Person:
Goldman,
Daniel I.
Goldman,
Daniel I.
Permanent Link
Associated Organization(s)
Organizational Unit
ORCID
ArchiveSpace Name Record
4 results
Publication Search Results
Now showing
1 - 4 of 4
-
ItemSimulation of compound anchor intrusion in dry sand by a hybrid FEM+SPH method( 2022-09) He, Haozhou ; Karsai, Andras ; Liu, Bangyuan ; Hammond III, Frank L. ; Goldman, Daniel I. ; Arson, ChloéThe intrusion of deformable compound anchors in dry sand is simulated by coupling the Finite Element Method (FEM) with Smoothed Particle Hydrodynamics (SPH). This novel approach can calculate granular flows at lower computational cost than SPH alone. The SPH and FEM domains interact through reaction forces calculated from balance equations and are assigned the same soil constitutive model (Drucker-Prager) and the same constitutive parameters (measured or calibrated). Experimental force-displacement curves are reproduced for penetration depths of 8 mm or more (respectively, 20 mm or more) for spike-shaped (respectively, fan-shaped) anchors with 1 to 6 blades. As the number of blades increases, simulations reveal that the granular flow under the anchor deviates from the vertical and that the horizontal granular flow transitions from orthoradial to radial. We interpret the strain field distribution as the result of soil arching, i.e., the transfer of stress from a yielding mass of soil onto adjoining stationary soil masses. Arching is fully active when the radial distance between blade end points is less than a critical length. In that case, the normal stress that acts on the compound anchor at a given depth reaches the normal stress that acts on a disk-shaped anchor of same radius. A single-blade anchor produces soil deformation and failure similar to Prandtl’s foundation sliding model. Multiblade anchors produce a complex failure mechanism that combines sliding and arching.
-
ItemMulti-functional foot use during running in the zebra-tailed lizard (Callisaurus draconoides)(Georgia Institute of Technology, 2012-05) Li, Chen ; Hsieh, S. Tonia ; Goldman, Daniel I.A diversity of animals that run on solid, level, flat, non-slip surfaces appear to bounce on their legs; elastic elements in the limbs can store and return energy during each step. The mechanics and energetics of running in natural terrain, particularly on surfaces that can yield and flow under stress, is less understood. The zebra-tailed lizard (Callisaurus draconoides), a small desert generalist with a large, elongate, tendinous hind foot, runs rapidly across a variety of natural substrates. We use high-speed video to obtain detailed three-dimensional running kinematics on solid and granular surfaces to reveal how leg, foot and substrate mechanics contribute to its high locomotor performance. Running at ~10bodylengthss–1 (~1ms–1), the center of mass oscillates like a spring-mass system on both substrates, with only 15% reduction in stride length on the granular surface. On the solid surface, a strut-spring model of the hind limb reveals that the hind foot saves ~40% of the mechanical work needed per step, significant for the lizardʼs small size. On the granular surface, a penetration force model and hypothesized subsurface foot rotation indicates that the hind foot paddles through fluidized granular medium, and that the energy lost per step during irreversible deformation of the substrate does not differ from the reduction in the mechanical energy of the center of mass. The upper hind leg muscles must perform three times as much mechanical work on the granular surface as on the solid surface to compensate for the greater energy lost within the foot and to the substrate.
-
ItemComparative studies reveal principles of movement on and within granular media(Georgia Institute of Technology, 2010-06) Ding, Yang ; Gravish, Nick ; Li, Chen ; Maladen, Ryan D. ; Mazouchova, Nicole ; Sharpe, Sarah S. ; Umbanhowar, Paul B. ; Goldman, Daniel I.Terrestrial locomotion can take place on complex substrates such as leaf litter, debris, and soil that flow or solidify in response to stress. While principles of movement in air and water are revealed through study of the hydrodynamic equations of fluid motion, discovery of principles of movement in complex terrestrial environments is less advanced in part because describing the physics of limb and body interaction with such environments remains challenging. We report progress our group has made in discovering principles of movement of organisms and models of organisms (robots) on and within granular materials (GM) like sand. We review current understanding of localized intrusion in GM relevant to foot and body interactions. We discuss the limb-ground interactions of a desert lizard, a hatchling sea turtle, and various robots and reveal that control of granular solidification can generate effective movement. We describe the sensitivity of movement on GM to gait parameters and discuss how changes in material state can strongly affect locomotor performance. We examine subsurface movement, common in desert animals like the sandfish lizard. High speed x-ray imaging resolves subsurface kinematics, while electromyography (EMG) allows muscle activation patterns to be studied. Our resistive force theory, numerical, and robotic models of sand-swimming reveal that subsurface swimming occurs in a “frictional fluid” whose properties differ from Newtonian fluids.
-
ItemSensitive dependence of the motion of a legged robot on granular media(Georgia Institute of Technology, 2009-03-03) Li, Chen ; Umbanhowar, Paul B. ; Komsuoglu, Haldun ; Koditschek, Daniel E. ; Goldman, Daniel I.Legged locomotion on flowing ground (e.g., granular media) is unlike locomotion on hard ground because feet experience both solid- and fluid-like forces during surface penetration. Recent bioinspired legged robots display speed relative to body size on hard ground comparable with high-performing organisms like cockroaches but suffer significant performance loss on flowing materials like sand. In laboratory experiments, we study the performance (speed) of a small (2.3 kg) 6-legged robot, SandBot, as it runs on a bed of granular media (1-mm poppy seeds). For an alternating tripod gait on the granular bed, standard gait control parameters achieve speeds at best 2 orders of magnitude smaller than the 2 body lengths/s (≈60 cm/s) for motion on hard ground. However, empirical adjustment of these control parameters away from the hard ground settings restores good performance, yielding top speeds of 30 cm/s. Robot speed depends sensitively on the packing fraction φ and the limb frequency ω, and a dramatic transition from rotary walking to slow swimming occurs when φ becomes small enough and/or ω large enough. We propose a kinematic model of the rotary walking mode based on generic features of penetration and slip of a curved limb in granular media. The model captures the dependence of robot speed on limb frequency and the transition between walking and swimming modes but highlights the need for a deeper understanding of the physics of granular media.