Computational Particle Mechanics最新文献

Abstract

The presence of alumina agglomerates seriously affects the current efficiency of the aluminum electrolysis process. The microstructure of agglomerate is difficult to obtain while it is crucial for exploring the thermophysical properties and its dissolution. A method has been proposed to explore the microstructure and thermophysical properties of the porous media. Quartet structure generation set (QSGS) was introduced to model the microstructure of two-dimensional and three-dimensional porous media. The particle phase area of the constructed model was obtained through MATLAB custom code and integration method. The thermophysical properties of alumina agglomerates were derived based on fractal theory and custom programs. The average dissolution rate was obtained and validated according to the thermophysical parameters of agglomerates. The results show that the deviation in describing the physical properties of alumina agglomerates is less than 10%, and the microstructure agrees well with SEM images. The porosity of the agglomerates is 0.58–0.61 and the density is about 2270–2280 kg m⁻³. The effective thermal conductivity of alumina agglomerate is 3.85–3.92 W m⁻¹ K⁻¹ and the average dissolution rate is about 6.83 × 10⁻⁵ kg s⁻¹.

Graphical abstract

This study proposed a novel fluidized bed (NRFB) accompanied by grid trays, air distributor, and other internals, which can realize the continuous production of gas–solid non-catalytic reactions. In the reactor, the reverse flow of the gas–solid phase enabled the solid particles to contact efficiently with the gas and to produce solid particles. The discrete phase model was used to simulate the characteristics of the gas–solid two-phase flow and distribution in NRFB with different types of air distributors and different amounts of grid trays. The improved equal-area torus method and the uniformity index were used to quantitatively investigate the particle’s time-average radial concentration in NRFB. The results show that the air distributor can effectively ensure the uniform distribution of gas in the discharge area in NRFB. “Core-annulus” structures occur in the dense phase section in the NRFB without grid tray. The radial distribution uniformity of particle concentration can be improved by about 17% with 9 grid trays installed in NRFB, and more particles would stay in the dense phase section, which is more suitable for reaction, which can effectively improve the reaction efficiency. The guidance for the construction of experimental equipment and fluidization operation can be provided by the results, which are of great significance for the continuous production of “gas–solid non-catalytic reactions” in fine chemical industries.

Abstract

Aiming at the problem of lower single granularity and uniformity of the existing air-suction seed-metering device under the condition of densely planted crops according to the agronomic requirements of soybean-maize strip intercropping mode, the disturbing effect of seeds on the seed-filling performance was studied to improve the seeding performance of the seed-metering device under the condition of high speed. Based on the theory of discrete element method (DEM), taking the air-suction seed-metering device designed for both soybean and maize as a model and maize variety of ‘Zhengdan 958’ suitable for densely planted as the research object, the DEM single-factor test was conducted on the influence of the structure, position, and number of bosses on disturbing performance with the average kinetic energy, average velocity, and average normal force of seeds as evaluation indexes. The results showed that the disturbing performance of seeds was better when the boss structure was D-type, the diameter of the base circle where bosses located was 160 mm, and the number of bosses was 13. To further improve the structural parameters of the D-type boss, the primary structural parameters, such as the side length and arc radius, were simulated by a single-factor test. The position, side length, and arc radius of the D-type boss were further optimized and verified using central composite design (CCD) based on the results of the single-factor test. The CCD results showed that the average kinetic energy of seeds was 7.39 × 10⁻⁷ J, the average velocity was 4.53 × 10⁻² m/s, and the average normal force was 6.18 × 10⁻² N when the diameter of the base circle where bosses located at 159.865 mm, the side length and arc radius of the D-type boss of 5.690 mm and 5.476 mm, which significantly enhanced the disturbing performance of the seed-metering device. The optimized boss structures and parameters of the seed-metering device were validated with an all-factor test of working speed and working pressure. When the working speed and working pressure were 4 ~ 6 km/h and 7 ~ 7.5 kPa, the qualified rate was 94.75% ~ 97.49%, the multiple rate was 0.92% ~ 1.43%, and the leakage rate was 1.59% ~ 3.82%, all of which were substantially lower than the original one. Therefore, the seed-filling performance of the seed-metering device will be improved by increasing the disturbance of seeds to a certain extent.

