Papers by Matthias Baitsch
Introduction to Geometrically Nonlinear Continuum Dislocation Theory, 2021
Introduction to Geometrically Nonlinear Continuum Dislocation Theory, 2021
Tunnelling and Underground Space Technology
The excavation process in mechanized tunneling can be improved by reconnaissance of the geology a... more The excavation process in mechanized tunneling can be improved by reconnaissance of the geology ahead. A nondestructive exploration can be achieved in means of seismic imaging. A full waveform inversion approach, which works in the frequency domain, is investigated for the application in tunneling. The approach tries to minimize the difference of seismic records from field observations and from a discretized ground model by changing the ground properties. The final ground model might be a representation of the geology. The used elastic wave modeling approach is described as well as the application of convolutional perfectly matched layers. The proposed inversion scheme uses the discrete adjoint gradient method, a multi-scale approach as well as the L-BFGS method. Numerical parameters are identified as well as a validation of the forward wave modeling approach is performed in advance to the inversion of every example. Two-dimensional blind tests with two different ground scenarios and with two different source and receiver station configurations are performed and analyzed, where only the seismic records, the source functions and the ambient ground properties are provided. Finally, an inversion for a three-dimensional tunnel model is performed and analyzed for three different source and receiver station configurations.
Isogeometric analysis (IGA) is based on a concept that uses the same base functions for represent... more Isogeometric analysis (IGA) is based on a concept that uses the same base functions for representing both the model geometry and the solution space. The most common base functions used in the IGA are NURBS (Non-Uniform Rational B-Splines) functions for their capability to analytically represent various geometries. In this paper, the IGA is applied in the free vibration analysis of rotation-free plane curved Bernoulli-Euler beam. The stiffness and mass matrices have been developed using basic concepts of continuum mechanics and the principle of virtual work. Geometry of the undeformed and deformed beam is defined using convective coordinates and cross section basis vectors. Results of the free vibration analysis for beam with arbitrary curvature are compared with the results obtained from the conventional finite element method (FEM) software. The significant advantages of the IGA approach over the FEM are shown and discussed
78th EAGE Conference and Exhibition 2016, 2016
Looking ahead of a tunnel is an important issue in order to have a smooth and safe construction p... more Looking ahead of a tunnel is an important issue in order to have a smooth and safe construction process. Seismic methods are used to locate the geological anomalies ahead of a tunnel; the waves reflected from the geological changes carry information about the location and mechanical properties of the objects. Different migration techniques and first arrivals of the reflected waves are commonly used to achieve the goal. Full waveforms carry more information about the geological structure of a domain than the first traveltimes of the reflected waves. This work emerges from the curiosity to see whether full waveforms can successfully image the velocity field in tunnel applications. There are two parties in this study. The first party chooses a synthetic model and provides the second party with the precisely calculated waveforms in the time domain. The second party has no prior information about the synthetic model except for the waveforms and the inversion is carried out in the frequency domain as a blind test. The aim is to see whether the velocity field can be successfully imaged with the full waveform inversion.
Advances in Engineering Software, 2010
Java is widely recognized as a good object-oriented programming language. However, it is often co... more Java is widely recognized as a good object-oriented programming language. However, it is often considered as too slow for numerically intensive applications. This paper presents a software toolkit that brings the computational efficiency of numerical Fortran libraries to Java. The toolkit is organized in two layers. In the first layer, Java wrappers provide access to numerical libraries like BLAS, LAPACK or NAG. The second layer comprises vector and matrix classes as well as classes for common linear algebra tasks. Numerical experiments show that this strategy can substantially improve the performance of Java-based numerical applications.
Introduction to Geometrically Nonlinear Continuum Dislocation Theory, 2021
This chapter presents the basics of geometrically nonlinear kinematics for continuously dislocate... more This chapter presents the basics of geometrically nonlinear kinematics for continuously dislocated crystals. It involves the multiplicative split of the deformation and the slip-system-based decomposition of the velocity gradient. Eventually, appropriate measures for the crystal’s strain and geometrically necessary dislocation densities are derived. 2.1 Vectors Describing Cubic Crystal Lattices Throughout this book, a single crystal with a cubic primitive lattice (Pearson symbol cP) is considered [1, p. 22]. On the one hand, this is done for the sake of simplicity and compactness of the model. On the other hand, the cP-crystal structure enables plane deformation for two active slip systems (in contrast to cFor cI-crystals). This way, a minimalistic multi-slip scenario can be studied. The orientation of the cubic elementary cell is characterized by three mutually perpendicular unit vectors âK , K ∈ {I, II, III} (cf. Fig. 2.1). These lattice vectors define an orthonormal coordinate sy...
