Influence of Proximity of the Seabed on Hydrodynamic Forces on a Submarine Piggyback Pipeline Under Wave Action

Abstract

Experimental investigations were mainly carried out to clarify the influence of the seabed proximity on hydrodynamic forces on a submarine piggyback pipeline under regular and irregular wave action. Nondimensional force coefficients for drag, inertia and lift on the piggyback pipeline were obtained with an equivalent diameter based on the Morison equation. The effect of the gap ratio e/D between the bottom of the large pipeline and the seabed on force coefficients of the piggyback pipeline was studied. The results indicated that the force coefficients initially decreased and then remained constant when e/D was beyond 0.5. In addition, a two-dimensional hybrid numerical model, FEM-k-ω-VOF, was applied for a numerical analysis. A comparison of numerical and experimental results showed that the calculated values of wave forces agreed well with those of the experiments and that the numerical model can be employed to predict the hydrodynamic forces on the submarine piggyback pipeline.