Harry Swinney - Profile on Academia.edu (original) (raw)
Papers by Harry Swinney
Physical Review E, 1999
Under many conditions, macroscopic grains flow like a fluid; kinetic theory predicts continuum eq... more Under many conditions, macroscopic grains flow like a fluid; kinetic theory predicts continuum equations of motion for this granular fluid. In order to test the theory, we perform event driven molecular simulations of a two-dimensional gas of inelastic hard disks, driven by contact with a heat bath. Even for strong dissipation, high densities, and small numbers of particles, we find that continuum theory describes the system well. With a bath that heats the gas homogeneously, strong velocity correlations produce a slightly smaller energy loss due to inelastic collisions than that predicted by kinetic theory. With an inhomogeneous heat bath, thermal or velocity gradients are induced. Determination of the resulting fluxes allows calculation of the thermal conductivity and shear viscosity, which are compared to the predictions of granular kinetic theory, and which can be used in continuum modeling of granular flows. The shear viscosity is close to the prediction of kinetic theory, while the thermal conductivity can be overestimated by a factor of 2; in each case, transport is lowered with increasing inelasticity.
Reply to comment by McDougall and Barker on “Buoyancy frequency profiles and internal semidiurnal tide turning depths in the oceans”
Journal of Geophysical Research: Oceans, 2014
Physica D: Nonlinear Phenomena, 1991
We report observations of the tip motion of spiral waves in excitable Belousov-Zhabotinskii reage... more We report observations of the tip motion of spiral waves in excitable Belousov-Zhabotinskii reagent. An open reactor is used to determine the time-asymptotic dynamics of the spiral tip as a function of a control parameter. We have observed a supercritical transition from simple rotation (one frequency) to compound rotation (two frequencies); the compound motion at onset closely resembles that predicted by two-species reaction-diffusion models. Measurements of the frequencies of the motion indicate that the compound rotation is quasiperiodic over the range studied; there is no evidence of frequency locking. The compound tip motion appears to result from fluctuations in the curvature of the spiral wave near its tip. We describe qualitatively the sequence of events during a single tip orbit and suggest that the refractory tail of the wave plays a dominant role in controlling the tip motion.
Physical Review E, 1999
Recent work demonstrates the inevitable role of convection during the growth of patterns in thin-... more Recent work demonstrates the inevitable role of convection during the growth of patterns in thin-layer electrochemical deposition. Convection is driven mainly by Coulombic forces due to local charges and by buoyant forces due to concentration gradients that lead to density gradients. Here we study by theoretical and numerical modeling the limiting regimes under which electroconvection or gravitoconvection prevail. The model describes the diffusive, migratory, and convective motion of ions in a fluid subject to an electric field. The equations are written in terms of dimensionless quantities, in particular, the gravity Grashof and the electrical Grashof numbers. The simulations reveal that gravitoconvection becomes increasingly important as the gravity Grashof number increases, while electroconvection becomes increasingly important as the electrical Grashof number increases. For both regimes the model predicts concentration, electric potential, and velocity patterns that are in qualitative agreement with typical electrodeposition experiments. In gravitoconvection, the model predicts the evolution, before collision, of the convection rolls near each electrode growing first as t 4/5 and then slowing down to t 1/2 ; the same scaling behavior was observed in experiments. After collision, the cathodic and anodic rolls merge into a single roll. In electroconvection, the model predicts the existence of vortex pairs formed by the electrical force on space charge accumulating near the growing filament tip. Such vortex rolls and pairs have been observed in experiments.
Our experiments on a vertically oscillated granular layer reveal that spatial patterns emerge in ... more Our experiments on a vertically oscillated granular layer reveal that spatial patterns emerge in two stages following a change of parameter into the pattern-forming regime: an initial, domain-forming stage and a later stage in which domains coarsen to form ultimately an extended regular pattern. We characterize the evolution of the pattern using a "disorder function" (ÿ), where ÿ is a moment of the disorder operator (Gunaratne et al., Phys. Rev. E 57 (1998) 5146). The disorder in the initial stage is found to be consistent with a decay given by (ÿ) ∼ t −ÿ=2 , in accord with theory that predicts that behavior in this stage should be universal for pattern forming systems. The ÿnal stage is non-universal.
