Describing-function method for estimating the performance of a dynamic system having nonlinear-power take-off, with application to wave-power conversion

Abstract This work reports part of a programme aimed at stimulating the use of control engineering methods and techniques in the wave-power arena. Here we use the Describing-Function method to estimate the performance of a dynamical energy-conversion system (a second-order system in this particular case) with nonlinear damping. The Describing-Function is used to model the nonlinearity, and the system is conceptually re-arranged to appear in closed-loop form; this arrangement is particularly convenient for the application of a graphical method of solution. By this means the motion and the mean-rate of energy conversion of the system can be rapidly evaluated. The method is primarily directed towards solving problems of wave-power conversion by nonlinear devices.