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 Q07: Non-Linear Dynamics and Chaos III |
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Chair: Harry Swinney, University of Texas Room: 211 |
Tuesday, November 26, 2019 7:45AM - 7:58AM |
Q07.00001: Transport by vortices formed by breaking internal waves on a continental slope Harry Swinney, Guilherme Salvador-Vieira, Michael Allshouse Oceanic internal waves generated by tidal flow over bottom topography can transport energy for thousands of kilometers, but in the open ocean material transport (a second-order effect) is not significant. However, when an internal wave impinges on a continental slope, it forms coherent vortices (called boluses) that can trap and transport particles and biota along the slope. The magnitude of such transport in the oceans is not known. While most previous studies examined bolus transport for model systems consisting of two layers of uniform density, the present laboratory experiments and numerical simulations examine how transport by boluses depends on the thickness of the pycnocline, the region in which the fluid density changes rapidly with depth. We find that bolus size, upslope displacement, and maximum available potential energy produced are optimized for a particular pycnocline thickness and are significantly larger in continuously stratified fluids than in two-layer models. Linking the observed transport relationships to ongoing observations of coastal boluses should provide more accurate estimates of the importance of bolus transport for global coastal ecosystems. [Preview Abstract] |
Tuesday, November 26, 2019 7:58AM - 8:11AM |
Q07.00002: Bacterial diodes: Rectified transport of swimming cells in porous media flow Jeffrey Guasto, Nicolas Waisbord Directed motility enables swimming microbes to navigate their porous habitats for resources, where self-propulsion competes with fluid flow to affect processes ranging from disease transmission and bioremediation. Despite this broad importance, how directed motility affects the self-transport and dispersion of microswimmers in flow through constricted pores remains unknown. Focusing on magnetotactic bacteria in a microfluidic porous medium, we show that upstream oriented cells, directed by a magnetic field, are localized and trapped in vortical orbits at a constriction. Vortical cell localization results in three distinct regimes of rectified bacterial conductivity through a throat, akin to a `bacterial diode', whereby cells swim upstream, become trapped within a pore, or are advected downstream with increasing flow speed. Langevin simulations reveal that the trapping regime results in near-complete transport suppression, while ephemoral trapping in the downstream regime enhances dispersion. We also show that vortical cell localization persists in three-dimensional flow through a packed microfluidic bed, emphasizing the relevance of this phenomenon in realistic hydraulic networks. [Preview Abstract] |
Tuesday, November 26, 2019 8:11AM - 8:24AM |
Q07.00003: Several uses of Hopf bifurcations in devices, biology and fluids Randall Tagg A casual conversation (c1987) with Jerry Gollub about the marginal oscillator detector used in early magnetic resonance experiments launched a fruitful direction of inquiry about Hopf bifurcations by several undergraduates and some graduate students. This includes use of a Wien bridge oscillator as a sensitive detector, uncovering some new features of this well-known circuit including aspects of dynamics on a torus near the initial bifurcation and explorations of noise near the bifurcation. Mention will be made of other perhaps unexpected aspects and potential uses of Hopf bifurcations (or closely related phenomena) in biology and fluids. [Preview Abstract] |
Tuesday, November 26, 2019 8:24AM - 8:37AM |
Q07.00004: Collaboration, Chaos (Conferences) and Managing with Nonlinear Dynamics Guideposts Neal Abraham In tribute to Jerry Gollub and Alfonso Albano I will review aspects of the influences of our shared interests in chaos and nonlinear dynamics on such things as the inter-departmental collaboration between the physics departments of Haverford College and Bryn Mawr College, a series of international conferences on the testing of experimental data for evidence of chaos and nonlinear dynamics, and various administrative philosophies and strategies we have used to support collaborations among faculty members, diverse departments, and institutions in such other settings as the Great Lakes Colleges Association, the Five College Consortium in western Massachusetts, Twinning Programs in Europe, international collaborations in optical nonlinear dynamics and chaos, and professional development for leaders of inter-institutional collaborations in higher education. [Preview Abstract] |
Tuesday, November 26, 2019 8:37AM - 8:50AM |
