Vortex-induced Vibration Of Marine Risers With Multi-parameters

Marine riser is an indispensable structure in marine oil and gas development system.It plays an important role in transmission between offshore oil an d g as ex plo ration equipment and offshore platforms.The flow field environment where the marine riser is located causes it to generate a periodic reciprocating vortex alternation in the second half of the riser during the sea current flushing process,causing vibration of the riser,which is fed back to the fluid part,causing wake changes.This phenomenon of coupling of fluids and solids is called the vortex-induced vibration phenomenon of t h e r i s e r b a s e d o n fluid-structure interaction and it affects the service life of the riser.Nowadays,many researchers have conducted more research on the vortex-induced vibration response of marine risers.However,most studies only consider the effect of a single parameter on the riser model.There are few studies on the vortex-induced vibration characteristics of marine risers under the combined effects of multiple parameters.Aimed at the above phenomenon,the thesis use the Laboratory model test and numerical simulation methods to study the response of marine riser vortex induced vibration under the multi-parameters condition.Firstly,the marine riser model tests in the laboratory were performed taking into account four parameters.Test parameters include: riser model material,boundary conditions,top tension,and external flow rate.Aluminum(Al),PMMA,and UPVC were selected as model materials.The boundary conditions are hinged at both ends(S-S)and articulated-fixed(S-F).Top tension chooses 5N,10 N and 65 N.External flow rates were 0.2 m/s,0.4 m/s,0.6 m/s,0.8 m/s,and 1.0 m/s.The experimental study analyzed the vortex-induced vibration response of the riser model under the coordination of 90 different working conditions.The study shows that four parameters affect the vortex-induced vibration of the marine riser: the material properties,boundary conditions and top tension of the riser are positively correlated with the natural frequency of the riser.The riser material properties,boundary conditions and top tension are negatively correlated with the riser vibration amplitude,and the external fluid velocity is positively correlated with the riser vibration amplitude.In the low flow area,the top tension needed to control the amplitude of the vortex-induced vibration of the riser is smaller;as the flow rate increases,the top tension required to control the amplitude of the vortex-induced vibration of the riser increases.With the increase of the top tension,the vortex-induced vibration frequency of the riser increases.Then,based on the computational fluid dynamics method,using the fluid-solid coupling calculation method combining transient model and flow field calculation in ANSYS Workbench software,the vortex-induced vibration response of marine risers was compared.Through numerical simulation,the natural frequencies of the risers of different materials,the rise resistance coefficient curves of the risers,displacement history curves,vibration frequency curves and vorticity figures were obtained,comparing with the experimental data,the variation trend of natural frequency is consistent with the model experiment,but the numerical simulation structure data is large.The main reason is that the influence of the wire on the flow field disturbance and noise can not be ignored during the test process.In the numerical simulation process,the material properties and boundary conditions are idealized and simplified,which has a partial impact on the results.Finally,through the gray theory correlation method,the correlation between the influence of the four parameters of material elastic modulus,boundary conditions,top tension and external flow velocity on the vortex-induced vibration of the riser is calculated,and the four parameters and riser vortex-induced vibration effects are solved.The correlation sequence shows that the riser material has the greatest impact on the vortex-induced vibration of the riser,the flow rate is the second,the boundary condition is the next,and the top tension is weaker than the other three factors.