@article{LahmerIlgLerch,
  author    = {Lahmer, Tom and Ilg, J. and Lerch, Reinhard},
  title     = {Variance-based sensitivity analyses of piezoelectric models},
  series = {Computer Modeling in Engineering \& Sciences},
  journal   = {Computer Modeling in Engineering \& Sciences},
  pages     = {105 -- 126},
  abstract  = {Variance-based sensitivity analyses of piezoelectric models},
  subject      = {Angewandte Mathematik},
  language  = {en}
}
@article{VuBacRafieeZhuangetal.,
  author    = {Vu-Bac, N. and Rafiee, Roham and Zhuang, Xiaoying and Lahmer, Tom and Rabczuk, Timon},
  title     = {Uncertainty quantification for multiscale modeling of polymer nanocomposites with correlated parameters},
  series = {Composites Part B: Engineering},
  journal   = {Composites Part B: Engineering},
  pages     = {446 -- 464},
  abstract  = {Uncertainty quantification for multiscale modeling of polymer nanocomposites with correlated parameters},
  subject      = {Angewandte Mathematik},
  language  = {en}
}
@inproceedings{JaouadiLahmer,
  author    = {Jaouadi, Zouhour and Lahmer, Tom},
  title     = {Topology optimization of structures subjected to multiple load cases by introducing the Epsilon constraint method},
  series = {Digital Proceedings, International Conference on the Applications of Computer Science and Mathematics in Architecture and Civil Engineering : July 20 - 22 2015, Bauhaus-University Weimar},
  booktitle = {Digital Proceedings, International Conference on the Applications of Computer Science and Mathematics in Architecture and Civil Engineering : July 20 - 22 2015, Bauhaus-University Weimar},
  editor    = {G{\"u}rlebeck, Klaus and Lahmer, Tom},
  organization    = {Bauhaus-Universit{\"a}t Weimar},
  issn      = {1611-4086},
  doi       = {10.25643/bauhaus-universitaet.2804},
  url       = {http://nbn-resolving.de/urn:nbn:de:gbv:wim2-20170314-28042},
  pages     = {7},
  abstract  = {A topology optimization method has been developed for structures subjected to multiple load cases (Example of a bridge pier subjected to wind loads, traffic, superstructure...). We formulate the problem as a multi-criterial optimization problem, where the compliance is computed for each load case. Then, the Epsilon constraint method (method proposed by Chankong and Haimes, 1971) is adapted. The strategy of this method is based on the concept of minimizing the maximum compliance resulting from the critical load case while the other remaining compliances are considered in the constraints. In each iteration, the compliances of all load cases are computed and only the maximum one is minimized. The topology optimization process is switching from one load to another according to the variation of the resulting compliance. In this work we will motivate and explain the proposed methodology and provide some numerical examples.},
  subject      = {Angewandte Informatik},
  language  = {en}
}
@article{ZhaoLuRabczuk,
  author    = {Zhao, Jiyun and Lu, Lixin and Rabczuk, Timon},
  title     = {The tensile and shear failure behavior dependence on chain length and temperature in amorphous polymers},
  series = {Computational Materials Science},
  journal   = {Computational Materials Science},
  pages     = {567 -- 572},
  abstract  = {The tensile and shear failure behavior dependence on chain length and temperature in amorphous polymers},
  subject      = {Angewandte Mathematik},
  language  = {en}
}
@article{BenZhaoZhangetal.,
  author    = {Ben, S. and Zhao, Jun-Hua and Zhang, Yancheng and Rabczuk, Timon},
  title     = {The interface strength and debonding for composite structures: review and recent developments},
  series = {Composite Structures},
  journal   = {Composite Structures},
  abstract  = {The interface strength and debonding for composite structures: review and recent developments},
  subject      = {Angewandte Mathematik},
  language  = {en}
}
@article{GhorashiValizadehMohammadietal.,
  author    = {Ghorashi, Seyed Shahram and Valizadeh, Navid and Mohammadi, S. and Rabczuk, Timon},
  title     = {T-spline based XIGA for Fracture Analysis of Orthotropic Media},
  series = {Computers \& Structures},
  journal   = {Computers \& Structures},
  pages     = {138 -- 146},
  abstract  = {T-spline based XIGA for Fracture Analysis of Orthotropic Media},
  subject      = {Angewandte Mathematik},
  language  = {en}
}
@phdthesis{Vu,
  author    = {Vu, Bac Nam},
  title     = {Stochastic uncertainty quantification for multiscale modeling of polymeric nanocomposites},
  doi       = {10.25643/bauhaus-universitaet.2555},
