Study On Vibration Control Of Offshore Platform Under Irregular Wave Loadings

With the exploitation of ocean oil and gas resources, the offshore construction has necessitated measures for safety insurance, including real-time detecting/monitoring, precautioning, controlling, etc. The research of offshore platform vibration control is developed to meet this need. In recent years, vibration control for shore structures has developed rapidly in contrast with little achievement for offshore structures whose environment's uncertainty has made it difficult to do research. Aiming at the vibration control of a certain offshore platform, the paper engages in offshore platform vibration control, researching the relative skills such as offshore platform structure parameter identification and vibration control and so on. It includes:Offshore platform structure system identification includes modal parameter identification and physical parameter identification. The study identifies the dynamic parameters of an offshore platform under environment excitation. Numerical simulation shows that the parameter identification of low modes is quite precise. The recursive equation for structural physical parameter identification of shearing system is developed. It explains the difference between the identification using complete structure modal parameter and the one using incomplete data and accounts for the reason of error when using incomplete data.Exact numerical system modal is needed to control structure vibration. For the purpose of control vibration on real time, dynamic condensation method is adopted to reduce the finite element model of a certain platform. The displacement responses of the two models under the environmental loadings agree with each other well. The vibration level of the platform was tested on spot. The excursion of the base frequency and its value is obtained by analyzing the tested data. Combined with thenumerical results, the causes of over-vibration of the platform are detected. The results can serve as the base for further offshore platform vibration control. According to the ocean environment, vibration control method using viscoelastic dampers is used to optimize the position of the dampers on actual platform and evaluate their control effectiveness. It can reduce displacement and acceleration response standard deviation of the top of platform by 32.3 % and 38.9 % respectively, compared with those of without dampers.The paper establishs the route and strategy of semi-active vibration controller based on a variable stiffness tuned mass damper (VSTMD) and considers the work of an actuator that is employed to ensure the long operational life span and reliability of the VSTMD. Adopting a set of the tested irregular wave data to simulate the long nonstationary loadings on the platform, the effectiveness of the VSTMD is appraised combining with the practical situation. The platform displacement standard deviation of the top of platform even can be reduced by 50% and by 30.2 % averagely compared with that of without VSTMD.