Wavy Whiskers in Phocid Seals Exhibit High Signal-to-Noise in Sensing Hydrodynamic Flows

Phocid seals can detect fish from distances up to 180 meters solely using undulating whiskers. The unique undulating surfaces of these whiskers have been found to minimize vortex-induced vibrations (VIVs). In our previous work, we measured the ratios of undulation wavelength (λ) to mean diameter $\left(D_{m}\right),\left(\lambda / D_{m}\right)$ in both harbor and grey seals, yielding values of approximately 4.36 and 4.63, respectively. In this study, we delve into the significance of the $\lambda / D_{m}$ ratio to the vibration responses of seal whiskers in a fluid flow. We conducted comprehensive fluid-structure interaction studies using COMSOL Multiphysics®, wherein we studied vibration responses of harbor and grey seal whisker structures with diverse $\lambda / D_{m}$ values in the oncoming flow. Our results indicate that seal whiskers exhibited a trough in their VIV responses and a peak in wake-induced vibration (WIV) responses at $\lambda / D_{m}$ values around 4 to 5. Our findings could imply that the evolutionary optimization of the $\lambda / D_{m}$ value enables seal whiskers with resistance to VIV and sensitivity to WIV.