Shock Waves in Granular Media
Shock Wave Science and Technology Reference Library, 2007
ABSTRACT Shock waves form in air when a bullet or aircraft exceeds the speed of sound. In a granu... more ABSTRACT Shock waves form in air when a bullet or aircraft exceeds the speed of sound. In a granular medium, the sound speed is small (typically 10 cm/s), so shock waves form for ordinary rather than extreme conditions. Our group has examined oblique and normal shock waves in granular flow past a wedge(E.C. Rericha et al., Phys. Rev. Lett. 88, 025403 (2002).) and in vertically oscillated granular layers, (J. Bougie et al., Phys. Rev. E 66, 051301 (2002).) using laboratory experiments, molecular dynamics simulations, and simulations of continuum equations for granular flow. The flows we consider reach Mach numbers greater than ten, a regime that is difficult to study in gas flows. We find that the shocks formed in flows of particles in a vacuum exhibit properties similar to those of shocks in supersonic gases, but there are some differences that arise because of the inelastic collisions between particles in granular media. The molecular dynamics and continuum simulations are found to describe the observations well. Increasing the restitution coefficient toward unity (decreasing the dissipation toward zero) does not lead to any qualitative change in behavior.
Experimental observation of sedimentation trajectories of single spheres in Hele-Shaw cells
ABSTRACT
Preliminary results on the granular drag force
Temperature Change in Melting of an Oscillated Granular Layer
... Session KH: Granular Flows IV. 5:15 PM6:59 PM, Monday, November 20, 2006. Tampa Marriott Wat... more ... Session KH: Granular Flows IV. 5:15 PM6:59 PM, Monday, November 20, 2006. Tampa Marriott Waterside Hotel and Marina Room: Florida Salon 6 Chair: Richard M. Lueptow, Northwestern University Abstract ID: BAPS.2006.DFD.KH.3. ...
Measuring the phase diagram of granular media
ABSTRACT The jamming transition in granular media has been the subject of several studies in the ... more ABSTRACT The jamming transition in granular media has been the subject of several studies in the last years. However, an experimental observation of phase diagram of granular media in three dimensions is still lacking. The goal of this study is to obtain such a diagram as a function of the shear stress, the packing fraction, phi, and the pressure in a granular bed. Shear stress is obtained by measuring the force, F, needed to pull-up a paddle immersed in a granular bed as a function of its packing fraction and the depth of immersion. We find that the value of this force is strongly depending the packing fraction: for low packing fraction (phi
Is random close packing of beads well defined?
Energy flux of internal waves generated by tidal flow over topography beneath a turning depth
Integrated Modeling and Analysis of Physical Oceanographic and Acoustic Processes
Internal wave generation by tidal flow over topography in the deep ocean
Spatiotemporal patterns in reaction-diffusion systems
We have measured the trajectory and visualized the wake of a single sphere falling in a fluid con... more We have measured the trajectory and visualized the wake of a single sphere falling in a fluid confined between two closely spaced glass plates (a Hele-Shaw cell). The position of a sedimenting sphere was measured to better than 0.001d, where d is the sphere diameter, for Reynolds numbers (based on the terminal velocity) between 20 and 330, for gaps between the plates ranging from 1.014d to 1.4d. For gaps in the range 1.01d-1.05d, the behaviour of the sedimenting sphere is found to be qualitatively similar to that of an unconfined cylinder in a uniform flow, but our sedimenting sphere begins to oscillate and shed von Kármán vortices for Re > 200, which is far greater than the Re = 49 for the onset of vortex shedding behind cylinders in an open flow. When the gap is increased to 1.10d-1.40d, the vortices behind the sphere are different -they are qualitatively similar to those behind a sphere sedimenting in the absence of confining walls. Our precision measurements of the velocity of a sedimenting sphere and the amplitude and frequency of the oscillations provide a benchmark for numerical simulations of the sedimentation of particles in fluids.
Spectral linewidth of light quasi-elastically scattered from xenon along the coexistence curve near the critical point
Comment on «Self-similarity of dissusion-limited aggregates and electrodeposition clusters»(and reply)
A one-dimensional reaction-diffusion equation is used to model a class of experimental open chemi... more A one-dimensional reaction-diffusion equation is used to model a class of experimental open chemical systems in which spatiotemporal patterns can be sustained indefinitely. Numerical simulations for the model in parameter regimes corresponding to experiment reveal only low-dimensional behavior. The observed bifurcation sequence leads from steady state concentration profiles to temporally chaotic patterns. The physical mechanism that causes this behavior is deduced from analysis of the local dynamics: localized oscillators appear at each end of the reactor and one of the oscillators acts as a periodic forcing for the other. The numerical results are in good qualitative agreement with the experiments.
