Studies on the Fluidized Snow Dynamics

Abstract

An inclined chute system and a fluidized snow bed were constructed in a cold laboratory and extensive measurements of mechanical properties of fluidized snow were carried out.In the steady part of the snow flow, where the thickness and velocities are roughly constant, velocity profiles were obtained at various chute inclinations.Assuming that the bulk densities are uniform with depth, a constitutive equation of a Bingham body was applied to simulate the obtained velocity profiles.The apparent viscosity coefficients obtained ranged from 8.3 X 10-2 to 4.5 X 10-1 Ns/m 2 and yield stress 0 to 10 N/m 2 for the bulk densities of 100 to 200 kg/m' and the shear rate of 60 to 70 S-I.On the other hand viscous properties of the fluidized snow which was produced with the fluidized-bed experiment system was investigated with the Brookfield viscometer.All sets of data showed that the relation between the shear stress and shear rate satisfied the constitutive equation of the Bingham body for the shear rate of 1 to 15 S-I.Viscosity coefficients of the fluidized snow obtained ranged from 10-2 to 10-1 Ns/m 2 ; yield stress were 0 to 10-2 N/m 2 It was also found that the viscosity increased rapidly with the bulk density.The viscosity coefficients obtained in the two different systems were compared in special reference to the shear rate of each experiment; The assumptions made in the former calculations were re-examined.Consequently it was revealed that shear stresses are linearly proportional to the shear rate in a lower shear rate region and shear stresses depend on the square of the shear rate in a higher shear rate region.Furthermore a constitutive equation which expresses the general dynamical properties of fluidized snow was found to be written as the sum of the dry friction, the viscous and the quadratic viscous terms.The dynamical properties of the fluidized snow obtained in the above experiments and analyses were applied to the numerical simulations of the fluidized snow flow motion along the chute and artificial and natural avalanches observed in the Shiai-dani region, showing a reasonable fit of the observed data.