A Lamprey-Based Undulatory Vehicle

A biologically-based autonomous underwater, vehicle modeled after a simple vertebrate, the sea lamprey, has been developed. This underwater robot has been designed for the specific mission of mine hunting in the littoral and sub-littoral zones where it will systematically search an area to identify and locate mines and obstacles. However, the technologies we have assembled are applicable to any task that requires underwater locomotion in a challenging, dynamic environment. The lamprey was selected as an animal model because of its ability of being free to move in three dimensions, its highly efficient and maneuverable form of locomotion, and its ability to navigate in currents. Introduction Sea lampreys (Petromyzon marinus) are among the most primitive vertebrates (Hardisty, 1981), having an elongated and flexible eel-like body (sub-cylindrical forward laterally compressed posteriorly) and as mature adults, averaging 2-3 feet in length. Although their swimming movements are often considered eel-like or anguilliform, they are characterized by the propagation time of flexion waves being equal to the period of the movement such that the body axis typically appears s-shaped (Ayers, 1992). We term this more constrained form of swimming lampriform. Despite this relatively simple organization, lamprey are capable of a rich repertoire of undulatory behavioral acts (Ayers, 1989). During the migration to and from the sea, lamprey encounter a variety of obstacles and hydrodynamic conditions. Different habitats through which the lamprey must travel could include streams, rivers, falls, rapids, lakes, estuaries, inter tidal zones and the open ocean. In addition to its high adaptability, lampriform swimming affords an additional advantage of energetic efficiency. Unlike carangiform swimmers which transfer considerable energy to the water in the generation of vortices (Triantafyllou et al, 1995), lampriform swimming features a reduced wake signature (Vorus, 1995). Thus the lamprey provides two major advantages of adaptability and efficiency as a model organism for a biomimetic underwater vehicle (Ayers et al., 2000). Kinematics of Swimming Lamprey swim by rhythmic lateral undulations of the body axis. The lamprey swims forward by propagating lateral axial undulations that increase in amplitude from nose to tail. Similar waves travelling from tail to nose can propel the lamprey backward. Rhythmic alteration of muscle activity on either side of the body axis produces a propulsive wave. Lamprey swimming is uncomplicated by pectoral, pelvic, or anal fins. Endurance rather than high speed is characteristic of pure anguilliform mode (Gosline, 1973).