Submarines with fish fins?
Engineers want their underwater survey vehicles to be able to do what fish can do
by David Catchpoole
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.
Related articles
Further reading
References
- 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.
Published: 19 September 2007(GMT+10)
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