RETRASO, a parallel code to model REactive TRAnsport of SOlutes

Abstract

Reactive transport of solutes in porous media has received an increasing attention due to a growing of the social sensibilitation on environmental and health problems caused by contamination of solutes. It is important, then, the characterization of reactive transport in order to predict accurately the behavior of solutes.

RETRASO is a code capable to simulate REactive TRAnsport of SOlutes. The code solves the reactive transport problem by substituting the chemical equations into a source/sink term of the transport equation leading to a system of non-linear partial differential equations. This system is discretized by applying the finite element method and the obtained discretized system is solved with the Newton-Raphson method (NR). For interesting cases, this size could be huge so, large computing time is required.

A parallel version of RETRASO has been developed to reduce the simulation time. The method used to parallelize is a SPMD (Single Program Multiple Data) with message passing communication for distributed memory architecture. As a result of the CPU profiling analysis; parallelization was focused on the following most consuming CPU time (more than 90%) parts: 1) the building of the Jacobian matrix of the NR linear system, and 2) solving the system itself. As communication between processors should be optimized for message passing models, a specific algorithm that minimizes the communication needs was designed for part (1). For solving the system, a linear solver module was developed at CEPBA (Centro Europeo de Paralelización de Barcelona, UPC).

The performance of the parallelized version of RETRASO was checked in a SGI ORIGIN 2000 machine with a PVM version based on sockets.