  url       = {http://nbn-resolving.de/urn:nbn:de:gbv:wim2-20160322-25551},
  school      = {Bauhaus-Universit{\"a}t Weimar},
  pages     = {265},
  abstract  = {Nanostructured materials are extensively applied in many fields of material science for new industrial applications, particularly in the automotive, aerospace industry due to their exceptional physical and mechanical properties. Experimental testing of nanomaterials is expensive, timeconsuming,challenging and sometimes unfeasible. Therefore,computational simulations have been employed as alternative method to predict macroscopic material properties. The behavior of polymeric nanocomposites (PNCs) are highly complex. The origins of macroscopic material properties reside in the properties and interactions taking place on finer scales. It is therefore essential to use multiscale modeling strategy to properly account for all large length and time scales associated with these material systems, which across many orders of magnitude. Numerous multiscale models of PNCs have been established, however, most of them connect only two scales. There are a few multiscale models for PNCs bridging four length scales (nano-, micro-, meso- and macro-scales). In addition, nanomaterials are stochastic in nature and the prediction of macroscopic mechanical properties are influenced by many factors such as fine-scale features. The predicted mechanical properties obtained by traditional approaches significantly deviate from the measured values in experiments due to neglecting uncertainty of material features. This discrepancy is indicated that the effective macroscopic properties of materials are highly sensitive to various sources of uncertainty, such as loading and boundary conditions and material characteristics, etc., while very few stochastic multiscale models for PNCs have been developed. Therefore, it is essential to construct PNC models within the framework of stochastic modeling and quantify the stochastic effect of the input parameters on the macroscopic mechanical properties of those materials. This study aims to develop computational models at four length scales (nano-, micro-, meso- and macro-scales) and hierarchical upscaling approaches bridging length scales from nano- to macro-scales. A framework for uncertainty quantification (UQ) applied to predict the mechanical properties of the PNCs in dependence of material features at different scales is studied. Sensitivity and uncertainty analysis are of great helps in quantifying the effect of input parameters, considering both main and interaction effects, on the mechanical properties of the PNCs. To achieve this major goal, the following tasks are carried out: At nano-scale, molecular dynamics (MD) were used to investigate deformation mechanism of glassy amorphous polyethylene (PE) in dependence of temperature and strain rate. Steered molecular dynamics (SMD)were also employed to investigate interfacial characteristic of the PNCs. At mico-scale, we developed an atomistic-based continuum model represented by a representative volume element (RVE) in which the SWNT's properties and the SWNT/polymer interphase are modeled at nano-scale, the surrounding polymer matrix is modeled by solid elements. Then, a two-parameter model was employed at meso-scale. A hierarchical multiscale approach has been developed to obtain the structure-property relations at one length scale and transfer the effect to the higher length scales. In particular, we homogenized the RVE into an equivalent fiber. The equivalent fiber was then employed in a micromechanical analysis (i.e. Mori-Tanaka model) to predict the effective macroscopic properties of the PNC. Furthermore, an averaging homogenization process was also used to obtain the effective stiffness of the PCN at meso-scale. Stochastic modeling and uncertainty quantification consist of the following ingredients: - Simple random sampling, Latin hypercube sampling, Sobol' quasirandom sequences, Iman and Conover's method (inducing correlation in Latin hypercube sampling) are employed to generate independent and dependent sample data, respectively. - Surrogate models, such as polynomial regression, moving least squares (MLS), hybrid method combining polynomial regression and MLS, Kriging regression, and penalized spline regression, are employed as an approximation of a mechanical model. The advantage of the surrogate models is the high computational efficiency and robust as they can be constructed from a limited amount of available data. - Global sensitivity analysis (SA) methods, such as variance-based methods for