Time filter

Source Type

Stuttgart Muhlhausen, Germany

Wirtz D.,University of Stuttgart | Karajan N.,DYNAmore GmbH | Haasdonk B.,University of Stuttgart
International Journal for Numerical Methods in Engineering

This work investigates the possibilities of acceleration and approximation of multiscale systems using kernel methods. The key element is to learn the interface between the different scales using a fast surrogate for the microscale model, which is given by multivariate kernel expansions. The expansions are computed using statistically representative samples of input and output of the microscale model. We apply both support vector machines and a vectorial kernel greedy algorithm as learning methods. We demonstrate the applicability of the resulting surrogate models using two multiscale models from different engineering disciplines. We consider, first, a human spine model coupling a macroscale multibody system with a microscale intervertebral spine disc model and, second, a model for simulation of saturation overshoots in porous media involving nonclassical shock waves. © 2014 John Wiley & Sons, Ltd. Source

Rupp T.K.,University of Stuttgart | Ehlers W.,University of Stuttgart | Karajan N.,University of Stuttgart | Karajan N.,DYNAmore GmbH | And 2 more authors.
Biomechanics and Modeling in Mechanobiology

Determining the internal dynamics of the human spine’s biological structure is one essential step that allows enhanced understanding of spinal degeneration processes. The unavailability of internal load figures in other methods highlights the importance of the forward dynamics approach as the most powerful approach to examine the internal degeneration of spinal structures. Consequently, a forward dynamics full-body model of the human body with a detailed lumbar spine is introduced. The aim was to determine the internal dynamics and the contribution of different spinal structures to loading. The multi-body model consists of the lower extremities, two feet, shanks and thighs, the pelvis, five lumbar vertebrae, and a lumped upper body including the head and both arms. All segments are modelled as rigid bodies. 202 muscles (legs, back, abdomen) are included as Hill-type elements. 58 nonlinear force elements are included to represent all spinal ligaments. The lumbar intervertebral discs were modelled nonlinearly. As results, internal kinematics, muscle forces, and internal loads for each biological structure are presented. A comparison between the nonlinear (new, enhanced modelling approach) and linear (standard modelling approach, bushing) modelling approaches of the intervertebral disc is presented. The model is available to all researchers as ready-to-use C/C++ code within our in-house multi-body simulation code demoa with all relevant binaries included. © 2015, Springer-Verlag Berlin Heidelberg. Source

Karajan N.,University of Stuttgart | Karajan N.,DYNAmore GmbH | Otto D.,University of Stuttgart | Oladyshkin S.,University of Stuttgart | Ehlers W.,University of Stuttgart
Biomechanics and Modeling in Mechanobiology

A possibility to simulate the mechanical behaviour of the human spine is given by modelling the stiffer structures, i.e. the vertebrae, as a discrete multi-body system (MBS), whereas the softer connecting tissue, i.e. the softer intervertebral discs (IVD), is represented in a continuum-mechanical sense using the finite-element method (FEM). From a modelling point of view, the mechanical behaviour of the IVD can be included into the MBS in two different ways. They can either be computed online in a so-called co-simulation of a MBS and a FEM or offline in a pre-computation step, where a representation of the discrete mechanical response of the IVD needs to be defined in terms of the applied degrees of freedom (DOF) of the MBS. For both methods, an appropriate homogenisation step needs to be applied to obtain the discrete mechanical response of the IVD, i.e. the resulting forces and moments. The goal of this paper was to present an efficient method to approximate the mechanical response of an IVD in an offline computation. In a previous paper (Karajan et al. in Biomech Model Mechanobiol 12(3):453–466, 2012), it was proven that a cubic polynomial for the homogenised forces and moments of the FE model is a suitable choice to approximate the purely elastic response as a coupled function of the DOF of the MBS. In this contribution, the polynomial chaos expansion (PCE) is applied to generate these high-dimensional polynomials. Following this, the main challenge is to determine suitable deformation states of the IVD for pre-computation, such that the polynomials can be constructed with high accuracy and low numerical cost. For the sake of a simple verification, the coupling method and the PCE are applied to the same simplified motion segment of the spine as was used in the previous paper, i.e. two cylindrical vertebrae and a cylindrical IVD in between. In a next step, the loading rates are included as variables in the polynomial response functions to account for a more realistic response of the overall viscoelastic intervertebral disc. Herein, an additive split into elastic and inelastic contributions to the homogenised forces and moments is applied. © 2014, Springer-Verlag Berlin Heidelberg. Source

Beer M.,National University of Singapore | Liebscher M.,DYNAmore GmbH
Computational Mechanics

Processes in engineeringmechanics often contain branching points at which the system can follow different physical paths. In this paper a method for the detection of these branching points is proposed for processes that are affected by noise. It is assumed that a bundle of process records are available from numerical simulations or from experiments, and branching points are concealed by the noise of the process. The bundle of process records is then evaluated at a series of discrete values of the independent process coordinates. At each discrete point of the process, the associated point set of process values is investigated with the aid of cluster analysis. The detected branching points are verified with a recursive algorithm. The revealed information about the branching points can be used to identify the physical and mechanical background for the branching. This helps to better understand a mechanical system and to design it optimal for a specific purpose. The proposed method is demonstrated by means of both a numerical example and a practical example of a crashworthiness investigation. © Springer-Verlag 2009. Source

Morganti S.,University of Pavia | Auricchio F.,University of Pavia | Benson D.J.,University of California at San Diego | Gambarin F.I.,Cardiology Unit | And 3 more authors.
Computer Methods in Applied Mechanics and Engineering

We investigate the use of Isogeometric Analysis for the model construction and simulation of aortic valve closure. We obtain converged results and compare with benchmark finite element analysis. We find that Isogeometric Analysis is capable of attaining the same accuracy with models consisting of two orders of magnitude fewer nodes than finite element models; analogous savings are observed also in terms of analysis time. Model construction and mesh refinement are likewise performed more efficiently with Isogeometric Analysis. © 2014 Elsevier B.V. Source

Discover hidden collaborations