Experiment and Simulation of the Shape and Stored Gas Characteristics of the Flexible Spherical Airbag for Underwater Compressed Air Energy Storage

Underwater compressed air energy storage (UCAES) is an advanced technology used in marine energy systems. Most components, such as turbines, compressors, and thermal energy storage (TES), can be deployed on offshore platforms or on land. However, underwater gas-storage devices, which are deployed in deep water, have specific characteristics. Flexible inflatables have become a viable alternative for underwater compressed air energy storage (UCAES) as air storage devices. Few studies have been conducted on the characteristics of partially inflated structures during the inflating and deflating processes. A tank experiment of a 1 m model of an underwater spherical airbag was performed to investigate the characteristics of the deformed shape, pressure, and volume of the stored compressed air. A finite element (FE) simulation of an airbag model with the same dimensions was established in Abaqus/Explicit. The simulation under shallow testing conditions was in good agreement with the experimental results. Furthermore, studies on the performance of a 4 m airbag prototype with different water depths are presented. The results indicated that the shape variation was only related to the volume (inflation ratio). The pressure varied approximately linearly with the inflation ratio during the quasi-static process from an empty shape to a zero-pressure shape. The operating depth had a slight effect on the deformation. Because the scaling factor influences the pressure difference of the surface at the same height proportion, the larger the dimensions of the airbag, the higher the pressure difference will be.