Numerical investigation of local scour around submerged pipeline in shoaling conditions

A two-dimensional numerical model is employed to predict local scour around submarine pipelines under water waves in shoaling condition. The motion of water under waves is simulated by solving the Reynolds Averaged Navier-Stokes (RANS) equations. The wave surface is traced by the Arbitrary Lagrangian-Eulerian (ALE) method. The evolution of the seabed surface near the pipeline is predicted by solving the conservation of the sediment mass, which transport in the water in the forms of bed load and suspended load. The main aim of this study is to investigate the effect of the seabed slope on the scour profiles and scour depth. To achieve this aim, numerical simulations of scour around a pipeline on a flat seabed and on a slope seabed with a slope angle of 5 degrees, 10 degrees and 15 degrees are conducted for various wave conditions. The numerical results show that present numerical results of equilibrium scour depth below pipeline agree the values calculated by the suggested formula quite well for beta = 0 degrees where beta is the slope angle. As beta/=0 degrees, the equilibrium scour depth agrees with the empirical formula as KC 8 and is greater than the latter for KC 8.