models with independent and dependent input parameters, Fourier-based techniques for performing variance-based methods and partial derivatives, elementary effects in the context of local SA, are used to quantify the effects of input parameters and their interactions on the mechanical properties of the PNCs. A bootstrap technique is used to assess the robustness of the global SA methods with respect to their performance. In addition, the probability distribution of mechanical properties are determined by using the probability plot method. The upper and lower bounds of the predicted Young's modulus according to 95 \% prediction intervals were provided. The above-mentioned methods study on the behaviour of intact materials. Novel numerical methods such as a node-based smoothed extended finite element method (NS-XFEM) and an edge-based smoothed phantom node method (ES-Phantom node) were developed for fracture problems. These methods can be used to account for crack at macro-scale for future works. The predicted mechanical properties were validated and verified. They show good agreement with previous experimental and simulations results.},
  subject      = {Polymere},
  language  = {en}
}
@misc{Almasi,
  type      = {Master Thesis},
  author    = {Almasi, Ashkan},
  title     = {Stochastic Analysis of Interfacial Effects on the Polymeric Nanocomposites},
  doi       = {10.25643/bauhaus-universitaet.2433},
  url       = {http://nbn-resolving.de/urn:nbn:de:gbv:wim2-20150709-24339},
  school      = {Bauhaus-Universit{\"a}t Weimar},
  abstract  = {The polymeric clay nanocomposites are a new class of materials of which recently have become the centre of attention due to their superior mechanical and physical properties. Several studies have been performed on the mechanical characterisation of these nanocomposites; however most of those studies have neglected the effect of the interfacial region between the clays and the matrix despite of its significant influence on the mechanical performance of the nanocomposites. There are different analytical methods to calculate the overall elastic material properties of the composites. In this study we use the Mori-Tanaka method to determine the overall stiffness of the composites for simple inclusion geometries of cylinder and sphere. Furthermore, the effect of interphase layer on the overall properties of composites is calculated. Here, we intend to get ounds for the effective mechanical properties to compare with the analytical results. Hence, we use linear displacement boundary conditions (LD) and uniform traction boundary conditions (UT) accordingly. Finally, the analytical results are compared with numerical results and they are in a good agreement. The next focus of this dissertation is a computational approach with a hierarchical multiscale method on the mesoscopic level. In other words, in this study we use the stochastic analysis and computational homogenization method to analyse the effect of thickness and stiffness of the interfacial region on the overall elastic properties of the clay/epoxy nanocomposites. The results show that the increase in interphase thickness, reduces the stiffness of the clay/epoxy naocomposites and this decrease becomes significant in higher clay contents. The results of the sensitivity analysis prove that the stiffness of the interphase layer has more significant effect on the final stiffness of nanocomposites. We also validate the results with the available experimental results from the literature which show good agreement.},
  language  = {en}
}
@inproceedings{TanLahmerSiddappa,
  author    = {Tan, Fengjie and Lahmer, Tom and Siddappa, Manju Gyaraganahalll},
  title     = {SECTION OPTIMIZATION AND RELIABILITY ANALYSIS OF ARCH-TYPE DAMS INCLUDING COUPLED MECHANICAL-THERMAL AND HYDRAULIC FIELDS},
  series = {Digital Proceedings, International Conference on the Applications of Computer Science and Mathematics in Architecture and Civil Engineering : July 20 - 22 2015, Bauhaus-University Weimar},
  booktitle = {Digital Proceedings, International Conference on the Applications of Computer Science and Mathematics in Architecture and Civil Engineering : July 20 - 22 2015, Bauhaus-University Weimar},
  editor    = {G{\"u}rlebeck, Klaus and Lahmer, Tom},
  organization    = {Bauhaus-Universit{\"a}t Weimar},
  issn      = {1611-4086},
  doi       = {10.25643/bauhaus-universitaet.2821},
  url       = {http://nbn-resolving.de/urn:nbn:de:gbv:wim2-20170314-28212},
  pages     = {8},
