Papers by Matthias Baitsch
Proceedings, May 10, 2016
Prediction of geological changes, such as caverns, fault zones, weakened zones, etc., ahead of a ... more Prediction of geological changes, such as caverns, fault zones, weakened zones, etc., ahead of a tunnel is crucial for the safety of the tunnel, the structures above it, and the tunnel boring machines in the case of the mechanized tunnelling. Enough number of boreholes can give an insight of the geological structure below the surface. However, too many boreholes, which are very costly in terms of both time and money, are usually needed to scan the geological structure of the ground. To avoid the high cost, looking ahead of the tunnel is usually done by carrying out a seismic survey. In this work, full waveform inversion (FWI) of the acoustic waves is used in a tunnel environment to predict geological changes in the domain. The aim of FWI is to find such an optimal computer model that matches with the field waveforms with all arrivals and amplitudes of the waves. To have a proper inverse model, the first step is to have a precise forward model. One of the crucial issues in forward wave modelling is the existence of the artificial boundaries which are treated by absorbing boundary techniques. For this study, perfectly matched layer (PML) technique is applied to have sharp absorbing boundaries at the spurious edges.
The real world behavior and the sensitiveness of structures are continuously gaining interest in ... more The real world behavior and the sensitiveness of structures are continuously gaining interest in structural design. This is a direct result of improvements due to advances made in modern computational mechanics. By that, the demands on structural optimization models representing an abstract and rational basis for computer-aided design also increase. To map reality, in particular, probabilistic phenomena are becoming essential and have to be taken into account. Within this contribution, two approaches are presented that allow for a realistic but simultaneously efficient reproduction of the probabilistic nature associated with structural design problems. First, a semi-deterministic approach is elucidated by which the random nature of geometric imperfections induced into a structural system can be caught. Second, a probabilistic approach is presented considering loads and stresses as random processes that lead to design quantities described by probability density functions.
This paper deals with the automated design and economic optimization of reinforced concrete frame... more This paper deals with the automated design and economic optimization of reinforced concrete frame bridges typically used in road construction. The optimization algorithms applied are (i) parallel genetic algorithms (PGA) and (ii) parallel memetic algorithms (PMA). The evaluation of solutions follows the Spanish Code for structural concrete. Stress resultants and envelopes of framed structures are computed by an internal matrix method program. Design loads for the earth fill and the traffic loads are in accordance to the Spanish code for road bridges. The structural optimization model contains in total 50 design variables: 3 geometrical design variables, 3 types of concrete and 44 variables defining reinforcement bar diameters and bar lengths. All variables introduced have been selected to achieve a model applicable in structural design practice. The evaluation module includes the ULS of fatigue plus other commonly checked service limit states of service and ultimate flexure and shea...
For engineers and architects, it is essential to understand and communicate how the structure (ca... more For engineers and architects, it is essential to understand and communicate how the structure (cantilever, truss girder, frame, etc.) they are designing behaves under loading. The Sketcha-lyze app, built on top of VTK[1] / VES[2] and avail- able in the App Store for free, aims to support professionals and students in this process by letting them sketch structural systems quickly and by providing deformations and internal forces of structural members immediately. The direct and intuitive way users can interact with the structural system on a tablet device makes it easy to try new ideas and encour- ages exploration of structural behavior by experimenting with geometry, loading, and dimensions. The Sketchalyze app (Figure 1) provides tools to sketch a structural system in a way that is familiar to people who have used a drawing program before. A finite element com- putational core computes deformations and section forces on the device and common techniques such as vector warp, mapped c...
In recent years, damages in welded connections plates of vertical tie rods of several arched stee... more In recent years, damages in welded connections plates of vertical tie rods of several arched steel bridges have been reported. These damages are due to fatigue caused by windinduced vibrations. In the present study, such phenomena are examined and the corresponding lifetime of a reference bridge in Münster-Hiltrup, Germany, is estimated, based on the actual shape of the connection plate. Also, the results obtained are compared to the expected lifetime of a connection plate, whose geometry has been optimized separately. The structural optimization, focussing on the shape of the cut at the hanger ends, has been carried out using evolution strategies.
This contribution introduces a framework that can be used as a basis for the development of inter... more This contribution introduces a framework that can be used as a basis for the development of interactive applications for the visualization of engineering models. Implemented in Java, the framework defines the application logic needed to translate model and simulation data into a three-dimensional graphical representation. Several high-level classes are provided that can be used to visualize e.g. structural elements, two-and three-dimensional continua and boundary conditions just by providing the data as required. New classes can easily be added if some required functionality is missing.
This contribution is on shape optimization of 3D continua using high-order finite elements. Since... more This contribution is on shape optimization of 3D continua using high-order finite elements. Since in the p-version of FEM the discretization error is controlled by raising the polynomial degree, adaptive remeshing procedures during optimization are not required. The element geometry is constructed using the blending function method in conjunction with NURBS surfaces in order to efficiently describe the geometry in terms of only a few design variables. Design elements for high-order finite elements are introduced which facilitate the generation of geometrical optimization models largely independent from the finite element mesh. A two level parallel scheme is employed in order to run the optimization on a cluster computer with about 100 CPUs.
In practical engineering design, it is essential to have access to a variety of different optimiz... more In practical engineering design, it is essential to have access to a variety of different optimization strategies. In this paper, a concept is presented which offers a unified interface to various, existing optimization packages. Through the use of the CORBA technology, this package can be used in a heterogenous client-server environment. By employing multiple CORBA servers complex optimization projects, such as structural optimization using FE components, can be easily developed.
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.
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.
Deterioration and damage in hanger connection plates of steel arch bridges, caused by wind induce... more Deterioration and damage in hanger connection plates of steel arch bridges, caused by wind induced vibrations, often have severe impact on the overall safety of the structure. In this paper, an approach for the shape optimization of such connection plates is presented. Herein, various lifetime oriented design criteria are discussed and some techniques for shape optimization using the p-version of finite elements are described. The actual optimization is carried out by using evolution strategies. First design studies show promising results.
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Papers by Matthias Baitsch