• Physics 16, 8
A simulation exhibits intimately why the “burst-and-coast” swimming technique is commonly extra environment friendly than steady swimming.
Some species of fish swim in a burst-and-coast mode, through which they alternate between undulating their our bodies and holding nonetheless whereas coasting. This mode is harder to mannequin than steady swimming, however researchers have now carried out detailed simulations of intermittent swimming with the intention to perceive its advantages for fish and its potential makes use of for fish-like robots [1]. Video from the simulations exhibits a digital fish first accelerating by wiggling after which coasting easily to just about a standstill. The staff discovered that the dearth of propulsion through the coasting part will be offset by the discount in drag from a extra streamlined physique posture. Nevertheless, this technique is just environment friendly when the parameters, such because the size of the burst interval, are optimized.
Whereas researchers have typically understood that intermittent swimming will be extra environment friendly—primarily based on experiments and analytical fashions—an in depth simulation has been troublesome, partly due to the nonsteady nature of the stream. Gen Li of the Japan Company for Marine-Earth Science and Expertise (JAMSTEC) and his colleagues have developed a two-stage protocol through which they first simulate a collection of lengthy burst-and-coast runs with a spread of amplitudes and frequencies for the fish undulations. They then lower and paste snippets from this simulation database to recreate arbitrary burst-and-coast swim patterns.
This process—which they’ve used beforehand [2]—allowed the researchers to seek out the optimum values of portions such because the frequency and amplitude of the undulations with out requiring enormous computational assets. It additionally allowed them to make an in depth comparability of the efficiencies of intermittent and steady swimming. The video exhibits one of many lengthy simulations that was used within the database, starting with 15 tail-beat cycles, adopted by a interval of coasting.
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Li and his colleagues have been capable of monitor the evolution of many portions, such because the drag, enter energy, and thrust, all of which exhibit fast modifications that weren’t beforehand noticed. They discovered that burst-and-coast swimming can require much less vitality than steady swimming, however the technique can flip very inefficient if, for instance, the size of every burst-and-coast cycle is simply too lengthy. Actual fish have presumably had thousands and thousands of years to good the sort of swimming, however builders of fish-like robots might want to tune the swimming parameters fastidiously to reduce the vitality expenditure, the researchers write.
–David Ehrenstein
David Ehrenstein is a Senior Editor for Physics Journal.
References
- G. Li et al., “Intermittent versus steady swimming: An optimization story,” Phys. Rev. Fluids 8, 013101 (2023).
- G. Li et al., “Burst-and-coast swimmers optimize gait by adapting distinctive intrinsic cycle,” Commun. Biol. 4, 40 (2021).