An invariant measure of disorder in patterns
Physical Review E, 1999
Under many conditions, macroscopic grains flow like a fluid; kinetic theory predicts continuum eq... more Under many conditions, macroscopic grains flow like a fluid; kinetic theory predicts continuum equations of motion for this granular fluid. In order to test the theory, we perform event driven molecular simulations of a two-dimensional gas of inelastic hard disks, driven by contact with a heat bath. Even for strong dissipation, high densities, and small numbers of particles, we find that continuum theory describes the system well. With a bath that heats the gas homogeneously, strong velocity correlations produce a slightly smaller energy loss due to inelastic collisions than that predicted by kinetic theory. With an inhomogeneous heat bath, thermal or velocity gradients are induced. Determination of the resulting fluxes allows calculation of the thermal conductivity and shear viscosity, which are compared to the predictions of granular kinetic theory, and which can be used in continuum modeling of granular flows. The shear viscosity is close to the prediction of kinetic theory, while the thermal conductivity can be overestimated by a factor of 2; in each case, transport is lowered with increasing inelasticity.
Reply to comment by McDougall and Barker on “Buoyancy frequency profiles and internal semidiurnal tide turning depths in the oceans”
Journal of Geophysical Research: Oceans, 2014
Physica D: Nonlinear Phenomena, 1991
We report observations of the tip motion of spiral waves in excitable Belousov-Zhabotinskii reage... more We report observations of the tip motion of spiral waves in excitable Belousov-Zhabotinskii reagent. An open reactor is used to determine the time-asymptotic dynamics of the spiral tip as a function of a control parameter. We have observed a supercritical transition from simple rotation (one frequency) to compound rotation (two frequencies); the compound motion at onset closely resembles that predicted by two-species reaction-diffusion models. Measurements of the frequencies of the motion indicate that the compound rotation is quasiperiodic over the range studied; there is no evidence of frequency locking. The compound tip motion appears to result from fluctuations in the curvature of the spiral wave near its tip. We describe qualitatively the sequence of events during a single tip orbit and suggest that the refractory tail of the wave plays a dominant role in controlling the tip motion.
Physical Review E, 1999
Recent work demonstrates the inevitable role of convection during the growth of patterns in thin-... more Recent work demonstrates the inevitable role of convection during the growth of patterns in thin-layer electrochemical deposition. Convection is driven mainly by Coulombic forces due to local charges and by buoyant forces due to concentration gradients that lead to density gradients. Here we study by theoretical and numerical modeling the limiting regimes under which electroconvection or gravitoconvection prevail. The model describes the diffusive, migratory, and convective motion of ions in a fluid subject to an electric field. The equations are written in terms of dimensionless quantities, in particular, the gravity Grashof and the electrical Grashof numbers. The simulations reveal that gravitoconvection becomes increasingly important as the gravity Grashof number increases, while electroconvection becomes increasingly important as the electrical Grashof number increases. For both regimes the model predicts concentration, electric potential, and velocity patterns that are in qualitative agreement with typical electrodeposition experiments. In gravitoconvection, the model predicts the evolution, before collision, of the convection rolls near each electrode growing first as t 4/5 and then slowing down to t 1/2 ; the same scaling behavior was observed in experiments. After collision, the cathodic and anodic rolls merge into a single roll. In electroconvection, the model predicts the existence of vortex pairs formed by the electrical force on space charge accumulating near the growing filament tip. Such vortex rolls and pairs have been observed in experiments.
Our experiments on a vertically oscillated granular layer reveal that spatial patterns emerge in ... more Our experiments on a vertically oscillated granular layer reveal that spatial patterns emerge in two stages following a change of parameter into the pattern-forming regime: an initial, domain-forming stage and a later stage in which domains coarsen to form ultimately an extended regular pattern. We characterize the evolution of the pattern using a "disorder function" (ÿ), where ÿ is a moment of the disorder operator (Gunaratne et al., Phys. Rev. E 57 (1998) 5146). The disorder in the initial stage is found to be consistent with a decay given by (ÿ) ∼ t −ÿ=2 , in accord with theory that predicts that behavior in this stage should be universal for pattern forming systems. The ÿnal stage is non-universal.
