@inproceedings{LahmerGhorashi, author = {Lahmer, Tom and Ghorashi, Seyed Shahram}, title = {XFEM-BASED CRACK IDENTIFICATION APPLYING REGULARIZING METHODS IN A MULTILEVEL APPROACH}, series = {Digital Proceedings, International Conference on the Applications of Computer Science and Mathematics in Architecture and Civil Engineering : July 04 - 06 2012, Bauhaus-University Weimar}, booktitle = {Digital Proceedings, International Conference on the Applications of Computer Science and Mathematics in Architecture and Civil Engineering : July 04 - 06 2012, Bauhaus-University Weimar}, editor = {G{\"u}rlebeck, Klaus and Lahmer, Tom and Werner, Frank}, organization = {Bauhaus-Universit{\"a}t Weimar}, issn = {1611-4086}, doi = {10.25643/bauhaus-universitaet.2771}, url = {http://nbn-resolving.de/urn:nbn:de:gbv:wim2-20170314-27717}, pages = {9}, abstract = {Many structures in different engineering applications suffer from cracking. In order to make reliable prognosis about the serviceability of those structures it is of utmost importance to identify cracks as precisely as possible by non-destructive testing. A novel approach (XIGA), which combines the Isogeometric Analysis (IGA) and the Extended Finite Element Method (XFEM) is used for the forward problem, namely the analysis of a cracked material, see [1]. Applying the NURBS (Non-Uniform Rational B-Spline) based approach from IGA together with the XFEM allows to describe effectively arbitrarily shaped cracks and avoids the necessity of remeshing during the crack identification problem. We want to exploit these advantages for the inverse problem of detecting existing cracks by non-destructive testing, see e.g. [2]. The quality of the reconstructed cracks however depends on two major issues, namely the quality of the measured data (measurement error) and the discretization of the crack model. The first one will be taken into account by applying regularizing methods with a posteriori stopping criteria. The second one is critical in the sense that too few degrees of freedom, i.e. the number of control points of the NURBS, do not allow for a precise description of the crack. An increased number of control points, however, increases the number of unknowns in the inverse analysis and intensifies the ill-posedness. The trade-off between accuracy and stability is aimed to be found by applying an inverse multilevel algorithm [3, 4] where the identification is started with short knot vectors which successively will be enlarged during the identification process.}, subject = {Angewandte Informatik}, language = {en} } @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{IlyaniAkmarLahmerBordasetal., author = {Ilyani Akmar, A.B. and Lahmer, Tom and Bordas, St{\´e}phane Pierre Alain and Beex, L.A.A. and Rabczuk, Timon}, title = {Uncertainty quantification of dry woven fabrics: A sensitivity analysis on material properties}, series = {Composite Structures}, journal = {Composite Structures}, doi = {10.1016/j.compstruct.2014.04.014}, pages = {1 -- 17}, abstract = {Uncertainty quantification of dry woven fabrics: A sensitivity analysis on material properties}, 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} } @article{GoebelLahmerOsburg, author = {G{\"o}bel, Luise and Lahmer, Tom and Osburg, Andrea}, title = {Uncertainty analysis in multiscale modeling of concrete based on continuum micromechanics}, series = {European Journal of Mechanics-A/Solids}, journal = {European Journal of Mechanics-A/Solids}, abstract = {Uncertainty analysis in multiscale modeling of concrete based on continuum micromechanics}, 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{NanthakumarLahmerZhuangetal., author = {Nanthakumar, S.S. and Lahmer, Tom and Zhuang, Xiaoying and Park, Harold S. and Rabczuk, Timon}, title = {Topology optimization of piezoelectric nanostructures}, series = {Journal of the Mechanics and Physics of Solids}, journal = {Journal of the Mechanics and Physics of Solids}, pages = {316 -- 335}, abstract = {Topology optimization of piezoelectric nanostructures}, subject = {Angewandte Mathematik}, language = {en} } @article{AlemuHabteLahmeretal., author = {Alemu, Yohannes L. and Habte, Bedilu and Lahmer, Tom and Urgessa, Girum}, title = {Topologically preoptimized ground structure (TPOGS) for the optimization of 3D RC buildings}, series = {Asian Journal of Civil Engineering}, volume = {2023}, journal = {Asian Journal of Civil Engineering}, publisher = {Springer International Publishing}, address = {Cham}, doi = {10.1007/s42107-023-00640-2}, url = {http://nbn-resolving.de/urn:nbn:de:gbv:wim2-20230517-63677}, pages = {1 -- 11}, abstract = {As an optimization that starts from a randomly selected structure generally does not guarantee reasonable optimality, the use of a systemic approach, named the ground structure, is widely accepted in steel-made truss and frame structural design. However, in the case of reinforced concrete (RC) structural optimization, because of the orthogonal orientation of structural members, randomly chosen or architect-sketched framing is used. Such a one-time fixed layout trend, in addition to its lack of a systemic approach, does not necessarily guarantee optimality. In this study, an approach for generating a candidate ground structure to be used for cost or weight minimization of 3D RC building structures with included slabs is developed. A multiobjective function at the floor optimization stage and a single objective function at the frame optimization stage are considered. A particle swarm optimization (PSO) method is employed for selecting the optimal ground structure. This method enables generating a simple, yet potential, real-world representation of topologically preoptimized ground structure while both structural and main architectural requirements are considered. This is supported by a case study for different floor domain sizes.