Identification of the Variance of the Wave Exciting Rolling Moment Using Ship's Random Response

摘要

In this work, a method for the identification of the variance of wave exciting rolling moment per unit virtual moment of inertia is introduced. The method uses the random decrement signature derived from the stationary random roll response measured at sea. The equivalent linear damping and restoring parameters are obtained from the random decrement signature using a neural networks algorithm. Equations describing the variances of roll velocity and angle are derived using the Fokker-Planck equation. These equations yield the value of the variance of the roll wave exciting moment upon substituting the values of the equivalent linear parameters. Numerically generated data were used to test the validity of the proposed method. It is shown that the error in the calculated variance is less than 7% for the range of waves used in this work. Since the method requires only the knowledge of the roll response at sea, it can be easily applied while the ship is at sea with no interruption to the ship's function.