Bulletin of the American Physical Society
APS March Meeting 2019
Volume 64, Number 2
Monday–Friday, March 4–8, 2019; Boston, Massachusetts
Session V56: Interactions of Elastic Structures with Fluids and Granular Matter II |
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Sponsoring Units: GSNP Chair: Douglas Holmes, Virginia Tech Room: BCEC 255 |
Thursday, March 7, 2019 2:30PM - 2:42PM |
V56.00001: Bioinspired soft fluidic channels Martin Brandenbourger, Corentin Coulais Taking inspiration from the lymphatic system, we devise millimetre scale fluidic channels made of soft asymmetric valves. |
(Author Not Attending)
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V56.00002: Hydro-elasto-capillary interactions for programmable microfluidics Herve Elettro, Francois Gallaire Soft microfibers can be strongly bent by capillary forces and can even be reversibly coiled inside fluid cavities. If present, hydrodynamic forces may compete with capillary forces, uncoil the microfiber and induce its deployment from its original coiled state. |
Thursday, March 7, 2019 2:54PM - 3:06PM |
V56.00003: Kirigami fog nets Pierre Bintein, Axel Cornu, Nicolas Vandewalle, Denis Terwagne Fog is harvested in numerous arid coastal regions by nets placed in dominant winds to catch water droplets. We study experimentally how flexible meshes can adapt their shapes to wind and avoid clogging by capillary effects, in order to maintain a good efficiency of fog collection. By considering aerodynamic, capture and drainage requirements together with mechanical constraints, we propose an optimal geometry for kirigami nets of a given material. |
Thursday, March 7, 2019 3:06PM - 3:18PM |
V56.00004: Capillary stresses in disordered unsaturated porous materials Siavash Monfared, Tingtao Zhou, Farhang Radjai, Roland JM Pellenq, Franz-Josef Ulm Capillary condensation in disordered porous materials - specifically, the interplay of spatial distribution of grains/pores, temperature and distribution of capillary stresses - is explored. This is achieved through lattice gas density functional theory and a recently proposed method for computing capillary stresses based on equivalency of lattice and phase field fluid models in the continuum limit. Gaining insights into the distribution of capillary stresses at a given relative humidity and temperature in disordered porous materials pave the way for fluid mixture coupling with solid deformation while enriching current methods for inferring pore size distribution and pore connectivity from adsorption/ desorption experiments. |
Thursday, March 7, 2019 3:18PM - 3:30PM |
V56.00005: Deformations in the hook and flagellum during bacterial flick motility Henry Fu, Mehdi Jabbarzadeh Dynamical bending, buckling, and polymorphic transformations of the thin flagellar filament are known to affect bacterial motility in fluids. The run-reverse-flick motility of monotrichous bacteria also involves the even more flexible hook which connects the flagellum to its rotary motor. First, I will discuss the role of dynamic bending of both the hook and flagellum during the initiation of flicks. We obtain accurate estimates of forces and torques on the hook that suggest that flicks occur for stresses below the (static) Euler buckling criterion, then provide a mechanistic model for flick initiation that requires combined bending of the hook and flagellum. We calculate the triggering torque-stiffness ratio and find that our predicted onset of dynamic instability corresponds well with experimental observations. Second, I will discuss a more efficient numerical treatment of the dynamics of an inextensible filament that will allow modeling of the complete dynamics of the flick as well as recently discovered unconventional bacterial flagellar motility modes. |
Thursday, March 7, 2019 3:30PM - 3:42PM |
V56.00006: On the unusual swimming gaits of sea-slugs. Shankar Venkataramani, Kenneth Yamamoto Nudibranches (sea-slugs) are a family of soft-bodied marine invertebrates. They typically crawl on the sea-floor, but some species (eg. Hexabranchus sanguineus ``Spanish dancer") are capable of free swimming. They possess a peculiar swimming gait, which we will argue comes from constraints on their geometry. I will present an analysis of free swimming sea-slugs that touches upon interesting questions in the mechanics of non-Euclidean thin sheets as well as on the interaction of such sheets with a fluid environment. I will also discuss potential applications our analysis to soft robots. |
Thursday, March 7, 2019 3:42PM - 3:54PM |