}, subject = {Bodenmechanik}, language = {en} } @article{LahmerNguyenTuanKoenkeetal., author = {Lahmer, Tom and Nguyen-Tuan, Long and K{\"o}nke, Carsten and Bettzieche, Volker}, title = {Thermo-hydro-mechanische 3-D-Simulation von Staumauern-Modellierung und Validierung}, series = {WASSERWIRTSCHAFT}, journal = {WASSERWIRTSCHAFT}, pages = {27 -- 30}, abstract = {Thermo-hydro-mechanische 3-D-Simulation von Staumauern-Modellierung und Validierung}, subject = {Angewandte Mathematik}, language = {de} } @inproceedings{GhorashiRabczukRodenasGarciaetal., author = {Ghorashi, Seyed Shahram and Rabczuk, Timon and R{\´o}denas Garc{\´i}a, Juan Jos{\´e} and Lahmer, Tom}, title = {T-SPLINE BASED XIGA FOR ADAPTIVE MODELING OF CRACKED BODIES}, series = {Digital Proceedings, International Conference on the Applications of Computer Science and Mathematics in Architecture and Civil Engineering : July 04 - 06 2012, Bauhaus-University Weimar}, booktitle = {Digital Proceedings, International Conference on the Applications of Computer Science and Mathematics in Architecture and Civil Engineering : July 04 - 06 2012, Bauhaus-University Weimar}, editor = {G{\"u}rlebeck, Klaus and Lahmer, Tom and Werner, Frank}, organization = {Bauhaus-Universit{\"a}t Weimar}, issn = {1611-4086}, doi = {10.25643/bauhaus-universitaet.2763}, url = {http://nbn-resolving.de/urn:nbn:de:gbv:wim2-20170314-27637}, pages = {13}, abstract = {Safety operation of important civil structures such as bridges can be estimated by using fracture analysis. Since the analytical methods are not capable of solving many complicated engineering problems, numerical methods have been increasingly adopted. In this paper, a part of isotropic material which contains a crack is considered as a partial model and the proposed model quality is evaluated. EXtended IsoGeometric Analysis (XIGA) is a new developed numerical approach [1, 2] which benefits from advantages of its origins: eXtended Finite Element Method (XFEM) and IsoGeometric Analysis (IGA). It is capable of simulating crack propagation problems with no remeshing necessity and capturing singular field at the crack tip by using the crack tip enrichment functions. Also, exact representation of geometry is possible using only few elements. XIGA has also been successfully applied for fracture analysis of cracked orthotropic bodies [3] and for simulation of curved cracks [4]. XIGA applies NURBS functions for both geometry description and solution field approximation. The drawback of NURBS functions is that local refinement cannot be defined regarding that it is based on tensorproduct constructs unless multiple patches are used which has also some limitations. In this contribution, the XIGA is further developed to make the local refinement feasible by using Tspline basis functions. Adopting a recovery based error estimator in the proposed approach for evaluation of the model quality and performing the adaptive processes is in progress. Finally, some numerical examples with available analytical solutions are investigated by the developed scheme.}, subject = {Angewandte Informatik}, language = {en} } @article{SteinLahmerBock, author = {Stein, Peter and Lahmer, Tom and Bock, Sebastian}, title = {Synthese und Analyse von gekoppelten Modellen im konstruktiven Ingenieurbau}, series = {Bautechnik}, journal = {Bautechnik}, pages = {8 -- 11}, abstract = {Synthese und Analyse von gekoppelten Modellen im konstruktiven Ingenieurbau}, subject = {Angewandte Mathematik}, language = {de} } @inproceedings{GoebelOsburgLahmer, author = {G{\"o}bel, Luise and Osburg, Andrea and Lahmer, Tom}, title = {STUDY OF ANALYTICAL MODELS OF THE MECHANICAL BEHAVIOR OF POLYMER-MODIFIED CONCRETE}, 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.2797}, url = {http://nbn-resolving.de/urn:nbn:de:gbv:wim2-20170314-27973}, pages = {9}, abstract = {Polymer modification of mortar and concrete is a widely used technique in order to improve their durability properties. Hitherto, the main application fields of such materials are repair and restoration of buildings. However, due to the constant increment of service life requirements and the cost efficiency, polymer modified concrete (PCC) is also used for construction purposes. Therefore, there is a demand for studying the mechanical properties of PCC and entitative differences compared to conventional concrete (CC). It is significant to investigate whether all the assumed hypotheses and existing analytical formulations about CC are also valid for PCC. In the present study, analytical models available in the literature are evaluated. These models are used for estimating mechanical properties of concrete. The investigated property in this study is the modulus of elasticity, which is estimated with respect to the value of compressive strength. One existing database was extended and adapted for polymer-modified concrete mixtures along with their experimentally measured mechanical properties. Based on the indexed data a comparison between model predictions and experiments was conducted by calculation of forecast errors.