Design analysis of a self stabilizing underwater sub-surface inspection robot using hydrodynamic ground effect

In this paper we discuss a micro submersible robot which can move across an underwater target surface at proximity (~1mm) using the stabilizing effects of the boundary layer interaction with the external surface. Underwater surface and subsurface inspection is of immense value whether in infrastructure maintenance like oil pipelines, ship bottoms or in security and defense, for recognizing and identifying target threats. For subsurface inspection using ultrasound testing (UT), reliable contact is generally needed; but the same can be achieved by positioning the UT transceiver at an odd multiple of quarter wavelength distance away from the target. However, depending on the frequency of the UT, this could be in the order of mm, which is a challenging distance to stabilize the inspection robot by sole use of actuators. In this paper, we present the concept of a self stabilizing underwater robot by exploring ground effects, and analyze how the variation of the underbody design affect this stability. We make simple transitions from an ellipsoidal base to rectangular one and extend further with inclusion of protrusions on the base. The simple design translation explicitly demonstrate how flow dynamics and stability changes with minimal design variations and what parameters are of importance for achieving desired behaviors. The results on this paper are based mostly on simulations with the goal of using the same to decide on the correct experiments required to validate the observed phenomenons.