Similar Model Experimental Study On Vibration Control Of Offshore Platforms

Offshore platforms are infrastructures for ocean resource development, the environment which the platform stays is very severe, which is affected by the winds, waves, ocean currents, and earthquakes combined effect. The protracted effects cause the platform vibration. Thereby platform fatigue failure is aggravated, reducing the system reliability, bringing many adverse effects for the production and life. The offshore platform structures will be induced vibration and noise when suffer outside excitation. The vibration and noise will affect the health of the workers, the work conditions of the equipment and instrument and the structural performance. It causes structural damage seriously to create the platform collapse disaster. Therefore, vibration control of offshore platforms has aroused great concern and become a hot research topic for marine and offshore engineering. Some research works are performed for similar model experimental study on vibration control of offshore platform in the thesis, which is associated with a research project sponsored by National Natural Science Foundation of China. The major aspects of the research are shown as follows.Firstly, on basis of offshore platform similar model, the finite element model is created by the ANSYS software, the mechanical analysis of the platform model is studied, the modal frequencies and mode shapes have been obtained, which provide the basic data for the design of vibration control device.Secondly, according to the simplified model of two-degree-of-freedom system, the theory of ETMD vibration control system is analyzed and the dynamic magnification factor is obtained. According to the dynamic magnification factor, the effects of each parameter of the vibration control system are analyzed, where the Matlab software is used.Thirdly, two anti-vibration devices are designed for the offshore platform similar model vibration control in order to control the vertical vibration and the horizontal vibration of the structure, respectively. Their working principle is described.Fourthly, the dynamic response of the offshore platform similar model is analyzed under earthquake loads and wave loads. In order to study the vibration control effect, the vertical anti-vibration device and horizontal anti-vibration devices are placed on the top of the platform model. The platform model vibration control effect is studied under the random wave load, seismic load as well as sine wave load. In accordance with vibration control effect, vibration control devices obtained the optimal range of each parameter.Fifthly, similar model experimental study on vibration control of platform is done. The horizontal anti-vibration device is placed in the top of platform model vibration. Taking into account the less model measuring points, the experiment uses the method of single-point excit and single-point output measurement. The sinusoidal load generated by the exciter is added to the loading point of the model. AZ208R collection box is used for the data acquisition. And the data analysis system of CRAS V6.2 is used for the data analysis.Sixthly, the vibration responses about the platform model are analyzed for with and without anti-vibration device. The results indicate that the anti-vibration device has good vibration control effect. The mass ratio of vibration system and platform model displacement response relationship is also studied. Compared the data of the experimental of the similar model vibration control with the data of simulation, which can be better tally. The experimental data errors of similar model vibration control are analyzed.In conclusion, the theoretical analysis, simulation analysis and experimental study show that vibration control device has good vibration control effect to the platform model.