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Artykuły w czasopismach na temat "Experimental Granular Mechanics"
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Hall, S. A., i J. Wright. "Three-dimensional experimental granular mechanics". Géotechnique Letters 5, nr 4 (grudzień 2015): 236–42. http://dx.doi.org/10.1680/jgele.15.00094.
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Goldshtein, Alexander, Michael Shapiro, Leonid Moldavsky i Mati Fichman. "Mechanics of collisional motion of granular materials. Part 2. Wave propagation through vibrofluidized granular layers". Journal of Fluid Mechanics 287 (25.03.1995): 349–82. http://dx.doi.org/10.1017/s002211209500098x.
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According to numerous experimental observations and theoretical models vibrated layers composed of large granules behave like a solid plastic body. In contrast, in this study experimental data are presented that reveal that, for constant vibration amplitudes A ≥ 1 cm with the frequency ω increasing from zero, all layers pass through three vibrational states, with the respective behaviours being as of (i) a solid plastic body, (ii) a liquid, (iii) a gas. In the liquid-like vibrational state transverse waves propagating along the layer width were observed. These waves were shown to be gravitational resonance waves, with the corresponding frequencies well correlated by the known formula for incompressible liquids. In the gas-like vibrational state compression (shock) and expansion waves propagating across the layer height, were observed.A theoretical model for time-periodic collisional vibrational regimes was developed on the basis of the Euler-like equations of a granular gas composed of inelastic spheres. The model shows that the vibrational granular state (bed porosity, shock wave speed, granular pressure and kinetic energy) is inter alia governed by the dimensionless parameter V = (Aω)/(hmg)1/2, with g, hm being the gravitational acceleration and the height of the resting layer, respectively. This is in contrast with the previous studies, where the behaviour of vibrated granular layers was interpreted in terms of the dimensionless acceleration Δ = (Aω2)/g. The proposed model was tested by processing the data obtained from photographs of the particle distribution within vibrated layers. Theoretical predictions of the particle average concentration compared favourably with the experimental data.Other phenomena observed in vibrated granular layers include the formation of caverns, circulatory motion of granules and synchronized periodic motion of two adjacent vibrated layers of different widths. The importance of the observed phenomena in relation to various technological processes involving bulk materials (vibromixing, vibroseparation, etc.) is discussed.
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Rusinek, R. "Experimental method for determination of the pressure distribution in granular solids". Research in Agricultural Engineering 49, No. 2 (8.02.2012): 61–64. http://dx.doi.org/10.17221/4954-rae.
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This paper presents two methods of determination of pressure distribution in rape seeds. The study utilized hydraulic pressure sensors with active rubber face and stress state transducer with six duralumin face sensors. This project utilized methodology well known from soil mechanics for determination stress in plant granular material. The hydraulic pressure sensors has been design to measure normal pressure in granular material. The stress transducer has been designed to measure pressure in six different directions, which orientation enable to calculate the stress state from the pressure measurements. The project enclose to design calibrations procedure. Calibration of each of sensors of stress transducer was performed both under air pressure and inside the bedding of rapeseeds. The preliminary tests of both pressure sensors developed for the direct in-bulk measurement within granular material allowed to determinations pressure distribution in granular materials. Experiments were performed inside bedding of rapeseeds of 6% moisture content.
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Hurley, R. C., S. A. Hall i J. P. Wright. "Multi-scale mechanics of granular solids from grain-resolved X-ray measurements". Proceedings of the Royal Society A: Mathematical, Physical and Engineering Sciences 473, nr 2207 (listopad 2017): 20170491. http://dx.doi.org/10.1098/rspa.2017.0491.
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This work discusses an experimental technique for studying the mechanics of three-dimensional (3D) granular solids. The approach combines 3D X-ray diffraction and X-ray computed tomography to measure grain-resolved strains, kinematics and contact fabric in the bulk of a granular solid, from which continuum strains, grain stresses, interparticle forces and coarse-grained elasto-plastic moduli can be determined. We demonstrate the experimental approach and analysis of selected results on a sample of 1099 stiff, frictional grains undergoing multiple uniaxial compression cycles. We investigate the inter-particle force network, elasto-plastic moduli and associated length scales, reversibility of mechanical responses during cyclic loading, the statistics of microscopic responses and microstructure–property relationships. This work serves to highlight both the fundamental insight into granular mechanics that is furnished by combined X-ray measurements and describes future directions in the field of granular materials that can be pursued with such approaches.
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Abdul Qadir Rahimoon. ""ABOUT STRESS TRANSMISSION THROUGH DISORDERED MEDIA CONFINED IN SILO GEOMETRY "". Bulletin of Toraighyrov University. Physics & Mathematics series, nr 1.2022 (28.03.2022): 48–57. http://dx.doi.org/10.48081/wnvy4031.
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"Granular materials are found everywhere around us. A fundamental understanding of the behaviour of these materials is bound to have profound economic benefits. To understand the macroscopic behaviour of granular media and its relationship with the microscopic properties are major objectives of granular mechanics. However, presently macroscopic equations are empiric because of the complexities at the microscopic level. Granular media exhibit properties that are different from those of solids, liquids and gas and much of their behavior has not been fully understood. In this paper a brief survey of Physics of confined granular media has been presented. This is accomplished by reviewing the experimental and theoretical work done to determine the properties of static granular media and concerning theories presented to explain the properties. The apparent mass measurement at the bottom of a granular pile confined in a vertical tube decreases for denser granular packing. The denser granular packing comprising of two different diameters of granules augment the apparent mass instead. This anomalous behavior occurs when small granules are stacked on the large ones. In the case of anomalous increase, a percolation effect is found and correlated with the augment of apparent mass at the bottom of granular column. "
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CIAMARRA, MASSIMO PICA, ANTONIO DE CANDIA, ANNALISA FIERRO, MARIO NICODEMI i ANTONIO CONIGLIO. "STATISTICAL MECHANICS OF STATIC GRANULAR PACKINGS UNDER GRAVITY". International Journal of Modern Physics B 23, nr 28n29 (20.11.2009): 5345–58. http://dx.doi.org/10.1142/s0217979209063675.
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Despite the large use of granular materials in the industry, and the large number of natural phenomena where granular materials are involved, a comprehensive theoretical framework of their physics is still missing. An important perspective was proposed almost 20 years ago by S.Edwards, which suggested the possibility of a statistical mechanics description of granular materials at rest in their mechanically stable states. This article focuses on the theoretical foundations and current understanding of a statistical mechanics approach of granular materials under gravity. Experimental and numerical results discussing such an approach and clarifying its limit of validity are described as well.
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Shukla, A., C. Y. Zhu i M. Sadd. "Angular dependence of dynamic load transfer due to explosive loading in granular aggregate chains". Journal of Strain Analysis for Engineering Design 23, nr 3 (1.07.1988): 121–27. http://dx.doi.org/10.1243/03093247v233121.
