Passive wake detection using seal whisker-inspired sensing

Abstract

This thesis is motivated by a series of biological experiments that display the harbor seal's extraordinary ability to track the wake of an object several seconds after it has swum by. They do so despite having auditory and visual cues blocked, pointing to use of their whiskers as sensors of minute water movements. In this work, I elucidate the basic fluid mechanisms that seals may employ to accomplish this detection. Key are the unique flow-induced vibration properties resulting from the geometry of the harbor seal whisker, which is undulatory and elliptical in cross-section.First, the vortex-induced vibration (VIV) characteristics of the whisker geometry are tested. Direct force measurements and flow visualizations on a rigid whisker model undergoing a range of 1-D imposed oscillations show that the geometry passively reduces VIV (factor of > 10), despite contributions from effective added mass and damping. Next, a biomimetic whisker sensor is designed and fabricated. The rigid whisker model is mounted on a four-armed flexure, allowing it to freely vibrate in both in-line and crossflow directions. Strain gauges on the flexure measure deflections at the base. Finally, this device is tested in a simplified version of the fish wake -seal whisker interaction scenario. The whisker is towed behind an upstream cylinder with larger diameter. Whereas in open water the whisker exhibits very low vibration when its long axis is aligned with the incoming flow, once it enters the wake it oscillates with large amplitude and its frequency coincides with the Strouhal frequency of the upstream cylinder. This makes the detection of an upstream wake as well as an estimation of the size of the wake-generating body possible. A slaloming motion among the wake vortices causes the whisker to oscillate in this manner. The same mechanism has been previously observed in energy-extracting foils and trout actively swimming behind bluff cylinders in a stream. Dave, Jason, Gabe, Pablo, Remi, and Yahya were postdocs when we first met.Thank you for being approachable and sharing much needed advice all along the way.Your love of science has inspired me to be more inquisitive.Brandon, Chris, Matthew, and Patrick were undergrads or high school students who spent their summers working in the Tow Tank with me. Thanks for giving me the chance to practice being a mentor, moving this research forward a lot faster than I could do on my own, and helping me lift the mega-whisker in and out of the tank! May you all keep on building and exploring.Thanks to Kathy Streeter and the New England Aquarium staff for helping me understand more about real harbor seals. They graciously collected shed whisker specimens and allowed me to take many close-up pictures of their seals.Thanks to all the people who helped me prepare for and make it through research cruises: Eric Hayden, Terry Hammar, and Hanu Singh for contributing their expertise 5 to help me make my first ocean-ready sensor, all parties involved in the first UNOLS Chief Scientist Training Cruise se...

Characterization of seal whisker morphology: implications for whisker-inspired flow control applications

“…The two ratios reflect different fluid dynamics mechanisms. Additionally, / λ = D 5 m and 2 are adopted in a flow sensor design ( [5,6]). These studies have investigated the effects of / λ D m and the role this parameter plays in the reduction of force produced from vortex shedding events found on undulating cylinder structures.…”

“…Further decomposition of the undulating features and their relationship to forces acting on the vibrissae indicated that both undulations on the major and minor axis contribute to the disruption of strong von Kármán vortex streets [16]. Inspired by the exceptional hydrodynamic traits of sea whiskers, efforts have been put into designing novel high-sensitivity flow sensors [5], and modifying the geometry of gas-turbine blades for enhanced performance [30]. Other applications utilizing the beaded vibrissae geometry as an effective passive flow control strategy include structures in consistent flow paths, such as wind turbine towers, sensor mounting supports on aircraft frames, and offshore oil drilling rigs.…”

Undulating Seal Whiskers Evolved Optimal Wavelength‐to‐Diameter Ratio for Efficient Reduction in Vortex‐Induced Vibrations

“… a) It is likely that the value of M was mistakenly underreported (by a factor of 2) in Ref. [ 14 ] as pointed out by Beem [ 53 ] in her PhD dissertation. …”

“…[ It is likely that the value of M was mistakenly underreported (by a factor of 2) in Ref. [14] as pointed out by Beem [53] in her PhD dissertation. whiskers was seen to oscillate about a linearly decreasing mean value, indicating a uniform taper from the whisker base to its tip.…”

Simulations of flow over a bio-inspired undulated cylinder with dynamically morphing topography

“…In a subsequent experimental investigation, a direct comparison to an elliptical cylinder was performed using particle velocimetry coupled with dynamic mode decomposition of the flow field and indicated strong disruption of the energy redistribution process in the wake [4], which varied with respect to angle of attack [5, 6]. The response to flow disturbances has also been documented computationally [7] and experimentally [8].…”