scholarly journals Modelling cohesion in snow avalanche flow

2015 ◽  
Vol 61 (229) ◽  
pp. 837-850 ◽  
Author(s):  
Perry Bartelt ◽  
Cesar Vera Valero ◽  
Thomas Feistl ◽  
Marc Christen ◽  
Yves Bühler ◽  
...  
Keyword(s):  
Stress Function ◽  
Mechanical Energy ◽  
Coulomb Stress ◽  
Flow Volume ◽  
Force Measurements ◽  
Dynamics Model ◽  
Model Calculations ◽  
Avalanche Flow ◽  
Shear Stress Function ◽  
Snow Temperature

AbstractFlowing snow is a cohesive granular material. Snow temperature and moisture content control the strength of the cohesive bonding between granules and therefore the outcome of granular interactions. Strong, cohesive interactions reduce the free mechanical energy in the avalanche core and therefore play a significant role in defining the avalanche flow regime. We introduce cohesion into avalanche dynamics model calculations by (1) treating cohesion as an additional internal binding energy that must be overcome to expand the avalanche flow volume, (2) modifying the Coulomb stress function to account for the increase in shear because of cohesive interactions and (3) increasing the activation energy to control the onset of avalanche fluidization. The modified shear stress function is based on force measurements in chute experiments with flowing snow. Example calculations are performed on ideal and real terrain to demonstrate how snow cohesion modifies avalanche flow and runout behaviour.

scholarly journals Snow Avalanche Impact Measurements at the Seehore Test Site in Aosta Valley (NW Italian Alps)

Geosciences ◽  
2019 ◽  
Vol 9 (11) ◽  
pp. 471
Author(s):  
Margherita Maggioni ◽  
Monica Barbero ◽  
Fabrizio Barpi ◽  
Mauro Borri-Brunetto ◽  
Valerio De Biagi ◽  
...  
Keyword(s):  
Flow Regimes ◽  
Test Site ◽  
Snow Avalanche ◽  
Hazard Mapping ◽  
Force Measurements ◽  
Italian Alps ◽  
Scientific Discussion ◽  
Impact Forces ◽  
Wide Range ◽  
Avalanche Flow

In full-scale snow avalanche test sites, structures such as pylons, plates, or dams have been used to measure impact forces and pressures from avalanches. Impact pressures are of extreme importance when dealing with issues such as hazard mapping and the design of buildings exposed to avalanches. In this paper, we present the force measurements recorded for five selected avalanches that occurred at the Seehore test site in Aosta Valley (NW Italian Alps). The five avalanches were small to medium-sized and cover a wide range in terms of snow characteristics and flow dynamics. Our aim was to analyze the force and pressure measurements with respect to the avalanche characteristics. We measured pressures in the range of 2 to 30 kPa. Though without exhaustive measurements of the avalanche flows, we found indications of different flow regimes. For example, we could appreciate some differences in the vertical profile of the pressures recorded for wet dense avalanches and powder ones. Being aware of the fact that more complete measurements are necessary to fully describe the avalanche flows, we think that the data of the five avalanches triggered at the Seehore test site might add some useful information to the ongoing scientific discussion on avalanche flow regimes and impact pressure.

Avalanche flow regime transitions in a changing climate

2020 ◽  
Author(s):  
Camille Ligneau ◽  
Betty Sovilla ◽  
Johan Gaume
Keyword(s):  
Climate Change ◽  
Snow Cover ◽  
Flow Regime ◽  
Flow Regimes ◽  
Future Climate Change ◽  
Hazard Mapping ◽  
Snow Avalanches ◽  
Avalanche Flow ◽  
Regime Transitions ◽  
Snow Temperature

<p>In the near future, climate change will impact the snow cover in Alpine regions. Higher precipitations and warmer temperatures are expected at lower altitude, leading to larger gradients of snow temperature, snow water content and snow depth between the top and the bottom of slopes. As a consequence, climate change will also indirectly influence the behavior of snow avalanches.</p><p>The present work aims to investigate how changes in snow cover properties will affect snow avalanches dynamics. Experimental studies allowed to characterize different avalanche flow regimes which result from particular combinations of snow physical and mechanical properties. In particular, expected variations of snow temperatures with elevation will cause more frequent and more extreme flow regime transitions inside the same avalanche. For example, a fast avalanche characterized by cold and low-cohesive snow in the upper part of the avalanche track will transform more frequently into a slow flow made of wet and heavy snow when the avalanche will entrain warm snow along the slope. A better understanding of these flow regime transitions, which have already been largely reported, is crucial, because it affects both daily danger assessment (e.g. forecasting services, road controls) and hazard mapping of avalanches.</p><p>To date, most avalanche modeling methods are not considering temperature effects and are then unable to simulate flow regime transitions and unprecedented scenarios. Our goal is then to develop a model capable of simulating reported flow regimes, flow transitions and the interactions between the snow cover and the flow (erosion, entrainment). Since these elements are not yet fully understood, we firstly model these mesoscopic processes using a 2D Discrete Element Model (DEM) in which varying particle cohesion and friction mimic the effect of changes in snow temperature. Flow regimes are simulated by granular assemblies put into motion by gravity on an inclined slope, which interact with a granular and erodible bed surface. Simulations are calibrated using experimental data coming from the avalanche test site located in Vallée de la Sionne, which record avalanches since more than 20 years. This modeling will then be used as an input to improve slope-scale models and make them more appropriate for avalanche risk management in the context of climate change.</p>