}, subject = {Angewandte Informatik}, language = {en} } @article{VuBacLahmerZhangetal., author = {Vu-Bac, N. and Lahmer, Tom and Zhang, Yancheng and Zhuang, Xiaoying and Rabczuk, Timon}, title = {Stochastic predictions of interfacial characteristic of polymeric nanocomposites (PNCs)}, series = {Composites Part B Engineering}, journal = {Composites Part B Engineering}, pages = {80 -- 95}, abstract = {Stochastic predictions of interfacial characteristic of polymeric nanocomposites (PNCs)}, subject = {Angewandte Mathematik}, language = {en} } @article{VuBacLahmerKeiteletal., author = {Vu-Bac, N. and Lahmer, Tom and Keitel, Holger and Zhao, Jun-Hua and Zhuang, Xiaoying and Rabczuk, Timon}, title = {Stochastic predictions of bulk properties of amorphous polyethylene based on molecular dynamics simulations}, series = {Mechanics of Materials}, journal = {Mechanics of Materials}, pages = {70 -- 84}, abstract = {Stochastic predictions of bulk properties of amorphous polyethylene based on molecular dynamics simulations}, subject = {Angewandte Mathematik}, 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} } @inproceedings{HartmannSmarslyLahmer, author = {Hartmann, Veronika and Smarsly, Kay and Lahmer, Tom}, title = {ROBUST SCHEDULING IN CONSTRUCTION ENGINEERING}, 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.2799}, url = {http://nbn-resolving.de/urn:nbn:de:gbv:wim2-20170314-27994}, pages = {5}, abstract = {In construction engineering, a schedule's input data, which is usually not exactly known in the planning phase, is considered deterministic when generating the schedule. As a result, construction schedules become unreliable and deadlines are often not met. While the optimization of construction schedules with respect to costs and makespan has been a matter of research in the past decades, the optimization of the robustness of construction schedules has received little attention. In this paper, the effects of uncertainties inherent to the input data of construction schedules are discussed. Possibilities are investigated to improve the reliability of construction schedules by considering alternative processes for certain tasks and by identifying the combination of processes generating the most robust schedule with respect to the makespan of a construction project.}, subject = {Angewandte Informatik}, language = {en} } @unpublished{AbbasKavrakovMorgenthaletal., author = {Abbas, Tajammal and Kavrakov, Igor and Morgenthal, Guido and Lahmer, Tom}, title = {Prediction of aeroelastic response of bridge decks using artificial neural networks}, doi = {10.25643/bauhaus-universitaet.4097}, url = {http://nbn-resolving.de/urn:nbn:de:gbv:wim2-20200225-40974}, abstract = {The assessment of wind-induced vibrations is considered vital for the design of long-span bridges. The aim of this research is to develop a methodological framework for robust and efficient prediction strategies for complex aerodynamic phenomena using hybrid models that employ numerical analyses as well as meta-models. Here, an approach to predict motion-induced aerodynamic forces is developed using artificial neural network (ANN). The ANN is implemented in the classical formulation and trained with a comprehensive dataset which is obtained from computational fluid dynamics forced vibration simulations. The input to the ANN is the response time histories of a bridge section, whereas the output is the motion-induced forces. The developed ANN has been tested for training and test data of different cross section geometries which provide promising predictions. The prediction is also performed for an ambient response input with multiple frequencies. Moreover, the trained ANN for aerodynamic forcing is coupled with the structural model to perform fully-coupled fluid--structure interaction analysis to determine the aeroelastic instability limit. The sensitivity of the ANN parameters to the model prediction quality and the efficiency has also been highlighted. The proposed methodology has wide application in the analysis and design of long-span bridges.}, subject = {Aerodynamik}, 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} } @article{KaltenbacherLahmerMohretal., author = {Kaltenbacher, Barbara and Lahmer, Tom and Mohr, Marcus and Kaltenbacher, Manfred}, title = {PDE based determination of piezoelectric material tensors}, series = {European Journal of Applied Mathematics}, journal = {European Journal of Applied Mathematics}, doi = {10.25643/bauhaus-universitaet.3595}, pages = {383 -- 416}, abstract = {PDE based determination of piezoelectric material tensors.