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
OPUS4-2993 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
OPUS4-2873 Konferenzveröffentlichung Most, Thomas Gürlebeck, Klaus; Könke, Carsten ESTIMATING UNCERTAINTIES FROM INACCURATE MEASUREMENT DATA USING MAXIMUM ENTROPY DISTRIBUTIONS Modern engineering design often considers uncertainties in geometrical and material parameters and in the loading conditions. Based on initial assumptions on the stochastic properties as mean values, standard deviations and the distribution functions of these uncertain parameters a probabilistic analysis is carried out. In many application fields probabilities of the exceedance of failure criteria are computed. The out-coming failure probability is strongly dependent on the initial assumptions on the random variable properties. Measurements are always more or less inaccurate data due to varying environmental conditions during the measurement procedure. Furthermore the estimation of stochastic properties from a limited number of realisation also causes uncertainties in these quantities. Thus the assumption of exactly known stochastic properties by neglecting these uncertainties may not lead to very useful probabilistic measures in a design process. In this paper we assume the stochastic properties of a random variable as uncertain quantities caused by so-called epistemic uncertainties. Instead of predefined distribution types we use the maximum entropy distribution which enables the description of a wide range of distribution functions based on the first four stochastic moments. These moments are taken again as random variables to model the epistemic scatter in the stochastic assumptions. The main point of this paper is the discussion on the estimation of these uncertain stochastic properties based on inaccurate measurements. We investigate the bootstrap algorithm for its applicability to quantify the uncertainties in the stochastic properties considering imprecise measurement data. Based on the obtained estimates we apply standard stochastic analysis on a simple example to demonstrate the difference and the necessity of the proposed approach. 14 urn:nbn:de:gbv:wim2-20170314-28732 10.25643/bauhaus-universitaet.2873 Graduiertenkolleg 1462
OPUS4-3453 Konferenzveröffentlichung Most, Thomas An adaptive response surface approach for structural reliability analyses based on support vector machines An adaptive response surface approach for structural reliability analyses based on support vector machines 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
OPUS4-3510 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
OPUS4-3521 Konferenzveröffentlichung Most, Thomas Anwendung netzfreier Diskretisierungsverfahren zur stochastischen Rissfortschrittsberechnung Anwendung netzfreier Diskretisierungsverfahren zur stochastischen Rissfortschrittsberechnung Institut für Strukturmechanik
OPUS4-3516 Konferenzveröffentlichung Brehm, Maik; Most, Thomas A four-node plane EAS-element for stochastic nonlinear materials A four-node plane EAS-element for stochastic nonlinear materials Institut für Strukturmechanik
OPUS4-3437 Konferenzveröffentlichung Most, Thomas An adaptive response surface approach for reliability analyses of high-dimensional problems An adaptive response surface approach for reliability analyses of high-dimensional problems Institut für Strukturmechanik
OPUS4-3455 Konferenzveröffentlichung Most, Thomas; Hofstetter, G.; Hofmann, Markus; Novák, D.; Lehký, D. Approximation of constitutive parameters for material models using artificial neural networks Approximation of constitutive parameters for material models using artificial neural networks Institut für Strukturmechanik
OPUS4-3443 Wissenschaftlicher Artikel Most, Thomas A natural neighbour-based moving least-squares approach for the element-free Galerkin method A natural neighbour-based moving least-squares approach for the element-free Galerkin method 28 International Journal for Numerical Methods in Engineering 224 252 Institut für Strukturmechanik
OPUS4-282 Konferenzveröffentlichung Brehm, Maik; Most, Thomas A Four-Node Plane EAS-Element for Stochastic Nonlinear Materials Iso-parametric finite elements with linear shape functions show in general a too stiff element behavior, called locking. By the investigation of structural parts under bending loading the so-called shear locking appears, because these elements can not reproduce pure bending modes. Many studies dealt with the locking problem and a number of methods to avoid the undesirable effects have been developed. Two well known methods are the >Assumed Natural Strain< (ANS) method and the >Enhanced Assumed Strain< (EAS) method. In this study the EAS method is applied to a four-node plane element with four EAS-parameters. The paper will describe the well-known linear formulation, its extension to nonlinear materials and the modeling of material uncertainties with random fields. For nonlinear material behavior the EAS parameters can not be determined directly. Here the problem is solved by using an internal iteration at the element level, which is much more efficient and stable than the determination via a global iteration. To verify the deterministic element behavior the results of common test examples are presented for linear and nonlinear materials. The modeling of material uncertainties is done by point-discretized random fields. To show the applicability of the element for stochastic finite element calculations Latin Hypercube Sampling was applied to investigate the stochastic hardening behavior of a cantilever beam with nonlinear material. The enhanced linear element can be applied as an alternative to higher-order finite elements where more nodes are necessary. The presented element formulation can be used in a similar manner to improve stochastic linear solid elements. 2003 urn:nbn:de:gbv:wim2-20111215-2825 10.25643/bauhaus-universitaet.282 Professur Informatik im Bauwesen
