NUMERICAL-SIMULATION OF OPEN COAST SURGES .1. EXPERIMENTS ON OFFSHOREBOUNDARY-CONDITIONS

The main purpose of this study is to identify the off-shore boundary c onditions which predict physically acceptable features in the time his tories of Bow parameters in shelf waters under idealized conditions an d to use those boundary conditions in simulation of real situations. W a 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 part ially clamped conditions which are expressed in terms of the derivativ es of eta lead to unrealistic shelf response of monotonously increasin g 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 bett er estimates of surges. Since, the clamped and Heapa-Orlanski conditio ns 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 ideali zed shell are also analyzed and they explain some of the features of t he numerically simulated surges.