Investigation of the Hydrodynamic Forces Exerted on Offshore Piggyback Pipelines due to Steady Currents

The oil and gas pipelines are among the most important offshore structures. In this study, the turbulent flow past piggyback pipelines and vortex shedding are numerically simulated under steady currents. Numerical simulation has been conducted for different values of the flow velocities, diameter ratios, and gap ratios; in order to investigate how the hydrodynamic forces of the small and large cylinders are affected. Evaluation of the numerical model revealed that the drag coefficient of small and large cylinder is increased as the flow velocity increase. For the large values of gap ratios, increasing of the flow velocity has less effect on the magnitude of the RMS lift force of the large cylinder whereas the RMS lift force of the large and small cylinders considerably increased by decreasing the gap ratio.