Fender system behavior in random seas
Ofoegbu, James Nwachukwu
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Fendering systems are widely used in offshore installations for attenuating the effects of the impact energy of ships and barges in berthing or moored conditions. This study focuses on investigating current design practices and, developing a rational and functional approach to address random loading effects exerted on fendering systems. These loadings are often a consequence of combined wind, wave and current excitation as well as more controlled vessel motions. Dimensional analysis is used to investigate the degree to which empirical design data can be collapsed and to provide an indication of the nonlinearity associated with the empirical data for fender sizing. In addition, model test data specifically measuring the normal fender force for a coupled mini-TLP/Tender Barge performed at the Offshore Technology Research Center (OTRC) model basin is used in this research investigation.. This data was characterized in terms of the typical statistical moments, which include the mean, standard deviation, skewness and kurtosis. The maxima and extreme values are extracted from the fender response data based upon a zero-crossing analysis and the results were studied in order to determine the underlying probability distribution function. Using selected parameter estimation techniques, coefficients of a best-fit two parameter model were determined. An illustrative example is presented and discussed that contrasts the deterministic and probabilistic models.