Study On Vortex-induced Vibration Of Large Displacement Flexible Riser Considering Fluid-structure Interaction

The research on vortex-induced vibration (VIV) of riser is a hot in the field ofoffshore engineering,which is due to the riser for offshore oil and gas development ofthe importance and the harsh enviromental condition they surffered.Once the riser wasdestruction,huge economic loss and enviromental pollution would be caused.TheVIV as the most important factor causing the fatigue damage of risers,become a hot assoon as it was put forword.Through decades of research,people had a relativelycomprehensive understanding of VIV，but it could not completely meet the needs ofpratical engineering.With regard to dynamic response of VIV,people usually adopts linear elastic rodmodel to deal with this problem ignoring the nonlinear effects.such as commonly usedsoftware Orcaflex,calculating the VIV without considering the fluid-structioninteraction.In the small length-diameter ratio、 single mode vortex sheddingfrequecency and low Reynolds numbers condition,the linearization was acceptablebecause of the low modal and small deformation vibration.In the largelength-diameter ratio、multi-mode shedding and high Reynolds numeber condition,thenonlinear effects must be taken into consideration,because the VIV will not onlyappear multi-mode viration phenomenon,but also can appear large deformation due tohigh order vibration.The coupling interaction between the riser and the flow field were studiedthrough a dynamic mesh model in CFX.The research work is summarized as follows:(1) The flow around the three-dimensional circular cylinder at different Reynoldsnumbers was investigated and the feasibility of this numerical method wasconfirmed in comparison to the available experimental,then the vortex-inducedlift and drag force at different Reynolds number considering the fluid-solidinteration was studied.(2) The vibration displacement and lift/drag coefficients of in-line and cross-flow voetex-induced vibration(VIV) was studied under different reduced velocitieswhen the mass ratio are7and3.24.(3) At present,almost all of the physical model experiments were based on the gravitysimilarity criterion,the numerical simulation experiment which meet the gravitysimilarity criterion and the Reynolds similarity criterion at the same time wasstudied in this paper.The vortex shedding modes,vibration displacement of VIV with two degrees offreedom and the effects of fluid-solid interation were studied and analysed in thispaper, instructive references about numerical study of VIV considering the fluid-solidinteration were provided.