bluuebunny/crossref_metadata_2025_split huggingface dataset:
Influence of various design parameters on the quality of optimal shape design in topology optimization analysis
Authors: Kutylowski Ryszard , Rasiak Bartosz 
Published: February 2009

AbstractThe paper presents the discrete structural topology optimization problem. The analysis was made for the formulation of optimal design with a compliance minimization (as the objective functional) of statically loaded continuum structures with constraints forced on mass of the structure. Two different algorithms were compared (one taken from the literature and the second originally prepared) in order to study influence of design parameters formulation on the calculations results. Optimal topologies were presented and discussed for several 2D examples, with various optimization process parameters in order to get the best results in the shortest possible time. Other goal of presented research is to find out the possibilities of applying proposed algorithm in the designing process of bridge girders. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Time Schedule Optimization of Satellites
Authors: Tietjen Jan , Büskens Christof , Knauer Matthias 
Published: February 2009

AbstractFor an effective monitoring of environmental activities by a satellite, the main goal is to achieve maximum coverage throughout a short period of time. Due to technical restrictions of the satellite hardware, it is only possible to use the camera for a limited time period per orbit, while rotating around the Earth. The main goal is to determine the time intervals for which the coverage with respect to given target areas is maximized and the restrictions such as contact to ground stations are satisfied. To obtain a continuous objective function for the sequential quadratic programming method, the coverage is modelled by polygons integrated on a sphere. For acceptable computing times, special investigations had to be made in order to achieve fast gradient computations. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Padé Approximations of and preservation of quadratic Lyapunov functions
Authors: Solmaz Selim , Corless Martin , Shorten Robert 
Published: February 2009

AbstractWe investigate whether or not quadratic Lyapunov functions are preserved under Padé approximations. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Exploiting Mixed Precision for Computing Eigenvalues of Symmetric Matrices and Singular Values
Authors: Drygalla Volker 
Published: February 2009

AbstractThe use of higher precision preconditioning for the symmetric eigenvalue problem and the singular value problem of general non–structured non–graded matrices are discussed. The matrix Q from the QR–decomposition as a preconditioner, applied to A with higher precision, in combination with Jacobi's method seems to allow the computation of all eigenvalues of symmetric positive definite matrices rsp. all singular values of general matrices to nearly full accuracy. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Algebraic multigrid preconditioning for iterative eigensolvers
Authors: Krüger Marcel 
Published: February 2009

AbstractThe objective is a comparative study of iterative solvers for eigenproblems arising from elliptic and self–adjoint partial differential operators. Typically only a few of the smallest eigenvalues of these problems are to be computed. We discuss various gradient based preconditioned eigensolvers which make use of algebraic multigrid preconditioning. We present some algorithms together with numerical results. Performance characteristics are derived by comparison with the solutions of standard problems. We show that known advantages of algebraic multigrid preconditioning (e.g. for boundary–value problems with large jumps in the coefficients) transfer to AMG–preconditioned eigensolvers. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Symmetric Permutations for I‐Matrices to Avoid Small Pivots During Incomplete Factorization
Authors: Mayer Jan 
Published: February 2009

AbstractIncomplete LU–factorizations have been very successful as preconditioners for solving sparse linear systems iteratively. However, for unsymmetric, indefinite systems small pivots (or even zero pivots) are often very detrimental to the quality of the preconditioner. A fairly recent strategy to deal with this problem has been to permute the rows of the matrix and to scale rows and columns to produce an I–matrix, a matrix having elements of modulus one on the diagonal and elements of at most modulus one elsewhere. These matrices are generally more suited for incomplete LU–factorization. I–matrices are preserved by symmetric permutation, i.e. by applying the same permutation to rows and columns of a matrix. We discuss different approaches for constructing such permutations which aim at improving the sparsity and diagonal dominance of an initial block. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
On a stopping rule for iterative orthogonalization of symmetric matrices
Authors: Popa Constantin 
Published: February 2009

AbstractIn this paper we consider three versions of Kovarik's iterative orthogonalization algorithms, for approximating the minimal norm solution of symmetric least squares problems. Although the convergence of these algorithms is linear, in practical applications we observed that a too big number of iterations can dramatically deteriorate the already obtained approximation. In this respect we analyse the above mentioned Kovarik–like methods according to the modifications they make on the “machine zero” eigenvalues of the problem (symmetric) matrix. We establish a theoretical almost optimal formula for the number of iterations necessary to obtain an enough accurate approximation, as well as to avoid the above mentioned troubles. Experiments on collocation discretization of a Fredholm first kind integral equation ilustrate the efficiency of our considerations. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Support size restrictions on time‐frequency representations of functions on finite abelian groups
Authors: Krahmer Felix , Pfander Götz , Rashkov Peter 
Published: February 2009

