Hydrodynamic Performance of an Undulatory Robot: Functional Roles of the Body and Caudal Fin Locomotion

Abstract

Both body undulation and caudal fin flapping play essential locomotive roles while a fish is swimming, but how these two affect the swimming performance and hydrodynamics of fish individually is yet to be known. We implemented a biomimetic robotic fish that travel along a servo towing system, which can be regarded as "treadmill" of the model. Hydrodynamics was studied as a function of the principal kinetic parameters of the undulatory body and caudal fin of the model in a selfpropelled condition, under which the time-averaged measured axial net force becomes zero. Thrust efficiency was estimated from two-dimensional digital particle image velocimetry (DPIV) measurements in the horizontal and mid-caudal fin plane. The Single-Row Reverse Karman wake (2S) is commonly observed in many previous studies of live fish swimming. However, we show that a Double-Row Two-Paired vortices (2P) wake was generated by the robotic model for most kinetic parameter combinations. Interestingly, the 2S wake emerged within the results of a narrow range of robotic caudal fin pitch angles (0≤θ≤10°), occurring concurrently with enhanced thrust efficiency. We also show that, compared with the effect of body wavelength (λ), the wake structure behind the robotic swimmer is more sensitive to the Strouhal number (St) and caudal fin pitch angle (θ).

Exploring the backward swimming ability of a robotic fish

“…Since we prefer that particles have more ability of exploration when started, and converge quickly when close to the goal, ! p is chosen as a simple function of iteration (17) where ! p ðiÞ represents the particles' inertial value in the i th iteration, and Iter max is the maximum number of iterations, set as 25 in this experiment.…”

“…[7][8][9][10][11][12][13] Since the first robotic fish was made at MIT, 14 researchers have built a variety of robotic fish. 15,12,[15][16][17][18][19] Improving the maneuverability of robotic fish is one of the most popular studies in the field, including the development of features such as sharp turning, rolling, front and back flips, and three-dimensional fin undulations. 5,[20][21][22] Few have considered the backward swimming performance of robotic fish, 21,[23][24][25][26] although backward swimming is observed in nature.…”

Evaluating the Fin-Ray Trajectory Tracking of Bio-Inspired Robotic Undulating Fins via an Experimental-Numerical Approach

“…The reverse Karman Street generates a high speed jet, associated with thrust generation. As each vortex is shed by individual undulating fins, it induces a water motion that is opposite to the wave travelling direction immediately behind the fin [4], [6], [16], [17].…”

“…In terms of biomimetics, it is important for mankind to learn and mimic the aforementioned distinguished abilities from natural biology to effectively promote the development of science and technology [1] [4]. Many biologically inspired robots have been proposed and developed during the past few years.…”

Theoretical Insights on Contraction-Type Iterative Learning Control for Biorobotic Systems with Preisach Hysteresis

“…Since 2001, bio-inspired undulating fin models [4][5][6][7][8][9][10][11] have been developed to investigate the undulation principles of knifefish. The aforementioned inconsistency does exist and has prevented robotic fish models from replicating the locomotion or behaviours of their biological counterparts.…”