Design and mechanical behaviors of an anti-shock composite protective layer for offshore wind power dynamic cable

To address the fracture problem of dynamic submarine cables and their protective sheaths caused by friction and collision with wind turbine platforms under harsh sea conditions, a multi-impact resistant composite protective layer was designed using ethylene vinyl acetate (EVA) foam and rubber as the main materials, which possess high elasticity and excellent cushioning properties. Mechanical property tests were conducted on EVA foam materials with various relative densities under different loading conditions using a universal testing machine and drop hammer. Energy absorption efficiency, densification strain, plateau stress and maximum specific energy absorption were introduced to characterize the mechanical properties of EVA foam. The effects of relative density, strain rate and repeated loading on the energy absorption characteristics of EVA foam were revealed. Based on the matching relationship between the energy absorption per unit volume of EVA foam and the kinetic energy of dynamic submarine cables to be absorbed, the optimal thickness of the protective layer was determined, and composite protective layer specimens were fabricated. Subsequently, drop hammer impact tests were performed to compare the cushioning and energy absorption characteristics of the composite protective layer with other materials, preliminarily verifying its high energy absorption efficiency. Further drop hammer impact tests were conducted to investigate the effects of impact energy and loading cycles on the cushioning and energy absorption characteristics of the composite protective layer. The experimental results displayed that: (1) under single impact, the peak force and maximum displacement of the composite protective layer showed a linear positive correlation with the drop hammer mass and impact velocity, with energy absorption efficiency reaching 85%; (2) under multiple impacts, the mechanical properties of the composite protective layer exhibited remarkable stability-the maximum displacement in the fourth impact increased by only 5.5% compared with the first impact, with fluctuations in energy absorption value and instantaneous rebound rate remaining below 5%. The composite protective layer demonstrates unique mechanical properties that provide effective long-term protection for dynamic submarine cables under harsh marine conditions.