The cruising range of autonomous underwater vehicles (AUVs) is limited by existing battery and propulsion technology. If more efficient propulsion could be developed, data collection by AUVs could be expanded greatly. Preliminary hydrodynamic studies of the flow past fish have suggested that a more efficient means of propulsion is possible. When fluid moves past objects (or when objects move through fluids), vortices or eddies are created behind, or in the wake of, the object. Hydrodynamicists know that vortices created by solid bodies, such as ships, induce drag (resistance) on the bodies. Fish, on the other hand, appear to use vortices in a beneficial way to reduce drag, thereby improving their swimming efficiency. It seems that aquatic life has evolved complex ways of using the physics of fluids for efficient locomotion.

During the initial stages of this research, Professor Triantafyllou and his colleagues decided to build an articulated, mechanical "fish." The researchers chose a blue-fin tuna because it is fast, has a relatively rigid torso, and swims with fairly small body and tail motions. RoboTuna was designed and built to gather data about how a robotic fish should be controlled in order to swim efficiently, and to deepen the understanding of the hydrodynamics of swimming fish. Various sensors and data collection systems were placed in and on the surface of RoboTuna and its supporting structure. RoboTuna emulates the process of swimming by passing a wave of variable amplitude down its body from nose to tail. These carefully choreographed motions apparently provide very beneficial “vorticity control.” The robot’s body-motion control software creates this wave based on a set of 13 experimental parameters. In a typical test, a specific set of swimming parameters is loaded into the body controller. During the swimming test, the robot’s high-speed data collection system simultaneously captures and stores all relevant sensor data. These force and displacement data are then used to generate a quantitative measure of swimming performance for a given run. Much future research will be required to understand vorticity control completely. Presently, more detailed investigation into the flow around and behind flapping foils/fish and how the variations in swimming motions affect the flow is under way. Use of advanced flow-visualization techniques, such as digital-particle-imaging velocimetry (DPIV), and accurate numerical models of the flow are part of this research effort.