scholarly journals Measurement and Analysis of the Motion of Dense Flow Avalanches

1985 ◽  
Vol 6 ◽  
pp. 26-34 ◽  
Author(s):  
B. Salm ◽  
H. Gubler
Keyword(s):  
Maximum Flow ◽  
Flow Speed ◽  
Random Fluctuation ◽  
Type Model ◽  
Model Calculations ◽  
Flow Speeds ◽  
Quantitative Understanding ◽  
Dense Flow ◽  
Avalanche Flow ◽  
Measured Flow

Continuous avalanche flow speed measurements from start to stop of dense flow avalanches, and localized flow depth and slope perpendicular flow speed profiles, have been measured using X-band radar equipment- Maximum flow speeds of up io 65 m/s have been measured in large avalanches. Comparison of measured flow speeds with Voellmy-type model calculations shows that traditionally chosen sets of parameters, evaluated from runout measurements, cannot model the measured high speeds in the track. To get an improved quantitative understanding of flowing avalanches, it is proposed that from the start to the stop different flow regimes with different mechanical characteristics are passed through. This is based on theoretical studies of the movement of granular materials, where in adddition to the flow velocity a mean random fluctuation velocity of grains is introduced. A partly or fully fluidized state may be taken according to whether the ratio of frictional to collisional energy loss is smaller or larger than unity. In a third regime the snow is non-fluidized, ie pure gliding of the rigid snow. A good agreement of measurements with the proposed mechanisms is shown.

Numerical Analysis of Wall Slip Effects on Flow of Newtonian and Non-Newtonian Fluids in Macro and Micro Contraction Channels

2006 ◽  
Vol 129 (1) ◽  
pp. 23-30 ◽  
Author(s):  
Alfeus Sunarso ◽  
Takehiro Yamamoto ◽  
Noriyasu Mori
Keyword(s):  
Shear Stress ◽  
Shear Rate ◽  
Wall Shear Stress ◽  
Newtonian Fluid ◽  
Stress Function ◽  
Slip Velocity ◽  
Wall Slip ◽  
Average Shear ◽  
Wall Shear ◽  
Shear Stress Function

We performed numerical simulation to investigate the effects of wall slip on flow behaviors of Newtonian and non-Newtonian fluids in macro and micro contraction channels. The results show that the wall slip introduces different vortex growth for the flow in micro channel as compared to that in macro channel, which are qualitatively in agreement with experimental results. The effects of slip on bulk flow behaviors depend on rheological property of the fluid. For Newtonian fluid, the wall slip always reduces the vortex length, while for non-Newtonian fluid, the strength of the slip determines whether the vortex length is reduced or increased. Analyses on the velocity and stress fields confirm the channel size dependent phenomena, such as the reduction of wall shear stress with the decrease in channel size. With the increase in average shear rate, the Newtonian fluid shows the reduction of wall shear stress that increases in the same trend with slip velocity-wall shear stress function, while for non-Newtonian fluid, the effect of the slip is suppressed by shear thinning effect and, therefore, the reduction of wall shear stress is less sensitive to the change in average shear rate and slip velocity-wall shear stress function.

scholarly journals Theoretical Analysis of Radiative Effects on Transient Free Convection Heat Transfer past a Hot Vertical Surface in Porous Media

2008 ◽  
Vol 13 (4) ◽  
pp. 419-432 ◽  
Author(s):  
S. K. Ghosh ◽  
O. Anwar Beg
Keyword(s):  
Heat Transfer ◽  
Boundary Layer ◽  
Porous Medium ◽  
Shear Stress ◽  
Free Convection ◽  
Thermal Radiation ◽  
Stress Function ◽  
Dimensionless Time ◽  
Permeability Parameter ◽  
Shear Stress Function

