Numerical Simulation of Open Coast Surges. Part I: Experiments on Offshore Boundary Conditions
Keywords:Shallow water flow field, numerical simulation, open coast surges, open ocean boundary conditions
AbstractThe main purpose of this study is to identify the off-shore boundary conditions which predict physically acceptable features in the time histories of flow parameters in shelf waters under idealized conditions and to use those boundary conditions in simulation of real situations. We examine the influence of different off shore boundary conditions on flow parameters in a rectangular shelf when shelf waters are subjected to uniform wind and idealized cyclone wind forcings. For uniform wind forcing, we show that the conventional forms of Orlanski and the partially clamped conditions which are expressed in terms of the derivatives of η lead to unrealistic shelf response of monotonously increasing surge histories. The clamped condition and a new off-shore boundary condition, which will be referred to as the Heaps-Orlanski condition, when applied along the off-shore boundary are observed to provide better estimates of surges. Since, the clamped and Heaps-Orlanski conditions predict nearly the same surge histories for uniform and stationary cyclonic wind forcings, a simpler clamped condition is recommended in surge simulation studies. The free modes of oscillation on this idealized shelf are also analyzed and they explain some of the features of the numerically simulated surges.