WAVE ESTIMATION FROM SHIP MOTION AND NONLINEAR SHIP RESPONSE ANALYSIS IN VERY ROUGH SEAS

Several papers have been presented on the estimation method for a wave spectrum with the frequency response function of a ship and its measured motion in waves. This is known to give a valid estimate of wave height in moderate seas. It is important to know whether it is also valid for very rough seas and so full-scale measurements of wave impact forces and the hull response of a ship have been conducted under these conditions. In this paper estimations of two wave encounters, using measured data of a ship's pitching and heaving, are presented and frequency response functions are derived from the Ordinary Strip Method. Nonlinear ship response analyses were carried out with estimated waves for confirmation purposes. It was found that the wave estimation method was valid for very rough seas if used with caution and that there was good agreement between measured and estimated ship motions.