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Search Results: 1 - 10 of 4892 matches for " granular material. "
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Quantum mechanical approach to sphere beds in the container-packing fractions and radial distribution function
Pietrow M.,G???3?…?od?…?o A.
International Agrophysics , 2000,
Abstract: This paper is a continuation of the work on the new approach to the packing problems of randomly embedded granular material proposed by G 3 … od … o and Pietrow. In previous paper a quantum mechanical approach (QMA) to packing was introduced and 2and 3-dimensional packing experiments for circles (spheres) were generated on this basis. Packing fractions were calculated to test the ability to build 2 and 3-dimensional beds with correct properties. In this paper we continue testing the QMA model.
Operational characteristics of four metering systems for agricultural fertilizers and amendments
Camacho-Tamayo, Jesus H.;Barbosa, Angela M.;Pérez, Nancy M.;Leiva, Fabio R.;Rodríguez, Gonzalo A.;
Engenharia Agrícola , 2009, DOI: 10.1590/S0100-69162009000400010
Abstract: the use of fertilizers and solid amendments in agriculture generates special interest for their effect on crop productivity, as well as for their environmental impact. the efficient use of these products demands knowing their physical and mechanical properties, the storing conditions effect and the operational characteristics of the metering systems used in the fertilizing equipment. in this context, the present study was developed with the purpose of evaluating the operational characteristics of different fertilizing metering systems and to determine the adequate metering system-product operational parameters, using powder lime, powder gypsum, granular 10-30-10 (n-p-k), and granular urea. operational differences were established among four types of commercial fertilizer metering systems, including wire auger, star-shaped feed wheel, feed screw and ridged traction wheel. the study found that the unloading rate depends directly on the fertilizer metering system's rotating speed and is affected by particle size, repose angle, bulk density and moisture content of the applied product. the wire auger and star-shaped feed wheel metering systems were adequate for the distribution of powder products and the feed screw for granulated fertilizers. furthermore, theoretical and experimental characteristic equations were established, defining curves for calibration and handling of the products plus the rotating speed range in which a better distributing behavior was achieved.
Heterogeneities in aging models of granular compaction
Arenzon, Jeferson J.;
Brazilian Journal of Physics , 2006, DOI: 10.1590/S0103-97332006000500004
Abstract: kinetically constrained models (kcm) are systems with trivial thermodynamics but often complex dynamical behavior due to constraints on the accessible paths followed by the system. exploring these properties, the kob-andersen (ka) model was introduced to study the slow dynamics of glass forming liquids and later extended to granular materials. in this last context, we present new results on the heterogeneous character of both in and out of equilibrium dynamics, further stretching the granular-glass analogy.
Granulometric analysis based on the energy of Wavelet Transform coefficients
Oliveira, Elisangela Fátima;Bianchi, Andrea Gomes Campos;Martins-Filho, Luiz de Siqueira;Machado, Romuel Figueiredo;
Rem: Revista Escola de Minas , 2010, DOI: 10.1590/S0370-44672010000200020
Abstract: a methodology for granulometric image analysis based on modeling the spatial energy of frequencies, using the wavelet transform is presented in this article. a brief review of the wavelet transform tool is presented, and the proposed methodology is detailed. the presented results were obtained using numerically and experimentally simulated images. these results show the relevant correlation between the energy of the wavelet coefficients and the size distribution of the analyzed objects.
Scale dependence of direct shear tests
Qiang Zhou,Hayley H. Shen,Brian T. Helenbrook,HongWu Zhang
Chinese Science Bulletin , 2009, DOI: 10.1007/s11434-009-0516-5
Abstract: Direct shear test has been widely used to measure the shear strength of soils and other particulate materials in industry because of its simplicity. However, the results can be dependent on the specimen size. The ASTM (American Society for Testing and Materials) publications suggest that for testing soils the shear box should be at least ten times the diameter of the largest particle and the height of the box should be no more than half of its diameter. These guidelines are empirically based. A series of two-dimensional numerical direct shear tests are performed to investigate this scaling effect. By analyzing the bulk friction, particle translation and rotation, percentage of sliding, average volume (area) and shear strain and the evolution of the shear band, we find that the traditional guidelines for direct shear tests are questionable. Scaling dependency of bulk friction on the property of granular materials is clearly present. Our current analysis points out that the scaling effects can vary significantly depending on the particle properties other than their sizes. Of all the parameters we observed, particle rotation appears to have a decisive correlation with the bulk friction. Formation of a shear band is universal. As the shearing progresses, particle rotation begins to concentrate near the shear plane. By defining the width of a shear band as the standard deviation of the distribution of translational gradient or the standard deviation of the distribution of particle rotation, quantitative evolutions of shear band are presented. Both measures of the shear band width dropped rapidly during pre-failure stage. After peak stress both measures begin to approach steady state as the bulk friction stabilizes to the residual stage. These observations suggest that structure formation inside the shear band controls the scaling effect.
