TY  - CHAP
A1  - Most, Thomas
A1  - Bucher, Christian
ED  - Gürlebeck, Klaus
ED  - Könke, Carsten
T1  - ADAPTIVE RESPONSE SURFACE APPROACH USING ARTIFICIAL NEURAL NETWORKS AND MOVING LEAST SQUARES
N2  - 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.
KW  - Architektur <Informatik>
KW  - CAD
KW  - Computerunterstütztes Verfahren
Y1  - 2006
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:gbv:wim2-20170327-29922
UR  - http://euklid.bauing.uni-weimar.de/ikm2006/index.php_lang=de&what=papers.html
ER  - 
TY  - JOUR
A1  - Most, Thomas
A1  - Bucher, Christian
T1  - A moving least squares weighting function for the element-free Galerkin method which almost fulfills essential boundary conditions
JF  - Structural Engineering and Mechanics
N2  - A moving least squares weighting function for the element-free Galerkin method which almost fulfills essential boundary conditions
KW  - Angewandte Mathematik
KW  - Strukturmechanik
Y1  - 2005
SP  - 315
EP  - 332
ER  - 
TY  - THES
A1  - Most, Thomas
T1  - Stochastic crack growth simulation in reinforced concrete structures by means of coupled finite element and meshless methods
N2  - 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.
N2  - Das komplexe Versagensverhalten von Betonstrukturen kann in der Regel nicht mit Standardbemessungsformeln beschrieben werden. Eine detaillierte numerische Analyse der Rissentwicklung in Beton ist für einige Problemstellungen unverzichtbar. In den letzten Jahrzehnten haben sich eine Vielzahl von Forschergruppen mit dieser Thematik aus-einandergesetzt. Dabei wurden verschiedene Modelle und Algorithmen entwickelt. Die meisten dieser Verfahren weisen jedoch verschiedene Probleme auf oder sind nur für Spezialfälle anwendbar. Das Ziel dieser Arbeit war die Entwicklung eines automatischen Algorithmus zur effizienten Simulation von mehrfacher Rissentwicklung in Beton- und Stahlbetonstrukturen mittlerer Größe. Dabei wurden netzfreie Verfahren angewendet, um die Änderung der Rissoberflächen abzubilden. Zwei netzfreie Interpolationstypen wurden im Hinblick auf eine unkomplizierte Anwendung angepaßt. Der Versagensprozess des Betons wurde mit Hilfe eines stabilen Risskriteriums in Kombination mit einem erwei-terten kohäsiven Rissmodell abgebildet. Dieses erweiterte Modell kann die Zusammenhänge bei kombinierter Rissöffnung und -gleitung sehr gut wiedergeben. Der entwickelte Algorithmus zur Risssimulation wurde in Hinblick auf eine stochastische Modellierung erweitert. Zu diesem Zweck wurde das Zufallsfeldkonzept für die Abbildung mehrerer untereinander korrelierter Materialparameter ergänzt.
T2  - Stochastische Rissfortschrittsberechnung in bewehrten Betonstrukturen unter Kopplung der Finiten Elemente Methode mit netzfreien Verfahren
KW  - Gitterfreie Methode
KW  - Stochastik
KW  - Risssimulation
KW  - Stahlbeton
KW  - Meshless method
KW  - stochastic
KW  - crack simulation
KW  - reinforced concrete
Y1  - 2005
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:gbv:wim2-20051219-7623
ER  - 
TY  - JOUR
A1  - Most, Thomas
A1  - Bucher, Christian
A1  - Schorling, York
T1  - Dynamic stability analysis of non-linear structures with geometrical imperfections under random loading
JF  - Journal of Sound and Vibration
N2  - Dynamic stability analysis of non-linear structures with geometrical imperfections under random loading
KW  - Angewandte Mathematik
KW  - Strukturmechanik
Y1  - 2004
SP  - 381
EP  - 400
ER  - 
TY  - JOUR
A1  - Most, Thomas
A1  - Eckardt, Stefan
T1  - Application of a hybrid parallelization technique to accelerate the numerical simulation of nonlinear mechanical problems
N2  - 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.
KW  - Framework <Informatik>
KW  - API
KW  - Parallelverarbeitung
KW  - Finite-Elemente-Methode
Y1  - 2004
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:gbv:wim2-20111215-2599
ER  - 
TY  - JOUR
A1  - Kirichuk, A.
A1  - Most, Thomas
A1  - Bucher, Christian
T1  - Numerical nonlinear analysis of kinematically excited shells
JF  - International Journal for Computational Civil and Structural Engineering
N2  - Numerical nonlinear analysis of kinematically excited shells
KW  - Angewandte Mathematik
KW  - Strukturmechanik
Y1  - 2003
SP  - 61
EP  - 74
ER  - 
TY  - CHAP
A1  - Most, Thomas
A1  - Bucher, Christian
T1  - Application of the "fictious crack model" to meshless crack growth simulations
N2  - 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.
KW  - Bruchmechanik
KW  - Rissbildung
KW  - Modellierung
Y1  - 2003
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:gbv:wim2-20111215-3359
ER  - 
TY  - CHAP
A1  - Brehm, Maik
A1  - Most, Thomas
T1  - A Four-Node Plane EAS-Element for Stochastic Nonlinear Materials
N2  - 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.
KW  - Nichtlineare Mechanik
KW  - Finite-Elemente-Methode
KW  - Zufallsvariable
Y1  - 2003
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:gbv:wim2-20111215-2825
ER  -