Abstract:The jamming transition in granular materials is well-known to exhibit hysteresis, wherein the level of shear stress required to trigger flow is larger than that below which flow stops. Although...
“…The extraction of solid-liquid friction coefficients is, however, very sensitive to mechanical noise and preparation effects, as the decreasing dependence of friction at low inertial numbers is a large source of instability, which can prevent access to the true I = 0 limit in free-surface geometries. We should also mention that the solid-liquid transition is strongly affected by non-local effects, as mechanical interactions at the grain scale are precisely responsible for nucleation or strengthening effects (Kamrin 2019;Perrin et al 2021), and improving our non-smooth numerical model to account for a non-local rheology would definitely provide additional insights into the role of spatial inhomogeneities in transient flows (Mowlavi & Kamrin 2021).…”
Section: Discussionmentioning
confidence: 99%
“…We should also mention that the solid–liquid transition is strongly affected by non-local effects, as mechanical interactions at the grain scale are precisely responsible for nucleation or strengthening effects (Kamrin 2019; Perrin et al. 2021), and improving our non-smooth numerical model to account for a non-local rheology would definitely provide additional insights into the role of spatial inhomogeneities in transient flows (Mowlavi & Kamrin 2021).…”
In this paper, transient granular flows are examined both numerically and experimentally. Simulations are performed using the continuous three-dimensional (3-D) granular model introduced in Daviet & Bertails-Descoubes (ACM Trans. Graph., vol. 35, no. 4, 2016b, p. 102), which represents the granular medium as an inelastic and dilatable continuum subject to the Drucker–Prager yield criterion in the dense regime. One notable feature of this numerical model is to resolve such a non-smooth rheology without any regularisation. We show that this non-smooth model, which relies on a constant friction coefficient, is able to reproduce with high fidelity various experimental granular collapses over inclined erodible beds, provided the friction coefficient is set to the avalanche angle – and not to the stop angle, as generally done. In order to better characterise the range of validity of the fully plastic rheology in the context of transient frictional flows, we further revisit scaling laws relating the shape of the final collapse deposit to the initial column aspect ratio, and accurately recover established power-law dependences up to aspect ratios of the order of 10. The influence of sidewall friction is then examined through experimental and simulated collapses with varying channel widths. The analysis offers a comprehensive framework for estimating the effective flow thickness in relation to the channel width, thereby challenging previously held assumptions regarding its estimation in the literature. Finally, we discuss the possibility to extend the constant coefficient model with a hysteretic model in order to refine the predictions of the early-stage dynamics of the collapse. This illustrates the potential effects of such phenomenology on transient flows, paving the way to more elaborate analysis.
“…The extraction of solid-liquid friction coefficients is, however, very sensitive to mechanical noise and preparation effects, as the decreasing dependence of friction at low inertial numbers is a large source of instability, which can prevent access to the true I = 0 limit in free-surface geometries. We should also mention that the solid-liquid transition is strongly affected by non-local effects, as mechanical interactions at the grain scale are precisely responsible for nucleation or strengthening effects (Kamrin 2019;Perrin et al 2021), and improving our non-smooth numerical model to account for a non-local rheology would definitely provide additional insights into the role of spatial inhomogeneities in transient flows (Mowlavi & Kamrin 2021).…”
Section: Discussionmentioning
confidence: 99%
“…We should also mention that the solid–liquid transition is strongly affected by non-local effects, as mechanical interactions at the grain scale are precisely responsible for nucleation or strengthening effects (Kamrin 2019; Perrin et al. 2021), and improving our non-smooth numerical model to account for a non-local rheology would definitely provide additional insights into the role of spatial inhomogeneities in transient flows (Mowlavi & Kamrin 2021).…”
In this paper, transient granular flows are examined both numerically and experimentally. Simulations are performed using the continuous three-dimensional (3-D) granular model introduced in Daviet & Bertails-Descoubes (ACM Trans. Graph., vol. 35, no. 4, 2016b, p. 102), which represents the granular medium as an inelastic and dilatable continuum subject to the Drucker–Prager yield criterion in the dense regime. One notable feature of this numerical model is to resolve such a non-smooth rheology without any regularisation. We show that this non-smooth model, which relies on a constant friction coefficient, is able to reproduce with high fidelity various experimental granular collapses over inclined erodible beds, provided the friction coefficient is set to the avalanche angle – and not to the stop angle, as generally done. In order to better characterise the range of validity of the fully plastic rheology in the context of transient frictional flows, we further revisit scaling laws relating the shape of the final collapse deposit to the initial column aspect ratio, and accurately recover established power-law dependences up to aspect ratios of the order of 10. The influence of sidewall friction is then examined through experimental and simulated collapses with varying channel widths. The analysis offers a comprehensive framework for estimating the effective flow thickness in relation to the channel width, thereby challenging previously held assumptions regarding its estimation in the literature. Finally, we discuss the possibility to extend the constant coefficient model with a hysteretic model in order to refine the predictions of the early-stage dynamics of the collapse. This illustrates the potential effects of such phenomenology on transient flows, paving the way to more elaborate analysis.