  abstract  = {From the design experiences of arch dams in the past, it has significant practical value to carry out the shape optimization of arch dams, which can fully make use of material characteristics and reduce the cost of constructions. Suitable variables need to be chosen to formulate the objective function, e.g. to minimize the total volume of the arch dam. Additionally a series of constraints are derived and a reasonable and convenient penalty function has been formed, which can easily enforce the characteristics of constraints and optimal design. For the optimization method, a Genetic Algorithm is adopted to perform a global search. Simultaneously, ANSYS is used to do the mechanical analysis under the coupling of thermal and hydraulic loads. One of the constraints of the newly designed dam is to fulfill requirements on the structural safety. Therefore, a reliability analysis is applied to offer a good decision supporting for matters concerning predictions of both safety and service life of the arch dam. By this, the key factors which would influence the stability and safety of arch dam significantly can be acquired, and supply a good way to take preventive measures to prolong ate the service life of an arch dam and enhances the safety of structure.},
  subject      = {Angewandte Informatik},
  language  = {en}
}
@article{HamdiaLahmerNguyenThoietal.,
  author    = {Hamdia, Khader and Lahmer, Tom and Nguyen-Thoi, T. and Rabczuk, Timon},
  title     = {Predicting The Fracture Toughness of PNCs: A Stochastic Approach Based on ANN and ANFIS},
  series = {Computational Materials Science},
  journal   = {Computational Materials Science},
  pages     = {304 -- 313},
  abstract  = {Predicting The Fracture Toughness of PNCs: A Stochastic Approach Based on ANN and ANFIS},
  subject      = {Angewandte Mathematik},
  language  = {en}
}
@inproceedings{NguyenTuanLahmerDatchevaetal.,
  author    = {Nguyen-Tuan, Long and Lahmer, Tom and Datcheva, Maria and Stoimenova, Eugenia and Schanz, Tom},
  title     = {PARAMETER IDENTIFICATION APPLYING IN COMPLEX THERMO-HYDRO-MECHANICAL PROBLEMS LIKE THE DESIGN OF BUFFER ELEMENTS},
  series = {Digital Proceedings, International Conference on the Applications of Computer Science and Mathematics in Architecture and Civil Engineering : July 20 - 22 2015, Bauhaus-University Weimar},
  booktitle = {Digital Proceedings, International Conference on the Applications of Computer Science and Mathematics in Architecture and Civil Engineering : July 20 - 22 2015, Bauhaus-University Weimar},
  editor    = {G{\"u}rlebeck, Klaus and Lahmer, Tom},
  organization    = {Bauhaus-Universit{\"a}t Weimar},
  issn      = {1611-4086},
  doi       = {10.25643/bauhaus-universitaet.2816},
  url       = {http://nbn-resolving.de/urn:nbn:de:gbv:wim2-20170314-28162},
  pages     = {6},
  abstract  = {This study contributes to the identification of coupled THM constitutive model parameters via back analysis against information-rich experiments. A sampling based back analysis approach is proposed comprising both the model parameter identification and the assessment of the reliability of identified model parameters. The results obtained in the context of buffer elements indicate that sensitive parameter estimates generally obey the normal distribution. According to the sensitivity of the parameters and the probability distribution of the samples we can provide confidence intervals for the estimated parameters and thus allow a qualitative estimation on the identified parameters which are in future work used as inputs for prognosis computations of buffer elements. These elements play e.g. an important role in the design of nuclear waste repositories.},
  subject      = {Angewandte Informatik},
  language  = {en}
}
@article{GhasemiBrighentiZhuangetal.,
  author    = {Ghasemi, Hamid and Brighenti, Roberto and Zhuang, Xiaoying and Muthu, Jacob and Rabczuk, Timon},
  title     = {Optimum fiber content and distribution in fiber-reinforced solids using a reliability and NURBS based sequential optimization approach},
  series = {Structural and Multidisciplinary Optimization},
  journal   = {Structural and Multidisciplinary Optimization},
  pages     = {99 -- 112},
  abstract  = {Optimum _ber content and distribution in _ber-reinforced solids using a reliability and NURBS based sequential optimization approach},
  subject      = {Angewandte Mathematik},
  language  = {en}
}
@article{ArashRabczukJiang,
  author    = {Arash, Behrouz and Rabczuk, Timon and Jiang, Jin-Wu},
  title     = {Nanoresonators and their applications: a state of the art review},
  series = {Applied Physics Reviews},
