Vibration Analysis of the Deep-sea Risers under Parametric Excitations
Yang Hezhen Li Huajun
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(1 School of Naval Architecture, Ocean and Civil Engineering, Shanghai Jiao Tong University, Shanghai 200030,China;2 College of Engineering, Ocean University of China, Qingdao 266100, China)
The study is focused in the lateral response and parametric instability of the deep-sea risers due to the parametric excitation. As offshore hydrocarbon resources exploration and exploitation moving to much deeper waters, risers play more important roles than before, and face with many technological challenges. Especially, parametric resonance will appear, when riser system parameters lie within unstable region. The riser resonance can create serious damages which cause environment pollution and economical loss. Unquestionably, the risers for ultra-deep water have complex dynamic characteristics. Firstly, the governing motion equation of the marine riser is formulated. Then the stability behavior of the risers with and without nonlinear damping is investigated by employing the Floquet theory. The numerical simulations for the lateral response of the risers are validated for four typical cases. During the numerical solution of the governing equation, the coupling between the modes was considered. Finally, special attention has been paid to the effect of damping for the parametric unstable region changes. The results show that damping can effectively reduce unstable regions. Several useful suggestions are proposed for the design of deep-sea riser structures.