WANDA-II UUV. Photo Credit: NRL.Navy.mil
Those who drive know that traveling is pretty easy on an empty freeway but maneuvering through cluttered streets where there are quick changes in the flow of traffic is rather difficult. On the streets there are many things to react to including pot holes, dips, speed bumps, changes in elevation, pedestrians, debris, and even accidents. This is a problem many vehicles run into including unmanned underwater vehicles (UUVs). In open water where flow is predictable, UUVs can travel very fast and maneuver rather easily; however, at low speeds, UUVs are not nearly as successful.
Researchers have turned to nature for inspiration trying to model a UUV that uses flapping fins to maneuver through difficult underwater environments. Many fish species use articulation of the pectorals fins to produce appropriate forces and moments propel themselves through the water and to react to dynamic changes in flow, physical obstacles, and wave forces near the shore.
A four-fin UUV named WANDA-II (Wrasse-inspired Agile Near-shore Deformable-fin Automaton) is the 2nd generation of this alternative propulsion UUV. The original prototype was 0.41 meters in length and the second has been scaled with modifications to a whopping 1.01 meters. WANDA-II has a cylinder housing for lithium batteries, control electronics, and inertial measurement sensors including three axis gyroscopes, three axis accelerometers, and compass. Other changes include increased payload space in the nose and rear and improved battery life due to better fin curvature design using less energy for more thrust and lift.
These fins are capable of producing thrust vectors in multiple directions through changes in curvature and stroke angle. All this is in the attempt to replicate the high level of controllability that fish species have near shore and in shallow water environments. The design of WANDA-II was based on computational fluid dynamics and preliminary experimental results from the first generation, so its design is not by chance or to simply look cool (even though it does).
This UUV can change heading by 180 degrees in less than 12 seconds and has a maximum forward speed of 1.2 meters per second which is a vast improvement over the first generation. Though impressive, the design of the fins was preliminary and therefore not optimized so there is definitely room for improvement for the future generations.
A four-fin UUV could be deployed in a variety of missions including harbor monitoring and protection, hull inspection, and covert shallow water operations. So basically it can be your secret spy eyes in the sea.
The bottom line is that traditional forms of propulsion are being challenged and new forms are arising. Makes you think what the future holds.