“…Moreover, the NGF model has analytical velocity field solutions in the limiting cases of and , which we can also use to check the code. Recall that the present formulation of NGF in our model does not include hysteresis, so is the same as in what follows; Mowlavi & Kamrin (2021) has explored incorporating hysteresis and non-local effects into a unified model. Figure 2.Comparing numerical solutions with analytical NGF solutions in the inclined chute.…”
Granular flow in a silo demonstrates multiple non-local rheological phenomena due to the finite size of grains. We solve the non-local granular fluidity continuum model in quasi-two-dimensional silo geometries and evaluate its ability to predict these non-local effects, including flow spreading and, importantly, clogging (arrest) when the opening is small enough. The model is augmented to include a free-separation criterion and is implemented numerically with an extension of the trans-phase granular flow solver described in Dunatunga & Kamrin (J. Fluid Mech., vol. 779, 2015, pp. 483–513), to produce full-field solutions. The implementation is validated against analytical results of the model in the inclined chute geometry, such as the solution for the critical thickness for flow arrest, and the velocity profile as a function of layer height. We then implement the model in the silo geometry and vary the apparent grain size. The model predicts a clogging criterion when the opening competes with the scale of the mean grain size, which agrees with previous experimental studies. For larger openings, the flow within the silo obtains a diffusive characteristic whose spread depends on the model's non-local amplitude and the mean grain size. The numerical tests are controlled for grid effects and a comparison study of coarse vs refined numerical simulations shows agreement in the pressure field, the shape of the arch in a clogged silo configuration and the velocity field in a flowing configuration.
“…2013, 2015; Kamrin & Henann 2015). In particular, Mowlavi & Kamrin (2021) have recently captured both the , phenomenology in one-dimensional time-dependent simulations with a non-local model that includes hysteresis. Applying such models in three dimensions to capture self-channelization and levee formation remains, however, a significant challenge for the future.…”
Section: Introductionmentioning
confidence: 99%
“…An alternative approach (to the depth-averaged one used in this paper) is therefore to use one of the non-local models for granular flow (Pouliquen & Forterre 2009;Kamrin & Koval 2012;Bouzid et al 2013Bouzid et al , 2015Kamrin & Henann 2015). In particular, Mowlavi & Kamrin (2021) have recently captured both the h stop , h start phenomenology in one-dimensional time-dependent simulations with a non-local model that includes hysteresis. Applying such models in three dimensions to capture self-channelization and levee formation remains, however, a significant challenge for the future.…”
Geophysical mass flows such as debris flows, dense pyroclastic flows and snow avalanches can self-channelize on shallow slopes. The confinement afforded by formed levees helps to maintain the flow depth, and hence mobility, allowing self-channelized flows to run out significantly farther than unconfined, spreading flows. Levee formation and self-channelization are strongly associated with particle-size segregation, but can also occur in monodisperse flows. This paper uses the monodisperse depth-averaged theory of Rocha et al. (J. Fluid Mech., vol. 876, 2019, pp. 591–641), which incorporates a hysteretic friction law and second-order depth-averaged viscous terms. Both of these are vital for the formation of a travelling wave that progressively deposits a pair of levees just behind the front. The three-dimensional velocity field is reconstructed in a frame moving with the front assuming Bagnold flow. This enables a bidisperse particle-size segregation theory to be used to solve for the large and small particle concentrations and particle paths in three-dimensions, for the first time. The model shows that the large particles tend to segregate to the surface of the flow, forming a carapace that extends over the centre of the channel, as well as along the external sides and base of the levee walls. The small particles segregate downwards, and are concentrated in the main channel and in the inner levee walls. This supports the contention that a low-friction channel lining provides a secondary mechanism for run-out enhancement. It is also shown that the entire theory scales with particle diameter, so experiments with millimetre-sized particles provide important insights into geophysical-scale flows with boulders and smaller rock fragments. The model shows that self-channelization does not need particle-size segregation to occur, but supports the hypothesis that particle-size segregation and the associated frictional feedback can significantly enhance both the flow mobility and the levee strength.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
