TY - CHAP A1 - Lahmer, Tom A1 - Ghorashi, Seyed Shahram ED - Gürlebeck, Klaus ED - Lahmer, Tom ED - Werner, Frank T1 - XFEM-BASED CRACK IDENTIFICATION APPLYING REGULARIZING METHODS IN A MULTILEVEL APPROACH T2 - Digital Proceedings, International Conference on the Applications of Computer Science and Mathematics in Architecture and Civil Engineering : July 04 - 06 2012, Bauhaus-University Weimar N2 - 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. KW - Angewandte Informatik KW - Angewandte Mathematik KW - Computerunterstütztes Verfahren Y1 - 2012 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:gbv:wim2-20170314-27717 UR - http://euklid.bauing.uni-weimar.de/ikm2012 SN - 1611-4086 ER - TY - JOUR A1 - Lahmer, Tom A1 - Ilg, J. A1 - Lerch, Reinhard T1 - Variance-based sensitivity analyses of piezoelectric models JF - Computer Modeling in Engineering & Sciences N2 - Variance-based sensitivity analyses of piezoelectric models KW - Angewandte Mathematik KW - Stochastik KW - Strukturmechanik Y1 - 2015 SP - 105 EP - 126 ER - TY - JOUR A1 - Ilyani Akmar, A.B. A1 - Lahmer, Tom A1 - Bordas, Stéphane Pierre Alain A1 - Beex, L.A.A. A1 - Rabczuk, Timon T1 - Uncertainty quantification of dry woven fabrics: A sensitivity analysis on material properties JF - Composite Structures N2 - Uncertainty quantification of dry woven fabrics: A sensitivity analysis on material properties KW - Angewandte Mathematik KW - Stochastik KW - Strukturmechanik Y1 - 2014 U6 - http://dx.doi.org/10.1016/j.compstruct.2014.04.014 SP - 1 EP - 17 ER - TY - JOUR A1 - Vu-Bac, N. A1 - Rafiee, Roham A1 - Zhuang, Xiaoying A1 - Lahmer, Tom A1 - Rabczuk, Timon T1 - Uncertainty quantification for multiscale modeling of polymer nanocomposites with correlated parameters JF - Composites Part B: Engineering N2 - Uncertainty quantification for multiscale modeling of polymer nanocomposites with correlated parameters KW - Angewandte Mathematik KW - Stochastik KW - Strukturmechanik Y1 - 2015 SP - 446 EP - 464 ER - TY - JOUR A1 - Göbel, Luise A1 - Lahmer, Tom A1 - Osburg, Andrea T1 - Uncertainty analysis in multiscale modeling of concrete based on continuum micromechanics JF - European Journal of Mechanics-A/Solids N2 - Uncertainty analysis in multiscale modeling of concrete based on continuum micromechanics KW - Angewandte Mathematik KW - Stochastik KW - Strukturmechanik Y1 - 2017 ER - TY - CHAP A1 - Jaouadi, Zouhour A1 - Lahmer, Tom ED - Gürlebeck, Klaus ED - Lahmer, Tom T1 - Topology optimization of structures subjected to multiple load cases by introducing the Epsilon constraint method T2 - Digital Proceedings, International Conference on the Applications of Computer Science and Mathematics in Architecture and Civil Engineering : July 20 - 22 2015, Bauhaus-University Weimar N2 - 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. KW - Angewandte Informatik KW - Angewandte Mathematik KW - Building Information Modeling KW - Computerunterstütztes Verfahren KW - Data, information and knowledge modeling in civil engineering; Function theoretic methods and PDE in engineering sciences; Mathematical methods for (robotics and) computer vision; Numerical modeling in engineering; Optimization in engineering applications Y1 - 2015 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:gbv:wim2-20170314-28042 SN - 1611-4086 ER - TY - JOUR A1 - Nanthakumar, S.S. A1 - Lahmer, Tom A1 - Zhuang, Xiaoying A1 - Park, Harold S. A1 - Rabczuk, Timon T1 - Topology optimization of piezoelectric nanostructures JF - Journal of the Mechanics and Physics of Solids N2 - Topology optimization of piezoelectric nanostructures KW - Angewandte Mathematik KW - Stochastik KW - Strukturmechanik Y1 - 2016 SP - 316 EP - 335 ER - TY - JOUR A1 - Alemu, Yohannes L. A1 - Habte, Bedilu A1 - Lahmer, Tom A1 - Urgessa, Girum T1 - Topologically preoptimized ground structure (TPOGS) for the optimization of 3D RC buildings JF - Asian Journal of Civil Engineering N2 - 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. KW - Bodenmechanik KW - Strukturanalyse KW - Optimierung KW - Stahlbetonkonstruktion KW - Dreidimensionales Modell KW - ground structure KW - TPOGS KW - topology optimization KW - 3D reinforced concrete buildings Y1 - 2023 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:gbv:wim2-20230517-63677 UR - https://link.springer.com/article/10.1007/s42107-023-00640-2 VL - 2023 SP - 1 EP - 11 PB - Springer International Publishing CY - Cham ER - TY - JOUR A1 - Lahmer, Tom A1 - Nguyen-Tuan, Long A1 - Könke, Carsten A1 - Bettzieche, Volker T1 - Thermo-hydro-mechanische 3-D-Simulation von Staumauern‐Modellierung und Validierung JF - WASSERWIRTSCHAFT N2 - Thermo-hydro-mechanische 3-D-Simulation von Staumauern‐Modellierung und Validierung KW - Angewandte Mathematik KW - Stochastik KW - Strukturmechanik Y1 - 2016 SP - 27 EP - 30 ER - TY - CHAP A1 - Ghorashi, Seyed Shahram A1 - Rabczuk, Timon A1 - Ródenas García, Juan José A1 - Lahmer, Tom ED - Gürlebeck, Klaus ED - Lahmer, Tom ED - Werner, Frank T1 - T-SPLINE BASED XIGA FOR ADAPTIVE MODELING OF CRACKED BODIES T2 - Digital Proceedings, International Conference on the Applications of Computer Science and Mathematics in Architecture and Civil Engineering : July 04 - 06 2012, Bauhaus-University Weimar N2 - 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. KW - Angewandte Informatik KW - Angewandte Mathematik KW - Computerunterstütztes Verfahren Y1 - 2012 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:gbv:wim2-20170314-27637 UR - http://euklid.bauing.uni-weimar.de/ikm2012 SN - 1611-4086 ER - TY - JOUR A1 - Stein, Peter A1 - Lahmer, Tom A1 - Bock, Sebastian T1 - Synthese und Analyse von gekoppelten Modellen im konstruktiven Ingenieurbau BT - Sonderdruck‐DFG Graduiertenkolleg JF - Bautechnik N2 - Synthese und Analyse von gekoppelten Modellen im konstruktiven Ingenieurbau KW - Angewandte Mathematik KW - Stochastik KW - Strukturmechanik Y1 - 2011 SP - 8 EP - 11 ER - TY - CHAP A1 - Göbel, Luise A1 - Osburg, Andrea A1 - Lahmer, Tom ED - Gürlebeck, Klaus ED - Lahmer, Tom T1 - STUDY OF ANALYTICAL MODELS OF THE MECHANICAL BEHAVIOR OF POLYMER-MODIFIED CONCRETE T2 - Digital Proceedings, International Conference on the Applications of Computer Science and Mathematics in Architecture and Civil Engineering : July 20 - 22 2015, Bauhaus-University Weimar N2 - 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. KW - Angewandte Informatik KW - Angewandte Mathematik KW - Building Information Modeling KW - Computerunterstütztes Verfahren KW - Data, information and knowledge modeling in civil engineering; Function theoretic methods and PDE in engineering sciences; Mathematical methods for (robotics and) computer vision; Numerical modeling in engineering; Optimization in engineering applications Y1 - 2015 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:gbv:wim2-20170314-27973 