Shock Waves in Granular Media
Shock Wave Science and Technology Reference Library, 2007
ABSTRACT Shock waves form in air when a bullet or aircraft exceeds the speed of sound. In a granu... more ABSTRACT Shock waves form in air when a bullet or aircraft exceeds the speed of sound. In a granular medium, the sound speed is small (typically 10 cm/s), so shock waves form for ordinary rather than extreme conditions. Our group has examined oblique and normal shock waves in granular flow past a wedge(E.C. Rericha et al., Phys. Rev. Lett. 88, 025403 (2002).) and in vertically oscillated granular layers, (J. Bougie et al., Phys. Rev. E 66, 051301 (2002).) using laboratory experiments, molecular dynamics simulations, and simulations of continuum equations for granular flow. The flows we consider reach Mach numbers greater than ten, a regime that is difficult to study in gas flows. We find that the shocks formed in flows of particles in a vacuum exhibit properties similar to those of shocks in supersonic gases, but there are some differences that arise because of the inelastic collisions between particles in granular media. The molecular dynamics and continuum simulations are found to describe the observations well. Increasing the restitution coefficient toward unity (decreasing the dissipation toward zero) does not lead to any qualitative change in behavior.
Experimental observation of sedimentation trajectories of single spheres in Hele-Shaw cells
ABSTRACT
Preliminary results on the granular drag force
Temperature Change in Melting of an Oscillated Granular Layer
... Session KH: Granular Flows IV. 5:15 PM6:59 PM, Monday, November 20, 2006. Tampa Marriott Wat... more ... Session KH: Granular Flows IV. 5:15 PM6:59 PM, Monday, November 20, 2006. Tampa Marriott Waterside Hotel and Marina Room: Florida Salon 6 Chair: Richard M. Lueptow, Northwestern University Abstract ID: BAPS.2006.DFD.KH.3. ...
Measuring the phase diagram of granular media
ABSTRACT The jamming transition in granular media has been the subject of several studies in the ... more ABSTRACT The jamming transition in granular media has been the subject of several studies in the last years. However, an experimental observation of phase diagram of granular media in three dimensions is still lacking. The goal of this study is to obtain such a diagram as a function of the shear stress, the packing fraction, phi, and the pressure in a granular bed. Shear stress is obtained by measuring the force, F, needed to pull-up a paddle immersed in a granular bed as a function of its packing fraction and the depth of immersion. We find that the value of this force is strongly depending the packing fraction: for low packing fraction (phi
Is random close packing of beads well defined?
Energy flux of internal waves generated by tidal flow over topography beneath a turning depth
Integrated Modeling and Analysis of Physical Oceanographic and Acoustic Processes
Internal wave generation by tidal flow over topography in the deep ocean
Spatiotemporal patterns in reaction-diffusion systems
We have measured the trajectory and visualized the wake of a single sphere falling in a fluid con... more We have measured the trajectory and visualized the wake of a single sphere falling in a fluid confined between two closely spaced glass plates (a Hele-Shaw cell). The position of a sedimenting sphere was measured to better than 0.001d, where d is the sphere diameter, for Reynolds numbers (based on the terminal velocity) between 20 and 330, for gaps between the plates ranging from 1.014d to 1.4d. For gaps in the range 1.01d-1.05d, the behaviour of the sedimenting sphere is found to be qualitatively similar to that of an unconfined cylinder in a uniform flow, but our sedimenting sphere begins to oscillate and shed von Kármán vortices for Re > 200, which is far greater than the Re = 49 for the onset of vortex shedding behind cylinders in an open flow. When the gap is increased to 1.10d-1.40d, the vortices behind the sphere are different -they are qualitatively similar to those behind a sphere sedimenting in the absence of confining walls. Our precision measurements of the velocity of a sedimenting sphere and the amplitude and frequency of the oscillations provide a benchmark for numerical simulations of the sedimentation of particles in fluids.
Spectral linewidth of light quasi-elastically scattered from xenon along the coexistence curve near the critical point
Comment on «Self-similarity of dissusion-limited aggregates and electrodeposition clusters»(and reply)
A one-dimensional reaction-diffusion equation is used to model a class of experimental open chemi... more A one-dimensional reaction-diffusion equation is used to model a class of experimental open chemical systems in which spatiotemporal patterns can be sustained indefinitely. Numerical simulations for the model in parameter regimes corresponding to experiment reveal only low-dimensional behavior. The observed bifurcation sequence leads from steady state concentration profiles to temporally chaotic patterns. The physical mechanism that causes this behavior is deduced from analysis of the local dynamics: localized oscillators appear at each end of the reactor and one of the oscillators acts as a periodic forcing for the other. The numerical results are in good qualitative agreement with the experiments.
An invariant measure of disorder in patterns