Abstract

Fine particles of ash and sand can deposit on the surfaces of cooling ducts, diminishing heat transfer efficiency and threatening the operation of turbine engines. The surface roughness of deposits can alter the nearby flow dynamics, and result in changes of subsequent particle collision and deposition. In this work, the effects of rib turbulence on particle deposition in cooling duct are numerically studied based on the wall modeled shear stress transport k–ω model with a UDF code correction for particle–wall impacts and the discrete particle model. A Gaussian probability density function is adopted to give the topology of deposited particles on the surface impacted by micron particles. We investigate how variables such as particle diameter and temperature impact collision and deposition processes. Additionally, the impact of ribbed turbulence on particle deposition is also discussed. The findings indicate that the impact ratio increases with particle diameter while exhibiting less sensitivity to temperature. Deposition ratios experience a significant decrease when particle size exceeds 1 μm. The temperature of the particles has a noteworthy influence on surface profile of deposits. Specifically, deposits on the wall surface, where particles are introduced by fluid injection, tend to assume a crane-like shape as the temperature rises. Notably, a more uniform deposition pattern is achieved when the particle temperature is low. In terms of particle distribution, low-velocity particles are more likely to accumulate in the windward region of the rib, especially at the junction of the rib wall, where the maximum deposition height is observed. Furthermore, deposits on the rib surface tend to grow, and the gap between the peak and valley widens as the particle temperature increases, as evident from the roughened rib surface features.

Tunnel excavation in weak surrounding rock areas is prone to landslide accidents, and the use of high-pressure rotary piles to pre-strengthen the soil in the local area can enhance the strength and bearing capacity of the surrounding rock. Discrete lattice spring model is established with the three-dimensional morphology modeling system of the rotary pile reinforcement. It is used to quantitatively characterize the reinforcement effects of high-pressure rotary piles, to analyze the influence of the reinforcement ratio and reinforcement function. The results show that compared with the deformation of unreinforced stratum, the high-pressure rotary pile can better control the ground surface settlement. The larger the reinforcement ratio is, the better the reinforcement effect of the rotary spray pile is, especially with the increase in reinforcement ratio, the contact between individual piles bites to form a row of piles, which can significantly improve the ability of the formation to resist deformation. Under the same reinforcement situation, the square root type reinforcement function has the best reinforcement effect, the line function has the middle reinforcement effect, and the quadratic type reinforcement function has the worst effect.

This research investigates how inserting notched gypsum filling between granite specimens affects their breakage under uniaxial compressive testing. Various thicknesses of gypsum filling slabs were placed between granite specimens, incorporating different dimensions and notch configurations. The investigated parameters include elastic modulus, Poisson’s ratio, uniaxial compressive strength, and Brazilian tensile strength of 5 GPa, 0.18, 7.4, and 1 MPa, respectively. Compression testing, at an axial load rate of 0.05 mm/min, was conducted on a total of 9 different models. Numerical simulations were performed on models with notched gypsum filling, varying thicknesses, and notch angles using Particle Flow Code in 2D. The results demonstrated that breakage behavior was primarily influenced by filling thickness and notch angle. The uniaxial compressive strengths in samples were found to be affected by fracture patterns and the breakage mechanism of the filling. The study revealed that the behavior of discontinuities is influenced by the number of induced tensile cracks, which increase with thicker filling. Acoustic emission (AE) hits during loading’s initial phase, a rapid increase in AE hits before the applied stress reached its peak, and significant AE hits accompanying each stress drop were observed. The breakage patterns and strengths were found to be similar in both experimental and numerical approaches.

With the increasing number of projects in cold regions and the widespread use of artificial freezing methods, conducting research on the dynamic properties of frozen soil has become a considerable issue that cannot be avoided in permafrost engineering. Currently, the numerical simulation research on the dynamic mechanical behavior of frozen soil is less concerned with the changes in stress, strain, and particle damage inside the material. The necessary conditions for conducting this study are compatible with the core idea of smooth particle hydrodynamics (SPH). In this study, the Eulerian SPH method was modified to address numerical oscillations and errors in solid mechanics, particularly impact dynamics problems. A numerical scheme for simulating the split Hopkinson pressure bar test was developed within the modified Eulerian SPH framework and implemented using self-programming. The frozen soil dynamic mechanical behavior was simulated under three strain rates. The accuracy and superiority of the SPH method were verified through calculations and experiments. The simulation captures the stress and strain responses within the sample at different moments during the impact process, indicating that the frozen soil strain rate-strengthening effect resulted from microcrack expansion and inertial effects.