Vibration Control Study Of Offshore Platforms Using Extended Tuned Mass Dampers System

The offshore platforms are the bases of offshore oil and gas exploitation. Vibration control techniques for offshore platforms are important methods to extend the service life, enhance reliability of the platforms and improve the comfortable feeling of the workers. Some researches on the effect of the extended tuned mass damper (ETMD) system and multiple extended tuned mass dampers (METMD) for vibration control of offshore platforms were done in this dissertation.Firstly, the ETMD system is constructed by using the equipments of offshore platform as the mass body. The offshore platform, on which one mass body is chosen as an ETMD system, is simplified as a double-degree-of-freedom system in the research. In order to analyze the influence of all parameters to the vibration control effects, the appraisal index of vibration control effect is introduced to study the vibration control effect of the ETMD system. The influence of all parameters to the vibration control effect of ETMD system is studied. The results show that the parameters, which influence the vibration control effect, are the ratios of damping, natural frequency and mass. The values of the parameters of the ETMD system determine the vibration control effect. Different values have different influence on the vibration control effect.Secondly, the optimal parameters and optimal parameter regions are given by making use of the software of MATLAB. The ETMD system has the best vibration control effect when the parameters take the optimal parameters and has better vibration control effect when the parameters take values in the optimal parameter regions.Thirdly, several ETMD systems, which have the different frequencies, are set on the platform in order to increase the vibration control effect. Firstly, the platform is simplified as a single-degree-of-freedom system to do research. Several ETMD systems are assigned on the platform in order to enlarge the frequency band of the controlled loads. Then, the platform, on which several mass body are chosen as ETMD systems, is simplified as a multiple-degree-of-freedom system to analyze the effect of frequency bandwidth, damp ratio and ETMD's number to the platform's vibration control and find out their optimal parameters. The vibration control effect on the offshore platform of the ETMD (METMD) system is simulated by using the software of ANSYS, which is subjected to random loads of wave and earthquake. It shows that the ETMD (METMD) system can reduce the vibration of the offshore platform effectively.Lastly, the response of the platform with the ETMD's vibration control under the ocean wave and earthquake loads is researched using the time-history method in the dissertation. The formula of the ocean wave load is derived based on the resistance force linearizing theory. And the loads of different significant wave height are gotten using the MATLAB program. In order to analyze the dynamic response and the vibration of the platform under the random seismic loads, El-centro, Taft and Ninghe seismic waves are chosen and their maximum acceleration have been adjusted according to 8 level fortification under rarely occurred earthquake. The ETMD system has the better vibration control effect under the two random loads mentioned above.In conclusion, the theoretical analysis and the simulation show that the ETMD system has marked effect for vibration control of offshore platforms. The similar model of the offshore platform, which is based on the new method for satisfying the similar condition of the natural frequency ratio, establishes the foundation of the next study. A model platform will be made to study the application of the offshore platform vibration control to the ETMD system in the follow-up research.