scholarly journals A depth-averaged debris-flow model that includes the effects of evolving dilatancy. II. Numerical predictions and experimental tests

2014 ◽  
Vol 470 (2170) ◽  
pp. 20130820 ◽  
Author(s):  
David L. George ◽  
Richard M. Iverson
Keyword(s):  
Debris Flow ◽  
Adaptive Mesh Refinement ◽  
Volume Fraction ◽  
Critical Role ◽  
Solid Volume Fraction ◽  
Fluid Pressure ◽  
Pore Fluid ◽  
Flow Dynamics ◽  
Pore Fluid Pressure ◽  
Numerical Predictions

We evaluate a new depth-averaged mathematical model that is designed to simulate all stages of debris-flow motion, from initiation to deposition. A companion paper shows how the model's five governing equations describe simultaneous evolution of flow thickness, solid volume fraction, basal pore-fluid pressure and two components of flow momentum. Each equation contains a source term that represents the influence of state-dependent granular dilatancy. Here, we recapitulate the equations and analyse their eigenstructure to show that they form a hyperbolic system with desirable stability properties. To solve the equations, we use a shock-capturing numerical scheme with adaptive mesh refinement, implemented in an open-source software package we call D-Claw. As tests of D-Claw, we compare model output with results from two sets of large-scale debris-flow experiments. One set focuses on flow initiation from landslides triggered by rising pore-water pressures, and the other focuses on downstream flow dynamics, runout and deposition. D-Claw performs well in predicting evolution of flow speeds, thicknesses and basal pore-fluid pressures measured in each type of experiment. Computational results illustrate the critical role of dilatancy in linking coevolution of the solid volume fraction and pore-fluid pressure, which mediates basal Coulomb friction and thereby regulates debris-flow dynamics.

scholarly journals A depth-averaged debris-flow model that includes the effects of evolving dilatancy. I. Physical basis

2014 ◽  
Vol 470 (2170) ◽  
pp. 20130819 ◽  
Author(s):  
Richard M. Iverson ◽  
David L. George
Keyword(s):  
Debris Flow ◽  
Volume Fraction ◽  
Solid Volume Fraction ◽  
Fluid Motion ◽  
Fluid Pressure ◽  
Flow Behaviour ◽  
Balance Equations ◽  
Two Phase ◽  
Dilatancy Angle ◽  
Dilation Rate

To simulate debris-flow behaviour from initiation to deposition, we derive a depth-averaged, two-phase model that combines concepts of critical-state soil mechanics, grain-flow mechanics and fluid mechanics. The model's balance equations describe coupled evolution of the solid volume fraction, m , basal pore-fluid pressure, flow thickness and two components of flow velocity. Basal friction is evaluated using a generalized Coulomb rule, and fluid motion is evaluated in a frame of reference that translates with the velocity of the granular phase, v s . Source terms in each of the depth-averaged balance equations account for the influence of the granular dilation rate, defined as the depth integral of ∇⋅ v s . Calculation of the dilation rate involves the effects of an elastic compressibility and an inelastic dilatancy angle proportional to m − m eq , where m eq is the value of m in equilibrium with the ambient stress state and flow rate. Normalization of the model equations shows that predicted debris-flow behaviour depends principally on the initial value of m − m eq and on the ratio of two fundamental timescales. One of these timescales governs downslope debris-flow motion, and the other governs pore-pressure relaxation that modifies Coulomb friction and regulates evolution of m . A companion paper presents a suite of model predictions and tests.

Laminar-turbulent transition in debris flow: measurement of basal pore fluid pressure in an open channel flow experiment

2020 ◽  
Author(s):  
Yuichi Sakai ◽  
Norifumi Hotta
Keyword(s):  
Reynolds Number ◽  
Debris Flow ◽  
Turbulent Flow ◽  
Debris Flows ◽  
Fluid Pressure ◽  
Pore Fluid ◽  
Transitional Flow ◽  
Flow Depth ◽  
Pore Fluid Pressure ◽  
Relative Flow

