Polynomial approximations of wave loading and superharmonic responses of fixed structures

Abstract

Besides the commonly considered drag force, inundation due to variable water surface is another important nonlinear effect of wave loading. Quadratic and quartic approximations of the inundation drag force are derived using the least squares method. Other nonlinear effects, including the second-order wave kinematics and nonlinear inertia wave forces, are also considered. Superharmonic forces and the corresponding structural responses due to different nonlinear effects are compared using a single mode representation of the fixed offshore structural system. The appropriate expressions that can serve as the basis for the Volterra series representation of the nonlinear wave forces are presented.