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1
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EN
The capillary bridge between ellipsoidal grains is modelled within an effective toroidal approximation. We analyse the case when major semi axes of grains are parallel.
2
Content available A method for determining sieve holes blocking degree
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EN
The aim of this paper is to describe the process of sieve holes blocking. A series of tests and their results revealed a dependence describing the value of an average screen blocking coefficient as a function of two main factors affecting the process. These parameters are the toss indicator and the content of difficult-to-screen particles in the feed. The experiments presented in the paper showed that description in mathematical terms of the sieve holes blocking process is complex and difficult. A third degree polynomial function with two variables enables determination of the value of an average screen blocking coefficient in the processes of screening for specific arrangements: screen–particle–toss indicator–content of difficult-to-screen particles.
3
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EN
A simple numerical procedure for determining the field of displacements of granular media in bins and hoppers is proposed. The procedure is based on the concept of Jerzy Litwiniszyn, who treated the gravity flow of granular media as a stochastic process. He and his co-workers presented analytical solutions to a certain number of simple problems concerning deformations of terrain caused by underground mining operations. The numerical procedure proposed in this paper is much more effective in solving numerous problems of practical significance.
4
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EN
The present paper is concerned with the simplified analysis of deformation and stress states in converging hoppers during filling and discharge of a granular material. The equilibrium conditions and stress-strain relations are satisfied for cylindrical slice elements assuming dependence of displacement and stress on radial coordinate. The elastic or elasto-plastic material model is used with the Coulomb yield condition and non-associated flow rule. The paper presents a detailed analysis of pressure evolution of a granular material on a hopper wall during the emptying process when the initial active state of pressure is transformed into the passive state. The growth of wall pressure associated with this process is demonstrated. The analytical treatment presented in this paper can be compared with the respective finite element solution.
5
Content available remote On the movement of granular materials in bins Part II: Three-dimensional problems
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EN
A simple numerical procedure for determining three-dimensional displacements of granular media in bins is proposed. In the previous paper [6] such a numerical procedure was limited to the two-dimensional analysis only. The proposed procedure is based on the concept published by Professor Jerzy Litwiniszyn, who treated the gravity flow of granular media as a stochastic process.
6
Content available remote Energy spectrum of frustrated granular materials
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EN
We study the statistical properties of low lying energy states for some special models of two dimensional frustrated granular materials.
EN
Presented work shows another "smart" material which is a system consisting of single grains encapsulated in thigh PCV envelope with internal underpressure. Such an approach to granular aggregates gives us the possibility to fit the external shape of the assembly to required form. Additionally, steering parameters like diameter of a single grain, material which it is made of, material and the thickness of assembly warp (an envelope which surrounds incoherent grains), and controlling of internal hypertension which occured within created system afforded to match demand by constructor materials properties in global scale.
EN
The paper reports results of an analysis concerning the infuence of a computational domain discretization method on the numerical stability of a model as well as the calculation error. The topology of a packed bed of a granular material consisting of granules contacting tangentially in one point makes the modeling of heat and mass transfer due to the fluid flow in such a domain a chalenging task. Therefore, the contribution of this paper constitutes a summary of discretization methods with discussion and guidelines allowing one to effectively select the most favourable method dedicated to discretization of the domain. The validation using Particle Image Velocimetry and evaluation of the impact of inflow velocity on the experimental and numerical research results are also presented in the paper.
9
Content available Concept of an adaptive-tuned particles impact damper
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EN
The most popular devices for attenuation of mechanical vibrations are dampers or shock absorbers. Two main energy dissipation strategies can be generally distinguished: passive and active (semi-active). Passive vibration isolation methods are the most commonly used, mainly because of their simplicity and low maintenance costs. Among passive vibration attenuation techniques, also Particle Impact Dampers (PID) are involved. Classical PID solutions have some certain limitations. This paper aims at presenting the new concept of an adaptive tuned PID damper that can pretend to be placed among semi-active energy dissipation methods.
10
Content available remote Mathematical Model for Special Granular Structures
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EN
The main objective of presented paper is to propose a mathematical (rheological) model capable to capture the real response of the special granular structures subjected to cyclic loading. ABS filled cylindrical form was subjected to triangular excitation rule with constant frequency and various underpressure values. Detailed analysis of the numerical model's response is provided and rheological model, capable to capture correctly the real behaviour of the special granular structures is proposed.
