Particle Flow Model Research Articles

Numerical investigation on the tracer followability of nitrogen droplets over the airfoil in cryogenic wind tunnel

Cryogenic wind tunnels (CWT) achieve high Reynolds number aerodynamic performance measurements by cooling the medium with liquid nitrogen. Utilization of naturally-occurring liquid nitrogen droplets as tracer particles for non-intrusive measurement applications in CWT shows great potential in the previous work. However, the droplet motion characteristics over the airfoil remain to be investigated, and the followability evaluation approach is lacking. Accordingly, an Euler-Lagrange model for transonic particle flow over the NACA0012–64 airfoil was established. The effect of flow characteristics on the particle motion was explored. The results reveal that the flow separation and shock wave phenomenon over the airfoil causing velocity deviation between airflow and droplet. The shock wave is the main deviation driver, and flow separation causing trace blind zones. Droplets larger than 10 μm fail to effectively follow the variation of airflow. The blind zone enlarges with angle of attack (AoA), particularly when AoA exceeding 10 degrees. Moreover, Stokes number is found to be inadequate for characterizing the followability of tracer particles in turbulent flow. Consequently, an evaluation method based on the Basset-Boussinesq-Oseen equation was developed. This research provides theoretical and technical support for advancing the use of nitrogen droplets as tracer particles in CWT.

Prediction of plasma path and analysis of axial fracturing properties in rock fragmentation by high-voltage pulsed discharge (RHPD)

Rock fragmentation by high-voltage pulsed discharge (RHPD) is widely utilized in resource recovery and energy extraction due to its low energy consumption and high efficiency. However, observing the plasma development process during RHPD presents challenges, and the frequency dependence of dielectric properties further complicates plasma path prediction and the analysis of fracturing properties in the axial direction of the plasma. To address these issues, we analyzed the development properties of plasma within rocks and established a segmented breakdown criterion that considered the propagation velocity of plasma. Additionally, utilizing a transient electromagnetic field model and a particle flow model (PFM), we established a multi-physics field model and proposed a predictive method for the plasma path in a rock–liquid combination environment. This allows for the quantification of the velocity, potential, and length of the plasma. Furthermore, we computed the time response of shock waves and analyzed the loading mechanism of shock waves. Based on the spatial distribution of plasma, the PFM was applied to simulate the fracturing properties of rocks under shock wave loading. Finally, we established a comprehensive experimental platform for RHPD and conducted three-dimensional reconstructions of the fractured area to validate the accuracy of plasma path prediction methods and fracturing properties analysis. This study significantly advances plasma development theory and provides insights for optimizing rock fragmentation efficiency.

Shear mechanical properties of aggregate cemented materials: a numerical study based on a particle flow modeling strategy

Shear mechanical properties of aggregate cemented materials: a numerical study based on a particle flow modeling strategy

A Study on the Borehole Wall Stability Analysis and Slurry Ratio Optimization for Construction of Pile in Complex Marine Strata.

In order to address the issue of hole collapse, which frequently arises when boring piles are being constructed in intricate marine strata, this paper discusses the influence of the slurry ratio on the slurry performance as well as the mechanism of slurry wall protection. It performs this by means of theoretical analysis, laboratory ratio testing, engineering analogies, numerical simulation, and field testing. Our findings demonstrate that adding sodium polyacrylate and sodium carboxymethyl cellulose can enhance mud's viscosity, contribute to flocculation, and improve the connection between mud and soil layers. Refering similar engineering cases, three optimization schemes are proposed for achieving a mud ratio that offers wall protection in complex marine strata. Furthermore, the particle flow model of slurry viscous fluid is established. The collapse of holes in the sand layer is reflected in the uneven radial displacement of hole walls and the invasion of mud particles. Increasing the viscosity of mud gradually transforms the uneven radial deformation of pore walls in the sand layer into a uniform radial deformation, whereas increasing the proportion of mud significantly decreases the radial displacement of hole walls. Additionally, when the mud pressure in the hole is 300 kPa and 600 kPa, the wall protection effect is better, and there is no particle penetration by substances such as sand. It is found that a high mud pressure can promote the diffusion of mud particles into the sand layer, while low mud pressure cannot balance the pressure on deep soil. The results of the field tests show that the ratio of water-clay-bentonite-CMC-Na-sodium carbonate = 700:110:90:1.5:0.5 used (where the mass percentage of each material is 77.8% water, 12.2% clay, 10% bentonite, 0.16% CMC-Na, and 0.05% sodium carbonate) can effectively prevent hole collapse and reduce the thickness of the sand layer at the bottom of the hole by 50%.

