NUMERICAL INVESTIGATION OF INTERNAL FLOW EFFECT ON THE CROSS-FLOW VORTEX-INDUCED VIBRATION

To examine the internal flow effect (IFE) on the vortex-induced vibration (VIV) of a flexible marine riser in the subcritical internal f low region, the cross-flow (CF) VIV of the riser with single-phase internal f lows is investigated employing a semi-empirical hydrodynamic force model. The governing equation can be established based on Hamilton Principle and solved by finite element method. A MATLAB code has been developed and it has been validated for IFE and VIV respectively. The numerical simulations of a flexible riser are carried out with different internal f low velocities and internal f low densities. The IFE on CF VIV is investigated by analyzing the dominant mode, dominant frequency and displacement response of the riser. It has demonstrated that with the increase of internal f low velocity and density, (1) the dominant mode of VIV can transfer to a higher order, accompanied by a jump increase of the dominant frequency; (2) the increase or decrease of the root mean square displacement of VIV depends on whether the dominant frequency approaches or departs from the vortex shedding frequency; (3) the travelling wave characteristics of VIV can be enhanced.