Bas in Oscillations In an Offshore Harbor

Abstract

ABSTRACT A numerical method using an integral equation approach derived from Green's theorem has been developed for calculating the steady-state, wave-induced oscillations inside an offshore harbor of arbitrary shape surrounded by the open sea. It solves the outside diffracted wave field as well as the radiating wave field due to the interaction between the harbor and the ocean waves through the harbor entrances. The method was verified by checking against known solutions. It was then used to study the water surface oscillations inside a breakwater enclosure protecting a proposed floating nuclear power plant in the Atlantic Ocean. Results of the investigation are presented in this paper. INTRODUCTION Due to the rapid growth of energy demand and considerations of environmental impact, among others, a new concept has been developed for locating nuclear power plants offshore in the coastal zone. Public Service Electric and Gas Co. (PSE&G) of New Jersey has proposed to install two 1,150-mw nuclear power plants (FNP's on moored floating platforms of a standardized design. The plants Will be protected by a semicircular rubble-mound main breakwater facing the ocean and a straight closure breakwater facing the coast, located about 3 miles offshore slightly north of Atlantic City. The proposed project has been named the Atlantic Generating Station (AGS). When a basin is connected to the open sea, the water surface inside the basin is subjected to the excitation of the incident waves propagating from the ocean into the basin entrance. A basin can be considered as a multiple-degree-of-freedom mechanical system with its appropriate inertial, dissipative, and restoring characteristics. The responding oscillation inside the basin is dependent upon the period of the incident wave and the basin and entrance configurations. This response may result in an amplification of wave heights inside the basin at certain incident wave frequencies, i.e., at the resonant frequencies of the basin system. It is essential to understand the characteristics of basin oscillations in order to determine the motions of the floating platforms and the required strength of their moorings. Most existing numerical methods for basin oscillation analysis are developed for ordinary harbors inland of straight coastlines, so that the solution for the diffracted wave field outside the harbor is available immediately. Such harbors have only one entrance. In such a case, the problem reduces to a solution of the radiating wave due to the interaction between the harbor and the ocean wave. The AGS harbor presents a different problem since it lies offshore, requiring solution for the diffracted wave field, and since it has two openings to the sea. LITERATURE REVIEW Miles and Munk1 investigated the case for a rectangular basin connected directly to the open sea and obtained a balance at the harbor mouth between the ocean wave entering the basin and the wave radiating from the harbor mouth back into the open sea by means of an integral equation in terms of a Green's function.