Most existing studies on the submarine pipeline hydrodynamics are either for the pipes above the seabed or for those buried in the seabed. In this study, the seabed proximity effects on the wave-induced hydrodynamics of the pipes with typical relative locations are investigated experimentally in a large fluid-structure-soil interaction flume. Experimental results indicate that when the pipe is above the seabed, the inertial coefficient CM and upward lift coefficient CLA increase with decreasing the gap-to-diameter ratios (e/D) for e/D < 0.5. With e/D decreasing from 1.0 to 0, the drag coefficient CD and downward lift coefficient CLT increasegraduallyandreachtheirpeak values at e/D≈0.1, then decrease as the pipe further approaching the seabed. When the pipe is buried in the seabed (e/D<0), the effect of inertia on the in-line force gets weaken. The maximum values of the downward and upward lift forces happen approximately under the wave crest and wave trough, respectively. Moreover, the pore pressure oscillation amplitudes increase on the upper-half segment of the pipe and decrease on its lower-half segment in comparison with those at the same depths in the far-field.
While submarine pipelines approaching or penetrating into the seabed, the hydrodynamics can undergo significant changes in both magnitude and phase. To better understand the variations of hydrodynamic forces with the gap/embedment ratio is vital for the on-bottom stability design of a submarine pipeline.
