Research On Sampled-Data Control For Offshore Platforms

The sampled-data control scheme for offshore platform with an active tuned mass damper(TMD)mechanism is studied in this paper.Details are as follows:Firstly,as for the offshore platform subject to the nonlinear hydrodynamic self-excited wave force,a sampled-data active control scheme is studyed.First of all,by introducing an artificial time-delay,the corresponding closed-loop system with the sampling measurements is cast into a continuous-time system.Then,based on a Lyapunov functional,a sufficient condition of the existence of a sampled-data controller is derived,and the sampled-data controller is obtained by solving linear matrix inequalities.At last,the effectiveness of the proposed control scheme is demonstrated.Simulation results show that compared the designed sampled-data controller with the nonlinear controller and the integral sliding mode controller,both the oscillation amplitudes of the offshore platform and the required control force under the former are smaller than the ones under the latter.Secondly,the robust sampled-data H_? control scheme for the offshore steel jacket platforms subject to both self-excited wave force and external disturbances is studyed.Firstly,by using an input delay approach,the corresponding closed-loop system is cast into a continuous-time system.Then,based on a Lyapunov functional,the H_? performance is established and the stability criteria for the closed-loop system is derived.Finally,the effectiveness of the proposed robust sampled-data H_? scheme is demonstrated.The simulation results show that to obtain almost the same control performance,the required control force under the robust sampled-data H_?controller is smaller than the one under the robust H_? controller.Thirdly,the non-fragile sampled-data control problem for offshore platforms subject to parametric perturbations of the system and admissible gain variations of the controller is studied.First of all,by purposefully introducing a time-varying time-delay into control channel,designing a sampleddata controller for the original system is transformed into synthesizing a state feedback controller for a time-varying time-delay system,and then,a sufficient condition on the existence of the system is derived and a robust non-fragile sampled-data controller is designed.Lastly,the effectiveness is investigated based on the simulation results,and compared with the robust sampled-data controller and the classical robust controller as well as the robust delayed controller,the oscillation amplitudes of the floors of the system under the three controllers are almost at the same level,while the control force required by the robust sampled-data controller is less than the one by the continuous-time controllers.