scholarly journals Robust experimental study of avalanche precursory events based on reproducible cycles of grain packing destabilizations

2021 ◽  
Vol 249 ◽  
pp. 03023
Author(s):  
Luc Oger ◽  
Renaud Delannay ◽  
Yves Le Gonidec
Keyword(s):  
Free Surface ◽  
Surface Activity ◽  
Laboratory Experiments ◽  
Linear Growth ◽  
Experimental Protocol ◽  
Statistical Inferences ◽  
Grain Packing ◽  
Quasi Stationary State ◽  
Weak Surface ◽  
Maximal Stability

Quasi-periodic collective displacements of grains at the free surface of a tilted grain packing constitute precursors of granular avalanches. Laboratory experiments are commonly performed by slowly tilting the packing from 0° to the maximal stability angle θA. In these conditions, the number of precursors is too small to assess reproducible and robust statistical analyses of the precursor activity. To go beyond this limitation, we have developed a specific experimental protocol consisting of tilting the packing with successive oscillation cycles. We use a high-resolution optical camera and process the images of the packing free surface to identify precursory events during many consecutive cycles of a single packing. We observe the same behavior for all half-cycles, forth and back: appearance of the first precursors after the same variation of inclination, exponential evolution of the weak surface activity for the first precursors and linear growth of stronger surface activity for the following ones. The experimental protocol provides both reproducible precursor measurements based on large sample statistical inferences and a quasi-stationary state after one full-cycle. This approach is very promising for highlighting the effects of external parameters, including humidity and packing geometry.

Withdrawal from a reservoir of stratified fluid

1981 ◽  
Vol 376 (1767) ◽  
pp. 499-523
Keyword(s):  
Free Surface ◽  
Velocity Field ◽  
Vertical Velocity ◽  
Mass Flux ◽  
Laboratory Experiments ◽  
Initial Period ◽  
Horizontal Layer ◽  
Horizontal Velocity ◽  
Viscous Stress ◽  
Similar Flows

A series of laboratory experiments are described in which the following major features of the flow field were observed. Well above the outlet the flow was essentially one of uniform vertical velocity, which is such that the free surface falls at a rate determined by the mass flux through the outlet, the isopycnics remaining horizontal. The small vertical velocity is converted to a considerably larger horizontal velocity in an essentially horizontal layer near the level of the outlet slot. The width of this withdrawal layer was almost constant over a large portion of the tank (except for the region near the outlet), and the velocity field within it was found to be steady after an initial period of establishment. Also the horizontal velocity at a given level in the withdrawal layer was found, to a good approximation, to vary linearly with the distance along the tank, and the velocity distribution, at a given station, was determined principally by the viscous stress, once a representative length had been established. For flows initiated in a uniform tank by suddenly opening a valve in the outlet line, the width of the withdrawal layer seemed to be uniquely determined on a scale, dependent on the flux, that appears to derive from terms that are negligible once the steady flow has been established. By placing suitable obstructions in the tank it was possible to obtain similar flows, but with various widths. We were also able to change the structure of the withdrawal layer by controlling the way the mass flux was brought to its final value, thereby establishing that the width of the withdrawal layer was dependent on its history.

scholarly journals Shallow free-surface Stokes flow around a corner

2020 ◽  
Vol 378 (2174) ◽  
pp. 20190515 ◽  
Author(s):  
Edward M. Hinton ◽  
Andrew J. Hogg ◽  
Herbert E. Huppert
Keyword(s):  
Free Surface ◽  
Stokes Flow ◽  
Channel Wall ◽  
Laboratory Experiments ◽  
Lateral Spreading ◽  
Simple Expression ◽  
Lava Flows ◽  
Theme Issue ◽  
Inclined Plane ◽  
Downstream Distance

The steady lateral spreading of a free-surface viscous flow down an inclined plane around a vertex from which the channel width increases linearly with downstream distance is investigated analytically, numerically and experimentally. From the vertex the channel wall opens by an angle α to the downslope direction and the viscous fluid spreads laterally along it before detaching. The motion is modelled using lubrication theory and the distance at which the flow detaches is computed as a function of α using analytical and numerical methods. Far downslope after detachment, it is shown that the motion is accurately modelled in terms of a similarity solution. Moreover, the detachment point is well approximated by a simple expression for a broad range of opening angles. The results are corroborated through a series of laboratory experiments and the implication for the design of barriers to divert lava flows are discussed. This article is part of the theme issue ‘Stokes at 200 (Part 1)’.

