Dense flows of grains are commonplace throughout natural and industrial environments, from snow-avalanches down the sides of mountains to flows of cereal down chutes as it is transported from one part of a factory to another. A ubiquitous feature in all of these flows is their ability to separate the different grain types when shaken, stirred, sheared or vibrated. Many flows are sheared through gravity and these flows are particularly efficient at segregating particles based on their size, with small particles percolating to the bottom of the flow and large particles collecting at the top. Within this mechanism, an asymmetry between the large and small particles has been observed, with small particles percolating downwards through many large particles at a faster rate than large particles rise upwards through many small particles. This alternative format thesis presents a revised continuum model for segregation of a bidisperse mixture that can account for this asymmetry. A general class of asymmetric segregation flux functions is introduced that gives rise to asymmetric velocities between the large and small grains. Exact solutions for segregation down an inclined chute, with homogenous and normally graded inflow conditions, show that the asymmetry can significantly enhance the distance for complete segregation. Experiments performed using a classical shear-box with refractive index matched scanning are able to quantify the asymmetry between large and small particles on both bulk and particle scales. The dynamics of a single small particle indicate that it not only falls down faster than a single large particle rises, but that it also exhibits a step-like motion compared to the smooth ascent of the large grain. This points towards an underlying asymmetry between the different sized constituents. The relationship between the segregation-time and the volume fraction of small grains is analysed, and solutions presented for the steady-state balance between segregation and diffusive remixing. These help to show the good agreement between the asymmetric model and experimental data. Segregation at the front of natural avalanches produces a recirculation zone, known as a `breaking size-segregation wave', in which large particles are initially segregated upwards, sheared towards the front of the flow, and overrun before being resegregated again. Solutions for the structure of this recirculation zone are derived using the asymmetric flux model, revealing a novel `lens-tail' structure. Critically, it is seen that a few large particles starting close to the bottom of the flow are swept a long way upstream and take a very long time to recirculate. The breaking size-segregation waves highlight the important interplay between segregation and the bulk velocity field. The properties of flowing monodisperse grains are explored through experiments on a cone that produce a beautiful radial fingering pattern. Equations developed in a conical coordinate system reproduce the measured linear relationship between fingering radius and initial flux, whilst also predicting the slowing and thinning dynamics of the flow. Overall, these results illustrate the complex nature of the granular rheology and provide perspectives for future modelling of segregation in dense granular flows.

Granular gas bed filters have been used in industry for a considerable period and mathematical descriptions of dust capture have allowed rigorous design of static beds. Provision for bed movement and electrostatic augmentation, which allows much thinner continuous beds to be used, requires adaptation of design methods for these phenomena. Design methods that allow for this are developed for a cross-flow bed with vertical bed movement and a number of granule and dust types. Direct current charging is applied to the bed itself and to the particles before they enter the bed. In the case of electrostatic augmentation, it is shown that simple models of spherical particles describe the mechanism adequately. The advantages of pre-charging dust particles before they enter the bed are indicated by calculation and proved experimentally. Parameters to describe the enhancement of filtration efficiency by the collected dust are obtained experimentally. It is shown that the factors controlling re-entrainment vary with particle size. For the dust particles less than 1,5 micrometers in size, re-entrainment is linked closely to the electrostatic capture mechanism which is dominant in that size range. For particles approaching 10 micrometer, re-entrainment can be neglected as the impaction efficiency, which is dominant for particles of this size and larger, approaches unity. A complex situation exists between these particle sizes as the magnitude and predominance of capture mechanisms in this region are determined by a number of operational parameters. It did not prove possible to develop predictive equations for re-entrainment efficiency using the results of this study. A number of heuristics are however developed that allow rational design by the use of the empirical parameters found, and that will be valid for the range of parameters used in this work. / Thesis (PhD(Chemical Engineering))--University of Pretoria, 2006. / Chemical Engineering / unrestricted

