Particle Coordinates Research Articles

Experimental study on the influence of particle morphology on compression characteristics of coral sand in South China Sea

Particle morphology is an important physical parameter that influences the engineering properties of coral sand, especially its compressibility. According to the quantitative analysis of particle morphology via the dynamic image analysis technology, a series of one-dimensional compression tests on coral sand and quartz sand with different particle morphology and densities were performed to reveal the effect of particle morphology on the compressibility of coral sand. The results demonstrated that the morphology of particles can be quantified using the shape-angularity group indicator (SAGI), whereas the SAGI of coral sand was greater than that of quartz sand. Coral sand exhibited a yield stress ranging from 1 to 2.5 MPa, and compressive deformations in both coral sand and quartz sand were dominated by irreversible plastic deformation. As the SAGI and densification increased, the number of particle coordination increased while the contact stress between grains decreased, which caused the yield stress of coral sand specimens to increase as well as the compression index and particle crushing rate to decrease. The SAGI of quartz sand particles remained relatively unchanged while that of coral sand particles gradually decreased after crushing, i.e., the coral sand particles developed a more regular shape after crushing.

A study of particle motion in Kwerk-type twisted blades: Effect of configuration on particle mixing performance by CFD–DEM

Static mixers could promote the particle mixing in industries. Experimental and numerical investigations of particle mixing and flow characteristics in the riser with static mixers are carried out. The instantaneous microscopic characteristics and energy loss in Kwerk-type static mixer (K-KSM) are evaluated by Computational Fluid Dynamics coupled with Discrete Element Method (CFD–DEM). A more suitable calculation method is proposed, which utilizes particle coordinates and the coordination number of central particles to calculate the instantaneous mixing degree of particles (PK). The PK, Residence Time Distribution (RTD) and collision correlation are analyzed at different superficial gas velocities (Ug) and mass flow rates (Ms). The results show that the performance of K-KSM is superior to that of KSM under current conditions. Back mixing and aggregation phenomena are eliminated at Ug > 5 m/s and Ms < 1.73 g/s, and the recommended regimes are Ug ≥ 6.0 m/s and Ms < 1.5 g/s.

Modeling of particle migration in piping based on an improved discrete element method

Pore-scale particle migration in piping is the main reason of the suffusion-induced damage, which poses a significant threat to earth-rock dams. In order to investigate the micro-mechanism of piping seepage process, an improved fluid-solid coupling discrete element method is proposed in this paper. In this method, particles in a packed model are divided into coarse- and fine particle groups. Pores can be defined based on the coordinates of the coarse particles and the Delaunay triangulation algorithm. A pore density flow method is introduced to calculate the overall fluid pressure of each pore and the fluid flow via pore throats. Further, the drag force on fine particles inside a pore can be calculated according to the fluid velocities of the neighboring four pore throats. The proposed method was implemented in the discrete element software MatDEM, and was successfully used to simulate fine particle migration of piping, the particle loss process, and the related variation of permeability coefficient. The pore-jamming phenomenon during the fine particle migration is observed. The model provides an effective way for the numerical analysis and mechanism study of piping seepage process at the pore scale.

Identification of force chains in wet coal dust layer and the effect of porosity on three-body contact stiffness

Aiming at the three-body contact problem of mechanical rough surface containing wet coal dust interface, the three-body contact model of rough surface containing wet coal dust interface is constructed by comprehensively considering the contact deformation of rough surface and contact characteristics of wet coal dust, and based on the crushing theory. By analysing the contact force, load-bearing particle size and adjacent contact angle thresholds of the wet coal dust layer, the force chain identification criterion is formulated. Finally, quantitative calculations of the force chain characteristics are performed to reveal the effect of different initial porosities on the three-body contact stiffness, which is verified experimentally. The results of the study show that the average contact force of the wet coal dust layer can be used as the force chain contact force threshold, the average particle size can be used as the force chain particle size threshold, and the force chain angle threshold is determined by the particle coordination number. As the initial porosity decreases, the number, length and stiffness of force chains in the wet coal dust layer increase significantly, and the stiffness reaches a maximum value of 2.007 × 108 pa/m at the moment of downward pressure to stabilisation, while the trend of force chain bending varies in the opposite direction, and its minimum bending degree decreases to 20°. The maximum relative error between the simulation and experimental results of three-body contact stiffness is 9.64%, which proves the accuracy of the force chain identification criterion and the quantitative calculation of three-body contact stiffness by force chain.