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An experimental investigation was conducted to study the dependence of packing geometry on the dynamic load transfer in two dimensional granular aggregate chains. The granular media was simulated by circular discs made of photoelastic material. The experimental method utilizes the combination of high speed photography and photoelasticity to visualize the dynamic load transfer phenomenon in two dimensional model chains subjected to explosive loading. The photographs thus obtained were analysed to get the normal and tangential loads at the contact points as a function of time. The results indicate that the load transfer is strongly dependent on the angle between the vectors drawn from the mass centres of the contacting granules.
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Aleksandrov, A. S., A. V. Smirnov i T. V. Semenova. "Stress Investigation in Pavement Layers and a New Nalculation Model". Materials Science Forum 945 (luty 2019): 813–20. http://dx.doi.org/10.4028/www.scientific.net/msf.945.813.
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The paper is devoted to the comparison results of experimental data and theoretical stress calculations (arising in pavement layers made from granular materials). The formulas of continuum mechanics and mechanics for granular materials and mathematical dependences, got in accordance with engineering calculation method, were taken as a calculation model. The experimental stress values, measured by Steven B.D. using ring stand (University of Canterbury), were applied as a standard. The ring stand ley us employ moving loads to the stand segments with pavement constructed over the ring stand. It was discovered that the best match of values of experimental and calculation data is got by stress computing based on formulas of mechanics for granular materials (M.E. Harr or I.I. Kandaurov) or continuum mechanics, but with O.C. Frohlich parameter added to С.R. Foster, R.G. Ahlvin and H.H. Ulery’s formula. This Frohlich parameter can be taken as a material parameter. In the conclusion the authors show the way of modification of the well-known approaches in mechanics for granular materials. This new way makes possible to calculate minimum principal stress σ3.The modified mathematical relationships of principal stress calculation can be used in models for elastic, plastic, elastic-plastic deformation calculations and in conditions of plasticity.
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Sornette, A., D. Sornette i P. Evesque. "Frustration and disorder in granular media and tectonic blocks: implications for earthquake complexity". Nonlinear Processes in Geophysics 1, nr 4 (31.12.1994): 209–18. http://dx.doi.org/10.5194/npg-1-209-1994.
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Abstract. We present exploratory analogies and speculations on the mechanisms underlying the organization of faulting and earthquake in the earth crust. The mechanical properties of the brittle lithosphere at scales of the order or larger than a few kilometers are proposed to be analogous to those of non-cohesive granular media, since both systems present stress amplitudes controlled by gravity, and shear band (faulting) localization is determined by a type of friction Mohr-Coulomb rupture criterion. here, we explore the implications of this correspondence with respect to the origin of tectonic and earthquake complexity, on the basis of the existing experimental data on granular media available in the mechanical literature. An important observation is that motions and deformations of non-cohesive granular media are characterized by important fluctuations both in time (sudden breaks, avalanches, which are analogous to earthquakes) and space (strain localizations, yield surfaces forming sometimes complex patterns). This is in apparent contradiction with the conventional wisdom in mechanics, based on the standard tendency to homogenize, which has led to dismiss fluctuations as experimental noise. On the basis of a second analogy with spinglasses and neural networks, based on the existence of block and grain packing disorder and block rotation "frustration", we suggest that these fluctuations observed both at large scales and at the block scale constitute an intrinsic signature of the mechanics of granular media. The space-time complexity observed in faulting and earthquake phenomenology is thus proposed to result form the special properties of the mechanics of granular media, dominated by the "frustration" of the kinematic deformations of its constitutive blocks.
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Elkholy, Karim N., i M. M. Khonsari. "Granular Collision Lubrication: Experimental Investigation and Comparison to Theory". Journal of Tribology 129, nr 4 (25.05.2007): 923–32. http://dx.doi.org/10.1115/1.2768613.
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An experimental investigation of the friction and lift characteristics of granular lubrication is presented. Experiments are carried out to demonstrate the vertical displacement (lift) observed in an annular shear cell apparatus. Results are presented for the friction coefficient as a function of the rotational speed and the applied load for several surface roughness combinations. Simulations of the kinetic theory for the granular material are performed and compared to the experimental results. The experiments provide an evidence for the formation of granular lift between two disks undergoing sliding motion.
Rozprawy doktorskie na temat "Experimental Granular Mechanics"
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Jadrnak, Sharon Marie. "Experimental studies of bimodal granular material flows". Thesis, Georgia Institute of Technology, 1989. http://hdl.handle.net/1853/16107.
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García, Aragón Juan Antonio. "Experimental and analytical investigations of granular-fluid mixtures down inclines". Thesis, McGill University, 1993. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=41021.
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Granular-fluid mixtures flowing down an incline in the grain-inertia regime were studied experimentally and analytically. The equations of motion are based on the kinetic theory for granular flow. The boundary conditions are formulated following two methods. The first is a simple mechanical approach based on the energy exchange at the wall. The other is based on the kinetic theory for granular flow. Solutions for dry granular flow down a chute are studied in order to compare both methods. The extension of the kinetic theory presented here, includes drag forces resulting from the interstitial fluid that cushions interparticle collisions and particle-wall collisions. Frictional stresses, produced when long term contacts are present, and fluid turbulent fluctuations are introduced in the model.The results are compared with measurements from an experimental chute in which the inclination, the solids flow rate and fluid flow rate are all varied. The theory is found to give a good qualitative account of the observed behaviour. Finally an application of the model to the description of the mechanical behaviour of the Nevado del Ruiz 1985 debris flow is attempted.
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Zoueshtiagh, Farzam. "Experimental and computational study of spiral patterns in granular media underneath a rotating fluid". Thesis, University of Warwick, 2001. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.247353.
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Bougouin, Alexis. "Etude expérimentale de l'effondrement d'une colonne fluide-grains". Thesis, Toulouse, INPT, 2017. http://www.theses.fr/2017INPT0113/document.
