Effect of ship size, forward speed and wave direction on relative wave height of container ships in rough seas

Abstract

This paper deals with the numerical calculations of relative wave height of ships in the rough seas. Linear potential theory has been applied for describing 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. The numerical results are compared not only with some experimental results but also with some other contemporary methods in frequency domain analysis used by others researchers. The numerical results of 3-D Green Function which has been solved by the method of singularities distributed over the hull surface is then used to analysis the results in time domain. For the simulation of the random sea, a fully probabilistic technique with unequal frequency spacing has been applied. Empirical non-linear roll damping has been incorporated to predict motion response in rough sea and time domain simulation of relative wave height of typical ship like container ships of different size and speed in short crested irregular waves have been carried out with different sea states. The numerical results of the maximum and significant values of irregular relative wave heights for different sea states have been discussed by comparing with some requirements by a Classification Society of shipping in order to assess if its rule consider enough allowance of deck load issue in case of severe sea states and it is evident from the numerical simulation that irrespective of the size of the ships, there is more prone to bow slamming or propeller emergence for the case of most severe sea state considered in this paper