Numerical modeling of flow and scour at pipelines

A numerical model for the description of fluid flow, and suspended and bed-load sediment transport, is presented. Density effects are included in the momentum (Reynolds) equations and in the turbulence (k and epsilon) equations. Changes in bed levels are calculated from sediment continuity, and the finite-element grid is adapted to the geometry. The Reynolds equations and the transport equation for suspended sediment are solved numerically using a Taylor-Galerkin finite-element method. The flow at a surface mounted cylinder in a steady how is predicted in good agreement with experiments. Periodic vortex shedding from a cylinder placed above a rigid bed is predicted in good agreement with laboratory experiments, provided that sufficiently detailed grids (similar to 5,000 nodes) are used. Scour calculations are performed for a cylinder in a steady flow with its underside placed at the level of the original hat bed. Predicted scour at a pipeline in steady flow is in good agreement with laboratory measurements reported in the literature.