•Initiation of the silo discharge generates the rarefaction wave in the stored material.•wave passage changes material characteristics.•Full mobilization of wall friction follows the wave ...front.•Mobilization of particle-particle friction lasts longer than the wave passage.•Wave passage generates wall pressure pulsations.
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The evolution of the stress distribution inside storage silos is an inherent effect in the dynamic operations of handling granular materials. Opening a discharge gate may result in a sudden increase in the lateral pressure with a simultaneous ramp down of vertical pressure, which generates severe pulsations of bin structures.
In the reported study, numerical simulations of the discharge initiation of a grain silo were performed. Discrete element method (DEM) simulations were carried out in a flat-bottomed cylindrical container 0.12 m in diameter and 0.5 m high. One hundred eighteen thousand polydisperse spherical particles with a diameter of 3.79 ± 0.05 mm and material parameters of wheat were used. Based on DEM modeling, the propagation of a rarefaction–compaction wave up the silo height during the start of the bin discharge was studied. It was found that the passage of the rarefaction wave resulted in dynamic changes of all considered micro- and macro- variables describing the behavior of the bulk of solids: particle-to-particle forces, averaged stress tensor, pressure exerted by particles on the bin structure and bulk characteristics of the material: the mobilization of particle–wall and particle–particle frictions and the lateral-to-vertical pressure ratio.
Design codes do not suggest recommendations for the calculations of insert loads and silo wall loads with inserts. Numerical simulations appear to be a promising means to fill this gap. The vertical ...loads on inserts immersed in wheat contained in a model silo were measured in static and discharge conditions. A flat floor, smooth wall test silo, 1.5 m in height and 0.4 m in diameter, was used. Inserts in the shape of cones, discs, and cylinders were axially suspended on three cords at three heights. A series of discrete element method (DEM) simulations were performed with an assembly of 75,000 spherical particles with a random uniform distribution of diameters with an average of 3.79 ± 0.04 mm placed in the cylindrical container with a diameter of 0.12 m. The set-up of the DEM simulations reproduced the results of the laboratory tests. Despite the very large differences in the number of particles in the real and simulated deposits, the results of simulations and laboratory testing were in good agreement. Thus, DEM was found to be a promising method for the estimation of loads exerted by stagnant or flowing granular material on inserts, as well as for the determination of dead zones and the geometry of the flow channel.
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•Loads on the internal objects immersed in stationary and moving bed investigated.•Close agreement of measured and simulated loads on inserts found.•Stress tensor derived from network of interparticle forces•Flow patterns visualized•Degree of mobilization of wall friction identified.
We present an experiment and the results of DEM simulations of the stress profile within a bulk of seeds in a shallow cylindrical model silo. The goal of our study is to understand the microscopic ...origins of the impact of friction mobilisation during particle-particle and particle-wall contacts on the distribution of stress in bulk of seeds. Experiments were performed with horse beans and field pea seeds. Mobilisation of friction was increased a) experimentally, by hanging a dead load on the wall of the cylindrical container holding seeds, and b) in DEM simulations, through small vertical movements of the silo wall. DEM simulations were performed with spherical particles and axially symmetric clusters of spheres containing rolling friction. It was found that the radial profile of the normal pressure σz(r) on the bottom of a shallow silo may be constant, increasing, or decreasing depending on the particle shape and filling method. Consequently, the radial profile of the shear stress τ(r) in the bulk of particles follows linear, convex, or concave relationships, respectively. Different trends of change of the radial profile of shear stress during down- and upward movement of the wall were observed. During downward movement of the wall the shear stress increased nearly uniformly along the radial position. During the upward movement a zone of change of shear stress was distinctly reduced. This effect may be a result of the participation of compressive and lack of tensional interactions in building of shear resistance.
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•DEM simulations of average stress consistent with experimental data•Linear, convex, or concave shape of radial profile of shear stress determined•Wall movement induced changes in radial profile of shear stress analyzed•Jaky's formula of the pressure ratio positively verified
We present a numerical analysis of the transmission of contact forces in a granular pile comprising 50,000 frictional, coarse spherical particles. The goal of our study is to understand the ...microscopic origins of macroscopic behaviours, such as the pressure dip at the centre of the base of a conical pile. The particles are 8.2mm in diameter with a standard deviation of 0.1mm to avoid ordering effects. The effects of the pouring method, inter-particle sliding friction and rolling friction on the distribution of static stress are examined. The analysed microscopic variables are the distributions of the values and directions of the contact forces as well as the degree of mobilisation of contact friction. The vertical, radial and shear stress components are derived from the discrete contact forces. The analysed macroscopic variables are the distribution of the stress components, mobilisation of internal friction and inclination of the major principal stress to the vertical. The simulation results show that certain combinations of the examined factors lead to the formation of dome-shaped structures of maximum values of mean pressure as determined by the stress distribution inside the pile as well as at its base.
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•The distribution of stress components inside a pile is shown.•The highest mobilisation of friction is in the top layers.•A pressure dip is associated with a loose packing structure.•A self-supporting dome is identified inside the pile.•The dome determines the transmission of forces to outer regions of the pile.
