Based on model tests, the statistical distribution of extreme values of wave-current in-line forces acting on vertical circular cylinder was analyzed in this paper. It is shown that the results calculated by the simplified method, proposed by authors, agree well with the test data; Weibull distribution is also adoptable in the region of high KC number, and the shape parameter a and scale parameter P are related well with KC number.
At present, for the design of coastal and offshore engineering structures, it is a tendency to use irregular wave theory to calculate and analyze wave loads, in which the distribution of extreme values of wave forces is important. This is especially so in the reliability analysis, where the probability distribution of extreme values of wave forces is fundamental to the analysis. It is well known that wave height corresponds to Rayleigh distribution in deep water and to Geruhovski distribution in shallow water. When the Morison equation is used for the calculation of in-line wave force acting on a slender cylinder, the inertia force component is linearly related to wav∼ height, but the drag force component is a nonlinear term, so it is supposed to individually consider the probability distribution of in-line wave force according to the ratio of inertia force component to drag force (Yu 1991). When there is a current combined with the wave field, the current force, as a constant, will cause the zero force line shift to one side of the periodically oscillating wave force, which introduces great difficulty to development of a theoretical statistical distribution of extreme values of wave-current forces. In order to meet the needs of engineering application, it is very meaningful to find out a simplified method (Li etal 1987).