The Horizontal Finite Strain On The Vortex-induced Vibration Response Of Tension Leg Offshore Platform

The tension leg platform (TLP) is a typical compliant flexible system with fluid and structure interaction. The oceanic environmental forces act on the TLP are quite complex. Compared with the traditional fixed platform, TLP is suitable for the application in the deep sea structure. This study is focused on the influence of the transverse finite strain on the response of the structure subjected to different vortex-shedding loads.Firstly, the platform (Deck, Column and Pontoon) is simplified by a hollow flexible beam supported by a torsional spring at the base and attached with a mass at the tip. Secondly, based on the characteristics of the high flexible and finite deformation of TLP in deep sea, the transverse finite strain is added into the motion equations and the effect of tip mass is taken account into, which are neglected in the literatures that only consider the axial deformation and flexibility deformation of TLP. The Hamilton' s principle and some reasonable hypothesises are adopted to obtain the coupled non-linear equations of motion and boundary conditions. Finally, the motion equations and the boundary conditions are discretized by using the finite difference methods, and solved numerically by Gear method.In this paper, the response of the planar model and three dimensions model subjected to the vortex-shedding loads have been investigated. In the planar motion, the influence of the transverse finite strain on the response of the structure subjected to different vortex-shedding loads is analyzed. The results show that transverse finite strain makes a great influence on the structural responses nearby the basic frequency of TLP, in which the amplitude of vortex-shedding load may have greater influence than that of the vortex-shedding frequency. In addition, the virtual work done by the tip mass gravity cannot be ignored as well.In the three dimension motion, the semi-empirical Morison equation is used to simulate fluid force. The influence of the transverse finite strains on the structural response subjected to variable current velocity and vortex-shedding load is investigated numerically. The numerical results indicate that transverse finite strains affect the structural response in two ways. It is neglectable in structural response in the direction of the...