ABSTRACT

Here in 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.

1. Introduction

As the sea transportation is being ever intensified in recent years, ships often have to wait in a harbour for a long time until they are allowed to load or offload at piers due to the limited cargo-handling capacity. It is well known that harbour oscillations can be excited by long waves such as swell and tsunami. The harbour response has long been investigated in the area of coastal engineering and there are ample sources of literature, for example, see Miles & Munk(1961) and Lee(1972). Ships moored in a harbour also are excited and they undergo motions of six-degrees of freedom.

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