Delayed adaptive output feedback sliding mode control for offshore platforms subject to nonlinear wave-induced force

In this paper the control problem for an offshore steel jacket platform subject to nonlinear wave-induced force is investigated by introducing several new types of adaptive sliding mode controllers. Three control schemes are presented to reduce the oscillation amplitudes of the offshore platform. The first scheme is named an adaptive output feedback integral sliding mode controller, which has a better performance in comparison with an integral sliding mode controller. By introducing an intentional time delay into the control channel, an adaptive output feedback integral sliding mode controller is proposed as the second scheme. This controller is called a delayed adaptive output feedback integral sliding mode controller. It shows a good performance in reduction of the internal oscillations and control force. In the third scheme, a combination of current states and delayed states is used in the sliding surface and control law. This control scheme is named a combinational delayed adaptive output feedback integral sliding mode controller. One advantage of this scheme is that it provides an appropriate response by increasing the time delay. According to the simulation results, the proposed control schemes can effectively improve the control performance of the offshore platform in comparison with several existing control schemes.