Showing papers in "Pamm in 2004"
TL;DR: In this paper, a multiscale model for asphalt is developed at the Christian Doppler Laboratory for performance-based optimization of flexible road pavements, which allows to relate macroscopic material properties of asphalt to properties of finer scales of observation.
Abstract: Accounting for the large variation of asphalt mixes, resulting from variations of constituents and composition, and from the allowance of additives, a multiscale model for asphalt is currently developed at the Christian Doppler Laboratory for “Performance-based optimization of flexible road pavements”. The multiscale concept allows to relate macroscopic material properties of asphalt to phenomena and material properties of finer scales of observation. Starting with the characterization of the finest scale, i.e., the bitumen-scale, Atomic Force Microscopy (AFM) is employed. Depending on the mode of measurement (tapping versus pulsed-force mode), the AFM provides insight into the surface topography or stiffness and adhesion properties of bitumen. The obtained results will serve as input for upscaling in the context of the multiscale model in order to obtain the homogenized material behavior of bitumen at the next-higher scale, i.e., the mastic-scale. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)
88 citations
TL;DR: In this article, the importance of mass conservation and order of the interpolation scheme were analyzed and the ideas presented in this paper are more general and the methods can be extended for unsteady, compressible 3D flow problems.
Abstract: In many particle methods the accurate interpolation of a velocity field represented on a computational grid to arbitrary positions is crucial [2, 5]. Here, the importance of mass conservation and order of the interpolation scheme were analyzed. Initially equally distributed particles were tracked in a stationary, incompressible 2d flow field using different interpolation schemes. It could be demonstrated that especially mass conservation is of great importance, in particular in the case of complex flow patterns. The ideas presented in this paper are more general and the methods can be extended for unsteady, compressible 3d flow problems. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)
45 citations
TL;DR: In this article, the Riccati equation is applied to a modified version of a controlled heat transfer model introduced by Troltzsch and Unger, and the LyaPack software package can be used to compute the optimal feedback without solving the ARE directly.
Abstract: We discuss how the theory developed by Banks and Kunisch can be applied to a modified version of a controlled heat transfer model introduced by Troltzsch and Unger. In the numerical implementation we use ALBERT(A) to establish the required FEM–semidiscretisation in space. The resulting algebraic Riccati equation (ARE) is of large dimension (n > 1000). It is shown how the LyaPack software package can be used to compute the optimal feedback without solving the ARE directly. In the closing section we present numerical results comparing different implementational approaches and cost functions. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)
35 citations
TL;DR: In this article, the authors apply the method of linear interpolation of Kurchatov to solve nonlinear operator equations in Banach spaces, using the principle of majorants of L. V. Kantorovich.
Abstract: Faculty of Applied Mathematics and Computer Science, Ivan Franko National University of Lviv, Universitetska 1, 79000Lviv, UkraineWe apply the method of linear interpolation of Kurchatov to solve nonlinear operator equations in Banach spaces. Using theprinciple of majorants of L. V. Kantorovich, we study the semilocal convergence of method of Kurchatov. Quadratic order ofconvergence of this method is determined. A priori and a posteriori estimations of method’s error are received.
34 citations
TL;DR: In this paper, a numerical solution strategy for calculating equilibrium free surfaces of a magnetic fluid under the action of magnetic field is proposed and applied to determine shapes of a linear magnetisable ferrofluid drop in a uniform magnetic field.
Abstract: A numerical solution strategy for calculating equilibrium free surfaces of a magnetic fluid under the action of a magnetic field is proposed and applied to determine shapes of a linear magnetisable ferrofluid drop in a uniform magnetic field. Hysteresis phenomena for the drop deformation and the drop shapes with ends, close to conical, were observed numerically. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)
27 citations
TL;DR: In this article, a geometrically exact Cosserat continuum model is investigated in variational form as a two-field minimization problem for the deformation φ and the independent microrotation.
