Granular convection driven by shearing inertial forces

Rodríguez-Liñán, Gustavo M.; Nahmad-Molinari, Yuri

doi:10.1103/physreve.73.011302

Cited by 9 publications

(4 citation statements)

References 21 publications

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“…(18)], critical V is equivalent to critical S and is also similar to our high-frequency limit. On the other hand, there have been experiments [29] at St ∼ 420 which showed a suppression of granular motions at frequencies <12 Hz, which may be similar to our lowfrequency limit. However, all of these experiments are at St 1, which differs from the St of our experiments.…”

Section: E Comparison With Previous Experimentssupporting

confidence: 87%

Effect of viscosity on the shaking-induced fluidization in a liquid-immersed granular medium

Yasuda

Sumita

2016

Phys. Rev. E

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A liquid-immersed granular medium is shaken vertically under a wide range of accelerations (Γ in dimensionless form) and frequencies (f) and its fluidization process is studied. The granular medium is formed by settling and consists of two size-graded layers (particle diameter d) such that the upper layer is fine grained and is less permeable. When Γ>Γ(c), a liquid-rich layer formed by the accumulated liquid at the two-layer boundary causes a gravitational instability. The upwellings of the instability are separated horizontally by a distance (wavelength) λ, and their amplitude grows exponentially with time [∝exp(pt)] at a growth rate p. We conduct experiments for two liquid viscosity cases such that the particle settling velocity (V(s)) of the same particle differs by a factor of 17. We find that for both cases, Γ(c) is at a minimum in an optimum frequency band centered at f∼100 Hz. However, the high-viscosity (HV) case has a smaller Γ(c), a shorter λ, and a faster dimensionless growth rate [p'=p/(V(s)/d)]. We also measure granular rheology under an oscillatory shear and find that (i) interparticle friction decreases when the strain amplitude becomes large and (ii) friction is smaller for the HV case. From (i), we infer that the shear strain of the shaking experiments becomes largest at around f∼100 Hz. We consider that (ii) is a consequence of liquid lubrication and is a reason for a smaller Γ(c) for the HV case. We show that the low- and high-frequency limits of the optimum frequency band can be explained by introducing critical values of dimensionless jerk (i.e., time derivative of acceleration) J and dimensionless shaking energy S. The low-frequency limit corresponds to the requirement that in order to unjam the particles, the period of shaking (1/f) must be shorter than the time needed for the particles to rearrange by settling (d/V(s)), which also explains why the HV case is fluidized at a lower f compared to the LV case. We apply the results of the linear stability analyses for Rayleigh-Taylor instability. Using the measured λ and p, we infer that (i) only a thin layer beneath the two-layer boundary is mobile and the rest of the lower layer remains jammed and (ii) the effective viscosity of the upper granular layer relative to the liquid is smaller for the HV case as a result of smaller friction.

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Section: E Comparison With Previous Experimentssupporting

confidence: 87%

Effect of viscosity on the shaking-induced fluidization in a liquid-immersed granular medium

Yasuda

Sumita

2016

Phys. Rev. E

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“…Available data for the convection velocity at the walls, which show an exponent in Eq. 1 between 1 and 2 [6,11], cannot directly be compared to our data as Hejmady et al [9] showed that the exponent for the near-wall velocity is close to unity, while the rise velocity (as derived from their rise times) possesses a much steeper dependence on excitation acceleration.…”

mentioning

confidence: 67%

“…With this mechanism, a collective motion of the medium can transport larger particles to the top, which come to rest there if the downward flow zone is too small to be entered by these particles. This effect has been studied experimentally [2][3][4][5][6][7][8][9][10][11] and theoretically [12][13][14][15], while the focus of the article at hand is on the extrapolation of the Brazil nut problem to reduced gravity conditions found on small Solar System bodies. The Brazil nut effect has been, for example, made responsible for observed surface structures on small asteroids [16,17].…”

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confidence: 99%

Granular convection and the Brazil nut effect in reduced gravity

et al. 2013

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We present laboratory experiments of a vertically vibrated granular medium consisting of 1-mm-diameter glass beads with embedded 8-mm-diameter intruder glass beads. The experiments were performed in the laboratory as well as in a parabolic flight under reduced-gravity conditions (on Martian and Lunar gravity levels). We measured the mean rise velocity of the large glass beads and present its dependence on the fill height of the sample containers, the excitation acceleration, and the ambient gravity level. We find that the rise velocity scales in the same manner for all three gravity regimes and roughly linearly with gravity.

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“…This secondary flow is considered key for important practical processes such as segregation [5]. The wealth of experimental evidence demonstrating that convective flows can occur in a granular material [e.g., [6][7][8][9] has led to significant theoretical effort, with a number of proposed mechanisms for granular convection [e.g., 6,[10][11][12][13].…”

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confidence: 99%

Granular Convection in Microgravity

et al. 2013

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We investigate the role of gravity on convection in a dense granular shear flow. Using a microgravity-modified Taylor-Couette shear cell under the conditions of parabolic flight microgravity, we demonstrate experimentally that secondary, convective-like flows in a sheared granular material are close to zero in microgravity and enhanced under high-gravity conditions, though the primary flow fields are unaffected by gravity. We suggest that gravity tunes the frictional particle-particle and particle-wall interactions, which have been proposed to drive the secondary flow. In addition, the degree of plastic deformation increases with increasing gravitational forces, supporting the notion that friction is the ultimate cause.

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Granular convection driven by shearing inertial forces

Cited by 9 publications

References 21 publications

Effect of viscosity on the shaking-induced fluidization in a liquid-immersed granular medium

Effect of viscosity on the shaking-induced fluidization in a liquid-immersed granular medium

Granular convection and the Brazil nut effect in reduced gravity

Granular Convection in Microgravity

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