}, 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{LahmerKoenkeBettzieche, author = {Lahmer, Tom and K{\"o}nke, Carsten and Bettzieche, Volker}, title = {Optimale Positionierung von Messeinrichtungen an Staumauern zur Bauwerks{\"u}berwachung}, series = {WASSERWIRTSCHAFT}, journal = {WASSERWIRTSCHAFT}, pages = {16 -- 16}, abstract = {Optimale Positionierung von Messeinrichtungen an Staumauern zur Bauwerks{\"u}berwachung}, subject = {Angewandte Mathematik}, language = {de} } @article{LahmerKoenkeBettzieche, author = {Lahmer, Tom and K{\"o}nke, Carsten and Bettzieche, Volker}, title = {Optimal positioning of sensors for the monitoring of water dams}, series = {WASSERWIRTSCHAFT}, journal = {WASSERWIRTSCHAFT}, pages = {16 -- 19}, abstract = {Optimal positioning of sensors for the monitoring of water dams}, subject = {Angewandte Mathematik}, language = {de} } @article{LahmerKaltenbacherSchulz, author = {Lahmer, Tom and Kaltenbacher, Barbara and Schulz, V.}, title = {Optimal measurement selection for piezoelectric material tensor identification}, series = {Inverse Problems in Science and Engineering}, journal = {Inverse Problems in Science and Engineering}, doi = {10.25643/bauhaus-universitaet.3593}, pages = {369 -- 387}, abstract = {Optimal measurement selection for piezoelectric material tensor identification.}, subject = {Angewandte Mathematik}, language = {en} } @article{Lahmer, author = {Lahmer, Tom}, title = {Optimal experimental design for nonlinear ill-posed problems applied to gravity dams}, series = {Inverse Problems}, journal = {Inverse Problems}, abstract = {Optimal experimental design for nonlinear ill-posed problems applied to gravity dams}, subject = {Angewandte Mathematik}, language = {en} } @article{NguyenTuanKoenkeBettziecheetal., author = {Nguyen-Tuan, Long and K{\"o}nke, Carsten and Bettzieche, Volker and Lahmer, Tom}, title = {Numerical modeling and validation for 3D coupled-nonlinear thermo-hydro-mechanical problems in masonry dams}, series = {Computers \& Structures}, journal = {Computers \& Structures}, pages = {143 -- 154}, abstract = {Numerical modeling and validation for 3D coupled-nonlinear thermo-hydro-mechanical problems in masonry dams}, subject = {Angewandte Mathematik}, language = {en} } @article{LahmerBockHildebrandetal., author = {Lahmer, Tom and Bock, Sebastian and Hildebrand, J{\"o}rg and G{\"u}rlebeck, Klaus}, title = {Non-destructive identification of residual stresses in steel under thermal loadings}, series = {Inverse Problems in Science and Engineering}, journal = {Inverse Problems in Science and Engineering}, pages = {1 -- 17}, abstract = {Non-destructive identification of residual stresses in steel under thermal loadings}, subject = {Angewandte Mathematik}, language = {en} } @article{ZhangNanthakumarLahmeretal., author = {Zhang, Chao and Nanthakumar, S.S. and Lahmer, Tom and Rabczuk, Timon}, title = {Multiple cracks identification for piezoelectric structures}, series = {International Journal of Fracture}, journal = {International Journal of Fracture}, pages = {1 -- 19}, abstract = {Multiple cracks identification for piezoelectric structures}, subject = {Angewandte Mathematik}, language = {en} } @article{Lahmer, author = {Lahmer, Tom}, title = {Modified Landweber iterations in a multilevel algorithm applied to inverse problems in piezoelectricity}, series = {Journal of Inverse and Ill-posed Problems}, journal = {Journal of Inverse and Ill-posed Problems}, pages = {585 -- 593}, abstract = {Modified Landweber iterations in a multilevel algorithm applied to inverse problems in piezoelectricity}, subject = {Angewandte Mathematik}, language = {en} } @article{HarirchianLahmer, author = {Harirchian, Ehsan and Lahmer, Tom}, title = {Improved Rapid Visual Earthquake Hazard Safety Evaluation of Existing Buildings Using a Type-2 Fuzzy Logic Model}, series = {Applied Sciences}, volume = {2020}, journal = {Applied Sciences}, number = {Volume 10, Issue 3, 2375}, publisher = {MDPI}, address = {Basel}, doi = {10.3390/app10072375}, url = {http://nbn-resolving.de/urn:nbn:de:gbv:wim2-20200331-41161}, pages = {14}, abstract = {Rapid Visual Screening (RVS) is a procedure that estimates structural scores for buildings and prioritizes their retrofit and upgrade requirements. Despite the speed and simplicity of RVS, many of the collected parameters are non-commensurable and include subjectivity due to visual observations. This might cause uncertainties in the evaluation, which emphasizes the use of a fuzzy-based method. This study aims to propose a novel RVS methodology based on the interval type-2 fuzzy logic system (IT2FLS) to set the priority of vulnerable building to undergo detailed assessment while covering uncertainties and minimizing their effects during evaluation. The proposed method estimates the vulnerability of a building, in terms of Damage Index, considering the number of stories, age of building, plan irregularity, vertical irregularity, building quality, and peak ground velocity, as inputs with a single output variable. Applicability of the proposed method has been investigated using a post-earthquake damage database of reinforced concrete buildings from the Bing{\"o}l and D{\"u}zce earthquakes in Turkey.