Meeting Abstract
Semi-aquatic animals possess specialized morphological features that affect the hydrodynamics of locomotion. Crocodilians have laterally compressed, serrated tails used for propulsion in aquatic environments and balance during terrestrial walking, however the hydrodynamic function of tail serrations is unknown. Most crocodilians ambush terrestrial prey at the shoreline, which requires camouflage and stealthy movement in shallow water. We hypothesize that serrations disrupt large-scale flow structures from tail movements and correspondingly reduce visible surface disturbance. To test this hypothesis, we translated 14” long 3-D printed panels with evenly spaced triangular serrations directly under the water surface with a linear actuator; a panel with no serrations was used as a control. Waves were visualized by recording the reflection of a fan-beam laser on the water surface in the path of the panel using a GoPro HERO6. From the video of the laser reflection, a waveform was extracted, filtered, and processed using Continuous Wavelet Transform (CWT), which detects non-stationary spatial disturbances at a continuous range of frequencies. In our preliminary analyses, global power spectra were calculated from three videos each of serrated and control panels, with the magnitude of power positively correlating with visible surface disturbance. We observed a 27% decrease in magnitude of power from the control to the serrated panel indicating that serrations did reduce visible surface disturbance. Understanding the effects of serrations on fluid flow could contribute to bio-inspired noise or turbulence reducing engineered systems, while using CWT to characterize surface disturbance creates a unique framework to study interface dynamics in a three-phase system.
