On the motion response of a ship moored in a rectangular harbour

Abstract

Herein a study is made on the motion response of a ship moored in a rectangular harbour excited by long waves within the framework of linear potential theory. The ship is assumed slender and moored in the harbour with constant depth and straight coastline. The matched asymptotic expansion technique is applied. To employ it, the fluid domain is divided into the ocean and the harbour regions. The latter is further subdivided into a field near the ship and the rest. Numerical results show that the ship motion is significantly amplified, when the harbour is resonated by incident waves. At resonant frequencies, the heave added mass becomes negative and the wave damping changes abruptly. The mode and magnitude of ship motion depend strongly on the incident wave frequency and on the position of ships inside the harbour. Experiments are performed for a moored ship model in a shallow basin for wave periods ranging from 2 to 3 seconds. Wave responses and ship motions are measured and compared with computations. It is found that the theory developed in this paper predicts them qualitatively well.