Dokument-ID Dokumenttyp Verfasser/Autoren Herausgeber Haupttitel Abstract Auflage Verlagsort Verlag Erscheinungsjahr Seitenzahl Schriftenreihe Titel Schriftenreihe Bandzahl ISBN Quelle der Hochschulschrift Konferenzname Quelle:Titel Quelle:Jahrgang Quelle:Heftnummer Quelle:Erste Seite Quelle:Letzte Seite URN DOI Abteilungen
OPUS4-301 Konferenzveröffentlichung Häfner, Stefan; Eckardt, Stefan; Könke, Carsten A geometrical inclusion-matrix model for the finite element analysis of concrete at multiple scales This paper introduces a method to generate adequate inclusion-matrix geometries of concrete in two and three dimensions, which are independent of any specific numerical discretization. The article starts with an analysis on shapes of natural aggregates and discusses corresponding mathematical realizations. As a first prototype a two-dimensional generation of a mesoscale model is introduced. Particle size distribution functions are analysed and prepared for simulating an adequate three-dimensional representation of the aggregates within a concrete structure. A sample geometry of a three-dimensional test cube is generated and the finite element analysis of its heterogeneous geometry by a uniform mesh is presented. Concluding, aspects of a multiscale analysis are discussed and possible enhancements are proposed. 2003 urn:nbn:de:gbv:wim2-20111215-3018 10.25643/bauhaus-universitaet.301 Professur Informatik im Bauwesen
OPUS4-259 Wissenschaftlicher Artikel Most, Thomas; Eckardt, Stefan Application of a hybrid parallelization technique to accelerate the numerical simulation of nonlinear mechanical problems This paper presents the combination of two different parallelization environments, OpenMP and MPI, in one numerical simulation tool. The computation of the system matrices and vectors is parallelized with OpenMP and the solution of the system of equations is done with the MPIbased solver MUMPS. The efficiency of both algorithms is shown on several linear and nonlinear examples using the Finite Element Method and a meshless discretization technique. 2004 urn:nbn:de:gbv:wim2-20111215-2599 10.25643/bauhaus-universitaet.259 Professur Informatik im Bauwesen
OPUS4-1416 Dissertation Eckardt, Stefan Adaptive heterogeneous multiscale models for the nonlinear simulation of concrete The nonlinear behavior of concrete can be attributed to the propagation of microcracks within the heterogeneous internal material structure. In this thesis, a mesoscale model is developed which allows for the explicit simulation of these microcracks. Consequently, the actual physical phenomena causing the complex nonlinear macroscopic behavior of concrete can be represented using rather simple material formulations. On the mesoscale, the numerical model explicitly resolves the components of the internal material structure. For concrete, a three-phase model consisting of aggregates, mortar matrix and interfacial transition zone is proposed. Based on prescribed grading curves, an efficient algorithm for the generation of three-dimensional aggregate distributions using ellipsoids is presented. In the numerical model, tensile failure of the mortar matrix is described using a continuum damage approach. In order to reduce spurious mesh sensitivities, introduced by the softening behavior of the matrix material, nonlocal integral-type material formulations are applied. The propagation of cracks at the interface between aggregates and mortar matrix is represented in a discrete way using a cohesive crack approach. The iterative solution procedure is stabilized using a new path following constraint within the framework of load-displacement-constraint methods which allows for an efficient representation of snap-back phenomena. In several examples, the influence of the randomly generated heterogeneous material structure on the stochastic scatter of the results is analyzed. Furthermore, the ability of mesoscale models to represent size effects is investigated. Mesoscale simulations require the discretization of the internal material structure. Compared to simulations on the macroscale, the numerical effort and the memory demand increases dramatically. Due to the complexity of the numerical model, mesoscale simulations are, in general, limited to small specimens. In this thesis, an adaptive heterogeneous multiscale approach is presented which allows for the incorporation of mesoscale models within nonlinear simulations of concrete structures. In heterogeneous multiscale models, only critical regions, i.e. regions in which damage develops, are resolved on the mesoscale, whereas undamaged or sparsely damage regions are modeled on the macroscale. A crucial point in simulations with heterogeneous multiscale models is the coupling of sub-domains discretized on different length scales. The sub-domains differ not only in the size of the finite elements but also in the constitutive description. In this thesis, different methods for the coupling of non-matching discretizations - constraint equations, the mortar method and the arlequin method - are investigated and the application to heterogeneous multiscale models is presented. Another important point is the detection of critical regions. An adaptive solution procedure allowing the transfer of macroscale sub-domains to the mesoscale is proposed. In this context, several indicators which trigger the model adaptation are introduced. Finally, the application of the proposed adaptive heterogeneous multiscale approach in nonlinear simulations of concrete structures is presented. 2009 Adaptive heterogene Mehrskalenmodelle zur nichtlinearen Simulation von Beton urn:nbn:de:gbv:wim2-20100317-15023 10.25643/bauhaus-universitaet.1416 Institut für Strukturmechanik
