On estimation of extreme ship response using upcrossing spectrum

Paper in proceeding, 2011

In this paper a simple method is proposed to estimate extreme ship response, which is defined by the upcrossing spectrum of the responses at high levels. The method requires limited statistical information about shipping and the corresponding responses. Since the real ship responses are often non-Gaussian, a transformed Gaussian approach using the cubic Hermite polynomials is employed. The parametric transformation is a function of the standard deviation, skewness, kurtosis and zero up-crossing frequency of a response which mainly varies with changing sea conditions and operation conditions. Parameters needed in the transformation are computed from their relations with encountered waves, characterized by the significant wave height here. The relations are derived from the measurements, but can be also computed by theoretical analysis. Finally, this method is compared and validated with the typical engineering approach, based on the full-scale measurements of a 2800 TEU container ship during the first six months of 2008. If no measured responses are available, the parameters of the transformation can be estimated using simple numerical analysis.