variables. The proposed microcapsule design is verified through computational fracture simulations.},
  subject      = {Beton},
  language  = {en}
}