The slack-taut state of tether is a particular adverse circumstance,which may influence the normal operation state of tension leg platform(TLP).The dynamic responses of TLP with slack-taut tether are studied with consideration of several nonlinear factors introduced by large amplitude motions.The time histories of stresses of tethers of a typical TLP in slack-taut state are given.In addition,the sensitivities of slack to stiffness and mass are investigated by varying the stiffness of tether and mass of TLP.It is found that slack is sensitive to the mass of TLP.The critical curved surfaces(over which indicates the slack) for the increase of mass are obtained.
An analytical method based on the eigenfunction expansion and the Graf's addition theorem for Bessel functions is developed to study the hydrodynamic interactions of an array of truncated circular cylinders with each cylinder oscillating independently in different prescribed modes. The hydrodynamic radiation and diffraction of linear waves by such an array of cylinders are investigated and the analytical solutions of the velocity potentials are obtained. After comparisons for degenerated cases and program verifications, several cases for an array of truncated cylinders with each cylinder oscillating independently in surge, sway, heave, roll, and pitch modes with different prescribed amplitudes, are studied and the hydrodynamic forces and moments acting on the cylinders are obtained.
＜正＞This paper concerned with vortex induced vibration of an elastically supported rigid circular cylinder in a...
XU Wan-hai~*,ZENG Xiao-hui,WU Ying-xiang Key Laboratory for Hydrodynamics and Ocean Engineering,Institute of Mechanics,Chinese Academy of Sciences, Beijing 100190,China
This article proposes a new wake oscillator model for vortex induced vibrations of an elastically supported rigid circular cylinder in a uniform current.The near wake dynamics related with the fluctuating nature of vortex shedding is modeled based on the classical van der Pol equation,combined with the equation for the oscillatory motion of the body.An appropriate approach is developed to estimate the empirical parameters in the wake oscillator model.The present predicted results are compared to the experimental data and previous wake oscillator model results.Good agreement with experimental results is found.
This paper presents the Hill instability analysis of Tension Leg Platform(TLP)tether in deep sea.The 2-D nonlinear beam model,which is undergoing coupled axial and transverse vibrations,is applied.The governing equations are reduced to nonlinear Hill equation by use of the Galerkin's method and the modes superposition principle.The Hill instability charted up to large parameters is obtained.An important parameter M is defined and can be expressed as the functions of tether length,the platform surge and heave motion amplitudes.Some example studies are performed for various environmental conditions.The results demonstrate that the nonlinear coupling between the axial and transverse vibrations has a significant effect on the response of structure.It needs to be considered for the accurate dynamic analysis of long TLP tether subjected to the combined platform surge and heave motions.
