Nonlinear Wave Forces on Large Offshore Structures

Current design of large offshore structures generally relies on recently developed diffraction programs based on small amplitude wave theory and the associated assumption of linearity. However, the severe wave heights encountered in practice make the use of small amplitude theory questionable and some consideration has centered on the estimation of nonlinearity effects. In Particular, Yamaguchi and Tsuchiya have recently attempted to extend to a second approximation the diffraction theory of MacCamy and Fuchs for a vertical circular cylinder. This technical note clarifies possible misconceptions arising in such an extension to the diffraction theory and indicates how a second approximation must rely primarily on experimental results.