A dilation-driven vortex flow in sheared granular materials explains a rheometric anomaly

Krishnaraj, K.; Nott, Prabhu R.

doi:10.1038/ncomms10630

Cited by 49 publications

(55 citation statements)

References 35 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…In flows such as simple shear, a density gradient is set up within the shear layers . The effect of dilatancy need not, however, be confined to the shear layers—we have recently shown in our group that dilatancy causes a large‐scale secondary flow in cylindrical Couette cells, thereby explaining a stress anomaly observed earlier . It is, therefore, of interest to study the distribution of

ϕ

in this problem.…”

Section: Resultsmentioning

confidence: 89%

“…To mimic the interaction of hard particles like glass beads, which are most commonly used in experiments, the normal and tangential spring stiffness coefficients,

k_{normaln}

and

k_{normalt}

are chosen as

10^{6} m_{normalp} g / d_{normalp}

and

\frac{2}{7} k_{normaln}

, respectively, where

m_{normalp}

is the mass of a particle of diameter

d_{normalp}

, and g is the acceleration due to gravity. The values of the damping coefficients chosen as are

{normalγ}_{normaln} = 180 \sqrt{g / d_{normalp}}, {normalγ}_{normalt} ​ = ​ 1 / 2 {normalγ}_{normaln}

, and the friction coefficient as

μ = 0.5

, which is in the range of typical values for glass beads .…”

Section: Simulation Methods and System Geometrymentioning

confidence: 99%

“…Here

d_{normalp}

denotes a nominal particle diameter. Polydispersity in the particle‐size reduces the formation of a crystalline structure, thereby resembling an experimentally realizable system . The cylindrical and bottom surfaces of the rotating container are roughened by coating them with rigid spheres of diameter 0.5

d_{normalp}

in a triangular close packed array.…”

Section: Simulation Methods and System Geometrymentioning

confidence: 99%

See 2 more Smart Citations

The lift on a disc immersed in a rotating granular bed

2017

Self Cite

View full text Add to dashboard Cite

The discrete element method has been used to study the lift F L on a stationary disc immersed coaxially in a slowly rotating cylinder containing a granular material. In a tall granular column, F L rises with the immersion depth h, but reaches a roughly constant asymptote at large h, in agreement with previous studies. Our results indicate that the argument in some earlier studies that F L is proportional to the static stress gradient is incorrect. Instead, our results show that the lift is caused by an asymmetry in the dilation and shear rate between the regions above and below the disc. We argue that the cause of the lift is similar to that in fluids, namely that it arises as a result of the disturbance in the velocity and density fields around the body due to its motion relative to the granular bed.Positive and negative values of ðz2hÞ correspond to the regions below and above the disc, respectively. Here the data of (a) and (b) correspond to H562 d p and H5222 d p , respectively, for a disc of thickness t510 d p and different depths of immersionh. Panel (c) shows the difference in the solids fraction (averaged in the same manner) between the lower and upper surfaces of the disc; the blue triangles and red asterisks are data for the short and tall columns, respectively. [Color figure can be viewed at wileyonlinelibrary.com] AIChE Journal

show abstract

ϕ

in this problem.…”

Section: Resultsmentioning

confidence: 89%

“…To mimic the interaction of hard particles like glass beads, which are most commonly used in experiments, the normal and tangential spring stiffness coefficients,

k_{normaln}

and

k_{normalt}

are chosen as

10^{6} m_{normalp} g / d_{normalp}

and

\frac{2}{7} k_{normaln}

, respectively, where

m_{normalp}

is the mass of a particle of diameter

d_{normalp}

, and g is the acceleration due to gravity. The values of the damping coefficients chosen as are

{normalγ}_{normaln} = 180 \sqrt{g / d_{normalp}}, {normalγ}_{normalt} ​ = ​ 1 / 2 {normalγ}_{normaln}

, and the friction coefficient as

μ = 0.5

, which is in the range of typical values for glass beads .…”

Section: Simulation Methods and System Geometrymentioning

confidence: 99%

“…Here

d_{normalp}

d_{normalp}

in a triangular close packed array.…”