Auto-amplifying dynamic behavior of heap and convection in granular material
Weizhong Chen,Rongjue Wei
Chinese Science Bulletin , 1998, DOI: 10.1007/BF02883565
Abstract: Two experiments have been carried out to understand the physical characteristics of surface heap and internal convection of granular material subjected to vertical vibration. The results show that they have a clear auteamplifying behavior. An effective force leading to the heap and cunvection has been obtained, which includes the square and cubic terms of the local height.
Formation of shear band in a granular material during triaxial compression test
Horabik J.,?…??ukaszuk J.,Grochowicz M.
International Agrophysics , 2000,
Abstract: Formation of shear band during triaxial compression test of a sample of granular material was investigated experimentally. A new method of displacement field fixation in the sample of granular material was proposed. The method allows to analyse of displacement distribution inside a sample of any course granular material. Thickness of the fully developed shear band obtained in the triaxial compression test of a mustard seed was found approximately 15 times bigger than the mean seed diameter.
Particles segregation in rotating drumbased on discrete element method
Wu Li, Huang Peng, Fu Shuaiqi
- , 2017, DOI: 10.3969/j.issn.1003-7985.2017.04.002
Abstract: In order to study particle segregation in the rotating drum, the movement of particles is studied by theoretical deduction and numerical simulation. According to the theoretical deduction, particles near the end wall are lifted higher by the friction of the end wall, which leads to small particles gathering in the middle of the drum. The model of particle motion is established based on the discrete element method. It can be shown from the simulation results that the particles accumulated higher near the end wall, which is consistent with the theoretical deduction. In addition, the effects from the aspects of the relative friction between particles, the friction between the end wall and particle, the drum aspect ratio and the rotation speed were explored by the simulation. From the simulation results, it can be pointed out that the friction of the end wall has a decisive influence on the axial segregation of the particles, and the other factors merely affect the accumulate forms of particles.
Research on the impact of mass fractions of multi-element granular structure on the mixing process
J. Kr???3lczyk,M. Tukiendorf
International Agrophysics , 2008,
Abstract: Knowledge concerning mechanisms that govern the mixing process of multi-element heterogeneous granular structures is still not sufficient. The description of a mixing process where one of the factors is the randomness of particle motion causes additional difficulties. In the article, the authors make an attempt to describe the mixing process of a nine-element system which is a collection of grains of different characterization, among others, the size of grains, densities, or the shape of the mixed elements. In order to describe the process, the cluster analysis is used and thanks to this, homogeneous subpopulations are distinguished out of items originating in heterogeneous population. In the described case, the heterogeneous population is the output data matrix in which to each element of the mixture there is assigned the percentage portion of the elements after 30 min of mixing obtained during the research. The research was carried out in industrial conditions in a vertical mixer with worm agitator. The total mass of the mixed material was 2000 kg. The dendrogram analysis illustrating taxonomic distance between the elements of the mixture allowed to describe which of the elements had the greatest impact on the course of the process in the researched device.
Aplica??o da alvenaria estrutural em sistemas de armazenamento de produtos agrícolas a granel
Marques Neto, José F. de A;Silva, Maria C. A. T. da;
Engenharia Agrícola , 2011, DOI: 10.1590/S0100-69162011000100020
Abstract: the storage of granular materials has had an important role in the agribusiness. storing granular materials in silos, instead of in bags or big-bags, has been an increase tendency. aiming at an economic and rational solution for storing granular materials this paper presents an alternative design: a multi-cell silo group composed of reinforced masonry rectangular cells coupled two by two in width, and a variable number of cells in length according to the volume of desired storage. such symmetrical system benefits the loading and the unloading operations, and guarantees the continuity between the receipt flow and the shipment flow. the silo bottom is designed as a double pyramidal central opening hopper. the hoppers are built in precast-concrete trussed panels. cells and hoppers are supported on reinforced concrete beams and columns. the thermal insulation needed to preserve the quality of the grains is obtained by using galvanized steel trapezoid tiles for the roof as well as for the lateral closure. an example is presented and the feasibility of the alternative design is discussed.
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