Online Identification of Equivalent Roll Center for Underwater Gliders to Weaken the Repeated Yawing

Underwater gliders (UG) experience unexpected yaw during each dormancy stage of the controller, necessitating additional adjustments, which manifests as repeated yawing throughout the entire profiling time. Repeated yawing is frequently observed during the long-term deployment of the UGs, which can negatively impact navigation stability and sensor sampling quality. To weaken the yawing in real-time, this letter proposes an online identification method for the equivalent roll center (ERC) of the UGs that rely on rolling the internal battery pack to induce banked turns. The ERC is the zero point position of the battery pack that prevents yawing in the on-site environment. The method is derived based on the approximate linear relationship between roll control and turn rate of the UGs. The influence of inherent errors, biofouling, and ocean currents on turning characteristics is quantitatively described based on the dynamic model. In a long-term sea trial, the online ERC identification results were compared with the true values obtained by fitting all data, verifying that the identification error was within an acceptable range and the repeated yawing was effectively weakened after ERC compensation. Finally, the contribution rates of various factors to ERC are calculated. As the profile progresses, it's found that ocean currents in the external environment have the most significant impact on ERC. This method does not rely on dynamic modeling and is therefore applicable to all UGs that use banked turning, which can effectively weaken their repeated yawing.