In the design of a storage silo usually an axially symmetric state of stress is assumed. However, unsymmetrical pressure distribution may occur because of such factors as: non-uniform humidity of the ...material, eccentric filling or/and discharge, and additional construction elements inside the deposit. Small internal construction members act similarly to structural imperfection and can initiate buckling, while larger flow obstacles can markedly alter the stress distribution.
A study was conducted to numerically simulate the effect of plane (2D) or block (3D) obstruction attached to the wall in a model grain silo holding wheat. This work compares the results of earlier laboratory testing and numerical simulations using the discrete element method (DEM).
Series of the DEM simulations were performed with an assembly of 75000 spherical particles with random uniform distribution of diameters with a mean of 3.8mm and range of ±1% placed in the cylindrical container with a diameter of 0.12m. The set-up of DEM simulations reproduced earlier laboratory tests performed in the model grain silo, 1.83m in diameter with flat floor and corrugated wall. Despite the very large difference in the number of particles in real and simulated deposits, the results of simulations and laboratory testing were in fairly good agreement.
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•Pressure distribution was examined as influenced by insert attached to the silo wall.•DEM was found to adequately reproduce an experimental results.•Internal insert may decrease dynamic peak of wall pressure.•Additional element inside the bed affected load distribution in the silo.
A new vane shear tester is proposed for the determination of the shear strength in consolidated samples of granular biomass. Measurements are performed using forest woodchips with a normal pressure ...in the range 5–30kPa applied at rotation rates of 3–13rpm. The maximum torque is found to be affected by the normal pressure and time of compression. The rotation speed is not found to have a significant influence on the shear strength. The new apparatus is an efficient tool for determining the mechanical characteristics of granular biomass. The results are in general agreement with those given by the standard Jenike method, but the new technique makes testing easier and faster. Quantitative differences between the results obtained using the two methods are possibly a result of the different modes of load application and the geometry of the shear surface.
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•The mechanical properties of granular biomass are required for design efficient operation and equipment.•New methods are required.•New vane tester was constructed for determination of shear and strength properties of granular biomass.•Results from vane test were compared with standard method.
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•Single-phase nanoparticles of CoxCe1-xO2-y exist only for x < 0.2 and their reducibility and catalytic activity increase with x.•Nanoparticles of Co3O4 are similarly active to the ...most active SPhSS: Co0.15Ce0.85O2-y.•Catalytic activity of Co3O4 increases with small additives of CoxCe1-xO2-y phase.•This synergy can be explained by specific activity of the interfacial areas.•Coexistence of both types nanoparticles seems to provide the highest activity.
Two different nanoparticle oxide systems are obtained depended on Co:Ce atomic ratio (R) using the same reverse nanoemulsion method. The single-phase solid solutions (SPhSS) are formed up to the ratio 1:4 < R < 1:5. The higher Co concentration results in segregation of Co3O4 phase forming nanocomposite of 2 types of nanoparticles (SPhSS and Co3O4). These nanomaterials were characterized using X-ray and electron diffraction, transmission electron microscopy together with linescan EDX analysis of individual nanoparticles, high-resolution XPS, TPR of preoxidized or pre-reduced samples, and testing activity in methanol total oxidation. The catalytic activity increases with increase of Co concentration in SPhSS and is preserved after deposition on alumina support. The catalytic activity of pure Co3O4 nanoparticles is comparable with the Co0.15Ce0.8O2-y solution and is increasing with Ce doping in the Co-rich 2-phase nanoparticle systems. Such a coexistence seems to be responsible for the highest catalytic activity in methanol oxidation.
C/Li2MnSiO4 nanocomposite material was obtained by sol–gel method followed by carbon coating process. Electrochemical properties of nanosized C/Li2MnSiO4 cathode composite were studied in terms of ...changes in the long range ordering of the crystalline structure. Structural morphology was determined using X-ray diffraction (XRD) and transmission electron microscopy (TEM). Ex-situ XRD studies confirmed amorphization of material during electrochemical process. Even though, C/Li2MnSiO4 composite revealed high discharge capacity (up to 185 mAh g−1) within 1.5–4.8 V, what corresponds to the exchange of more than one lithium-ion per formula unit (1.11 mole Li+). Electrochemical impedance spectroscopy (EIS) studies showed substantial changes in electrical properties of Li2MnSiO4 during amorphization process. The obtained results suggest that electrochemically formed amorphous Li2MnSiO4 has much higher electrical conductivity and Li+ ions diffusibility than as-obtained in sol–gel process crystalline one.
•C/Li2MnSiO4 nanocomposite was obtained by sol–gel method and carbon coating process.•Fine and uniform carbon nanocoatings on nanometric Li2MnSiO4 material were obtained.•Amorphous Li2MnSiO4 was formed during electrochemical process.•DLi+ was calculated for charged and discharged C/Li2MnSiO4 material.•C/Li2MnSiO4 nanocomposite revealed high discharge capacity 185 mA h g−1 at 1.5–4.8 V.
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