Study On The Vortex-Induced Motion Of Tension Leg Platform Considering The Impact Of Wake

With the increasing exploitation of oil and gas resources on land, many countries of the world turned their attention to the sea. The development of the offshore platform provides a basis for marine oil and gas resources exploitation. After the development of more than half a century, tension leg platform(TLP) has three major series which are based on the classical TLP. TLP is a kind of semi-rigid and half compliant platform. Out-of-plane movement(roll, pitch and heave) for TLP is small which is equivalent to rigid, while the in-plane movement(surge, sway and yaw) is flexible movement.This paper is started from the related factors of the vortex-induced motion(VIM) excitation, as flow velocity, flow direction and frequency ratios, and study the characteristics of VIM like frequency lock-in, loading conditions of four columns and vortex shedding modals. Flow around cylinder is the basis of the study on the VIM. In this paper, flow around cylinder of single cylinder and TLP columns is simulated combining with the SST k-co turbulence model, using Gambit software to establish 2-D computing grid and Fluent software to calculate the force of each column and monitor the drag and lift coefficient. VIM involves complex fluid-structure interaction. Based on the study of flow around cylinder, fluid-structure interaction is studied when TLP has a movement which includes lateral movement, longitudinal movement and two-direction movement. User Defined Functions which includes the movement of TLP is embedded into Fluent, then dynamic mesh technology is adopt to update. The load condition of columns and vortex shedding modals under different flow directions,different motion amplitudes and different frequency ratios is mainly analyzed. The frequency domain characteristics is also analyzed through frequency domain analysis. Based on the analysis above, the conclusions are as follows:the results of flow around single cylinder meet the classic flow around cylinder conclusion, the results of flow around cylinder of TLP columns are different from single cylinder as the downstream columns are located in the wake of upstream columns; the results of VIM are influenced by motion amplitudes, frequency ratios and differnet trajectories.Vortex-induced motion is a hot problem considered by ocean engineering and is also a complex fluid dynamics issue, therefore, study on vortex-induced motion has a very important significance. This paper can offer valuable reference for the design of the TLP and it is helpful for the later study on VIM. Therefore, the present study is not only of engineering importance but also of great academic value.