Numerical model for wave-induced scour below a submarine pipeline

A vertical two-dimensional numerical model for local scour beneath an offshore pipeline exposed to waves is developed in this study. Waves are modeled as sinusoidally oscillatory flows, and the phase-resolved velocity field around the pipeline is simulated by solving the Reynolds-averaged Navier-Stokes equations with a k-omega turbulence closure. Both suspended and bed loads of sediment transport are considered in the model. A special technique for coupling the solution of the flow field to the scour calculation is developed to accommodate different timescales of the flow and morphological changes. The seabed morphology calculation is based on the period-averaged sediment transport rate with a morphological time step that is chosen by designating a maximum allowable bed deformation in each update. Numerical tests indicate that this technique significantly reduces, the computational costs and is of acceptable accuracy. A sand-slide method is employed after each bed update to smooth out small bed irregularities. The model is applied to simulate three cases of wave-induced scour below a pipeline where laboratory measurements were published in the literature. The predicted scour-hole profiles compare favorably with the laboratory observations.