Structural design and optimization in engineering address increasingly non-standard optimization ... more Structural design and optimization in engineering address increasingly non-standard optimization problems (NSP). These problems are characterized by complex topology conditions of the optimization space (w.r.t. nonlinearity, multimodality, discontinuity etc.). By that, NSP can only be solved by means of computer simulations. Hereby, the corresponding numerical approaches applied often tend to be noisy. Examples for NSP occur in robust optimization, where the solution has to be robust with respect to e.g. implementation errors, production tolerances, uncertain environment conditions etc. However, a generally applicable strategy for solving such problem types always equally efficient is not available. To improve the situation, in this paper a distributed agent-based optimization approach for solving NSPs is introduced. The approach elaborated consists of a network of cooperating but also competing strategy agents that wrap various optimization methods (e.g. SQP, DE, ES, PSO etc.) usin...
In this paper, we present an optimization model which incorporates uncertainty induced by geometr... more In this paper, we present an optimization model which incorporates uncertainty induced by geometrical imperfections. Within the model, geometrical imperfections are represented by means of random fields. The induced uncertainties are then treated using the concept of a convex model. The resultant problem is then solved in a two stage optimization procedure. An arched girder is used to demonstrate the capabilities of the proposed approach. NOMENCLATURE x ∈ R design vector f0 objective function f1 . . . fm constraint functions y ∈ R vector of imperfection variables h imperfection shape r(t,x) perfect system curve r(t,x,y) imperfect system curve Cov[·, ·] covariance of two random numbers b correlation length B covariance matrix of discretized random field B covariance matrix of discretized random field with constraints Sy convex set of allowed imperfection vectors ui(x,y) structural response quantity vi(x) structural response for controlling imperfection shape INTRODUCTION Today, optim...
PAMM
Within the recently proposed Continuum Dislocation Theory (CDT), numerical solutions of simple sh... more Within the recently proposed Continuum Dislocation Theory (CDT), numerical solutions of simple shear test for single crystals strip using finite elements are performed. Under the assumption of plane constrained deformation of crystal having only one active slip system, the plastic slip, the dislocation density as well as the stress-strain curve are computed. The results of numerical simulations are compared with those obtained from analytical solutions which show good agreement.
Applied Mathematical Modelling
Ingenieure sind aufbauend auf gründlicher Planung, intelligentem Entwurf, solider Konstruktion ... more Ingenieure sind aufbauend auf gründlicher Planung, intelligentem Entwurf, solider Konstruktion und sorgfältiger Herstellung seit jeher bestrebt, optimale technische Systeme zu entwickeln. Auch die Prozesse, die von Ingenieuren eingeleitet und verant-wortet ...
The optimization of continuous structures requires careful attention to discretization errors. Co... more The optimization of continuous structures requires careful attention to discretization errors. Compared to ordinary low order formulation (h-elements) in conjunction with an adaptive mesh refinement in each optimization step, the use of high order finite elements (so called p-elements) has several advantages. However, compared to the h-method a higher order finite element analysis program poses higher demands from a software engineering point of view. In this article the basics of an object oriented higher order finite element system especially tailored to the use in structural optimization is presented. Besides the design of the system, aspects related to the employed implementation language Java are discussed.
In this contribution the software design and implementation of an analysis server for the computa... more In this contribution the software design and implementation of an analysis server for the computation of failure probabilities in structural engineering is presented. The structures considered are described in terms of an equivalent Finite Element model, the stochastic properties, like e.g. the scatter of the material behavior or the incoming load, are represented using suitable random variables. Within the software framework, a Client-Server-Architecture has been implemented, employing the middleware CORBA for the communication between the distributed modules. The analysis server offers the possibility to compute failure probabilities for stochastically defined structures. Therefore, several different approximation (FORM, SORM) and simulation methods (Monte Carlo Simulation and Importance Sampling) have been implemented. This paper closes in showing several examples computed on the analysis server.
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Papers by Matthias Baitsch