We present a novel method for simulating hydrodynamic phenomena. This particle-based method combines features from molecular dynamics and lattice-gas automata. I t is shown theoretically as well as in simulations that a quantitative description of isothermal Navier-Stokes flow is obtained with relatively few particles. Computationally, the method is much faster than molecular dynamics, and the at same time it is much more flexible than lattice-gas automata schemes.

We have studied the flow of suspensions of solid spheres under steady shear using a newly developed flow simulator. For the first time, the complicated interplay between hydrodynamic interactions and solids' variable configuration under flo$ conditions in which large departures from equilibrium configurations occur can be simulated in full 3D. For volume fractions up to 35%, viscosities have been obtained that are in excellent agreement with experiments reported in the literature.Determining the steady-shear viscosity of a suspension of equally sized hard spheres in a Newtonian fluid may be regarded as a basic model problem for studying suspension behaviour. The monodisperse hard-sphere system has been extensively studied, experimentally [1,2], theoretically [3-91, and by computer simulations [lo, 111. The theoretical and simulation efforts up to now had to make simplifying assumptions, because full treatment of all relevant aspects, i.e. multibody hydrodynamic interactions, Brownian motion and temporal and spatial correlation of sphere positions in a flow field, is extremely difficult. Usually, one or more aspects are ignored, and the validity of the resulting viscosity data is limited to extreme (from a practical point of view less relevant) cases: dilute suspensions [3,4], equilibrium sphere configurations [4-lo], or sphere monolayers [ 111.In contrast, practical applications usually deal with concentrated suspensions at shear rates giving rise to nonequilibrium configurations. This can easily be seen by considering the two relevant time scales: 1) the time over which Brownian diffusion restores the equilibrium configuration, R 2 / D o (here R represents the sphere radius and Do = kT/6xpoR the single-sphere diffusion coefficient with po the solvent viscosity), and 2) the time needed for the flow to perturb the microstructure significantly: l/f (with i. the shear rate). The ratio between these two time scales, the Peclet number Pe = f R z /Do, measures the <

SynopsisA novel method of investigating the link between molecular features of polymer molecules and the rheological properties of dilute polymer solutions has been investigated. It applies the dissipative particle dynamics (DPD) computer simulation technique, which introduces a lattice-gas automata time-stepping procedure into a molecular-dynamics scheme, to model bead-and-spring-type representations of polymer chains. Investigations of static and dynamic scaling relationships show that the scaling of radius of gyration and relaxation time with the number of beads are consistent with the predictions of the Rouse-Zimm model. Both hydrodynamic interaction and excluded volume emerge naturally from the DPD polymer model, indicating that a realistic description of the dynamics of a dilute polymer solution can be obtained within this framework, and that very efficient computer simulations are possible. 0 1995 Society of Rheology.

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In 1989 it has been reported how an operational black/volatile oil reservoir simulator of IMPEC type has been successfully parallelised for a medium-scale (10-100 processors) local memory MIMD architecture1. The present paper reviews the principles underlying the parallelisation and describes the further development of the parallel simulator. Some attention is given to the linear solver which is of conjugate gradient type, with a local, block-wise preconditioner. A novel acceleration method, CGSTAB, for the solution of non-symmetric linear systems is described. The parallel simulator is now being evaluated in an operational environment. It has been installed on a 90 processor, 5500,000 Meiko M40 that should support two simultaneous job streams, each running at one quarter to one half (depending on the input) of the speed of a 1 processor Cray-XMP. So, at present, parallel computing leads to a substantial reduction of computing cost. In the very near future however, parallel computing machinery of the same family but based on the latest hardware, will beat traditional sequential computers on absolute performance too.