  journal   = {Applied Physics Reviews},
  abstract  = {Nanoresonators and their applications: a state of the art review},
  subject      = {Angewandte Mathematik},
  language  = {en}
}
@article{MortazaviRabczuk,
  author    = {Mortazavi, Bohayra and Rabczuk, Timon},
  title     = {Multiscale modeling of heat conduction in graphene laminates},
  series = {Carbon},
  journal   = {Carbon},
  pages     = {1 -- 7},
  abstract  = {Multiscale modeling of heat conduction in graphene laminates},
  subject      = {Angewandte Mathematik},
  language  = {en}
}
@article{IlyaniAkmarKramerRabczuk,
  author    = {Ilyani Akmar, A.B. and Kramer, O. and Rabczuk, Timon},
  title     = {Multi-objective evolutionary optimization of sandwich structures: An evaluation by elitist non-dominated sorting evolution strategy},
  series = {American Journal of Engineering and Applied Sciences},
  journal   = {American Journal of Engineering and Applied Sciences},
  doi       = {10.3844/ajeassp.2015.185.201},
  url       = {http://nbn-resolving.de/urn:nbn:de:gbv:wim2-20170418-31402},
  pages     = {185 -- 201},
  abstract  = {In this study, an application of evolutionary multi-objective optimization algorithms on the optimization of sandwich structures is presented. The solution strategy is known as Elitist Non-Dominated Sorting Evolution Strategy (ENSES) wherein Evolution Strategies (ES) as Evolutionary Algorithm (EA) in the elitist Non-dominated Sorting Genetic algorithm (NSGA-II) procedure. Evolutionary algorithm seems a compatible approach to resolve multi-objective optimization problems because it is inspired by natural evolution, which closely linked to Artificial Intelligence (AI) techniques and elitism has shown an important factor for improving evolutionary multi-objective search. In order to evaluate the notion of performance by ENSES, the well-known study case of sandwich structures are reconsidered. For Case 1, the goals of the multi-objective optimization are minimization of the deflection and the weight of the sandwich structures. The length, the core and skin thicknesses are the design variables of Case 1. For Case 2, the objective functions are the fabrication cost, the beam weight and the end deflection of the sandwich structures. There are four design variables i.e., the weld height, the weld length, the beam depth and the beam width in Case 2. Numerical results are presented in terms of Paretooptimal solutions for both evaluated cases.},
  subject      = {Optimierung},
  language  = {en}
}
@article{MortazaviPereiraJiangetal.,
  author    = {Mortazavi, Bohayra and Pereira, Luiz Felipe C. and Jiang, Jin-Wu and Rabczuk, Timon},
  title     = {Modelling heat conduction in polycrystalline hexagonal boron-nitride films},
  series = {Scientific Reports},
  journal   = {Scientific Reports},
  doi       = {10.1038/srep13228},
  url       = {http://nbn-resolving.de/urn:nbn:de:gbv:wim2-20170425-31534},
  abstract  = {We conducted extensive molecular dynamics simulations to investigate the thermal conductivity of polycrystalline hexagonal boron-nitride (h-BN) films. To this aim, we constructed large atomistic models of polycrystalline h-BN sheets with random and uniform grain configuration. By performing equilibrium molecular dynamics (EMD) simulations, we investigated the influence of the average grain size on the thermal conductivity of polycrystalline h-BN films at various temperatures. Using the EMD results, we constructed finite element models of polycrystalline h-BN sheets to probe the thermal conductivity of samples with larger grain sizes. Our multiscale investigations not only provide a general viewpoint regarding the heat conduction in h-BN films but also propose that polycrystalline h-BN sheets present high thermal conductivity comparable to monocrystalline sheets.},
  subject      = {W{\"a}rmeleitf{\"a}higkeit},
  language  = {en}
}
@article{KumarSinghMishraetal.,
  author    = {Kumar, S. and Singh, I. and Mishra, B.K. and Rabczuk, Timon},
  title     = {Modeling and Simulation of Kinked Cracks by Virtual Node XFEM},
  series = {Computer Methods in Applied Mechanics and Engineering},
  journal   = {Computer Methods in Applied Mechanics and Engineering},
  pages     = {1425 -- 1466},
  abstract  = {Modeling and Simulation of Kinked Cracks by Virtual Node XFEM},
  subject      = {Angewandte Mathematik},
  language  = {en}
}
@phdthesis{Jia,
  author    = {Jia, Yue},
  title     = {Methods based on B-splines for model representation, numerical analysis and image registration},
  doi       = {10.25643/bauhaus-universitaet.2484},