Integrated theoretical and experimental analysis is carried out in this work to investigate the fundamental failure mechanisms and flow patterns involved in the process of fluid injection into dense granular media. The experimental work is conducted with aqueous glycerin solutions, utilizing a novel setup based on a Hele-Shaw cell filled with dense dry sand. The two dimensional nature of the setup allows direct visualization and imaging analysis of the real-time fluid and grain kinematics. The experimental results reveal that the fluid flow patterns show a transition from simple radial flow to a ramified morphology while the granular media behaviors change from that of rigid porous media to localized failure that lead to development of fluid channels. Based on the failure/flow patterns, four distinct failure/flow regimes can be identified, namely, (i) a simple radial flow regime, (ii) an infiltration-dominated regime, (iii) a grain displacement-dominated regime, and (iv) a viscous fingering-dominated regime. These distinct failure/flow regimes emerge as a result of competition among various energy dissipation mechanisms, namely, viscous dissipation through infiltration, dissipation due to grain displacements, and viscous dissipation through flow in thin channels and can be classified based on the characteristic times associated with fluid injection, hydromechanical coupling and viscoelastoplasticity. The injection process is also analyzed numerically using the discrete element method (DEM) coupled with two fluid flow scheme, a fixed coarse grid scheme based on computational fluid dynamics (CFD) and a pore network modeling scheme. The numerical results from the two complementary methods reproduce phenomena consistent with the experimental observations and justify the concept of associating the displacement regimes with the partition among energy dissipation mechanisms. The research in this work, though fundamental in nature, will have direct impacts on many engineering problems in civil, environmental and petroleum engineering such as ground improvement, environmental remediation and reservoir stimulation.

Ce travail est financé par le fond européen Interreg VA (projet "PowderReg"). L'optimisation du transport, du stockage et du mélange des dispersions granulaires passe par le contrôle de leur écoulement, par exemple en ajoutant des vibrations mécaniques. Ce travail permet d'apporter une meilleure compréhension de l'influence des vibrations sur la rhéologie apparente de dispersions granulaires modèles dans le régime quasi-statique. Des travaux expérimentaux et numériques sont réalisés afin de sonder les modifications de la dynamique locale ainsi que les hétérogénéités qui apparaissent lors de leur mise en écoulement. Deux géométries présentant des intérêts fondamentaux, géophysiques et industriels sont étudiées : la cellule de type Couette et le plan incliné. Dans un premier temps, des mesures iso-indice couplées à de la fluorescence induite par laser ont été réalisées sur des suspensions granulaires dans une cellule de type Couette sous vibrations. Les vibrations rendent la rhéologie locale en homogénéisant le système. Elles suppriment la contrainte seuil apparente et font apparaître un plateau Newtonien à bas gradient, intrinsèque à la dynamique locale qui est de nature diffusive. Il est apparu que le temps de réarrangement des particules, dépendant de l'intensité des vibrations, est relié au volume libre disponible autour de chaque particule. L'étude numérique de cette géométrie dans le cas d'une dispersion granulaire sèche a mis en évidence des résultats similaires. Dans un second temps, des écoulements de dispersions de grains secs sur un plan incliné vibrant ont été réalisés. Des travaux numériques sur cette même géométrie ont permis d'enrichir cette étude. Les résultats mettent en évidence l'existence de deux régimes sous vibrations. Le comportement dans le régime dominé par la gravité n'est pas influencé par les vibrations, et un profil de Bagnold est observé. Les vibrations permettent principalement de baisser la friction basale, influant alors la hauteur des dépôts. Dans le régime dominé par les vibrations, les écoulements sont déclenchés par les vibrations elles-mêmes. Il est apparu qu'elles induisent des fluctuations de vitesses, qui créées alors une température granulaire. Cette température permet d'activer les réorganisations à l'échelle de la particule, éliminant le seuil apparent responsable du blocage des écoulements et permettant leur contrôle au travers du taux de cisaillement / This work is funded by the European Founds Interreg VA ("PowderReg" project). The optimization of the transport, storage and mixture of granular dispersions involves their flow control, by adding mechanical vibrations, for example. The present work enables a better understanding of the influence of the vibrations on the apparent rheology of model granular dispersions in the quasi-static regime. Experimental and numerical studies were carried out in order to probe the modifications of the local dynamic and heterogeneities that appear during the flow. Two geometries, interesting for diverse applications in fundamental science, geophysics and industries, were studied: the Couette cell geometry and the inclined plane. In the first step, refractive-index matching technique, coupled to the planar laser induced fluorescence was used to make measurements in granular suspensions in a vibrated Couette cell geometry. Vibrations make the rheology local by homogenizing the system. They suppress the yield stress and result in the appearance of a Newtonian plateau at the low shear, intrinsic to the local dynamic, which is diffusive in nature. It appears that the rearrangement time of the particles, depending on the intensity of the vibrations, is linked to a free volume available around each particle. The numerical study of this geometry in the case of a dry granular dispersion shows similar results. In the second step, flows of dry granular dispersions down the inclined and vibrated plane were realized. This study was completed with a numerical work. The results demonstrated the existence of two distinct regimes under vibrations. The behavior in the gravity-driven regime is not affected by the vibrations and a Bagnold profile is observed. The vibrations mainly cause the decrease of the basal friction and thus influence the height of the deposits. In the vibration-driven regime, however, flows are triggered by the vibrations themselves. It appears that they induce velocity fluctuations that create a granular temperature. That temperature allows the activation of the reorganizations at the grain scale. This suppresses the apparent yield responsible for the flow jamming, and thus enables their control through the shear rate

