Research On Vortex-induced Vibration Of Marine Risers With Buoyancy Modules

As an important component in the ocean oil and gas exploration, risers are oftensubject to hostile environmental conditions which can lead to vertex-induced vibration(VIV) easily. With the continuous development of ocean oil and gas exploration, VIVcausing fatigue failure of marine risers can not be ignored. At present, most of therecent investigations carried out by the domestic and overseas scholars are mainlyfocused on singer and bare marine risers by adopting three-dimensional numericalsimulation. However, researches on risers configured with buoyancy modules arerarely found in papers.Numerical simulation is used to investigate VIV of risers with different coverageof buoyancy modules in this paper. The results of numerical simulations and theresults of model experiments are compared in order to validate the feasibility of themethod. The results show that the bigger the RMS displacement is, the larger thecoverage of buoyancy modules is. The dominated response frequency of risers isrelated to the coverage of buoyancy modules. Due to the different diameters, the liftand drag forces of different sections seem competitive, which may lead that risersshow more main frequencies. Risers with more buoyancy modules have responsedominated by vortex shedding on the large diameter buoyancy modules while riserswith less buoyancy modules have response dominated by vortex shedding on thesmall diameter bare riser. Meanwhile, the variations of coverage have effects on thevortexes released from the risers. The results form both numerical simulations andmodel experiments are similar to each other which prove the method in this paper isfeasible.The gravity similarity theory is also used to get scale models from the originalrisers and then the research method similar to the one above is also applied. Theresponses of risers with buoyancy modules and bare risers are mainly observed fromthe results. The response frequencies and RMS displacements are analyzed under different tensions. The response frequencies are coincided with those deduced fromStrouhal number. The vortexes are chaotic. And the trends of RMS displacements inthis chapter are similar to those in last chapter. The conclusion in this paper would behelpful to provide reference for research on risers configured with buoyancy modulesand risers installation.