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Autour de nous, les systèmes granulaires sont omniprésents et rarement dissociés d'une phase liquide ou gazeuse. L'interaction entre les deux phases (solide et fluide) implique une dynamique d'écoulement complexe de ces systèmes couplés. Cette thèse expérimentale a pour but de caractériser la dynamique d'effondrement gravitaire instationnaire d'une colonne fluide-grains dans différentes configurations de mélange diphasique. Considérant uniquement l'effet des grains au sein du fluide, la dynamique d'écoulement d'une suspension isodense dans l'air est d'abord abordée avec une description macroscopique. En particulier, La rhéologie du fluide apparent est extraite à partir de l'évolution temporelle du front en utilisant des solutions auto-similaires, modèles de la dynamique de propagation aux temps longs. Sur la gamme du nombre de Reynolds étudiée, la dynamique d'écoulement de la suspension est décrite comme celle d'un fluide apparent Newtonien ou non-Newtonien (rhéofluidifiant, rhéoépaississant, viscoplastique) dépendant des paramètres considérés (fraction volumique, viscosité du fluide interstitiel, diamètre des grains, protocole de préparation). Afin de décrire la configuration opposée d'un massif sédimentaire pour lequel les interactions entre particules solides deviennent dominantes, la configuration d'une colonne granulaire dense saturée en fluide, i.e. où les grains sont plus lourds que le fluide porteur, est ensuite étudiée. Un travail préliminaire est consacré à la caractérisation de l'effondrement d'une colonne granulaire totalement immergée dans un fluide. Le rôle dissipatif de ce dernier sur le milieu granulaire est mis en évidence par une analyse de la dynamique d'effondrement et des caractéristiques du dépôt final. Cette caractérisation permet de classifier les régimes d'effondrement en fonction de la viscosité et de la masse volumique du fluide environnant, i.e. du nombre de Stokes et du rapport de masse volumique entre le fluide et les grains. Dans le cas triphasique, i.e. lorsque la colonne fluide-grains s'effondre dans l'air, la dynamique peut être fortement affectée par les effets capillaires à travers le nombre de Bond qui contrôle alors la mise en mouvement de la colonne initiale. Quand ces effets deviennent négligeables à l'échelle de la colonne et à celle du grain, le fluide interstitiel peut jouer un rôle moteur ou dissipatif vis-à-vis dumilieu granulaire conduisant à une longueur d'étalement plus ou moins importante en comparaison au cas sec. Le rôle du fluide interstitiel dépend essentiellement de sa viscosité modifiant, par la même occasion, la dynamique d'effondrement. Enfin, une étude préliminaire sur la dynamique d'écoulement d'une suspension non-isodense, initialement homogène, est réalisée. Cette configuration, à la transition des situations décrites précédemment, permet d'aborder le couplage de la dynamique de sédimentation des grains et celle du courant. En particulier, nous observons que la vitesse de sédimentation décroît avec l'augmentation de la fraction volumiqueinitiale en particulesOn the Earth's surface, granular medias are ubiquitous and they are rarely dissociated from a liquid or a gas. The fluid-solid interaction leads to a complex flow dynamics of these coupled systems. This experimental work aims at characterizing the dynamics of the unsteady gravitydrivencollapse of a granular-fluid column within different configurations of the diphasic mixture. First, the flow dynamics of a neutrally buoyant suspension in air are characterized based on a macroscopic description of the flow. In particular, the rheological parameters of the apparent fluid have been extracted using the temporal evolution of the propagating front and self-similar solutions, models of the propagating dynamics at long times. In the considered range of the Reynolds number, the flow dynamics are described as an apparent Newtonian or non-Newtonian (shear-thinning/-thickening, viscoplastic) fluid depending on the various parameters (volume fraction, viscosity of the interstitial fluid, particle diameter, mixing protocol). In order to describe the opposite case of a sedimentary environment where particle-particle interaction becomes dominant, a second part of this work investigates the case of a fluid-saturated granular collapse, i.e. for which particles are heavier than the carrier fluid, in a dense packing configuration. For this purpose, a first part of the study is dedicated to characterize the collapse of an immersed granular column. The dissipative role of the fluid on the granular media is highlighted by an analysis of the collapse dynamics and the characteristics of the final deposit. This characterization allows to classify the regimes of the collapse depending on the viscosity and the density of the surrounding fluid, i.e. the Stokes number and the fluid-grain density ratio. In the triphasic case, i.e. when the granular-fluid column collapses in air, the dynamics may be strongly affected by capillary effects through the Bond number which controls the initial dynamics of the column. When these effects can be neglected (large Bond number) at the column and grain scales, the interstitial fluid can have a driven or a dissipative role on the granular media leading to a runout length more or less extended in comparison to the dry case. The role of the interstitial fluid depends mainly on its viscosity which also modifies the collapse dynamics. Finally, a preliminary study is realized on the flow dynamics of an initially homogeneous negative buoyant suspension column. This case, which makes the transition between the above mentioned configurations, allows to study the coupling between the settling dynamics of particles and this of the current. In particular, we observe that the settling velocity decreases with the increase of the initial volume fraction of particles
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Robbe-Saule, Manon. "Modélisation expérimentale de génération de tsunami par effondrement granulaire". Thesis, Université Paris-Saclay (ComUE), 2019. http://www.theses.fr/2019SACLS497/document.
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Des événements géologiques passés ont montré que les glissements de terrain, près des côtes, impliquant des volumes de quelques milliers de mètre cube à plusieurs centaines de kilomètres cube, peuvent provoquer des vagues de tsunami d’une amplitude considérable. La vague générée et l’effondrement représentent tous deux un danger important pour la population et les infrastructures situées sur ou proche des côtes. Une modélisation réaliste nécessite de tenir compte de la nature granulaire du glissement de terrain. Nous avons développé dans ce travail de thèse, une série d’expériences de laboratoire à petite échelle, pour étudier en détail le processus de génération de vague par l’effondrement d’une colonne granulaire, initialement sèche, dans l’eau. Tout un ensemble de paramètres est testé : (1) la masse granulaire impliquée (hauteur, volume, rapport d’aspect, granulométrie et densité), (2) la hauteur d’eau et (3) la configuration géométrique (plan horizontal ou plan incliné). Des expériences quasi-bidimensionnelle en canal rectangulaire, permettent d’enregistrer à la fois l’évolution temporelle de l’effondrement granulaire et celle de la surface libre de l’eau. Nous montrons que le processus de génération des vagues est piloté par la dynamique collective de l’effondrement des grains à la surface de l’eau. Nous identifions une dépendance linéaire claire entre l’amplitude relative de la vague principale et un nombre de Froude défini comme le rapport des vitesses d’avancée du front granulaire et de la vague solitaire. En particulier, l’amplitude de la vague atteint sa valeur maximale pour une profondeur d’eau intermédiaire. Le transfert d’énergie global a montré que seulement quelques pourcents de l’énergie potentielle initiale de la colonne sont transférés à la vague, issus notamment d’une perte d’énergie considérable dans l’effondrement granulaire lui-même. Enfin, nous soulignons la faible influence du diamètre et de la masse volumique des grains dans la génération de la vague. Cela suggère que la masse de l’effondrement est de faible importance par rapport à son volume. Un autre résultat intéressant est la dépendance linéaire de l’amplitude relative de la vague avec le volume immergé du dépôt final. Cette loi nous permet d’estimer l’amplitude de la vague pour des événements passés et potentiels. Malgré les échelles, géométries diverses et variées de ces événements, et l’incertitude des données, cette loi empirique provenant de notre expérience à petite échelle prédit des vagues similaires à d’autres modèles numériques ou expérimentauxVarious past geological events have shown that landslides near coastlines, involving volumes from a few thousand cubic meters to several cubic kilometers, can lead to tsunami waves with significant amplitude. The generated wave and the collapse both represent an important hazard for the population and infrastructure located on or near the coast. Realistic modeling requires considering the granular nature of landslides. Here, we developed a new set of small-scale laboratory experiments to investigate in detail the wave generated by the collapse of an aerial granular column into water. An entire set of parameters are tested: (1) the falling granular mass (height, volume, aspect ratio, grain size and density), (2) the water layer height and (3) the geometrical configuration (horizontal or inclined plane). From quasi-bidimensional experiments in a rectangular channel we record both the time evolution of the granular collapse and of the generated wave. We show that the wave generation process is driven by the collective dynamics of the granular collapse at the water free surface. We identify a clear linear dependence between the relative wave amplitude and a Froude number defined as the ratio of the granular front velocity and the solitary wave velocity. The wave amplitude reaches its maximum value at an intermediate water depth. The total energy transfer shows that only a few percent of the initial potential energy of the column is transferred to the wave, suggesting a considerable energy loss in the granular collapse itself. Finally, we highlight the low influence diameter and density of the falling grain in the generation of the wave. This suggests that the mass of the collapse is of low importance compared to its volume. Another interesting result is the linear dependence of the relative wave amplitude with the relative immersed volume of the final deposit. This allows us to estimate the wave amplitude generated by past or potential events in Nature. Despite the various scales and geometries of these natural events, and the uncertainty of the data, our empirical law, from our small-scale experiment, predicts waves similar to other numerical or experimental models
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Lachaussée, Florent. "Érosion et transport de particules au voisinage d'un obstacle". Thesis, Université Paris-Saclay (ComUE), 2018. http://www.theses.fr/2018SACLS377/document.
