Numerical Derivation of Hydrodynamic Forces and Invention of a New Diving Technique for the Batoid Underwater Robot

Abstract

AbstractAs part of a design project for a batoid-inspired underwater robot, its dive to a predetermined depth is questioned here. Previously, the vehicle was designed with a streamlined hull shape that resembles a Dasyatis batoid fish, and the fish locomotion was imitated using undulating fins at each side. We did not, however, provide a buoyancy engine or any fins to turn the vessel in the vertical plane and conduct diving maneuvers. We expect to leave the vessel on the water surface, and it dives to a desired depth and then maintains a constant pitch angle and a constant forward speed. A new technique is invented here: the thrust forces of the two fins are shifted off the central top-bottom symmetry plane of the hull, therefore producing a pitching moment on the vessel. An initial trim is also introduced by shifting the center of mass forward the center of buoyancy. Therefore, the vessel is initially bowed down and, by its out-of-plane thrust force, adjusts its pitch attitude. The question is whether a final balance between the thrust force and the hydrodynamic forces will be feasible. The hydrodynamic forces at such forward speeds and attack angles were numerically derived using the computational fluid dynamics powerful software ANSYS-CFX.