ON NONCAUSAL IMPULSE-RESPONSE FUNCTIONS RELATED TO PROPAGATING WATER-WAVES

Particular attention is drawn to the non-causality of two impulse resp onse functions, one of which relates the excitation force on an immers ed body to the incident wave elevation at the body's reference positio n, while the other relates the incident wave elevations at two differe nt positions along the line of wave propagation. An explanation is pro posed for the non-causality of the impulse response functions, in spit e of the fact wave propagation is a causal process. An indication is g iven of how far 'upstream' the incident wave elevation should be measu red in order to be able to know, with reasonable accuracy, the current heave excitation force on a floating truncated cylinder with vertical axis, given current and past wave-elevation measurements. This provid es a method for wave prediction, which is required for optimum control of the oscillation of the immersed body. Copyright (C) 1996 Elsevier Science Limited.