Flow Measurements Above A DBD Plasma Actuator Array By Means Of Defocusing PTV

Lagrangian defocusing particle tracking velocimetry (DPTV) measurements are conducted in a thin, wall-parallel volume above a plasma actuator array that is applied to mimic the effect of wall oscillations by inducing alternating, wall-parallel forcing in opposite directions into the air above the actuator surface. The aim of the experiments is to capture the plasma-induced flow structures in otherwise quiescent air in order to increase the understanding of different actuation parameters. For this purpose, high-speed particle image velocimetry equipment with one camera is used in a DPTV setup, where the out-of-plane particle coordinate is obtained through the diameter of a defocused particle image. On this basis, an approach for continuous particle tracking in several consecutive frames is presented, allowing to derive three component, three dimensional velocity and acceleration data. Light reflections that occur on the adjacent actuator surface give raise to particular challenges concerning the measurement uncertainty estimation as well as the calibration procedure for the evaluation of the wall-normal coordinate of tracer particles. To overcome the latter, a calibration approach is presented for which solid particles are applied to the actuator surface and their particle image diameter is captured at different camera positions in a separate measurement. The estimation of in-plane and out-of-plane displacement measurement uncertainties is conducted following a newly-developed procedure where the deviation of particle displacements from a straight track is evaluated for measurements in quasi-quiescent air. The obtained results show the suitability of DPTV measurement technique for the practical application of the characterization of flow structures above a plasma actuator array. The measurement accuracy is found to be limited due to the available illumination, which depends on the used components. The measured flow fields together with optical and electrical measurement data allow for a further analysis of the present forcing strategy. Particularly, by recording phase-resolved, three-dimensional flow velocity and acceleration fields in the vicinity of the wall, the spatio-temporal occurrence and homogeneity of the near-wall forcing effects can be analyzed in future investigations.

Investigation of meso-mechanical properties of Jinping dolomitic marble based on flat-joint model

Brittle rock has the mechanical characteristics of a high ratio of uniaxial compressive strength to tensile strength, brittle-ductile transition, and so on. The mineral meso-structure of brittle rock shows the interlocking behavior and there are some microcracks between the mineral grains, so it is difficult to analyze the mechanical characteristics accurately with a regular constitutive model. The previous numerical models have some limitations when applied to brittle rock, that they cannot provide sufficient internal interlocking and are incapable of considering the microcracks. These limitations are addressed by using the updated flat-joint contact model to join notional polygonal particles with an initial gap and increasing the particle coordination number by adding flat-joint contacts to more particles that are within some non-zero distance of one another via the range coefficient contact identification method. A comparison of experimental and numerical results confirms that the updated flat-jointed model provides a good match with the mechanical properties of brittle rock. In this paper, we investigate the influence of mineral meso-structure (micro-cracks, range coefficient, and radius multiplier) on the meso-mechanical properties of Jinping dolomitic marble via the updated flat-joint contact model under direct-tension tests and compression tests. It is found that the updated model can reproduce the microstructure effect of brittle rock and can better simulate the mechanical characteristics of the brittle rock than conventional models, such as high strength ratio, brittle-ductile transition, initial nonlinearity, and different modulus in compression and tension.

A novel data-driven reduced-order model for the fast prediction of gas-solid heat transfer in fluidized beds

Computational fluid dynamics − discrete element method (CFD-DEM) emerges as a promising tool to model dense gas–solid two-phase flow in fluidized beds, yet the numerical efficiency is still far from being satisfactory. Accordingly, this work develops a proper orthogonal decomposition (POD) reduced-order model (ROM) based on the CFD-DEM method for the fast prediction of gas–solid flow and heat transfer in a bubbling fluidized bed (BFB). The POD method is employed to decompose particle coordinates and temperature into spatial modes and time evolution coefficients. The radial basis function neural network (RBFNN) and temporal convolutional neural network (TCN) are utilized to predict the time evolution coefficients. Regarding the POD modes, the particle temperature exhibits an obvious monotonic or periodic characteristic compared to the particle coordinates, indicating the potential for long-term prediction. The RBFNN-ROM and TCN-ROM reconstruct the flow field effectively, achieving acceleration ratios of 2000 and 3000, respectively. The ROM developed in this study holds the potential to enable real-time prediction of industrial processes, thus paving the way for the realization of digital twins.

