Hydrodynamic forces on a pipeline with uneven embedment

Hydrodynamic forces on a pipeline with uneven embedment on either side, subject to oscillatory flow, are investigated numerically. Two-dimensional Reynolds-Averaged Navier-Stokes equations with a κ-ω turbulent model are solved to simulate the flow in the fluid. It is assumed the seepage flow in the seabed is governed by Darcy's law and Laplace equation is solved to calculate the pore pressure under the assumption of isotropic and homogenous seabed. The effects of embedment depths and KC numbers on the hydrodynamic force are investigated. The flow structure and pressure distribution around the pipeline are discussed. The inline force and lift exerting on the pipeline are presented in the form of peak values and Fourier coefficients. It is found that flow structures around the pipeline are asymmetric due to the difference of seabed levels on the two sides of the pipeline. The degree of asymmetry increases with the increase of |e₁-e₂|/D. Obvious difference exists between the hydrodynamic forces experienced by the pipeline in two succeeding halves of a period due to the asymmetric flow structure around the pipeline. The peak values of inline force and lift reduce as e₂/D increase for all values of e₁ examined in this study. The maximum error of the inline force and lift predicted by using sixth order Fourier series is about 4%.