Hydrodynamic Analysis of a Spread-Moored Platform in the Open Sea

摘要

A moored construction-type platform excited by irregular random surface gravity waves was studied in the laboratory, in the field, and theoretically. The platform was spread moored by four 2-1/2-inch die-lock chains in about 165 feet of water in the open Pacific Ocean. Water level variations at three locations, ship rotations and accelerations, mooring forces, and wind velocities were measured in sea states 2 and 3, and a simulated sea state 4 in the laboratory. Three recordings each of the prototype and model tests were analyzed using time series techniques to provide apparent amplitude response operators for all ship motions and mooring forces. The motions of the barge when excited by regular uniform surface gravity waves were predicted using the linear theory of ship motion. The fundamental analytical tool used in the computations is the well-known slender body theory. Agreement between theory, model, and prototype results is considered to be excellent for the surge, sway, roll, heave, and pitch motions. Agreement for the yaw motion is poor. It is concluded that the most probable value of the annual maximum force induced on any of the moorings is 120 kips. The present mooring configuration possesses sufficient reserve strength to preclude failure of the moorings due to wave-induced motions. (Author)