Coastal Engineering Journal

A sloping-slit caisson breakwater, designed by the authors, was constructed at a fishery port using the new "precast-form caisson" (PFC) method. The sloping-slit caisson combines the advantages of an upright-slit caisson and a sloping-top caisson. It reduces wave forces by a front slit and a wave chamber. The downward force acting on the slope increases the caisson stability. It was found that the PFC method simplifies construction and saves labor in construction of the caisson.

A periodical solution of linear long wave was obtained when considering the laminar or turbulent shear stress in the entire flow depth. The solution provides the variation of wave height due to bottom topography and bottom friction. The decay modulus of wave height and the phase differences between velocity, shear stress and water elevation obtained by the laminar flow solution are compared with those predicted by the laminar boundary layer theory. It is shown that the boundary layer approximation cannot be applied to the case where the water depth is small and the wave period is long. Using the turbulent flow solution, the variation of reflection coefficient due to bottom friction is examined. The reflection coefficient depends not only on the Iribarren number but also on the number of waves on a sloping beach and the bottom roughness. An empirical roughness coefficient n is obtained by equating the bottom shear stress evaluated by Manning's friction formula to that evaluated by the present theory. The proper value of n can be determined by considering bottom roughness only.

The program SWAN (Simulating WAves Nearshore) is a third-generation wave model used to compute the spectra of random short-crested, wind-generated waves on Eulerian grids. Presently there is no release of the SWAN code to execute on parallel computers and computations are limited to a single processor. This paper shows how to easily create a version of the SWAN code that can execute on parallel platforms using a simple approximation. The approximation is to solve the transport equation as a stationary problem at every time level. This is referred to as a quasi time-accurate approximation to differentiate it from a truly time-accurate computation where the transport equation is solved as a nonstationary problem. Using this approximation, the individual integrations at different times are independent, and coarse-grain parallelism can be easily exploited using the Message Passing Interface (MPI) parallel programming system.

This study compares the quasi time-accurate method in Part I: Method, with the time-accurate version of SWAN for a simulation of 1995 Hurricane Luis and a Gulf of Mexico storm that occurred in September 2000. Using the quasi time-accurate method, significant reductions in wall times were achieved relative to time-accurate computations. Examination of the error norms show that the quasi time-accurate method agrees well with the time-accurate results. Thus, the MPI quasi time-accurate method, because of its efficiency, can play an important role for cases where the time-dependent forcing terms are the dominant influence on wave conditions.