Single jet impinging verticial motion analysis of an underwater robot in the vicinity of a submerged surface

Anticipated growth of sub-sea technologies for security, infrastructure inspection, and exploration, motivates a deeper understanding of dynamics of underwater navigation in proximity to a submerged target surface. In this paper we discuss the phenomenon of a smooth, submersible micro robot with a single bottom jet that enables hovering and sliding over underwater surfaces. Such motion has applications to both visual and contact inspection methods of underwater surfaces: pipelines, oil rig infrastructure, ships, or even threats like underwater mines. Examples are air hockey, where disks move on a film of air (sliding); and hovercraft or vertical/short takeoff and landing (V/STOL) vehicles in proximity to the ground (hovering). The common feature is using the fluid between the body and an external surface to generate forces. The phenomenon is widely known in the context of motion over land and water surface, with air as the fluid, but has not been utilized for underwater motion. In our research we exploit the fluid flow between a submerged surface and a robot with a single active thrust jet coming out of the bottom. A lot of work has been done on single and double jets impinging on the ground for V/STOL, particularly for NASA, but no analogous studies exist on how a water jet affects the dynamics of an underwater drone moving near submerged surfaces. Preliminary results from simulations and initial experiments show unique phenomena of multiple stable equilibrium points with varying thrust forces. Further, for a fixed thrust force we demonstrate two stable regions: in extremely close proximity, when the robot rests on a thin fluid film which enables it to glide; and another with robot a body length or more away. Stability at close proximity is relevant to on-contact inspection such as ultrasonic testing. A larger gap has application in visual imaging, where a combination of thrust jets and ground effect lift enable the robot to hover at fixed distances from the target surface. This paper, through CFD simulations and preliminary experimental results, presents a basic robot design which is can be adapted for a wide range of underwater inspection tasks.