scholarly journals Granular surface avalanching induced by drainage from a narrow silo

2018 ◽  
Vol 856 ◽  
pp. 444-469 ◽  
Author(s):  
C.-Y. Hung ◽  
P. Aussillous ◽  
H. Capart
Keyword(s):  
Granular Flow ◽  
High Speed ◽  
Kinematic Model ◽  
Surface Flow ◽  
Surface Shape ◽  
Near Surface ◽  
Granular Rheology ◽  
Constant Rate ◽  
Theory And Experiments ◽  
Granular Surface

Using theory and experiments, we investigate granular surface avalanching due to material outflow from a narrow silo. The assumed silo geometry is a deep rectangular box, of moderate spanwise width and small gap thickness between smooth front and back walls. A small orifice deep below the free surface lets grains drain out at a constant rate. The resulting granular flows can therefore be assumed quasi-two-dimensional and quasi-steady over most of the surface descent history. To model these flows, we couple a kinematic model of deep granular flow with a dynamic model of shallow surface avalanching. We then compare the calculated flow fields with detailed particle tracking measurements, letting the silo ascend relative to the high-speed camera to increase spatial resolution. The results show that the avalanching surface shape and near-surface flow are controlled by the spanwise gradient in subsidence velocity, and how this gradient is in turn controlled by the height above orifice and the gap thickness. Whereas the deep flow pattern is rate independent, shallow avalanching is paced by the granular rheology.

High-speed granular chute flows

2012 ◽  
Vol 710 ◽  
pp. 35-71 ◽  
Author(s):  
Alex J. Holyoake ◽  
Jim N. McElwaine
Keyword(s):  
Granular Flow ◽  
High Speed ◽  
Transverse Velocity ◽  
Multiple Points ◽  
Longitudinal Vortices ◽  
Flow Models ◽  
Maximum Value ◽  
Constant Rate ◽  
Experimental Findings ◽  
Steep Slopes

AbstractThis paper reports experimental findings on the flow of sand down a steep chute. Nearly all granular flow models have a maximum value for the friction and therefore predict that flows on steep slopes will accelerate at a constant rate until the interaction with the ambient fluid becomes important. This prediction has not been tested by previous work, which has focused on relatively low slope angles where steady, fully developed flows occur after short distances. We test this by investigating flows over a much greater range of slope angles (30–50${}^{\ensuremath{\circ} } $) and flow depths (4–130 particle diameters). We examine flows with two basal conditions, one flat and frictional, the other bumpy. The latter imposes a no-slip condition for slow, deep flows, but permits some degree of slip for high flow velocities. The data suggests that friction can be much larger than theories such as the $\ensuremath{\mu} (I)$ rheology proposed by Jop, Forterre & Pouliquen (Nature, vol. 441, 2006) suggest and that there may be constant velocity states above the angle of vanishing ${h}_{\mathit{stop}} $. Although these flows do not vary in time, all but the flows on the bumpy base at low inclinations accelerate down the slope. A recirculation mechanism sustains flows with a maximum mass flux of $20~\mathrm{kg} ~{\mathrm{s} }^{\ensuremath{-} 1} $, allowing observations to be made at multiple points for each flow for an indefinite period. Flows with Froude number in the range 0.1–25 and bulk inertial number 0.1–2.7 were observed in the dense regime, with surface velocities in the range 0.2–5.6 $\mathrm{m} ~{\mathrm{s} }^{\ensuremath{-} 1} $. Previous studies have focused on $I\lessapprox 0. 5$. We show that a numerical implementation of the $\ensuremath{\mu} (I)$ rheology does not fully capture the accelerating dynamics or the transverse velocity profile on the bumpy base. We also observe the transverse separation of the flow into a dense core flanked by dilute regions and the formation of longitudinal vortices.

scholarly journals Formation of RADARSAT backscatter feature and undulating firn stratigraphy at an ice-stream margin