<p>The fluidity of a debris flow varies by grain size. Flows containing principally coarse grains are considered to be laminar and those featuring largely incohesive fine grains turbulent. The transition from laminar to turbulent flow depends on the ratio of flow depth to grain size (i.e., the relative flow depth). Debris flows with relative flow depths of approximately 10 are entirely laminar; those with relative flow depths over approximately 20 exhibit transitional flow behavior from entirely laminar to partially turbulent. This transitional flow has been investigated in the laboratory using the resistance law and the vertical distribution of streamwise velocity. The flow exhibits a two-layer structure; the lower layer remains laminar but the upper layer becomes turbulent. However, transition modeling remains incomplete given the lack of data on the internal stresses associated with transitional flow. Here, we studied the laminar-turbulent transitions of debris flows by measuring basal pore fluid pressures using flume tests.</p><p>We flowed saturated monodisperse granular materials over an open-channel rigid bed; we used sediment particles of diameters 2.9, 2.2, 1.3, 0.8, 0.5, and 0.2 mm. When the debris flow attained the steady state, the flow depth and basal pore fluid pressure were measured using an ultrasonic sensor and pressure gages respectively, and the basal total normal stress estimated using the bulk density of the debris flow assessed at the downstream end.</p><p>The relative flow depths ranged from 5 to 130. Comparisons among the measured pore fluid pressures and the hydrostatic and total normal stresses indicated that a pore fluid pressure of 0.2 mm differed greatly from the hydrostatic pressure, equaling, in fact, the total normal stress, and indicating fully turbulent flow. In contrast, pore fluid pressures of 2.9, 2.2, and 1.3 mm were slightly higher than the hydrostatic pressures, indicating that the Reynolds stresses of the pore fluid due to the strong shears imparted by the sediment particles were in play; flow was entirely laminar. Pore fluid pressures of 0.8 and 0.5 mm were intermediate between the hydrostatic and total normal stresses, indicating the transition from fully laminar to partially turbulent flow.</p><p>By analogy with the Reynolds number for Newtonian fluid, we investigated the transition based on the non-dimensional number for debris flows (thus, the ratios of inertial to dynamic stresses caused by interparticle collisions and the Reynolds stresses of the debris flow pore fluid). This identified the critical Reynolds number in terms of transition commencement. We describe the transitional flow behavior of monodisperse granular debris flows using a two-layered model in which the position of the between-layer interface is estimated based on that critical Reynolds number.</p>

scholarly journals Correction to: Stress and pore fluid pressure control of seismicity rate changes following the 2016 Kumamoto earthquake, Japan

2021 ◽  
Vol 73 (1) ◽  
Author(s):  
Kodai Nakagomi ◽  
Toshiko Terakawa ◽  
Satoshi Matsumoto ◽  
Shinichiro Horikawa
Keyword(s):  
Fluid Pressure ◽  
Pressure Control ◽  
Pore Fluid ◽  
2016 Kumamoto Earthquake ◽  
Pore Fluid Pressure ◽  
Seismicity Rate ◽  
Kumamoto Earthquake ◽  
The 2016 Kumamoto Earthquake ◽  
Seismicity Rate Changes

An amendment to this paper has been published and can be accessed via the original article.

scholarly journals Confined flow of suspensions modelled by a frictional rheology

2014 ◽  
Vol 759 ◽  
pp. 197-235 ◽  
Author(s):  
Brice Lecampion ◽  
Dmitry I. Garagash
Keyword(s):  
Shear Stress ◽  
Friction Coefficient ◽  
Normal Stress ◽  
Volume Fraction ◽  
Solid Volume Fraction ◽  
Numerical Predictions ◽  
Dry Granular Flow ◽  
Neutrally Buoyant ◽  
Constitutive Parameters ◽  
Axial Development