The purpose of the present investigation deals with the unsteady free convective flow of a viscous incompressible gray, absorbing-emitting but non-scattering, optically-thick fluid occupying a semi-infinite porous regime adjacent to an infinite moving hot vertical plate with constant velocity. We employ a Darcian viscous flow model for the porous medium. The momentum and thermal boundary layer equations are non-dimensionalized using appropriate transformations and then solved subject to physically realistic boundary conditions using the Laplace transform technique. Thermal radiation effects are simulated via a radiation-conduction parameter, Kr, based on the Rosseland diffusion approximation. The influence of Grashof (free convection) number, radiation-conduction parameter (Kr), inverse permeability parameter (Kp) and dimensionless time (t) are studied graphically. We observe that increasing thermal radiation parameter causes a noticeable increase in the flow velocity, u. Temperature, θ, is significantly increased within the boundary layer with a rise in Kr since the latter represents the relative contribution of thermal radiation heat transfer to thermal conduction heat transfer. Increased radiation therefore augments heat transfer, heats the fluid and increases the thickness of the momentum and thermal boundary layers. Velocity is found to decrease with an increase in Kp (inverse permeability parameter) as are shear stress function ( ∂u/∂y | y=0) magnitudes owing to greater resistance of the porous medium for lower permeabilities, which decelerate the flow. An increase in Kr however boosts the shear stress function magnitudes i.e. serves to accelerate the flow. Temperature gradient, ∂θ/∂y | y=0 is also positively affected by an increase in thermal radiation (Kr) and with time. The present study has applications in geological convection, forest fire propagation, glass heat treatment processes at high temperature, metallurgical processing etc.

scholarly journals Nonlinear Finite Element Analysis Formulation for Shear in Reinforced Concrete Beams

2019 ◽  
Vol 9 (17) ◽  
pp. 3503 ◽  
Author(s):  
Sang-Ho Kim ◽  
Sun-Jin Han ◽  
Kang Kim
Keyword(s):  
Shear Stress ◽  
Reinforced Concrete ◽  
Stress Function ◽  
Shear Stresses ◽  
Rc Beams ◽  
Test Results ◽  
Proposed Model ◽  
Load Displacement ◽  
Shear Stress Function ◽  
Column Element

This study suggests a novel beam-column element formulation that utilizes an equilibrium-driven shear stress function. The beam shear is obtained from the bi-axial states of micro-planes, through matrix condensation and zero vertical traction assumptions. This properly remedies the shear stiffening of a one-dimensional beam-column element, keeping its degrees of freedom to a minimum. For verification of the proposed method, a total of seven shear test results of reinforced concrete (RC) beams were collected from the literature, in which the key variables were the reinforcement ratio, the presence of shear reinforcement, and section shape. The advantages are clearly shown in the shear stresses distributions being accurately described and the global load-displacement relations being successfully obtained and matching well with various test results. The proposed model shows satisfactory descriptions of the monotonic load-displacement response of the RC beams failing in multiple modes that vary from diagonal-tension to flexural-compression. In addition, more accurate and reliable information of sectional responses including sectional shear deformation and stresses is collected, leading to better prediction of a potential shear failure mode. Finally, the advantages of the proposed model are demonstrated by comparing the analysis results of an RCT-beam by using the different shear assumptions that include the constant and parabolic shear strains, constant shear flow, and the proposed shear stress function.

scholarly journals Force networks, torque balance and Airy stress in the planar vertex model of a confluent epithelium

2020 ◽  
Vol 476 (2237) ◽  
pp. 20190716
Author(s):  
Oliver E. Jensen ◽  
Emma Johns ◽  
Sarah Woolner
Keyword(s):  
Stress Function ◽  
Cell Shape ◽  
Degrees Of Freedom ◽  
Mechanical Energy ◽  
Energy Functional ◽  
Airy Stress Function ◽  
Vertex Model ◽  
Convex Polygons ◽  
Neighbouring Cell ◽  
Standard Energy

The vertex model is a popular framework for modelling tightly packed biological cells, such as confluent epithelia. Cells are described by convex polygons tiling the plane and their equilibrium is found by minimizing a global mechanical energy, with vertex locations treated as degrees of freedom. Drawing on analogies with granular materials, we describe the force network for a localized monolayer and derive the corresponding discrete Airy stress function, expressed for each N -sided cell as N scalars defined over kites covering the cell. We show how a torque balance (commonly overlooked in implementations of the vertex model) requires each internal vertex to lie at the orthocentre of the triangle formed by neighbouring edge centroids. Torque balance also places a geometric constraint on the stress in the neighbourhood of cellular trijunctions, and requires cell edges to be orthogonal to the links of a dual network that connect neighbouring cell centres and thereby triangulate the monolayer. We show how the Airy stress function depends on cell shape when a standard energy functional is adopted, and discuss implications for computational implementations of the model.

Sign in / Sign up

Export Citation Format

Share Document