bluuebunny/crossref_metadata_2025_split huggingface dataset:
Efficient Aerodynamic Shape Optimization in MDO Context
Authors: Fazzolari Antonio , Gauger Nicolas R. , Brezillon Jöel 
Published: December 2005

AbstractThe aerospace industry is increasingly relying on advanced numerical flow simulation tools in the early aircraft design phase. Today's flow solvers, which are based on the solution of the compressible Euler and Navier‐Stokes equations, are able to predict aerodynamic behaviour of aircraft components under different flow conditions quite well [1]. Within the next few years numerical shape optimization will play a strategic role for future aircraft design. It offers the possibility of designing or improving aircraft components with respect to a pre‐specified figure of merit, subject to geometrical and physical constraints. Here, aero‐structural analysis is necessary to reach physically meaningful optimum wing designs. The use of single disciplinary optimizations applied in sequence is not only inefficient but in some cases is known to lead to wrong, non‐optimal designs [2]. Although multidisciplinary optimizations (MDO) are possible with classical approaches for sensitivity evaluations by means of finite differences, these methods are extremely expensive in terms of calculation time, requiring the reiterated solution of the coupled problem for every design variable.However, adjoint approaches allow the evaluation of these sensitivities in an efficient way and lead to high accuracy. Firstly, we present the development and application of a continuous adjoint approach for single disciplinary aerodynamic shape design. This approach was previously developed at the German Aerospace Center (DLR) [3] and was the starting point for the extension to aero‐structural wing designs. Secondly, we describe the adjoint approach and its implementation for the evaluation of the sensitivities for coupled aero‐structure optimization problems [4] and its application to the drag reduction of the AMP wing by constant lift while taking into account the static deformation of this wing caused by the aerodynamic forces (see figures). Finally, we show the application of the coupled aero‐structural adjoint approach for the Breguet formula of aircraft range, where in addition to the lift to drag ratio the weight of the AMP wing is taken into account (see figures). (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Preconditioning of One‐Shot Pseudo‐Timestepping Methods for Shape Optimization
Authors: Gherman Ilia , Schulz Volker 
Published: December 2005

AbstractOne‐shot pseudo‐timestepping [1, 2] has proven to be a powerful approach for the solution of optimal design problems in engineering applications. It blends well in within pre‐existing pseudo‐timestepping simulation solvers. The goal of this approach is to transform the equations for the necessary optimality conditions of the optimal design problem into an ordinary differential equation (ODE) and then solve the pseudo‐time embedded state, co‐state and design equations all at once. Similar approaches have been considered in [4, 5]. An application of this method to a real‐world example within the MEGADESIGN‐Project has been presented in [3]. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Simultaneous pseudo‐time stepping for aerodynamic shape optimization
Authors: Hazra Subhendu Bikash , Gauger Nicolas R. 
Published: December 2005

AbstractIn this paper we discuss about numerical methods for aerodynamic shape optimization problems. These problems require efficient CFD techniques to solve the state (as well as costate) equations and fast algorithms for solving the optimization problems. Both of these are independent active areas of research since long time. Wide range of applications in science and engineering involve solution of optimization problems where the governing PDEs appear as constraints. Therefore, merging the two for the purpose of practical applicability is relatively new. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Real‐Time Solution of Bi‐Level Optimal Control Problems
Authors: Knauer Matthias , Büskens Christof , Lasch Peter 
Published: December 2005

AbstractBi‐level optimal control problems are presented as an extension to classical optimal control problems. Hereby, additional constraints for the primary problem are considered, which depend on the optimal solution of a secondary optimal control problem. A demanding problem is the numerical complexity, since at any point in time the solution of the optimal control problem as well as a complete solution of the secondary problem have to be determined. Hence we deal with two dependent variables in time. The numerical solution of the bi‐level problem is illustrated by an application of a container crane. Jerk and energy optimal trajectories with free final time are calculated under the terminal condition that the crane system comes to be at rest at a predefined location. In enlargement additional constraints are investigated to ensure that the crane system can be brought to a rest position by a safety stop at a free but admissible location in minimal time from any state of the trajectory. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Static Output Feedback ℋ︁∞–Synthesis by solving the ℋ︁∞–NSDP
Authors: Leibfritz Friedemann 
Published: December 2005

AbstractWe consider the solution of the static output feedback (SOF) ℋ︁∞ control design problem. In particular, we solve the corresponding non–convex and nonlinear semidefinite program (NSDP), the so–called ℋ︁∞–NSDP, by a suitable optimization solver. Finally, we demonstrate the behavior of the solver on the COMPleibbenchmark collection. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Optimization of open cross sections of thin‐walled beams with plate‐shell‐flanges
Authors: Maćkiewicz Mikołaj , Magnucki Krzysztof 
Published: December 2005

