Research on the Estimation of Ocean Wave Spectra Based on Running Ship Motions

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There is no need to say that for the design and management of ship or floating bodies it is important to grasp the real state of ocean waves in quantitative manner. It is also important on the view point of preventing abnormal sea disaster. Usually instrumental measurement of ocean waves is made by ships in standing condition or moored floating bodies and it is very difficult to measure waves from running ship, so even today main source of ocean wave statistics is owed to visual observation.So,in this research we aimed to estimate directional spectrum of ocean waves in real time, introducing micro computer on board and using information on ship motions.On the first stage of this project, we conducted towing ship experiment in our towing tank which can generate directional spectrum waves and comparing those results with theoretical calculation, we examine the reliability of theoretical calculation of ship motions in directional spectrum waves.In the next, we developed a system which can estimate directional spectrum waves in real times by obtaining ship motions from sensors on board. In this system the frequency response functions of ship motions are given theoretically. Those functions are examined in the first stage and then we made numerical simulation on this system.Finally, we applied this system in real ship experiment and it was found that this system can be used practically.