Research On Output Feedback H_? Control For Offshore Platforms

As one of typical structure located in the hostile ocean sur-roundings,the offshore steel jacket platforms are inescapably subject to stochastic external dynamic loadings including wave forces,wind,earth-quake,ice and current,in addition to enduring the static loadings,such as the dead load and the weight of deck equipment.Among those dynamic loadings,wave forces and earthquake are two typical loadings.At present,many of research on active control for offshore platform subject to wave forces have been presented,whereas the research on vibration control for offshore platform under earthquake are relatively fewer.Although the du-ration time and occurring frequency of earthquake are less than that of wave forces,the intense vibration induced by earthquake,which can cause an enormous destruction for offshore platform in a short period of time.There-fore,it is necessary to decrease vibration amplitudes of platform structure by using active control methods.The paper is concerned with active con-trol methods for an offshore steel jacket platform under wave forces and earthquake.Details are as follows:Firstly,we study the output feedback H_?tracking control for an off-shore platform under nonlinear wave forces.First of all,an uncertain dy-namic model of the offshore platform subject to nonlinear wave forces is es-tablished.Then,the design method of a robust output feedback H_?tracking controller for offshore steel jacket platform is given,based on Lyapunov-Krasovskii stability theorem,a sufficient condition for the existence of the robust output feedback H_?tracking controller can be obtained.At last,nu-merical simulations are given to illustrate the effectiveness and superiority of the proposed active control schemes.Secondly,we study the network-based modelling and active control for an offshore platform under earthquake.A network-based model of the offshore platform under earthquake is established first.Then,A network-based output feedback H_?control scheme is given,based on Lyapunov-Krasovskii stability theorem,a sufficient condition for the existence of the network-based output feedback H_?controller can be obtained.simulation results show that the proposed network-based output feedback H_?control scheme is effective to suppress the vibration amplitudes of the offshore platform and enable to reduce the control cost.