SN - 1611-4086 ER - TY - JOUR A1 - Vu-Bac, N. A1 - Lahmer, Tom A1 - Zhang, Yancheng A1 - Zhuang, Xiaoying A1 - Rabczuk, Timon T1 - Stochastic predictions of interfacial characteristic of polymeric nanocomposites (PNCs) JF - Composites Part B Engineering N2 - Stochastic predictions of interfacial characteristic of polymeric nanocomposites (PNCs) KW - Angewandte Mathematik KW - Stochastik KW - Strukturmechanik Y1 - 2014 SP - 80 EP - 95 ER - TY - JOUR A1 - Vu-Bac, N. A1 - Lahmer, Tom A1 - Keitel, Holger A1 - Zhao, Jun-Hua A1 - Zhuang, Xiaoying A1 - Rabczuk, Timon T1 - Stochastic predictions of bulk properties of amorphous polyethylene based on molecular dynamics simulations JF - Mechanics of Materials N2 - Stochastic predictions of bulk properties of amorphous polyethylene based on molecular dynamics simulations KW - Angewandte Mathematik KW - Stochastik KW - Strukturmechanik Y1 - 2014 SP - 70 EP - 84 ER - TY - CHAP A1 - Tan, Fengjie A1 - Lahmer, Tom A1 - Siddappa, Manju Gyaraganahalll ED - Gürlebeck, Klaus ED - Lahmer, Tom T1 - SECTION OPTIMIZATION AND RELIABILITY ANALYSIS OF ARCH-TYPE DAMS INCLUDING COUPLED MECHANICAL-THERMAL AND HYDRAULIC FIELDS T2 - Digital Proceedings, International Conference on the Applications of Computer Science and Mathematics in Architecture and Civil Engineering : July 20 - 22 2015, Bauhaus-University Weimar N2 - 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. KW - Angewandte Informatik KW - Angewandte Mathematik KW - Building Information Modeling KW - Computerunterstütztes Verfahren KW - Data, information and knowledge modeling in civil engineering; Function theoretic methods and PDE in engineering sciences; Mathematical methods for (robotics and) computer vision; Numerical modeling in engineering; Optimization in engineering applications Y1 - 2015 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:gbv:wim2-20170314-28212 SN - 1611-4086 ER - TY - CHAP A1 - Hartmann, Veronika A1 - Smarsly, Kay A1 - Lahmer, Tom ED - Gürlebeck, Klaus ED - Lahmer, Tom T1 - ROBUST SCHEDULING IN CONSTRUCTION ENGINEERING T2 - Digital Proceedings, International Conference on the Applications of Computer Science and Mathematics in Architecture and Civil Engineering : July 20 - 22 2015, Bauhaus-University Weimar N2 - 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. KW - Angewandte Informatik KW - Angewandte Mathematik KW - Building Information Modeling KW - Computerunterstütztes Verfahren KW - Data, information and knowledge modeling in civil engineering; Function theoretic methods and PDE in engineering sciences; Mathematical methods for (robotics and) computer vision; Numerical modeling in engineering; Optimization in engineering applications Y1 - 2015 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:gbv:wim2-20170314-27994 SN - 1611-4086 ER - TY - INPR A1 - Abbas, Tajammal A1 - Kavrakov, Igor A1 - Morgenthal, Guido A1 - Lahmer, Tom T1 - Prediction of aeroelastic response of bridge decks using artificial neural networks N2 - 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. KW - Aerodynamik KW - Artificial neural network KW - Ingenieurwissenschaften KW - Bridge KW - Bridge aerodynamics KW - Aerodynamic derivatives KW - Motion-induced forces KW - Bridges Y1 - 2020 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:gbv:wim2-20200225-40974 N1 - This is the pre-peer reviewed version of