OPUS4-3412 Wissenschaftlicher Artikel Most, Thomas; Ishii, H.; Geng, X.; Bolzern, P.; Colaneri, P.; De Nicolao, G. Discussion on Almost sure stability of stochastic linear systems with ergodic parameters Discussion on Almost sure stability of stochastic linear systems with ergodic parameters 6 European Journal of Control 124 130 Institut für Strukturmechanik
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
OPUS4-3445 Wissenschaftlicher Artikel Most, Thomas; Bucher, Christian Energy-based simulation of concrete cracking using an improved mixed-mode cohesive crack model within a meshless discretization Energy-based simulation of concrete cracking using an improved mixed-mode cohesive crack model within a meshless discretization 20 International Journal for Numerical and Analytical Methods in Geomechanics 285 305 Institut für Strukturmechanik
OPUS4-3499 Konferenzveröffentlichung Most, Thomas; Unger, Jörg F.; Bucher, Christian Stochastic crack growth simulation in R/C structures by means of meshless methods Stochastic crack growth simulation in R/C structures by means of meshless methods Institut für Strukturmechanik
OPUS4-3484 Wissenschaftlicher Artikel Most, Thomas; Bucher, Christian A moving least squares weighting function for the element-free Galerkin method which almost fulfills essential boundary conditions A moving least squares weighting function for the element-free Galerkin method which almost fulfills essential boundary conditions 17 Structural Engineering and Mechanics 315 332 Institut für Strukturmechanik
OPUS4-3535 Konferenzveröffentlichung Most, Thomas; Bucher, Christian Stochastic dynamic stability analysis for nonlinear structures Stochastic dynamic stability analysis for nonlinear structures Institut für Strukturmechanik
OPUS4-3508 Konferenzveröffentlichung Most, Thomas; Unger, Jörg F.; Bucher, Christian Stochastic modeling of cohesive crack propagation using meshless discretization techniques Stochastic modeling of cohesive crack propagation using meshless discretization techniques Institut für Strukturmechanik
OPUS4-3509 Konferenzveröffentlichung Most, Thomas; Bucher, Christian Stochastic modeling of cohesive crack evolution in concrete using meshless interpolation techniques Stochastic modeling of cohesive crack evolution in concrete using meshless interpolation techniques Institut für Strukturmechanik
OPUS4-3462 Wissenschaftlicher Artikel Most, Thomas; Bucher, Christian Stochastic simulation of cracking in concrete structures using multi-parameter random fields Stochastic simulation of cracking in concrete structures using multi-parameter random fields 19 International Journal of Reliability and Safety 168 187 Institut für Strukturmechanik
OPUS4-3444 Wissenschaftlicher Artikel Most, Thomas; Bucher, Christian Probabilistic analysis of concrete cracking using neural networks and random fields Probabilistic analysis of concrete cracking using neural networks and random fields 10 Probabilistic Engineering Mechanics 219 229 Institut für Strukturmechanik
OPUS4-3514 Wissenschaftlicher Artikel Kirichuk, A.; Most, Thomas; Bucher, Christian Numerical nonlinear analysis of kinematically excited shells Numerical nonlinear analysis of kinematically excited shells 13 International Journal for Computational Civil and Structural Engineering 61 74 Institut für Strukturmechanik
OPUS4-3549 Konferenzveröffentlichung Schorling, York; Most, Thomas; Bucher, Christian Stability Analysis for Imperfect Systems with Random Loading Stability Analysis for Imperfect Systems with Random Loading Institut für Strukturmechanik
OPUS4-2994 Konferenzveröffentlichung Most, Thomas; Bucher, Christian; Macke, M. Gürlebeck, Klaus; Könke, Carsten A NATURAL NEIGHBOR BASED MOVING LEAST SQUARES APPROACH WITH INTERPOLATING WEIGHTING FUNCTION The Element-free Galerkin Method has become a very popular tool for the simulation of mechanical problems with moving boundaries. The internally applied Moving Least Squares approximation uses in general Gaussian or cubic weighting functions and has compact support. Due to the approximative character of this method the obtained shape functions do not fulfill the interpolation condition, which causes additional numerical effort for the imposition of the essential boundary conditions. The application of a singular weighting function, which leads to singular coefficient matrices at the nodes, can solve this problem, but requires a very careful placement of the integration points. Special procedures for the handling of such singular matrices were proposed in literature, which require additional numerical effort. In this paper a non-singular weighting function is presented, which