V56.00007: Buckling Instability to Control the Swimming Direction in Bacterial Flagella Mohammad Khalid Jawed, Weicheng Huang, Mojtaba Forghani We analyze the control of a uniflagellar soft robot in low Reynolds fluid. Inspired by the locomotion of bacteria, we consider a robot comprised of a flagellum - a flexible helical filament - attached to a spherical head. The flagellum rotates about the head at a controlled angular velocity and generates a propulsive force that moves the robot forward. When the angular velocity exceeds a threshold value, the hydrodynamic force by the fluid can cause the flagellum to buckle, characterized by a dramatic change in shape. A fluid-structure interaction model that combines Discrete Elastic Rods algorithm with Lighthill's Slender Body Theory is employed to simulate the system. We demonstrate that the robot can follow a prescribed path in three dimensional space by exploiting buckling of the flagellum. The control scheme involves only a single scalar input - the angular velocity of the flagellum. We also show that the complexity of the dynamics can be captured using a deep neural network, from which we identify the input-output functional relationship between the control inputs and the trajectory of the robot. Our study underscores the potential role of buckling in the locomotion of natural bacteria. |
Thursday, March 7, 2019 3:54PM - 4:06PM |
V56.00008: Modelling the Transition from Fracture to Granular Flow Joel Clemmer, Mark Owen Robbins As a brittle solid is loaded, crack growth leads to fracture and fragmentation. The system then transitions to granular flow where these fragments continue to break down into smaller grains in a process known as comminution. To explore this transition, we created a discrete element model of an isotropic, brittle material. The solid is modelled as a disordered packing of locally interacting spheres. Interactions include an attractive and a repulsive pairwise force as well as a three-body angular stiffness. If stretched a critical distance, the attractive and angular interactions will break. The relative strength of interactions can be tuned to control the material’s elastic response (Poisson’s ratio) as well as the ratio of mode 1 to mode 2 fracture toughness. We use this model to explore how material properties, initial defect density, and strain rate affect both the transition to granular flow and the resulting rheology and comminution. We track the stress response of the system, the spatial and temporal locations of crack growth, and the evolution of the grain size distribution. The grain size distribution shows power-law behavior and with increasing strain rates one can identify a decreasing maximum grain size. |
Thursday, March 7, 2019 4:06PM - 4:18PM |
V56.00009: Hydraulically Driven Jamming of Rods Jordan Kennedy, Lakshminarayanan Mahadevan Hydraulically driven flow of filament-like objects has a broad range of natural and industrial applications such as log jams in rivers, or the clogging of an open channel irrigation ditch in agriculture. To investigate the phase space of the jamming of rods in a fluid driven flow, we have performed experiments on buoyant particles over a range of aspect ratios in an open channel flume with a gated restriction, and quantify the results as a function of channel geometry, Froude number and density of logs in the channel. |
Thursday, March 7, 2019 4:18PM - 4:30PM |
V56.00010: Hydraulic fracturing dynamics in natural and artificial low-permeability porous media Thomas Cochard Despite the impact that hydraulic fracturing has on the energy sector, the physical mechanisms that control its efficiency and environmental impacts remain poorly understood in part because of the complex heterogeneous structures of the natural low permeability formations. We developed an experimental approach to study the hydraulic fracture propagation in both natural and model low-permeability media. Natural shale sample, thin sections of Mancos Shale, and engineered gels have been hydro-fractured under controlled conditions. The combination of high-speed imaging during the process and X-ray tomography before and after allows us to monitor the fracture propagation and gives insight on how heterogeneities drive hydraulic fracturing dynamics. |
Thursday, March 7, 2019 4:30PM - 4:42PM |
V56.00011: Scaling and spatial correlations in the quasibrittle process zone Jaron Kent-Dobias, James Patarasp Sethna We describe a scaling theory for the spatial distributions of damage and stress in the process zone of cracks propagating through quasibrittle materials. Brittle but disordered, these materials are ubiquitous in everyday life, including concrete, shell, and bone. Like in ductile materials, propagating cracks in quasibrittle materials have an extended process zone surrounding the crack surface, but unlike ductile materials this zone is comprised of a large complicated region of microfracture with correlated damage across many length scales. As a result, fracture in these materials exhibits strong sample size and shape dependence whose underlying nature evades standard analysis. Motivated by simulations of disordered fuse networks, our results work towards explaining the way damage and stress are correlated in and around the process zone and use renormalization group ideas first developed by Shekhawat et al. (PRL 110(18), 185505) to grapple with their system size dependence. |
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