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Tue, 17 Oct 2000 00:00:00 +0200Tue, 17 Oct 2000 00:00:00 +0200A Comparison of Simulation Methods for Rarefied Gas Flows
https://kluedo.ub.uni-kl.de/frontdoor/index/index/docId/730
Simulation methods like DSMC are an efficient tool to compute rarefied gas flows. Using supercomputers it is possible to include various real gas effects like vibrational energies or chemical reactions in a gas mixture. Nevertheless it is still necessary to improve the accuracy of the current simulation methods in order to reduce the computational effort. To support this task the paper presents a comparison of the classical DSMC method with the so called finite Pointset Method. This new approach was developed during several years in the framework of the European space project HERMES. The comparison given in the paper is based on two different testcases: a spatially homogeneous relaxation problem and a 2-dimensional axisymmetric flow problem at high Mach numbers.Jens Struckmeier; Konrad Steinerpreprinthttps://kluedo.ub.uni-kl.de/frontdoor/index/index/docId/730Tue, 17 Oct 2000 00:00:00 +0200An Adaptive Wavelet Galerkin Algorithm for one and two Dimensional Flame Computations
https://kluedo.ub.uni-kl.de/frontdoor/index/index/docId/731
This paper is concerned with the development of a self-adaptive spatial descretization for PDEs using a wavelet basis. A Petrov-Galerkin method [LPT91] is used to reduce the determination of the unknown at the new time step to the computation of scalar products. These have to be discretized in an appropriate way. We investigate this point in detail and devise an algorithm that has linear operation count with respect to the number of unknowns. It is tested with spline wavelets and Meyer wavelets retaining the latter for their better localisation at finite precision. The algorithm is then applied to the one dimensional thermodiffusive equations. We show that the adaption strategy merits to be modified in order to take into account the particular and very strong nonlinearity of this problem. Finally, a supplementary Fourier discretization permits the computation of two dimensional flame fronts.J. Fröhlich; K. Schneiderpreprinthttps://kluedo.ub.uni-kl.de/frontdoor/index/index/docId/731Tue, 17 Oct 2000 00:00:00 +0200Multivariate First-Order Integer-Valued Autoregressions
https://kluedo.ub.uni-kl.de/frontdoor/index/index/docId/734
Jürgen Franke; T. Rao Subbapreprinthttps://kluedo.ub.uni-kl.de/frontdoor/index/index/docId/734Tue, 17 Oct 2000 00:00:00 +0200Exact Solutions of Discrete Kinetic Models and Stationary Problems for the Plane Broadwell Model
https://kluedo.ub.uni-kl.de/frontdoor/index/index/docId/738
A.V. Bobylevpreprinthttps://kluedo.ub.uni-kl.de/frontdoor/index/index/docId/738Tue, 17 Oct 2000 00:00:00 +0200On a Kinetic Model for Shallow Water Waves
https://kluedo.ub.uni-kl.de/frontdoor/index/index/docId/528
The system of shallow water waves is one of the classical examples for nonlinear, twodimensional conservation laws. The paper investigates a simple kinetic equation depending on a parameter e which leads for e to 0 to the system of shallow water waves. The corresponding equilibrium distribution function has a compact support which depends on the eigenvalues of the hyperbolic system. It is shown that this kind of kinetic approach is restricted to a special class of nonlinear conservation laws. The kinetic model is used to develop a simple particle method for the numerical solution of shallow water waves. The particle method can be implemented in a straightforward way and produces in test examples sufficiently accurate results.Jens Struckmeierpreprinthttps://kluedo.ub.uni-kl.de/frontdoor/index/index/docId/528Mon, 03 Apr 2000 00:00:00 +0200An Analysis of Baganoff" s Shuffle Algorithm
https://kluedo.ub.uni-kl.de/frontdoor/index/index/docId/725
The paper presents the shuffle algorithm proposed by Baganoff, which can be implemented in simulation methods for the Boltzmann equation to simplify the binary collision process. It is shown that the shuffle algborithm is a discrete approximation of an isotropic collision law. The transition probability as well as the scattering cross section of the shuffle algorithm are opposed to the corresponding quantities of a hard-sphere model. The discrepancy between measures on a sphere is introduced in order to quantify the approximation error by using the shuffle algorithm.Konrad Steinerpreprinthttps://kluedo.ub.uni-kl.de/frontdoor/index/index/docId/725Mon, 03 Apr 2000 00:00:00 +0200Tensor Spherical Harmonics and Tensor Spherical Splines
https://kluedo.ub.uni-kl.de/frontdoor/index/index/docId/726
In this paper, we deal with the problem of spherical interpolation of discretely given data of tensorial type. To this end, spherical tensor fields are investigated and a decomposition formula is described. Tensor spherical harmonics are introduced as eigenfunctions of a tensorial analogon to the Beltrami operator and discussed in detail. Based on these preliminaries, a spline interpolation process is described and error estimates are presented. Furthermore, some relations between the spline basis functions and the theory of radial basis functions are developed.Willi Freeden; T. Gervens; Michael Schreinerpreprinthttps://kluedo.ub.uni-kl.de/frontdoor/index/index/docId/726Mon, 03 Apr 2000 00:00:00 +0200Construction of Particlesets to Simulate Rarefied Gases
https://kluedo.ub.uni-kl.de/frontdoor/index/index/docId/727
In this paper a new method is introduced to construct asymptotically f-distributed sequences of points in the IR^d. The algorithm is based on a transformation proposed by E. Hlawka and R. Mück. For the numerical tests a new procedure to evaluate the f-discrepancy in two dimensions is proposed.Michael Hackpreprinthttps://kluedo.ub.uni-kl.de/frontdoor/index/index/docId/727Mon, 03 Apr 2000 00:00:00 +0200Domain Decomposition: Linking Kinetic and Aerodynamic Descriptions
