Knowledge about the stiffness of fish fins, and whether stiffness is modulated during swimming, is important for understanding the mechanics of a fin's force production. However, the mechanical properties of fins have not been studied during natural swimming, in part because of a lack of instrumentation. To remedy this, a vortex generator was developed that produces traveling vortices of adjustable strength which can be used to perturb the fins of swimming fish. Experiments were conducted to understand how the generator's settings affected the resulting vortex rings. A variety of vortices (14-32 mm diameter traveling at 371-2155 mm s-1) were produced that elicited adequate responses from the fish fins to help us to understand the fin's mechanical properties at various swimming speeds (0-350 mm s-1).
Keywords: Bluegill sunfish; Fish swimming; Mechanical properties; Perturbation; Stiffness; Vortex ring.
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