2013 ◽  
Vol 54 (64) ◽  
pp. 90-96 ◽  
Author(s):  
Felix Ng ◽  
Edward C. King
Keyword(s):  
Flow Field ◽  
Steady Flow ◽  
Kinematic Model ◽  
Ice Sheets ◽  
Surface Flow ◽  
Three Dimensions ◽  
West Antarctica ◽  
Near Surface ◽  
Backscatter Intensity ◽  
Ice Stream

AbstractOn RADARSAT imagery, the southern margin of the onset zone of Bindschadler Ice Stream, West Antarctica, manifests a multi-banded feature, with brightness varying across the bands and oscillating along each band. Ground-based radar profiles across the margin reveal folds in the firn stratigraphy associated with this pattern and provide evidence for correlation between the depth of shallow isochrones and the RADARSAT backscatter intensity on each profile, allowing us to interpret the banded feature for firn-layer geometry in three dimensions. We use a kinematic model of isochrone depth evolution to show how layer folding and the band expression may result from deformation and advection in the near-surface flow field at ice-stream margins, even with steady flow. The model predicts the formation of longitudinally patterned bands when the ice-stream acceleration fluctuates along flow. Concerted study of the planform and stratigraphy of other RADARSAT-detected features on the ice sheets may help us understand their origin.

Granular surface flow on an asymmetric conical heap

2019 ◽  
Vol 865 ◽  
pp. 41-59 ◽  
Author(s):  
Sandip Mandal ◽  
D. V. Khakhar
Keyword(s):  
Layer Thickness ◽  
Mass Flow ◽  
High Speed ◽  
Surface Flow ◽  
Operating Conditions ◽  
Angle Of Repose ◽  
Flow Rates ◽  
Mass Flow Rates ◽  
Predicted Values ◽  
Granular Surface

We carry out an experimental study of the granular surface flow of nearly monodisperse glass beads on a conical heap formed on a rough circular disc by a narrow stream of the particles from a hopper, with the pouring point displaced from the centre of the disc. During the growth phase, an axisymmetric heap is formed, which grows either by periodic avalanches or by non-periodic avalanches that occur randomly over the azimuthal location of the heap, depending on the operating conditions and system properties. The dynamics of heap growth is characterized by the variation of the heap height, angle of repose and the angular velocity of the periodic avalanche with time, for different mass flow rates from the hopper. When the base of the heap reaches the edge of the disc closest to the pouring point, the heap stops growing and a steady surface flow of particles is developed on the heap surface, with particles flowing over the edge of the disc into a collection tray. The geometry is a unique example of a granular flow on an erodible bed without any bounding side walls. The corresponding steady state geometry of the asymmetric heap is characterized by means of surface contours and angles of repose. The streamwise and transverse surface velocities are measured using high-speed video photography and image analysis for different mass flow rates. The flowing layer thickness is measured by immersing a coated needle in the flow at different positions on the mid-line of the flow. The surface angle of the flowing layer is found to be significantly smaller than the angle of repose and to be independent of the mass flow rate. The velocity profiles at different streamwise positions for different mass flow rates are found to be geometrically similar and are well described by Gaussian functions. The flowing layer thickness is calculated from a model using the measured surface velocities. The predicted values match the measured values quite well.

scholarly journals Observation and analysis of diving beetle movements while swimming

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Debo Qi ◽  
Chengchun Zhang ◽  
Jingwei He ◽  
Yongli Yue ◽  
Jing Wang ◽  
...  
Keyword(s):  
Swimming Speed ◽  
High Speed ◽  
Kinematic Model ◽  
Movement Pattern ◽  
Unmanned Vehicles ◽  
Power Stroke ◽  
Cross Sectional ◽  
Motion Data ◽  
The Cross ◽  
Diving Beetle

