Identification of the variance of the wave exciting rolling moment using ship's random response

In this research, the variance of wave exciting rolling moment has been identified using ship roll response only. The data of ship rolling motion were obtained from ship rolling simulations as well as from ship model tests. The random decrement technique has been used to extract the free roll decay curves from the stationary random response. The roll damping and restoring moments can then be obtained from the extracted free decay curves using a neural network technique. The predicted rolling parameters were then used to calculate the variance of wave exciting rolling moment.; The simulated data are used to demonstrate the validity of the proposed method. The application of the method to the experimental data showed the influence of the wave model frequency, the wave height, and the GM value on the variance of the wave exciting rolling moment in irregular beam waves. This method is only based on the time history of the ship rolling displacement to estimate the variance of wave exciting rolling moment. Moreover, the roll response of a ship can be easily measured using an accelerometer while the ship is at sea. The analysis can be done on line at sea. The estimated variance value will give captains an important parameter for the assessment of ship safety.