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L'écoulement d'un fluide au-dessus d'un lit granulaire peut provoquer son érosion lorsque la contrainte exercée dépasse une valeur seuil. La présence d'un obstacle immergé dans l'écoulement induit une perturbation, entraînant une survitesse locale du fluide et une plus grande contrainte. L'érosion est alors localement renforcée, phénomène également appelé affouillement. Dans ce travail, nous étudions expérimentalement cette situation d'érosion complexe à l'échelle du laboratoire. Nous nous intéressons en particulier à la question du seuil d'affouillement, c'est-à-dire la vitesse d'approche du fluide minimale nécessaire à l'apparition de l'érosion au voisinage de l'obstacle. Ce faisant, nous observons que deux motifs d'érosion différents peuvent se développer au voisinage d'un obstacle : si le classique affouillement en fer à cheval au pied de l’obstacle domine aux vitesses d'écoulement élevées, on observe pour des vitesses plus faibles un nouveau motif en aval, que nous appelons affouillement en oreilles de lapin. Les seuils d'apparition de ces deux motifs d'érosion sont mesurés visuellement pour différents grains et obstacles. En complément de ces observations, nous utilisons une technique de relevé topographique par profilométrie laser. Le suivi temporel de la topographie du lit au cours du processus d'affouillement nous permet de caractériser la morphologie des deux types de motifs, et de comprendre la compétition entre leurs dynamiques d'apparition par la mesure des temps caractéristiques de formation. L'affouillement en oreilles de lapin est dans la plupart des cas perturbé dans son développement par la formation plus rapide de l'affouillement en fer à cheval. L'étude de l'écoulement, s'appuyant notamment sur des mesures de vélocimétrie par image de particules (PIV), nous renseigne sur les contraintes exercées par le fluide sur les grains, avec ou sans obstacle. Nous pouvons ainsi expliquer les valeurs de seuil d'apparition mesurées pour les deux motifs d'affouillement, qui sont associés à différentes structures de l'écoulementErosion occurs when a fluid flowing over a granular bed exerts a large enough shear stress. When the fluid encounters an obstacle, the modification of the flow leads to a local over speed, and thus on an increase of the shear stress in the vicinity of the obstacle. As a result, the erosion is locally enhanced and is called scouring. In this work, we investigate this complicated situation experimentally at the laboratory scale. In particular, we address the question of the scouring threshold, i.e., the minimum critical approach velocity of the fluid leading to erosion in the vicinity of the obstacle. We report the existence of two different scouring patterns: the traditional horseshoe scour at the base of the obstacle, which dominates at large flow velocities, and we also highlight another scouring pattern downstream, which is called rabbit ear scour, at moderate speeds. We determine the onset of both erosion patterns visually using different grains and obstacles. Besides, we measure the bed topography over time using a laser profilometer. By monitoring the bed topography during the scouring process, we characterize the morphology of both scouring patterns and rationalize their competitive dynamics by measuring their formation timescale. In most cases, the rabbit ear scour development is inhibited by the faster horseshoe scour growth. The characterization of the flow using Particles Image Velocimetry (PIV), provides information on the shear stress exerted by the fluid flow on the grains, with and without obstacle. We can thus rationalize the threshold values for both scouring patterns, associated with different flow structures
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Kasangaki, Gilbert Joseph. "Experimental study of hydro-mechanical behaviour of granular materials". Thesis, Heriot-Watt University, 2012. http://hdl.handle.net/10399/2659.
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Inadequate knowledge of the behaviour of wet granular materials such as unsaturated soils or wet and sticky industrial bulk solids formed the basis of the current research project in which selected granular materials were experimentally characterised. The main objective was to investigate the hydro-mechanical behaviour. Specifically, the following were studied: effect of particle size, particle shape, drying-wetting cycles and void ratio on the water retention behaviour of granular materials, and effect of suction on the shear behaviour and flowability of granular materials. A total of 85 pressure plate tests, 13 triaxial compression tests with the axis translation technique used to control suction in unsaturated tests and 52 silo model tests were successfully conducted to respectively measure water retention characteristics, stress-strain and shear strength, and flowability of glass beads of high sphericity (~95% roundness) and Leighton Buzzard sand (~82% roundness). With these deliberately simple materials each considered factor was isolated and investigated at a time something hugely challenging to achieve with many unsaturated soils. Many pertinent features of hydro-mechanical behaviour observed for most soils were well captured with spherical glass beads meaning that particle-water interaction alone can produce the typical unsaturated behaviour and the particle size and shape significantly affected the behaviour. Further drying-wetting cycles did not alter the WRCs of both glass beads and sand except in the saturated capillary regime suggesting that factors other than the inert water-particle interaction through the liquid bridges are responsible for the discrepancy between the first drying-wetting cycle WRC and the subsequent drying-wetting cycles WRCs often observed in clayey soils. It’s discovered that the additional inter-particle bonding force introduced through the liquid bridges maintained by the matric suction serves to increase the stiffness, volumetric stability and shear strength of the material. The rate of increase of strength diminished with increase in matric suction. The study noted that the Beverloo law is valid for estimation of the dry mass discharge rate and that moisture alone is sufficient to maintain stable arching action depending on the hopper outlet. The study generated new knowledge in form of the effect of the material particle properties on the bulk hydro-mechanical behaviour of granular materials. An approach has also been proposed for estimating the flowability and minimum hopper outlet diameter for the wet noncohesive bulk solids.
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Harich, Rim. "Etude experimentale de la transition Jamming dans un milieu granulaire vibré". Phd thesis, Université Pierre et Marie Curie - Paris VI, 2010. http://pastel.archives-ouvertes.fr/pastel-00559024.