Effectiveness Evaluation Criteria of Using Fine Powders of Secondary Concrete as a Component of Composite Binder

2021 ◽  
Vol 1017 ◽  
pp. 163-171
Author(s):  
Tatiana Drozdyuk ◽  
Arkady Ayzenshtadt ◽  
Sergey Aksenov
Keyword(s):  
Free Surface ◽  
Surface Energy ◽  
Surface Activity ◽  
Free Surface Energy ◽  
Hydration Reaction ◽  
Critical Surface ◽  
Critical Surface Tension ◽  
Composite Binder ◽  
Fine Powders ◽  
Highly Dispersed

The paper considers the possibility of using energy criteria (surface activity, free surface energy) to quantify the efficiency of a highly dispersed system consisting of fine particles of secondary concrete as a component of composite binder of the hydration type of hardening. Using the G.A. Zisman method, the value of the critical surface tension was determined for secondary concrete fractions with different degrees of dispersion, which gives an idea of the free surface energy of a surface area unit. Based on the experimental data for determining the specific surface area and critical surface tension, the free surface energy and surface activity of the studied concrete powder were calculated, which can serve as criteria for quantitative energy characteristics of raw materials for the production of composite binders. Calorimetric studies related to measurements of the thermal effects of the hydration reaction of highly dispersed samples of secondary concrete have shown that this process is exothermic, the enthalpy of hydration of which is comparable to a similar parameter for cement. It was experimentally shown that fine powders of secondary concrete are effective as components of a composite binder, but they need to be pre-activated to optimal parameters, one of which is surface activity. In addition, the symbasis of changes in surface activity, the specific heat of the hydration reaction of highly dispersed concrete fractions and the compressive strength of fine-grained concrete samples made by using a composite binder containing a highly dispersed fraction of secondary concrete was established.

Free-surface effects on spin-up

1988 ◽  
Vol 187 ◽  
pp. 395-407 ◽  
Author(s):  
Ulf CederlÖf
Keyword(s):  
Boundary Layer ◽  
Free Surface ◽  
Froude Number ◽  
Reasonable Agreement ◽  
Laboratory Experiments ◽  
Dynamic Effect ◽  
Delayed Response ◽  
Inertial Oscillations ◽  
Homogeneous Fluid ◽  
Singular Vortex

The effects of a free surface on the spin-up of a homogeneous fluid are studied, both analytically and experimentally. The analysis is carried out in cylindrical geometry and shows that the spin-up process is strongly modified as the rotational Froude number F = 4ω2L2/gH becomes large. The dynamic effect of the free surface causes delayed response outside a sidewall boundary layer of thickness LF−½. The timescale in the slowly decaying core is larger than the usual spin-up time by a factor of order F. A set of laboratory experiments using a cylinder with a parabolic bottom were carried out in order to test the theory. Reasonable agreement is found in all the experiments except close to the centre where an interesting deviation was observed, especially in cases corresponding to smaller Froude numbers. The deviation consisted of an anticyclonic vortex at the centre. It is shown that this phenomenon might be explained by Lagrangian mean motion resulting from inertial oscillations. In fact, the analysis shows that this motion produces a singular vortex at the centre.

scholarly journals On mathematical approaches to modelling slender liquid jets with a curved trajectory

