Research On Delayed Non-fragile Control For Offshore Steel Jacket Platforms

The offshore platforms are an important technology equip-ment, which widely used in developing oil and gas on the sea. Locatedin the marine environment, offshore platforms are subject to many kind-s of loadings, such as earthquake, wave, flow and current, as well as thenonlinear self-excited wave forces which arises form the flexibility of thestructure induce the vibration of offshore platforms. Therefore, the studyof economic, security, and reliable damping control technology to improvethe security and stability of the system of offshore platform performance,improvethe platform operating officerof workenvironmentand ensure thenormal operation of equipment has an extremely important theoretical andpractical value.In this paper, delayed non-fragile control and robust H_∞control areintroduced to offshore platform damping control. The effect of gain per-turbations and time delay of controller are discussed. The specific contentsare as follows:Firstly,westudythedesignprocessofdelayednon-fragilecontrolschemefor offshore platform under nonlinear self-excited wave force. First, thesimplified model of offshore platform under nonlinear self-excited waveforce is given, and the sufficient condition for the presence of delayed non-fragile control scheme is obtained. Second, two special form of delay non-fragile control laws and their presence of sufficient condition is obtained.Third, the simulations results show that: i) Under the condition of gainperturbation, compared with delayed controller, the displacements of thesystem under the delayed non-fragile controller are much smaller, and therequired control force is much less; ii) The method of artificially introduc-ing time delay into non-fragile controller, can further improve the system control effect; iii) Compared with delayed dynamic output feedback con-troller, the upper bound on the delayed non-fragile controller designed inthis paper is greater.Secondly, we study the positive effects of time delay on delayed ro-bust non-fragile H_∞control scheme for the uncertain system of offshoreplatform. First, the model of offshore platform under the parameter pertur-bation, the affect of nonlinear self-excited wave force and external distur-bance force is given. Moreover, the sufficient condition for the presenceof delayed robust non-fragile H_∞control scheme is obtained. Second, forthe purpose of the comparison, the special form of delay non-fragile con-trol laws and their presence of sufficient condition is obtained. Third, nu-merical examples show that: i) Regardless of the nominal system is stilluncertain systems, the method of artificially introducing time delay intonon-fragile controller, can further improve the system control effect; ii)Compared with control methods in the references, the upper bound on thedelayed robust non-fragile H_∞controller is greater.