OPUS4-3404 Wissenschaftlicher Artikel Könke, Carsten; Eckardt, Stefan; Häfner, Stefan; Luther, Torsten; Unger, Jörg F. Multiscale simulation methods in damage prediction of brittle and ductile materials Multiscale simulation methods in damage prediction of brittle and ductile materials 19 International Journal for Multiscale Computational Engineering 17 36 Institut für Strukturmechanik
OPUS4-3409 Wissenschaftlicher Artikel Eckardt, Stefan; Könke, Carsten Adaptive damage simulation of concrete using heterogeneous multiscale models Adaptive damage simulation of concrete using heterogeneous multiscale models 22 Journal of Algorithms & Computational Technology 275 297 Institut für Strukturmechanik
OPUS4-3478 Konferenzveröffentlichung Most, Thomas; Eckardt, Stefan; Schrader, Kai; Deckner, T. An improved cohesive crack model for combined crack opening and sliding under cyclic loading An improved cohesive crack model for combined crack opening and sliding under cyclic loading Institut für Strukturmechanik
OPUS4-3482 Wissenschaftlicher Artikel Bruhin, R.; Stock, U.A.; Drücker, J.-P.; Azhari, T.; Wippermann, J.; Albes, J.M.; Hintze, D.; Eckardt, Stefan; Könke, Carsten; Wahlers, T. Numerical simulation techniques to study the structural response of the human chest following median sternotomy Numerical simulation techniques to study the structural response of the human chest following median sternotomy 7 The Annals of Thoracic Surgery 623 630 Institut für Strukturmechanik
OPUS4-3446 Wissenschaftlicher Artikel Unger, Jörg F.; Eckardt, Stefan; Könke, Carsten Modelling of cohesive crack growth in concrete structures with the extended finite element method Modelling of cohesive crack growth in concrete structures with the extended finite element method 13 Computer Methods in Applied Mechanics and Engineering 4087 4100 Institut für Strukturmechanik
OPUS4-3448 Konferenzveröffentlichung Eckardt, Stefan; Könke, Carsten Coupling techniques for heterogeneous multiscale models of concrete Coupling techniques for heterogeneous multiscale models of concrete Institut für Strukturmechanik
OPUS4-3460 Wissenschaftlicher Artikel Häfner, Stefan; Eckardt, Stefan; Luther, Torsten; Könke, Carsten Mesoscale modeling of concrete: Geometry and numerics Mesoscale modeling of concrete: Geometry and numerics 11 Computers and Structures 450 461 Institut für Strukturmechanik
OPUS4-3491 Konferenzveröffentlichung Eckardt, Stefan; Könke, Carsten Damage simulation of concrete on the mesoscale Damage simulation of concrete on the mesoscale Institut für Strukturmechanik
OPUS4-3494 Konferenzveröffentlichung Könke, Carsten; Eckardt, Stefan; Häfner, Stefan; Luther, Torsten; Unger, Jörg F. Schädigungs- und Verbundmodellierung für Stahlbetontragwerke Schädigungs- und Verbundmodellierung für Stahlbetontragwerke Institut für Strukturmechanik
OPUS4-3471 Konferenzveröffentlichung Könke, Carsten; Eckardt, Stefan; Häfner, Stefan Spatial and temporal multiscale simulations of damage processes for concrete Spatial and temporal multiscale simulations of damage processes for concrete Institut für Strukturmechanik
OPUS4-3510 Konferenzveröffentlichung Most, Thomas; Eckardt, Stefan Application of a hybrid parallelisation technique to accelerate the numerical simulation of nonlinear mechanical problems Application of a hybrid parallelisation technique to accelerate the numerical simulation of nonlinear mechanical problems Institut für Strukturmechanik
OPUS4-3500 Konferenzveröffentlichung Unger, Jörg F.; Eckardt, Stefan; Könke, Carsten Numerical Models for the simulation of concrete on the mesoscale Numerical Models for the simulation of concrete on the mesoscale Institut für Strukturmechanik
OPUS4-3506 Konferenzveröffentlichung Eckardt, Stefan; Häfner, Stefan; Könke, Carsten Simulation of the fracture behaviour of concrete using continuum damage models at the mesoscale Simulation of the fracture behaviour of concrete using continuum damage models at the mesoscale Institut für Strukturmechanik
