Simulation Analysis On Viv Of Variable Cross Cylinder And Fluid-Solid Coupling Of Sampler

With the exploration and development of energy continues to advance to the deep sea,the problem of fluid-structure coupling in ocean engineering is attracting more and more attention.Vortex-induced vibration is a typical fluid-structure coupling problem in ocean engineering.Long-term vortex-induced vibration response can lead to structural fatigue failure,and reduce the performance of the structure.In recent years,the relevant scholars have proposed tandem float TLP platform,the tension legs show variable cross-section form,but for the variable crosssection structure of the vortex-induced vibration is less.Therefore,it is very important to study the vortex-induced vibration response of the variable cross-section structure.In the falling process of gravity corer,due to the influence of fluid force,gravity and cable force,the gravity corer can not penetrate into the seabed vertically when it comes into contact with the seabed,resulting in low sampling efficiency.Therefore,it is necessary to simulate and analyze the motion response of the gravity corer,and then improve its sampling efficiency.First,for the vortex-induced vibration problem,the vibration of the column is simplified to the mass-damping-spring model.Based on the CFD software FLUENT,the dynamic layering method are used to establish the two-dimensional single-cylinder vortex-induced vibration model,the fourth order Runge-Kutta method are used to solve the structural motion control equations.The vibration response of the cylinder is analyzed and discussed.The influence of the in-line motion on the transverse motion is analyzed by comparing the vibration response of the single-degree-of-freedom and the vibration response of the two-degree-of-freedom cylinder.Secondly,due to the fact that the slender structure of the riser and so on is mostly distributed in the form of clusters,it is very important to study the multi-column in the form of tandem.The vortex-induced vibration model of tandem double cylinder is established by using overlapping grid method,and the vortex-induced vibration response of tandem double column is discussed.The vibration response of tandem double column is analyzed and discussed in terms of vortex pattern and vibration frequency.Thirdly,with the development of TLP platform,the structure of variable cross-section is more and more widely used in ocean engineering.The study of vortex-induced vibration in variable cross-section structure is becoming more and more urgent.Based on the calculation model of two-dimensional cylinder vortex-induced vibration,the vortex-induced vibration models of three-dimensional cylinder and three-dimensional variable cross-section cylinder are established by layering dynamic method.The accuracy of the model is verified and the threedimensional vortex-induced vibration response is discussed and analyzed.Finally,in the case of two-dimension,the numerical calculation model of the descent process of the sampler under the action of current is established.The vertical movement and the rotating in the descent process of the sampler is considered.The fluid-structure coupling problem in the process of the falling of the sampler is simulated and analyzed.The motion response of the sampler under the action of fluid force,gravity and cable force is discussed,and the influence of the fairing on the motion response of the sampler is analyzed.