Research On Robust H_∞Guaranteed Cost Control For Offshore Steel Jacket Platforms

This paper is concerned with the problem of Robust H_∞guar-anteed cost control strategy for offshore steel jacket platforms subjectedto nonlinear self-excited wave forces and external disturbances. Based onlinear matrix inequality technique and Lyapunov theory, the parameter un-certainty model problem and the robustness of time delay introduced tostate feedback control channel are discussed.First, according to nonlinear self-excited wave forces and external dis-turbances, H_∞guaranteedcostcontrolschemeforoffshoresteeljacketplat-forms is proposed. To reduce the design conservatism of the traditionalH_∞approach, the guaranteed cost control approach is introduced. Suffi-cient conditions for the existence of H_∞guaranteed cost controller for theclosed-loopsystemarederived. Thennumericalexampleshavebeenintro-duced. Theresultsclearlyshowthatthe H_∞guaranteedcostcontrolschemeprovides a lower conservatism.Further, for the parameter uncertain model, robust H_∞guaranteed costcontrol scheme is introduced. Based on inequality method, sufficient con-ditions for the existence of robust H_∞guaranteed cost controller for theclosed-loop system are derived. Simulation results show the effectivenessof the proposed scheme.Considering the effects of time delay on system performance, it isadded to the control channel. Sufficient conditions for the existence ofmemory robust H_∞guaranteed cost controller are derived. An improvedconecomplementaryalgorithmisdesignedtoselecttheH_∞guaranteedcostcontrol law. Simulation results clearly show that an appropriate time delaycould reduce the control energy, and also guaranteed the control perfor- mance.