A Weakening Rheology of Dry Granular Flows With Extensive Brittle Grain Damage in High‐Speed Rotary Shear Experiments

2020 ◽  
Vol 47 (11) ◽  
Author(s):  
Wei Hu ◽  
Ching Shung Chang ◽  
Mauri McSaveney ◽  
Runqiu Huang ◽  
Qiang Xu ◽  
...  
Keyword(s):  
High Speed ◽  
Granular Flows ◽  
Rotary Shear ◽  
Grain Damage

Velocity and Volume Fraction Measurements of Granular Flows in a Steep Flume

2021 ◽  
Author(s):  
Luca Sarno ◽  
Maria Nicolina Papa ◽  
Luigi Carleo ◽  
Paolo Villani
Keyword(s):  
High Speed ◽  
Volume Fraction ◽  
Solid Volume Fraction ◽  
Granular Flows ◽  
Indirect Measurement ◽  
Measuring Instruments ◽  
Second Order Statistics ◽  
Granular Dynamics ◽  
Image Velocimetry ◽  
Near Wall

ABSTRACT Laboratory experiments on granular flows remain essential tools for gaining insight into several aspects of granular dynamics that are inaccessible from field-scale investigations. Here, we report an experimental campaign on steady dry granular flows in a flume with inclination of 35°. Different flow rates are investigated by adjusting an inflow gate, while various kinematic boundary conditions are observed by varying the basal roughness. The flume is instrumented with high-speed cameras and a no-flicker LED lamp to get reliable particle image velocimetry measurements in terms of both time averages and second-order statistics (i.e., granular temperature). The same measuring instruments are also used to obtain concurrent estimations of the solid volume fraction at the sidewall by employing the stochastic-optical method (SOM). This innovative approach uses a measurable quantity, called two-dimensional volume fraction, which is correlated with the near-wall volume fraction and is obtainable from digital images under controlled illumination conditions. The knowledge of this quantity allows the indirect measurement of the near-wall volume fraction thanks to a stochastic transfer function previously obtained from numerical simulations of distributions of randomly dispersed spheres. The combined measurements of velocity and volume fraction allow a better understanding of the flow dynamics and reveal the superposition of different flow regimes along the flow depth, where frictional and collisional mechanisms exhibit varying relative magnitudes.

scholarly journals High speed confined granular flows down inclined: numerical simulations

2017 ◽  
Vol 140 ◽  
pp. 03081 ◽  
Author(s):  
Velotiana Jean-Luc Ralaiarisoa ◽  
Alexandre Valance ◽  
Nicolas Brodu ◽  
Renaud Delannay
Keyword(s):  
Numerical Simulations ◽  
High Speed ◽  
Granular Flows

The Granular Lubricated Journal Bearing: Evidence of Lift Formation

2019 ◽  
Vol 141 (4) ◽  
Author(s):  
Venkata K. Jasti ◽  
Martin C. Marinack ◽  
Deepak Patil ◽  
C. Fred Higgs
Keyword(s):  
Carrying Capacity ◽  
Granular Flow ◽  
High Speed ◽  
Journal Bearing ◽  
Hydrodynamic Lubrication ◽  
Flow Behavior ◽  
Extreme Environments ◽  
Granular Flows ◽  
Load Carrying Capacity ◽  
Load Carrying

This work demonstrates that granular flows (i.e., macroscale, noncohesive spheres) entrained into an eccentrically converging gap can indeed actually exhibit lubrication behavior as prior models postulated. The physics of hydrodynamic lubrication is quite well understood and liquid lubricants perform well for conventional applications. Unfortunately, in certain cases such as high-speed and high-temperature environments, liquid lubricants break down making it impossible to establish a stable liquid film. Therefore, it has been previously proposed that granular media in sliding convergent interfaces can generate load carrying capacity, and thus, granular flow lubrication. It is a possible alternative lubrication mechanism that researchers have been exploring for extreme environments, or wheel-regolith traction, or for elucidating the spreadability of additive manufacturing materials. While the load carrying capacity of granular flows has been previously demonstrated, this work attempts to more directly uncover the hydrodynamic-like granular flow behavior in an experimental journal bearing configuration. An enlarged granular lubricated journal bearing (GLJB) setup has been developed and demonstrated. The setup was made transparent in order to visualize and video capture the granular collision activity at high resolution. In addition, a computational image processing program has been developed to process the resulting images and to noninvasively track the “lift” generated by granular flow during the journal bearing operation. The results of the lift caused by granular flow as a function of journal rotation rate are presented as well.

