Bulletin of the American Physical Society
71st Annual Meeting of the APS Division of Fluid Dynamics
Volume 63, Number 13
Sunday–Tuesday, November 18–20, 2018; Atlanta, Georgia
Session E23: Biological Fluid Dynamics: Hairs and Cilia |
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Chair: Daniel Tam, Delft University of Technology Room: Georgia World Congress Center B311 |
Sunday, November 18, 2018 5:10PM - 5:23PM |
E23.00001: Abstract Withdrawn
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Sunday, November 18, 2018 5:23PM - 5:36PM |
E23.00002: A machine learning approach for analyzing complex vibrational signals from real seal whiskers Christin T Murphy, Caleb Martin, Jennifer A Franck, Andrew Guarendi, Aren Hellum, Hong Nguyen, William Martin Seals use their whiskers to extract detailed information from the fluid environment and sense prey. We examined the vibration features that correlate with hydrodynamic excitation, using single point laser vibrometery to record the vibrations from harbor seal whiskers in a recirculating water tunnel. The recorded spectra reveal a complex vibrational response with features dependent on flow speed (0.5-2.5 m/s), whisker angle of attack, and presence or absence of an upstream disturbance. A machine learning approach was used to successfully predict the presence of an upstream cylinder, based on the power spectral density (PSD) of the vibrational signal, with comparable performance (>85%) across a variety of simple models. When classifiers were run with amplitude values removed but frequency bin information retained, only a 5% loss in test accuracy resulted, indicating that the relevant feature difference between signals is shape of the PSD, rather than overall amplitudes. In tandem with the experiments, computational fluid dynamics are performed based off of CT scans of seal whiskers. The results from the vibration analysis will be used to inform fluid structure interaction (FSI) computations as a means to connect the fluid dynamics to the frequency response of the whisker. |
Sunday, November 18, 2018 5:36PM - 5:49PM |
E23.00003: On the validity of Stokes equations in ciliary flows Da Wei, Marie-Eve Aubin-Tam, Daniel Seewai Tam Flagellar and ciliary flows at low Reynolds number are usually modeled by solving Stokes equations under given boundary conditions. These equations are time-invariant, which are valid when the viscous forces dominate over the inertia forces. The validity of this assumption for ciliary flows of high frequency (10-100 Hz) requires careful experimental examination. To investigate ciliary flows, we developed a time-resolved optical-tweezers based velocimetry (OTV). Our flow velocity measurements differ dramatically from that predicted by a stokeslet field. In particular, the periodic flow velocity is gradually phase delayed at increasing distances from the cilium; and the amplitude of the oscillatory flow component decays at a much faster rate (1/r^3) than the stokes prediction (1/r). This indicates that the quasi-steady approximation and the use of Stokes equations for unsteady ciliary flows are often not justified, and the finite timescale for vorticity diffusion cannot be neglected. Our results |
Sunday, November 18, 2018 5:49PM - 6:02PM |
E23.00004: Inertia-driven fluid transport of a ciliary structure Daegyu Lim, Mohsen Lahooti, Daegyoum Kim Cilia play an important role in many biological systems. Although most cilia in nature are found in low Reynolds number, cilia of the high-Reynolds-number regime also exist. One example is cilia of a combjelly, which is known to have the largest cilia in animal kingdom. The length of these cilia is the order of millimetres, and they can induce irreversible flow in an inertia-dominant regime for propulsion and feeding. To better understand the function of a ciliary structure, it is necessary to study the effect of Reynolds number in the wide range of O(1) – O(100) on the characteristics of fluid transport. For this aim, we conduct 2D simulation using the immersed boundary method, and, as a model, choose the symmetric motion of a simple ciliary structure. By identifying Lagrangian coherent structure using finite-time Lypunov exponent, we elucidate how the region of active fluid transport changes with Reynolds number. In addition, the symmetry breaking of cilia, which stroke symmetrically on two side walls of a channel, and its dependency on the Reynolds number are examined in the context of vortex-vortex interaction |
Sunday, November 18, 2018 6:02PM - 6:15PM |
E23.00005: Population Dynamics in Two-Dimensional Compressible Turbulence Giorgia Guccione, Roberto Benzi, Federico Toschi The dynamics and genetics of populations of microorganisms in marine environments is a fascinating scientific topic at the crossroads of biology, statistical physics and fluid dynamics. |
Sunday, November 18, 2018 6:15PM - 6:28PM |
E23.00006: Unidirected motion and negative viscosity in microphase separationwith an active polar component Giuseppe Negro, Giuseppe Gonnella, Antonio Lamura Active fluids are systems where active components present in the fluid (microtubules with molecular motors such as kinesin or actomyosin bundles) display interesting collective ordering properties. Active fluids also exhibit peculiar rheological properties. Depending on the characteristic of the active stress, activity is capable to heighten viscosity, enough todevelop shear-thickening properties in contractile systems or induce in extensile suspensions a ”superfluid” regime under suitable condition. We present results of LBM simulations for the behavior of a phase separating symmetric mixture of a passive isotropic fluid and an active polar gel under an applied shear flow. For small values of contractile activity(e.g., an actomyosin solution) and shear rates we observe the coexistence of phases characterized by passive and active droplets. In this case the constitutive curves show evidence of shear thickening behavior. For extensile activity (e.g., materials based on bacterial suspensions), instead, the constitutive curves indicates the presence of states characterized by negative viscosity. These states are marked by a negative slope of the velocity profile at the center of the channel, opposite to that of the applied shear. |
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