VIV And Vibration Control Of Offshore Pipeline Considering Three Dimensional And Whole Field Fluid-structure Interaction

Marine pipelines are critical structures in the development of marine oil and gas.Their stability and durability are directly related to the safety of oil and gas exploitation,the stability of economy,the constant supply of energy and the protection of marine ecological environment.Due to the complexity of marine environment,marine pipelines tend to have vortex-induced vibration under the effect of ocean currents.Thus structural damage was caused after a long-time use,resulting in huge economic losses and causing pollution to marine environment.Therefore,the research on vortex-induced vibration under the current of oceanic conduits has important social significance and scientific value.At present,the theoretical research of vortex induced vibration in pipelines is mainly divided into simplified model considering the beam theory and fluid load,two-dimensional mass-spring-damping model considering flow field,and three-dimensional solid pipe model considering three-dimensional full fluid-solid coupling.For the sake of computational efficiency,most of the current researches adopt the first two methods.In this paper,a three-dimensional solid pipe model considering fluid-solid coupling of the whole field is adopted,in which solid elements are used in the structure,and the fluid is solved on the basis of an Arbitrary Lagrange Euler(ALE)method for fluid flow in a continuously deformed geometric domain.The mold tube separates the fluid from the tube circumference and the fluid exerts a force on the structural wall due to viscous drag and fluid pressure so that the mold tube deforms under the action of the fluid load,thereby causing the fluid to flow along the new flow path,fluid and structure of the interaction is so looping.The three-dimensional solid element can describe the structural characteristics of the marine pipeline more accurately and the auxiliary vibration suppression facilities for the purpose of vibration control.The simulation of the whole fluid field more realistically reflects the fluid's effect on the structure,Provide a more accurate numerical simulation model.In this paper,the main work of the subject of vortex-induced vibration control of marine pipelines is as follows:Based on the COMSOL,the finite element model of the vortex-induced vibration of the marine pipeline is established within a three-dimensional whole field of fluid-solid interaction.Analysis of vortex-induced vibration response of the pipeline is made from aspects of the displacement of cross-flow,in-line flow and the lift and drag coefficient.The results indicate that with the increase of the reduced velocity,the amplitude of the lateral flow increases first and then decreases,which shows obvious vortex-induced resonance.It can provide an accurate reference for the later research on simulation numerical simulation of the cowl and the partition plate in vibration control.This paper has studied the effect of different-sized fairing on the vortex-induced vibration response of marine pipelines,and the method of reducing vibration is discussed.The results show that the incorporation of the fairing changes the vortex shedding mode of the structural wakes and thus affects the fluid loading,so that the starting point of the vortex-induced vibration locking zone of the pipeline structure is pushed backward and the span of the locking zone is also elongated.After the fairing is added,the natural frequency of the structure changes little compared with the bare tube.Therefore,the same reduction speed can be used to compare and analyze the vibration suppression effect of the fairing at the same flow rate.The Zf/D=0.5 fairing has the best effect on the suppression of the displacement response amplitude,while the Lf/D =0.75 fairing has the best effect of weakening the lift coefficient amplitude.The average weakening effect of the fairing of Lf/D = 1 is optimal in the whole range of low,medium and high velocity.Lf is the length of the fairing and D is the diameter of the pipe.Then the effect of different size partition plates on the vortex-induced vibration response of marine pipelines is further explored,and the optimal partition plate length is obtained.The results show that the addition of the partition plates changes the fluid load and the vortex shedding mode in the wake region.The addition of divider plate necessitates a greater flow velocity of the structure transverse to the maximum amplitude of vibration.The addition of divider plate has a certain impact on the natural frequency of the structure.The reduction speed at higher flow rate is obviously different from bare pipe at the same flow rate.The partition plate of Lp/D=0.5 has the best performance on the weakening of the displacement response amplitude,while Lp/D=1's divider has the best effect of the average weakening effect on the amplitude of drag coefficient and the lift coefficient.Lf is the length of the divider and D is the diameter of the pipe.The comprehensive performance of the partition plate is better than that of the fairing in weakening the amplitude of the displacement and the rise resistance coefficient.Dividers of different sizes have a different emphasis on reducing the amplitude of the displacement and that of the resistance coefficient.In practical project,we should take into consideration the specific marine environment,structural parameters and purpose of the target project in order to set the priority to displacement and resistance control and select the most appropriate size for vibration damping device.