Q07.00005: Inverted Peristaltic Pumping in Brain? Bruce Gluckman, Francesco Costanzo Clearance of brain waste products -- metabolites and macromolecules -- has been implicated in diseases such as Alzheimer's Disease. Brain does not have a lymphatic system, so the mechanics of clearance are unknown. The glymphatics model -- that traveling diameter variations of penetrating cerebral arterioles due to heart-driven blood pressure pulsations induces an inverted peristaltic pumping of fluid into and through brain -- is an attractive model. Here we investigate through rigorous Arbitrary Lagrangian-Eularian fluid structure interaction modeling different physical formulations and relevant parameters, and whether the biological constraints of the system could support significant flows. Special attention is given to the explicit boundary conditions and values of the problem. The flowrates generated can be significant under many conditions, but not within biophysically relevant pressure differences that otherwise deform the brain tissue. [Preview Abstract] |
Tuesday, November 26, 2019 8:50AM - 9:03AM |
Q07.00006: Stickslips with Granular Particles JC Tsai, Cheng-En Tsai We study the emergence of stick-slip instabilities with densely packed granular particles that are sheared continuously. Such behavior occurs in a route of transition between suspension dynamics and plastic flows, as a result of changing the shear rate. Counterpart experiments are designed in order to identify the origin of stick-slips between two particles. We discuss the possible connection between the system-sized avalanches and the local instabilities. [Preview Abstract] |
Tuesday, November 26, 2019 9:03AM - 9:16AM |
Q07.00007: Spatially resolved dynamical transitions in shear thickening fluids Jeffrey Urbach, Vikram Rathee, Daniel Blair Dense particulate suspensions exhibit a dramatic increase in average viscosity above a critical, material-dependent shear stress, but the microscopic origins of this shear thickening (ST) remains poorly understood. Using boundary stress microscopy (BSM), we have directly measured the spatially resolved surface stresses during ST, and reported clearly defined dynamic localized regions of substantially increased stress that appear intermittently at stresses above a critical value [1]. Here we present measurements that reveal localized transitions to a fully jammed solid-like phase (SLP) that makes direct contact with the shearing boundaries. The SLPs fracture, bifurcate, and interact in a complex manner that depends on the measurement conditions (constant shear rate vs constant stress). These results demonstrate the ability of BSM reveal rich spatiotemporal dynamics of the thickening transition that are not observable in standard bulk rheology.1 [1] V. Rathee, D. L. Blair, J. S. Urbach, \textit{PNAS} \textbf{114}, 8740 (2017). [Preview Abstract] |
Tuesday, November 26, 2019 9:16AM - 9:29AM |
Q07.00008: Exotic patterns in Faraday waves Laurette Tuckerman, Rahul Agrawal, Ali-higo Ebo-Adou, Lyes Kahouadji, Juan Marin, Nicolas Perinet, Jalel Chergui, Damir Juric, Seungwon Shin For the Faraday instability, by which standing waves appear on the free surface of a vertically vibrated fluid layer, the wavelength is controlled by the forcing frequency rather than by the fluid depth, making it easy to destabilize multiple wavelengths everywhere simultaneously. In the 1990s, this technique was used to produce fascinating new phenomena such as quasipatterns by Edwards \& Fauve and superlattices by Gollub, Pier \& Kudrolli. This in turn sparked a renaissance of interest in Faraday waves, leading to new mathematical theories and numerical simulations. We will discuss some of the exotic patterns found in recent numerical simulations, such as quasi-hexagons alternating with beaded stripes, a supersquare divided into four subsquares with synchronized diagonal blocks, Platonic solids alternating with their duals while drifting, and a twisted sheared secondary instability of square waves. [Preview Abstract] |
Tuesday, November 26, 2019 9:29AM - 9:42AM |
Q07.00009: Rotational Dynamics of Dense Granular Systems. Wolfgang Losert This study builds on my postdoctoral work in the Gollub lab on particle tracking based analysis of dense granular flows. In the work presented here we analyze the reversibility of both translation and rotations of granular materials in three-dimensions under cyclic compression, Using transparent acrylic beads with cylindrical holes and index matching techniques, we are not only capable of tracking displacements but also able to follow rotations. We observe that for moderate compression amplitudes, up to one bead diameter, the translational displacements of the beads after each cycle become mostly reversible after an initial transient. However, granular rotations are irreversible. The translational and rotational displacements are only weakly correlated, indicating that rotational motion depends on more subtle changes in contact distributions. We are able to recreate these observations in particle dynamics simulations. Simulations allow us to assess the forces and torques in the system undergoing cyclic forcing. [Preview Abstract] |
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