Now showing items 1-20 of 24

    • Absence of inelastic collapse in a realistic three ball model 

      Goldman, Daniel I.; Shattuck, M. D.; Bizon, C.; McCormick, W. D.; Swift, J. B.; Swinney, Harry L. (Georgia Institute of TechnologyAmerican Physical Society, 1998-04)
      Inelastic collapse, the process in which a number of partially inelastic balls dissipate their energy through an infinite number of collisions in a finite amount of time, is studied for three balls on an infinite line and ...
    • Colloquium: Biophysical principles of undulatory self-propulsion in granular media 

      Goldman, Daniel I. (Georgia Institute of Technology, 2014)
      Biological locomotion, movement within environments through self-deformation, encompasses a range of time and length scales in an organism. These include the electrophysiology of the nervous system, the dynamics of muscle ...
    • Continuum-type stability balloon in oscillated granular layers 

      De Bruyn, John R.; Bizon, C.; Shattuck, M. D.; Goldman, Daniel I.; Swift, J. B.; Swinney, Harry L. (Georgia Institute of TechnologyAmerican Physical Society, 1998-08-17)
      The stability of convection rolls in a fluid heated from below is limited by secondary instabilities, including the skew-varicose and crossroll instabilities. We observe a stability boundary defined by these same instabilities ...
    • Crucial role of sidewalls in velocity distributions in quasi-two-dimensional granular gases 

      van Zon, J. S.; Kreft, J.; Goldman, Daniel I.; Miracle, D.; Swift, J. B.; Swinney, Harry L. (Georgia Institute of TechnologyAmerican Physical Society, 2004-10-19)
      Our experiments and three-dimensional molecular dynamics simulations of particles confined to a vertical monolayer by closely spaced frictional walls (sidewalls) yield velocity distributions with non-Gaussian tails and a ...
    • Drag induced lift in granular media 

      Ding, Yang; Gravish, Nick; Goldman, Daniel I. (Georgia Institute of TechnologyAmerican Physical Society, 2011-01-14)
      Laboratory experiments and numerical simulation reveal that a submerged intruder dragged horizontally at a constant velocity within a granular medium experiences a lift force whose sign and magnitude depend on the intruder ...
    • Dynamics of drag and force distributions for projectile impact in a granular medium 

      Ciamarra, Massimo Pica; Lara, Antonio H.; Lee, Andrew T.; Goldman, Daniel I.; Vishik, Inna; Swinney, Harry L. (Georgia Institute of TechnologyAmerican Physical Society, 2004-05-14)
      Our experiments and molecular dynamics simulations on a projectile penetrating a two-dimensional granular medium reveal that the mean deceleration of the projectile is constant and proportional to the impact velocity. Thus, ...
    • Effect of Volume Fraction on Granular Aavalanche Dynamics 

      Gravish, Nick; Goldman, Daniel I. (Georgia Institute of TechnologyAmerican Physical Society, 2014)
      We study the evolution and failure of a granular slope as a function of prepared volume fraction, φ0. We rotated an initially horizontal layer of granular material (0.3-mm-diam glass spheres) to a 45◦ angle while we monitor ...
    • The Effectiveness of Resistive Force Theory in Granular Locomotion 

      Zhang, Tingnan; Goldman, Daniel I. (Georgia Institute of TechnologyAmerican Institute of Physics, 2014)
      Resistive force theory (RFT) is often used to analyze the movement of microscopic organisms swimming in fluids. In RFT, a body is partitioned into infinitesimal segments, each of which generates thrust and experiences ...
    • Entangled granular media 

      Gravish, Nick; Franklin, Scott V.; Hu, David L.; Goldman, Daniel I. (Georgia Institute of TechnologyAmerican Physical Society, 2012-05-17)
      We study the geometrically induced cohesion of ensembles of granular“u particles” that mechanically entangle through particle interpenetration. We vary the length-to-width ratio l/w of the u particles and form them into ...
    • Force and flow at the onset of drag in plowed granular media 

      Gravish, Nick; Umbanhowar, Paul B.; Goldman, Daniel I. (Georgia Institute of TechnologyAmerican Physical Society, 2014)
      We study the transient drag force F[subscript D] on a localized intruder in a granular medium composed of spherical glass particles. A flat plate is translated horizontally from rest through the granular medium to observe ...
    • Force and flow transition in plowed granular media 

