Bulletin of the American Physical Society
APS March Meeting 2020
Volume 65, Number 1
Monday–Friday, March 2–6, 2020; Denver, Colorado
Session L15: Fluid Structure Interactions |
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Sponsoring Units: DFD GSNP Chair: Claudio Falcon, Univ de Chile Room: 210/212 |
Wednesday, March 4, 2020 8:00AM - 8:12AM |
L15.00001: Observation of broad-band water wave guiding in shallow water Claudio Falcon, Fabián Sepulveda, Diego Guzmán, Rodrigo Vicencio We report on the observation and characterization of broad-band wave guiding of surface gravity waves in an open channel in the shallow water limit. The wave guide is constructed by changing locally the depth of the fluid layer, which creates conditions for surfaces waves to propagate along the guide. We present experimental and numerical results of this shallow water wave guiding, which can be straightforwardly matched to the one-dimensional wave equation of shallow water waves. Furthermore, we also probe the possibility of wave guiding in curve guides and measure how this changes wave propagation. |
Wednesday, March 4, 2020 8:12AM - 8:24AM |
L15.00002: Designing an All-Carbon Membrane for Water Desalination David Tomanek, Andrii Kyrylchuk We design an all-carbon membrane for the filtration and desalination of water. A unique layered assembly of carbon nanostructures including graphite oxide (GO), buckypaper consisting of carbon nanotubes, and a strong carbon fabric provides high mechanical strength and thermal stability, resilience to harsh chemical cleaning agents and electrical conductivity, thus addressing major shortcomings of commercial reverse osmosis membranes. We use ab initio density functional theory calculations to obtain atomic-level insight into the permeation of water molecules in-between GO layers and across in-layer vacancy defects. Our calculations elucidate the reason for selective rejection of solvated Na+ ions in an optimized GO membrane that is structurally stabilized in a sandwich arrangement in-between layers of buckypaper, which are protected on both sides by strong carbon fabric layers. |
Wednesday, March 4, 2020 8:24AM - 8:36AM |
L15.00003: Separation and collision dynamics in biomimetic wind-driven fog harvesting Aida Shahrokhian, Fan Kiat Chan, Jiansheng Feng, Mattia Gazzola, Hunter King In regions where foggy days are recurrent and other water sources scarce, harvesting fog is a practical solution. Physical and behavioral techniques developed over eons by plants and animals in these regions can provide useful insight to do it better. O.unguicularis, a Namib desert beetle, goes to the top of the sand dunes on foggy days and uses its forewings to intercept the inertial microdroplets carried by the wind. Adaptation of this beetle has been extensively studied through the lens of surface wettability and its role in transporting accumulated water. Yet, how the interaction between flow dynamics and surface topography of beetle elytra can induce collision of droplets and increase accumulation of water has not been considered. Here, we show in careful experiments accompanied by numerical flow simulations that surface morphology, independent of wettability, plays a dominant role in deposition efficiency of beetle-like geometries. Furthermore, we investigate the potential role of hydrodynamic forces in near collision dynamics where surface mechanics and texture can limit the possibility of collision. The results suggest that manipulation of the collision mechanism via geometry and mechanics can be an alternative driver of the physical adaptation of the fog basking beetles. |
Wednesday, March 4, 2020 8:36AM - 8:48AM |
L15.00004: Pair interaction between sedimenting polar objects in the Stokes regime Alyssa Conway, Narayanan Menon, Rahul Chajwa, Sriram Ramaswamy We study triangles placed in a quasi-two-dimensional container and sedimented at low Reynolds number as a model of the stokesian sedimentation of polar objects. Individual polar objects, unlike non-polar axisymmetric objects, rotate as they sediment due to coupling between the orientational and translational degrees of freedom and ultimately reorient into stable orientations [Jayaweera, Mason, J. Fluid Mech. 22 (1965)]. In order to study the pair interaction between polar objects, we sediment pairs of triangles with initial conditions that include both stable and unstable orientations of the individual triangles. Surprisingly, none of the periodic motions observed [Chajwa, Menon, Phys. Rev. Lett. 122 (2019)] with non-polar object pairs are seen with pairs of triangles. Instead, we observe that triangles reorient and translate away from each other until both objects achieve a stable orientation. As a special case, we also observe that equilateral triangle pairs (which have three-fold, rather than polar, symmetry) continuously rotate in their steady state. |
Wednesday, March 4, 2020 8:48AM - 9:00AM |
L15.00005: Sedimenting disk arrays: waves and transient growth Rahul Chajwa, Rama Govindarajan, Narayanan Menon, Sriram Ramaswamy We study experimentally the Stokesian sedimentation (Re ∼ 10-4) of one-dimensional lattice of disks in a quasi two-dimensional geometry with trajectories of disk centres lying in a plane. We induce initial positional perturbations over a uniformly spaced configuration of disks with their separation vectors and normals aligned, and perpendicular to gravity. For various perturbation wavenumbers q and interparticle separations d, we find two classes of behaviour: (i) wavelike propagation of orientations coupled with number-density fluctuations and (ii) clumping instability resembling that of spheres, decorated with orientations. We construct equations of motion using pairwise addition of forces and torques in an array of spheroids. Linear stability analysis of the dispersion relation predicts non-modal transient growth, which we observe experimentally; and a phase boundary in the q-d plane separating neutrally stable and unstable regimes, consistent with our experimental observations. We predict a critical density of the lattice of spheroids below which all wavenumbers are asymptotically linearly stable, showing that orientable particles need not be subject to the inevitable clumping instability of spheres. |
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