In this paper, we present a CFD approach for riser vortex induced vibration (VIV) analysis in uniform current. The riser has a L/D of 1400, and is partitioned into 30 segments with uniform current specified on each segment. The drag and lift coefficients of each segment are then calculated using an unsteady Navier-Stokes numerical method on an overset (Chimera) grid system. These drag and lift coefficients are assembled to determine the riser displacements for each riser segment. The riser motion equation is expressed through riser modal shape superposition, and integrated in time domain by using Runge-Kutta scheme. At each time step the data grids for each riser segment are updated according to the riser's instantaneous displacements. The predicted riser VIV results are compared to the experimental data and previous publications. General agreements are observed. It is concluded that the present numerical method is valid and effective for riser VIV prediction.
Riser vortex induced vibration has been an active research area over the past twenty years, majority of the work is focused in 2D or short risers. Recently experiments on long riser (L/D=1400) have been conducted at Marintek's Ocean Basin in Trondheim (Trim et al. 2005). Figure 1 shows the testing schematics plan view. The riser model has a mass ratio of 1.6, and length of 38m. It is towed through the wave basin to generate desired current conditions. The testing was performed under different the current conditions, i.e. uniform and sheared current. Some experimental data are published in Trim's paper (2005). This VIV experiment has generated considerable interest since it published some detail experimental results of riser VIV with large L/D. As the offshore oil and gas industry is heading toward ultra deepwater fields, to disclose and understand the characteristics of long riser VIV is of particular importance for field development and riser system design.
