Flow around a pipeline and its stability in subsea trench

Offshore subsea pipelines must be stable against external loadings, which a re mostly due to waves and currents. To determine the stability of a subsea pipeline on the seabed, the Morrison equation has been applied with predic tion of inertia and drag Forces. When the pipeline is placed in a trench, t he force acting on it is reduced considerably. Therefore, to consider the s tability of a Pipeline in a trench, one must employ reduction factors. To i nvestigate the stability of various trenches, we numerically simulated flow s over various trenches and compared them with experimental data from PIV ( Particle Image Velocimetry) measurements. The present results were produced at Reynolds numbers ranging from 6 X 10(3) to 3 X 10(5) based on the diame ter of the cylinder. Quasi-periodic flow patterns computed by large-eddy si mulation were compared with experimental data in terms of mean flow charact eristics for typical trench configurations (W/H=1 and H/D=3, 4). The stabil ity for various trench conditions was addressed in terms of mean amplitudes of oscillating Lift and drag, and the reduction factor for each case was s uggested for pipeline design.