On the influence of head motion on the swimming kinematics of robotic fish

Abstract

Up to now bio-inspired fish-mimicking robots fail when competing with the swimming performance of real fish. While tail motion has been studied extensively, the influence of the head motion is still not fully understood and its active control is challenging.
In this experimental study, we show that head yawing strongly impacts on the propulsion force and determines the optimal fin actuation amplitude and tail beat frequency when aiming for a maximal propulsion force. In a parametric experimental study on a tethered 367 mm long fish robot the pivot point location of the head yaw has been varied along with tail beat frequency and actuation amplitude. The experiments took place in a still water tank and the swimming force has been measured with a single axis load cell. The robot is actuated with non-conventional area actuators based on micro fiber composites. 105 parameter sets have been investigated while the highest pivot point distance of roughly 0.36 body length from the nose tip provided the highest propulsion force of 500~mN with the lowest actuation frequency of 2.5 Hz and the highest head motion amplitude of a magnitude of 0.18 body length. Even though the pivot point location on a free swimming robot is a consequence of the complex fluid-structure interactions of fish and fluid, the results provide valuable information for the design of fish mimicking robots and questions the paradigm that head yaw is a simple recoil effect from tail motion and has to be minimized for an effective propulsion.
In this experimental study, we show that head motion, fin actuation amplitude, tail beat frequency and propulsion force interact with the head pivot point location and strongly impact on the swimming capacity.

Adaptivity of a leaf-inspired wind energy harvester with respect to wind speed and direction

“…Many other remedies are directly inspired by living mechanisms. In this regard, the aero/hydrodynamics of birds and other creatures were intensively reviewed as potential inspirations for biomimetic flow control techniques [16][17][18][19], and the kinesiology of living creatures like fishes and butterflies and their possible impact on performance of life-inspired robots were studied [20,21]. Here, the remedies on lift enhancement [22,23], drag reduction [24][25][26], increasing lift-to-drag ratio [27,28], improving aerodynamic robustness [29], and modulation of aerodynamic forces and moments [30] are not discussed in detail.…”