Bulletin of the American Physical Society
72nd Annual Meeting of the APS Division of Fluid Dynamics
Volume 64, Number 13
Saturday–Tuesday, November 23–26, 2019; Seattle, Washington
Session S07: Non-Linear Dynamics and Chaos IV |
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Chair: Patrick Tabeling, ESPCI Paris Room: 211 |
Tuesday, November 26, 2019 10:31AM - 10:44AM |
S07.00001: Representative subsampling of sedimenting blood Howard Stone, Bhargav Rallabandi, Janine Nunes, Antonio Perazzo, Sergey Gershtein It is often necessary to extract a small amount of a suspension, such as blood, from a larger sample of the same material for the purposes of diagnostics, testing or imaging. A practical challenge is that blood sediments noticeably on the time scale of a few minutes, making a representative subsampling of the original sample challenging. Guided by experimental data, we develop a Kynch sedimentation model to discuss design considerations that ensure a representative subsampling of blood, from a container of constant cross-sectional area, for the entire range of physiologically relevant hematocrit over a specified time of interest. Additionally, we show that this design may be modified to exploit the sedimentation and perform the subsampling to achieve either higher or lower hematocrit relative to that of the original sample. Thus, our method provides a simple tool to either concentrate or dilute small quantities of blood or other sedimenting suspensions. [Preview Abstract] |
Tuesday, November 26, 2019 10:44AM - 10:57AM |
S07.00002: Rearrangement Dynamics in Dense Particulate Systems Douglas Durian Together at Penn, Jerry Gollub and I jointly supervised the PhD theses of two superlative graduate students as part of Penn’s MRSEC: Kerstin Nordstrom (assistant professor, Mount Holyoke) and Jennifer Rieser (postdoc, Georgia Tech). In this talk I will review Kerstin’s work on dynamical heterogeneities in a compressed suspension of hydrogel particles under shear. In particular, flow is mediated by intermittent rearrangements that diverge in size as a universal power law of the local relaxation time, i.e. the reciprocal of the strain rate for this system. But how can one tell where rearrangements are likely to occur, and whether they will encourage or discourage further rearrangements nearby? This bears on the age-old question of ductile versus brittle response to large-scale deformation, which we are now tackling by analysis of experiments using Machine Learning methods to classify the local structural environment of each particle. [Preview Abstract] |
Tuesday, November 26, 2019 10:57AM - 11:10AM |
S07.00003: Disentangling Resolution, Precision, and Inherent Stochasticity in Fluid Mixing Nicholas Ouellette, Lei Fang, Sanjeeva Balasuriya Reliable measurement, simulation, and analysis of dynamical systems rely on appropriately bounded uncertainty. Errors that lead to uncertainty naturally arise from finite precision or resolution, but an additional unappreciated source of uncertainty is the effective stochasticity associated with nonlinear dynamics. Here we describe and quantify the interplay between these three sources of uncertainty using a recently developed framework known as stochastic sensitivity theory. Using fluid mixing as a test case and considering data from an analytical flow, a laboratory experiment, and geophysical observations, we show how to delimit regimes that are limited by finite resolution or by inherent stochasticity. We arrive at the surprising conclusion that in some cases, refining the resolution of a measurement or simulation can actually be counterproductive and lead to an outcome that is less faithful to the true dynamics. [Preview Abstract] |
Tuesday, November 26, 2019 11:10AM - 11:23AM |
S07.00004: Nonlinear Granular Electrostatics Troy Shinbrot Anyone who has run a sandblasting machine can attest that flowing sand generates a robust and painful stream of electric shocks to the operator. The same mechanism that produces these shocks also generates lightning in sandstorms, and influences the formation of asteroids as well as industrial systems such as fluidized beds. We describe recent progress showing that multiple length and time scales are involved in granular charging, which produces surprising effects. These include distinct charge patterns for positively and negatively charging surfaces, and competing charging and discharging times that can predictably lead to decreased electrification with increased frequency of vibration of granular beds. None of this work is of the calibre of Jerry Gollub's, but I present it as an homage: work that I think he would have enjoyed. [Preview Abstract] |
Tuesday, November 26, 2019 11:23AM - 11:36AM |
S07.00005: Chaos and disorder in microfluidics Patrick Tabeling Dynamics obviously plays an important role in microfluidics: how long does it take for a biochemical reaction to develop, how long does it take for a microdroplet to form... More specifically, chaotic dynamics plays an important role in the domain of micromixing. Devices based on chaotic mixing, designed to accelerate mixing, are now currently used in the laboratories. To celebrate the memory of Jerry, I will show a few examples where chaos and disorder, in the way he liked to think about, are exploited to develop certain functionalities in microfluidic devices. [Preview Abstract] |
Tuesday, November 26, 2019 11:36AM - 11:49AM |
S07.00006: Taylor dispersion of active Brownian particles John Brady, Zhiwei Peng Compared to the well-studied Taylor dispersion of passive Brownian particles, an understanding of the dispersion of active Brownian particles (ABPs) in a pressure-driven flow is less developed. From a small wavenumber expansion of the Smoluchowski equation for the particle distribution, we explicitly derive an effective advection-diffusion equation for the cross-sectional average of the particle number density. We characterize the effective longitudinal dispersivity of ABPs in relation to the flow speed, the intrinsic swimming speed of the ABPs and their Brownian diffusion. In particular, the dispersion of ABPs includes the classical shear-enhanced (Taylor) dispersion and an active contribution called the swim diffusivity. While pressure-driven flow always enhances particle diffusion through the classical Taylor dispersion process, it can either enhance or hinder the swim diffusivity. As a result, the dispersivity of ABPs exhibits a non-monotonic variation as a function of the flow speed. Our continuum theory is corroborated by a direct Brownian dynamics simulation of the Langevin equations governing the motion of each ABP. [Preview Abstract] |
Tuesday, November 26, 2019 11:49AM - 12:02PM |
S07.00007: The Tropically Enhanced Instability of Oceanic Western Boundary Currents Christopher Edwards, Joseph Pedlosky A linear stability analysis of the shallow-water system in the tropical ocean examines the stability of the western boundary current and its latitudinal dependence. Despite a highly idealized formulation that assumes a purely meridional basic state and makes a local f-plane approximation, the stability analysis successfully predicts a length scale of the disturbance, a latitude for its origin, and a critical Reynolds number that agree well with accompanying numerical results. Realistic western boundary current profiles undergo a horizontal shear instability that is partially stabilized by viscosity. Calculations of the growth rate at several latitudes indicate that the instability is enhanced in the Tropics where the internal deformation radius is a maximum. [Preview Abstract] |
Tuesday, November 26, 2019 12:02PM - 12:15PM |
S07.00008: Watercolors - Measuring the light field in natural waters. Nicholas Tufillaro Visible light is one the few wavelengths that has any significant transmissivity through natural waters: oceans, lakes, streams, and ponds. Light is a primary tool for investigating biological or physical processes in water from sensors in orbit, instruments on ships, or spectrometers in the water itself. I will focus on describing how to see --- in vivo --- the activities of phytoplankton in natural waters, both individual micro-swimmers (\textasciitilde 10 microns) up-to large assemblages of diatoms (\textasciitilde 10 km), and how these measurements are used to understand and gauge biological productivity at both the watershed and global scale. The talk will also discuss a few challenges in trying to do precision measurements in natural environments, instead of the our more natural habitat, the `lab,' and some of the changes that are helpful to optical instrument designs, measurement procedures, and data analysis. [Preview Abstract] |
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