In this paper a three-dimensional fixed offshore platform modeled by Finite Element Method in deep water is studied. The non-linearity in wave drag force and wave-structure interaction are taken into account to analyze the response of the structure. The structural response statistics, which have Gaussian distributions, are used to evaluate the effect of structure without TMD and with TMD. And an optimal method to design TMD controlling the first mode of the multi-mode structure is proposed. Moreover occurrence probabilities of sea states on the site of platform are considered to predict the long-term effect of a TMD. Simulation results demonstrate that the long-term effect of a well-designed TMD is good and the practical use of TMD is possible due to the good stability of its optimal parameters under different sea states.
As the amount of oil near the shores decreases, the need to tap oil resources located in deep waters or hostile environments increases. Therefore, improvements in the design and construction practices of offshore drilling and production platforms are necessary. It is essential that theses platforms be able to withstand the action of wind, waves and earthquakes under both operation and extreme conditions. Vibration caused by waves results in accumulation of fatigue-related damage to the platforms and can threaten their safety and operation. To prevent fatigue damage and protect the operations and crew of the platforms, also to improve the livability of platforms, vibration control of offshore platforms is a big challenge to encounter. When analyzing the vibration of fixed platforms in deep waters, the random hydrodynamic forces in the structure system should be predicted properly regarding both the non-linearity arising from hydrodynamic drag force and the wave-structure interaction, so as to obtain the whole structure response realistically.