Abstract: We study a geometrically exact Cosserat continuum model. The model is investigated in variational form as a two-field minimization problem for the deformation φ and the independent microrotation . The elastic energy is assumed to depend quadratically on the micropolar stretch tensor _ and super-quadratically on the curvature . Depending on the values of constitutive parameters, existence of minimizers in Sobolev-spaces can be shown. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)
25 citations
TL;DR: Computational results indicate that the direct solution algorithm presented is suitable for optimization in small and medium-sized gas networks.
Abstract: Operative planning in gas networks with prescribed binary decisions yields large scale nonlinear programs defined on graphs. We study the structure of the KKT systems arising in interior methods and present a customized direct solution algorithm. Computational results indicate that the algorithm is suitable for optimization in small and medium-sized gas networks. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)
22 citations
TL;DR: In this article, a primal-dual interior point method for optimal control problems with PDE constraints is considered, and the algorithm is directly applied to the infinite dimensional problem and the existence and convergence of the central path are analyzed.
Abstract: A primal-dual interior point method for optimal control problems with PDE constraints is considered. The algorithm is directly applied to the infinite dimensional problem. Existence and convergence of the central path are analyzed. Numerical results from an inexact continuation method applied to a model problem are shown. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)
21 citations
TL;DR: In this paper, a state and input parameterizing flat output for flexible structures and open-loop control of a Timoshenko beam model is presented. But this model is not suitable for the boundary control of flexible structures.
Abstract: Modal coordinates are used to construct a state and input parameterizing flat output for flexible structures and to design open-loop controls. This is illustrated for the boundary control of a Timoshenko beam model. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)
20 citations
TL;DR: In this paper, Rump's method for solving parametric interval linear systems is generalized based on new sufficient regularity conditions, which expands its scope of applicability over a class of co-dependent parametric matrices.
Abstract: Based on new sufficient regularity conditions, Rump's method for solving parametric interval linear systems is generalized which expands its scope of applicability over a class of co-called column-dependent parametric matrices. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)
20 citations
TL;DR: In this paper, the influence of the masticatory system on the human mandible was modeled by adaptive finite element techniques, and the fibres were expanded to fan-like vector fields similar to the anatomical reality.
Abstract: Structural mechanics simulation of bony organs is of general medical and biomechanical interest, because of the interdependence of the inner architecture of bone and its functional loading already stated by Wolff in 1892.
This work is part of a detailed research project concerning the human mandible. By adaptive finite element techniques, stress/strain profiles occurring in the bony structure under biting were simulated. Estimates of the discretization errors, local grid refinement, and multilevel techniques guarantee the reliability and efficiency of the method.
In general, our simulation requires a representation of the organ's geometry, an appropriate material description, and the load case due to teeth, muscle, or joint forces. In this paper, we want to focus on the influence of the masticatory system. Our goal is to capture the physiological situation as far as possible. By means of visualization techniques developed by the group, we are able to extract individual muscle fibres from computed tomography data. By a special algorithm, the fibres are expanded to fanlike (esp. for the musc. temporalis) coherent vector fields similar to the anatomical reality. The activity of the fibres can be adapted according to compartmentalisation of the muscles as measured by electromyological experiments. A refined sensitivity analysis proved remarkable impact of the presented approach on the simulation results. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)
TL;DR: In this paper, a simple thermodynamical consistent anisotropic damage model is constructed, basing on the assumption that damage mainly takes place in the fiber directions as a result of breakage of collagen cross-links.
Abstract: Arteries are reinforced by helically arranged collagen fibers and posses orthotropic elastic properties. In this paper a polyconvex anisotropic energy is used in order to guarantee the existence of minimizers for the purely elastic boundary value problem. Anisotropic discontinuous damage effects, which are induced by decreasing stiffness of particular fibers, are observed in a certain range of overexpansion. A simple thermodynamical consistent anisotropic damage model is constructed, basing on the assumption that damage mainly takes place in the fiber directions as a result of breakage of collagen cross-links. Finally a cycled overexpansion of a test material from an artery is analyzed in order to show the main characteristics of the proposed model.
