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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. [ABSTRACT FROM AUTHOR]

Abstract Prediction of a ship's roll motion in parametric roll and dead ship condition using CFD and experiments is time consuming and expensive, while a reliable equation based method can drastically decrease the computation time. The commonly used roll motion equation contains roll mass and added mass moment of inertia, damping and restoring terms and associated coefficients. Improving the prediction of these coefficients increases the accuracy of the method. There is a lack of precise calculation for the roll added mass moment of inertia, which is commonly estimated using semi-empirical techniques and as a percentage of the roll mass moment of inertia coefficient. This paper presents a new method to determine the roll added mass moment of inertia using CFD simulations based on a harmonic excitation roll motion technique and the results are compared against Bhattacharyya's method. The influences of excitation frequency, Froude number, roll angle and appendages on the roll motion characteristics and the roll added mass moment of inertia coefficient are investigated. In addition, the roll added mass moment of inertia coefficients on the model scale and full scale ship are computed to investigate the scale effect. [ABSTRACT FROM AUTHOR]

Simulation of a ship's roll motion through equation-based approaches requires restoring moment, added mass moment of inertia and damping coefficients. Accurate estimation of these coefficients enhances the prediction of ship roll response at a resonance condition. However, the magnitude of these coefficients in regular beam seas and close to a resonance condition is unknown. The present study adopts numerical and experimental simulations to investigate the effects of different wave heights and wave frequencies on ship motion characteristics. The motion characteristics results from numerical simulations are compared against experimental measurements, and a good correlation is achieved. The restoring moment in dynamic conditions is calculated and compared to the hydrostatic restoring moment. The dynamic restoring moment is greater than the hydrostatic restoring moment for some wave frequencies and smaller for other wave frequencies. The magnitudes of roll damping and added mass moment of inertia coefficients are calculated at different wave heights and frequencies, and the results yield that there is quite a nonlinear relationship between the roll hydrodynamic coefficients and roll motion characteristics. • Numerical and experimental investigations of ship motions in regular beam waves. • Roll restoring moment in dynamic and static conditions are compared. • Roll added mass moment of inertia is computed in different regular beam waves. • Roll damping is computed in different regular beam waves. [ABSTRACT FROM AUTHOR]