Particle flow numerical simulation model for coal and gas outburst and its microscopic outburst mechanism description

The finite difference model and particle flow model were constructed to reproduce the process of coal and gas outburst in front of the tunnel. The reliability of the particle flow model was verified by studying the internal stress, gas pressure, and related parameters of gas and coal two-phase flow. Then the process of coal and gas outburst is described from a microscopic perspective. The results show that the particle flow numerical model of coal and gas outburst is in line with reality and can intuitively and conveniently monitor relevant parameters; The concentrated stress caused by excavation of tunnels can reach 1.2 times the in-situ stress; High stress causes the adhesion between coal particles to break down, which is the main reason for the initiation of coal and gas outbursts; The intermittent breakthrough of gas on the coal particle collection that blocks the release channel has caused pulsating characteristics of coal and gas outbursts.

Brittle Failure Modes and Mechanisms in Foliated Rock Under Uniaxial Compression: Laboratory Testing and Particle Flow Modeling

Brittle Failure Modes and Mechanisms in Foliated Rock Under Uniaxial Compression: Laboratory Testing and Particle Flow Modeling

Study on the formation mechanism of shale thermal cracks based on particle flow numerical simulation

Thermal effects on rock mass are involved in many fields, including enhanced oil and gas recovery, unconventional oil and gas development, and nuclear waste deep placement. Temperature change will produce thermal stress in rock mass, leading to thermal cracking. Thermal cracking of shale is frequently involved in these fields. The mechanism of thermal cracking formation in shale is studied in this paper using the method of indoor heating experiment and particle flow method, which discovered that it is difficult to produce obvious thermal cracking in shale matrix, and only a few intercrystalline and intercrystalline fractures and shrinkage fractures of organic matter occur locally. Based on the particle flow method, a shale particle flow model is built that is highly consistent with the macro and micro characteristics of shale, while the systematic calibration method for shale particle flow model microscopic parameters can realize effective calibration of shale particle flow mechanical model microscopic parameters. Using a linked thermodynamic coupling model of shale particle flow based on the mechanical model of shale particle flow, the impacts of heating modes, natural micro cracks, and confining pressures on the thermal cracking evolution of shale were studied.

Multi-level coarse-grained discrete element method modeling of cylinder particle flow in a rotating drum

The coarse-grained discrete element method (DEM) is probably a feasible option for simulating an actual drum-type biomass boiler, which contains over 10 million cylinder particles. A multi-level study was conducted based on particle and coarse-grained level data to evaluate the adequacy of the coarse-grained approach in terms of geometrical characteristics, kinematic features, and dynamic properties. Two scaling laws for contact parameters were used and compared during the simulations. The results show that the coarse-grained approach can accurately predict the positions of the free surface and active-passive interface, the mixing index, and the orientation properties. Deviations in the velocity fields may occur due to the worse flowability of coarse-grained particles near the free surface. The efficiency is significantly improved by the coarse-grained model compared with the corresponding original case (the same DEM code without a coarse-grained model was used for the original simulations).

Fracturing process and initiation mechanism of hard rock tunnels with different shapes: particle flow modeling and analytical study

Fracturing process and initiation mechanism of hard rock tunnels with different shapes: particle flow modeling and analytical study

Investigating the Influence of Joint Angles on Rock Mechanical Behavior of Rock Mass Using Two-Dimensional and Three-Dimensional Numerical Models

