Transition mechanism of debris flows over rigid bed to over erodible bed

Egashira, Shinji; Itoh, Takahiro; Takeuchi, Hitoshi

doi:10.1016/s1464-1909(00)00235-5

Cited by 43 publications

(37 citation statements)

References 5 publications

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“…Different approximations of velocity profile were determined in the two cases and it was shown that for a granular flow in equilibrium with the immobile bed phase, variations of grain concentration and friction angle along the vertical cannot be neglected. Granular flow over an erodible bottom have been recently examined by Egashira et al (2000) who developed a constitutive model that highlights the differences in velocity and volumetric concentration profiles of a mixture over a rigid and an erodible bottom.…”

Section: Introductionmentioning

confidence: 99%

Granular flow in equilibrium with the bottom: experimental analysis and theoretical prediction

Zanuttigh

Lamberti

2002

Nonlin. Processes Geophys.

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Abstract. The paper presents measurements performed on the granular flow that develops in a drum partially filled with sand grains and rotating at various speeds. The aims of the paper are: to provide experimental evidence and measurements on grain flow in a drum; to compare theoretical and experimental velocity profiles; to point out discrepancies among theory and experiments.Velocity and "temperature" profiles were obtained with a Laser Doppler Anemometer (LDA) in the mid-section of the stream, where the flow is usually uniform; image analysis and visual observations of the flow were also carried out to evaluate the local slope, the depths of the characteristic flow regions and the concentration of the granular material. A semi-empirical relation that fits the experimental velocity profiles is presented and compared with Takahashi's velocity distributions for rigid and erodible bed.As proven by the distributions of free surface elevation, velocity, volumetric concentration and grain size across the drum, the three-dimensional nature of the flow field is not negligible.By increasing the drum rotation speed, in correspondence with critical and supercritical flows, changes in the flow regime are observed with formation of quasi-stationary surface waves. Wave development is described by analysing the extension and form of the experimental and theoretical velocity profiles. Wave effects on measurements are quantified and checked comparing the free-surface velocity-discharge relation obtained from experiments and from Takahashi's model for erodible bed.

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Section: Introductionmentioning

confidence: 99%

Granular flow in equilibrium with the bottom: experimental analysis and theoretical prediction

Zanuttigh

Lamberti

2002

Nonlin. Processes Geophys.

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“…A transition from flow over a rigid bed to flow over an erodible bed leads to increased flow resistance caused by a difference in shear stress distribution, thus altering the velocity and the velocity gradient at the bed [10]. Slope angle was seen to be a controlling factor in the effects of entrainable material [22], with a critical angle of 12 • identified, below which entrainment decreases runout and above which it may increase run-out by 40 %.…”

Section: State Of Current Entrainment Researchmentioning

confidence: 98%

Visualization of the internal flow properties and the material exchange interface in an entraining viscous Newtonian gravity current

2013

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In order to simulate a simple entraining geophysical flow, a viscous Newtonian gravity current is released from a reservoir by a dam-break and flows along a rigid horizontal bed until it meets a layer of entrainable material of finite depth, identical to the current. The goal is to examine the entrainment mechanisms by observing the interaction between the incoming flow and the loose bed. The sole parameter varied is the initial volume of the gravity current, thus altering its height and velocity. The gravity current plunges or spills into the entrainable bed and the velocity of the flow front becomes linear with time. The bed material is directly affected: motion is generated in the fluid far downstream of, and in that lying beneath the encroaching front. Shear bands are identified, separating horizontal flow downstream from flow with a strong vertical component close to the step. Downstream of the step the flow is horizontal and stratified, with no slip on the bottom boundary and very low shear near the surface. Between these two regions may lie transitional zones with linear velocity profiles, separated by horizontal bands of high shear; the number of transitional zones in the cross-section varies with the initial volume of the dam-break.

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“…Assumption c is suggested by the experimental data recorded in Egashira, Itoh and Takeuchi [5], which show that the solid volume fraction decreases almost linearly along the avalanche depth, except near the free surface, where it abruptly goes to zero. As a simplified first approach, we suppose that the solid volume fraction at (ξ,ξ,t) is only slightly different from its depth-averaged value at (ξ,t), see (6.2).…”

Section: Ordering Approximationsmentioning

confidence: 99%

Modeling shallow gravity-driven solid-fluid mixtures over arbitrary topography

Luca¹,

Tai²,

Kuo³

2009

Communications in Mathematical Sciences

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Abstract. The purpose of this paper is to derive modeling equations for debris flows on real terrain. Thus, we use curvilinear coordinates adapted to the topography as introduced, e.g., by Bouchut and Westdickenberg [F. Bouchut and M. Westdickenberg, Commun. Math. Sci., 2(3), 2004], and develop depth-averaged models of gravity-driven saturated mixtures of solid grains and pore fluid on an arbitrary rigid basal surface. First, by only specifying the interaction force and ordering approximations in terms of an aspect ratio between a typical length perpendicular to the topography, and a typical length parallel to the topography, we derive the governing equations for the shallow flow of a binary mixture, driven by gravitational force. In doing so, the non-uniformity through the avalanche depth of the constituent velocities and of the solid volume fraction is accounted for by coefficients of Boussinesq type. Then, the material behaviour peculiarities of both constituents properly enter the theory. One constituent is a granular solid. For its stresses we propose three models, one of them of Mohr-Coulomb type. The other constituent is a Newtonian/non-Newtonian fluid with small viscosity, obeying a viscous bottom friction condition. The final governing equations for the shallow flow of the mixture, incorporating the constitutive assumptions, are deduced, and the limiting equilibrium is then investigated.

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Transition mechanism of debris flows over rigid bed to over erodible bed

Cited by 43 publications

References 5 publications

Granular flow in equilibrium with the bottom: experimental analysis and theoretical prediction

Granular flow in equilibrium with the bottom: experimental analysis and theoretical prediction

Visualization of the internal flow properties and the material exchange interface in an entraining viscous Newtonian gravity current

Modeling shallow gravity-driven solid-fluid mixtures over arbitrary topography

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