— Strategies for swimming through water using soft bodies
Building a soft swimming robot can be a daunting task. However, nature can help us with lots of inspiration. Here, we introduce four kinds of swimming gaits that can fit soft robots.
Lift-powered swimming resembles a bird's flapping-wing flight; it depends on the cyclic flipping motion of a hydrofoil to generate a hydrodynamic lift force: $L$. Hydrodynamic analysis reveals subtle details of this kind of locomotion. Still, the basic movement is a periodic oscillation of one or more fins in the direction orthogonal to the velocity of the body. So they are also called oscillatory swimming.
Depending on the animal, a hydrofoil can take very different forms.
Vertical caudal fin of tuna
The extended pectoral fin of manta rays
Horizontal caudal fin of cetaceans
Flippers of sea turtles
$$ L\approx \frac{1}{2} \rho_\text{water}Av^2C $$
where $A$ is hydrofoil’s surface area, $v$ is the velocity between the hydrofoil and the ambient water stream, and $C$ describes to the hydrofoil’s orientation with respect to the stream flow.
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Based on this equation, what would be good strategies to increase the lift force and hence swimming speed?
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