A Study Of Vortex-Induced Vibration Of A Wavy Cylinder At Low Reynolds Number

With the development of science and technology,human's demand for energy is growing.As the gradual reduction of terrestrial oil reserves,the exploitation of deep-sea oil has become the main way to solve the oil energy crisis.As one of the main joints connecting offshore resources and offshore platforms,the research of vibration response of marine riser is one of the hot topics in international academic and ocean engineering.When the flexible riser is placed at a certain velocity,the vortex shedding occurs in the wake area of the riser.Vortex Induced Vibration is generated by the interaction between vortex and riser vibration.VIV).Vortex-induced vibration response is an important characteristic of the riser,and it is also the main factor of structural damage caused by fatigue damage.There are many factors which affect the vortex-induced vibration response of riser,such as the velocity of incoming flow,the direction of flow,the stiffness of riser,the cross-sectional shape and the interaction of riser groups.Among them,the cross-sectional shape of the possibility of many changes in different cross-sectional shape may lead to completely different riser dynamic characteristics.In this paper,the vibration response of a flexible cylinder riser with the sinusoidal variation of cross-section along the spanwise direction under low Reynolds number is investigated.The concrete work is as follows:1)In this paper,the response of an infinitely long flexible riser is simulated by investigating a riser response satisfying the periodic conditions.In view of the high complexity of the response at high Reynolds number,this paper gives priority to the case of low Reynolds number,select the Reynolds number Re = 100.In this paper,nektar++ software is used under ubuntu system for calculation.2)A fixed length of 4? is chosen to give either an initial standing wave disturbance of one period or an initial traveling wave disturbance.The influence and variation of the cross section along the sine wave on the vibration response of the riser are investigated.Among them,the parameters of sine-wave section mainly include the sine wave's wavelength and amplitude.The responses of different lengths and amplitudes are compared with those of the fixed-section flexible.The influence of cross-section variation on the response is obtained.The results show that,the change of cross section has very limited effect on the amplitude under fixed length.3)The response of riser vibration is mainly traveling wave and standing wave.The riser with different cross sections is studied under different initial conditions.4)Select the length of the wave,also give the initial perturbation of a cycle.The response and variation of the variable cross-section cable vibration under varying length are investigated.The results show that,when the length changes,the amplitude varies with different status.