scholarly journals Experimental investigation of high speed granular flows down inclines

2017 ◽  
Vol 140 ◽  
pp. 03057 ◽  
Author(s):  
Joris Heyman ◽  
Philippe Boltenhagen ◽  
Renaud Delannay ◽  
Alexandre Valance
Keyword(s):  
Experimental Investigation ◽  
High Speed ◽  
Granular Flows

scholarly journals Partial regularisation of the incompressible 𝜇(I)-rheology for granular flow

2017 ◽  
Vol 828 ◽  
pp. 5-32 ◽  
Author(s):  
T. Barker ◽  
J. M. N. T. Gray
Keyword(s):  
High Speed ◽  
Numerical Solutions ◽  
Stokes Equations ◽  
Functional Dependence ◽  
Granular Flows ◽  
Two Dimensions ◽  
Navier Stokes ◽  
Major Step ◽  
Ill Posed ◽  
Well Posed

In recent years considerable progress has been made in the continuum modelling of granular flows, in particular the $\unicode[STIX]{x1D707}(I)$-rheology, which links the local viscosity in a flow to the strain rate and pressure through the non-dimensional inertial number $I$. This formulation greatly benefits from its similarity to the incompressible Navier–Stokes equations as it allows many existing numerical methods to be used. Unfortunately, this system of equations is ill posed when the inertial number is too high or too low. The consequence of ill posedness is that the growth rate of small perturbations tends to infinity in the high wavenumber limit. Due to this, numerical solutions are grid dependent and cannot be taken as being physically realistic. In this paper changes to the functional form of the $\unicode[STIX]{x1D707}(I)$ curve are considered, in order to maximise the range of well-posed inertial numbers, while preserving the overall structure of the equations. It is found that when the inertial number is low there exist curves for which the equations are guaranteed to be well posed. However when the inertial number is very large the equations are found to be ill posed regardless of the functional dependence of $\unicode[STIX]{x1D707}$ on $I$. A new $\unicode[STIX]{x1D707}(I)$ curve, which is inspired by the analysis of the governing equations and by experimental data, is proposed here. In order to test this regularised rheology, transient granular flows on inclined planes are studied. It is found that simulations of flows, which show signs of ill posedness with unregularised models, are numerically stable and match key experimental observations when the regularised model is used. This paper details two-dimensional transient computations of decelerating flows where the inertial number tends to zero, high-speed flows that have large inertial numbers, and flows which develop into granular rollwaves. This is the first time that granular rollwaves have been simulated in two dimensions, which represents a major step towards the simulation of other complex granular flows.

scholarly journals Experimental Investigation on the Impact Dynamics of Saturated Granular Flows on Rigid Barriers

2021 ◽  
Vol 27 (1) ◽  
pp. 127-138
Author(s):  
Nicoletta Sanvitale ◽  
Elisabeth Bowman ◽  
Miguel Angel Cabrera
Keyword(s):  
Particle Size ◽  
High Speed ◽  
Impact Load ◽  
Granular Flows ◽  
Normal Pressure ◽  
Impact Behavior ◽  
Small Scale ◽  
Rigid Barrier ◽  
Fluid Saturation ◽  
The Impact

ABSTRACT Debris flows involve the high-speed downslope motion of rocks, soil, and water. Their high flow velocity and high potential for impact loading make them one of the most hazardous types of gravitational mass flows. This study focused on the roles of particle size grading and degree of fluid saturation on impact behavior of fluid-saturated granular flows on a model rigid barrier in a small-scale flume. The use of a transparent debris-flow model and plane laser-induced fluorescence allowed the motion of particles and fluid within the medium to be examined and tracked using image processing. In this study, experiments were conducted on flows consisting of two uniform and one well-graded particle size gradings at three different fluid contents. The evolution of the velocity profiles, impact load, bed normal pressure, and fluid pore pressure for the different flows were measured and analyzed in order to gain a quantitative comparison of their behavior before, during, and after impact.

Longitudinal Ridges in Long Runout Landslides: on the Applicability of High-Speed Granular Flow Mechanisms.