AbstractWe obtain uncertainty principles for finite abelian groups that relate the cardinality of the support of a function to the cardinality of the support of its short–time Fourier transform. These uncertainty principles are based on well–established uncertainty principles for the Fourier transform. In terms of applications, the uncertainty principle for the short–time Fourier transform implies the existence of a class of equal norm tight Gabor frames that are maximally robust to erasures. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Study on numerical simulation methods of the railway vehicle‐track dynamic interaction
Authors: Yoshimura Akiyoshi , Miwa Masahiro , Kawasaki Yoshiyuki 
Published: February 2009

AbstractA very efficient numerical simulation method of the railway vehicle–track dynamic interaction is described. When a vehicle runs at high speed on the railway track, contact forces between a wheel and a rail vary dynamically due to the profile irregularities existing on the surface of the rail. A large variation of contact forces causes undesired deteriorations of a track and its substructures. Therefore these dynamic contact forces are of main concern of the railway engineers. However it is very difficult to measure such dynamic contact forces directly. So it is important to develop an appropriate numerical simulation model and identify structural factors having a large influence on the variation of contact forces.When a contact force is expressed by the linearized Hertzian contact spring model, the equation of motions of the system is expressed as a second–order linear time–variant differential equation which has a time–dependent stiffness coefficient. Applying a well–known Newmark direct integration method, a numerical simulation is reduced to solving iteratively a time–variant, large–scale sparse, symmetric positive–definite linear system.In this study, by defining a special vector named a contact point one, it is shown that this time–variant stiffness coefficient can be expressed simply as a product of the contact point vector and its transpose and so the Sherman–Morrison–Woodbury formula applied for updating the inverse of the coefficient matrix. As a result, the execution of numerical simulation can be carried out very efficiently. A comparison of the computational time is given. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Quasi‐Minimal Residual Eigenpairs
Authors: Zemke Jens‐Peter M. 
Published: February 2009

AbstractWe consider the extraction of approximate eigenpairs from a given Krylov subspace that are optimal, or at least quasi–optimal with respect to the normwise backward error. An algorithm based on Newton–Grassmannian optimization and a simple example are given; a useful graphical method of comparison with other extraction methods is briefly sketched. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Strong Convergence in Stabilised Degenerate Convex Problems
Authors: Boiger Wolfgang , Carstensen Carsten 
Published: February 2009

AbstractSolutions to non–convex variational problems typically exhibit enforced finer and finer oscillations called microstructures such that the infimal energy is not attained. Those oscillations are physically meaningful, but finite element approximations typically experience dramatic difficulty in their reproduction. The relaxation of the non–convex minimisation problem by (semi–)convexification leads to a macroscopic model for the effective energy. The resulting discrete macroscopic problem is degenerate in the sense that it is convex but not strictly convex. This paper discusses a modified discretisation by adding a stabilisation term to the discrete energy. It will be announced that, for a wide class of problems, this stabilisation technique leads to strong H1–convergence of the macroscipic variables even on unstructured triangulations. This is in contrast to the work [2] for quasi–uniform triangulations and enables the use of adaptive algorithms for the stabilised formulations. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
A hybrid approach to 3‐level FETI
Authors: Klawonn Axel , Rheinbach Oliver 
Published: February 2009

AbstractFinite Element Tearing and Interconnecting (FETI) methods are nonoverlapping domain decomposition methods which have been proven to be very robust and parallel scalable for a class of elliptic partial differential equations. These methods are also called dual domain decomposition methods since the continuity accross the subdomain boundaries is enforced by Lagrange multipliers and, after elimination of the primal variables, the remaining Schur complement system is solved iteratively in the Lagrange multiplier space using a Krylov space method. Domain decomposition methods iterating on the primal variables are called primal substructuring methods. FETI and FETI–DP methods are different members of the family of dual domain decomposition methods. Their standard versions have in common that the local subproblems and a small global problem are solved exactly by a direct method, essentially representing two different levels within the algorithm. Several extensions of dual and primal iterative substructuring beyond two levels have been proposed in the past, see, e.g., [7] for FETI–DP, and, e.g., Tu [13,12,11] or [9] and [1] for BDDC. In the present article, a hybrid FETI/FETI–DP method is considered and some numerical results are presented. It is noted that independently, there is ongoing research on hybrid FETI methods by Jungho Lee of the Courant Institute. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Meshless Finite Difference Operators from Moving Least Squares Interpolation: Applications to PDEs and Convergence Results
Authors: Nowak Oliver 
Published: February 2009

