San Francisco Bay Model Exhibit at the Exploratorium Science Museum of San Francisco, CA. The exhibit
allows users to place drifters throughout the Bay and watch how they move around due to river inflow
and the tides. The three-dimensional model was built by
Dan Collins and the interactive software was developed by Gene Cooper.
SUNTANS computes the drifter trajectories given the initial locations as input by the user.
Vivien Chua developed the SUNTANS implementation for San Francisco Bay.
Overview
SUNTANS is a nonhydrostatic, unstructured-grid, parallel, coastal
ocean simulation tool that solves the Navier-Stokes equations under
the Boussinesq approximation with a large-eddy simulation of the
resolved motions. The
formulation is based on the method outlined by
Casulli in his 1999 papers, where the free-surface and vertical
diffusion are discretized with the theta-method, which eliminates
the Courant condition associated with fast free-surface waves and the
friction term associated with small vertical grid spacings at the
free-surface and bottom boundaries. The grid employs z-levels in the
vertical and triangular cells in the planform. Advection of momentum
is accomplished with the second-order accurate unstructured-grid
scheme of Perot (2000), and scalar advection is
accomplished semi-implicitly using the method of
Gross (1999), in which continuity of volume and
mass are guaranteed when wetting and drying is employed. The wetting
and drying capabilities of SUNTANS enable its use for coastal as well
as estuarine domains. The theta-method for the free-surface yields
a two-dimensional Poisson equation, and the nonhydrostatic pressure is
governed by a three-dimensional Poisson equation. These are both
solved with the preconditioned conjugate gradient algorithm with
diagonal preconditioning. SUNTANS is written in the C programming
language, and the message-passing interface
(MPI) is employed for use
in a distributed memory parallel computing environment.
Load balancing and grid-partitioning are being managed with the
ParMETIS package.
The grids for SUNTANS are unstructured in the planform and employ z-levels in the vertical.
We employ stair-stepped grids in the vertical in order to eliminate errors in computing the baroclinic pressure gradients as well as to enable volume and scalar conservation when computing
integrals over each water column. Accurate resolution of complex topography will be accomplished with the use of the immersed boundary method (IBM).
16 processor load-balanced partitioning of Monterey Bay with 250,000 planform grid cells and 120 vertical
levels (18.2 million total).
The partitions in the deep (red, 3000 m) regions have less surface area than those in the shallow (blue, 200 m) regions because inactive
cells are not stored. This yields a 37% savings in memory for this particular grid.