the following article: https://www.sciencedirect.com/science/article/abs/pii/S0045794920300018?via%3Dihub, https://doi.org/10.1016/j.compstruc.2020.106198 ER - TY - JOUR A1 - Hamdia, Khader A1 - Lahmer, Tom A1 - Nguyen-Thoi, T. A1 - Rabczuk, Timon T1 - Predicting The Fracture Toughness of PNCs: A Stochastic Approach Based on ANN and ANFIS JF - Computational Materials Science N2 - Predicting The Fracture Toughness of PNCs: A Stochastic Approach Based on ANN and ANFIS KW - Angewandte Mathematik KW - Stochastik KW - Strukturmechanik Y1 - 2015 SP - 304 EP - 313 ER - TY - JOUR A1 - Kaltenbacher, Barbara A1 - Lahmer, Tom A1 - Mohr, Marcus A1 - Kaltenbacher, Manfred T1 - PDE based determination of piezoelectric material tensors JF - European Journal of Applied Mathematics N2 - PDE based determination of piezoelectric material tensors. KW - Angewandte Mathematik KW - Stochastik KW - Strukturmechanik Y1 - 2006 U6 - http://dx.doi.org/10.25643/bauhaus-universitaet.3595 SP - 383 EP - 416 ER - TY - CHAP A1 - Nguyen-Tuan, Long A1 - Lahmer, Tom A1 - Datcheva, Maria A1 - Stoimenova, Eugenia A1 - Schanz, Tom ED - Gürlebeck, Klaus ED - Lahmer, Tom T1 - PARAMETER IDENTIFICATION APPLYING IN COMPLEX THERMO-HYDRO-MECHANICAL PROBLEMS LIKE THE DESIGN OF BUFFER ELEMENTS T2 - Digital Proceedings, International Conference on the Applications of Computer Science and Mathematics in Architecture and Civil Engineering : July 20 - 22 2015, Bauhaus-University Weimar N2 - 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. KW - Angewandte Informatik KW - Angewandte Mathematik KW - Building Information Modeling KW - Computerunterstütztes Verfahren KW - Data, information and knowledge modeling in civil engineering; Function theoretic methods and PDE in engineering sciences; Mathematical methods for (robotics and) computer vision; Numerical modeling in engineering; Optimization in engineering applications Y1 - 2015 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:gbv:wim2-20170314-28162 SN - 1611-4086 ER - TY - JOUR A1 - Lahmer, Tom A1 - Könke, Carsten A1 - Bettzieche, Volker T1 - Optimale Positionierung von Messeinrichtungen an Staumauern zur Bauwerksüberwachung JF - WASSERWIRTSCHAFT N2 - Optimale Positionierung von Messeinrichtungen an Staumauern zur Bauwerksüberwachung KW - Angewandte Mathematik KW - Stochastik KW - Strukturmechanik Y1 - 2010 SP - 16 EP - 16 ER - TY - JOUR A1 - Lahmer, Tom A1 - Könke, Carsten A1 - Bettzieche, Volker T1 - Optimal positioning of sensors for the monitoring of water dams JF - WASSERWIRTSCHAFT N2 - Optimal positioning of sensors for the monitoring of water dams KW - Angewandte Mathematik KW - Stochastik KW - Strukturmechanik Y1 - 2010 SP - 16 EP - 19 ER - TY - JOUR A1 - Lahmer, Tom A1 - Kaltenbacher, Barbara A1 - Schulz, V. T1 - Optimal measurement selection for piezoelectric material tensor identification JF - Inverse Problems in Science and Engineering N2 - Optimal measurement selection for piezoelectric material tensor identification. KW - Angewandte Mathematik KW - Stochastik KW - Strukturmechanik Y1 - 2008 U6 - http://dx.doi.org/10.25643/bauhaus-universitaet.3593 SP - 369 EP - 387 ER - TY - JOUR A1 - Lahmer, Tom T1 - Optimal experimental design for nonlinear ill-posed problems applied to gravity dams JF - Inverse Problems N2 - Optimal experimental design for nonlinear ill-posed problems applied to gravity dams KW - Angewandte Mathematik KW - Stochastik KW - Strukturmechanik Y1 - 2011 ER - TY - JOUR A1 - Nguyen-Tuan, Long A1 - Könke, Carsten A1 - Bettzieche, Volker A1 - Lahmer, Tom T1 - Numerical modeling and validation for 3D coupled-nonlinear thermo-hydro-mechanical problems in masonry dams JF - Computers & Structures N2 - Numerical modeling and validation for 3D coupled-nonlinear thermo-hydro-mechanical problems in masonry dams KW - Angewandte Mathematik KW - Stochastik KW - Strukturmechanik Y1 - 2017 SP - 143 EP - 154 ER - TY - JOUR A1 - Lahmer, Tom A1 - Bock, Sebastian A1 - Hildebrand, Jörg A1 - Gürlebeck, Klaus T1 - Non-destructive identification of residual stresses in steel under thermal loadings JF - Inverse Problems in Science and Engineering N2 - Non-destructive identification of residual stresses in steel under thermal loadings KW - Angewandte Mathematik KW - Stochastik KW - Strukturmechanik Y1 - 2016 SP - 1 EP - 17 ER - TY - JOUR A1 - Zhang, Chao A1 - Nanthakumar, S.S. A1 - Lahmer, Tom A1 - Rabczuk, Timon T1 - Multiple cracks identification for piezoelectric structures JF - International Journal of Fracture N2 - Multiple cracks identification for piezoelectric structures KW - Angewandte Mathematik KW - Stochastik KW - Strukturmechanik Y1 - 2017 SP - 1 EP - 19 ER - TY - JOUR A1 - Lahmer, Tom T1 - Modified Landweber iterations in a multilevel algorithm applied to inverse problems in piezoelectricity JF - Journal of Inverse and Ill-posed Problems N2 - Modified Landweber iterations in a multilevel algorithm applied to inverse problems in piezoelectricity KW - Angewandte Mathematik KW - Stochastik KW - Strukturmechanik Y1 - 2009 SP - 585 EP - 593 ER - TY - JOUR A1 - Harirchian, Ehsan A1 - Lahmer, Tom T1 - Improved Rapid Visual Earthquake Hazard Safety Evaluation of Existing Buildings Using a Type-2 Fuzzy Logic Model JF - Applied Sciences N2 - 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 Bingöl and Düzce earthquakes in Turkey. KW - Fuzzy-Logik KW - Erdbeben KW - Fuzzy Logic KW - Rapid Visual Screening KW - Vulnerability assessment KW - OA-Publikationsfonds2020 Y1 - 2020 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:gbv:wim2-20200331-41161 UR - https://www.mdpi.com/2076-3417/10/7/2375 VL - 2020 IS - Volume 10, Issue 3, 2375 PB - MDPI CY - Basel ER - TY - JOUR A1 - Achenbach, Marcus A1 - Lahmer, Tom A1 - Morgenthal, Guido T1 - 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 JF - Fire Safety Journal 87 N2 - 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. KW - Sensitivitätsanalyse KW - Thermodynamische Eigenschaft KW - Fire resistance; Parameter optimization; Sensitivity analysis; Thermal properties Y1 - 2017 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:gbv:wim2-20170331-30929 UR - http://www.sciencedirect.com/science/article/pii/S0379711216301965 SP - 80 EP - 86 ER - TY - JOUR A1 - Knabe, Tina A1 - Datcheva, Maria A1 - Lahmer, Tom A1 - Cotecchia, F. A1 - Schanz, Tom T1 - Identification of constitutive parameters of soil using an optimization strategy and statistical analysis JF - Computers and Geotechnics N2 - Identification of constitutive parameters of soil using an optimization strategy and statistical analysis KW - Angewandte Mathematik KW - Stochastik KW - Strukturmechanik Y1 - 2013 SP - 143 EP - 157 ER - TY - CHAP A1 - Lahmer, Tom ED - Gürlebeck, Klaus ED - Könke, Carsten T1 - HYDRO-MECHANICAL COUPLED FIELD SYSTEM IDENTIFICATION - APPLICATION