Bibliography and Article Abstracts
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Bibliography and Article Abstracts |
Summary: The paper describes one-dimensional motion of the two-layer model of powder-snow avalanches down a wide slope using the Kulikovskiy and Sveshnikova (1977) model. This model can be used to describe the transformation of dense avalanche into powder-snow one. It also references articles for description of dense avalanches Eglit (1968), Grigorian and others (1967) and for powder-snow avalanches Eglit (1983), Eglit and Vel?tishchev (1985) and Nazarov (1991, 1992, 1993).
Author states that Kulikovskiy and Sveshnikova model is based of four equations that describe volume, mass, momentum variations and deformation of the cloud, rather than the Scheiwiller model which includes 2 more equations for turbulent kinetic energy and its dissipation. According to the author "the crucial difference between Kulikovskiy and Sveshnikova model and many other models of a snow cloud, e.g. Beghin and others (1981) is that the growth rate of an avalanche is not prescribed but is founded by solving the basic system of equations."
Abstract: The equations of a modified two-layer model of a snow-powder avalanche are derived and the results of a numerical investigation are given. The aim of the modification is to simplify the model and give a clearer physical meaning to the individual terms of the equations. For this, the core of the avalanche is redefined as a layer with unchanged (high) density; the direction of mass transfer between the core and cloud is fixed; the upper boundary of the cloud is modeled by a discontinuity at which the concentration of the snow powder falls to zero.
Abstract: In this paper the powder snow avalanche is considered as a two-phase flow (air and snow particles). The equations governing this flow are the fluid mechanics conservation laws. The mass and the momentum conservation are considered for each phase. The interaction between the two phases takes into account the drag force between the particle and the air. Owing to high turbulence in the powder flow, a closure model was used based on a modified k-emodel in order to take into account the reduction of turbulence energy by the particles. The dense avalanche is modeled using the shallow water equations. The formation and the development of the powder avalanche is modeled using a mass and momentum exchanges between the powder flow and the dense flow. The flow area is digitized horizontally and vertically using a finite elements mesh. The numerical scheme is obtained by integrating the equations on each cell. The model thus built was calibrated using laboratory measurements of density current carried out in a flume. The model was successfully applied to reproduce many avalanches observed in France. At the end of this paper, an application of this model to an engineering case study is presented. It concerns the Uzengili path where an avalanche occurred in 1993. In this paper we use the integrated dense/powder avalanche model to define the effect of a powder avalanche flow in this path. Different simulations allow display of maps of the exposed zones for different available snow depths in the starting zone. The results were mapped in terms of dynamic pressure field and recommendations are proposed to the local authorities.
Abstract: A powder snow avalanche is referred to as the turbulent flow of a cloud of dense fluid (suspension of snow particles) in an ambient one (the air) down an incline. This buoyant cloud can be channeled in a couloir (two-dimensional or 2-D buoyant cloud) or spread laterally on an open field (three-dimensional cloud). Between these two extreme cases one can meet all kinds of flow depending on mountain relief.
Previous laboratory experiments in a water flume concerned only 2-D flows. 3-D flows are the subject of the present paper. From ?thermal theory? it is possible to obtain laws about velocity and density of the flowing cloud.
A hundred experiments were carried out in a large tank containing fresh water along a tilting plane. It was shown that the height, length, and width growth rates of the clouds, between 15° and 90°, were linear functions of the slope. On the other hand the variation of the front velocity was shown to be in accordance with the proposed theoretical analysis.
The results of this modeling can be applied to a real case of a powder snow avalanche flowing down a slope if there is no entrainment of the snow from the ground. This 'no entrainment assumption' corresponds generally to the last stage of the flow. Some practical examples are proposed.
Abstract: A powder-snow avalanche can be considered as the flow of a turbulent buoyant volume of heavy fluid (air-snow suspension) in an ambient fluid, the air. In the dynamics of such a flow, two mechanisms must be taken into account: the air entrainment and the snow entrainment inside the avalanche. From fluid mechanics equations (mass conservation and momentum equations) formulae were obtained giving velocity and density of the avalanche as a function of the slope path, the growth rate of the avalanche and fresh snow-cover characteristics. On the other hand, laboratory simulations gave (among others) experimental results about the growth rates of buoyant clouds. From these theoretical and experimental studies, practical examples are proposed with given path profiles and snow-cover characteristics. Such examples can be generalized to any other cases.