TL;DR: Simulation results of a stochastic programming model for optimizing the electricity portfolio of a German municipal power utility are presented and analyzed and the model aims to minimize risk and expected overall cost simultaneously.
Abstract: We compare different multiperiod risk measures taken from the class of polyhedral risk measures with respect to the effect they show when used in the objective of a stochastic program. For this purpose, simulation results of a stochastic programming model for optimizing the electricity portfolio of a German municipal power utility are presented and analyzed. This model aims to minimize risk and expected overall cost simultaneously. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)
TL;DR: In this paper, an approach for a biorthogonal basis constructed by the lifting scheme is presented, which allows the choice of the smoothness at least of the primal wavelet in a very natural way.
Abstract: Several applications require to retrieve a certain pattern from a signal where the actual scaling of the pattern is not known before. We consider applications like evaluation of mass spectrograms, detection of component wearout by observing the current of an engine, detection of pollutions of rotor spinning machines, decomposition of (audio) signals into time-frequency atoms.
We try to solve this problem with discrete wavelet transforms where the wavelet function is constructed to match the given pattern. An approach for a biorthogonal basis constructed by the lifting scheme is presented. This method is rather simple and fast and allows the choice of the smoothness at least of the primal wavelet in a very natural way. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)
TL;DR: In order to solve optimization tasks with both equality and inequality constraints the PSO algorithm has been extended by the Augmented Lagrangian Multiplier Method and shows often superior results and is quite simple to implement.
Abstract: In recent years, stochastic optimization methods have gained increasing attention in parameter optimization of mechanical systems Most popular techniques are Evolutionary Computation and the Simulating Annealing algorithm, which are applied more frequently to mechanical problems due to the increasing computing resources available now Since theses methods do not require any gradient information, they are well suited for non-smooth or discontinuous optimization tasks occurring in nonlinear multibody systems In addition to these techniques, Kennedy and Eberhart [5] introduced the Particle Swarm Optimization method (PSO) based on the simulation of bird flocking In this work, the efficiency of an extended PSO algorithm has been compared with an Evolutionary Strategy (ES) [6] and an Adapted Simulated Annealing method (ASA) [4] In order to solve optimization tasks with both equality and inequality constraints the PSO algorithm has been extended by the Augmented Lagrangian Multiplier Method [2] The proposed method shows often superior results and is quite simple to implement (© 2004 WILEY-VCH Verlag GmbH & Co KGaA, Weinheim)
TL;DR: In this article, the Coulombs law is used for the analysis of many technical problems with frictional contact, which implies a constant friction coefficient µ. This assumption is sufficient for many applications in structural mechanics; however in the special case of rubber friction on rough surfaces the resulting simplification cannot be accepted.
Abstract: Within the analysis of many technical problems with frictional contact, Coulombs law is used, which implies a constant friction coefficient µ. This assumption is sufficient for many applications in structural mechanics; however in the special case of rubber friction on rough surfaces the resulting simplification cannot be accepted. The physical interactions between tire and road surface are very complex and still widely unknown. As it is apparent from experiments, the friction coefficient depends heavily on various parameters like sliding velocity, surface roughness, normal forces and temperature change.
TL;DR: In this article, the authors consider linear multi-step methods for stochastic differential equations and present a theorem ensuring their numerical stability and strong convergence and use this to study the properties of two-step schemes with small noise.
Abstract: We consider linear multi-step methods for stochastic differential equations and present a theorem ensuring their numerical stability and strong convergence. We use this to study the properties of two-step schemes for stochastic differential equations with small noise. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)
TL;DR: In this paper, a new definition of a rotational spring that can be used in the simplified computational model for the computation of transverse displacements of cracked beam structures due to transverse load is presented.
