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

Seals are well-known for their remarkable hydrodynamic trail-followingcapabilities made possible by undulating flow-sensing whiskers that enablethe seals to detect fish swimming as far as 180 m away. In this work, theform-function relationship in the undulating whiskers of two different phocidseal species, viz. harbor and gray seals, is studied. The geometry and materialproperties of excised harbor and grey seal whiskers are systematicallycharacterized using blue light 3D scanning, optical and scanning electronmicroscopy, and nanoindentation. The effect of the undulating geometry onthe whiskers’ vibration in uniform water flow is studied using bothexperimental (piezoelectric MEMS and 3D-printed piezoresistive sensorsdeveloped in-house) and numerical (finite element method) techniques. Theresults indicate that the dimensionless ratio of undulation wavelength tomean whisker diameter (𝝀/Dm) in phocid seals may have evolved to be in theoptimal range of 4.4–4.6, enabling an order-of-magnitude reduction invortex-induced vibrations (compared to a similarly-shaped circular cylinder)and, consequently, an enhanced flow sensing capability with minimalself-induced noise. The results highlight the importance of the dimensionless𝝀/Dmratio in the biomimetic design of seal whisker-inspiredvibration-resistant structures, such as marine risers and wake detectionsensors for submarines.