Reprint Address: Centre Technique du Genie Rural, des Eaux et des Forets, Domaine Universitaire, BP 114, 38402 S.-Martin-d'Heres, France.
ABSTRACT: To provide engineers with a better tool, we have developed a program for avalanche computation. After a brief description of the mathematical model and the assumptions, we describe influence of physical and numerical parameters, which allows a better understanding of the physical phenomenon which we call an avalanche. The satisfactory agreement between computations and observations allows us to assume that the model is well founded; further experiments will allow us to improve this simulation tool.
ABSTRACT: A numerical computer model, bases on the finite differencing of the Navier-Stokes fluid equations, is used to simulate snow-avalanche flow. In order to verify and calibrate the numerical model, snow-flow tests 0.2m deep with flow velocities between 0-18m/s were conducted. Data concerning position, velocity, and flow depth versus time were collected and compared to model runs on the computer. The frictional force on moving snow is investigated and found to be modeled by a term that is proportional to the square of the flow velocity.
Articles to be received (library loan)
Abstract: Two models are considered in this paper: one was proposed in Kulikovskiy and Sveshnikova (1977) and is referred here as KS-model, the second was described in Beghin and Brugnot (1983), and is referred here as BB-model. Both models treat the powder avalanche as a cloud of finite length and calculate the front velocity, the dimension and the mean density of the cloud. They are very similar as the geometry of the cloud is assumed to be an elliptic half-cylinder. The BB-model is included in a software presently used in France for design purposes. It contains some simplifying assumptions that are not needed in the KS-model. The aim of this paper is to study the validity of the BB-model simplifications by comparison of the two models. We first simulate the Beghin and others (1981) experiments in water by KS-model and then compare the two models' results in the case of a snow avalanche on a uniform slope. We find that an appropriate choice of the air entrainment coefficient value for the KS-model leads to reasonable similar results for the two models, in both cases for large ranges of slope and cloud density.
(Author abstract) 13 Refs.
Abstract: A continuum theory for the dynamics of powder snow avalanches is developed. They are treated as free surface two-phase flows of snow particles and air, coupled by momentum transfer. Closure of the equations is achieved by a k-emodel for the turbulence and by a linear relationship between interphase momentum transfer and the relative velocity of the phases. Numerical solutions obtained by means of the Kantorovich technique are presented for steady plane flow. They are compared with measurements from the small-scale laboratory simulation of powder snow avalanches as turbulent mixtures of polystyrene particles and water. Methods of measuring particle phase velocity profiles and particle phase volume fraction profiles in steady chute flow are presented. A theoretical model for the transition from the flow avalanche regime to the powder snow avalanche regime is outlined.
(Edited author abstract) Refs.
Abstract: The continuum model of a snow avalanche is abandoned, and instead an avalanche is modeled as a collection of 103 particles that move randomly and independently subject to gravity and resistive forces which have a random fluctuation computed by Monte-Carlo simulation. The model includes entrainment at the avalanche front and the possibility of varying resistive parameters with speed and slope position. Particle statistics computed for an avalanche event in Norway, April 1982, provide a reasonable simulation of recorded speeds and debris distribution.
(Author abstract) Refs.
Reprint Address: Fac of Engineering, Nagaoka Univ of Technology, Nagaoka, Niigata, Japan.
ABSTRACT: Appropriate expressions describing the motion of powder-snow avalanches are derived. The model consists of four equations, i.e. the conservation equations of fluid mass, snow-particle mass, momentum of the cloud, and kinetic energy of the turbulence. Insofar as the density difference between the avalanche and the ambient air becomes rather large compared with the density of the ambient air, the Boussinesq approximation, which is typically used to analyze density currents, cannot be adopted in the present case. As opposed to previous models, the total buoyancy of a powder-snow avalanche is allowed to change freely via erosion from and deposition on to a static snow layer on a slope. In the model, the snow-particle entrainment rate from the slope is directly linked to the level of turbulence. A discontinuous, large-scale powder-snow avalanche occurred on 26 January 1986 near Maseguchi, Niigata Prefecture, Japan. The present model is employed to simulate that part of the avalanche above any dense core.
(From author abstract)