Nonlinear and Robust Control Schemes for Offshore Steel Jacket Platforms

This paper presents two control schemes to control the dynamicresponse of an offshore steel jacket platform due to wave-inducedforces. The objective of the controllers is to greatly reduce theinternal system oscillations and to obtain a smooth response ofthe steel jacket platform when subjected to nonlinear self-excitedhydrodynamic forces. The first controller is a nonlinearcontroller whose design is based on Lyapunov theory. The secondcontroller is a robust state feedback linear controller whosedesign is based on an optimal control approach. Both controlschemes guarantee the asymptotic stability of the system. Thetheoretical developments are illustrated through simulationresults of the proposed control schemes. Furthermore, theperformance of the offshore steel jacket platform is presentedwhen a direct velocity feedback controller is applied to thesystem. It is found that the performance of the system with theproposed controllers is better than the performance of the systemwith the direct velocity feedback controller.