Vortex-induced nonlinear vibrations of TLP tethers under circumstances of platform oscillation

A time domain analysis is presented for predicting vorex-shedding induced transverse vibration of tension leg platform (TLP) tethers which are subject to wave,current and oscillatory displacements at their upper end both in horizontal and vertical directions.Periodical variations of tether's tension caused by heaving oscillation of TLP play the role of a parametric exciter to vortex-induced vibration,and make it more complicared.In this paper,the conditions of structure-flow resonant caused by vortex,accounting for the effects of tension's parametric excitation are discussed;a method for analysis of TLP tether's dynamic responses to vortex and heaving oscillation is put forth.The time history of displacements,bending moments and shear forces of the tether are computed by the presented.It is shown clearly that the parametric excitation can raise the amplitudes of vortex-induced transverse vibration,increase the components of high frequent responses.The importance of tension variation for fatigue design of TLP tethers is illustrated.