STATE-SPACE MODELING OF A VERTICAL CYLINDER IN HEAVE

The (first-order) wave forces on structures interacting with ocean wav es may be represented by complex transfer functions in the frequency d omain or by convolution integrals in the time domain. The integration kernels are causal for radiation forces, but not necessarily so for ex citation (scattering) forces. As a convenient approximation, these int egrals may be replaced by a finite-order system of differential equati ons with constant coefficients. This method is applied to a heaving cy linder with a vertical axis, and good approximations are obtained when the order of the differential equation system is three for the radiat ion force and five for the excitation force. The corresponding state-s pace model for the heave motion response due to the incident wave elev ation has an order of 10, but it is demonstrated that it is possible t o reduce the order to five without increasing the inaccuracy in the he ave motion too much. (C) 1996 Elsevier Science Ltd.