AbstractThe fast swimming speed, flexible cornering, and high propulsion efficiency of diving beetles are primarily achieved by their two powerful hind legs. Unlike other aquatic organisms, such as turtle, jellyfish, fish and frog et al., the diving beetle could complete retreating motion without turning around, and the turning radius is small for this kind of propulsion mode. However, most bionic vehicles have not contained these advantages, the study about this propulsion method is useful for the design of bionic robots. In this paper, the swimming videos of the diving beetle, including forwarding, turning and retreating, were captured by two synchronized high-speed cameras, and were analyzed via SIMI Motion. The analysis results revealed that the swimming speed initially increased quickly to a maximum at 60% of the power stroke, and then decreased. During the power stroke, the diving beetle stretched its tibias and tarsi, the bristles on both sides of which were shaped like paddles, to maximize the cross-sectional areas against the water to achieve the maximum thrust. During the recovery stroke, the diving beetle rotated its tarsi and folded the bristles to minimize the cross-sectional areas to reduce the drag force. For one turning motion (turn right about 90 degrees), it takes only one motion cycle for the diving beetle to complete it. During the retreating motion, the average acceleration was close to 9.8 m/s2 in the first 25 ms. Finally, based on the diving beetle's hind-leg movement pattern, a kinematic model was constructed, and according to this model and the motion data of the joint angles, the motion trajectories of the hind legs were obtained by using MATLAB. Since the advantages of this propulsion method, it may become a new bionic propulsion method, and the motion data and kinematic model of the hind legs will be helpful in the design of bionic underwater unmanned vehicles.

scholarly journals About mathematical simulation of processes for high-speed loading of materials on Department of Physical Mechanics of St. Petersburg State University

2020 ◽  
Vol 65 (4) ◽  
pp. 699-713
Author(s):  
Victor A. Morozov ◽  
◽  
Vsevolod I. Bogatko ◽  
Andrey B. Yakovlev ◽  
◽  
...  
Keyword(s):  
Mathematical Simulation ◽  
High Speed ◽  
Surface Region ◽  
Pulse Method ◽  
Magnetic Pulse ◽  
State University ◽  
Natural Experiments ◽  
Near Surface ◽  
Metal Rings ◽  
Physical Mechanics

The researches of shock-wave processes in the constructional materials are actual, but carrying out of natural experiments is extremely inconvenient and expensive, and sometimes it is even impossible to replicate. Therefore basically all researches of these problems are reduced to various cases of simulation of processes for high-speed loading of materials in the laboratory circumstances. In the paper we consider following directions of mathematical simulation of processes for high-speed loading of materials that were made on department of physical mechanics of St. Petersburg State University: the simulation of shock-loaded media by using of dynamics of dislocations; the simulation of high-speed loading of media with the account of the relaxation phenomena in a near-surface region; the simulation of propagation of the short elastoplastic impulse in medium under the condition of influence of a weak magnetic field; the generation of mathematical models of deformation and destruction of thin metal rings by a magnetic-pulse method; the simulation of crack propagation during the short-term pulse loading.

Some clues as to the formation of protrusions by Fundulus deep cells

1977 ◽  
Vol 26 (1) ◽  
pp. 139-150
Author(s):  
C. Tickle ◽  
J.P. Trinkaus
Keyword(s):  
Cell Surface ◽  
Negative Pressure ◽  
Surface Flow ◽  
Contractile Properties ◽  
Cell Locomotion ◽  
Local Phenomenon ◽  
Constant Rate

One of the ways in which Fundulus deep cells move in vivo is by putting out long, fingerlike protrusions. This involves a change in the shape of the cell as a whole, with cytoplasmic flow, and is not just a local phenomenon. Moreover, particles on the cell surface move toward a protrusion as it is forming, suggesting surface flow. The role of surface flow is discussed both on a grown level and in respect to molecular fluidity. Long, stable protrusions can be pulled from cells by the application of negative pressure at a constant rate and these behave in a similar way to those formed during cell locomotion. Such long protrusions must be structured. The importance of contractile properties of the cytoplasm in the formation of protrusions was studied by treating cells with media that modify cellular contractility.

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