2018 ◽  
Vol 844 ◽  
pp. 905-916 ◽  
Author(s):  
S. P. Decent ◽  
E. I. Părău ◽  
M. J. H. Simmons ◽  
J. Uddin
Keyword(s):  
Differential Geometry ◽  
Free Surface ◽  
Laboratory Experiments ◽  
Free Surface Flows ◽  
Liquid Jets ◽  
Computational Results ◽  
Cylindrical Container ◽  
Leading Order ◽  
Surface Flows

Slender liquid jets that have a curved trajectory have been examined in a range of papers using a method introduced in Wallworket al.(Proc. IUTAM Symp. on Free-Surface Flows, 2000, Kluwer;J. Fluid Mech., vol. 459, 2002, pp. 43–65) and Decentet al.(J. Engng Maths, vol. 42, 2002, pp. 265–282), for jets that emerge from an orifice on the surface of a rotating cylindrical container, successfully comparing computational results to measurements arising from laboratory experiments. Wallworket al.(2000, 2002) and Decentet al.(2002) based their analyses on the slenderness of the jet, and neglected the torsion of the centreline of the jet, which is valid since in most situations examined the torsion is zero or small. Shikhmurzaev & Sisoev (J. Fluid Mech., vol. 819, 2017, pp. 352–400) used differential geometry and incorporated the torsion. This paper shows that these two methods produce identical results at leading order when the torsion is zero or when the torsion is$O(1)$, in an asymptotic framework based upon the slenderness of the jet, and shows that the method of Wallworket al.(2000, 2002) and Decentet al.(2002) is accurate for parameters corresponding to scenarios previously examined and also when the torsion is$O(1)$. It is shown that the method of Shikhmurzaev & Sisoev (2017) should be used when the torsion is asymptotically large or when the jet is not slender.

scholarly journals Channelized free-surface flow of cohesionless granular avalanches in a chute with shallow lateral curvature

1999 ◽  
Vol 392 ◽  
pp. 73-100 ◽  
Author(s):  
M. WIELAND ◽  
J. M. N. T. GRAY ◽  
K. HUTTER
Keyword(s):  
Free Surface ◽  
Numerical Simulations ◽  
Laboratory Experiments ◽  
Free Surface Flow ◽  
Surface Flow ◽  
Smooth Transition ◽  
Lateral Confinement ◽  
Lateral Curvature ◽  
Granular Deposit ◽  
Good Agreement

A series of laboratory experiments and numerical simulations have been performed to investigate the rapid fluid-like flow of a finite mass of granular material down a chute with partial lateral confinement. The chute consists of a section inclined at 40° to the horizontal, which is connected to a plane run-out zone by a smooth transition. The flow is confined on the inclined section by a shallow parabolic cross-slope profile. Photogrammetric techniques have been used to determine the position of the evolving boundary during the flow, and the free-surface height of the stationary granular deposit in the run-out zone. The results of three experiments with different granular materials are presented and shown to be in very good agreement with numerical simulations based on the Savage–Hutter theory for granular avalanches. The basal topography over which the avalanche flows has a strong channelizing effect on the inclined section of the chute. As the avalanche reaches the run-out zone, where the lateral confinement ceases, the head spreads out to give the avalanche a characteristic ‘tadpole’ shape. Sharp gradients in the avalanche thickness and velocity began to develop at the interface between the nose and tail of the avalanche as it came to rest, indicating that a shock wave develops close to the end of the experiments.

scholarly journals On a slender dry patch in a liquid film draining under gravity down an inclined plane

2001 ◽  
Vol 12 (3) ◽  
pp. 233-252 ◽  
Author(s):  
S. K. WILSON ◽  
B. R. DUFFY ◽  
S. H. DAVIS
Keyword(s):  
Surface Tension ◽  
Free Surface ◽  
Liquid Film ◽  
Similarity Solutions ◽  
Inclined Plane ◽  
First Case ◽  
Transverse Profile ◽  
Dry Patch ◽  
Strong Surface ◽  
Weak Surface