Numerical testing is an ideal testing method in the research on the mechanical behaviors of jointed rock. However, there are few systematic studies focused on the comparison between the two-dimensional (2D) and the three-dimensional (3D) simulation effects on rock mechanical behaviors, particularly those of jointed rock. In this paper, a particle flow model was established by utilizing PFC2D and PFC3D to represent the rock materials, and the rock (especially jointed rock) mechanical behaviors (uniaxial compressive strength UCS, tensile strength TS, crack initiation stress level Kσ, and the pattern of crack initiation) between 2D and 3D models were compared and analyzed. As expected, the result shows that the UCS and TS showed an increasing tendency with the increase in the joint angle (β) for both the 2D and the 3D models, and the strength of the 3D model was less than that of the 2D model under uniaxial compression but was greater than that of the 2D model under uniaxial tension. The crack initiation and Kσ of the specimens were essentially the same for the 2D and 3D models, and the tensile stresses are more concentrated than the compressive stresses before the failure of the specimen; the uniaxial tensile failure more closely approached abrupt failure than the uniaxial compression failure. The tensile cracks were often initiated at the tips of the joints for both the 2D and 3D models, but they were initiated in the middle of the joints when β was low (β = 0° and β = 15° in both the 2D and 3D models) under uniaxial compression and when β reached 90° under uniaxial tensile. The test results were validated and further analyzed with mathematical analysis. This study has relative referential value to experiments on jointed rock and to analysis of the instability fractures of engineering rock mass.

Effects of solid particle surface roughness on particle velocity fluctuation in multi-zone waste heat recovery heat exchanger

The velocity fluctuation affects the safe operation of the heat exchanger when the particles flow through the heat exchanger. The particle flow model of heat exchanger is established based on the discrete element method to investigate the correlation between surface roughness and particle velocity fluctuation. Many studies have used static friction coefficients to characterize the particle roughness. The particle velocity fluctuation in heat exchanger is analyzed, and the effects of the static friction coefficient on the particle velocity fluctuation are studied. The results showed that when the particles flow stably, the force chain structure between the particles is a process of breaking and rapidly reconstructing. This force characteristic of the particles causes the constant fluctuation of the particle velocity, which fluctuation frequency varies from 0.05 Hz to 0.08 Hz. The velocity fluctuations of the particles located at the top of the heat exchanger are particularly violent. The direction of the force chain distribution gradually moves horizontally with the increase of the static friction coefficient, and the velocity fluctuation in the vertical orientation becomes more intense. The amplitude of velocity fluctuation increases from 0.6 × 10−3 m/s to 1.3 × 10−3 m/s. The results are helpful to understand the dynamic behavior of particle in heat exchanger during flow and provide the basis for subsequent improvements.

A Case Study of Cutting Performance by a Transverse Cutting Head Based on Three-Dimensional Particle Flow Model

Roadheaders have been increasingly used in a variety of tunnel cross-sections and roadway excavations. The appropriate setting of key construction parameters of the roadheader can maintain the excellent cutting performance of the roadheader during excavation. In this respect, this paper reviews in detail the previous studies on various experiments and numerical simulations affecting the cutting performance parameters of roadheader. A method for simulating the breaking process during the mechanical cutting of rock was then introduced using the Particle Flow Code in 3 Dimensions (PFC3D). In the numerical simulations, we used the parallel bond model to simulate the studied rock material and completed the calibration of the mesoscopic parameters by numerical simulation tests. In the simulations, we set different cutting modes, cutting depths and cutting thicknesses to study the rock breaking process of the transverse cutter head in a highly weathered granite environment from a microscopic perspective. The simulations indicated that the cutting mode, cutting depth and cutting thickness have significant effects on the cutting force and specific energy consumption. It is feasible to use the available space to the fullest and effectively reduce the wear of the picks by adopting the undercutting mode. The cutting efficiency can be improved and the specific energy consumption of cutting can be significantly decreased by increasing the cutting depth. The optimal cutting depth for highly weathered granite is 13 cm. As the cutting thickness increases, the cutting head's normal and rolling forces increase linearly, and the cutting efficiency improves. Under the condition of highly weathered granite, the maximum cutting thickness of the Erkat ER1500 transverse cutting head is 12.5 cm. Overall, the results indicate that the discrete element method is a powerful tool for simulating rock cutting process.

Overlying main roof breaking characteristic and its effect on the stability of gob-side entry

In this study, to figure out the deformation mechanism, a particle flow model was used to simulate the deformation of surrounding rock in a deeply buried entry. The fracture evolution, stress, and porosity of surrounding rock in the process of the main roof breaking, meanwhile, the displacement after entry being excavated were recorded and analyzed in the simulation. The results show that the main roof breaking is different from the ideally elastic–plastic simply supported beam for it has two more plastic zones on both sides of the beam and its support points tend to move. In addition, the stress reduction zone in the coal seam is about 10 m where the coal body and surrounding rock are almost completely broken and porosity is surprisingly increasing from 0.01 to 0.39 in coal and 0.23 in the main roof. The displacement concentrated on the ribs of entry, especially on the coal pillar. The continuous and large deformation that appears in the stress reduction zone results from the nearly completely broken state of the surrounding rock. The tradeoff between the stress reduction and the broken state of the surrounding rock should be considered when choosing the location of the gob-side entry.