Enabling three-dimensional real-space analysis of ionic colloidal crystallization.

Structures of molecular crystals are identified using scattering techniques because we cannot see inside them. Micrometre-sized colloidal particles enable the real-time observation of crystallization with optical microscopy, but in practice this is still hampered by a lack of 'X-ray vision'. Here we introduce a system of index-matched fluorescently labelled colloidal particles and demonstrate the robust formation of ionic crystals in aqueous solution, with structures that can be controlled by size ratio and salt concentration. Full three-dimensional coordinates of particles are distinguished through in situ confocal microscopy, and the crystal structures are identified via comparison of their simulated scattering pattern with known atomic arrangements. Finally, we leverage our ability to look inside colloidal crystals to observe the motion of defects and crystal melting in time and space and to reveal the origin of crystal twinning. Using this platform, the path to real-time analysis of ionic colloidal crystallization is now 'crystal clear'.

A particle-level discrete element model for simulating the performance of MRFs

The particle dynamics model of MRFs (MRFs) is based on the discrete element technique, which takes into account essential MRF variables such as magnetic field, particle parameters, particle volume fraction, carrier fluid properties, and other parameters. Firstly, to digitally characterize the microstructure of MRFs, the particle coordination number, as a new perspective is creatively proposed. The validity and predictability of the created model are then tested in conjunction with the rheological performance studies by comparing it to the known continuous medium model. Finally, based on the proposed model, the influence of each influencing factor on the magnetorheological effect is simulated and regularity analysis is given from the perspective of particles. Linking macroscopic qualities and MRF microstructure, which offers a theoretical basis for the preparation of MRFs with improved performance and prediction of performance under various working situations.

Pressure of Coulomb systems with volume-dependent long-range potentials

In this work, we consider the pressure of Coulomb systems, in which particles interact via a volume-dependent potential (in particular, the Ewald potential and its angular-averaged version (Demyanov and Levashov 2022 J. Phys. A: Math. Theor. 55 385202)). We confirm that the expression for the virial pressure should be corrected in this case. We show that the corrected virial pressure coincides with the formula obtained by differentiation of free energy if the potential energy is a homogeneous function of particle coordinates and a cell length. As a consequence, we find out that the expression for the pressure in the recent paper by Liang et al (2022 J. Chem. Phys. 157 144102) is incorrect.

Study on the motion characteristics of bedload sediment particles under different sediment transport intensities

AbstractBedload studies at the particle scale may help grasp the essence of the problem. Existing studies suffer from short filming durations, limited data volume, and a narrow range of sediment transport intensity variations. This paper employs the high‐speed photography technology and conducts experimental studies on bedload particle motion under 8 different sediment transport intensities. Using the latest image processing technology, over 6 million sediment particle coordinate points and nearly 400,000 particle motion trajectory curves were automatically obtained and used to compare the motion characteristics of bedload particles under different sediment transport intensities. The results show that under low sediment transport intensity, both the number of moving particles and particle motion velocity contribute to the bedload sediment transport rate, while under high‐intensity conditions, the transport rate mainly depends on the number of moving particles. The probability density distribution of sediment transport rate is concentrated and varies within a small range under low‐intensity conditions, exhibiting a tailing phenomenon. In contrast, under high‐intensity conditions, the range of sediment transport rate values increases, and the probability density curve tends to be symmetric, more closely approximating a normal distribution. Additionally, the paper compares the longitudinal and transverse motion velocities of particles and the coefficient of variation of the bedload sediment transport rate.

Distribution and movement of fine particles injected in a gas–solid fluidized bed with hydrocarbon liquid spray

In a gas–solid fluidized bed with hydrocarbon liquid spray, a liquid-affected zone (cloudy zone) and a gas–solid zone (non-cloudy zone) coexist. Fine particles with different diameters are injected and shuttle between the two zones to simulate the motion of growing catalyst particles in an industrial fluidized bed reactor. The movement and distribution patterns of the fine particles are investigated via high-speed image and infrared image approaches developed. The probability density based on the coordinates of fine particles reflects clearly the distribution characteristics of fine particles in the bed at different times. Fine particles with smaller diameters are more easily enriched locally during the injection and diffusion process. Moreover, the proportion of fine particles in the cloudy zone to the total fine particles increases with the diameter of fine particles.