https://kluedo.ub.uni-kl.de/frontdoor/index/index/docId/729
We discuss how kinetic and aerodynamic descriptions of a gas can be matched at some prescribed boundary. The boundary (matching) conditions arise from requirement that the relevant moments (p,u,...) of the particle density function be continuous at the boundary, and from the requirement that the closure relation, by which the aerodynamic equations (holding on one side of the boundary) arise from the kinetic equation (holding on the other side), be satisfied at the boundary. We do a case study involving the Knudsen gas equation on one side and a system involving the Burgers equation on the other side in section 2, and a discussion for the coupling of the full Boltzmann equation with the compressible Navier-Stokes equations in section 3.Reinhard Illner; Helmut Neunzertpreprinthttps://kluedo.ub.uni-kl.de/frontdoor/index/index/docId/729Mon, 03 Apr 2000 00:00:00 +0200Fast Generation of Low-Discrepancy Sequences
https://kluedo.ub.uni-kl.de/frontdoor/index/index/docId/732
The paper presents a fast implementation of a constructive method to generate a special class of low-discrepancy sequences which are based on Van Neumann-Kakutani tranformations. Such sequences can be used in various simulation codes where it is necessary to generate a certain number of uniformly distributed random numbers on the unit interval.; From a theoretical point of view the uniformity of a sequence is measured in terms of the discrepancy which is a special distance between a finite set of points and the uniform distribution on the unit interval.; Numerical results are given on the cost efficiency of different generators on different hardware architectures as well as on the corresponding uniformity of the sequences. As an example for the efficient use of low-discrepancy sequences in a complex simulation code results are presented for the simulation of a hypersonic rarefied gas flow.Jens Struckmeierpreprinthttps://kluedo.ub.uni-kl.de/frontdoor/index/index/docId/732Mon, 03 Apr 2000 00:00:00 +02003D Eddy-Current Computation Using Krylov Subspace Methods
https://kluedo.ub.uni-kl.de/frontdoor/index/index/docId/733
This paper considers the numerical solution of a transmission boundary-value problem for the time-harmonic Maxwell equations with the help of a special finite volume discretization. Applying this technique to several three-dimensional test problems, we obtain large, sparse, complex linear systems, which are solved by using BiCG, CGS, BiCGSTAB resp., GMRES. We combine these methods with suitably chosen preconditioning matrices and compare the speed of convergence.Martin Reißelpreprinthttps://kluedo.ub.uni-kl.de/frontdoor/index/index/docId/733Mon, 03 Apr 2000 00:00:00 +0200Nonorthogonal Expansions on the Sphere
https://kluedo.ub.uni-kl.de/frontdoor/index/index/docId/736
Discrete families of functions with the property that every function in a certain space can be represented by its formal Fourier series expansion are developed on the sphere. A Fourier series type expansion is obviously true if the family is an orthonormal basis of a Hilbert space, but it also can hold in situations where the family is not orthogonal and is overcomplete. Furthermore, all functions in our approach are axisymmetric (depending only on the spherical distance) so that they can be used adequately in (rotation) invariant pseudodifferential equations on the frames (ii) Gauss- Weierstrass frames, and (iii) frames consisting of locally supported kernel functions. Abel-Poisson frames form families of harmonic functions and provide us with powerful approximation tools in potential theory. Gauss-Weierstrass frames are intimately related to the diffusion equation on the sphere and play an important role in multiscale descriptions of image processing on the sphere. The third class enables us to discuss spherical Fourier expansions by means of axisymmetric finite elements.Willi Freeden; Michael Schreinerpreprinthttps://kluedo.ub.uni-kl.de/frontdoor/index/index/docId/736Mon, 03 Apr 2000 00:00:00 +0200Generalized Weighted Spline Approximation on the Sphere
https://kluedo.ub.uni-kl.de/frontdoor/index/index/docId/737
Spline functions that interpolate data given on the sphere are developed in a weighted Sobolev space setting. The flexibility of the weights makes possible the choice of the approximating function in a way which emphasizes attributes desirable for the particular application area. Examples show that certain choices of the weight sequences yield known methods. A pointwise convergence theorem containing explicit constants yields a useable error bound.Willi Freeden; R. Frankepreprinthttps://kluedo.ub.uni-kl.de/frontdoor/index/index/docId/737Mon, 03 Apr 2000 00:00:00 +0200Modelling and Numerical Simulation of Collisions
https://kluedo.ub.uni-kl.de/frontdoor/index/index/docId/735
In these lectures we will mainly treat a billard game. Our particles will be hard spheres. Not always: We will also touch cases, where particles have interior energies due to rotation or vibration, which they exchange in a collision, and we will talk about chemical reactions happening during a collision. But many essential aspects occur already in the billard case which will be therefore paradigmatic. I do not know enough about semiconductors to handle collisions there - the Boltzmann case is certainly different but may give some idea even for the other cases.Helmut Neunzertpreprinthttps://kluedo.ub.uni-kl.de/frontdoor/index/index/docId/735Fri, 01 Jan 1993 00:00:00 +0100