Numerical investigation of wave-induced local scour around a submarine pipeline

A two-dimensional numerical model is developed in this work to predict the local scour around subsea pipelines induced by the orbital fluid motion due to free-surface water waves. Instead of being simplified as an oscillatory flow, the motion of the wave surface is predicted numerically. The numerical model is based on the two-dimensional Reynolds-Averaged Navier-Stokes equations with the Shear-Stress Transport (SST) k-ω turbulence closure. The Petrove Galerkin Finite Element Method (PG-FEM) is used to discretize the governing equations. In order to account for the free surface of water waves and the seabed evolution due to local scour, an Arbitrary Lagrangian-Eulerian (ALE) method is employed. Both suspended and bed load sediment transportation rates are considered to predict the evolution of seabed profile. The numerical model is validated against available numerical results and experimental data of wave propagation over submerged structures and local scour around submarine pipeline in steady current. Then, the numerical simulations are carried out for local scour around a submerged pipeline in water waves. Comparisons with laboratory measurements show that the present numerical model works well in predicting the equilibrium profile of local scour, which sheds lights on the numerical simulations of local scour under waves in shallow water, where the waves are expected to be strongly non-linear.