Research On Active Control For Offshore Steel Jacket Platforms With Actuator Time-delays

Active control schemes for offshore steeljacket platform shavebeen aroused extensive concern in recent decades. In the active controlof the offshore platforms, time-delays may appear in the control channelwhere it is taken by the actuator to build up the active control force. There-fore, this paper is concerned with stabilization control and H∞output feed-back control for offshore platforms with actuator time-delays, and furtherdiscusses robust H∞output feedback control for uncertain offshore plat-forms. Details are as follows:Firstly, we study stabilization control for offshore platforms subject tononlinear self-excited wave forces. Two state feedback stabilization con-trolschemesareproposedtoreducethevibrationamplitudesofthesystem-s. One scheme is that for the systems without actuator time-delay, a statefeedback controller is designed. Compared with the nonlinear controller,both the control force and the vibration amplitudes of the systems underthe state feedback controller are much reduced; and compared with the dy-namic output feedback controller and the integral sliding mode controller,the required control force under the state feedback controller are signifi-cantly reduced. The other scheme is that based on the integral inequalityapproach, adelay-dependentstatefeedbackcontroller, whichcanbesolvedby using the cone complementarity algorithm, is developed to control thesystems with actuator time-delays. Compared with the state feedback con-troller, the delay-dependent state feedback controller is less conservativewithactuatortime-delays. Inaddition,itiscapableofimprovingthecontrolperformance of the offshore platforms significantly, which are illustratedby simulation results. Secondly, we study H∞output feedback control for offshore steel jack-et platforms subject to nonlinear self-excited wave forces and external dis-turbances. Based on integral inequality method, a sufficient condition forthe existence of the delay-dependent H∞output feedback control law willbe given first, then by using the cone complementarity algorithm we cansolve the controller gain matrix. Secondly, for the system without actuatortime-delays, a H∞output feedback controller is designed. Further, the de-signmethodofrobust H∞outputfeedbackcontrollerforoffshoreplatformsunder parameter perturbation is discussed. It is found through simulationresultsthatcomparedwith H∞outputfeedbackcontroller, delay-dependentH∞outputfeedbackcontrollercanimprovethecontrolperformancesignif-icantly.