TO WATER RESERVOIRS N2 - 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. KW - Angewandte Informatik KW - Angewandte Mathematik KW - Architektur KW - Computerunterstütztes Verfahren KW - Computer Science Models in Engineering; Multiscale and Multiphysical Models; Scientific Computing Y1 - 2010 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:gbv:wim2-20170314-28650 UR - http://euklid.bauing.uni-weimar.de/ikm2009/paper.html SN - 1611-4086 ER - TY - JOUR A1 - Achenbach, Marcus A1 - Lahmer, Tom A1 - Morgenthal, Guido T1 - Global Sensitivity Analysis of Reinforced Concrete Walls Subjected to Standard Fire - A Comparison of Methods JF - 14th International Probabilistic Workshop N2 - Global Sensitivity Analysis of Reinforced Concrete Walls Subjected to Standard Fire—A Comparison of Methods KW - Angewandte Mathematik KW - Stochastik KW - Strukturmechanik Y1 - 2017 SP - 97 EP - 106 ER - TY - JOUR A1 - Nguyen-Tuan, Long A1 - Lahmer, Tom A1 - Datcheva, Maria A1 - Schanz, Tom T1 - Global and local sensitivity analyses for coupled thermo‐hydro‐mechanical problems JF - International Journal for Numerical and Analytical Methods in Geomechanics N2 - Global and local sensitivity analyses for coupled thermo‐hydro‐mechanical problems KW - Angewandte Mathematik KW - Stochastik KW - Strukturmechanik Y1 - 2016 ER - TY - JOUR A1 - Lahmer, Tom T1 - FEM-Based determination of real and complex elastic, dielectric, and piezoelectric moduli in piezoceramic materials JF - IEEE Transactions on Ultrasonics, Ferroelectrics, and Frequency Control N2 - 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. KW - Finite-Elemente-Methode KW - Piezoelectric materials KW - Dielectric materials KW - Computational modeling KW - Frequency KW - Finite element methods KW - Manufacturing KW - Impedance measurement KW - Partial differential equations KW - Resonance KW - Resonanz Y1 - 2008 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:gbv:wim2-20171030-36083 ER - TY - JOUR A1 - Lahmer, Tom A1 - Kaltenbacher, Manfred A1 - Kaltenbacher, Barbara A1 - Lerch, Reinhard A1 - Leder, Erich T1 - Fem-based determination of real and complex elastic, dielectric, and piezoelectric moduli in piezoceramic materials JF - IEEE transactions on ultrasonics, ferroelectrics, and frequency control N2 - Fem-based determination of real and complex elastic, dielectric, and piezoelectric moduli in piezoceramic materials. KW - Angewandte Mathematik KW - Stochastik KW - Strukturmechanik Y1 - 2008 U6 - http://dx.doi.org/10.25643/bauhaus-universitaet.3594 ER - TY - JOUR A1 - Nguyen-Vinh, H. A1 - Bakar, I. A1 - Msekh, Mohammed Abdulrazzak A1 - Song, Jeong-Hoon A1 - Muthu, Jacob A1 - Zi, Goangseup A1 - Le, P. A1 - Bordas, Stéphane Pierre Alain A1 - Simpson, R. A1 - Natarajan, S. A1 - Lahmer, Tom A1 - Rabczuk, Timon T1 - Extended Finite Element Method for Dynamic Fracture of Piezo-Electric Materials JF - Engineering Fracture Mechanics N2 - 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. KW - Angewandte Mathematik KW - Stochastik KW - Strukturmechanik Y1 - 2012 U6 - http://dx.doi.org/10.1016/j.engfracmech.2012.04.025 SP - 19 EP - 31 ER - TY - JOUR A1 - Kumari, Vandana A1 - Harirchian, Ehsan A1 - Lahmer, Tom A1 - Rasulzade, Shahla T1 - Evaluation of Machine Learning and Web-Based Process for Damage Score Estimation of Existing Buildings JF - Buildings N2 - 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 