NUMERICAL STUDY OF HYDRODYNAMIC FORCES ON A SUBMARINE PIGGYBACK PIPELINE UNDER WAVE ACTION

In the paper, a 2D numerical model is established to simulate the hydrodynamic forces on a submarine piggyback pipeline under regular wave action. The two-dimensional Reynolds-averaged Navier-Stokes equations with a k-omega turbulence model closure are solved by using a three-step Taylor-Galerlcin finite element method (FEM). A Computational Lagrangian-Eulerian Advection Remap Volume of Fluid (CLEAR-VOF) method is employed to simulate free surface problems, which is inherently compatible with unstructured meshes and finite element method. The numerical results of in-line force and lift (transverse) force on the piggyback pipeline for e/D=G/D=0.25 and KC=25.1 are compared with physical model test results, which are conducted in a marine environmental flume in the State Key Laboratory of Coastal and Offshore Engineering, Dalian University of Technology, China. It is indicated that the numerical results coincide with the experimental results and that the numerical model can be used to predict the hydrodynamic forces on the piggyback pipeline under wave action. Based on the numerical model, the surface pressure distribution and the motion of vortices around the piggyback pipeline for e/D=G/D=0.25, KC=25.1 are investigated, and a characteristic vortex pattern around the piggyback pipeline denoted "antiphase-synchronized" pattern is recognized.