Thss thesis presents the results of an experimental programme on the static mono-tonic response of cohesive-frictional granular materials. The purpose of this experimental programme was to gain insight into the mechanical behaviour of uncemented sands, and sands with small percentages of cementation. With this objective in sight, the research involved understanding and delineating the e ects of four variables: the intermediate principal stress, stress inclination, cohesion (or cementation), and particle morphology. The hollow cylinder torsion (HCT) apparatus, which allows control over both the magnitude and direction of principal stresses, was used in this study to carry out a series of elemental tests on the model materials. The test results were analysed in a plasticity theory based framework of critical state soil mechanics. Drained and undrained HCT tests were conducted on a model angular sand to understand the combined influence of intermediate principal stress ratio (b) and principal stress inclination ( ). Sand specimens were reconstituted to a given density and confining pressure, and were sheared to large strains towards a critical state. The stresses at the critical state with varying `b' were mapped on an octahedral plane to obtain a critical state locus. The shape of this locus closely resembles a curved triangle. Also these specimens showed increased non-coaxiality between the stress and strain increment directions at lower strains. This non-coaxiality decreased significantly, and the response at the critical state was by and large coaxial. The effect of `b' and ` ' on the flow potential, phase transformation, and critical state was also investigated. At phase transformation, ` ' plays a more dominant role in determining the flow potential than `b'. The shape and size of the critical state locus remained the same immaterial of the drainage conditions. Next, small amounts of cohesion (using ordinary Portland cement) was added to this sand ensemble to study the mechanical behaviour of weakly cemented sands. The peak in the stress strain curve was used to signal the breakdown of cohesion further leading to a complete destructuring of the sand at the critical state. The response of the cemented sand changes from brittle to ductile with increase in confining pressure, while reverses with increase in density and `b'. Stress-dilatancy response for the weakly cemented materials shows the non coincidence of peak stress ratio and maximum value of dilation unlike purely frictional materials. This mismatch in peak stress ratio and maximum dilation diminishes with increase in confining pressure. The peak stress (cemented structured sand) locus and the critical state (destructured) locus were constructed on the octahedral plane from these HCT tests. The critical state locus of the cemented sand when it is completely destructured almost coincides with the critical state locus of the clean sand. Using this experimental data set, some important stress-dilatancy relationships (like Zhang and Salgado) and failure criteria (Lade's isotropic single hardening failure criteria and SMP failure criteria) were benchmarked and their prediction capabilities of such models were discussed in detail. The effect of particle morphology was also investigated in this testing programme. Rounded glass ballotini and angular quartzitic sand which occupy two extreme shapes were selected, and a series of HCT tests at different `b' values were con-ducted. A larger sized CS locus was obtained for angular particles and it encompassed the critical state locus of the spherical glass ballotini. Spherical particles exhibit a predominantly dilative behaviour, however present a lower strength at the critical state. The mobilization of strength as a result of rearrangement of angular particles and the consequent interlocking is higher. Even with contractive behaviour which is reflected in the higher values of critical state friction angle and the larger size of the yield locus for sand. Finally, a series of unconfined compression tests were performed to understand if there exists a scale separation in cohesive frictional materials. Specimens were reconstituted to a range of sizes while maintaining a constant aspect ratio and density. As the specimen size increased, the peak strength also increases, counter to an idea of a generalized continuum for all model systems. The observed secondary length scale (in addition to the continuum length scale) is obverse to the one observed in quasi-brittle materials such as concrete, rock. In order to ascertain the reason behind this phenomenon, a series of tomography studies were carried out on these contact-bound ensembles. The presence of cohesion between the grains brings about an \entanglement" between the grains, which contributes to increase in strength, with increase in the size of the sample. This in e ect bringing forth a second length scale that controls the behaviour of these cohesive frictional granular materials. This experimental data set provides quantification of various aspects of the me-chanical response of both cemented and uncemented granular materials under myriad stress conditions. This data set is also extremely useful in developing and bench-marking constitutive models and simulations.