AbstractThe paper is devoted to a monosymetrical cold‐formed thin‐walled beam with open cross section. Its flange consists of plates and circular shells. The beam is under pure bending. The cross section is characterized by dimensionless parameters. The authors are searching for an optimal cross section shape of considered beam. This optimal shape is determined by means of parametric optimization. The dimensionless objective function is so defined as to comprise both cross section area and a maximal allowable bending moment. The constraints follow from the local buckling conditions and geometric restrictions. Moreover, there are optimized cross sections of beams, for which the shear center is located either in the web or in the centroid of the cross section. Results are compared and analyzed. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Different Optimization Models for Crack‐Free Laser Welding
Authors: Petzet Verena , Pesch Hans Josef , Prikhodovsky Andrey , Ploshikhin Vasily 
Published: December 2005

AbstractConventional laser beam welding of aluminum alloys often leads to hot cracking. This is caused by a complex process where thermo‐mechanical and metallurgical aspects are involved; cf. [3], [2]. A possibility to prevent hot crack initiation yields the multi‐beam welding technique (cf. [2]), where additional laser beams are led parallelly besides the main laser beam. There by optimal positions, sizes, and powers of the additional laser beams play an important role otherwise hot cracking can even be enhanced.In [1], [4], resp., a mechanical 1D and thermal 2D model of hot cracking was derived. It provides the basis for different formulations of constrained nonlinear programming problems to identify the optimal parameters of the additional laser beams. In the present paper a comparison between these formulations and between two different optimizers for the so far best formulation are presented. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
On Low Mach Number Preconditioning of Finite Volume Schemes
Authors: Birken Philipp , Meister Andreas 
Published: December 2005

AbstractA finite volume method for inviscid unsteady flows at low Mach numbers is studied. The method uses a preconditioning of the dissipation term within the numerical flux function only. It can be observed by numerical experiments, as well as by analysis, that the preconditioned scheme yields a physically corrected pressure distribution and combined with an explicit time integrator it is stable if the time step Δt satisfies the requirement to be 𝒪(M 2) as the Mach number M tends to zero, whereas the corresponding standard method remains stable up to Δt = 𝒪(M ),M → 0, though producing unphysical results. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Oscillatory instabilities of high‐resolution TVD central schemes for hyperbolic conservation laws
Authors: Breuß Michael 
Published: December 2005

AbstractEven if a numerical scheme for hyperbolic conservation laws is total variation diminishing, it can create oscillations at data extrema. We show that such oscillations can reduce the overall accuracy of a method considerably, effectively reducing a high‐resolution scheme to first order accuracy. The phenomenon is investigated and we derive accurate non‐staggered accurate central schemes not featuring this weakness. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Adaptive Frame Algorithms for Elliptic Operator Equations
Authors: Dahlke Stephan , Fornasier Massimo , Raasch Thorsten 
Published: December 2005

AbstractWe discuss the use of Gelfand frames for the adaptive numerical solution of linear elliptic operator equations. After a transformation into an equivalent infinite–dimensional system Lu = f in frame coordinates, the operator equation can be solved within a prescribed target accuracy by approximate Richardson or gradient iteration schemes. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Fast Wavelet BEM on Complex Geometries
Authors: Harbrecht H. , Kähler U. , Schneider R. 
Published: December 2005

AbstractThis paper is devoted to the fast solution of boundary integral equations on unstructured meshes by the Galerkin scheme. Since traditional discretizations yield densely populated system matrices it is necessary to use fast techniques like ACA, the multipole method or wavelet matrix compression, which will be the topic of the present paper. On the given, possibly unstructered, mesh we construct a wavelet basis providing vanishing moments with respect to the traces of polynomials in the space. With this basis at hand, the system matrix in wavelet coordinates can be compressed to 𝒪(N logN ) relevant matrix coefficients, where N denotes the number of unknowns. The compressed system matrix can be computed within suboptimal complexity by using fast multipole or ℋ︁‐matrix techniques. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Multiscale Flow Simulation by Adaptive Finite Volume Particle Methods
Authors: Iske Armin 
Published: December 2005

AbstractWe report on recent developments concerning adaptive finite particle methods, which are used for the numerical simulation of multiscale phenomena in time‐dependent evolution processes. The proposed concept relies on a finite volume approach, which we combine with WENO reconstruction from particle average values. In this method, polyharmonic splines are key tools for both the optimal recovery from scattered particle averages and the construction of customized adaption rules. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
On the Turbulence Modelling of 3D‐Atmospheric Boundary Layer Flow
Authors: Sládek I. , Kozel K. , Jaňour Z. 
Published: December 2005

