Analysis Of Vortex-induced Vibration Of Fiber Composite Marine Riser Under Ocean Current

As the world's economies continue to grow,many countries gradually pay attention to the development and utilization of marine resources.The marine riser is an indispensable structure in the exploitation of marine resources.The material properties of marine risers are an important factor restricting their application in the deep sea.With the increase of the water depth,the traditional metal marine riser has increased its top tension requirements due to its own weight,which has restrained its application in the deep sea.Fiber reinforced polymer(FRP)composite materials have good corrosion resistance,thermal insulation and fatigue resistance.These characteristics make it a new form of riser of marine engineering,but it also faces the problem of fatigue damage caused by the vortex-induced vibration(VIV)induced by the marine environment.Compared with traditional metal marine risers,the research on the dynamic characteristics of fiber composite marine risers is still in its infancy,and there are many deficiencies.This paper considers three factors,which are the type of riser,the length to diameter ratio of the riser,and the ocean current.Use orthogonal tests to determine the combination of structural and environmental factors,based on computational fluid dynamics(Computational Fluid Dynamics,CFD)method with ANSYS Workbench platform.The numerical simulation of vortex-induced vibration of these combinations with fluid-structure interaction is used to obtain relevant data.The effects of different factors and parameters on the vortex-induced vibration of the riser were analyzed.Studies have shown that under the same condition,the fiber composite marine riser has a larger vibration amplitude in the cross-flow and in the downstream direction than the traditional metal marine riser;and the longer the riser and the faster flow velocity,the greater the vibration amplitude of the riser.The overall stress on the fiber composite marine riser is less than that of the metal marine riser,and the locations of the highest stress generally appear at both ends of the riser.By comparing the safety factors of each fiber layer of two fiber composite marine risers(orthogonal fiber composite marine risers,optimized design fiber composite marine risers),the transeverse stress is the main factor for the failure of each fiber layer of the fiber composite marine riser.The optimized fiber composite marine riser can make better use of the strength of the fiber and improve the mechanical properties of the riser.Finally,using the grey theory correlation method,the effect of the five parameters(tensile elastic modulus and flexural elastic modulus determined by the type of riser;top tension determined by the type of riser and the length of the riser;length to diameter ratio of the riser and the velocity of the ocean current)on the riser vortex-induced vibration is studied.Then the correlation sequence of the influence of these five parameters on the vortex-induced vibration of the risers are solved.It is found that the velocity of the ocean current has the largest influence on the vortex-induced vibration of the riser,followed by the length to diameter ratio,then the top tension,and at last are the tensile elastic modulus and the bending elastic modulus.