AbstractWe give a brief introduction to moving least squares interpolation, which is followed by some reflections on the construction of meshless finite difference operators for derivative approximation and present finally a Korovkin–type convergence result for the pure interpolation approach. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Numerical solution of transonic and subsonic flow of compressible inviscid and viscous fluid
Authors: Punčochářová Petra , Kozel Karel , Horáček Jaromír , Fürst Jiří 
Published: February 2009

AbstractThe work presents two numerical solutions of compressible flows problems with high and very low Mach numbers. Both problems are numerically solved by finite volume method and the explicit MacCormack scheme using a grid of quadrilateral cells. Moved grid of quadrilateral cells is considered in the form of conservation laws using Arbitrary Lagrangian–Eulerian method. In the first case, inviscid transonic flow through cascade DCA 8% is presented and the numerical results are compared to experimental data. The second case, numerical solution of unsteady viscous flow in the channel for upstream Mach number M∞=0.012 and frequency of the wall motions 100 Hz is presented. The unsteady case can represent a simplified model of airflow coming from the trachea, through the glottal region with periodically vibrating vocal folds to the human vocal tract. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
On the Steffensen method under the generalized Lipschitz conditions for the divided difference operator
Authors: Shakhno S. M. 
Published: February 2009

AbstractConvergence of the Steffensen method for solving nonlinear operator equations in the Banach spaces under the generalized Lipschitz condition for the first–order divided differences is investigated. The conditions and quadratic speed of convergence of this method are found. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Discrete concepts for elliptic optimal control problems with constraints on the gradient of the state
Authors: Deckelnick Klaus , Günther Andreas , Hinze Michael 
Published: February 2009

AbstractWe consider elliptic optimal control problems with constraints on the gradient of the state and propose two distinguish concepts for their discretization. The first concept uses piecewise linear, continuous finite element Ansatz functions for the state, while the second concept uses the lowest order Raviart–Thomas mixed finite element. In both cases variational discretization from [5] is used for the controls. We present optimal finite element error estimates for the numerical solutions and confirm our theoretical findings by a numerical experiment. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
On convergence of Lavrentiev regularization for semilinear parabolic optimal control problems with pointwise control and state constraints
Authors: Neitzel Ira , Tröltzsch Fredi 
Published: February 2009

AbstractWe consider Lavrentiev regularization for a class of semilinear parabolic optimal control problems with control constraints and pointwise state constraints and review convergence results for local solutions under Slater type assumptions as well as quadratic growth conditions. Moreover, we state a local uniqueness result for local optima under the assumptions of strict separability of the active sets as well as a second order sufficient condition for the regularized solution. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Reduction of vibration due to change in mass configuration
Authors: Brząkała Aneta , Wójcicki Zbigniew , Majcher Krzysztof 
Published: February 2009

AbstractThe paper concerns the elimination of vibration due to changing the centre of gravity of a system. It is shown that the damping effect can be generated in an oscillating pendulum by a continuous motion of an auxiliary mass. A simple system in form of a variable length pendulum is considered. It is seen that if the pendulum length function is correctly chosen, the Coriolis force will cause additional damping effect in the system. The Floquet method is used to investigate the linear system stability. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Analysis of the Dynamics of Slender Continua Using Karhunen‐Loève‐Transformation
Authors: Göbel M. , Kreuzer E. 
Published: February 2009

AbstractThe dynamics of continua with very small diameter–to–length ratio, like bridges or drill–strings, has been object of mechanical analysis for a long time. While it is often possible to create a well–suited mechanical model, it is difficult to determine the exact current loads and the exact operational state. For drill–strings, the load of the drill–bit depends on the material of the rock, but also on other unknown disturbances like differential sticking which can occur along the drill–string without being noticed directly. Karhunen–Loève–Transformation (KLT) provides a possibility to describe the dynamics of a continuous system with few Characteristic Functions (CF), as long as the motion of the system is stationary. On the other hand, the resulting CFs of the KLT are sensitive to changes in the dynamic system behavior. These changes can result e. g. from the occurrence of stick–slip of the bit or differential sticking of the string. On the basis of a simple model, we show that this sensitivity can be used to detect and characterize such changes. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
A semi‐active isolator for torsional vibrations
Authors: Ineichen L. 
Published: February 2009

