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Stokes flow around cylinders in a bounded two-dimensional domain using multipole-accelerated boundary element methods

✍ Scribed by A. A. Mammoli; M. S. Ingber


Publisher
John Wiley and Sons
Year
1999
Tongue
English
Weight
217 KB
Volume
44
Category
Article
ISSN
0029-5981

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✦ Synopsis


The multipole technique has recently received attention in the ÿeld of boundary element analysis as a means of reducing the order of data storage and calculation time requirements from O(N 2 ) (iterative solvers) or O(N 3 ) (gaussian elimination) to O(N log N ) or O(N ), where N is the number of nodes in the discretized system. Such a reduction in the growth of the calculation time and data storage is crucial in applications where N is large, such as when modelling the macroscopic behaviour of suspensions of particles. In such cases, a minimum of 1000 particles is needed to obtain statistically meaningful results, leading to systems with N of the order of 10 000 for the smallest problems. When only boundary velocities are known, the indirect boundary element formulation for Stokes ow results in Fredholm equations of the second kind, which generally produce a well-posed set of equations when discretized, a necessary requirement for iterative solution methods. The direct boundary element formulation, on the other hand, results in Fredholm equations of the ÿrst kind, which, upon discretization, produce illconditioned systems of equations. The model system here is a two-dimensional wide-gap couette viscometer, where particles are suspended in the uid between the cylinders. This is a typical system that is e ciently modelled using boundary element method simulations. The multipolar technique is applied to both direct and indirect formulations. It is found that the indirect approach is su ciently well-conditioned to allow the use of fast multipole methods. The direct approach results in severe ill-conditioning, to a point where application of the multipole method leads to non-convergence of the solution iteration.


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