Recently, Sweden
called off the hunt for a submarine after a week-long underwater search in the
Stockholm archipelago. Triggered by a reported sighting of a Russian submarine,
the alleged 'invasion' had been widely anticipated by military specialists and
the media. Work by the Russian and the Allied militaries to develop underwater
devices for information gathering are currently underway. Their aim is to reach
areas which are difficult or even impossible for divers to reach; to inspect
and clear mines on the sea floor, or even combat enemy scuba divers. The
existing effort undertaken trains guard-dolphins; however,
animal-rights-activists have opined that using dolphins for military reasons is
inhumane, and may harm the world's ecology as rivals might seek to eliminate
the threat by killing off the species. Hence, alternative strategies have been
put in place to develop unmanned underwater systems as the replacement for
military-trained dolphins.
To be able to be
operable remotely, small, sophisticated and intelligent enough to operate
autonomously underwater, these devices must be flexible, and able to operate in
narrow spaces like a snake. Inspired by Anguilliform fish, due to their
superior flexibility compared to the other fish forms, a team in Singapore has
developed and built a prototype for an eel-like robotic fish. A snake-like form
also gives the Anguilliform Robot amphibious potential, owing to the similarity
in undulatory locomotion in water and on solid ground. Mechanically, this
robotic fish consists of N-links and N−1 joints, and is controlled by the
torques applied to the joints. It was designed to move forward, and backward,
as well as turnaround through different reference inputs driven by a 3D coupled
Andronov-Hopf oscillators, an artificial neural network, and an outer amplitude
modulator. Results validate the effectiveness of the proposed controllers was
able to swim forward and backward as predicted.
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