Undulatory locomotion

Undulatory locomotion is propulsion produced by traveling waves of bending along an animal’s body or fin. The waves push against surrounding water, air, or another substrate to generate thrust.

Traveling wave: A disturbance whose pattern moves through space over time. Undulatory propulsion depends on a bending pattern that travels along the body or fin.
Axial skeleton: The bones and supporting structures along an animal’s central body axis. Its flexibility and joints constrain how bending waves travel through the trunk.
Biomimetic robot: A robot whose design or behavior is inspired by biological systems. Undulatory animals provide models for robots that propel themselves by bending.
Oscillatory locomotion: Propulsion generated by repeated back-and-forth movement of an appendage or body part. Oscillation can produce thrust without a bending wave traveling along the body.
Hydrodynamics: The study of fluids in motion and the forces they exert. In water, the moving body transfers momentum to fluid to produce thrust.
Myomere: A repeated segment of skeletal muscle found along the bodies of many fishes. Segmented muscle activation bends the body in coordinated waves.
Robotic fish: An aquatic robot designed to swim with fish-like body or fin motions. Many robotic fish reproduce traveling body waves to achieve quiet, maneuverable propulsion.
Paddling: Locomotion driven by repeated strokes of limbs or appendages against a surrounding medium. Paddling uses discrete strokes rather than a traveling sequence of body bends.
Reynolds number: A dimensionless ratio comparing inertial and viscous effects in fluid flow. It helps explain why viscous forces matter differently for small swimmers.
Muscle activation: The recruitment and force production of muscle fibers under neural control. Changing activation timing along the body creates traveling patterns of contraction.

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