Implementation of an important wave model on parallel architectures

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SWAN (Simulating WAves Nearshore), developed at the Delft University of Technology, is an important third generation wave model used to simulate short-crested wind-generated waves in shallow water areas such as coastal regions and inland waters. The model solves a four-dimensional (2 spatial dimensions, wave direction, and wave frequency) spectral action balance equation using a semi-implicit upwind scheme. Relative to other less advanced wave models, SWAN is more computationally demanding, and a parallel version is necessary in order to decrease turn-around time, improve the model resolution for large coastal regions, and migrate SWAN into Navy operational use. In this paper we present a new parallel implementation of SWAN using a pipelined parallel approach which does not alter the order of operations in the sequential numerical algorithm. The implementation uses OpenMP compiler directives and runs on shared-memory multiprocessor computers. This approach represents a non-traditional, i.e., not loop-level, way of using OpenMP. Performance measurements show that turn-around time for high-resolution model applications can be significantly reduced with the parallel implementation. The parallel implementation has been verified and model output matches bit-for-bit with the original sequential code for both stationary and non-stationary cases. The new parallel code has already been incorporated into the next official release of SWAN and is beginning transition into operational use.