Research On Nonlinear Vibration Characteristic Of Large Dimension Deep-sea Risers

Riser connects platform with pipeline or wellhead in tough environment. Issuesabout risers always are the hot topic in offshore oil engineering. By far, the researchon shallow sea risers has come into a mature time, but the one on deep sea risers justis in preliminary step.The loadings on deep sea risers include: wave, current and wind. Besides,movement of platforms can induce coupled movement of risers, which sometimesbring the fatigue problem of risers. Deep sea risers are flexible with relatively largevalue of L/D. In different ranges of L/D, vibration characteristic of risers has not yetbeen dicussed up to now inland. Research on it is not deep enough. In allusion tostatus quo, vibration characteristic of risers will be the focus of this article which aimat giving beneficial suggestion to correlative issues in DNV-2002 last design criterion.The main two parts of this article are:(1) Research on vibration characteristic of shallow sea risers(2) Research on nonlinear vibration characteristic of deep sea risersThe most distinctive differences between shallow sea risers and deep sea risersare: the geometric nonlinear induced by large dimension, the coupling of movementsbetween platforms and risers. Based on Lump-Mass method, combined with ANSYS,response will be calculated. On deep-sea risers' modal research, based on classicaltheory, Matlab code is utilized to calculate modal result which will be compared withANSYS result. Besides, in ANSYS analyzing process, preprocessing andpostprocessing will be done with APDL code. And about coupling problem, becauseexcursion frequence of platforms is pretty smaller than vibration frequency of risersand mass quite bigger than riser's, for simplification, fix platforms on workingposition first, then take the coupling into account later.The question for discussion in this article is practical in engineering and hasimportant theory significance.