Numerical simulations of the flow past cross-flow oscillating circular cylinders and marine riser pipes

Presented in this paper is a comparison between numerical and experimental investigations of the Vortex-Induced Vibrations of a model scale marine riser pipe, length-to-diameter ratio of approximately 1400, that was subjected to sub-critical Reynolds number flows. The experiments, which were commissioned by the Norweigan Deepwater Programme, were carried out at Marintek's Ocean Basin in Trondheim in 2003. The numerical simulations are performed using a coupled Computational Fluid-Structural dynamics code. The fluid flow is computed using Large Eddy Simulation, on multiple two-dimensional strips that are positioned at intervals along the length of the riser. The numerical riser response predictions are found to agree well with the experimental measurements. Of particular note was the occurrence in the simulations of harmonic responses at multiples of the principal oscillation frequency; in the cross-flow direction at three and five times the cross-flow oscillation frequency, and in the in-line direction at two and three times the in-line oscillation frequency. Also presented in the paper are the results of a rigorous benchmarking of the code's two-dimensional flow solver against high-quality data from forced cross-flow oscillation experiments performed at sub-critical Reynolds numbers; the code predicted the lift force and phase angle variations well, although agreement in the mean drag force variation was less good.