On Testing a Ship Model in Transient Water Waves

Abstract

The ship model experiment in head waves at zero speed were carried out by using transient water waves, and the time histories of wave, heave and pitch amplitude were measured. Then, the experimental results were analysed according to two criteria, that is, both frequency domain and time domain.In consequence of the present investigation, next properties on the ship motion in transient waves were obtained.1) Wave-ship motion system at the same position are one of the linear system. The obtained amplitude ratios and phase lags between waves and ship motions in transient water waves coincide with the measured results in regular water waves. Also, the predicted time histories of ship motions by using the measured wave time histories exactly correspond to the measured ship motion time histories.2) Ship motion-ship motion systems between different points are equal to the wave-wave linear systems, that is, so-called the position shift systems. But, the position shift linear system can not applied in the cases that the concentrating position of transient water waves is existent between the input position and the output position.3) The linear systems of wave height as an input and ship motion at separated position as an output come into existence. But, if the concentrating point of transient water waves exists between the considered points, the linear systems will can not adopt for these points.From the above mentioned results, it can be considered that testing ship models in transient water waves is one of the useful method for the investigation of the ship frequency response function in waves.