Investigation of the Dynamic Loads on a Vertically Oscillating Circular Cylinder Close to the Sea Bed: The Role of Viscosity

The flow around an oscillating cylinder close to a horizontal solid boundary is studied to gather information about the load acting on pipelines, while they are laid on the sea bottom. The problem is simplified assuming that the pipeline section is rigid and oscillates harmonically only in the normal-to-seabed direction so that the problem can be tackled in two dimensions. A computational fluid dynamics (CFD) solver is used to take into account viscous effects in the hypothesis of laminar flow conditions. This best suits the conditions of pipeline layering when the Reynolds number, Re=Um·D/ν, ranges in order of 450–120,000, while the Keulegan–Carpenter number, KC=Um·D/T, ranges in order of 0.45–2. Nonetheless, boundary layer separation and vortex shedding are considered. Focus is on the determination of the lift force for which a novel analytical approximate expression is proposed. Such an analytical result can provide useful support to the studies related with the structural analysis of the pipe laying.