}, subject = {Fuzzy-Logik}, language = {en} } @article{AchenbachLahmerMorgenthal, author = {Achenbach, Marcus and Lahmer, Tom and Morgenthal, Guido}, title = {Identification of the thermal properties of concrete for the temperature calculation of concrete slabs and columns subjected to a standard fire—Methodology and proposal for simplified formulations}, series = {Fire Safety Journal 87}, journal = {Fire Safety Journal 87}, doi = {10.1016/j.firesaf.2016.12.003}, url = {http://nbn-resolving.de/urn:nbn:de:gbv:wim2-20170331-30929}, pages = {80 -- 86}, abstract = {The fire resistance of concrete members is controlled by the temperature distribution of the considered cross section. The thermal analysis can be performed with the advanced temperature dependent physical properties provided by 5EN6 1992-1-2. But the recalculation of laboratory tests on columns from 5TU6 Braunschweig shows, that there are deviations between the calculated and measured temperatures. Therefore it can be assumed, that the mathematical formulation of these thermal properties could be improved. A sensitivity analysis is performed to identify the governing parameters of the temperature calculation and a nonlinear optimization method is used to enhance the formulation of the thermal properties. The proposed simplified properties are partly validated by the recalculation of measured temperatures of concrete columns. These first results show, that the scatter of the differences from the calculated to the measured temperatures can be reduced by the proposed simple model for the thermal analysis of concrete.}, subject = {Sensitivit{\"a}tsanalyse}, language = {en} } @article{KnabeDatchevaLahmeretal., author = {Knabe, Tina and Datcheva, Maria and Lahmer, Tom and Cotecchia, F. and Schanz, Tom}, title = {Identification of constitutive parameters of soil using an optimization strategy and statistical analysis}, series = {Computers and Geotechnics}, journal = {Computers and Geotechnics}, pages = {143 -- 157}, abstract = {Identification of constitutive parameters of soil using an optimization strategy and statistical analysis}, subject = {Angewandte Mathematik}, language = {en} } @inproceedings{Lahmer, author = {Lahmer, Tom}, title = {HYDRO-MECHANICAL COUPLED FIELD SYSTEM IDENTIFICATION - APPLICATION TO WATER RESERVOIRS}, editor = {G{\"u}rlebeck, Klaus and K{\"o}nke, Carsten}, organization = {Bauhaus-Universit{\"a}t Weimar}, issn = {1611-4086}, doi = {10.25643/bauhaus-universitaet.2865}, url = {http://nbn-resolving.de/urn:nbn:de:gbv:wim2-20170314-28650}, pages = {14}, abstract = {In this paper we present an inverse method which is capable of identifying system components in a hydro-mechanically coupled system, i.e. for fluid flow in porous media. As an example we regard water dams that were constructed more than hundred years ago but which are still in use. Over the time ageing processes have changed the condition of these dams. Within the dams fissures might have grown. The proposed method is designed to locate these fissures out of combined mechanical and hydraulic measurements. In a numerical example the fissures or damaged zones are described by a smeared crack model. The task is now to identify simultaneously the spatial distribution of Young's modulus and the hydraulic permeability due to the fact, that in regions where damages are present, the mechanical stiffness of the system is reduced and the permeability increased. The inversion is shown to be an ill-posed problem. As a consequence regularizing methods have to be applied, where the nonlinear Landweber method (a gradient type method combined with a discrepancy principle) has proven to be an efficient choice.}, subject = {Angewandte Informatik}, language = {en} } @article{AchenbachLahmerMorgenthal, author = {Achenbach, Marcus and Lahmer, Tom and Morgenthal, Guido}, title = {Global Sensitivity Analysis of Reinforced Concrete Walls Subjected to Standard Fire - A Comparison of Methods}, series = {14th International Probabilistic Workshop}, journal = {14th International Probabilistic Workshop}, pages = {97 -- 106}, abstract = {Global Sensitivity Analysis of Reinforced Concrete Walls Subjected to Standard Fire—A Comparison of Methods}, subject = {Angewandte Mathematik}, language = {en} } @article{NguyenTuanLahmerDatchevaetal., author = {Nguyen-Tuan, Long and Lahmer, Tom and Datcheva, Maria and Schanz, Tom}, title = {Global and local sensitivity analyses for coupled thermo-hydro-mechanical problems}, series = {International Journal for Numerical and Analytical Methods in Geomechanics}, journal = {International Journal for Numerical and Analytical Methods in Geomechanics}, abstract = {Global and local sensitivity analyses for coupled thermo-hydro-mechanical problems}, subject = {Angewandte Mathematik}, language = {en} } @article{Lahmer, author = {Lahmer, Tom}, title = {FEM-Based determination of real and complex elastic, dielectric, and piezoelectric moduli in piezoceramic materials}, series = {IEEE Transactions on Ultrasonics, Ferroelectrics, and Frequency Control}, journal = {IEEE Transactions on Ultrasonics, Ferroelectrics, and Frequency Control}, doi = {10.25643/bauhaus-universitaet.3608}, url = {http://nbn-resolving.de/urn:nbn:de:gbv:wim2-20171030-36083}, abstract = {We propose an enhanced iterative scheme for the precise reconstruction of piezoelectric material parameters from electric impedance and mechanical displacement measurements. It is based on finite-element simulations of the full three-dimensional piezoelectric equations, combined with an inexact Newton or nonlinear Landweber iterative inversion scheme. We apply our method to two piezoelectric materials and test its performance. For the first material, the manufacturer provides a full data set; for the second one, no material data set is available. For both cases, our inverse scheme, using electric impedance measurements as input data, performs well.