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Durant cette thèse, nous avons réalisé une étude expérimentale 2D d'un milieu granulaire dense vibré dans des conditions proches de la transition de blocage. Une des particularités de notre dispositif expérimental est le rôle joué par la gravité, qui introduit une pression de confinement variable spatialement. De plus, en combinant notre étude dynamique du milieu granulaire à une approche rhéologique, cela nous a permis de préciser le rôle des vibrations sur la mobilité de l'intrus au sein de la phase dense agitée. Dans le chapitre 3, une étude macroscopique d'agitation et de compacité du milieu a été conduite. Un des résultats majeurs est l'obtention d'une expression reliant compacité, pression et agitation, différente de ce qui est attendu de l'équation d'état associée à la théorie cinétique des gaz granulaires. Cette expression est validée pour des milieux fortement dissipatifs associés à des grandes hauteurs d'empilement. En revanche, pour des faibles hauteurs d'empilement, on retrouve bien le comportement standard des gaz granulaires. L'observation d'un comportement inverse à celui attendu pour un gaz dissipatif illustre bien le caractère non collisionel du mode de transfert énergétique. Cela suggère entre autres, un rôle important de la structure de l'empilement dans la transmission de l'énergie, particulièrement au voisinage des configurations à faibles nombres de contacts. Une question centrale est donc de comprendre l'origine de la relation obtenue en clarifiant le rôle des transports élastiques dans ces empilements à la fois désordonnés et fragiles. Par exemple, expérimentalement, il serait intéressant de déterminer comment évolue le nombre de contacts moyen par grain lorsque la compacité diminue et que l'énergie cinétique moyenne stockée dans l'empilement chute fortement. Cette caractérisation du comportement macroscopique a été complétée par une étude microscopique de la mobilité individuelle des grains. Nous avons vu qu'au sein d'un même empilement vibré pouvaient coexister plusieurs régimes (bloqué, sous diffusif, diffusif) et que cela amenait à une certaine hétérogénéité de la dynamique du milieu. Au nal, nous avons caractérisé la mobilité moyenne des grains à travers la compacité locale du milieu mais aussi en introduisant une échelle de temps qui met en évidence un comportement non local, directement relié à une mesure de l'hétérogénéité dynamique de l'ensemble de l'empilement. Enfin, en analysant les champs de déplacement des grains et leurs corrélations spatiales, nous avons pu identifier une échelle spatiale mésoscopique homogène sur l'ensemble de la cellule et correspondant à des mouvements collectifs. Il serait intéressant par la suite d'étudier les relations entre cette échelle mésoscopique et la mobilité d'un grain. À cet effet, nous avons commencé à étudier la densité des modes propres associés à la matrice de corrélation des déplacements individuels des grains. Nous avons vu que pour les phases les plus bloquées, il existe de fortes analogies avec les modes "mous" identifiés pour les systèmes élastiques désordonnés proches de la transition de blocage. Cette partie de notre travail non rapportée dans cette thèse, nécessite donc quelques précautions et un développement plus approfondis. Le dernier chapitre complète notre description du milieu granulaire par l'étude de la mobilité d'un intrus au sein de la phase vibrée dans des conditions identiques à celle du chapitre 3. La densité de cet intrus est telle qu'il coule verticalement. Nous avons montré qu'il était possible à partir des trajectoires, de déduire une relation entre un coefficient de friction effectif et la vitesse locale de l'intrus. En outre, le comportement dynamique de la chute étant très intermittent, nous avons séparé et analysé les phases de blocage et de coulée. Il émerge de cette étude un comportement pathologique associé à la dynamique de blocage qui modifie fortement les lois d'écoulement et éventuellement la rhéologie du système. Nous avons finalement pu proposer une méthode permettant de déterminer une loi effective de rhéologie pour un milieu granulaire dense vibré. Une étude paramétrique complète variant la taille de l'intrus serait nécessaire pour compléter l'étude. Néanmoins, les premiers résultats semblent indiquer un comportement rhéologique similaire de celui observé dans les milieux granulaires cisaillés, c'est à dire l'existence d'un régime rhéo-épaississant tel que la friction effective augmente avec le taux de cisaillement. Cette étude a été complétée par l'analyse des champs de déplacement au passage de l'intrus. Ceci a permis de montrer que la coulée s'effectue à travers un couple intrus-vortex qui provoque des réorganisations à grande échelle à l'intérieur du milieu. Bien que ces résultats apportent une certain éclairage expérimental sur certains aspects de la transition de blocage, ils engendrent également de nombreuses questions qui appellent à des mesures complémentaires.
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Karmakar, Somnath [Verfasser], i Ralf [Akademischer Betreuer] Seemann. "Experimental investigations of mechanical properties of wet granular materials / Somnath Karmakar. Betreuer: Ralf Seemann". Saarbrücken : Saarländische Universitäts- und Landesbibliothek, 2014. http://d-nb.info/1072418525/34.
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Aboul, Hosn Rodaina. "Suffusion and its effects on the mechanical behavior of granular soils : numerical and experimental investigations". Thesis, Université Grenoble Alpes (ComUE), 2017. http://www.theses.fr/2017GREAI082/document.