AbstractModern combustion engines produce strong rotational vibrations which could damage elements of the drive train such as the gearbox. A solution to this problem is to mount an isolating device on the output side of the motor. Its function is to filter the torque oscillations to deliver a clean averaged torque to the rest of the drive train. Passive systems have limitations, so that the design of such systems is always a compromise between the effectiveness of the isolation and maximal transmittable average torque. We propose a semi–active system that includes a degressive spring and a hydraulic actuator which can filter effectively the vibrations even if the average torque is high. This isolator is adaptive and doesn't need any command. The stability of this system of the third order is analysed with an averaging method. This leads to some considerations about the design of the control valve of the hydraulic actuator. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Boundary integral equations for viscous incompressible flows in porous media or past porous bodies
Authors: Kohr Mirela , Kohr Gabriela , Wendland Wolfgang L. 
Published: February 2009

AbstractThe purpose of this paper is to present the existence and uniqueness result for a boundary value problem which describes the flow of a viscous incompressible fluid past an arbitrary porous particle with a Lyapunov boundary, which is embedded in a second porous medium, by using the Brinkman model and the potential theory. We use a boundary integral method that reduces the problem to a system of second kind Fredholm integral equations that has a unique solution in some Hölder spaces. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Nonlinear vibration of a quarter‐car model excited by the road surface profile
Authors: Litak Grzegorz , Borowiec Marek 
Published: February 2009

AbstractWe examine the Melnikov criterion for a transition to chaos in case of a single–degree–of–freedom nonlinear oscillator with the Duffing potential with a nonlinear hard stiffness and a kinematic excitation term caused by the road profile. Using the new effective Hamiltonian we have examined appearance of homoclinic orbits in a quarter car model. Cross–sections of stable and unstable manifolds defined the condition of transition to chaos through a homoclinic bifurcation. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Elimination of tall building vibration resulting from ground motions
Authors: Majcher Krzysztof , Brząkała Aneta , Wójcicki Zbigniew 
Published: February 2009

AbstractIn this paper, the vibration problems of tall buildings are considered. The focus is on vibration caused by earthquakes, semi–seismic phenomena and ground vibrations of other origins. The construction consists of the main system and a vibration eliminator (passive tuned mass damper – pendulum type) which is attuned to the first eigenfrequency of the main structure. The analysis focuses on elimination of structure vibration caused by horizontal components of ground motions, while the functioning of the eliminator is simultaneously influenced by the vertical component (parametric effect – the possibility of improper functioning of the device). The vertical periodic movement of the support point can cause changes of the vibration eliminator's stiffness. In such a case parametric excitation occurs in the system, which signifies that parametric resonance may appear. The numerical analysis of the problem was performed with the Newmark method in conjunction with FEM. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Analysis of Nonlinear Quadratic Control in Infinite Time
Authors: Popescu Mihai 
Published: February 2009

AbstractThis study refers to minimization of quadratic functionals in infinite time. The coefficients of the quadratic form are quadratic matrices, function of the state variable. Dynamic constraints are represented by a bilinear differential systems of the form. The necessary extremum conditions determine the adjoint variables λ and the control variables u as functions of state variable, respectively the adjoint system corresponding to those functions. Thus it will be obtained a matrix differential equation where the solution representing the positive defined symmetric matrix P(x), verifies the Riccati algebraic equation. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Elimination of resonant vibration in cable stayed bridges and footbridges by active steering of tension in cables
Authors: Pakos Wojciech , Grosel Jacek , Wójcicki Zbigniew 
Published: February 2009

AbstractThe paper presented proposes a new approach to the elimination of vibration in cable stayed bridges and footbridges which may be applied to dynamic analysis of modern cable stayed bridges with typical structure systems. The reduction of the vibration is to be achieved by way of active steering of the tension in cables. The problem of eigenproblem sensitivity analysis with respect to change of the cable tension in cable stayed footbridges and bridges is considered. In the future, the information gained from the sensitivity analysis may be used to calculate how to steer the cable tension in a way that will ensure the most efficient resonant vibration elimination. Particular notice has been paid to the vibration of cables. The matrix equation of motion of a three–dimensional computer model of the structure has been created with the help of a non–standard use of standard computer software leaning on Finite Element Method (FEM). The system Mathematica and the authors' own program have also been used to analyze the eigenproblem sensitivity of bridges. An example has been provided. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Accessibility Conditions of Distributed‐Parameter Systems
Authors: Rieger Karl , Schlacher Kurt 
Published: February 2009

AbstractThis contribution is focused on the accessibility of distributed–parameter systems, where in particular the exact accessibility along a trajectory is considered. Based on a covariant description of a dynamic system within a differential geometrical framework a system–theoretical analysis is motivated by a transformation group approach and it is shown how (local) accessibility criteria can be derived successively. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)