Abstract: The paper describes the reasons for the derivation of a new definition of a rotational spring that can be utilised in the simplified computational model for the computation of transverse displacements of cracked beam structures due to transverse load. This definition plays an extremely important role in the inverse identification of cracks. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)
TL;DR: In this article, the stability of repeatedly bent flange of a thin-walled beam is investigated using an analytical description of the whole flange as a thinwalled structure with the use of an energetic method.
Abstract: The paper is devoted to stability of repeatedly bent flange of a thin-walled beam. In classical approach each segment of the flange is considered as a simple plate. The paper provides an analytical description of the whole flange as a thin-walled structure with the use of an energetic method. An explicit formula defining the critical load of the flange was obtained. This enables to perform a numerical analysis of a family of thin-walled beams. Additionally, a numerical analysis with FEM was carried out. The results of both approaches have been compared. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)
TL;DR: Based on a new method, the computation of eigenvalue avoidance for such problems to almost machine precision for the Laplace operator in planar domains is presented.
Abstract: The phenomenon of eigenvalue avoidance is of growing interest in applications ranging from quantum mechanics to the theory of the Riemann zeta function. Until now the computation of eigenvalues of the Laplace operator in planar domains has been a difficult problem, making it hard to compute eigenvalue avoidance. Based on a new method this paper presents the computation of eigenvalue avoidance for such problems to almost machine precision.
TL;DR: In this article, a Fourier spectral method is employed in the azimuthal direction combined with mode clipping to alleviate time-step restrictions due to a very fine grid spacing near the singularity at the axis (r = 0).
Abstract: A wide range of flows of practical interest occur in cylindrical geometries. In order to simulate such flows, an available compact finite-difference simulation code [1] was adapted by introducing a mapping that expresses cylindrical coordinates as generalized coordinates. This formulation is conservative and avoids problems associated with the classical formulation of the Navier-Stokes equations in cylindrical coordinates. The coordinate singularity treatment follows [2] and is modified for generalized coordinates. To retain high-order numerical accuracy, a Fourier spectral method is employed in the azimuthal direction combined with mode clipping to alleviate time-step restrictions due to a very fine grid spacing near the singularity at the axis (r = 0). An implementation of this scheme was successfully validated by a simulation of a tripolar vortex formation and by comparison with linear stability theory. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)
TL;DR: In this article, the effects of the compression of a yeast cell under high hydrostatic pressure (HHP) were modeled and simulated numerically, and the deformation of the cell under pressure deviated strongly from isotropic volume reduction.
Abstract: The mechanical effects of the compression of a yeast cell (Saccharomyces cerevisiae) under high hydrostatic pressure (HHP) are modeled and simulated numerically. The deformation of the cell under pressure deviates strongly from isotropic volume reduction. In the cell wall, von-Mises stress reaches the critical value upon failure at a pressure load between 415Mpa and 460MPa. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)
TL;DR: A mathematical model with stochastic input data for mean-risk optimization of electricity portfolios containing several physical components and energy derivative products and the effects of varying weighting of risk is presented.
Abstract: We present a mathematical model with stochastic input data for mean-risk optimization of electricity portfolios containing several physical components and energy derivative products. The model is designed for the optimization horizon of one year in hourly discretization. The aim consists in maximizing the mean book value of the portfolio at the end of the optimization horizon and, at the same time, in minimizing the risk of the portfolio decisions. The risk is measured by the conditional value-at-risk and by some multiperiod extension of CVaR, respectively.We present numerical results for a large-scale realistic problem adapted to a municipal power utility and study the effects of varying weighting of risk. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)
TL;DR: In this paper, the authors investigated the Lyapunov equation with the matrix sign function method and obtained the factorized solution using a partitioned Newton iteration, where one part of the iteration uses formatted arithmetic for the hierarchical matrix format while the other part converges to an approximate full-rank factor of the solution.
