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  • 1
    Electronic Resource
    Electronic Resource
    Properties of Detonation Waves (1996)
    Chichester, West Sussex : Wiley-Blackwell
    Mathematical Methods in the Applied Sciences 19 (1996), S. 1279-1301 
    Details
    ISSN: 0170-4214
    Keywords: Engineering ; Numerical Methods and Modeling
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics
    Notes: The phenomenon of unphysical wave propagation speeds sometimes occurs in numerical computations of detonation waves on coarse grids. The strong detonation wave splits into two parts, a weak detonation which travels with the speed of one cell per time step and an ordinary shock wave.We analyse a simplified set of equations and look for travelling wave solutions. It is shown that the solution depends on the dimensionless number Kr = μK/Qρ1. Here μ is the viscosity, K is the rate of reaction, Q is the heat release available in the process and ρ1 is the density at the unburnt state. It is shown that the density peak of the travelling wave depends on Kr and also, that if Kr is sufficiently large there is no travelling wave solution. The erroneous behaviour above is explained as an effect of the artificial viscosity necessarily inherent in the numerical methods when coarse grids are used. To prevent this unphysical behaviour we suggest the use of an ‘artificial rate of reaction’ such that the actual value of Kr used in the numerical method retains its correct physical value.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
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    Paper (German National Licenses)
  • 2
    Electronic Resource
    Electronic Resource
    Properties of simple model problems for reacting gas flows (1994)
    Chichester, West Sussex : Wiley-Blackwell
    Mathematical Methods in the Applied Sciences 17 (1994), S. 577-596 
    Details
    ISSN: 0170-4214
    Keywords: Mathematics and Statistics ; Applied Mathematics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics
    Notes: The compressible Navier-Stokes equations for reacting gases are extremely complex. Simpler models have been considered, and for these completely non-physical propagation speeds have been observed. These model problems are stiff, meaning that several different scales are present in the solution. Numerical solution of non-reacting flows almost always involves addition of extra dissipation. It will be shown that this action will render a totally wrong propagation speed for a simple model equation of reacting flows. This problem will be accentuated by increasing stiffness of the problem. Existence and uniqueness of a solution to this model equation is proved. The dependence of the propagation speed on the viscosity and a term governing the stiffness (comparable to the reaction rate for a more complete model) is investigated. A remedy for the wrong propagation speed for this simple model equation is proposed such that the speed is correct although the front is smeared out.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/mma.1670170802
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  • 3
    Electronic Resource
    Electronic Resource
    A data-parallel approach to multiblock flow computations (1994)
    Chichester : Wiley-Blackwell
    International Journal for Numerical Methods in Fluids 19 (1994), S. 707-721 
    Details
    ISSN: 0271-2091
    Keywords: Data-parallel ; Block-structured mesh ; Compressible flow ; Load balancing ; Boundary conditions ; Code portability ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Multiblock methods are often employed to compute flows in complex geometries. While such methods lend themselves in a natural way to coarse-grain parallel processing by the distribution of different blocks to different processors, in some situations a fine-grain data-parallel implementation may be more appropriate. A study is presented of the resolution of the Euler equations for compressible flow on a block-structured mesh, illustrating the advantages of the data-parallel approach. Particular emphasis is placed on a dynamic block management strategy that allows computations to be undertaken only for blocks where useful work is to be performed. In addition, appropriate choices of initial and boundary conditions that enchance solution convergence are presented. Finally, code portability between five different massively parallel computer systems is examined and an analysis of the performance results obtained on different parallel systems is presented.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/fld.1650190806
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