2021 ◽  
Author(s):  
Giulia Magnarini ◽  
Thomas Mitchell ◽  
Peter Grindrod ◽  
Liran Goren
Keyword(s):  
Granular Flow ◽  
High Speed ◽  
Tensile Deformation ◽  
Granular Flows ◽  
Friction Material ◽  
Fault Mechanics ◽  
The Moon ◽  
Mechanical Instability ◽  
Long Runout ◽  
Erosion Rates

<p>Long runout landslides are a particular type of mass-wasting phenomena that belongs to the category of surface processes associated with rapid strain rates. The reduction of friction that has to be invoked to explain their high velocities and exceptional travel distance over nearly horizontal surfaces has yet to find satisfactory explanation. Inspired by fault mechanics studies, thermally-activated mechanisms can explain the dynamic frictional strength loss during sliding along the initial failure surface and the early development of velocities higher than expected. However, as slides continue moving along nearly horizontal valley floors, the weakening mechanisms required to sustain their exceptional behaviour are less certain.</p><p>Long runout landslides are found ubiquitous in our solar system and the slow erosion rates that operate on extraterrestrial planetary bodies allow the preservation of their geomorphological record. The availability of the latest high-resolution imagery of the surface of Mars and the Moon allows to conduct detailed morphometric analysis not so granted on our planet. On the other hand, on Earth, the partial loss of the geomorphological record due to fast erosion rates is compensated by the accessibility of sites that enable us to conduct field work. In order to better understand the mechanisms responsible for the apparent friction weakening we use a comparative planetary geology approach, in the attempt to link the morphology and the internal structures of long runout landslide deposits to the mechanisms involved during the emplacement of such catastrophic events.</p><p>We focused on the distinctive longitudinal ridges that mark the surface of the landslide deposits. The formation mechanism of longitudinal ridges in long runout landslides has been proposed to require ice, as this low friction material would allow the spreading of the deposit, causing the development of longitudinal ridges by tensile deformation of the slide. However, ice-free laboratory experiments on rapid granular flows have demonstrated that longitudinal ridges can form as a consequence of helicoidal cells that generate from a mechanical instability, which onset requires a rough surface and a velocity threshold to be surpassed. Moreover, such experiments have showed that the wavelength of the longitudinal ridges is always 2 to 3 times the thickness of the flow.</p><p>We here present the results from three case studies: the 63-km-long Coprates Labe landslide in Valles Marineris on Mars; the 4-km-long El Magnifico landslide in Chile, Earth; and the 50-km-long Tsiolkovskiy crater landslide, at the far side of the Moon. We found that the wavelength of the longitudinal ridges is consistently 2 to 3 times the thickness of the landslide deposit, in agreement with experimental work on rapid granular flows. The recurrence of such scaling relationship suggests a scale- and environment-independent mechanism. We discuss the applicability of high-speed granular flow convection-style mechanisms to long runout landslides and speculate on the existence of an alternative vibration-assisted mechanism.</p>

Failure mechanism of two-dimensional granular columns: Numerical simulation and experiments

2015 ◽  
Vol 37 (4) ◽  
pp. 239-250
Author(s):  
Nguyen Tien Cuong ◽  
Bui Hong Ha ◽  
Ryoichi Fukagawa
Keyword(s):  
Numerical Model ◽  
High Speed ◽  
Soil Mechanics ◽  
Granular Flows ◽  
Destruction Process ◽  
Sph Method ◽  
Deformation Problem ◽  
Particle Hydrodynamics ◽  
Calculation Results ◽  
Granular Column

In this article, two typical experiments for two types of destruction of granular column were performed by 2D soil model. High speed camera was used to record the movements of the destruction of the granular column. The images clearly showed the whole development of granular flows. The destruction process of the granular column in the two experiments is a big deformation problem of soil mechanics. To simulate the destruction process of the granular column, a model solving the problem of soil mechanics by Smoothed Particle Hydrodynamics (SPH) method was developed. The basic equations of problems of soil mechanics using the Drucker-Prager constitutive model were discretized using SPH method. The calculation results of the numerical model developed by us were compared with the experiment results obtained at the same time since the destruction of the granular column started. This was the first time by comparing and analyzing in details the characteristics of the process of destruction and developments of granular flows for the two typical types of destruction of granular column, it was shown that the numerical model describes quite accurately the characteristics of granular flows in both space and~time.

scholarly journals High-speed confined granular flows down smooth inclines: scaling and wall friction laws

2020 ◽  
Vol 22 (4) ◽  
Author(s):  
Yajuan Zhu ◽  
Renaud Delannay ◽  
Alexandre Valance
Keyword(s):  
High Speed ◽  
Granular Flows ◽  
Wall Friction ◽  
Friction Laws
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