}, subject = {Finite-Elemente-Methode}, language = {en} } @article{LahmerKaltenbacherKaltenbacheretal., author = {Lahmer, Tom and Kaltenbacher, Manfred and Kaltenbacher, Barbara and Lerch, Reinhard and Leder, Erich}, title = {Fem-based determination of real and complex elastic, dielectric, and piezoelectric moduli in piezoceramic materials}, series = {IEEE transactions on ultrasonics, ferroelectrics, and frequency control}, journal = {IEEE transactions on ultrasonics, ferroelectrics, and frequency control}, doi = {10.25643/bauhaus-universitaet.3594}, abstract = {Fem-based determination of real and complex elastic, dielectric, and piezoelectric moduli in piezoceramic materials.}, subject = {Angewandte Mathematik}, language = {en} } @article{NguyenVinhBakarMsekhetal., author = {Nguyen-Vinh, H. and Bakar, I. and Msekh, Mohammed Abdulrazzak and Song, Jeong-Hoon and Muthu, Jacob and Zi, Goangseup and Le, P. and Bordas, St{\´e}phane Pierre Alain and Simpson, R. and Natarajan, S. and Lahmer, Tom and Rabczuk, Timon}, title = {Extended Finite Element Method for Dynamic Fracture of Piezo-Electric Materials}, series = {Engineering Fracture Mechanics}, journal = {Engineering Fracture Mechanics}, doi = {10.1016/j.engfracmech.2012.04.025}, pages = {19 -- 31}, abstract = {We present an extended finite element formulation for dynamic fracture of piezo-electric materials. The method is developed in the context of linear elastic fracture mechanics. It is applied to mode I and mixed mode-fracture for quasi-steady cracks. An implicit time integration scheme is exploited. The results are compared to results obtained with the boundary element method and show excellent agreement.}, subject = {Angewandte Mathematik}, language = {en} } @article{KumariHarirchianLahmeretal., author = {Kumari, Vandana and Harirchian, Ehsan and Lahmer, Tom and Rasulzade, Shahla}, title = {Evaluation of Machine Learning and Web-Based Process for Damage Score Estimation of Existing Buildings}, series = {Buildings}, volume = {2022}, journal = {Buildings}, number = {Volume 12, issue 5, article 578}, publisher = {MDPI}, address = {Basel}, doi = {10.3390/buildings12050578}, url = {http://nbn-resolving.de/urn:nbn:de:gbv:wim2-20220509-46387}, pages = {1 -- 23}, abstract = {The seismic vulnerability assessment of existing reinforced concrete (RC) buildings is a significant source of disaster mitigation plans and rescue services. Different countries evolved various Rapid Visual Screening (RVS) techniques and methodologies to deal with the devastating consequences of earthquakes on the structural characteristics of buildings and human casualties. Artificial intelligence (AI) methods, such as machine learning (ML) algorithm-based methods, are increasingly used in various scientific and technical applications. The investigation toward using these techniques in civil engineering applications has shown encouraging results and reduced human intervention, including uncertainties and biased judgment. In this study, several known non-parametric algorithms are investigated toward RVS using a dataset employing different earthquakes. Moreover, the methodology encourages the possibility of examining the buildings' vulnerability based on the factors related to the buildings' importance and exposure. In addition, a web-based application built on Django is introduced. The interface is designed with the idea to ease the seismic vulnerability investigation in real-time. The concept was validated using two case studies, and the achieved results showed the proposed approach's potential efficiency}, subject = {Maschinelles Lernen}, language = {en} } @article{KeitelKarakiLahmeretal., author = {Keitel, Holger and Karaki, Ghada and Lahmer, Tom and Nikulla, Susanne and Zabel, Volkmar}, title = {Evaluation of coupled partial models in structural engineering using graph theory and sensitivity analysis}, series = {Engineering structures}, journal = {Engineering structures}, pages = {3726 -- 3736}, abstract = {Evaluation of coupled partial models in structural engineering using graph theory and sensitivity analysis}, subject = {Angewandte Mathematik}, language = {en} } @article{HauckLahmerKaltenbacher, author = {Hauck, A. and Lahmer, Tom and Kaltenbacher, Manfred}, title = {Enhanced homogenization technique for magnetomechanical systems using the generalized finite element method}, series = {COMPEL: The international journal for computation and mathematics in electrical and electronic engineering}, journal = {COMPEL: The international journal for computation and mathematics in electrical and electronic engineering}, pages = {935 -- 947}, abstract = {Enhanced homogenization technique for magnetomechanical systems using the generalized finite element method}, subject = {Angewandte Mathematik}, language = {en} } @article{AlkamLahmer, author = {Alkam, Feras and Lahmer, Tom}, title = {Eigenfrequency-Based Bayesian Approach for Damage Identification in Catenary Poles}, series = {Infrastructures}, volume = {2021}, journal = {Infrastructures}, number = {Volume 6, issue 4, article 57}, publisher = {MDPI}, address = {Basel}, doi = {10.3390/infrastructures6040057}, url = {http://nbn-resolving.de/urn:nbn:de:gbv:wim2-20210510-44256}, pages = {1 -- 19}, abstract = {This study proposes an efficient Bayesian, frequency-based damage identification approach to identify damages in cantilever structures with an acceptable error rate, even at high noise levels. The catenary poles of electric high-speed train systems were selected as a realistic case study to cover the objectives of this study. Compared to other frequency-based damage detection approaches described in the literature, the proposed approach is efficiently able to detect damages in cantilever structures to higher levels of damage detection, namely identifying both the damage location and severity using a low-cost structural health monitoring (SHM) system with a limited number of sensors; for example, accelerometers. The integration of Bayesian inference, as a stochastic framework, in the proposed approach, makes it possible to utilize the benefit of data fusion in merging the informative data from multiple damage features, which increases the quality and accuracy of the results. The findings provide the decision-maker with the information required to manage the maintenance, repair, or replacement procedures.}, subject = {Fahrleitung}, language = {en} } @article{SchmidtLahmer, author = {Schmidt, Albrecht and Lahmer, Tom}, title = {Efficient domain decomposition based reliability analysis for polymorphic uncertain material parameters}, series = {Proceedings in Applied Mathematics \& Mechanics}, volume = {2021}, journal = {Proceedings in Applied Mathematics \& Mechanics}, number = {Volume 21, issue 1}, publisher = {Wiley-VHC}, address = {Weinheim}, doi = {10.1002/pamm.202100014}, url = {http://nbn-resolving.de/urn:nbn:de:gbv:wim2-20220112-45563}, pages = {1 -- 4}, abstract = {Realistic uncertainty description incorporating aleatoric and epistemic uncertainties can be described within the framework of polymorphic uncertainty, which is computationally demanding. Utilizing a domain decomposition approach for random field based uncertainty models the proposed level-based sampling method can reduce these computational costs significantly and shows good agreement with a standard sampling technique. While 2-level configurations tend to get unstable with decreasing sampling density 3-level setups show encouraging results for the investigated reliability analysis of a structural unit square.}, subject = {Polymorphie}, language = {en} } @article{HarirchianLahmerBuddhirajuetal., author = {Harirchian, Ehsan and Lahmer, Tom and Buddhiraju, Sreekanth and Mohammad, Kifaytullah and Mosavi, Amir}, title = {Earthquake Safety Assessment of Buildings through Rapid Visual Screening}, series = {Buildings}, volume = {2020}, journal = {Buildings}, number = {Volume 10, Issue 3}, publisher = {MDPI}, doi = {10.3390/buildings10030051}, url = {http://nbn-resolving.de/urn:nbn:de:gbv:wim2-20200331-41153}, pages = {15}, abstract = {Earthquake is among the most devastating natural disasters causing severe economical, environmental, and social destruction. Earthquake safety assessment and building hazard monitoring can highly contribute to urban sustainability through identification and insight into optimum materials and structures. While the vulnerability of structures mainly depends on the structural resistance, the safety assessment of buildings can be highly challenging. In this paper, we consider the Rapid Visual Screening (RVS) method, which is a qualitative procedure for estimating structural scores for buildings suitable for medium- to high-seismic cases. This paper presents an overview of the common RVS methods, i.e., FEMA P-154, IITK-GGSDMA, and EMPI. To examine the accuracy and validation, a practical comparison is performed between their assessment and observed damage of reinforced concrete buildings from a street survey in the Bing{\"o}l region, Turkey, after the 1 May 2003 earthquake. The results demonstrate that the application of RVS methods for preliminary damage estimation is a vital tool. Furthermore, the comparative analysis showed that FEMA P-154 creates an assessment that overestimates damage states and is not economically viable, while EMPI and IITK-GGSDMA provide more accurate and practical estimation, respectively.}, subject = {Maschinelles Lernen}, language = {en} } @article{HarirchianLahmerRasulzade, author = {Harirchian, Ehsan and Lahmer, Tom and Rasulzade, Shahla}, title = {Earthquake Hazard Safety Assessment of Existing Buildings Using Optimized Multi-Layer Perceptron Neural Network}, series = {Energies}, volume = {2020}, journal = {Energies}, number = {Volume 13, Issue 8, 2060}, publisher = {MDPI}, address = {Basel}, doi = {10.3390/en13082060}, url = {http://nbn-resolving.de/urn:nbn:de:gbv:wim2-20200504-41575}, pages = {16}, abstract = {The latest earthquakes have proven that several existing buildings, particularly in developing countries, are not secured from damages of earthquake. A variety of statistical and machine-learning approaches have been proposed to identify vulnerable buildings for the prioritization of retrofitting. The present work aims to investigate earthquake susceptibility through the combination of six building performance variables that can be used to obtain an optimal prediction of the damage state of reinforced concrete buildings using artificial neural network (ANN). In this regard, a multi-layer perceptron network is trained and optimized using a database of 484 damaged buildings from the D{\"u}zce earthquake in Turkey. The results demonstrate the feasibility and effectiveness of the selected ANN approach to classify concrete structural damage that can be used as a preliminary assessment technique to identify vulnerable buildings in disaster risk-management programs.