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

Abstract

Seals with beaded whiskers-the majority of true seals (Phocids)-are able to trace even minute disturbance caused by prey fish in the ambient flow using only sensory input from their whiskers. The unique three-dimensional undulating morphology of seal whiskers has been associated with their capability of suppressing vortex-induced vibration and reducing drag. The exceptional hydrodynamic traits of seal whiskers are of great interest in renovating the design of aero-propulsion flow components and high-sensitivity flow sensors. It is essential to have well-documented data of seal whisker morphology with statistically meaningful generalization, as the solid foundation for whisker-inspired flow control applications. However, the available whisker morphology data is either incomplete, with measurements of only a few key parameters, or based on a very limited sample size in case studies. This work characterizes the morphology of 27 beaded seal whiskers (harbor seal and elephant seal), using high-resolution computer-tomography scanning at NASA's Glenn Research Center in Cleveland, OH. Over two thousand cross-sectional slices for every individual whisker sample are reconstructed, to generate three-dimensional morphology. This is followed by detailed statistical analysis of a set of key parameters, under an established framework (Hanke et al 2010 J. Exp. Biol. 213 2665-72). While the length parameters are generally consistent with previous studies, we note that the angle of incidence of elliptical cross-sections varies in a wide range, with a majority falling between [Formula: see text] and [Formula: see text]. Angles of incidence at both peaks and troughs appear to roughly follow a Gaussian distribution, but no clear preference of orientation is identified. We discuss the current knowledge of whisker-inspired flow studies, focusing on choices of morphology parameters. The new understanding of whisker morphology can better inform future design of high-sensitivity flow sensors and aero-propulsion flow structures.

Ecomorphology reveals Euler spiral of mammalian whiskers

“…Whisker morphology can vary between species, for example, many phocids have undulating, beaded whiskers (Ginter et al, 2012; Ginter, Fish, & Marshall, 2010; Hanke et al, 2010; Rinehart, Shyam, & Zhang, 2017), and aquatic mammals are thought to have more innervated whiskers than terrestrial species (Dehnhardt & Mauck, 2008; Mattson & Marshall, 2016; Mcgovern, Marshall, & Davis, 2015; Miersch et al, 2011; Rice, Mance, & Munger, 1986). Some aquatic species use their whiskers for both, touch and hydrodynamic sensing, such as California sea lions ( Zalophus californianus ; Gläser, Wieskotten, Otter, Dehnhardt, & Hanke, 2011; Milne & Grant, 2014) and Harbour seals ( Phoca vitulina ; Dehnhardt, Mauck, & Bleckmann, 1998; Grant, Wieskotten, Wengst, Prescott, & Dehnhardt, 2013), which may indicate functional differences between aquatic and terrestrial whiskers (Jones & Marshall, 2019; Sprowls & Marshall, 2019).…”

Flow over seal whiskers: Importance of geometric features for force and frequency response

“…The whisker model described above is constructed from average measurements of digital photography from 13 adult harbor seal whiskers, which exhibit considerable variation in some geometric parameters, specifically the angles of incidence α and β [ 12 ]. A follow-up investigation by Rinehart et al [ 13 ] performs independent whisker characterization using 27 whiskers from harbor and elephant seals. Among the findings are smaller mean angles of incidence, α and β , of 0.303 and 1.079 degrees respectively, in contrast with the larger angles presented by Hanke et al of α = 15.27 degrees and β = 17.60 degrees.…”

“…Hans et al explore four different geometric models and demonstrate that both coordinate directions of undulation amplitudes are necessary for maximum drag-reduction benefits, however, the angle of incidence has only a weak influence on drag [ 14 ]. In a recent work, Liu et al [ 15 ] investigate a geometric model based on the parameter values presented in the work of Rinehart et al [ 13 ]. Results indicate that the undulations in opposing directions must alternate with one another along the span of the seal whisker for optimal hydrodynamic force reduction.…”

Wind-resilient civil structures: What can we learn from nature

“…Such strategies include adding O-rings and helicoidal wires and supplementing external momentum to the boundary-layer flow (Lim and Lee 2004;Lin et al 2016;Morrison et al 2016;Kim and Yoon 2017) to alter the boundary-layer behavior and wake dynamics. Bioinspired flow control strategies have emerged as one of the new tools to address this issue (Guttag and Reis 2017;Rinehart et al 2017). For instance, the morphable cylinder inspired by the Saguaro cacti will be discussed in the section on Saguaro cacti.…”