Calculation on the Heaving and Pitching of Ships by the Strip Method

In general it is very difficult and needs much time to calculate theoretically the heaving and pitching motions of a ship in waves even if when she is traveling in two dimensional regular waves and in a direction normal to the wave crests. So the authors tried to calculate the ship motions above mentioned by the strip method using the high speed computer IBM 7044, and succeeded to put it into practical use, that is, it became possible to calculate the motions about 6070 conditions of one ship only in 12 minutes and with rather good accuracy.We used the equations of motion proposed by Watanabe. Solving these equations, we obtained the added mass coefficients and damping coefficients by curve fitting from the values calculated previously by Tasai's method for the cylinders with Lewis form section. In this way we could reduce the calculating time very much.Next we compared our results with Gerritsma's experimental values about Series 60 models, and found that the accuracy of calculation could be improved when the damping coefficient for the heave was corrected for the three dimensional effect. So we estimated this correction factor as the function of block coefficient and nondimensional circular frequency of encounter of a ship to waves, and corrected the calculating manner. The test results at Mitsubishi experimental tank were found to fit to our corrected values very well.