Temperature Variation of Rock during Deformation and Fracturing: Particle Flow Modeling Method and Mechanism Analyses

The rock deformation and failure characteristics and mechanisms are very important for stability evaluation and hazard control in rock engineering. The process of rock deformation and failure is often accompanied by temperature changes. It is of great significance to study the characteristics and mechanism of temperature variation in rock under deformation and fracturing for a better understanding of rock failure and to obtain some probable precursor information for guiding the prediction of the mechanical behavior of rock. However, most of the studies are based on observations in the field and laboratory tests, while it is still required to develop an effective method for modeling and calculating the temperature variation of rock during the deformation and failure processes. In this paper, a particle flow modeling method based on energy analyses is proposed for simulating the temperature variation of rocks, considering four temperature effects, including the thermoelastic effect, friction effect, damping effect, and heat conduction effect. The four effects are analyzed, and the theoretical equations have been provided. On this basis, the numerical model is built and calibrated according to the laboratory uniaxial compressive experiment on a marble specimen, and a comparison study has been conducted between the laboratory and numerical experiment results. It is found that the numerical model can well simulate the average value and distribution of the temperature variation of rock specimens, so this method can be applied for studying the mechanism of temperature variation more comprehensively during the whole process of rock deformation and fracturing compared with the continuous modeling methods. With this method, it is shown that the temperature change has three different stages with different characteristics during the uniaxial compression experiments. In the different stages, the different effects play different roles in temperature variation, and stress distribution and crack propagation have obvious influences on the local distribution of temperature. Further investigations have also been conducted in a series of sensitive analyses on the influences of four factors, including the thermal conductivity, friction coefficient, thermal expansion coefficient, and particle size ratio. The results show that they have different influences on the thermal and mechanical behaviors of the rock specimens during the deformation and failure process, while the thermal expansion coefficient and the particle size ratio have more significant impacts than the other two factors. These findings increase our knowledge on the characteristics and mechanism of temperature variation in rock during the deformation and fracturing process, and the proposed modeling method can be used in more studies for deformation and fracturing analyses in rock experiments and engineering.

Particle flow modeling for the crack growth analysis of non-persistent cracks

particle flow modeling for the crack growth analysis of non-persistent cracks

Effect of Loading Rate on the Mechanical Properties of Weakly Cemented Sandstone

Weakly cemented rocks are characterized by low strength, loose structure, and easy disintegration. High-intensity mining activities can damage and rupture such rock bodies and induce damage, such as flaking and roofing on roadways. To reveal the mining intensity influence on the weakly cemented rocks’ deformation and damage, a numerical particle flow model of weakly cemented sandstone was established based on particle flow theory. Uniaxial compression simulation tests were conducted at four loading rates of 0.01, 0.1, 0.5, and 1 mm/min to study the weakly cemented sandstone’s stress–strain relationship, damage rupture, acoustic emission, and energy evolution. The results show that, with an increased loading rate, the uniaxial compressive strength of weakly cemented sandstone increases exponentially, and the rupture mode transforms from brittle damage to ductile damage; the greater the loading rate, the greater the degree of damage and crushing range of the rock. Further, with an increased loading rate, the peak hysteresis of rock acoustic emission events decreases, and the number of events increases; the energy accumulated in the rock increases, thus intensifying the degree of rock damage. Therefore, the possibility of engineering disasters should be considered when conducting high-speed underground mining activities.