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La suffusion est un cas particulier d'érosion interne qui apparait dans les ouvrages hydrauliques. Elle se caractérise par le détachement et le transport des particules fines à travers les gros grains sous l'action d'un écoulement hydraulique en laissant derrière un squelette granulaire dont les caractéristiques en termes de densité et d'arrangement géométrique granulaire ont été changées. De telles modifications dans la micro-structure du sol peuvent conduire à des déformations à l'échelle macroscopique et peuvent influencer le comportement mécanique du sol. Ce travail a été consacré à l'étude du mécanisme de suffusion et à son impact sur les propriétés mécaniques des sols non-cohésifs. Pour atteindre cet objectif, deux approches ont été suivies dans ce travail: l'une numérique et l'autre expérimentale. Un modèle numérique discret a été défini pour décrire quantitativement le comportement macroscopique du sol et analyser la micro-structure des assemblages granulaires. Il est basé sur l'utilisation de particules sphériques et la résistance au roulement aux contacts, ainsi que sur une nouvelle méthode de compactage des échantillons pour simuler celle utilisée au laboratoire, et atteindre une large gamme de densités initiales. Le modèle a été validé par comparaison de résultats numériques et de données expérimentales. Ce modèle a d'abord été appliqué sur des assemblages granulaires avec des teneur en fines différentes afin d'étudier le rôle des particules fines pour une micro-structure de sol donnée, sans tenir compte d'un processus d'érosion. Il a été montré qu'il existe un pourcentage de fines, en dessous de la teneur seuil, où des particules fines peuvent commencer à participer au transfert de force, et que, si la suffusion s'initie et mobilise ces particules, ceci pourra affecter le comportement macroscopique du sol. Par la suite, une cinétique simplifiée d'extraction du grain a été proposée pour décrire le processus de suffusion. Elle est basée sur une approche de couplage fluide-solide partielle. L'intérêt de cette procédure d'extraction est que, d'une part, elle tient en compte des critères géométriques et hydrauliques complexes; d'autre part, le modèle induit un coût de calcul raisonnable. Cette procédure a été validée sur la base d'essais expérimentaux de suffusion effectués avec un dispositif nouvellement développé. Les conséquences de cette érosion sur les propriétés mécaniques des sols ont été caractérisées par la réalisation en laboratoire et la simulation d'essais de compression triaxiale. Le développement de la suffusion et ses conséquences sur le comportement macroscopique sont discutés en terme de densité et granulométrie initiale du sol, de chargement hydraulique et du type de particules érodées (actives ou inactive vis-à-vis du transfert de force)Suffusion is a particular case of internal erosion taking place in hydraulic earth structures. It is characterized by the detachment and migration of fine particles by interstitial flow leaving behind the granular skeleton. Such modifications in the soil microstructure may lead to deformations at the macroscopic scale and may influence the mechanical behavior of the soil. This research was devoted to investigate the suffusion mechanism and its impact on the mechanical properties of cohesionless soils. To achieve this objective, two approaches were followed in this work: numerical and experimental approaches. A discrete numerical model was defined to describe quantitatively the soil macroscopic behavior and to analyze the microstructure of granular assemblies. It is based on the use of spherical particles and contact rolling resistance, as well as a new method of compaction to mimic the one used in laboratory and to reach a wide range of initial densities. The model was validated through comparison of numerical results with experimental data. This model was first applied on granular assemblies with different fines contents to study the role of fine particles with respect to a given soil microstructure, without taking into account an erosion process. It was shown that there exists a fines content, below the threshold, where fine particles may start to participate in the force transfer that if suffusion initiates and mobilizes these particles, it may affect the macroscopic behavior of the soil. Thereafter, a simplified kinetics of grain extraction was proposed to describe the suffusion process. It was based on a one-way fluid-solid coupling approach. The importance of this extraction procedure is that, on one hand, it takes into account complex geometric and hydraulic criteria; on the other hand, the model involves an affordable computational cost. This procedure was validated based on experimental tests carried out using a newly developed suffusion apparatus. Consequences of this erosion on the mechanical properties of soils were characterized from experimental and simulated triaxial compression tests. Suffusion development and its consequences on the macroscopic behavior are discussed from the results obtained in terms of the initial soil density and gradation, the hydraulic loading and the type of eroded particles (active or inactive in the force transfer)
Książki na temat "Experimental Granular Mechanics"
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Tejchman, Jacek. Confined Granular Flow in Silos: Experimental and Numerical Investigations. Heidelberg: Springer International Publishing, 2013.
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Tejchman, Jacek. Confined Granular Flow in Silos: Experimental and Numerical Investigations. Springer International Publishing AG, 2015.
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Tejchman, Jacek. Confined Granular Flow in Silos: Experimental and Numerical Investigations. Springer, 2013.
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Vaicis, Ivo. Shape Optimization of Mechanical System Elements Considering Uncertainty. RTU Press, 2022. http://dx.doi.org/10.7250/9789934227356.
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In the Thesis a new method is developed for optimising the shape of mechanical elements by considering the interaction of these elements with a multiphase uncertainty environment whose approximation model achieves a significant number of degrees of freedom (DOF). The Thesis analyses the process of dust formation during the handling of granular material. Different experimental designs are used to derive metamodels and to analyse the segregation of granular material in the silo discharge depending on the oscillation frequency, amplitude, and geometrical characteristics of the silo.
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Eimanis, Mārcis. Usage of Double-Helical Propulsion Principle in Underwater Vehicles. RTU Press, 2022. http://dx.doi.org/10.7250/9789934227370.
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The Thesis describes a new underwater vehicle propulsion type developed by the author. Flow and vehicle interaction dynamics are studied, and factors impacting the flow, control methods and the ability to move in other media (in addition to fluid) are reviewed. A geometry of the propulsion system was created by studying its hydrodynamic properties using special CFD software. A mathematical model for the control system was created. The dynamics of the underwater vehicle were modelled with the multibody dynamics modelling software MSC Adams, using the developed control system and the water resistance model developed with CFD software. Flow dynamics were combined with multibody mechanism dynamics using the metamodeling and numerical experiment approach. Numerical experiments in bulk or granular media were performed using the discrete element method, simulating the vehicle movement using the EDEM software. Within the framework of the Thesis, a prototype of the model was also created for observing the model behaviour in real-life conditions. High-quality and good fit results were obtained from the mathematical model and the physical prototype dynamics, proving the performance of both the new propulsion principle and the control system.
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Louchet, Francois. Snow Avalanches. Oxford University Press, 2020. http://dx.doi.org/10.1093/oso/9780198866930.001.0001.
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This work is a critical update of the most recent and innovative developments of the avalanche science. It aims at re-founding it on clear scientific bases, from field observations and experiments up to strong mathematical and physical analysis and modeling. It points out snow peculiarities, regarding both static mechanical properties and flow dynamics, that may strongly differ from those of compact solids for the former, and of Newtonian fluids for the latter. It analyzes the general processes involved in avalanche release, in terms of brittle fracture and ductile plasticity, specific friction laws, flow of healable granular materials, percolation concepts, cellular automata, scale invariance, criticality, theory of dynamical systems, bifurcations, etc. As a result, slab triggering (including remote triggering) can be summarized by the “slab avalanche release in 4 steps” concept, based on weak layer local collapse and subsequent propagation driven by slab weight. The frequent abortion of many incipient avalanches is easily explained in terms of snow grain dynamical healing. Sluffs and full-depth avalanches are also analyzed. Such advances pave the way for significant progress in risk evaluation procedures. In the present context of a speeding-up climate warming, possible evolutions of snow cover extent and stability are also tentatively discussed. We show how, in mountainous areas, the present analysis can be extended to other gravitational failures (rock-falls, landslides) that are likely to take over from avalanches in such circumstances. The text is supported by on-line links to field experiments and lectures on triggering mechanisms, risk management, and decision making.
Części książek na temat "Experimental Granular Mechanics"
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Góngora-Leyva, Ever, Gerardo Ruiz-Chavarría, Ángel Columbié-Navarro i Yoalbis Retirado-Mediacejas. "The Cooling of a Granular Material in a Rotating Horizontal Cylinder". W Experimental and Computational Fluid Mechanics, 197–205. Cham: Springer International Publishing, 2013. http://dx.doi.org/10.1007/978-3-319-00116-6_14.
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Jongchansitto, Pawarut, Xavier Balandraud, Michel Grédiac i Ittichai Preechawuttipong. "Measurement of Stress Network in Granular Materials from Infrared Measurement". W Experimental and Applied Mechanics, Volume 6, 163–66. Cham: Springer International Publishing, 2014. http://dx.doi.org/10.1007/978-3-319-06989-0_22.
