Numerical Research Of Vortex-induced Vibration Of Cylindrical Structures Based On An Iteration Method

Vortex-induced vibration(VIV)is commonly observed in engineering structures in petroleum industry,seafloor oil transport pipelines,for instance.Similar cylinder structures are likely to suffer from fatigue failure triggered by periodical loads caused by VIV.Researches on VIV of cylindrical structures have great practical significance in engineering as a result.Numerical simulation is gaining more and more emphasis from its high economical efficiency as well as its rationality.In order to solve the VIV response of cylindrical structures,the FLUENT solver is used in solving N-S equation,while a iteration method characterized by extracting motion parameters is proposed to solve cylinder movement,to calculate the response of one degree of freedom and two degree of freedom cylinders in uniform flow.Simulations using SST k-? model and Realizable k-? model are conducted.The VIV amplitude of engineering structures are calculated adopting the Euler beam model.The results demonstrate that the method adopted is capable of providing reasonable predictions on VIV problems.The frequency lock phenomenon,beat vibration and different vortex shedding modes are captured in the simulation.Main conclusions are given as follows.Damping ratio and mass ratio have significant effects on VIV respond.The lift coefficient and the amplitude of the cylinder will transform from multi-frequency oscillation to single frequency oscillation,and the maximum amplitude will decrease as damping ratio increases.Compared to high mass ratio cylinders,low mass ratio cylinders can excite higher amplitude,larger lift coefficient,and the phase angle reverse corresponds with a larger reduced velocity.Both SST k-? model and Realizable k-? model can capture the typical features of VIV.SST k-? model has captured 2P vortex shedding mode,but the amplitude of the upper branch was smaller,and the peak value of the root mean square of lift coefficient frms and phase angle reverse correspond with smaller incoming flow compared to experimental data.While Realizable k-? model failed to capture the 2P mode,the amplitude of the upper branch was larger,and the phase angle reverse corresponds with lager incoming flow.Length ratio has significant influence on VIV amplitude.Larger amplitude can be excited on structures with bigger length ratio.The mass and damping of structures can be increased based on designing protocols to lower the VIV response.The research has important theoretical and practical significance on numerical calculation and the suppression of VIV on engineering structures.