Design and modal analysis of a large-scale underwater compressed gas energy storage accumulator

In underwater compressed gas energy storage (UWCGES) systems, compressed gas can be stored in artificial energy storage accumulators. The accumulator should be capable of sustaining complex gas-water-structure-soil coupled loads throughout the long service time. In this study, a large-scale accumulator with reliable anchoring is designed to sustain complex and cyclic loads when deployed on the soft seabed. The large accumulator is composed of a composite suction caisson foundation and an open rigid concrete gas storage tank. The anchoring force is provided via both the weight of the accumulator and the uplift-bearing force of the composite suction caisson foundation. A safety factor of 1.26 is achieved in terms of the designed accumulator. The large accumulator is threatened by potential current-induced vibration. Thus, the wet modal analyses are conducted to reveal the natural frequencies of the accumulator under various operating conditions. The modal frequencies and vibration modes are obtained with the software ANSYS. The results show that the added mass effect of water on modal frequency cannot be neglected. The wet modal frequency of the first ten orders of the large-scale accumulator is between 10.56 and 20.15 Hz, which is much higher than the vortex shedding frequency of 0.0125 Hz. Thus, the risk of current-induced vibration is quite low in terms of the designed 1200 m³ accumulator.