Quantifying the stable impact forces of submarine debris flows on laid-on-seabed pipelines

Two novel methodologies, termed Approach I and Approach II, have recently been developed to quantify the hydrodynamic coefficients of submarine debris flows acting on deepsea pipelines. Prior applications of these approaches mainly considered pipelines suspended highly above the seabed, leaving the influence of seafloor effects largely unexamined. In practice, however, pipelines are typically installed directly on the seabed, underscoring the need to evaluate hydrodynamic coefficients under realistic boundary conditions. To address this gap, we conducted simulations using ANSYS CFX to examine the interactions of two debris flow types, each at nine velocities, with two pipeline configurations: on-bottom and semi-embedded. Seven outer diameters were analyzed for each configuration. The results show that both configurations yield stable hydrodynamic coefficients, primarily due to the suppression of vortex shedding by the seabed. Based on these findings, empirical formulas for drag and lift coefficients were established for both configurations using Approaches I and II. The drag coefficient formula for on-bottom pipelines obtained via Approach II was further validated against experimental data, showing strong agreement. A quantitative comparison with existing approaches highlights the applicability of the proposed methods. Overall, these formulations provide a reliable framework for predicting stable impact forces of debris flows on seabed pipelines.