CORRECTION FACTORS FOR NONLINEAR RUNUP AND WAVE-FORCES ON A LARGE CYLINDER

A recently developed numerical method for second-order wave diffraction is summarized and is used to develop a simplified approach to predicting nonlinear runup and maximum wave loads for large coastal and offshore structures subjected to regular waves. The perturbation method on which the method is based is extended to provide correction factors for the runup and maximum loads. These correction factors apply directly to the predictions of linear diffraction theory, and are independent of the wave height. The correction factors for runup, maximum force and maximum overturning moment are provided for a range of geometric parameters relating to the case of a large circular cylinder extending from the seabed to the free surface. Nonlinear runup and load maxima calculated by the correction factors are compared with the results of previous experimental studies; in general, favourable agreement is obtained. An example application of the proposed procedure is provided, the importance of nonlinear effects in the evaluation of runup and wave loads is discussed, and the limitations of the results are indicated.