Anchor damage is one of the main risk factors for the safe operation of submarine cables. Additionally, due to a scour effect induced by seabed currents, submarine cables are prone to exposure or even suspension, increasing the risk of being dragged by anchors. Therefore, it is necessary to study the global response of exposed and suspended submarine cables subjected to anchor dragging. In this study, the tensile and bending stiffnesses of submarine cables are calculated by theoretical methods, and the accuracy of these calculations is verified by establishing a detailed finite element model. Then, the mechanical properties of the submarine cables are equivalently modeled using beam elements, and a large-scale finite element model for exposed and suspended cables under anchor dragging is established. Considering different dragging forces, exposed lengths, spanning lengths, and spanning heights, the overall deformation and mechanical responses of exposed and suspended cables are analyzed separately. The results show that under dragging forces, axial forces are uniformly distributed along exposed and suspended segments, while bending moments concentrate at the central hooking area and the ends of exposed and suspended segments. The influence of dragging force, exposed length, spanning length, and spanning height on the stress and deformation of submarine cables is significant. The results can be used for submarine cable damage assessments caused by anchor dragging.

Free spans of submarine pipelines are prone to be subjected to vortex-induced vibration (VIV) under the action of currents, leading to fatigue damage of submarine pipelines. In the traditional method, the fatigue damage is predicted assuming that the length of free span is a constant. However, the free-span length may vary in time and space due to local scour and sand wave migration in engineering practice. This study proposed probabilistic methods to predict the fatigue life of the free spans by considering the effect of variant span length and span position. Truncated Gaussian, Raileigh and Uniform distributions of span length due to local scour, and a sinusoidal pattern with a constant migration rate is assumed for the sand wave due to the lack of field scan data. The fatigue life of a 120 m long span under a constant current-induced flow with the velocity of 0.7 m/s has been assessed. Results show that comparing with the fatigue life of a fixed span, the present method leads to an increase in the fatigue life by about ten times.

In this paper, 500kV AC submarine cable was taken as the object, the finite element software COMSOL was used to establish the simulation model of fluid-structure coupling, and the force of the suspended submarine cable was analyzed. The stress distribution of the lead alloy sheath of the cable in four specific directions and the location of the maximum stress value was obtained. On this basis, the relationship between the suspended length and the stress value was obtained by changing the suspended length of the submarine cable. According to the initial yield stress value of the lead alloy sheath, the reference suspended length of the preliminary damaged cable structure was given, which provides some theoretical analysis for the online monitoring of the submarine cable. The results show that when the suspended length reached 7.05 meters, the maximum stress value of the lead alloy sheath at the initial yield stress is 1.97×10 ⁷ (N/m ² ).

Hydrodynamic coefficients of subsea suspended pipelines are crucial for fatigue and stability assessments. The effect of the gap height to diameter ratio e/D (0.1 ≤ e/D ≤ 2.0) and boundary layer thickness to diameter ratio δ/D (0.5 ≤ δ/D ≤ 3.0) on the force coefficients under unidirectional current conditions with the Reynolds numbers Re in the range of 1 × 10⁴ ≤ Re ≤ 1 × 10⁵ are investigated via numerical simulations. The results show that the average drag coefficient increases, whereas the average lift coefficient decreases gradually with the increasing e/D. The vortex shedding is inhibited by the wall for e/D < 0.24, starts at e/D = 0.24, becomes stronger with the increase in e/D in the range from 0.24 to 0.5, and approximates to that behind a wall-free cylinder for e/D > 0.5. The effect of δ/D can be eliminated if the coefficients are normalized by the undisturbed flow velocity at the height of the center of the pipeline. Moreover, empirical prediction formulas are proposed describing the drag and lift coefficients as the function of e/D, which can be applied to engineering designs related to free spans.

A 2D numerical model for viscous flow is established in OpenFOAM version 10 to analyze the hydrodynamic response of submarine power cables for offshore wind turbines under combined wave–current conditions. It focuses on analyzing the effect of the cable suspension ratio e/D and the current-to-wave velocity ratio U_c/U_m on the Morison coefficient of the suspended cable. The results indicate that for the cable suspension ratio e/D of less than 0.5, the strength of the dependence of both the drag coefficient C_d and inertia coefficient C_M on the cable suspension ratio e/D is significantly influenced by the current-wave-ratio U_c/U_m, while this dependence becomes less pronounced for e/D greater than 0.5. And the inertia force coefficient C_M decreases monotonically with the current-to-wave velocity ratio U_c/U_m, while the drag force coefficient C_d demonstrates a more complex, non-monotonic relationship with it. Based on the simulation results in this paper, a quantitative relationship between C_d, C_M, and the key governing parameters is established using a two-layer feedforward neural network model, providing a method for predicting wave–current forces on subsea suspended cables.