EN
A simplified analysis of deformation and stress states in converging hoppers during filling and discharge of granular material is presented. In particular we discuss a method for solving the set of differential equations governing the flow of granular material in a plane wedge hopper. The equilibrium conditions and stress-strain relations are satisfied for the planar slice elements assuming the dependence of displacement and stress on the Cartesian coordinate z. The transient flow of an icompressible, cohesionless granular material in a two-dimensional converging hopper is considered. We assume the material to be in elastic or elasto-plastic states within the hopper satisfying the Coulomb yield condition and the non-associated flow rule. The paper presents a detailed analysis of the evolution of pressure acting on the hopper wall during the filling and emptying processes when the initial active state of pressure is transformed into a passive state. Analytical and numerical analyses are presented. It is shown that at the initial stage of the emptying process a considerable switch overpressure develops, exceeding the steady-state passive pressure several times.
EN
The paper deals with investigations of the effect of the stochastic distribution of the initial void ratio in granular bodies on shear localization during shearing of an infinite granular layer 500 mm high with free dilatancy under plane strain conditions. The initial void ratio was assumed to be stochastic with a correlated random field generated by a conditional rejection method by Walukiewicz et al (1997). To simulate mechanical behaviour of a cohesionless granular material during a monotonous deformation path, a micro-polar hypoplastic constitutive law was used, which takes into account particle rotations, curvatures, non-symmetric stresses, couple stresses and the mean grain diameter as a characteristic length. The proposed model captures the salient mechanical features of granular bodies in a wide range of densities and pressures with a single set of constants. In addition, the comparative FE-analyses were carried out with a uniform and spatially non-correlated random fields of the initial void ratio.
PL
Przedstawiono wyniki badań doświadczalnych ilustrujących takie cechy ośrodków sypkich, które je odróżniają od innych materiałów. W przypadku suchego ośrodka sypkiego są to charakterystyczne zmiany objętości przy ścinaniu, które zależą od początkowego stanu takiego materiału. Jeżeli ośrodek ciągle się zagęszcza, to ma on charakter kontraktywny; natomiast jeśli najpierw się zagęszcza, a potem rozluźnia, to mówimy o ośrodku dylatywnym. Dylatancja rozpoczyna się, gdy ścieżka naprężenia efektywnego przekroczy tzw. linię niestabilności. Omówiono tę charakterystykę ośrodków sypkich, jak też pojęcie linii stanu ustalonego, która oddziela stany kontraktywne od dylatywnych w pewnej przestrzeni charakteryzującej stan ośrodka sypkiego. Omówiono też zachowanie nawodnionego ośrodka sypkiego przy ścinaniu, w warunkach bez odpływu wody z porów. Pokazano, że w ośrodku kontraktywnym następuje generacja ciśnienia wody w porach, która prowadzi do upłynnienia tego materiału, to jest do stanu przypominającego ciecz. W gruntach dylatywnych początkowo następuje generacja ciśnienia porowego, a po przekroczeniu linii niestabilności następuje makroskopowe wzmocnienie materiału. Zasygnalizowano problemy praktyczne, w których upłynnienie odgrywa główną rolę oraz zasugerowano nowe obszary badań teoretycznych.
EN
Some properties of granular materials which distinguish them from other states of matter are described. In the case of dry granular matter, or fluid saturated, but with free drainage of pore-fluid allowed, such a specific property is the ability to contract/dilate during shearing. Contraction means a reduction of volume, whilst dilation is a volumetric increase. In the case of fluid-saturated granular material, but in undrained conditions, reaction of granular matter during shearing is even more interesting, as pore-fluid pressure changes take place and respective regrouping of effective stresses. Therefore, the macroscopic properties of fluid-saturated granular material also change. The material which initially displays macroscopic properties of a solid body becomes increasingly weaker, and then, depending on its initial state and the loading history, such a mixture may liquefy, i.e. it displays the macroscopic properties typical for fluids. Experimental results illustrating the above described phenomena are shown and some practical aspects described. The concepts of instability and steady state lines are introduced and new fields of research suggested.
Open Physics
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2012
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tom 10
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nr 3
715-722
EN
At medium ice concentrations, sea ice consists of separate floes of different sizes interacting with each other through inelastic collisions, in a way similar to two-dimensional polydisperse granular gases. The dynamics of this type of ice cover is poorly understood. In this paper, a molecular-dynamics sea-ice model based on simplified momentum equations and a hard-disk collision model is used to analyze processes of cluster formation in sea-ice floes. The clusters, formed due to size-dependent equilibrium velocities of floes under a given forcing, have statistical properties dependent on the average ice concentration and on the parameters of the floe-size distribution. In particular, in terms of the size of the largest cluster in the system, two regimes are observed: one at low and one at high ice concentration. At high ice concentration, the dominating cluster spans the entire model domain and contains the majority of floes. The exponent of the cluster-size distribution increases with increasing exponent of the floe-size distribution. The results are discussed from the point of view of the collisional contribution to the internal stress in the ice, as well as from the role of clustering in the floe-formation processes. Thus, they may contribute to the formulation of more reliable sea-ice rheology models valid at medium ice concentrations.
