Study On Fluid-Structure Interaction Vibration Characteristics Of Carcass For Fluid Conveying Flexible Pipes

Marine flexible pipe is an indispensable fluid transport component in the field of ocean engineering,its structure is relatively complex,especially the carcass that are in direct contact with the transport medium.The carcass has a continuous corrugated cavity wall structure,and the structure is easy to occur flow-induced vibration under the fluidstructure interaction,make the pipeline under the influence of alternate load for a long time,resulting in fatigue damage.Therefore,it is necessary to study the fluid-structure interaction vibration problem of the flexible pipe carcass.The purpose of this paper is to establish a simplified model that can accurately reflect the vibration law of the carcass and has universality,to find the dynamic characteristics of internal flow field in the simplified model,and to study the influence of the corrugated cavity structure of the carcass on the fluid-structure interaction vibration characteristics of the pipeline.Firstly,based on the Timoshenko beam theory with flowing liquid,a simplified model of fluid-structure interaction motion equation of flexible pipe carcass fixed at both ends under the fluid-structure interaction is established.Then,using the natural mode function of Euler-Bernoulli beam,the theoretical calculation formulas of the first four natural frequencies,critical flow velocity and critical pressure of the model are solved.In addition,the parameters of fluid flow rate,fluid pressure,spacing between cavities,etc.are analyzed,and the range of parameters that can significantly change the natural frequency of the model is obtained.Secondly,the meshing method of the cavity flow field in the simplified model of the carcass is discussed.The optimal flow field analysis model is determined by the grid convergence analysis.Then,using CFX,the pressure and velocity changes of the vortex shedding phenomenon in the cavity flow field under different fluid flow rates,fluid pressures and inter-cavity spacing are analyzed.By calculating the Steroha number under different parameters,the range of parameters that can cause the flow-induced vibration of the cavity structure is obtained.Finally,the fluid-structure interaction simulation method is used to solve the first eight natural frequencies and vibration modes of the finite element model of the carcass.By comparing with the theoretical natural frequency,the finite element model is verified to be accurate.The displacement-time curve and Von Mises stress-time curve of different detection points in the X,Y and Z directions are analyzed.By comparing the relevant vibration parameters of the straight pipe under the same fluid condition,the vibration characteristics and laws of the carcass under fluid-structure interaction are obtained.The research results in this paper can be used to predict and evaluate the dynamic behavior of marine flexible pipes.It has certain engineering reference value for the operation and vibration suppression of flexible pipe systems.