KW - Maschinelles Lernen KW - rapid assessment KW - Machine learning KW - Vulnerability assessment KW - OA-Publikationsfonds2022 Y1 - 2022 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:gbv:wim2-20220509-46387 UR - https://www.mdpi.com/2075-5309/12/5/578 VL - 2022 IS - Volume 12, issue 5, article 578 SP - 1 EP - 23 PB - MDPI CY - Basel ER - TY - JOUR A1 - Keitel, Holger A1 - Karaki, Ghada A1 - Lahmer, Tom A1 - Nikulla, Susanne A1 - Zabel, Volkmar T1 - Evaluation of coupled partial models in structural engineering using graph theory and sensitivity analysis JF - Engineering structures N2 - Evaluation of coupled partial models in structural engineering using graph theory and sensitivity analysis KW - Angewandte Mathematik KW - Stochastik KW - Strukturmechanik Y1 - 2011 SP - 3726 EP - 3736 ER - TY - JOUR A1 - Hauck, A. A1 - Lahmer, Tom A1 - Kaltenbacher, Manfred T1 - Enhanced homogenization technique for magnetomechanical systems using the generalized finite element method JF - COMPEL: The international journal for computation and mathematics in electrical and electronic engineering N2 - Enhanced homogenization technique for magnetomechanical systems using the generalized finite element method KW - Angewandte Mathematik KW - Stochastik KW - Strukturmechanik Y1 - 2009 SP - 935 EP - 947 ER - TY - JOUR A1 - Alkam, Feras A1 - Lahmer, Tom T1 - Eigenfrequency-Based Bayesian Approach for Damage Identification in Catenary Poles JF - Infrastructures N2 - 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. KW - Fahrleitung KW - Schaden KW - Fahrleitungsmast KW - Schadenserkennung KW - vibration-based damage identification KW - Bayesian inference Y1 - 2021 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:gbv:wim2-20210510-44256 UR - https://www.mdpi.com/2412-3811/6/4/57 VL - 2021 IS - Volume 6, issue 4, article 57 SP - 1 EP - 19 PB - MDPI CY - Basel ER - TY - JOUR A1 - Schmidt, Albrecht A1 - Lahmer, Tom T1 - Efficient domain decomposition based reliability analysis for polymorphic uncertain material parameters JF - Proceedings in Applied Mathematics & Mechanics N2 - 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. KW - Polymorphie KW - Stoffeigenschaft KW - Stochastik KW - polymorphe Unschärfemodellierung KW - Materialverhalten KW - hybride Werkstoffe Y1 - 2021 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:gbv:wim2-20220112-45563 UR - https://onlinelibrary.wiley.com/doi/full/10.1002/pamm.202100014 VL - 2021 IS - Volume 21, issue 1 SP - 1 EP - 4 PB - Wiley-VHC CY - Weinheim ER - TY - JOUR A1 - Harirchian, Ehsan A1 - Lahmer, Tom A1 - Buddhiraju, Sreekanth A1 - Mohammad, Kifaytullah A1 - Mosavi, Amir T1 - Earthquake Safety Assessment of Buildings through Rapid Visual Screening JF - Buildings N2 - 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 Bingöl 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. KW - Maschinelles Lernen KW - Machine learning KW - Erdbeben KW - buildings KW - earthquake safety assessment KW - earthquake KW - extreme events KW - seismic assessment KW - natural hazard KW - mitigation KW - rapid visual screening Y1 - 2020 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:gbv:wim2-20200331-41153 UR - https://www.mdpi.com/2075-5309/10/3/51 VL - 2020 IS - Volume 10, Issue 3 PB - MDPI ER - TY - JOUR A1 - Harirchian, Ehsan A1 - Lahmer, Tom A1 - Rasulzade, Shahla T1 - Earthquake Hazard Safety Assessment of