<p dir="ltr">The ability to predict and manipulate how a particulate material will flow in a process is challenging for industry and researchers alike. This dissertation presents the results of a model-directed, experimental approach using a concentric cylinder rheometer titled along an axis to enable continuous chute flow of granular media. Experiments were performed using draining flows for constant and oscillatory applied shear rates. Multiple flow and stress sensors were used to investigate the interaction of mass holdup, shear rate, specific torque, particle velocity, discharge mass flow rate, and wall pressure. Depending on the flow configuration, linear ranges were observed wherein the specific torque remained steady during draining. This finding enabled systematic testing of flow behavior as a function of dimensionless shear rates. Results suggest changes in the specific torque, wall slip, and outflow variance occur with the transition from the quasi-static to dense-inertial flow regimes. A pump-curve analogy was also identified for the relationship between the outlet mass flow rate and the specific power relationship for the constant shear rate experiments. Oscillatory shear rate experiments show a significant influence of the phase shift between the applied shear rate and the specific torque. Adding an asperity to the rotor revealed rate-dependent patterns in bulk flow and force chain dynamics. Overall, the study offers valuable insights into the effects of shear rate and boundary conditions on dense granular flows. The effects of particle characteristics (e.g., size and shape distributions, friction, cohesivity) and material properties (e.g., density, modulus) remain topics for future work. </p>

This thesis provides a report on the numerical analysis of stress distributions within granular materials held in silos and hoppers. Stress distributions within granular materials stored in silos and hoppers have been the subject of research for over 100 years, work starting in this field in 1895 (Janssen). Knowledge of stress distributions within the granular materials contained is essential to allow structural design of the silo and hopper shell and attachments, and to allow estimation of likelihood and location of cohesive arch formation. National design codes for silos and hoppers (including BS EN 1993-4-1:2007 Eurocode 3 and DIN 1055-6:2005-03) are based on approximate techniques that assume vertical and horizontal directions of principal stresses, with constant horizontal stress across the silos. According to the knowledge of the author there are no industrial standards that allow calculation of loading on inserts within hoppers. The objective of the research project is to develop algorithms to predict stresses in hoppers and silos using principal stress arc geometry methods, and implementation of these methods in various silo and hopper configurations including those with inserts for the purposes of aiding flow. The research project algorithms are spreadsheet- and QB64 platform-based, and are able to produce stress distributions within silos and hoppers. This is achieved by extension of the principal stress arc method of analysis. The new algorithms allow prediction of common flow problems and provide new information on structural loading of silos and hoppers, including inserts used to promote flow. The research project models allow estimation of azimuthal stresses within three-dimensional case studies.