In this paper two similarity solutions describing a steady, slender, symmetric dry patch in an infinitely wide liquid film draining under gravity down an inclined plane are obtained. The first solution, which predicts that the dry patch has a parabolic shape and that the transverse profile of the free surface always has a monotonically increasing shape, is appropriate for weak surface-tension effects and far from the apex of the dry patch. The second solution, which predicts that the dry patch has a quartic shape and that the transverse profile of the free surface has a capillary ridge near the contact line and decays in an oscillatory manner far from it, is appropriate for strong surface-tension effects (in particular, when the plane is nearly vertical) and near (but not too close) to the apex of the dry patch. With the average volume flux per unit width (or equivalently with the uniform height of the layer far from the dry patch) prescribed, both solutions contain a free parameter. For each value of this parameter there is a unique solution in the first case and either no solution or a one-parameter family of solutions in the second case. The solutions capture some of the qualitative features observed in experiments.

scholarly journals The effects of surface tension on the initial development of a free surface adjacent to an accelerated plate

2015 ◽  
Vol 776 ◽  
pp. 37-73 ◽  
Author(s):  
J. Uddin ◽  
D. J. Needham
Keyword(s):  
Surface Tension ◽  
Free Surface ◽  
Local Structure ◽  
Contact Point ◽  
Initial Development ◽  
Early Stages ◽  
Inviscid Incompressible Fluid ◽  
Stationary Layer ◽  
Weak Surface ◽  
Theoretical Results

When a vertical rigid plate is uniformly accelerated horizontally from rest into an initially stationary layer of inviscid incompressible fluid, the free surface will undergo a deformation in the locality of the contact point. This deformation of the free surface will, in the early stages, cause a jet to rise up the plate. An understanding of the local structure of the free surface in the early stages of motion is vital in many situations, and has been developed in detail by King & Needham (J. Fluid Mech., vol. 268, 1994, pp. 89–101). In this work we consider the effects of introducing weak surface tension, characterized by the inverse Weber number $\mathscr{W}$, into the problem considered by King & Needham. Our approach is based upon matched asymptotic expansions as $\mathscr{W}\rightarrow 0$. It is found that four asymptotic regions are needed to describe the problem. The three largest regions have analytical solutions, whilst a numerical method based on finite differences is used to solve the time-dependent harmonic boundary value problem in the last region. Our results identify the local structure of the jet near the vicinity of the contact point, and we highlight a number of key features, including the height of this jet as well as its thickness and strength. We also present some preliminary experimental results that capture the spatial structure near the contact point, and we then show promising comparisons with the theoretical results obtained within this paper.

scholarly journals Surface Expression of a Wall Fountain: Application to Subglacial Discharge Plumes

2020 ◽  
Vol 50 (5) ◽  
pp. 1245-1263 ◽  
Author(s):  
Craig D. McConnochie ◽  
Claudia Cenedese ◽  
Jim N. McElwaine
Keyword(s):  
Free Surface ◽  
Laboratory Experiments ◽  
Surface Expression ◽  
Ambient Fluid ◽  
Buoyant Jet ◽  
Homogeneous Fluid ◽  
Length Width ◽  
Negatively Buoyant Jet ◽  
Negative Buoyancy ◽  
Negatively Buoyant

AbstractWe use laboratory experiments and theoretical modeling to investigate the surface expression of a subglacial discharge plume, as occurs at many fjords around Greenland. The experiments consider a fountain that is released vertically into a homogeneous fluid, adjacent either to a vertical or a sloping wall, that then spreads horizontally at the free surface before sinking back to the bottom. We present a model that separates the fountain into two separate regions: a vertical fountain and a horizontal, negatively buoyant jet. The model is compared to laboratory experiments that are conducted over a range of volume fluxes, density differences, and ambient fluid depths. It is shown that the nondimensionalized length, width, and aspect ratio of the surface expression are dependent on the Froude number, calculated at the start of the negatively buoyant jet. The model is applied to observations of the surface expression from a Greenland subglacial discharge plume. In the case where the discharge plume reaches the surface with negative buoyancy the model can be used to estimate the discharge properties at the base of the glacier.

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