Numerical Investigation of velocity on local scour below subsea pipeline in steady flow

Local scour below a subsea pipeline is investigated numerically for gap ratios (e0/D) -0.3 to 0.1 and shield parameter to critical shield parameter ratio ranging from υͬυc 0.3 to 1.49. The positive and negative gap ratio represent that the pipeline is above and below (sagged into) the undisturbed flat sand surface, respectively. The aim of this study is to investigate the effect of Shields parameter ratio on the scour development. Shear stress transport (SST) k-ω turbulence equations͕ sediment transport rates, and Reynolds-Averaged Navier Stokes ;RANSͿ equations are solved to simulate the flow͘ It is found that the scour depth increases nearly with the increase of the Shields parameter ratio in the clear water regime (Shields parameter is less than 1). In the live bed regime, the Shields parameter does not have effect on the scour depth. This study further found that lowering pipeline position increases the scour depth in the live bed condition but does not change the scour depth much in the clear water condition.