Examining surface contact impacts of air-droppable underwater gliders

Underwater gliders are robotic vehicles used to collect oceanographic data such as water temperature, salinity, and chlorophyll levels. Those launched into the sea from aircraft — air-droppable underwater gliders (ADUGs) — have significantly advanced such information-gathering capacities. But their massive impacts upon contact with water can compromise their success and even damage the vehicles themselves.

Ma et al. sought to address the issue by examining standard ADUG characteristics upon entering hydrostatic water. They crafted a three-dimensional numerical model of the ADUG, accounting for its structural details and material attributes.

“The ADUG’s intricate shape, featuring wings and an antenna, subjects it to a more substantial water impact load compared to a simplified version,” said author Peng Wang. “Multiple factors, including velocity of entry and entry angle, play a role in influencing impact load. For instance, when the entry angle increases, the glider disrupts more water, resulting in greater energy loss and a heavier impact load.”

The team demarked three distinct phases of water entry. In the first, the ADUG’s head makes contact with the water, generating a compression wave. During the second, as the wings enter the water, the submerged area and fluid resistance grow. Finally, in the third, with the glider fully submerged, the velocity stabilizes, and the peak acceleration diminishes.

“Our research offers precious insights for improving ADUG design and deployment and paves a robust foundation for future investigations of ADUGs in wave environments and other intricate scenarios,” said Wang. “On a broader scale, our methodologies and findings can be extended to other air-droppable apparatuses with complex shapes, fueling the evolution of underwater vehicles and associated technologies.”

Source: “Study on water entry characteristics of an air-droppable underwater glider in hydrostatic water,” by Wei Ma, Haitong Lou, Xuecheng Li, Peng Wang, Liugen Wang, Wendong Niu, Ming Yang, Shai Fa, Jieru Song, and Shaoqiong Yang, Physics of Fluids (2024). The article can be accessed at https://doi.org/10.1063/5.0244047 .