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Mathematical and algorithmic issues in multiphysics coupling.
The modeling of fluid/structure interaction is of growing importance in both energy and environmental applications. Because of the inherent complexity, these problems must be simulated on parallel machines in order to achieve high resolution. The purpose of this research was to investigate techniques for coupling flow and geomechanics in porous media that are suitable for parallel computation. In particular, our main objective was to develop an iterative technique which can be as accurate as a fully coupled model but which allows for robust and efficient coupling of existing complex models (software). A parallel linear elastic module was developed which was coupled to a three phase three-component black oil model in IPARS (Integrated Parallel Accurate Reservoir Simulator). An iterative de-coupling technique was introduced at each time step. The resulting nonlinear iteration involved solving for displacements and flow sequentially. Rock compressibility was used in the flow model to account for the effect of deformation on the pore volume. Convergence was achieved when the mass balance for each component satisfied a given tolerance. This approach was validated by comparison with a fully coupled approach implemented in the British PetroledAmoco ACRES simulator. Another objective of this work was to develop an efficient parallel solver for the elasticity equations. A preconditioned conjugate gradient solver was implemented to solve the algebraic system arising from tensor product linear Galerkin approximations for the displacements. Three preconditioners were developed: LSOR (line successive over-relaxation), block Jacobi, and agglomeration multi-grid. The latter approach involved coarsening the 3D system to 2D and using LSOR as a smoother that is followed by applying geometric multi-grid with SOR (successive over-relaxation) as a smoother. Preliminary tests on a 64-node Beowulf cluster at CSM indicate that the agglomeration multi-grid approach is robust and efficient
Molecular Cloud Structure in the Magellanic Clouds: Effect of Metallicity
The chemical structure of neutral clouds in low metallicity environments is
examined with particular emphasis on the H to H_2 and C+ to CO transitions. We
observed near-IR H_2 lines and the CO J=1-0 line from 30 Doradus and N159/N160
in the Large Magellanic Cloud and from DEM S 16, DEM S 37, and LI-SMC 36 in the
Small Magellanic Cloud. We find that the H_2 emission is UV-excited and that
(weak) CO emission always exists (in our surveyed regions) toward positions
where H_2 and [CII] emission have been detected. Using a PDR code and a
radiative transfer code, we simulate the emission of line radiation from
spherical clouds and from large planar clouds. Because the [CII] emission and
H_2 emission arise on the surface of the cloud and the lines are optically
thin, these lines are not affected by changes in the relative sizes of the
neutral cloud and the CO bearing core, while the optically thick CO emission
can be strongly affected. The sizes of clouds are estimated by measuring the
deviation of CO emission strength from that predicted by a planar cloud model
of a given size. The average cloud column density and therefore size increases
as the metallicity decreases. Our result agrees with the photoionization
regulated star formation theory by Mc Kee (1989).Comment: 45 Pages including 15 figures. To be published in the ApJ May 10,
1998 issue, Vol. 49
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