A tube heat transfer prediction model considering static friction coefficient of dense particle flow

Particulate material is an important heat transfer medium in industry. The heat transfer process of dense particle flow around tubes has important applications in industrial waste heat and solar energy conversion. However, rapid prediction of particle heat transfer processes is still worth investigating, especially when the particle flow is affected by the coefficient of friction. A heat transfer model of dense particle flow around a tube was established, the effects of particle size, density and static friction coefficient on the heat transfer characteristics were explored, and a heat transfer prediction equation considering the static friction coefficient was constructed originally. The results show that the particle size has the most significant effect on the heat transfer. As the particle size increases from 2 mm to 4 mm, the average effective heat transfer coefficient of the tube decreases from 262.35 W/(m2·K) to 217.31 W/(m2·K). The effect of particle density on the heat transfer is reflected in the difference in the heat capacity of the particles, and has little effect on the flow of the particles. The particle static friction coefficient mainly affects heat transfer by affecting the flow state of the particle flow. The average contact number decreases from 63.9 to 38.9. The relative error of the modified model is reduced from 8.9% to 3.78%.

A Study of Strength Parameter Evolution and a Statistical Damage Constitutive Model of Cemented Sand and Gravel.

Cemented sand and gravel (CSG) has a wide range of applications in dam construction, and its properties are between rockfill and roller compacted concrete (RCC). A difference in gel content will result in a variance in CSG's structure and mechanical properties. To investigate the intricate structural mechanical properties of CSG, this study conducted a series of laboratory tests and associated discrete element analyses. Accordingly, the evolution law of the strength parameters of CSG is explored and a statistical damage constitutive model suitable for CSG is established. The main contributions of this study are as follows: (1) The failure mechanism of the CSG was described from the microscopic level, and the evolution law of the strength parameter cohesion and friction angle of the CSG was analyzed and summarized. (2) Based on the particle flow model, the energy development law and the spatiotemporal distribution law of acoustic emission (AE) provide illustrations of the strain hardening-softening transition features and the interaction between cohesion and friction of CSG. (3) The evolution function between the strength parameter and the strain softening parameter was built, and the critical strain softening parameter was determined by the microcrack evolution law of the particle flow model. (4) The accuracy of the evolution curve was confirmed by comparing it to experimental results. (5) Based on the relationship between cohesion loss and material damage, a statistical damage constitutive model was developed using the improved Mohr-Coulomb strength criterion as the micro strength function. The constitutive model can accurately describe the stress-strain curves of CSG with different gel content. Furthermore, the model reflects the strain hardening-softening properties of CSG and reveals the relationship between the weakening of cohesion and material damage at the microscopic level. These findings provide valuable guidelines for investigating the damage laws and microcosmic failure features of CSG and other relevant materials.

Study on energy transition of dense particulate flow in a horizontal agitator

Hammer mill cuttings cleaner is an efficient low-temperature drying cuttings equipment. In order to investigate the main components of energy dissipation and the flow characteristics of granular flow in grinding systems. The energy dissipation model of dense particle flow is established by numerical simulation and validated by macroscopic experiment. The results show that the particle flow mainly moves in a circle along the wall of cylindrical vessel. The main parts of energy dissipation are sliding friction consumption of particle, the inelastic collision between particles and sliding friction between particles and container; the input energy is a linear function of particle filling rate. The flat blade can provide higher efficiency at the same operational conditions. The study lays a theoretical foundation for the industrial application of Thermal-mechanical cuttings cleaner of drill cuttings and provides a reference for the optimization of blade configuration.

Particle Flow Analysis of Acoustic Emission Features of Rock under Rock Burst Stress Path

The AE (acoustic emission) features could reflect the process of fracture initiation and propagation in rocks. Taking Lalin railway tunnel granite as an example, a three-dimensional particle flow numerical model of rock was established based on the PFC (particle flow code). The mechanical properties between particles were simulated using parallel bond. The rock burst stress path was simulated using the movement of the wall in the particle flow model. The results of uniaxial compression tests in a laboratory were used to calibrate the mesoscale mechanical parameters of the particle flow model. AE features of rock deformation and failure under different confining pressures were then studied. It shows that the unloading direction of rock may produce strong dilatation deformation during rock burst; with the increase of confining pressure, the more obvious dilatation deformation and the more possibility of serious rock burst to occur; the unloading failure of rock reveals that rock burst is a mixed failure of tensile and shear, and the tensile cracks account for about 70%; the number of AE events of rock unloading failure occur at the top and bottom of the rock first and then expand rapidly to the middle part until the rock is completely destroyed; in the process of rock burst, AE rupture strength is relatively concentrated, the number of AE events surge obviously, and the number of AE events in surge period account for more than 80% of all AE events. The results presented herein may be referable in analyzing the mechanism of rock burst.