Ship roll restoring moment calculation in beam sea condition

Abstract

Accurate calculation of restoring moment, virtual mass moment of inertia and damping moment increases the accuracy of a ship’s dynamic stability simulation. The current methods of approximating the roll restoring moment are based on hydrostatic calculations. These methods fail to consider the dynamic conditions and variation of upward buoyancy and wave location with respect to the model. In the current study, experimental and numerical simulations are conducted at beam sea condition to investigate the behaviour of model. The model is excited by regular waves at different heights and frequencies to measure the motion characteristics and the restoring moment in dynamic conditions. The motion characteristics of the model obtained from the numerical simulation are compared against the experimental measurements, and a good agreement is found. The results show that the restoring moments in the dynamic condition have significant differences compared to the static condition. The magnitude of restoring moment in dynamic condition is measured based on the variation of heave motion of the model and the location of the wave’s crest and trough with respect to the model.