leads to an exact fulfillment of the interpolation condition. This weighting function leads to regular values of the weights and the coefficient matrices in the whole interpolation domain even at the nodes. Furthermore this function gives much more stable results for varying size of the influence radius and for strongly distorted nodal arrangements than classical weighting function types. Nevertheless, for practical applications the results are similar as these obtained with the regularized weighting type presented by the authors in previous publications. Finally a new concept will be presented, which enables an efficient analysis of systems with strongly varying node density. In this concept the nodal influence domains are adapted depending on the nodal configuration by interpolating the influence radius for each direction from the distances to the natural neighbor nodes. This approach requires a Voronoi diagram of the domain, which is available in this study since Delaunay triangles are used as integration background cells. In the numerical examples it will be shown, that this method leads to a more uniform and reduced number of influencing nodes for systems with varying node density than the classical circular influence domains, which means that the small additional numerical effort for interpolating the influence radius leads to remarkable reduction of the total numerical cost in a linear analysis while obtaining similar results. For nonlinear calculations this advantage would be even more significant. 17 urn:nbn:de:gbv:wim2-20170327-29943 10.25643/bauhaus-universitaet.2994 Institut für Strukturmechanik
OPUS4-3502 Wissenschaftlicher Artikel Most, Thomas; Bucher, Christian; Schorling, York Dynamic stability analysis of non-linear structures with geometrical imperfections under random loading Dynamic stability analysis of non-linear structures with geometrical imperfections under random loading 19 Journal of Sound and Vibration 381 400 Institut für Strukturmechanik
OPUS4-3408 Wissenschaftlicher Artikel Bucher, Christian; Most, Thomas A comparison of approximate response functions in structural reliability analysis A comparison of approximate response functions in structural reliability analysis 9 Probabilistic Engineering Mechanics 154 163 Institut für Strukturmechanik
OPUS4-3498 Konferenzveröffentlichung Most, Thomas; Bucher, Christian Mixed mode crack simulation using Virtual Crack Extension and a normal/shear cohesive crack model within a meshless discretization Mixed mode crack simulation using Virtual Crack Extension and a normal/shear cohesive crack model within a meshless discretization Institut für Strukturmechanik
OPUS4-3476 Konferenzveröffentlichung Most, Thomas; Bucher, Christian Adaptive response surface approach using artificial neural networks and Moving Least Squares Adaptive response surface approach using artificial neural networks and Moving Least Squares Institut für Strukturmechanik
OPUS4-3523 Konferenzveröffentlichung Most, Thomas; Bucher, Christian Moving Least Squares-elements for stochastic crack propagation simulations coupled with stochastic finite elements Moving Least Squares-elements for stochastic crack propagation simulations coupled with stochastic finite elements Institut für Strukturmechanik
OPUS4-335 Konferenzveröffentlichung Most, Thomas; Bucher, Christian Application of the "fictious crack model" to meshless crack growth simulations In this paper a meshless component is presented, which internally uses the common meshless interpolation technique >Moving Least Squares<. In contrast to usual meshless integration schemes like the cell quadrature and the nodal integration in this study integration zones with triangular geometry spanned by three nodes are used for 2D analysis. The boundary of the structure is defined by boundary nodes, which are similar to finite element nodes. By using the neighborhood relations of the integration zones an efficient search algorithm to detected the nodes in the influence of the integration points was developed. The components are directly coupled with finite elements by using a penalty method. An widely accepted model to describe the fracture behavior of concrete is the >Fictitious Crack Model< which is applied in this study, which differentiates between micro cracks and macro cracks, with and without force transmission over the crack surface, respectively. In this study the crack surface is discretized by node pairs in form of a polygon, which is part of the boundary. To apply the >Fictitious Crack Model< finite interface elements are included between the crack surface nodes. The determination of the maximum principal strain at the crack tip is done by introducing an influence area around the singularity. On a practical example it is shown that the included elements improve the model by the transmission of the surface forces during monotonic loading and by the representation of the contact forces of closed cracks during reverse loading. 2003 urn:nbn:de:gbv:wim2-20111215-3359 10.25643/bauhaus-universitaet.335 Professur Informatik im Bauwesen