OPUS4-2947 Konferenzveröffentlichung Eckardt, Stefan; Könke, Carsten Gürlebeck, Klaus; Könke, Carsten ADAPTIVE SIMULATION OF THE DAMAGE BEHAVIOR OF CONCRETE USING HETEROGENEOUS MULTISCALE MODELS In this paper an adaptive heterogeneous multiscale model, which couples two substructures with different length scales into one numerical model is introduced for the simulation of damage in concrete. In the presented approach the initiation, propagation and coalescence of microcracks is simulated using a mesoscale model, which explicitly represents the heterogeneous material structure of concrete. The mesoscale model is restricted to the damaged parts of the structure, whereas the undamaged regions are simulated on the macroscale. As a result an adaptive enlargement of the mesoscale model during the simulation is necessary. In the first part of the paper the generation of the heterogeneous mesoscopic structure of concrete, the finite element discretization of the mesoscale model, the applied isotropic damage model and the cohesive zone model are briefly introduced. Furthermore the mesoscale simulation of a uniaxial tension test of a concrete prism is presented and own obtained numerical results are compared to experimental results. The second part is focused on the adaptive heterogeneous multiscale approach. Indicators for the model adaptation and for the coupling between the different numerical models will be introduced. The transfer from the macroscale to the mesoscale and the adaptive enlargement of the mesoscale substructure will be presented in detail. A nonlinear simulation of a realistic structure using an adaptive heterogeneous multiscale model is presented at the end of the paper to show the applicability of the proposed approach to large-scale structures. 15 urn:nbn:de:gbv:wim2-20170327-29478 10.25643/bauhaus-universitaet.2947 Institut für Strukturmechanik
OPUS4-2993 Konferenzveröffentlichung Most, Thomas; Eckardt, Stefan; Schrader, Kai; Deckner, T. Gürlebeck, Klaus; Könke, Carsten AN IMPROVED COHESIVE CRACK MODEL FOR COMBINED CRACK OPENING AND SLIDING UNDER CYCLIC LOADING The modeling of crack propagation in plain and reinforced concrete structures is still a field for many researchers. If a macroscopic description of the cohesive cracking process of concrete is applied, generally the Fictitious Crack Model is utilized, where a force transmission over micro cracks is assumed. In the most applications of this concept the cohesive model represents the relation between the normal crack opening and the normal stress, which is mostly defined as an exponential softening function, independently from the shear stresses in tangential direction. The cohesive forces are then calculated only from the normal stresses. By Carol et al. 1997 an improved model was developed using a coupled relation between the normal and shear damage based on an elasto-plastic constitutive formulation. This model is based on a hyperbolic yield surface depending on the normal and the shear stresses and on the tensile and shear strength. This model also represents the effect of shear traction induced crack opening. Due to the elasto-plastic formulation, where the inelastic crack opening is represented by plastic strains, this model is limited for applications with monotonic loading. In order to enable the application for cases with un- and reloading the existing model is extended in this study using a combined plastic-damage formulation, which enables the modeling of crack opening and crack closure. Furthermore the corresponding algorithmic implementation using a return mapping approach is presented and the model is verified by means of several numerical examples. Finally an investigation concerning the identification of the model parameters by means of neural networks is presented. In this analysis an inverse approximation of the model parameters is performed by using a given set of points of the load displacement curves as input values and the model parameters as output terms. It will be shown, that the elasto-plastic model parameters could be identified well with this approach, but require a huge number of simulations. 20 urn:nbn:de:gbv:wim2-20170327-29933 10.25643/bauhaus-universitaet.2993 Institut für Strukturmechanik
OPUS4-2841 Konferenzveröffentlichung Eckardt, Stefan; Könke, Carsten Gürlebeck, Klaus; Könke, Carsten ENERGY RELEASE CONTROL FOR NONLINEAR MESOSCALE SIMULATIONS In nonlinear simulations the loading is, in general, applied in an incremental way. Path-following algorithms are used to trace the equilibrium path during the failure process. Standard displacement controlled solution strategies fail if snap-back phenomena occur. In this contribution, a path-following algorithm based on the dissipation of the inelastic energy is presented which allows for the simulation of snap-backs. Since the constraint is defined in terms of the internal energy, the algorithm is not restricted to continuum damage models. Furthermore, no a priori knowledge about the final damage distribution is required. The performance of the proposed algorithm is illustrated using nonlinear mesoscale simulations. 5 urn:nbn:de:gbv:wim2-20170314-28414 10.25643/bauhaus-universitaet.2841 Institut für Strukturmechanik