Effects of obstacle's curvature on shock dynamics of gravity-driven granular flows impacting a circular cylinder

2021 ◽  
Vol 293 ◽  
pp. 106343
Author(s):  
Zheng Chen ◽  
Dieter Rickenmann ◽  
Yi Zhang ◽  
Siming He
Keyword(s):  
Circular Cylinder ◽  
Granular Flows ◽  
Shock Dynamics ◽  
Gravity Driven

Effects of Obstacle’s Curvature on Shock Waves in Gravity-Driven Experimental Flows Impacting a Circular Cylinder or a Wall

2020 ◽  
Author(s):  
Zheng Chen ◽  
Siming He ◽  
Dieter Rickenmann
Keyword(s):  
Shock Wave ◽  
Circular Cylinder ◽  
Pressure Sensors ◽  
Granular Flows ◽  
Impact Pressure ◽  
Small Scale ◽  
Cylinder Surface ◽  
Seismic Signals ◽  
Dynamic Impact ◽  
The Impact

<p>Geophysical granular flows such as rock and snow avalanches, flow-like landslides, debris flows, and pyroclastic flows are driven by gravity and often impact on engineering structures located in gullies and slopes as they flow down, generating dynamic impact pressures and causing a major threat to infrastructures. It is necessary to understand the physical mechanism of such granular flows impacting obstacles to improve the design of protective structures and the hazard assessment related to such structures. In this study, the small-scale laboratory experiments were performed to investigate the dynamic impact caused by granular flow around a circular cylinder with variable radius of curvatures and the dynamic impact against a flat wall. Pressure sensors were used to measure the impact pressure of granular flows at both the upstream cylinder surface and at the bottom of the channel. Accelerometers were mounted on the underside of channel to record the seismic signals generated by the granular flows before and during the impact with the obstacle. Flow velocities and flow depths were determined by using high-precision cameras. The results show that a bow shock wave is generated upstream of the cylinder, causing dynamic pressures on both the obstacle and the bottom of the channel. The dimensionless standoff distance of the granular shock wave decreases nonlinearly or almost exponentially with increasing Froude number (Fr) in the range of 5.5 to 11.0. The dimensionless pinch-off distance and dimensionless run-up height grow linearly with increasing Fr, and they were significantly influenced by the radius of curvature of the structure at the stagnation point (RCSSP). The dimensionless impact pressure on the structure surface is sensitive to the RCSSP, while the differences decrease as Fr increases; Seismic signals generated at the underside of the channel and at the top of the cylinder were also recorded to assist in analyzing the effects of RCSSP.</p>

Discrete Element Studies of Gravity-Driven Dense Granular Flows in Vertical Cylindrical Tubes

2016 ◽  
Author(s):  
Yesaswi N. Chilamkurti ◽  
Richard D. Gould
Keyword(s):  
Granular Flows ◽  
Discrete Element ◽  
Current Paper ◽  
Wall Friction ◽  
Geometrical Parameters ◽  
Soft Particle ◽  
Flow Physics ◽  
Cylindrical Tubes ◽  
Gravity Driven ◽  
Dense Granular Flows

The current paper focusses on the characterization of gravity-driven dry granular flows in cylindrical tubes. With a motive of using dense particulate media as heat transfer fluids (HTF), the main focus was to address the characteristics of flow regimes with a packing fraction of ∼60%. In a previous work [1], experimental and computational studies were conducted to understand the effects of different geometrical parameters on the flow physics. The current paper is an extension of that work to gain more insights into the granular flow physics. The three-dimensional computer simulations were conducted by implementing the Discrete Element Method (DEM) for the Lagrangian modelling of particles. Hertz-Mindilin models were used for the soft-particle formulations of inter-particulate contacts. Simulations were conducted to examine the particulate velocities and flow rates to understand the rheology in the dense flow regime. Past studies suggested the existence of a Gaussian mean velocity profile for dense gravity-driven granular flows. These observations were further analyzed by studying the influence of geometrical parameters on the same. The current work thus focusses on studying the rheology of dense granular flows and obtaining a better understanding of the velocity profiles, the wall friction characteristics, and the particle-wall contact behavior.

scholarly journals Experimental and Computational Studies of Gravity-Driven Dense Granular Flows

2015 ◽  
Author(s):  
Yesaswi N. Chilamkurti ◽  
Richard D. Gould
Keyword(s):  
Three Dimensional ◽  
Granular Flows ◽  
Packing Fraction ◽  
Velocity Shear ◽  
Spherical Particles ◽  
Tube Length ◽  
Soft Particle ◽  
Mean Velocity ◽  
Gravity Driven ◽  
Dense Granular Flows

The current paper focusses on the characterization of gravity-driven dry granular flows in cylindrical tubes. With a motive of using dense particulate media as heat transfer fluids (HTF), the study was primarily focused to address the characteristics of flow regimes with a packing fraction of ∼60%. Experiments were conducted to understand the effects of different flow parameters, including: tube radius, tube inclination, tube length and exit diameter. These studies were conducted on two types of spherical particles — glass and ceramic — with mean diameters of 150 μm and 300 μm respectively. The experimental data was correlated with the semi-empirical equation based on Beverloo’s law. In addition, the same flow configuration was studied through three-dimensional computer simulations by implementing the Discrete Element Method for the Lagrangian modelling of particles. A soft-particle formulation was used with Hertz-Mindilin contact models to resolve the interaction forces between particles. The simulation results were used to examine the velocity, shear rate and packing fraction profiles to study the detailed flow dynamics. Curve-fits were developed for the mean velocity profiles which could be used in developing hydrodynamic analogies for granular flows. The current work thus identifies the basic features of gravity driven dense granular flows that could form a basis for defining their rheology.

