Identification and maximum impact force modeling investigation for critical slugging in underwater compressed gas energy storage systems

Underwater compressed gas (air, natural gas, hydrogen, etc.) energy storage (UWCGES) is an emerging tech-nology that is suitable for ocean energy storage. Liquid accumulation in gas transmission pipelines can be a significant obstacle in UWCGES systems. In this study, an experimental investigation is conducted to improve the understanding of the kinematics of liquid accumulation. A pressure signal is used for identifying the state of fluid flow in the pipe. Seven kinds of time-domain features are selected through monotonicity. An adaptive evaluation method for slug flow is proposed. The fused features are submitted as a Gaussian distribution through Box-Cox transformation (BCT), and +/- 3 sigma criterion is set as the threshold range to adaptively identify slug flow. Beyond this, a maximum impact force model is established and the largest impact force produced during slugging is predicted. It is found that the inlet velocity, followed by the inclination angle of the pipe and the volume of liquid accumulation, most notably influences the impact force. The model and results have the potential to be further developed for remote monitoring of liquid accumulation in pipelines, which is important for UWCGES systems.