Existing Buildings Using Optimized Multi-Layer Perceptron Neural Network JF - Energies N2 - 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 Düzce 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. KW - Erdbeben KW - Maschinelles Lernen KW - earthquake damage KW - seismic vulnerability KW - artificial neural network KW - OA-Publikationsfonds2020 Y1 - 2020 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:gbv:wim2-20200504-41575 UR - https://www.mdpi.com/1996-1073/13/8/2060/htm VL - 2020 IS - Volume 13, Issue 8, 2060 PB - MDPI CY - Basel ER - TY - JOUR A1 - Nanthakumar, S.S. A1 - Lahmer, Tom A1 - Rabczuk, Timon T1 - Detection of multiple flaws in piezoelectric structures using XFEM and level sets JF - International Journal for Numerical Methods in Engineering N2 - Detection of multiple flaws in piezoelectric structures using XFEM and level sets KW - Angewandte Mathematik KW - Stochastik KW - Strukturmechanik Y1 - 2016 SP - 960 ER - TY - JOUR A1 - Nanthakumar, S.S. A1 - Lahmer, Tom A1 - Rabczuk, Timon T1 - Detection of multiple flaws in piezoelectric structures using XFEM and level sets JF - Computer Methods in Applied Mechanics and Engineering N2 - Detection of multiple flaws in piezoelectric structures using XFEM and level sets KW - Angewandte Mathematik KW - Stochastik KW - Strukturmechanik Y1 - 2014 SP - 98 EP - 112 ER - TY - JOUR A1 - Nanthakumar, S.S. A1 - Lahmer, Tom A1 - Zhuang, Xiaoying A1 - Zi, Goangseup A1 - Rabczuk, Timon T1 - Detection of material interfaces using a regularized level set method in piezoelectric structures JF - Inverse Problems in Science and Engineering N2 - Detection of material interfaces using a regularized level set method in piezoelectric structures KW - Angewandte Mathematik KW - Stochastik KW - Strukturmechanik Y1 - 2016 SP - 153 EP - 176 ER - TY - JOUR A1 - Nanthakumar, S.S. A1 - Lahmer, Tom A1 - Zhuang, Xiaoying A1 - Zi, Goangseup A1 - Rabczuk, Timon T1 - Detection of material interfaces using a regularized level set method in piezoelectric structures JF - Inverse Problems in Science and Engineering N2 - Detection of material interfaces using a regularized level set method in piezoelectric structures KW - Angewandte Mathematik KW - Stochastik KW - Strukturmechanik Y1 - 2015 ER - TY - JOUR A1 - Nanthakumar, S.S. A1 - Lahmer, Tom A1 - Rabczuk, Timon T1 - Detection of flaws in piezoelectric structures using extended FEM JF - International Journal for Numerical Methods in Engineering N2 - Detection of flaws in piezoelectric structures using extended FEM KW - Angewandte Mathematik KW - Stochastik KW - Strukturmechanik Y1 - 2013 SP - 373 EP - 389 ER - TY - JOUR A1 - Al-Yasiri, Zainab Riyadh Shaker A1 - Mutashar, Hayder Majid A1 - Gürlebeck, Klaus A1 - Lahmer, Tom ED - Shafiullah, GM T1 - Damage Sensitive Signals for the Assessment of the Conditions of Wind Turbine Rotor Blades Using Electromagnetic Waves JF - Infrastructures N2 - 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. KW - Windkraftwerk KW - Rotorblatt KW - Elektrostatische Welle KW - MATLAB KW - wind turbine rotor blades KW - electromagnetic waves KW - crack detection KW - Empire XPU 8.01 KW - Matlab KW - OA-Publikationsfonds2022 Y1 - 2022 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:gbv:wim2-20220831-47093 UR - https://www.mdpi.com/2412-3811/7/8/104 VL - 2022 IS - Volume 7, Issue 8 (August 2022), article 104 PB - MDPI CY - Basel ER -