      Gravish, Nick; Umbanhowar, Paul B.; Goldman, Daniel I. (Georgia Institute of TechnologyAmerican Physical Society, 2010-09-06)
      We use plate drag to study the response of granular media to localized forcing as a function of volume fractionϕ. A bifurcation in the force and flow occurs at the onset of dilatancy ϕ [subscript c]. Below ϕ [subscript ...
    • Granular impact and the critical packing state 

      Umbanhowar, Paul B.; Goldman, Daniel I. (Georgia Institute of TechnologyAmerican Physical Society, 2010-07-15)
      Impact dynamics during collisions of spheres with granular media reveal a pronounced and nontrivial dependence on volume fraction ϕ. Postimpact crater morphology identifies the critical packing state ϕcps, where sheared ...
    • Kink-induced transport and segregation in oscillated granular layers 

      Moon, Sung Joon; Goldman, Daniel I.; Swift, J. B.; Swinney, Harry L. (Georgia Institute of TechnologyAmerican Physical Society, 2003-09-26)
      We use experiments and molecular dynamics simulations of vertically oscillated granular layers to study horizontal particle segregation induced by a kink (a boundary between domains oscillating out of phase). Counterrotating ...
    • Lattice dynamics and melting of a nonequilibrium pattern 

      Goldman, Daniel I.; Shattuck, M. D.; Moon, Sung Joon; Swift, J. B.; Swinney, Harry L. (Georgia Institute of TechnologyAmerican Physical Society, 2003-03-14)
      We present a new description of nonequilibrium square patterns as a harmonically coupled crystal lattice. In a vertically oscillating granular layer, different transverse normal modes of the granular square-lattice pattern ...
    • Lift-off dynamics in a simple jumping robot 

      Aguilar, Jeffrey; Lesov, Alex; Wiesenfeld, Kurt; Goldman, Daniel I. (Georgia Institute of TechnologyAmerican Physical Society, 2012-10-26)
      We study vertical jumping in a simple robot comprising an actuated mass-spring arrangement. The actuator frequency and phase are systematically varied to find optimal performance. Optimal jumps occur above and below (but ...
    • Mach cone in a shallow granular fluid 

      Heil, Patrick; Rericha, Erin C.; Goldman, Daniel I.; Swinney, Harry L. (Georgia Institute of TechnologyAmerican Physical Society, 2004-12-23)
      We study the V-shaped wake (Mach cone) formed by a cylindrical rod moving through a thin, vertically vibrated granular layer. The wake, analogous to a shock (hydraulic jump) in shallow water, appears for rod velocities vR ...
    • March of the SandBots 

      Goldman, Daniel I.; Komsuoglu, Haldun; Koditschek, Daniel E. (Georgia Institute of TechnologyInstitute of Electrical and Electronics Engineers, 2009-04)
      Goldman at Georgia Tech, Koditschek and Komsuoglu at the University of Pennsylvania, in Philadelphia, and other collaborators - are hoping that by studying the zebra-tailed lizard and a menagerie of other desert-dwelling ...
    • Mechanics of undulatory swimming in a frictional fluid 

      Ding, Yang; Sharpe, Sarah S.; Masse, Andrew; Goldman, Daniel I. (Georgia Institute of TechnologyPublic Library of Science, 2012-12)
      The sandfish lizard (Scincus scincus) swims within granular media (sand) using axial body undulations to propel itself without the use of limbs. In previous work we predicted average swimming speed by developing a numerical ...
    • Noise, coherent fluctuations, and the onset of order in an oscillated granular fluid 

      Goldman, Daniel I.; Swift, J. B.; Swinney, Harry L. (Georgia Institute of TechnologyAmerican Physical Society, 2004-04-30)
      We study fluctuations in a vertically oscillated layer of grains below the critical acceleration for the onset of ordered standing waves. As onset is approached, transient disordered waves with a characteristic length scale ...
    • Persistent holes in a fluid 

      Merkt, Florian S.; Deegan, Robert D.; Goldman, Daniel I.; Rericha, Erin C.; Swinney, Harry L. (Georgia Institute of TechnologyAmerican Physical Society, 2004-05-07)
      We observe stable holes in a vertically oscillated 0.5 cm deep aqueous suspension of cornstarch. Holes appear only if a finite perturbation is applied to the layer for accelerations α above 10g. Holes are circular and ...