AUVAC

DARPA Blue Wolf Program

The Blue Wolf program will develop and demonstrate an integrated underwater vehicle capable of operating at speed-range combinations previously unachievable in fixed-size platforms, while retaining traditional volume and weight fractions for payloads and electronics.

The Blue Wolf program will focus on rapid testing and maturation of novel energy, hydrodynamic lift, and drag reduction technologies, which will be developed and tested at-sea to confirm maturity and performance. Blue Wolf will modify existing hardware and systems to establish the vehicle baseline (a “reference vehicle”), and will seek technical solutions to achieve the program metrics specified in the classified addendum.

A Mission Oriented Metric to Assess the Benefits of Biologically Inspired Propulsion

In this study, we quantify the potential mission specific benefits of biomimetic propulsion as a function of environmental conditions and operational requirements for a small unmanned underwater vehicle (UUV) mission. The benchmark mission requires the UUV to persist in shallow water for 24hr within a specified radius around the desired station, preceded and followed by a 40km transit

The achievable time on station for the nominal vehicle using biologically inspired propulsion is compared to that of the same vehicle using currently available thrusters. The comparison is carried out across a range of sea-states, with varying requirements for station keeping precision, and with a range of assumptions about the performance improvements provided by biomimetic propulsion. The expected magnitude and frequency of wave disturbances in shallow water are generated using U.S. Army Corps of Engineers guidelines for harbor design and construction.

If biomimetic propulsors can deliver on the promise of significantly improved effectiveness in generating low speed maneuvering forces, fin propelled vehicle can perform a high precision 24 hour station keeping mission in 3x higher waves than the thruster propelled vehicle. In rough conditions, the fin propelled vehicle can perform the mission with 10x higher precision.

AN ALTERNATIVE PROPULSION CONCEPT FOR SMALL UNDERWATER VEHICLE APPLICATIONS

ABSTRACT
This paper applies the folding blade concept to propeller designs for unmanned undersea vehicle (UUV), unmanned surface vehicle (USV) and torpedo systems. The folding propeller blades will enhance a propeller’s performance for these small vehicle systems. The design boundary for a folding propeller is expanded because the propeller diameter is not limited by the size of the launch device, which usually is close to the diameter of the vehicle. With a larger propeller diameter, blades work more effectively and have less influence from the vehicle hull boundary layer. The propeller blades are unfolded by the centrifugal force after leaving the launch unit. The capability of launching these vehicles is enhanced for fewer numbers of folded blades with a reduced manufacturing cost. A foldable single rotor propeller design case will be given in the paper to demonstrate the proposed benefit by comparing with the performance of a generic single-stage propeller system, which is a two-blade-row propeller with a stator and a rotor. Another major thrust of the present paper focuses on the manufacturing cost comparisons between a folding blade propeller and a fixed blade propeller. In order to compare the cost for various folding designs, a cost scheme is developed and validated with cost estimates obtained from propeller manufacturing shops. The paper will conclude with quantitative gains in performance and in manufacturing cost saving.

Towards Amphibious Robots: Asymmetric Flapping Foil Motion Underwater Produces Large Thrust Efficiently

The development of amphibious robots requires actuation that enables them to crawl as well as swim; sea turtles
are excellent examples of amphibious functionality, that can serve as the biomimetic model for the development of amphibious robots.

In this paper we have implemented the observed swimming kinematics of Myrtle, a green sea turtle Chelonia Mydas residing in the Giant Ocean Tank of the New England Aquarium, on the 1.5-meter long biomimetic vehicle Finnegan the RoboTurtle. It is shown that these kinematics result in outstanding performance in (a) rapid pitching, and (b) rapid level turning. The turning radius for the rigid hull vehicle is 0.8 body lengths, a remarkable improvement in turning ability for a rigid hull vehicle.

Still Finnegan’s performance lags the live turtle’s performance by about 20%. Careful observations have shown that turtles employ a fin motion in-line with the direction of locomotion; this degree of freedom was not available to the Finnegan fins, as presently designed. Experimental tests on a flapping fin equipped with this third degree of freedom have shown that the in-line motion enhances the fin’s performance.

This hydrodynamic result is doubly beneficial to an amphibious robot, because it allows for further enhancements in the hydrodynamic function of fins, while the in-line motion allows the same fins to be used for crawling on land.