AbstractWe investigate in detail the problem of confined pressure-driven laminar flow of neutrally buoyant non-Brownian suspensions using a frictional rheology based on the recent proposal of Boyer et al. (Phys. Rev. Lett., vol. 107 (18), 2011, 188301). The friction coefficient (shear stress over particle normal stress) and solid volume fraction are taken as functions of the dimensionless viscous number $I$ defined as the ratio between the fluid shear stress and the particle normal stress. We clarify the contributions of the contact and hydrodynamic interactions on the evolution of the friction coefficient between the dilute and dense regimes reducing the phenomenological constitutive description to three physical parameters. We also propose an extension of this constitutive framework from the flowing regime (bounded by the maximum flowing solid volume fraction) to the fully jammed state (the random close packing limit). We obtain an analytical solution of the fully developed flow in channel and pipe for the frictional suspension rheology. The result can be transposed to dry granular flow upon appropriate redefinition of the dimensionless number $I$. The predictions are in excellent agreement with available experimental results for neutrally buoyant suspensions, when using the values of the constitutive parameters obtained independently from stress-controlled rheological measurements. In particular, the frictional rheology correctly predicts the transition from Poiseuille to plug flow and the associated particles migration with the increase of the entrance solid volume fraction. We also numerically solve for the axial development of the flow from the inlet of the channel/pipe toward the fully developed state. The available experimental data are in good agreement with our numerical predictions, when using an accepted phenomenological description of the relative phase slip obtained independently from batch-settlement experiments. The solution of the axial development of the flow notably provides a quantitative estimation of the entrance length effect in a pipe for suspensions when the continuum assumption is valid. Practically, the latter requires that the predicted width of the central (jammed) plug is wider than one particle diameter. A simple analytical expression for development length, inversely proportional to the gap-averaged diffusivity of a frictional suspension, is shown to encapsulate the numerical solution in the entire range of flow conditions from dilute to dense.

Heatline and Massline Visualization of Hydromagnetic Double Diffusive Convective Flow of Nanofluid Within a Porous Trapezoidal Cavity

2021 ◽  
Vol 10 (2) ◽  
pp. 270-284
Author(s):  
Bikash C. Saha ◽  
T. R. Mahapatra ◽  
Dulal Pal
Keyword(s):  
Aspect Ratio ◽  
Convective Flow ◽  
Volume Fraction ◽  
Solid Volume Fraction ◽  
Darcy Number ◽  
Temperature Fields ◽  
Computational Domain ◽  
Aspect Ratios ◽  
Numerical Predictions ◽  
Double Diffusive

Double diffusive convective flow of nanofluid within a porous trapezoidal cavity of various aspect ratios consisting of Al2O3 nanoparticle in the presence of applied magnetic field in the direction perpendicular to the parallel top and bottom walls is analysed. The side walls of the cavity are maintained at constant temperature and concentration while its horizontal walls are insulated and impermeable. The irregular physical domain of the problem is transformed to a regular unit square computational domain. The governing equations have been solved by second order of finite difference method (FDM). Based upon numerical predictions, the effects of pertinent parameters such as Rayleigh number, Darcy number, aspect ratio, solid volume fraction and inclination angle on the flow and temperature fields and the heat transfer performance of the enclosure are examined. It is found that the intensity of heat and mass transfer increases with the increase in the Darcy number and aspect ratio. It is also observed that as the solid volume fraction increases there is increase in the average Nusselt number but reverse effect is observed on the average Sherwood number.

scholarly journals Heat transfer analysis of nanofluid flow through backward facing step

2020 ◽  
Vol 307 ◽  
pp. 01010 ◽  
Author(s):  
Ahlem Boudiaf ◽  
Fetta Danane ◽  
Youb Khaled Benkahla ◽  
Walid Berabou ◽  
Mahdi Benzema ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Volume Fraction ◽  
Solid Volume Fraction ◽  
Thermal Characteristics ◽  
Heat Transfer Analysis ◽  
Backward Facing Step ◽  
Nanofluid Flow ◽  
Numerical Predictions ◽  
Flow Through ◽  
Volume Method

This paper presents the numerical predictions of hydrodynamic and thermal characteristics of nanofluid flow through backward facing step. The governing equations are solved through the finite volume method, as described by Patankar, by taking into account the associated boundary conditions. Empirical relations were used to give the effective dynamic viscosity and the thermal conductivity of the nanofluid. Effects of different key parameters such as Reynolds number, nanoparticle solid volume fraction and nanoparticle solid diameter on the heat transfer and fluid flow are investigated. The results are discussed in terms of the average Nusselt number and streamlines.

Sign in / Sign up

Export Citation Format

Share Document