| The exploration and development of the oil and gas in the deep sea has become the general direction in the oil and gas industry both at home and abroad gradually. The offshore drilling is more difficult and expensive than the land drilling, so the complex and bad environment of the deep sea makes a higher requirement to the drilling equipment in the offshore. The deepwater drilling riser which can separate the seawater, provide a circulating path for the drilling fluid and guide the drilling tool down and back is the key equipment to connect the drilling platform with the subsea wellhead. The deepwater drilling riser's acting form of the load is more complex with its whole length getting longer and the problem of fatigue damage caused by the action of the sea flow becomes more and more severe with the increasing drilling depth. So this paper carried out the riser mechanics characteristic and the study of vortex induced vibration of deepwater drilling from the following points.(1) Finish the collection and analysis of the deepwater drilling riser system composition, environmental loading, duty parameter, mechanical property, vortex-induced vibration and its vibration abatement, and put forward the research program and route in this paper.(2) Analyze the mechanics model unit of the deepwater drilling riser, and establish the Equilibrium differential equation. Establish the analysis model of the deepwater drilling riser with the length of 1200m using the OrcaFlex software to provide the basis for the choice of parameter condition below. The influence of changing the wall thickness of the deepwater drilling riser, the tension ratio and the drilling fluid density to the deepwater drilling riser's natural frequency is studied, and the results of the analysis is the Vortex-induced vibration frequency's reference conditions, which shows the importance of the Vortex-induced vibration in causing the fatigue failure of the deepwater drilling riser.(3) Get the effects of the different factor's change to the deepwater drilling riser's mechanical response characteristics by researching the parameter sensitivity analysis of the deepwater riser with the environmental factors and operation factors. Select the key influence factor, and conduct the orthogonal analysis to the sensitivity parameter, then acquire the influence degree of each key factor to the deepwater drilling riser system's rigidity and strength.(4) Establish the 2-d flow numerical model of the deepwater drilling riser using the Fluent software, and research that how the drilling riser's characteristics of the flow field around, lift drag coefficient and the vortex shedding frequency are changing in different flow velocity Then get the effects of the vortex-induced vibration to the drilling riser in different depth using the relation of lift drag coefficient and the vortex shedding frequency with the change of the flow velocity.(5) Combining the vortex-induced vibration induced mechanism, design a vortex-induced suppression device with the curved tail based on the mechanism of vortex-induced vibration through the contrastive analysis to the strengths and weaknesses of current vortex-induced vibration suppression device. Then analyzed and compared the results with the vortex-induced vibration characteristic parameters, which shows that such structure when the curved tail's radial is designed less has a significant effect in restraining the vortex-induced vibration.In conclusion, the researches in this paper will provide the technical support for developing mechanical property, vortex-induced vibration and its vibration abatement, will provide important guiding significance for the deepwater drilling riser design and safe operation, and will play an important role in promoting the localization development and industrial application of the deepwater drilling riser. So, the researches in this paper will not only have important theoretical meaning and academic value, but also have expansive application prospect. |
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