Patterns in gravity-driven granular flows

2008 ◽  
pp. 117-166
Author(s):  
Igor S. Aranson ◽  
Lev S. Tsimring
Keyword(s):  
Granular Flows ◽  
Gravity Driven

scholarly journals Diffusion and Mixing in Gravity-Driven Dense Granular Flows

2004 ◽  
Vol 92 (17) ◽  
Author(s):  
Jaehyuk Choi ◽  
Arshad Kudrolli ◽  
Rodolfo R. Rosales ◽  
Martin Z. Bazant
Keyword(s):  
Granular Flows ◽  
Gravity Driven ◽  
Dense Granular Flows

scholarly journals Experimental and numerical study of granular flow and fence interaction

2004 ◽  
Vol 38 ◽  
pp. 135-138 ◽  
Author(s):  
Thierry Faug ◽  
Mohamed Naaim ◽  
Florence Naaim-Bouvet
Keyword(s):  
Granular Flow ◽  
Numerical Study ◽  
Slope Angle ◽  
Granular Flows ◽  
Snow Avalanches ◽  
Shallow Water Theory ◽  
Gravity Driven ◽  
Deposition Processes ◽  
Set Up ◽  
Good Agreement

AbstractDense snow avalanches are regarded as dry granular flows. This paper presents experimental and numerical modelling of deposition processes occurring when a gravity-driven granular flow meets a fence. A specific experimental device was set up, and a numerical model based on shallow-water theory and including a deposition model was used. Both tools were used to quantify how the retained volume upstream of the fence is influenced by the channel inclination and the obstacle height. We identified two regimes depending on the slope angle. In the slope-angle range where a steady flow is possible, the retained volume has two contributions: deposition along the channel due to the roughness of the bed and deposition due to the fence. The retained volume results only from the fence effects for higher slopes. The effects of slope on the retained volume also showed these two regimes. For low slopes, the retained volume decreases strongly with increasing slope. For higher slopes, the retained volume decreases weakly with increasing slope. Comparison between the experiments and computed data showed good agreement concerning the effect of fence height on the retained volume.

scholarly journals Force fluctuations at the transition from quasi-static to inertial granular flow

Soft Matter ◽  
2019 ◽  
Vol 15 (42) ◽  
pp. 8532-8542 ◽  
Author(s):  
A. L. Thomas ◽  
Zhu Tang ◽  
Karen E. Daniels ◽  
N. M. Vriend
Keyword(s):  
Granular Flow ◽  
Granular Flows ◽  
Force Fluctuations ◽  
Gravity Driven

We analyse the rheology of gravity-driven, dry granular flows in experiments where individual forces within the flow bulk are measured.

scholarly journals A simple analytical model for pressure on obstacles induced by snow avalanches

2010 ◽  
Vol 51 (54) ◽  
pp. 1-8 ◽  
Author(s):  
Thierry Faug ◽  
Benoit Chanut ◽  
Rémi Beguin ◽  
Mohamed Naaim ◽  
Emmanuel Thibert ◽  
...  
Keyword(s):  
Analytical Model ◽  
Dead Zone ◽  
Granular Flows ◽  
Mitigation Measures ◽  
Snow Avalanches ◽  
Simple Analytical Model ◽  
Inclined Plane ◽  
Gravity Driven ◽  
D Model ◽  
Protection Dams

AbstractThe forces snow avalanches are able to exert on protection dams or buildings are of crucial interest in order to improve avalanche mitigation measures and to quantify the mechanical vulnerability of structures likely to be damaged by snow avalanches. This paper presents an analytical model that is able to calculate these forces taking into account dead-zone mechanisms. First, we present a 2-D analytical hydrodynamic model describing the forces on a wall overflown by gravity-driven flows down an inclined plane. Second, the 2-D model is successfully validated on discrete simulations of granular flows. Third, we provide ingredients to extend the 2-D model to flows of dry and cold snow. Fourth, we propose a simplified 3-D analytical model taking into account lateral fluxes. Finally, the predictions from the simplified 3-D analytical model are successfully compared to recent measurements on two full-scale snow avalanches released at the Lautaret site in France.

scholarly journals Dynamical fluctuations in dense granular flows

2009 ◽  
Vol 367 (1909) ◽  
pp. 5109-5121 ◽  
Author(s):  
Emily Gardel ◽  
E. Sitaridou ◽  
Kevin Facto ◽  
E. Keene ◽  
K. Hattam ◽  
...  
Keyword(s):  
Low Frequency ◽  
Granular Flows ◽  
Friction Angle ◽  
Coarse Grained ◽  
Velocity Fluctuations ◽  
Long Range Correlations ◽  
Force Fluctuations ◽  
Local Structures ◽  
Show Evidence ◽  
Gravity Driven

We have made measurements of force and velocity fluctuations in a variety of dense, gravity-driven granular flows under flow conditions close to the threshold of jamming. The measurements reveal a microscopic state that evolves rapidly from entirely collisional to largely frictional, as the system is taken close to jamming. On coarse-grained time scales, some descriptors of the dynamics—such as the probability distribution of force fluctuations, or the mean friction angle—do not reflect this profound change in the micromechanics of the flow. Other quantities, such as the frequency spectrum of force fluctuations, change significantly, developing low-frequency structure in the fluctuations as jamming is approached. We also show evidence of spatial structure, with force fluctuations being organized into local collision chains. These local structures propagate rapidly in the flow, with consequences far away from their origin, leading to long-range correlations in velocity fluctuations.

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