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.
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.
A Nonlinear Fluid Damping (NFD) in the form of the square-velocity is applied in the response analysis of Vortex-Induced Vibrations (VIV). Its nonlinear hydrodynamic effects on the coupled wake and structure oscillators are investigated. A comparison between the coupled systems with the linear and nonlinear fluid dampings and experiments shows that the NFD model can well describe response characteristics, such as the amplification of body displacement at lock-in and frequency lock-in, both at high and low mass ratios. Particularly, the predicted peak amplitude of the body in the Griffin plot is in good agreement with experimental data and empirical equation, indicating the significant effect of the NFD on the structure motion.
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.
