Numerical Study on the Stability of a Riprap for Submarine Cables and the Protective Solution Under Waterflow Incidence

This study presents a numerical investigation into riprap stability for submarine cable protection under high-speed incident waterflow conditions. A coupled CFD-DEM numerical model, implemented within the ANSYS 2024 R1 platform, was developed and validated against controlled laboratory experiments. The stability of the riprap was systematically evaluated across a range of incident waterflow velocities and slope ratios. Numerical results show that localized high-velocity waterflow regions—characterized by intense shear stress—are the predominant destabilizing mechanism governing riprap failure. Elevated incident waterflow velocity intensified localized hydrodynamic disturbances over the riprap top and upstream-facing slope, triggering incipient motion, stone detachment, and subsequent transport of surface armor rocks. As the riprap slope became steeper, the threshold waterflow velocity for instability decreased from 4.2 m/s to 3.6 m/s. Furthermore, interconnecting plates—deployed as an active protective solution—suppress flow-induced erosion over the riprap surface and mitigate localized instability, thereby enhancing global structural stability.