A nonlinear controller for offshore structures under wave excitations

Abstract

In this paper, a new feedback-control design is developed and applied to an offshore structure under wave excitation. The nonlinear Morison equation is employed to estimate the wave forces. The feedback-control design proceeds in two consecutive stages: a nominal stage based on linear quadratic theory for regulating a linear part of the system dynamics, and an adjustment stage in the form of a nonlinear controller with a tuning gain factor for accommodating the nonlinearities while maintaining the overall stability. A SIMULINK model is designed to simulate the response of a three-floor steel jacket platform example. Results of the simulation of this structure with and without feedback-control are discussed to demonstrate the effectiveness of this control method.