Artificial Fish Dives Into Unknown Waters
Domestic security officials aim to replace human divers with an autonomous underwater vehicle whose design is derived from nature: the tuna, one of the fastest and most maneuverable fish in the sea. The vehicle would be used primarily to inspect ship hulls for contraband, saving divers from hazardous trips into hard-to-reach areas below the waterline where oil and other toxic chemicals are part of the mix. Designers also envision the tuna-modeled robot could also be used for search and rescue missions.
The Biomimetic In-Oil Swimmer (BIOSwimmer) is an autonomous underwater vehicle (AUV) being developed by Boston Engineering Corporation’s Advanced Systems Group, in Waltham, Massachusetts, for the U.S. Department of Homeland Security (DHS). This tuna look-alike can be operated either by remote control with a tethered cable or pre-programmed to operate autonomously, according to David Taylor, specialist, cargo security, Border and Maritime Security Division, Science and Technology Directorate, DHS, and program manager for the BIOSwimmer program.
“It was originally designed as a vehicle that could go inside cargo tanks and look in oil cargos for contraband,” he explains. Based on subsequent feedback from DHS Customs and Border Protection (CBP) field officers, the BIOSwimmer’s design has been modified to function primarily as an AUV that examines ship hulls.
The bright yellow mechanical fish is five feet long and weighs 90 pounds without its electronic mission payloads, which makes the basic BIOSwimmer manportable. Electronic equipment packages of as much as 750 cubic inches can be housed in its payload bays. The BIOSwimmer has pectoral, dorsal and tail fins to aid in navigation and, like a tuna, its primary propulsion comes from its tail section moving back and forth through the water. In addition to the motor-driven tail, the BIOSwimmer’s small electric propeller provides additional forward thrust. The battery-powered BIOSwimmer is designed to provide between 1.5 and 2.25 kilowatts per hour of onboard electrical power for propulsion and mission components. The current design of the BIOSwimmer is rated to dive to a maximum depth of 300 feet.
The BIOSwimmer’s sleek shape is the latest device that capitalizes on the science of biomimetics. “We’re using nature as a basis for designing and engineering a system that works exceedingly well. Tuna have had millions of years to develop their ability to move in the water with astounding efficiency. Hopefully, we won’t take that long,” Taylor adds.
In both form and function, the BIOSwimmer “looks like a fish and mimics a fish,” he says, commenting on the fact that the prototype looks and moves like one of the fastest and most agile fish in the sea. “It’s got both the size and the ability to move through the water quickly. This is a good balance between a fish with some girth and a streamlined capability,” he comments. Other, more streamlined fish were explored as the model for the BIOSwimmer, such as the barracuda, but its slender shape would not have allowed it to carry large payloads.
The BIOSwimmer’s speed and agility also give it advantages not found in more traditional underwater unmanned or remotely operated vehicles (UUV/ROVs). “Because it’s streamlined, it has certain capabilities to go through the water better than a traditional ROV,” explains Taylor. Traditional ROVs, for example, have water thrusters that provide only vertical and lateral movements. “Because it’s designed like a fish, it isn’t affected by currents, and it has better station-keeping capabilities outside the hull of a ship that it is inspecting,” he adds, explaining the need for the BIOSwimmer to remain in a fixed position for an indefinite amount of time in spite of surrounding currents as it performs its inspection duties.
Taylor says the BIOSwimmer’s capability for speed is important for surveillance, inspection and, in another one of the AUV’s anticipated missions, search and rescue. Speed also is essential in getting to the location of a wide-area search, or inspection of a very large ship, he explains. Taylor would not, however, divulge the exact speed of the device for reasons of operational security.
Taylor acknowledges some trade-offs with the tuna shape, such as limits to the type and placement of particular sensors, but overall the advantages of the BIOSwimmer’s highly agile design outweigh any disadvantages. For example, currently human divers check inbound ships for contraband placed on the hull. Divers often face unknown dangers working in what he calls “difficult environments.” The BIOSwimmer also provides operational flexibility, including its ability to operate in the water longer than a human diver.
Along with its two-part propulsion system, the BIOSwimmer is equipped with an onboard obstacle-avoidance sonar system and a closed-circuit television camera that is used primarily for hull inspections. “It can use the sonar to get in close proximity to the hull,” he explains. The sonar also is employed to compensate for the murky water found in most harbors and allows the BIOSwimmer to maneuver as close to a ship’s hull as possible to examine the smallest details, he adds.
Production versions of the BIOSwimmer would be built to accommodate still-to-be-designed sensor packages that can be installed in its payload modules in the nose and mid-section of the craft and detect radiological and chemical threats.
The BIOSwimmer is designed primarily for human operation using a laptop personal computer tethered with a cable. “You can see the cameras; you can see information about the thrusting; and you can control its movement with a joystick,” Taylor explains. However, tethered operations present their own limitations; for example, a cable could become snagged in a ship’s propellers or harbor debris or on other below-water-level navigation hazards.
This is where the ability to operate autonomously comes into play. “An autonomous operation gives you freedom of action,” Taylor relates. But he also explains that just as there are trade-offs in using the tuna as a form factor model for the BIOSwimmer, compromises must be made in autonomous operation. “You have to pre-program exact operations, and it’s difficult to get real-time information through the water,” he says, acknowledging the difficulty in transmitting electronic data signals in a maritime environment. “In this case, you send it out and bring the vehicle back in, then download the information,” Taylor outlines, adding that the BIOSwimmer does not at this time take advantage of developments in military research that have refined the ability of electronic devices to transmit through water. He reveals, however, that designers are exploring the concept of a tethered float that could serve as a surface wireless data relay for future iterations of the BIOSwimmer, but that capability currently is not operational with the prototype being tested. Other ocean-going underwater unmanned vehicles are being developed and evaluated by the U.S. Department of Defense (SIGNAL Magazine, November 2012, “Swarming To a Better Robot”).
The BIOSwimmer’s two-year development process is part of the DHS Science and Technology Directorate’s Small Business Initiative program. Three contracts, each worth around $250,000, were awarded as part of the first design proposal phase several years ago. The DHS awarded $750,000 to Boston Engineering for the second phase of the program, which includes construction of the working prototype.
Testing of a second prototype is expected to begin this fall at the Port of Houston. Tests will include in-water examinations of a variety of ship hulls in one of the busiest ports in the nation. Taylor concludes that there is no timetable for the production and delivery of the first operational BIOSwimmer, saying a decision will depend primarily on CBP’s budget and an evaluation of the performance of the prototype in subsequent harbor testing.