Dynamic Response Analysis Of Coupled Parametric Vibration And Vortex-induced Vibration For Top-Tension Riser In Deep-sea

The risers are the key facilities in the oil and gas exploration in deep sea, theservice environment is very complicated. The dynamic response is studiedconsidering the coupling between heave motion of the platform andVIV.The two riser models are proposed: one is the theorical analysis model, the axialforce is const and the riser is pinned; the other one is practical model, the axial forceis varying with the water-depth, and the top of the riser is connected to thetension-ring. First, the natural vibration characteristics of deep-water riser are studiedto confirm the frequency and the modal; Secondly, the vibration analysis model isproposed considering the coupling between the parametric excitation caused by theheave motion of platform and VIV to discuss the parameter instability and thedamping’s effect to the instability. Finally, the dynamic responses of VIV and coupledVIV-Parametric excitation are calculated using the numerical evaluation, also thecumulative damage is computed considering the S-N curve and Miner theory.Parameters of the riser and marine environment are changed to study therelationship between dynamic response and these parameters.Research shows that the frequencies are different between the two models, as thepractical model’s results are smaller than the theorical model’s results. For theparameteric instability, when the heave frequency is twice the natural frequency of theriser, the first order parametric instibility occured, this zone is the most important anddangerous zone. When calculating the dynamic response, the parametric excitationmakes the response larger than that without parametric excitation, and the cumulativedamage is much bigger than which has no parametric excitation, the same asparametric excitation’s effect to the cumulative damage. As a result, when design thedeep-water riser, the coupling between parameter excitation and VIV must beconsidered.