Abstract: We investigate the solution of the Lyapunov equation with the matrix sign function method. In order to obtain the factorized solution we use a partitioned Newton iteration, where one part of the iteration uses formatted arithmetic for the hierarchical matrix format while the other part converges to an approximate full-rank factor of the solution. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)
TL;DR: In this article, the deformation itself occurs during the sliding of a rubber element across the micro-scaled asperities of a rough surface, which is simulated in time domain and compared to experiments.
Abstract: Friction, especially friction of elastomers, can cause acoustic problems like noise, squeal and comfort drawbacks like vibrations and wear. Therefore, rubber friction affects the function of many products in technical applications, e.g. seals, belts and tires. It can be classified according to different physical phenomena like adhesion, hysteresis, cohesion and viscous friction, see [3]. The topic of this paper is hysteresis friction of rubber that is caused by the energy dissipation due to internal material damping during the process of deformation. The deformation itself occurs during the sliding of a rubber element across the micro-scaled asperities of a rough surface. In this paper, the sliding process of a rubber element over real surfaces is simulated in time domain and compared to experiments. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)
TL;DR: This work investigates the impact of the box‐splitting techniques on the overall performance of the solver and proposes a new approach combining some of the simple heuristics in a hybrid way.
Abstract: Many different heuristics have been proposed for selecting the subdivision direction in branch‐and‐bound result-verifying nonlinear solvers. We investigate the impact of the box-splitting techniques on the overall performance of the solver and propose a new approach combining some of the simple heuristics in a hybrid way. Numerical experiments with medium‐ sized example problems indicate that our approach is successful.
TL;DR: In this article, the authors proposed to apply the more efficient and more economic tuned liquid column damper (TLCD), which relies on the motion of a liquid mass in a sealed tube to counteract the external motion, while a built-in orifice plate induces turbulent damping forces that dissipate kinetic energy.
Abstract: The excessive lateral vibrations of Londons Millenium Bridge and the Toda Park Bridge in Japan due to a large number of crossing pedestrians have raised an unexpected problem in footbridge constructions. Secondary tuned structures, like the conventional tuned mass damper (TMD) or the tuned liquid damper (TLD) were installed to the bridge in order to suppress these vibrations. In the present investigation it is proposed to apply the more efficient and more economic tuned liquid column damper (TLCD), which relies on the motion of a liquid mass in a sealed tube to counteract the external motion, while a built-in orifice plate induces turbulent damping forces that dissipate kinetic energy. For optimal tuning of TLCDs the natural frequency and equivalent linear damping coefficient have to be chosen suitable, likewise to the conventional TMDs, as given in Den Hartog [1]. The advantages of TLCDs are: simple tuning of natural frequency and damping, low cost of design and maintenance and a simple construction. A mathematical model of a three degree-of-freedom (DOF) bridge coupled with an optimal tuned TLCD is derived and analyzed numerically. Furthermore, a small scale experimental model set-up has been constructed in the laboratory of the TU-Insitute. The experimental results are in good agreement with the theoretical predictions and indicate that TLCDs are effective damping devices for the undesired pedestrian induced footbridge vibrations. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)
TL;DR: A new approach for the reduction of large‐scale second order systems is presented, resulting in a system of second order structure by first reducing the equivalent state space model using Krylov subspace methods and then converting it into the second order type representation of the original model.
Abstract: A new approach for the reduction of large-scale second order systems is presented, resulting in a system of second order structure. We first reduce the equivalent state space model using Krylov subspace methods and then convert the reduced model back into the second order type representation of the original model.
TL;DR: In this paper, the stability problem of an axially compressed open elastic circular cylindrical shell is studied and two curvilinear edges of the shell are simply supported while two straight edges are free.
Abstract: The paper is devoted to stability problem of an axially compressed open elastic circular cylindrical shell. Two curvilinear edges of the open cylindrical shell are simply supported while two straight edges are free. Two load cases of the shell are assumed. The first load case - was the invariable axially normal force intensity, and the second load case - the linearly varying axially normal force intensity. Critical loads of the shell for both load cases are determined. These critical loads are compared with a classical load for closed circular cylindrical shell. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)