| Vortex induced vibration is the key factor that causes the fatigue damage of deepwater risers.The theory is being enriched gradually. But, the early studies are mainly about the cross-flow vibration, the in-line vibration was restrained. Few studies have focused on the two-degrees-of-freedom vibration of the risers. Which because the early phenomena presented the amplitude of the in-line vibration was small, it can be neglected.But recent studies found that the consideration of in-line vibration will affect the mode of the vortex and also the amplitude of the cross-flow vibration. But so far, there isn't a systematic study for the two-degrees-of-freedom vibration both at home and abroad.The aim of this paper is to study the dynamic characteristics and the fatigue damage of the deepwater top-tensioned risers with two-degrees-of-freedom, and also develop the relative system.The contents are as following.Putting forward the modified lift force model considering the added mass and the added damping. Test and verify the lift force model.To study the influence of the mass ratio m* and the frequency ratio (f*=frequency in in-line direction/ frequency in cross-flow direction) on the dynamic characteristics and the fatigue damage of the deepwater top-tensioned risers.To develop the dynamic analysis and fatigue analysis system based on the MATLAB language. The above-mentioned contents are the main contents included in the study.The followings are the main conclusions.When m*>6.0, the in-line vibration can be neglected compared to the cross-flow vibration, and also the in-line frequency will be twice of the cross-flow frequency. When m*<6.0, the amplitude of the in-line vibration shows a remarkable increase especially for the'lock-in' state in in-line direction. Meanwhile, the f* is equal to 1.0 besides 2.0.With different f*, the in-line vibration restricts the cross-flow vibration with a wide bound for the low reduced velocity. When the 6.3 |
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