Active Vibration Reduction Methods For Offshore Platform With Nonlinear Energy Sink Mechanisms

The offshore platform is affected by earthquake,strong wind and other loads in the complex environment,which brings severe vibration.The traditional method of vibration reduction of offshore platform is using tuned mass damper(TMD)combined with some control methods.However,due to the narrow excitation frequency band,TMD can not do well in reducing vibration in some case.For nonlinear energy sink(NES),it has no fixed frequency and has a good damping effect.At present,there is few research on vibration reduction combined with offshore platform.Taking the fixed jacket platform as the object,this paper studies different active NES damping methods.The main research contents are as follows:(1)The vibration reduction method of offshore platform based on NES under seismic excitation is studied.The dynamic model of offshore platform based on NES under earthquake is established,the parameter optimization design of NES and TMD is given,and the control effect of NES and TMD on offshore platform under earthquake is shown.The simulation results show that NES plays a significant role in improving the stability of offshore platform,and NES has better anti-detuning performance than TMD.(2)The approximate optimal control problem of offshore platform based on NES is studied.The nonlinear dynamic model of offshore platform based on NES under wave force is established.In this paper,an optimal control design method based on parameter perturbation method is proposed,the conditions for the existence of nonlinear optimal controller are obtained,and an iterative algorithm for calculating approximate optimal controller is given.The simulation results show that the approximate optimal controller based on NES can significantly reduce the vibration amplitude of offshore structures.(3)The problem of observer-based NES sliding modeH_∞control of offshore platform is studied.By considering the coupled nonlinear characteristics of unmodeled dynamics,system uncertainties and external wave forces,an observer-based nonlinear system model of offshore platform is established,and an observer-based NES sliding modeH_∞control method is proposed.the existence condition and design algorithm of sliding modeH_∞controller are given.Simulation results show that the observer-based sliding modeH_∞controller can effectively reduce the vibration amplitude of the offshore platform.