Abstract Summary
New technical developments and industrialisation of floating wind turbines will allow the construction of wind energy farms in regions with larger water depths and high-energy potential. This increase in renewable capacity will require the adoption of energy storage solutions to overcome the intermittent nature of wind resources. Among available storage solutions, mechanical systems have one of the highest round-trip efficiencies. Subsea gravity energy storage systems (SGESS) could take advantage of the deeper water of this new energy frontier where high storage capacities can be achieved along the water column. In the proposed technology, drum hoists mounted on barges or platforms lift concrete cylinders with hundreds of tonnes to store gravitational potential energy, which can be released by inverting the motor's operation. The total energy storage capacity is a function of the depth and the number of units installed, while the power is determined by the (dis)charging velocities and the number of units operating simultaneously. The present study addresses the potential effect of vortex-induced vibration (VIV) on the dynamic behaviour of the energy storage modules. In order to analyse the system response, an in-house state-of-the-art semi-empirical VIV model was adapted, integrated with a spherical pendulum and implemented in a time domain simulation in python. The numerical model estimates the amplitude and frequency of oscillation in both in-line and cross-flow directions as a function of the physical and geometrical characteristics of the cylindrical weights, length of the cables and velocity of the sea currents. Results are used to assess the risk of collisions between modules and to provide a baseline for the design of the SGESS.