}, subject = {Erdbeben}, language = {en} } @article{NanthakumarLahmerRabczuk, author = {Nanthakumar, S.S. and Lahmer, Tom and Rabczuk, Timon}, title = {Detection of multiple flaws in piezoelectric structures using XFEM and level sets}, series = {International Journal for Numerical Methods in Engineering}, journal = {International Journal for Numerical Methods in Engineering}, pages = {960}, abstract = {Detection of multiple flaws in piezoelectric structures using XFEM and level sets}, subject = {Angewandte Mathematik}, language = {en} } @article{NanthakumarLahmerRabczuk, author = {Nanthakumar, S.S. and Lahmer, Tom and Rabczuk, Timon}, title = {Detection of multiple flaws in piezoelectric structures using XFEM and level sets}, series = {Computer Methods in Applied Mechanics and Engineering}, journal = {Computer Methods in Applied Mechanics and Engineering}, pages = {98 -- 112}, abstract = {Detection of multiple flaws in piezoelectric structures using XFEM and level sets}, subject = {Angewandte Mathematik}, language = {en} } @article{NanthakumarLahmerZhuangetal., author = {Nanthakumar, S.S. and Lahmer, Tom and Zhuang, Xiaoying and Zi, Goangseup and Rabczuk, Timon}, title = {Detection of material interfaces using a regularized level set method in piezoelectric structures}, series = {Inverse Problems in Science and Engineering}, journal = {Inverse Problems in Science and Engineering}, pages = {153 -- 176}, abstract = {Detection of material interfaces using a regularized level set method in piezoelectric structures}, subject = {Angewandte Mathematik}, language = {en} } @article{NanthakumarLahmerZhuangetal., author = {Nanthakumar, S.S. and Lahmer, Tom and Zhuang, Xiaoying and Zi, Goangseup and Rabczuk, Timon}, title = {Detection of material interfaces using a regularized level set method in piezoelectric structures}, series = {Inverse Problems in Science and Engineering}, journal = {Inverse Problems in Science and Engineering}, abstract = {Detection of material interfaces using a regularized level set method in piezoelectric structures}, subject = {Angewandte Mathematik}, language = {en} } @article{NanthakumarLahmerRabczuk, author = {Nanthakumar, S.S. and Lahmer, Tom and Rabczuk, Timon}, title = {Detection of flaws in piezoelectric structures using extended FEM}, series = {International Journal for Numerical Methods in Engineering}, journal = {International Journal for Numerical Methods in Engineering}, pages = {373 -- 389}, abstract = {Detection of flaws in piezoelectric structures using extended FEM}, subject = {Angewandte Mathematik}, language = {en} } @article{AlYasiriMutasharGuerlebecketal., author = {Al-Yasiri, Zainab Riyadh Shaker and Mutashar, Hayder Majid and G{\"u}rlebeck, Klaus and Lahmer, Tom}, title = {Damage Sensitive Signals for the Assessment of the Conditions of Wind Turbine Rotor Blades Using Electromagnetic Waves}, series = {Infrastructures}, volume = {2022}, journal = {Infrastructures}, number = {Volume 7, Issue 8 (August 2022), article 104}, editor = {Shafiullah, GM}, publisher = {MDPI}, address = {Basel}, doi = {10.3390/infrastructures7080104}, url = {http://nbn-resolving.de/urn:nbn:de:gbv:wim2-20220831-47093}, pages = {18}, abstract = {One of the most important renewable energy technologies used nowadays are wind power turbines. In this paper, we are interested in identifying the operating status of wind turbines, especially rotor blades, by means of multiphysical models. It is a state-of-the-art technology to test mechanical structures with ultrasonic-based methods. However, due to the density and the required high resolution, the testing is performed with high-frequency waves, which cannot penetrate the structure in depth. Therefore, there is a need to adopt techniques in the fields of multiphysical model-based inversion schemes or data-driven structural health monitoring. Before investing effort in the development of such approaches, further insights and approaches are necessary to make the techniques applicable to structures such as wind power plants (blades). Among the expected developments, further accelerations of the so-called "forward codes" for a more efficient implementation of the wave equation could be envisaged. Here, we employ electromagnetic waves for the early detection of cracks. Because in many practical situations, it is not possible to apply techniques from tomography (characterized by multiple sources and sensor pairs), we focus here on the question of whether the existence of cracks can be determined by using only one source for the sent waves.}, subject = {Windkraftwerk}, language = {en} }