In this paper we study the fluidization of 1204 spheres at Reynolds numbers in the thousands using the method of distributed Lagrange multipliers. The results of the simulation are compared with a real experiment. This is the first direct numerical simulation of a real fluidized bed at the finite Reynolds number encountered in the applications. The simulations are processed like real experiments for straight lines in lot-log plots leading to power laws as in celebrated correlations of Richardson and Zaki [1954]. The numerical method allows for the first ever direct calculation of the slip velocity and other averaged values used in two-fluid continuum models. The computation and the experiment show that a single particle may be in balance under weight and drag for an interval of fluidizing velocities; the expectation that the fluidizing velocity is unique is not realized. The numerical method reveals that the dynamic pressure actually decreases slowly with the fluidizing velocity. Tentative interpretations of these new results are discussed.

Capacitance extraction is an important problem that has been extensively studied. This paper presents a significant improvement for the fast multipole accelerated boundary element method. We first introduce an algebraic transformation to convert the n × n dense capacitance coefficient matrix into a sparse matrix with O(n) nonzero entries. We then use incomplete Cholesky factorization or incomplete LU factorization to produce an effective preconditioner for the sparse linear system. Simulation results show that our algorithm drastically reduces the number of iterations needed to solve the linear system associated with the boundary element method. For the k × k bus crossing benchmark, our algorithm uses 3-4 iterations, compared to 10-20 iterations used by the previous algorithms such as FastCap [1] and HiCap [2]. As a result, our algorithm is 2-20 times faster than those algorithms. Our algorithm is also superior to the multi-scale method [3] because our preconditioner reduces the number of iterations further and applies to multiple dielectrics.

The generalized Stokes problem, which arises frequently in the simulation of timedependent Navier-Stokes equations for incompressible fluid flow, gives rise to symmetric linear systems of equations. These systems are indefinite due to a set of linear constraints on the velocity, causing difficulty for most preconditioners and iterative methods. This paper presents a novel method to obtain a preconditioned linear system from the original one which is then solved by an iterative method. This new method generates a basis for the velocity space and solves a reduced system which is symmetric and positive definite. Numerical experiments indicating superior convergence compared to existing methods are presented. A natural extension of this method to elliptic problems is also proposed, along with theoretical bounds on the rate of convergence, and results of experiments demonstrating robust and effective preconditioning.

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