Thesis (MSc)--Stellenbosch University, 2015. / ENGLISH ABSTRACT: This research study investigates the influence of specimen geometry and grading curve, on the performance of a typical South African unbound granular material. The experimental design incorporates three grading curves to evaluate the influence of grading. In addition, to evaluate the influence of specimen geometry, two specimen sizes were included into the experimental design. Laboratory testing consisted of monotonic tri-axial tests to evaluate the shear performance (Cohesion and Friction Angle) and more complex short duration dynamic tri-axial tests to evaluate the load spreading ability/stiffness (Resilient Modulus) of the selected materials. In order to achieve the objectives of this study, a large tri-axial apparatus was needed that could accommodate specimens as large as 300mm ϕ * 600mm high. This would allow a full grading of large aggregate (up to 50mm particle size) to be accurately evaluated. Further development and commissioning of such a large triaxial apparatus therefore formed part of this study. The representative parent material selected for testing consisted of a G2 graded crushed Hornfels stone. The material was dried and sieved into fractions where after it was carefully reconstituted to allow for accurate control of specimen grading during specimen preparation. The three grading curves consisted of two adjusted grading curves (referred to as S19 and G19C), adjusted from the full G2 grading, and the full G2 grading itself (referred to as the Full grading curve). Material property tests, Sieve Analysis, Bulk Relative Density (BRD) and Optimum Moisture Content (OMC) tests were performed to gain an understanding of the material characteristics. Moisture-Density relationship curves were developed to identify a common Moisture Content that, for all three grading curves, would yield a common Dry Density. A Moisture Content of 4.7% was identified that would yield a Dry Density of 2340 kg/m3 for all three grading curves. This density could be achieved for both sizes of specimen preparation apparatuses without damaging material particles. Specimens were compacted using the representative vibratory hammer compaction method, sealed and left for 24 hours to allow redistribution of moisture and initial development of Cohesion. The shear parameters (Cohesion and Friction Angle) were investigated through monotonic tri-axial testing. It was found that Cohesion and Friction Angle are influenced by both grading curve and specimen geometry. Cohesion was found to reduce as the coarseness of the material grading increased (i.e. finer S19 grading yielded higher Cohesion than its coarser G19C counterpart) and the Friction Angle was found to increase with increase coarseness (i.e. finer S19 grading yielded lower Friction Angles when compared to the G19C grading). The influence of specimen geometry was also investigated. It was observed than Cohesion decreased with an increase in specimen size. Friction Angle on the other hand was found to increase with increased specimen size. From dynamic tri-axial test results, it was observed that the Resilient Modulus is influenced by both specimen geometry and grading curve. The influence of specimen geometry however is complex and no constant trend throughout the grading curves tested could be identified. Grading curve however was found to increase the Resilient Modulus for coarser gradings (i.e. coarser G19C vs finer S19). Increased large particle-to-particle contact area yields higher friction within the material specimen, resulting in lower strains induced by higher stresses, i.e. higher Resilient Modulus. It was shown, for both monotonic and dynamic tri-axial tests, that the coarser G19C grading curve yields more representative results to that of the Full grading curve when compared to the finer S19 grading. This was observed for shear and resilient performance properties. Additionally, a simple design case study yields similar trends. In conclusion, material characterisation plays an important role in the design of unbound granular materials (UGM’s). Current laboratory characterisation techniques however used adjusted gradings to limit the effects stemming from the ratio between specimen diameter and maximum particle size. This research has shown that some of the current practices do not best represent the true in-situ grading. It has been shown that both grading curve and specimen geometry influence the performance of UGM’s which, in turn, influences the design of a pavement structure. Therefore, accurate modelling of the true in-situ grading, through testing apparatuses capable of accommodating in-situ gradings, is required. / AFRIKAANSE OPSOMMING: Hierdie navorsingsstudie evalueer die invloed van proefstukgeometrie en gradering, op die gedragseienskappe