WIT Press

Comparison Of Three Probability Models For Offshore Structural Response Due To Morison Wave Loading


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WIT Press


G. Najafian


Offshore structures are exposed to random wave loading in the ocean environment and hence the probability distribution of their response to wave loading is of great value in probabilistic analysis of these structures. Due to nonlinearity of the wave load mechanism and also due to intermittency of wave loading on members in the splash zone, the response is often non-Gaussian. Two probability models have frequently been used in the past for offshore structural response due to random Morison wave loading: a) the Pierson--Holmes distribution and b) a third-order polynomial function of a Gaussian random variable. Recent work has, however, demonstrated that none of these two models can accurately predict the tails of the response distribution. A new probability model has therefore been introduced to overcome this deficiency. Analysis of simulated response data has demonstrated that this new model, though not perfect, is considerably better than either of the foregoing two models. Keywords: offshore structures, response, probability distribution, wave loading, Morison’s equation. 1 Introduction For an offshore structure, wind, wave and gravitational forces are all important sources of loading. The dominant load, however, is normally due to windgenerated random waves. Although some types of these structures can be designed by equivalent deterministic methods, it is inherently much more satisfactory to account for the randomness of the wave loading by establishing the probabilistic properties of the loading and the resulting responses. The major obstacle in the probabilistic analysis of the response due to wave and current


offshore structures, response, probability distribution, wave loading, Morison’s equation.