Numerical Study on Sea Keeping Performances of Ship by Exact Linear 3-D Potential Method

Abstract

This paper deals with the numerical calculations of sea-keeping performances of ship in irregular sea condition. Here linear potential theory has been applied for describing the fluid motion and 3-D sink-source technique has been used to determine hydrodynamic forces for surface ship advancing in waves at constant forward speed. Numerical coding based on 3-D potential method has been tested in an extensive manner keeping an eye with the criteria recommended by various ITTC committees [1]. The numerical accuracy of the coding has been examined using some experiment results as well as some other contemporary numerical calculations given by some authors for the case of frequency domain analysis. Taking a typical Panamax Container Vessel and in order to simulate its sea-keeping performances in real sea condition, the frequency domain analysis has been performed. The result is then used for time domain simulation in short crested irregular waves. Unequal frequency spacing has been taken into account to get longer simulation time and also empirical nonlinear roll damping has been taken in the way of time domain simulation. From this time domain simulation, relative wave height has been calculated which could sometimes damage deck equipment as well as posing a risks to personnel in severe sea condition. The effect of speed & wave direction on relative wave height has been considered and finally the numerical results of the maximum and significant values of irregular relative wave heights for these conditions are discussed.