van ‘n tipiese Suid Afrikaanse ongebinde granulêre aggregaat. Om die invloed van gradering te evalueer, is ‘n eksperimentele ontwerp ontwikkel wat drie materiaal graderings insluit. Verder, om die invloed van proefstukgeometrie te evalueer, is twee proefstukgroottes toegevoeg tot die eksperimentele ontwerp. Monotoniese drie-assige toetse is uitgevoer om die skuifsterkte (Kohesie en Wrywingshoek) van die materiaal te ondersoek. Addisioneel is die styfheid (Veerkragmodulus) van die materiaal ondersoek deur dinamiese drieassige toetse. Om die doelwitte van hierdie studie te bereik was ‘n groot skaalse die-assige toets apparaat benodig wat groot, 300mm ϕ * 600mm hoogte, proefstukke kan akkommodeer. So ‘n apparaat laat toe dat die volle gradering van aggregaat (tot en met 50mm korrels) akkuraat geëvalueer kan word. Daarom vorm die ontwikkeling en opstelling van so ‘n apparaat deel van hierdie studie. Die tipiese Hornfels gebreekte klip, met ‘n G2 gradering, wat ondersoek is, was gedroog en in verskeie fraksies gesif om die akkuraatheid van proefstuk voorbereiding te beheer. Die drie graderings bestaan uit twee aangepaste graderings (S19 en G19C gradering skale), aangepas vanaf die volle G2 gradering, en die vol G2 gradering homself (verwys na as die “Full” gradering skaal). Materiaal gedragstoetse, Sif Analises, Nat Gekompakteerde Relatiewe Digtheid (BRD) en Optimum Vog Inhoud (OVI) toetse, was uitgevoer om die materiaal eienskappe te ondersoek. Om ‘n gemeenskaplike Vog Inhoud en Droë Digtheid, wat vir al drie graderings geld, te vind, is Vog-Digtheid verhoudingskurwes ontwikkel. Vanaf die kurwes is identifiseer dat ‘n Vog Inhoud van 4.7% ‘n Droë Digtheid van 2340 kg/m3 vir al drie graderings sal lewer. Vibrasie kompaksie is toegepas om albei skale van proefstukke te kompakteer waarna die proefstukke vir 24 uur geseel is om vogverspreiding en ontwikkeling van Kohesie toe te laat. Monotoniese drie-assige toetse is uitgevoer om die skuifsterkte parameters (Kohesie en Wrywingshoek) te ondersoek. Die resultate het gewys dat beide gradering en proefstukgeometrie die Kohesie en Wrywinshoek beinvloed. gradering lewer hoër Kohesie waardes i.v.m. die growwer G19C gradering). Die Wrywingshoek is gevind om te verhoog soos die grofheid van die gradering verhoog (m.a.w. die fyner S19 gradering het laer Wrywingshoeke gelewer i.v.m. die growwer G19C gradering). Resultate het verder gewys dat groter proefstukke laer Kohesie en hoër Wrywingshoeke lewer. Daar kan wel gedebateer word dat variasie in materiaal die verandering van die skuifsterkte parameters gee, maar die proefstukvariasie is beperk om sodoende die invloed daarvan onopmerkbaar te maak.. Verder is die verlaging in Kohesie en verhoging in Wrywingshoek, a.g.v. ‘n vergroting in proefstuk grootte, vir albei aangepaste graderings geobserveer. Dit is ‘n moontlike aanduiding dat die verandering nie materiaal afhanklik is nie maar eerder beinvloed word deur die grens toestande tydens kompaksie. Dinamiese drie-assige toets resultate het gewys dat die Veerkragmodulus beinvloed word deur beide proefstuk geometrie en gradering. Daar is gevind dat die invloed van proefstukgeometrie kompleks is, en geen konstante verhouding, wat vir alle toets graderings geld, kon identifiseer word nie. Vir die invloed van gradering is daar gewys dat die Veerkragmodulus hoër is vir die growwer gradering (m.a.w. G19C gradering lewer hoër styfheid as S19 gradering). ‘n Verhoging in korrel-tot-korrel kontak area lewer hoër interne wrywing in die proefstuk wat bydrae tot laer vervorming by hoër spannings, m.a.w. hoër Veerkragmodulus. Baie interessant, vir beide monotoniese en dinamiese drie-assige toetse is gevind dat die growwer G19C gradering, i.v.m. die fyner S19 gradering, die ware G2 (Full) gradering beter verteenwoordig. Hierdie observasie is geldig vir beide die skuifsterkte parameters en weerstands eienskappe. Aggregaat karakterisering is ‘n belangrike deel in die ontwerp van ‘n ongebinde granulêre materiaal laag. Huidige karakterisering metodes gebruik aangepaste graderings sodat resultate nie beinvloed word deur die verhouding tussen proefstuk diameter en maksimum klipgrootte nie. Hierdie ondersoek het gevind dat van die huidige aanpassings nie die ware gradering verteenwoordig nie. Die resultate wys dat beide gradering en proefstuk geometrie die gedrag van die ongebinde granulêre materiaal beinvloed, so ook die ontwerp van ‘n padstruktuur. Daar is dus ‘n behoefte om die ware gradering te ondersoek wat slegs moontlik is met groot skaalse toets apparaat, wat groot klip korrels kan toets. Verder, indien daar ‘n verstandhouding tussen huidige (klein skaalse) toets apparaat en groot skaalse apparaat ontwikkel kan word, kan resultate aangepas word, vanaf die klein skaalse resultate, om die ware materiaal gedrag meer te verteenwoordig.