EN
This paper concerns problems related to complex response of Special Granular Structures (SGS) on applied external loading. Typical experimental results acquired from uniaxial compression tests are presented. For the most part influences of underpressure and strain rate are discussed. Universal dependencies between determined Young modulus values and underpressures and proof stresses vs. underpressures are introduced. Finally complex behavior of SGS is analyzed basing on experimentally obtained surfaces: E=f(V,p) and k=(V,p).
EN
Internal friction in granular plant materials is a very complex phenomenon. This is due to a vast number of factors that determine the behaviour of these materials. This article looks at exploring the impact of porosity, the repose angle, and moisture on the value of the internal friction angle and cohesion. Statistical analysis showed that the influence of the examined factors on the parameters of friction is statistically significant. Nonlinear estimation was performed, which allowed developing functions describing the mentioned relationship, for which the goodness-of-fit (depending on the material type) ranged from 0.813 to 0.915 for the internal friction angle and from 0.748 to 0.963 in the case of cohesion. It has been found that internal friction and cohesion need further research that will take into account additional factors defining the examined material in a more accurate manner.
PL
Tarcie wewnętrzne roślinnych materiałów ziarnistych jest zjawiskiem bardzo złożonym. Wynika to z dużej ilości czynników determinujących zachowanie się tych materiałów. W artykule podjęto próbę określenia wpływu porowatości, kąta usypu oraz wilgotności na wartość kąta tarcia wewnętrznego i kohezję. Analiza statystyczna wykazała istotność wpływu badanych czynników na parametry tarcia. Przeprowadzono estymację nieliniową, która pozwoliła na zaproponowanie funkcji opisujących wspomnianą zależność, dla których uzyskano współczynnik dopasowania (w zależności od rodzaju materiału) od 0.813 do 0.915 dla kąta tarcia wewnętrznego oraz od 0.748 do 0.963 dla kohezji. Stwierdzono, że zarówno w przypadku kąta tarcia wewnętrznego, jak i kohezji należy prowadzić dalsze badania, uwzględniając dodatkowe czynniki, w sposób dokładniejszy charakteryzujące badany materiał.
17
Content available remote A non-linear constitutive relation for flowing granular materials
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EN
We study the flow of granular materials down an inclined plane. We assume steady fully developed conditions. The constitutive relation is that of Rajagopal and Massoudi (1990), where the material parameters are given by the theory of Boyle and Massoudi (1990). We do not consider the effects of ?granular temperature? (a measure of the fluctuating component of the velocity of the grains). The material parameters are given in this model as functions of volume fraction, particle diameter, restitution coefficient, and the excluded volume. The momentum equations are non-dimensionalized and the resulting coupled non-linear ordinary differential equations are solved numerically; the results are presented for the volume fraction and velocity profiles for different dimensionless numbers.
18
Content available remote Averaged equations for developing flow of a fluid-solid mixture
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EN
A mathematical description of a mixture of a Newtonian fluid infused with particulate solids is presented within the context of Mixture Theory. In the absence of any thermal effects, the balance of mass and balance of linear momentum equations for each component are averaged over the cross section of the flow to obtain ordinary differential equations describing developing flow between parallel plates. The resulting coupled equations describe the variation of the average velocities and volume fraction in the direction of flow, and represent a simplified approximate set of equations which are used in engineering applications.
PL
Przedstawiono badania dotyczące procesu suszenia materiałów ziarnistych w złożu kompozytowym odniesionym do technologii wytwarzania wieloskładnikowych paliw zbrykietowanych. Opracowano równania procesu suszenia dla materiałów mogących stanowić osnowę złóż kompozytowych.
EN
The paper shows the studies of granular materials’ drying process in the composite bed. This bed consists of the essential product and the matrix, and it is used in the technology of multicomponent briquette production.
20
Content available remote Evolution of shear localisation in earth pressure problems of a retaining wall
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EN
The paper deals with numerical investigations of the evolution of shear localisation in granular bodies for earth pressure problems of a retaining wall in conditions of plane strain. The passive and active failure of a retaining wall in sand is discussed. The calculations are carried out with a rigid and very rough retaining wall undergoing horizontal translation, rotation around the top and rotation around the bottom. The behaviour of dry sand is numerically modelled with a finite element method using a hypoplastic constitutive relation within a polar (Cosserat) continuum. The constitutive relation is obtained through extension by polar quantities, viz. rotations, curvatures and couple stresses, using the mean grain diameter as a characteristic length. During FE-calculations, the attention is laid on the influence of different wall movements on shear localisation. In addition, the effects of the initial void ratio, distribution of the initial void ratio and mean grain diameter, pressure level and size of the sand body and retaining wall is investigated in the case of a passive wall translation. The FE-results are compared with corresponding experimental results of laboratory model tests.
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