The incredible sensing abilities of seals

Whiskers are natural sensory wonders. The tactile sensory hairs, though nerveless, deliver external information through the highly innervated follicles of both land and aquatic mammals. While the whiskers of land mammals are round in cross-section and possess about 100 to 120 nerves per follicle, seal whiskers are flattened and ten times more innervated. This sensitivity is comparable to the touch of a human hand.

The wavy whiskers of harbor seals are particularly sensitive. Most studies have focused on how seal whiskers vibrate when their flat surface aligns with water flow direction. Real-world conditions are much more complex. Geng et al. computationally investigated undulated whisker sensitivity related to flow speed and orientation.

“In the wild, seal whiskers encounter different angles and flow conditions, and it’s unclear whether the ability to reduce self-induced vibrations holds under these varying conditions,” said author Qian Xue.

The team varied the angle of attack and velocity of an elastically mounted idealized seal whisker in water at a low speed and measured the resulting vibration under each condition. The results indicate that vortex-induced vibrations are suppressed only at a zero angle of attack because of the change in underlying vortex dynamics, suggesting that while the seals may adopt a zero angle of attack, deviations may be interpreted as signals.

“The research establishes a scientific foundation for designing innovative, whisker-like hydrodynamic sensors, and may inspire other engineering applications aimed at reducing flow-induced vibrations in structures such as offshore struts, mooring lines, risers, cable-stayed bridges, and wind-turbine towers,” said Xue.

Source: “Single degree of freedom vortex induced vibrations of undulatory seal whiskers at low Reynolds number and various angles of attack: A computational fluid dynamics study,” by Biao Geng, Xudong Zheng, and Qian Xue, Physics of Fluids (2024). This article can be accessed at https://doi.org/10.1063/5.0227544 .