A tri-variate moment projection method for multi-dimensional particle population balance dynamics

This study develops a tri-variate moment projection method (TVMPM) for solving particle dynamics problems governed by the population balance equations involving any three internal coordinates of particles, such as volume, surface area, component mass, etc. By leveraging the concept of conditional moments, the multi-dimensional moments are expressed as the product of marginal moments and several conditional moments, facilitating the solution of high-dimensional moments. To obtain abscissas and conditional weights in different dimensions for reconstructing moments, a three-dimensional (3-D) adaptive Blumstein-Wheeler algorithm is proposed and implemented, which can also improve the stability in the third dimension, where ill-conditioning issues are more likely to arise. More importantly, by fixing the smallest particle abscissas, TVMPM can directly track the weight of the smallest particles, thereby closing the shrinkage and fragmentation terms. An analysis of the sources of errors arising from this approach is also presented. To mitigate potential interference from external factors, constant kernels for inception, growth, coagulation, shrinkage and fragmentation are employed to validate the effectiveness of TVMPM. The resulting moments from TVMPM are computed for both individual and combined processes, and subsequently compared with the moments derived from the direct simulation algorithm (DSA). The results demonstrate that TVMPM maintains a high level of accuracy across various numbers of quadrature nodes for particle dynamics with 3-D internal coordinates, while significantly reducing computational efforts compared to DSA. This study reveals that the developed algorithms and framework are promising for further extending MPM to higher dimensions. Moreover, owing to its accuracy and efficiency, TVMPM shows great potential for implementation in computational fluid dynamics (CFD) for particle dynamics in realistic systems.

Integrated monitoring method of flood free surface and surface velocity in a laboratory compound channel

River flooding can pose a significant threat to people's lives and properties on the floodplain. Due to the difficulty and potential danger of monitoring field river floods, laboratory experiments have become the main and key method for exploring flood propagation and evaluating potential flood risks. However, the complex three-dimensional flow state of floods in the compound channel makes current measurement techniques inadequate for meeting monitoring requirements. To this end, a new technique is developed in this study that can simultaneously monitor the flood free surface and the surface velocity in the laboratory compound channel. The developed measurement technique combines stereoscopy and the particle tracking velocimetry (PTV) method through the pixel coordinate fitting method, so that the coordinates of the tracer particles can be reconstructed in the three-dimensional state. This method can not only increase the basic data in the free surface construction but can also capture the complex three-dimensional flood flow behavior. The proposed technology was applied to measure the free surface of flood propagation in a laboratory compound channel. Water level, flow velocity, wave velocity, and wave height were simultaneously measured. The measurement accuracy was verified using wave probes, spatial planes, and fringe projection techniques. The results indicate that the water level measurement error is approximately 1.6 mm, and the flow velocity measurement error is around 3 %. The developed measurement system is simpler than previous methods based on light reflection or absorption. Most importantly, it can simultaneously measure both the flood free surface and surface velocity by only sowing tracer particles on the water surface. The current measurement technology offers a new tool for studying flood propagation in a laboratory compound channel.

Quasi-classical theory of cyclotron resonance with accounting for dissipation

Based on the quasi-classical version of the canonical Caldirola–Kanai quantization, non-relativistic cyclotron resonance in a dissipative medium is studied. The corresponding particle propagator in the coordinate representation is found. It is shown that the combined effect of dissipation and a constant magnetic field reduces to the suppression of the quantum properties of a charged particle. In turn, a time-varying electric field that causes cyclotron resonance does not exhibit similar properties and does not affect the uncertainties of the particle coordinates.

Causes of the high friction angle of diatomaceous soil: microscale and nanoscale insights

Diatomaceous soil has geotechnical properties that differ fundamentally from those of common non-diatomaceous soils due to the presence of diatom microfossils with biological origins. Despite its dominant fines content, diatomaceous soil usually has high frictional shear resistance (approaching that of sand). Currently, the exact role of diatoms in controlling soil strength and underlying mechanisms remain obscure. Here, the frictional strength of diatomaceous soil is evaluated by way of angle of repose and direct simple shear tests on diatom–kaolin mixtures with differing diatom content. The microscale and nanoscale structures are characterised in detail using scanning electron and atomic force microscopy to establish how soil structure evolves with diatom content and shear. For the studied diatom–kaolin mixtures, the angle of repose and internal frictional angle are high and increase with diatom content, especially when the diatom content exceeds 20%. Diatom content controls the frictional strength through its intricate morphology (cylindrical, saucer and disc shapes), very rough surface (hundreds of times rougher than flaky minerals) and stiff frustules with high Young's modulus. These features increase the particle coordination number and produce interparticle interlockings, both of which prevent particle rearrangement during shear and improve the frictional strength. This paper provides new insights into the multiscale structure of diatoms and improves understanding of the shear strength of diatomaceous soils.

