Submarines, UUV’s, and surface combatants all use the same or similar control surfaces like rudders, ailerons, flaps, and elevators to maneuver easily and safely underwater. (For more information on how control surfaces work here are some entertaining and educational videos). At high speeds and predictable flow areas, maneuverability using control surfaces is pretty effective, however, at low speeds this is not the case. There is a need for advanced low-speed maneuverability and the mitigation of cavitation-induced noise for all types of surface and underwater vehicles (check out WANDA). A solution to both that would avoid the use of high energy actuators would be ideal and the reduction or elimination of control surfaces in future designs would be even better. Theoretically.
Ducted propellers have been implemented in recent designs but changing the direction of flow out the trailing end through electro-mechanical actuators has been difficult to implement. Shape memory alloys (SMA) can make this deformable ‘Smart Duct’ a reality. A Smart Duct is a deformable shroud that changes the direction of flow of the propeller wash to provide a direct steering force to the vehicle. The duct itself is an electrically actuated structure that is covered by a flexible hydro-dynamically smooth sheathing whose primary movers are a set of high strength Nickel-Titanium SMA actuator cables. So basically…it’s a duct that can flex in different directions to get you moving where you want to go. A pretty basic idea but has tremendous value if it can be made and implemented correctly. SMA technology has made a series of successful demonstrations that allow for high force actuation that also greatly reduces the volume, weight, and number of moving parts as compared to competing designs. Typically made out of Nickle-Titanium, a 3% to 4% strain is possible with cyclic loads which is pretty dang impressive.
In January 2004, testing was done on the Smart Duct demonstrator at the Naval Surface Warfare Center, Carderock Division. The first tests were done with an empty duct in a water tunnel with a flow rate of 14.7 fps. The duct was able to flex and achieved a deflection of 0.7 in and resisted a peak force of 69 lb. A propeller + Smart Duct system was also tested as well and achieved similar results. Overall what these numbers mean is that effective flow turning angles of up to 15 degrees at thrust levels of operational submarines is possible with the Smart Duct. This is a pretty huge achievement. The future of this type of technology will possibly change the design of submarines and UUVs so be on the lookout for Smart Ducts. For more information please visit http://www.continuum-dynamics.com/lib-pro-duct.html.