Hydrodynamic Forces of Subsea Small-Diameter Pipeline in a Deep/Wide Trench

Accurate predictions of the hydrodynamic forces on a pipeline or cable in a trench are of both fundamental and practical significance. Existing design guidance (DNV-RP-F109) enables forces to be estimated based on a simplified model of a pipeline in a trapezoidal trench with very limited dependence of hydrodynamic forces on incoming flow and some trench geometry parameters, such as the slope of the trench θ, the trench-width-to-pipeline-diameter ratio W* and the trench-height-to-pipeline-diameter ratio H*. The present study conducts a series of two-dimensional (2-D) and three-dimensional (3-D) direct numerical simulations of steady flow past a pipeline placed at the bottom of a smooth trench over a range of trench configurations (θ = 0°–30°, W* = 3–20 and H* = 1–20). The pipeline Reynolds numbers vary from 500 to 3900 based on incoming steady flow velocity and pipeline diameter, meaning that these results are a preliminary investigation of the problem rather than representing typical pipeline/cable/trench/ flow conditions. This paper explores the dependence of trench configurations on flow characteristics and hydrodynamic forces.