AbstractThe paper presents a mathematical and numerical investigation of the 3D–flow in the atmospheric boundary layer (ABL) over complex relief. The two–equation k ‐ ε model is applied to account for the turbulence. The flow is also supposed to be viscous, incompressible and stationary. The boundary conditions are realized through the wall‐functions. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Numerical simulation of a three dimensional quantum dot
Authors: Voss Heinrich 
Published: December 2005

AbstractWe consider the problem to compute relevant energy states and corresponding wave functions of a three dimensional semiconductor quantum dot. Let Ωq ⊂ ℝ3 be a domain occupied by the quantum dot, which is embedded in a matrix Ωm of different material. A typical example is an InAs pyramidal quantum dot embedded in a cuboid GaAs matrix. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Approximating Jacobians by the TR2 formula
Authors: Griewank Andreas , Korzec Maciek 
Published: December 2005

AbstractIn the context of KKT systems for nonlinear optimization one wishes to approximate rectangular Jacobian matrices of active constraints. A possible approximation is the Two‐Sided‐Rank‐One update (TR1) motivated in [1]. Since its denominator can easily become small we tried to prevent a possible blow up and achieve better approximations with the newly introduced Two‐Sided‐Rank‐Two update (TR2), which otherwise preserves the good qualities of the TR1. We motivate, introduce and discuss the two low‐rank‐updates. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Efficient similarity factorization of rank‐1 modifications
Authors: Schlenkrich Sebastian , Griewank Andreas , Walther Andrea 
Published: December 2005

AbstractFor the solution of stiff ODEs by implicit methods one has to solve sequences of algebraic systems, whose Jacobian is the identity minus a multiple of the 'system' Jacobian of the right hand side. The latter can be successively approximated by a new 'two‐sided rank‐1' formula yielding only a moderate increase in the number of iterations compared to Newton's method. However, so far we have only been able to achieve the reduction in the linear algebra effort per integration step from O (n 3) to O (n 2) as long as the size is kept constant. To obtain an effort of O (n 2) seems to require an update of a similarity reduction of the system Jacobian to Hessenberg form or even a band matrix. As we have found no O (n 2) algorithms for updating such factorizations in literature, we discuss an idea to approximate the update with enough accuracy to ensure rapid convergence of the underlying implicit equation solver. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
An Iterative Technique for Construction of Invariant Subspaces
Authors: Zítko Jan , Ulrychová Iveta 
Published: December 2005

AbstractThe restarted GMRES(m ) method for solving linear systems Ax = b is attractive when a good preconditioner is available. The determining of efficient preconditioners is often connected to a construction of an A –invariant subspace corresponding to eigenvalues closest to zero. One class of methods for determination of invariant subspaces is based on the construction of polynomial filters. We study the usage of Tchebychev polynomials for constructing suitable filters. Applying filters on the initial restart vectors amplifies the components of eigenvectors belonging to the small (wanted) eigenvalues and damp the remaining (unwanted) components. The presented convergence theorem describes the repeated application of filters for the construction of the wanted eigenspace of the matrix A . (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Verringerung der thermischen Belastung eines Hyperschall‐Flugsystems durch Trajektorienoptimierung
Authors: Chudej Kurt , Wächter Markus , LeBras Florent 
Published: December 2005

AbstractWir stellen eine Flugbahnoptimierung eines Hyperschall‐Flugsystems vor, die Beschränkungen der thermischen Belastung beinhaltet. Hierzu wird ein neu entwickeltes zweidimensionales Modell für das Thermalschutzsystem benutzt. Die Nebenbedingung in Form einer partiellen Differentialgleichung wird durch die Linienmethode in eine gewöhnliche Differentialgleichung transformiert. Außerdem wurde die aktive Kühlung des Triebwerks mitberücksichtigt. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Stability Analysis of a Reduced Heat Exchanger Model
Authors: Hanke Michael , Olsson K. Henrik A. , Strömgren Magnus 
Published: December 2005

AbstractWe consider the mathematical model of a heat exchanger in a heat pumping system using carbon dioxide as refridgerant. From the Euler equations of compressible fluid flow we derive a reduced model, called the zero Mach‐number limit, by eliminating time scales associated with soundwaves. The reduced model is a highly nonlinear partial differential‐algebraic equation (PDAE). We analyse the stability of this model and show that it is possible to use simple spatial discretisations within the method of lines (MOL), a standard practice in many system simulation software, to simulate the system. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Warped MPDAE Models including Minimisation Criteria for the Simulation of RF Signals
Authors: Pulch Roland 
Published: December 2005