<p align="justify">Ce travail consiste à étudier des systèmes constitués par un grand nombre de grains, auxquels de l’énergie cinétique est fournie, et à étudier leurs similarités et leurs différences avec des fluides traditionnels. Je me concentre principalement sur la nature de non-équilibre de ces fluides granulaires, en montrant que, même si les méthodes de méchanique statistique y sont applicables, leurs propriétés sont très différentes de celles de systèmes à l’équilibre ou proches de l’équilibre :</p> <ul><li>Les fluides granulaires présentent des phénomènes de transport qui n’ont pas d’équivalent dans des fluides moléculaires, tels qu’un couplage spécifique entre flux de chaleur et gradient de densité. <li>Leur distribution de vitesse est en général différente de la distribution de Maxwell-Boltzmann, et présente une surpopulation pour les grandes vitesses. <li>Dans le cas de mélanges, différentes espèces de grains sont en général caractérisées par des énergies cinétiques différentes, i.e. ces systèmes sont sujet à une non-equipartition de leur énergie. <li>Ces fluides ont tendance à former des inhomogénéités spatiales spontanément. Cette propriété est illustrée en étudiant l’expérience du Demon de Maxwell appliquée aux systèmes granulaires.</ul> <p align="justify">Chacune de ces particularités est discutée en détail dans des chapitres distincts, où l’on applique différentes méthodes de méchanique statistique (équation de Boltzmann, transition de phase, mean field models…) et où l’on vérifie les prédictions théoriques par simulations numériques (MD, Monte Carlo…).</p>

In geotechnical engineering, granular flows are often studied as a means to further the understanding of the mechanisms that drive landslide motion. High quality experimental data is essential in providing evidence for the development and verification of new theoretical methods that link complex grain interactions to the extended mobility of some landslide events. At present, limited experimental data is available that captures the full range of landslide mobility. In an attempt to add to the present data sources, high quality experimental data was obtained through the use of high speed cameras and physical modelling using a geotechnical centrifuge and a large scale landslide flume. These modelling techniques allow for landslide motion, representative of field scale events, to be observed in a well-defined and controlled setting. A series of nine tests were performed in a geotechnical centrifuge under varying slope inclinations and Coriolis conditions. The effects of Coriolis on landslide mobility were evident when comparing final deposit shapes and total runout. The effects of Coriolis were more pronounced for higher velocity situations and when material was travelling on the horizontal base section opposed to the sloped section of the physical model. A series of thirty tests were performed using a large scale flume under varying source volumes and basal friction conditions, capturing the grain scale interactions and overall runout behaviour. The grain interactions and ultimately the flow behavioural regimes developed were a function of material source volume and boundary roughness. The dimensionless inertial number was used to classify flows into behavioural regimes, but was found to break down when describing transitions to the granular gas behavioural regime. The runout-time results and final deposit shapes showed significant variation between test configurations, indicating the effects of volume and basal friction on overall mobility. Using the depth averaged numerical model, DAN, it was found that a single set of empirically derived frictional parameters (i.e. specific to internal and basal friction conditions) was appropriate for matching the overall mobility of the experimental flows over a range of flow volumes and slope inclinations. / Thesis (Master, Civil Engineering) -- Queen's University, 2013-09-25 15:48:54.761