PREDICTION OF VORTEX-INDUCED VIBRATION OF FLEXIBLE RISER USING IMPROVED WAKE-OSCILLATOR MODEL

For the aim of improving the Wake-oscillator Model, an analytical model for vortex-induced vibration of flexible riser under non-uniform current is presented, in which the variation of added mass and the nonlinear relationship between amplitude response and the reduced velocity are considered. By means of empirical formula combining iteration computation, the improved analytical model can be conveniently implemented by computer code and has a simpler and faster computation process than CFD so as to be suitable to the application in practical engineering. This model is validated by comparing with experiments and numerical simulations. Our results show that the improved model can predict VIV (Vortex-Induced Vibration) response and lock-in range more accurately. At last, illustrative examples are given in which the amplitude of response of flexible riser experiencing VIV under action of non-uniform current is calculated and effects of riser tension and flow distribution along span of riser are explored. It is implied that with changes of tension and current distribution, lock-in domains of modes move along riser, thus the total responses of riser are synthesis of response for locked modes.