Numerical Investigation of the Landslide Cover Thickness Effect on the Drag Forces Acting on Submarine Pipelines

Ranking among the most threatening and challenging marine geological disasters, submarine landslides of different magnitudes have destroyed various pipelines, attracting widespread attention from the scientific and engineering communities. However, the relative size and spatial relation of landslides and pipelines, especially the landslide cover thickness above the pipeline, have not been explored in previous studies. As a result, the conventional analysis methods continue to change, and the practical application of these methods is difficult when a general criterion is lacking. In this study, three parameters, namely, the landslide cover thickness H_C, pipeline diameter D, and span height H_S, are first proposed to clarify this problem, and a unified standard analysis model is established. Second, the drag forces on pipelines with five values of H_C and two values of H_S under four typical Reynolds numbers are systematically analyzed using a validated computational fluid dynamic method. These analyses indicate that with increasing H_C, the drag force gradually increases; however, the growth law of the drag force deviates under different H_S conditions. Notably, considering the effect of H_C, the maximum drag force can be increased to as much as five times the original value, and therefore, this effect cannot be ignored. Furthermore, the cause of the drag force variation is revealed by the evolution of the flow fields (e.g., streamlines, velocity vectors, and pressure). Finally, a reference value of the drag force coefficient and an adjustment factor $f_{{\psi }_C}$ are proposed, and a standard chart methodology is established to evaluate the drag forces.