NearCoM: SHORECIRC Circulation Module

Authors:

Ib Svendsen, Kevin Haas, and Qun Zhao

Contact information:

Kevin Haas

Department of Civil and Environmental Engineering, Georgia Tech Savannah, Savannah, GA, 31407

Documentation:

Svendsen, I. A., Haas, K., and Zhao, Q., 2004, ``Quasi-3D Nearshore Circulation Model SHORECIRC: Version 2.0", Research Report, Center for Applied Coastal Research, University of Delaware. (pdf)

Overview:

The SHORECIRC (SC) quasi-3D nearshore circluation model has been developed over the past ten years and includes effects of short wave forcing, wind stresses, and non-linear mechanisms such as finite amplitude of the IG wave motions and the dispersive mixing due to depth variations described below. Early 2D circulation models assume uniformity over depth of all velocities. However, it was found that the assumption of depth uniform velocities neglects some very important mechanisms that may significantly change the results. This mechanism, which has been termed the dispersive mixing, resolved a paradox about the origin of the lateral mixing in the generation of longshore currents. It essentially implies that even inside the surfzone on a long straight coast 95\% or more of the lateral mixing can be due to the vertical variation of the current velocities and only 5\% due to breaker generated turbulence. The SC model is further provided with an absorbing-generating boundary condition which allows waves reflected inside the computational domain to freely propagate out through the seaward boundary while incoming waves are phased into the model domain at the same boundary. In addition it uses a generalized wave/current bottom friction model. It is based on a robust, high-order numerical scheme, and is very fast. For a reasonably large coastal domain (400m by 1000m, say) it has been found that it operates at near real time on a modern PC. A subgrid turbulence model is used to describe the fine turbulence structure not resolved by the model. Thus the results essentially corresponds to a Large Eddy Simulation (LES) of the flow field, that captures the large vortices as in simulations of rip currents. The present version of the SC model system consists of two major elements: 1) A component that solves the short-wave averaged equations giving a 2D-horizontal variation of the current/IG-wave pattern. 2) A component that evaluates the analytical solutions to the vertical distribution of horizontal velocities in the time varying currents/infra-gravity waves.

Use and initialization of the module:

The input file, input_winc.dat, is used to specify all the model parameters including boudanry conditions, numerical parameters, physical parameters, and output sensor locations.

Variables provided by the circulation module:

Variables provided by SHORECIRC are: time-averaged, depth-averaged current field vertical profile of current velocity bottom current velocity time-averaged surface elevation bottom stresses turbulent eddy viscosity.

Variables required by the wave module:

water depth (read initially from master program, updated by the sediment module ); wave radiation stresses, or wave forcing; wave flux; wave height; wave direction; wave period (or wave peak period); wave number; wave group speed.