  url       = {http://nbn-resolving.de/urn:nbn:de:gbv:wim2-20151210-24849},
  school      = {Bauhaus-Universit{\"a}t Weimar},
  pages     = {200},
  abstract  = {The thesis consists of inter-connected parts for modeling and analysis using newly developed isogeometric methods. The main parts are reproducing kernel triangular B-splines, extended isogeometric analysis for solving weakly discontinuous problems, collocation methods using superconvergent points, and B-spline basis in image registration applications. Each topic is oriented towards application of isogeometric analysis basis functions to ease the process of integrating the modeling and analysis phases of simulation. First, we develop reproducing a kernel triangular B-spline-based FEM for solving PDEs. We review the triangular B-splines and their properties. By definition, the triangular basis function is very flexible in modeling complicated domains. However, instability results when it is applied for analysis. We modify the triangular B-spline by a reproducing kernel technique, calculating a correction term for the triangular kernel function from the chosen surrounding basis. The improved triangular basis is capable to obtain the results with higher accuracy and almost optimal convergence rates. Second, we propose an extended isogeometric analysis for dealing with weakly discontinuous problems such as material interfaces. The original IGA is combined with XFEM-like enrichments which are continuous functions themselves but with discontinuous derivatives. Consequently, the resulting solution space can approximate solutions with weak discontinuities. The method is also applied to curved material interfaces, where the inverse mapping and the curved triangular elements are considered. Third, we develop an IGA collocation method using superconvergent points. The collocation methods are efficient because no numerical integration is needed. In particular when higher polynomial basis applied, the method has a lower computational cost than Galerkin methods. However, the positions of the collocation points are crucial for the accuracy of the method, as they affect the convergent rate significantly. The proposed IGA collocation method uses superconvergent points instead of the traditional Greville abscissae points. The numerical results show the proposed method can have better accuracy and optimal convergence rates, while the traditional IGA collocation has optimal convergence only for even polynomial degrees. Lastly, we propose a novel dynamic multilevel technique for handling image registration. It is application of the B-spline functions in image processing. The procedure considered aims to align a target image from a reference image by a spatial transformation. The method starts with an energy function which is the same as a FEM-based image registration. However, we simplify the solving procedure, working on the energy function directly. We dynamically solve for control points which are coefficients of B-spline basis functions. The new approach is more simple and fast. Moreover, it is also enhanced by a multilevel technique in order to prevent instabilities. The numerical testing consists of two artificial images, four real bio-medical MRI brain and CT heart images, and they show our registration method is accurate, fast and efficient, especially for large deformation problems.},
  subject      = {Finite-Elemente-Methode},
  language  = {en}
}
@article{MortazaviCunibertiRabczuk,
  author    = {Mortazavi, Bohayra and Cuniberti, G. and Rabczuk, Timon},
  title     = {Mechanical properties and thermal conductivity of graphitic carbon nitride: A molecular dynamics study},
  series = {Computational Materials Science},
  journal   = {Computational Materials Science},
  pages     = {285 -- 289},
  abstract  = {Mechanical properties and thermal conductivity of graphitic carbon nitride: A molecular dynamics study},
  subject      = {Angewandte Mathematik},
  language  = {en}
}
@article{ThaiNguyenXuanBordasetal.,
  author    = {Thai, Chien H. and Nguyen-Xuan, Hung and Bordas, St{\´e}phane Pierre Alain and Nguyen-Thanh, Nhon and Rabczuk, Timon},
  title     = {Isogeometric analysis of laminated composite plates using the higher-order shear deformation theory},
  series = {Mechanics of Advanced Materials and Structures},
  journal   = {Mechanics of Advanced Materials and Structures},
  pages     = {451 -- 469},
  abstract  = {Isogeometric analysis of laminated composite plates using the higher-order shear deformation theory},
  subject      = {Angewandte Mathematik},
  language  = {en}
}