Video
Why Fish Swim Intermittently
A simulation exhibits intimately why the “burst-and-coast” swimming technique is usually extra environment friendly than steady swimming.
et al. [ G. Li. [ 1 The burst-and-coast pattern used by some fish can be more efficient than swimming at a constant speed. In this simulation, a fish executes 15 tail-beat cycles, followed by a period of gliding, during which it slows to nearly a standstill. (Colors represent vorticity—rotational flow—with dark red representing the most strongly counterclockwise flow and dark blue the most strongly clockwise flow.) The burst-and-coast pattern used by some fish can be more efficient than swimming at a constant speed. In this simulation, a fish executes 15 tail-beat cycles, followed by a period of gliding, during which it slows to nearly a standstill. (Colors rep… Show more
Some species of fish swim in a burst-and-coast mode, in which they alternate between undulating their bodies and holding still while coasting. This mode is more difficult to model than continuous swimming, but researchers have now performed detailed simulations of intermittent swimming in order to understand its benefits for fish and its potential uses for fish-like robots [1]. Video from the simulations exhibits a digital fish first accelerating by wiggling after which coasting easily to almost a standstill. The workforce discovered that the dearth of propulsion throughout the coasting section could be offset by the discount in drag from a extra streamlined physique posture. Nevertheless, this technique is barely environment friendly when the parameters, such because the size of the burst interval, are optimized.
Whereas researchers have typically understood that intermittent swimming could 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 movement. Gen Li of the Japan Company for Marine-Earth Science and Expertise (JAMSTEC) and his colleagues have developed a two-stage protocol by which they first simulate a collection of lengthy burst-and-coast runs with a variety of amplitudes and frequencies for the fish undulations. They then reduce 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.
Roberto/inventory.adobe.com Strategic swimmer. The red-nose tetra fish (Hemigrammus bleheri) makes use of the burst-and-coast swimming sample.
Roberto/inventory.adobe.com Strategic swimmer. The red-nose tetra fish (Hemigrammus bleheri) makes use of the burst-and-coast swimming sample. ×
Li and his colleagues have been in a position to monitor the evolution of many portions, such because the drag, enter energy, and thrust, all of which exhibit speedy 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 just too lengthy. Actual fish have presumably had thousands and thousands of years to excellent such a swimming, however builders of fish-like robots might want to tune the swimming parameters rigorously to reduce the vitality expenditure, the researchers write.
–David Ehrenstein
David Ehrenstein is a Senior Editor for Physics Journal.
