Not only is the tuna a strong swimmer, but the front portion of its body remains stable as it propels itself through water. This unique style of movement was the inspiration for a U.S. Navy project, which employed biomimickry practices to create the optimal design for an autonomous unmanned underwater vehicle.
The so-called tuna robot, designed in partnership with Boston Engineering, builds off the seaworthy profile of the tuna and includes a propulsion system, a single oscillating foil, appropriately placed fins, and a finely-tuned muscular and sensory control system. The full set of technology makes the tuna robot efficient at a variety of speeds, unlike a traditional thruster propulsion system, which is typically optimized to operate at a single velocity.
By mimicking the tuna’s fast speed and dexterity—the fish cruises at approximately 60 mph, can turn 180 degrees and accelerates to about 22 mph in less than two lengths of its own body—the tuna robot is optimized for a wide range of applications that other autonomous unmanned underwater vehicles simply can’t accommodate due to limitations in size or maneuverability, according to Mark Smithers, vice president and chief technology officer at Boston Engineering.
The fact that the tuna’s front portion of the body doesn’t move when in motion is essential to the in-water robot design, Smithers said. “The fact that the front portion of the animal is mainly stationary when swimming is important because when you are carrying sensors, you don’t want everything moving all over the place and messing up what you are carrying on board,” he explained. “Compare that to a snake which slithers back and forth and no part of body is stationary in the path of motion.”
Because of those characteristics, the tuna robot can be put to task on a wide range of applications, from seeking out mines in the shallow waters of harbors or along shorelines or for locating contraband like hidden drugs or guns. There are also possible applications in the oil and gas industry such as using the robotic tuna to do more frequent monitoring of gas pipelines, not to mention as a tool for inspecting bridge erosion, Smithers said.
While biomimicry practices lay the foundation for the design concept, modern-day 3D modeling and simulation tools are essential to bringing that design to life, Smithers said. PTC’s Creo 3D CAD tool was critical to the modeling effort, particularly for the surfacing and simulation aspects.
The team used a 40-in. tuna caught off the coast of Gloucester, MA, as the basis for the CAD model, but because nature doesn’t follow easy geometric formulas, PTC Creo’s Interactive Surface Design Extension (ISDX) was instrumental in capturing the exact design.
“A tuna profile changes along the length as it does along the width,” noted Will Ober, a mechanical engineer involved in the project. “If you took a cross section, you’d see it doesn’t produce an easily and mathematically predictable profile.”
The software’s parametric modeling and freeform flexibility allowed the designers to build curves in multiple planes simultaneously, Ober explained, while also ensuring they could add surfaces between curves and modify them until they were satisfied with the shape.
Creo’s simulation capabilities also factored into the overall design effort. “Any time you can cycle something in motion on the screen, it lets you look for gotchas that engineers might not see otherwise,” Smithers said, explaining the team used Creo’s simulation capabilities to calculate forces and trajectories while also checking for interferences. “Without being able to cycle something in motion and simulate the environment in CAD, you’ve find out problems only after prototyping, which is time and money.”
Check out this video to see the tuna robot in motion.