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Bek, M., A. Oseli, I. Saprunov, N. Holeček, B. S. von Bernstorff i I. Emri. "Effect of Pressure on Damping Properties of Granular Polymeric Materials". W Conference Proceedings of the Society for Experimental Mechanics Series, 109–15. Cham: Springer International Publishing, 2016. http://dx.doi.org/10.1007/978-3-319-21762-8_13.
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Serrano, D. A., G. Ruíz Chavarría, S. Álvarez i A. Medina. "Mass Flow Rate of Granular Material from an L-Valve Without Aeration". W Selected Topics of Computational and Experimental Fluid Mechanics, 303–9. Cham: Springer International Publishing, 2015. http://dx.doi.org/10.1007/978-3-319-11487-3_20.
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Trujillo, Leonardo, i Leonardo Di G. Sigalotti. "Theoretical Physics of Granular Fluids and Solids". W Computational and Experimental Fluid Mechanics with Applications to Physics, Engineering and the Environment, 165–91. Cham: Springer International Publishing, 2014. http://dx.doi.org/10.1007/978-3-319-00191-3_8.
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Bek, M., J. Gonzalez-Gutierrez i I. Emri. "New Methodology for Steady-State Friction Measurements of Granular Materials Under Pressure". W Conference Proceedings of the Society for Experimental Mechanics Series, 105–13. Cham: Springer International Publishing, 2016. http://dx.doi.org/10.1007/978-3-319-42028-8_13.
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Karanjgaokar, Nikhil, i Guruswami Ravichandran. "Experimental Inference of Inter-Particle Forces in Granular Systems Using Digital Image Correlation". W Advancement of Optical Methods in Experimental Mechanics, Volume 3, 379–85. Cham: Springer International Publishing, 2014. http://dx.doi.org/10.1007/978-3-319-06986-9_45.
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Marín, Juan F., Juan C. Petit, Leonardo Di G. Sigalotti i Leonardo Trujillo. "Integral Representation for Continuous Matter Fields in Granular Dynamics". W Computational and Experimental Fluid Mechanics with Applications to Physics, Engineering and the Environment, 473–80. Cham: Springer International Publishing, 2014. http://dx.doi.org/10.1007/978-3-319-00191-3_33.
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Jongchansitto, Pawarut, Damien Boyer, Itthichai Preechawuttipong i Xavier Balandraud. "Identification of Interparticle Contacts in Granular Media Using Mechanoluminescent Material". W Advancements in Optical Methods & Digital Image Correlation in Experimental Mechanics, Volume 3, 87–92. Cham: Springer International Publishing, 2019. http://dx.doi.org/10.1007/978-3-030-30009-8_12.
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Petit, Juan C., Juan F. Marín i Leonardo Trujillo. "On the Construction of a Continuous Theory for Granular Flows". W Computational and Experimental Fluid Mechanics with Applications to Physics, Engineering and the Environment, 463–71. Cham: Springer International Publishing, 2014. http://dx.doi.org/10.1007/978-3-319-00191-3_32.
Pełny tekst źródłaStreszczenia konferencji na temat "Experimental Granular Mechanics"
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Liao, C. C., i S. S. Hsiau. "The granular mixing in a slurry rotating drum". W Fourth International Conference on Experimental Mechanics, redaktorzy Chenggen Quan, Kemao Qian, Anand K. Asundi i Fook S. Chau. SPIE, 2009. http://dx.doi.org/10.1117/12.851260.
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Kandasami, R. K., i T. G. Murthy. "Experimental studies on the mechanics of cohesive frictional granular media". W POWDERS AND GRAINS 2013: Proceedings of the 7th International Conference on Micromechanics of Granular Media. AIP, 2013. http://dx.doi.org/10.1063/1.4812099.
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Haidl, J., Z. Chára i V. Matoušek. "Experimental Validation of Granular Flow Kinetic Theory Under Turbulent Flow Conditions". W Topical Problems of Fluid Mechanics 2022. Institute of Thermomechanics of the Czech Academy of Sciences, 2022. http://dx.doi.org/10.14311/tpfm.2022.011.
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The mixed classical and extended kinetic theory of granular flows is used for modeling the characteristics of particles-water turbulent sheet flow. The open-source solver sedFoam v3.1 is used for the 1-D and 2-D flow simulations. The simulation results are compared to the experimental data measured in the open channel. After that, the simulation parameters are optimized to achieve the best possible agreement between the simulation and the experimental results. The unsatisfactory performance of the KT models and the observed simulation instabilities are discussed.
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Liu, Junyi, Baoyu Guo i Zhengsong Qiu. "Experimental Investigation on Wellbore Strengthening Mechanism and Tight Fracture Plugging Drilling Fluid Based on Granular Matter Mechanics". W International Petroleum Technology Conference. International Petroleum Technology Conference, 2019. http://dx.doi.org/10.2523/19144-ms.
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Liu, Junyi, Baoyu Guo i Zhengsong Qiu. "Experimental Investigation on Wellbore Strengthening Mechanism and Tight Fracture Plugging Drilling Fluid Based on Granular Matter Mechanics". W International Petroleum Technology Conference. International Petroleum Technology Conference, 2019. http://dx.doi.org/10.2523/iptc-19144-ms.
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Hagengruber, Tyler L. "Strength effects of microfracture on granular microstructures evaluated by FDEM direct numerical simulation". W 56TH US ROCK MECHANICS / GEOMECHANICS SYMPOSIUM. OnePetro, 2022. http://dx.doi.org/10.56952/arma-2022-2209.
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We present results of an investigation into the mechanisms of damage in granular microstructures conducted through direct numerical simulation with the combined Finite-Discrete Element Method (FDEM). Scanning Electron Microscope (SEM) images of a pressed crystalline powder are directly meshed, resolving grain-grain interfaces. Semi-ductile microfracture is simulated by prescribing a combination of inter-granular brittle fracture and intra-granular grain plasticity. Pristine (undamaged) and damaged microstructures are simulated in uniaxial compression tests and compared to experimental uniaxial compression measurements from literature. The simulation results show that the observed microscale mechanisms of damage (microfracture predominantly around and sometimes through grains and crack associated pore-growth) can well explain degradation of strength observed in the laboratory measurements. A method of tracing grain boundaries from SEM images is described and applied to meshing of a microstructure damaged through cyclic thermal loading. By calibrating the simulations to the damaged and undamaged experimental measurements, micro-mechanical/structural insight is gained into the mechanisms of damage for the material. The results show that the SEM-based micro-characterization of damage can explain the degradation in effective strength observed in the testing and can be accurately modeled using the presented methods.
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Saeki, Masato. "Impact Damping With Granular Materials". W ASME 2001 International Mechanical Engineering Congress and Exposition. American Society of Mechanical Engineers, 2001. http://dx.doi.org/10.1115/imece2001/ad-23745.
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Abstract The performance of an impact damper with granular materials in horizontally and vertically vibrating systems is investigated both experimentally and analytically. The motion of the damper is solved by the discrete element method, which is often used in investigations of soil mechanics and powder technology. This method makes it possible to consider the effect of granularity on the damping performance. In this method, the dynamics of the entire system is determined by analysis of the motion of the individual particles. The validity of this numerical method is examined by comparison with the experimental results. The difference in the damping effect in horizontally and vertically vibrating systems is considered.
