Submarines with fish fins?
Engineers want their underwater survey vehicles to be able to do what fish can do
This is the pre-publication version which was subsequently revised to appear in Creation 31(3):22–23.
A bluegill sunfish (Lepomis macrochirus)—copying its pectoral fin movements is no simple matter. In fact, even describing its fin movements is no simple matter, either.4
Out in the deep seas and oceans of the world, propeller-driven submarines can generally handle straight-line travel quite well, so long as their propellers don’t become entangled in cables or stray mooring ropes, etc.1
However, getting such craft to manoeuvre safely in closer proximity to the sea bed’s undulations and crags is quite a different matter. But it’s no problem for fish—as researchers at the Massachusetts Institute of Technology have noted. Inspired by the staggeringly efficient swimming motion of the bluegill sunfish, MIT engineers are striving to build a mechanical fin that could one day propel robotic submarines.2,3
The submarines, also known as ‘autonomous underwater vehicles’ (AUVs), would be used for a variety of functions, from mapping the ocean floor and surveying shipwrecks, to military purposes such as minesweeping and inspecting harbours. Little wonder then, that the submarine engineers are so eager to mimic the action of the bluegill sunfish.
researchers chose to copy the bluegill sunfish ‘because of its distinctive swimming motion, which results in a constant forward thrust with no backward drag’
‘If we could produce AUVs that can hover and turn and store energy and do all the things a fish does, they’ll be much better than the remotely operated vehicles we have now,’ said James Tangorra, one of the project researchers. According to MIT news, he and the other researchers chose to copy the bluegill sunfish ‘because of its distinctive swimming motion, which results in a constant forward thrust with no backward drag. In contrast, a human performing the breaststroke inevitably experiences drag during the recovery phase of the stroke.’
However, it’s no simple matter to copy the sunfish’s fin motion.4 The researchers have broken down its fin movement into no fewer than 19 components, in an attempt to identify which ones are critical to achieving the fish’s powerful forward thrust. It would greatly simplify the researchers’ task if they didn’t have to mimic all of the sunfish’s fin movements. As James Tangorra explained: ‘We want to figure out what parts are important for propulsion and copy those.’
Writing in the Bioinspiration & Biomimetics journal of their progress to date, the team reported the testing of a mechanical fin made of a thin, flexible polymer that conducts electricity.
When an electric current is made to run across the base of the artificial fin, the fin sweeps forward, similar to a sunfish fin. By strategically changing the direction of the electric current, the mechanical fin can be induced to curl forward at the upper and lower edges. However, the researchers acknowledge that it has been a challenge to make the fin sweep and curl at the same time. Placing Mylar strips along the artificial fins to restrict movement to the desired direction certainly helped, but the team is still looking for alternative solutions that work better.
The researchers also hope to study other aspects of the sunfish’s movement, such as how the fish’s different fins interact with each other and with the fish’s body. They want to know how all the various movements are coordinated such that overall movement and manoeuvering of the fish is achieved so smoothly. That information will no doubt help the engineers to adapt ‘nature’s principles’ to the design of the robotic submarines.
And just who is responsible for those design principles that the researchers are so keen to copy? None other than the Master Engineer of course, the One who looked at the fish fins He had made (along with everything else) and declared them ‘very good’ (Genesis 1:31)—a description with which human engineers would surely have to agree.(Also available in Spanish)
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- BBC News, Rescuers battle to free sub crew, http://news.bbc.co.uk/1/hi/world/europe/4127586.stm#text, published 7th August 2005, accessed. 4th September 2007. Return to Text.
- Trafton, A., MIT team building robotic fin for submarines, MIT news, web.mit.edu/newsoffice/2007/robofin-0730.html, pub. 30 July 2007, acc. 2 August 2007. Return to Text.
- Tangorra, J., Anquetil, P., Fofonoff, T., Chen, A., Del Zio, M., and Hunter, I., The application of conducting polymers to a biorobotic fin propulsor, Bioinspiration & Biomimetics 2(2007):S6–S17, June 2007; online pdf at <www.iop.org/EJ/article/1748-3190/2/2/S02/bb7_2_s02.pdf> (acc. 5th September 2007). Return to Text.
- As the researchers explained in their research paper (Ref. 2): ‘The sunfish pectoral fin moves in a complex manner that is not easily described using traditional rowing or flapping kinematics.’ Return to Text.