Section: Simulation Methods and System Geometrymentioning

confidence: 99%

See 1 more Smart Citation

The lift on a disc immersed in a rotating granular bed

2017

Self Cite

View full text Add to dashboard Cite

show abstract

“…While being generally well-posed, the compressible µ(I)-rheology was also shown to be unstable for some flow conditions, both at large and small inertial number, calling for a deeper analysis of the unstable modes appearing in compressible flows. Indeed, secondary flows and resonances of dense inertial granular flows may originate from such instabilities (Börzsönyi et al 2009;Trulsson et al 2013;Brodu et al 2015;Krishnaraj & Nott 2016). Although the asymptotic analysis at large wavenumbers provides precious information on the good behaviour of the problem, it is not sufficient to probe the general linear stability picture of the flow, neither its asymptotic stability at long times.…”

Section: Resultsmentioning

confidence: 99%

Compressibility regularizes the 𝜇(I)-rheology for dense granular flows

et al. 2017

View full text Add to dashboard Cite

The µ(I)-rheology was recently proposed as a potential candidate to model the incompressible flow of frictional grains in the dense inertial regime. However, this rheology was shown to be ill-posed in the mathematical sense for a large range of parameters, notably in the low and large inertial number limits (Barker et al. 2015). In this rapid communication, we extend the stability analysis of Barker et al. (2015) to compressible flows. We show that compressibility regularizes mostly the equations, making the problem well-posed for all parameters, with the condition that sufficient dissipation be associated with volume changes. In addition to the usual Coulomb shear friction coefficient µ, we introduce a bulk friction coefficient µ b , associated with volume changes and show that the problem is well-posed if µ b > 1 − 7µ/6. Moreover, we show that the ill-posed domain defined by Barker et al. (2015) transforms into a domain where the flow is unstable but remains well-posed when compressibility is taken into account. These results suggest the importance of taking into account dynamic compressibility for the modelling of dense granular flows and open new perspectives to investigate the emission and propagation of acoustic waves inside these flows.

show abstract

“…Most previously employed heat equations for calculating temperature rise during earthquakes have assumed that heat diffuses away from the faults merely by conduction (Fialko & Khazan, 2005;Lachenbruch, 1980;Tanaka et al, 2006). However, research in granular physics reveals that sheared granular materials develop transient granular vortices (Combe et al, 2015;Krishnaraj & Nott, 2016;Miller et al, 2013;Radjai & Roux, 2002), which can significantly boost heat transfer across shear layers through solid particle mixing (Rognon & Einav, 2010). The implications of this novel granular convective mechanism of heat transfer in earthquake physics remain unexplored, though previous observations have highlighted its relevance (Rognon & Einav, 2010).…”

Section: Introductionmentioning

confidence: 99%

Faults Get Colder Through Transient Granular Vortices

Einav

Rognon

Miller

et al. 2018

Geophysical Research Letters

View full text Add to dashboard Cite

Fault temperatures govern their weakening and control the dynamics of earthquakes during slip. Despite predictions of significant temperature rise within fault gouges during earthquake events, observations of frictional melting zones along exhumed faults are relatively rare. Could there be a heat transfer mechanism, previously not considered, that results in ubiquitously colder faults during earthquakes? We demonstrate that the remarkable, previously neglected mechanism of heat transfer through transient granular vortices may be at the core of this. We present and analyze results from perpetual simple shear experiments on a system of granular disks with which we are able to quantify the sizes and lifetimes of granular vortices within fault gouges during earthquakes. We then develop a formula that captures the contribution these vortices have on heat transfer. Using this formula, we show that crustal faults such as those in the San Andreas system may experience a maximum temperature rise 5 to 10 times lower than previously thought.

show abstract

A dilation-driven vortex flow in sheared granular materials explains a rheometric anomaly

Cited by 49 publications

References 35 publications

The lift on a disc immersed in a rotating granular bed

The lift on a disc immersed in a rotating granular bed

Compressibility regularizes the 𝜇(I)-rheology for dense granular flows

Faults Get Colder Through Transient Granular Vortices

Contact Info

Product

Resources

About