OPUS4-2992 Konferenzveröffentlichung Most, Thomas; Bucher, Christian Gürlebeck, Klaus; Könke, Carsten ADAPTIVE RESPONSE SURFACE APPROACH USING ARTIFICIAL NEURAL NETWORKS AND MOVING LEAST SQUARES In engineering science the modeling and numerical analysis of complex systems and relations plays an important role. In order to realize such an investigation, for example a stochastic analysis, in a reasonable computational time, approximation procedure have been developed. A very famous approach is the response surface method, where the relation between input and output quantities is represented for example by global polynomials or local interpolation schemes as Moving Least Squares (MLS). In recent years artificial neural networks (ANN) have been applied as well for such purposes. Recently an adaptive response surface approach for reliability analyses was proposed, which is very efficient concerning the number of expensive limit state function evaluations. Due to the applied simplex interpolation the procedure is limited to small dimensions. In this paper this approach is extended for larger dimensions using combined ANN and MLS response surfaces for evaluating the adaptation criterion with only one set of joined limit state points. As adaptation criterion a combination by using the maximum difference in the conditional probabilities of failure and the maximum difference in the approximated radii is applied. Compared to response surfaces on directional samples or to plain directional sampling the failure probability can be estimated with a much smaller number of limit state points. 13 urn:nbn:de:gbv:wim2-20170327-29922 10.25643/bauhaus-universitaet.2992 Institut für Strukturmechanik
OPUS4-3475 Konferenzveröffentlichung Most, Thomas; Bucher, Christian Application of an adaptive response surface approach for efficient structural reliability analysis Application of an adaptive response surface approach for efficient structural reliability analysis Institut für Strukturmechanik
OPUS4-3465 Konferenzveröffentlichung Bucher, Christian; Most, Thomas Application of approximate response functions in structural reliability analysis Application of approximate response functions in structural reliability analysis Institut für Strukturmechanik
OPUS4-3497 Konferenzveröffentlichung Most, Thomas; Bucher, Christian Stochastic dynamic stability analysis of shell structures Stochastic dynamic stability analysis of shell structures Institut für Strukturmechanik
OPUS4-3411 Wissenschaftlicher Artikel Most, Thomas; Bucher, Christian New concepts for moving least squares: An interpolating non-singular weighting function and weighted nodal least squares New concepts for moving least squares: An interpolating non-singular weighting function and weighted nodal least squares 9 Engineering Analysis with Boundary Elements 461 470 Institut für Strukturmechanik
OPUS4-3477 Konferenzveröffentlichung Most, Thomas; Bucher, Christian An enhanced moving least squares interpolation for the element-free Galerkin method An enhanced moving least squares interpolation for the element-free Galerkin method Institut für Strukturmechanik
OPUS4-3522 Konferenzveröffentlichung Most, Thomas; Bucher, Christian Application of the "Fictitious Crack Model" to meshless crack growth simulations Application of the "Fictitious Crack Model" to meshless crack growth simulations Institut für Strukturmechanik
OPUS4-3511 Konferenzveröffentlichung Unger, Jörg F.; Most, Thomas; Bucher, Christian; Könke, Carsten Adaptation of the natural element method for crack growth simulations Adaptation of the natural element method for crack growth simulations Institut für Strukturmechanik
OPUS4-725 Dissertation Most, Thomas Stochastic crack growth simulation in reinforced concrete structures by means of coupled finite element and meshless methods The complex failure process of concrete structures can not be described in detail by standard engineering design formulas. The numerical analysis of crack development in concrete is essential for several problems. In the last decades a large number of research groups have dealt with this topic and several models and algorithms were developed. However, most of these methods show some difficulties and are limited to special cases. The goal of this study was to develop an automatic algorithm for the efficient simulation of multiple cracking in plain and reinforced concrete structures of medium size. For this purpose meshless methods were used to describe the growth of crack surfaces. Two meshless interpolation schemes were improved for a simple application. The cracking process of concrete has been modeled using a stable criterion for crack growth in combination with an improved cohesive crack model which can represent the failure process under combined crack opening and crack sliding very well. This crack growth algorithm was extended in order to represent the fluctuations of the concrete properties by enlarging the single-parameter random field concept for multiple correlated material parameters. 2005 Stochastische Rissfortschrittsberechnung in bewehrten Betonstrukturen unter Kopplung der Finiten Elemente Methode mit netzfreien Verfahren urn:nbn:de:gbv:wim2-20051219-7623 10.25643/bauhaus-universitaet.725 Professur Baumechanik
OPUS4-3454 Konferenzveröffentlichung Most, Thomas; Bucher, Christian Adaptive response surface approach for reliability analysis using advanced meta-models Adaptive response surface approach for reliability analysis using advanced meta-models Institut für Strukturmechanik