Structure of Argon Solid Phases Formed from the Liquid State at Different Isobaric Cooling Rates

By the method of molecular dynamics, computer simulation of the processes of isobaric cooling of argon particle systems under initial conditions with a temperature of 150 K at pressure values from 0.1 to 4 MPa to a temperature of 40 K with cooling rates of 108, 109, 1010, 1011 and 1012 K/s was performed. As a result of a computer experiment, coordinate arrays of particles were obtained, which were subjected to the procedure of three-dimensional Voronoi partitioning to identify and calculate the number of elementary cells of the crystal structure. Analysis of the structure of argon solid phases formed during isobaric cooling allowed us to deduce an estimated pattern between the concentration of FCC (face-centered cubic) cells in solid argon and the cooling rate from the liquid state. The evaluation of the orientation of the axes of translation of crystal cells in the array of particle coordinates made it possible to classify the solid phases formed as a result of cooling as single crystals, glassy media with the inclusion of clusters and single cells of FCC structures. It was revealed that during isobaric cooling at a rate not exceeding 108 K/s, argon completely crystallizes, at isobaric cooling rates of 109–1010 K/s, the union of elementary cells of the crystal structure into clusters is observed in glassy argon, and at rates of 1011 K/s and higher at pressures of 1 MPa and lower, solid vitreous phases of argon are formed in which no crystal structure cells are detected.

Structure Robustness of Highly Dispersed Pt/Al2O3 Catalyst for Propane Dehydrogenation during Oxychlorination Regeneration Process

The structure and performance stability of a Pt-based catalyst for propane dehydrogenation during its reaction–regeneration cycles is one of the key factors for its commercial application. A 0.3% Pt/Al2O3 catalyst with a sub-nanometric particle size was prepared and two different types of regeneration processes, long-term dichloroethane oxychlorination and a reaction–oxidation–oxychlorination cycle, were investigated on this catalyst. The fresh, sintered and regenerated catalyst was characterized by HAADF-STEM, CO-DRIFTS, XPS, CO chemisorption and N2 physisorption, and its catalytic performance for propane dehydrogenation was also tested. The results show that the catalysts tend to have a similar particle size, coordination environment and catalytic performance with the extension of the regeneration time or an increase in the number of cycles in the two regeneration processes, and a common steady state could be achieved on the catalysts. This indicates that structure of the catalyst tends to approach its equilibrium state in the regeneration process, during which the utilization efficiency of Pt is maximized by increasing the dispersion of Pt and its intrinsic activity, and the structural robustness is secured. The performance of the catalyst is comparable to that of a single-atom Pt/Al2O3 catalyst.

Демонстрационный эксперимент при изучении распределения Больцмана

We offer a technique and methodology for using a lecture experiment to measure the dependence of particle concentration on height. Steel balls in a vertical cell with glass walls play the role of particles participating in the chaotic movement, which is initiated by the vibrating bottom of the cuvette. Video recording of the cuvette with moving balls is carried out using a standard web camera. The developed real-time image processing program determines the vertical coordinates of particles, performs averaging over several frames, and plots graphs of the measured dependence of the average particle concentration on height and functions that approximate the experimental curves.

Fractional Laplacian Spinning Particle in External Electromagnetic Field

We construct a fractional Laplacian spinning particle model in an external electromagnetic field that generalizes a standard relativistic spinning particle model without anti-commuting spin variables. The one-dimensional fractional Laplacian in world-line variable λ governs the kinetic energy that is non-local in λ. The interaction between the particle’s charge and the electromagnetic four-potential is non-local in λ, while the interaction between the particle’s spin tensor and the electromagnetic field is standard. By applying the variational principle, we obtain the equations of motion for particle coordinates. We solve analytically the equations of motion in two particular cases: the constant electric and magnetic field. For more complex field configurations, the equations are, in general, non-local and non-linear. By making the assumption of a much weaker interaction term between the charge and four-potential compared with the interaction between spinning degrees of freedom and the electromagnetic field, we obtain approximate analytical solutions in the case of a quadratic electromagnetic potential.