A new Nonhydrostatic Parallel Coastal Ocean Model

We introduce a new parallel model for the coastal ocean, SUNTANS, or Stanford Unstructured Terrain-following Adaptive Navier-Stokes Simulator, that is capable of simulating many of the physical processes, from the surface to the bed, using a large-eddy simulation for the resolved motions. The code is based on the unstructured algorithms described by V. Casulli in his 1999-2001 papers. The nonhydrostatic Boussinesq equations with a semi-implicit time discretization are solved on an unstructured horizontal grid with layers in the vertical. The momentum and scalar fields are advected using higher-order interpolation, and the nonhydrostatic pressure and free surface are computed with a preconditioned conjugate gradient algorithm using the PETSc (Parallel Extensible Toolkit for Scientific Computation) package. Load balancing and grid-partitioning are managed with the ParMetis (Parallel Graph partitioning and Sparse Matrix Ordering) package. Using a Smagorinsky model for the unresolved motions in the large-eddy simulation, we demonstrate the efficiency and effectiveness of our model by computing the energy cascade of nonhydrostatic internal waves on an idealized oceanic ridge. Because the code can be made into a primitive-equation code by omitting the nonhydrostatic pressure, we compare the energy spectra for the nonhydrostatic case to the hydrostatic case and determine regions of elevated nonhydrostacy. This sets the stage for the next step of development, which will employ an adaptive solver to resolve more accurately the regions of nonhydrostatic activity. The support of the NSF via an ITR/Oceanography grant and the ONR via an Ocean Modeling Grant is appreciated.