AbstractIn radio frequency (RF) applications, electric circuits produce signals including widely separated time scales. A multidimensional representation yields an efficient model by decoupling the time scales. Consequently, a warped multirate partial differential algebraic equation (MPDAE) describes the circuit's behaviour. The appropriate determination of an arising local frequency function is crucial for the efficiency of this approach. Variational calculus implies a necessary condition to a specific solution, which exhibits a minimal amount of oscillations in the whole domain of dependence. We apply a similar strategy to minimise oscillatory performance in some boundary values only. Now variational calculus yields a boundary condition, which can easily be used in numerical methods. We compare the results of both minimisation criteria in a simulation of a warped MPDAE model. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Explicit Order 1.5 Schemes for the Strong Approximation of Itô Stochastic Differential Equations
Authors: Rößler Andreas 
Published: December 2005

AbstractA new class of stochastic Runge‐Kutta (SRK) methods for the strong approximation of It ô stochastic differential equation systems w.r.t. an one‐dimensionalWiener process is introduced. Some coefficients for a SRK method converging at least with order 1.5 in the strong sense are presented. Further, a special SRK scheme having deterministic order 4.0 is proposed for stochastic differential equations with small noise. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Multirate hierarchical time integration for electronic circuits
Authors: ter Maten J. , Verhoeven A. , El Guennouni A. , Beelen Th. 
Published: December 2005

AbstractElectrical circuits are hierarchically defined, in which electrical components are combined with submodels. These last ones may contain submodels themselves. This construction gives options for dedicated time integration procedures. We describe an extension that allows for a dynamically partitioned multirate time integration that retains a number of hierarchical efficiencies. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
State of the Art on the Error Reduction in AFEM
Authors: Carstensen Carsten 
Published: December 2005

AbstractThe a priori convergence of finite element methods (FEMs) is justified by some density property of the sequence of finite element spaces which essentially assumes some global mesh‐refining. Adaptive finite element methods (AFEMs) avoid an overall refinement in each refinement step to save degrees of freedom and hopefully lead to an improved efficiency. Hence, the a priori convergence of AFEMs isnotguaranteed automatically and, in fact, crucially depends on algorithmic details. This presentation aims at a survey on error reduction and convergence properties. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Convergence of adaptive finite element methods in elastoplasticity
Authors: Carstensen Carsten , Orlando Antonio 
Published: December 2005

AbstractWe show that an adaptive conforming finite element method for the solution of a variational inequality of the second kind, as model of one implicit time step of the primal problem of plasticity with positive hardening, yields the energy reduction property and the R ‐linear convergence of the stresses. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Performance Optimization for the Parallel Gauss–Seidel Smoother
Authors: Gräbel Jens , Lang Bruno , Ueberholz Peer 
Published: December 2005

AbstractSimulation, e.g., in the field of computational fluid dynamics, accounts for a major part of the computing time on highperformance systems. Many simulation packages still rely on Gauss–Seidel iteration, either as the main linear solver or as a smoother for multigrid schemes. Straight‐forward implementations of this solver have efficiency problems on today's most common high‐performance computers, i.e., multiprocessor clusters with pronounced memory hierarchies. In this work we present two simple techniques for improving the performance of the parallel Gauss–Seidel method for the 3D Poisson equation by optimizing cache usage as well as reducing the number of communication steps. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
On the strong stability of differential equations and difference schemes
Authors: Jovanović Boško S. 
Published: December 2005

AbstractPaper deals with the construction of a priori estimates for the solution of Cauchy problem for an abstract linear differential equation in Hilbert space under perturbations of the initial condition, right‐hand side, and operators of the problem. It is shown that a priori estimates of strong stability can be obtained directly on the basis of various a priori estimates for the solution of the Cauchy problem. The perturbations of the operators of the problem are estimated in the corresponding operator norms. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
First Order LSFEM for Second Order Hyperbolic Problems
Authors: Kayser‐Herold O. , Matthies H. G. 
Published: December 2005

AbstractIn the last years the interest in least squares finite element methods has grown due to some interesting properties of these methods (cf. the monographs [1], [2]). While for many elliptic problems the theoretical background has been established, only a few articles analyse least squares methods for transient problems. In this article some new stability estimates for the least squares method for the wave equation in 1 and 2 dimensions are derived. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Finite element and matched asymptotic expansion methods for chemical reactor flow problems
Authors: Skrzypacz Piotr , Tobiska Lutz 
Published: December 2005

AbstractThe study of flow behaviour in packed beds is an important part of the development of powerful and economical reactors. The considered averaged flow in the reactor channel filled with pelletes is modelled by the Brinkman‐Forchheimer‐extended Darcy equation. For the nonlinear problem subjected to Dirichlet boundary conditions we show existence and uniqueness (for small data) of weak solutions. The velocity profiles exhibit boundary layers which have to be resolved numerically. We present error estimates for inf‐sup stable finite element pairs. In the case of fully developed flow and high Reynolds number the finite element solution can be compared to the flow profile obtained by using the method of matched asymptotic expansions. Finally, numerical simulations for flows in fixed bed and packed bed membrane reactors are discussed. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)