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Croll, Andrew B., Antoinette Tordesillas, David Carey i Bekele Gurmessa. "Experimental evidence and structural mechanics analysis of force chain buckling at the microscale in a 2D polymeric granular layer". W POWDERS AND GRAINS 2013: Proceedings of the 7th International Conference on Micromechanics of Granular Media. AIP, 2013. http://dx.doi.org/10.1063/1.4811954.
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Mieldazys, Ramunas, Egle Jotautiene, Aloyzas Gaudutis i Algirdas Jasinskas. "Comparison of physical mechanical properties of granulated fertilizer produced from composted cattle and dried cow, Pig and poultry manure". W 22nd International Scientific Conference Engineering for Rural Development. Latvia University of Life Sciences and Technologies, Faculty of Engineering, 2023. http://dx.doi.org/10.22616/erdev.2023.22.tf051.
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The advantages of granular organic fertilizers are more convenient handling, storage, transportation, compared to traditional management of manure with litter. Manure granulation can increase the bulk density, improve storability, reduce transportation costs, and make these materials easier to handle using traditional existing handling and storage equipment. There were prepared four experimental samples of various manure mill and granules in laboratory conditions. For granule production a 7.5 kW granulator, with a horizontal 6 mm matrix was used. During the research, the physical-mechanical characteristics were estimated: biometric properties (dimensions, mass), raw material and granule volume and density, humidity, and granule strength of various composition cattle, cow, pig, and poultry manure material. Cattle manure compost contained the most material (65%) of the mass fraction, up to 0.25 mm. In dried cow, pig, and poultry manure, the amount of fraction material was mostly from 1 to 2 mm. The obtained results show that the highest bulk density of the prepared mill was from cow manure and the lowest bulk density was from poultry manure. The highest moisture content was also for cow manure, and the lowest determined moisture content was for poultry manure samples. The highest density was determined for cattle manure compost granules. The highest compressive strength, in the horizontal plane, was determined for hen manure granules, the force required to crush them reached 657 N. The aim of this work is to compare the main physical and mechanical properties of the studied manure material and produced experimental granules.
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Evesque, Pierre. "Evidence for a new force in dissipative system derived from Boltzmann equation: Consequence for the mechanics of the material point, experimental evidences and possible applications". W POWDERS AND GRAINS 2013: Proceedings of the 7th International Conference on Micromechanics of Granular Media. AIP, 2013. http://dx.doi.org/10.1063/1.4812048.
Pełny tekst źródłaRaporty organizacyjne na temat "Experimental Granular Mechanics"
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Tan, Peng, i Nicholas Sitar. Parallel Level-Set DEM (LS-DEM) Development and Application to the Study of Deformation and Flow of Granular Media. Pacific Earthquake Engineering Research Center, University of California, Berkeley, CA, marzec 2023. http://dx.doi.org/10.55461/kmiz5819.
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We present a systematic investigation of computational approaches to the modeling of granular materials. Granular materials are ubiquitous in everyday life and in a variety of engineering and industrial applications. Despite the apparent simplicity of the laws governing particle-scale interactions, predicting the continuum mechanical response of granular materials still poses extraordinary challenges. This is largely due to the complex history dependence resulting from continuous rearrangement of the microstructure of granular material, as well as the mechanical interlocking due to grain morphology and surface roughness. X-Ray Computed Tomography (XRCT) is used to characterize the grain morphology and the fabric of the granular media, naturally deposited sand in this study. The Level-Set based Discrete Element Method (LS-DEM) is then used to bridge the granular behavior gap between the micro and macro scale. The LS-DEM establishes a one-to-one correspondence between granular objects and numerical avatars and captures the details of grain morphology and surface roughness. However, the high-fidelity representation significantly increases the demands on computational resources. To this end a parallel version of LS-DEM is introduced to significantly decrease the computational demands. The code employs a binning algorithm, which reduces the search complexity of contact detection from O(n2) to O(n), and a domain decomposition strategy is used to elicit parallel computing in a memory- and communication-efficient manner. The parallel implementation shows good scalability and efficiency. High fidelity LS avatars obtained from XRCT images of naturally deposited sand are then used to replicate the results of triaxial tests using the new, parallel LS-DEM code. The result show that both micro- and macro-mechanical behavior of natural material is well captured and is consistent with experimental data, confirming experimental observation that the primary source of peak strength of sand is the mechanical interlocking between irregularly shaped grains. Specifically, triaxial test simulations with a flexible membrane produce a very good match to experimentally observed relationships between deviatoric stress and mobilized friction angle for naturally deposited sand. We then explore the viability of modeling dynamic problems with a new formulation of an impulse based LS-DEM. The new formulation is stable, fast, and energy conservative. However, it can be numerically stiff when the assembly has substantial mass differences between particles. We also demonstrate the feasibility of modeling deformable structures in the rigid body framework and propose several enhancements to improve the convergence of collision resolution, including a hybrid time integration scheme to separately handle at rest contacts and dynamic collisions. Finally, we extend the impulse-based LS-DEM to include arbitrarily shaped topographic surfaces and exploit its algorithmic advantages to demonstrate the feasibility of modeling realistic behavior of granular flows. The novel formulation significantly improves performance of dynamic simulations by allowing larger time steps, which is advantageous for observing the full development of physical phenomena such as rock avalanches, which we present as an illustrative example.
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Matthew, Gray. Data from "Winter is Coming – Temperature Affects Immune Defenses and Susceptibility to Batrachochytrium salamandrivorans". University of Tennessee, Knoxville Libraries, styczeń 2021. http://dx.doi.org/10.7290/t7sallfxxe.
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Environmental temperature is a key factor driving various biological processes, including immune defenses and host-pathogen interactions. Here, we evaluated the effects of environmental temperature on the pathogenicity of the emerging fungus, Batrachochytrium salamandrivorans (Bsal), using controlled laboratory experiments, and measured components of host immune defense to identify regulating mechanisms. We found that adult and juvenile Notophthalmus viridescens died faster due to Bsal chytridiomycosis at 14 ºC than at 6 and 22 ºC. Pathogen replication rates, total available proteins on the skin, and microbiome composition likely drove these relationships. Temperature-dependent skin microbiome composition in our laboratory experiments matched seasonal trends in wild N. viridescens, adding validity to these results. We also found that hydrophobic peptide production after two months post-exposure to Bsal was reduced in infected animals compared to controls, perhaps due to peptide release earlier in infection or impaired granular gland function in diseased animals. Using our temperature-dependent infection results, we performed a geographic analysis that suggested that N. viridescens populations in the northeastern United States and southeastern Canada are at greatest risk for Bsal invasion. Our results indicate that environmental temperature will play a key role in the epidemiology of Bsal and provide evidence that temperature manipulations may be a viable Bsal management strategy.