Elliptical Particles Research Articles

Preparation of Porous Ellipsoidal Bismuth Oxyhalide Microspheres and Their Photocatalytic Performances.

Well-dispersed and uniform porous ellipsoidal-shaped bismuth oxyhalides (nominal composition: 80%BiOCl/20%BiOI) microspheres were obtained by a facile solvothermal method, in which process the use of polyvinylpyrrolidone (PVP) as template agent was found to be crucial. At 150 °C, elliptical porous particles with a particle size of 0.79 μm were formed. Instead of forming solid solutions, the study of X-ray diffraction (XRD) and high-resolution transmission electron microscopy (HRTEM) shows that the prepared 80%BiOCl/20%BiOI microspheres are composite of BiOCl and BiOI in nature and the obtained crystallite size is about 5.6 nm. The optical bandgap of 80%BiOCl/20%BiOI was measured to be 2.93 eV, which is between the bandgap values of BiOCl and BiOI. The 80%BiOCl/20%BiOI microspheres were able to decompose various organic dyes (rhodamine B-RhB, methyl orange-MO, methylene blue-MB, methyl violet-MV) under an illuminated condition with the degradation rate in the order of RhB > MB > MV > MO, and 98% of RhB can be degraded in 90 min. Radical scavenger tests showed that photogenerated holes are the main active species for the photocatalytic decomposition of all of the tested organic dyes. Our results show that the obtained porous ellipsoidal-shaped 80%BiOCl/20%BiOI microspheres are promising for the degradation of various organic pollutants under the illumination of visible light.

Study on mesoscopic numerical parameters in numerical tests of sand-pebble geology

To study the influence of the meso-mechanical parameters of sand-pebble on macro-mechanical properties, the numerical simulation method of discrete-element method and the sand-pebble numerical triaxial tests are used, a test method for elliptical particles is proposed and the sensitivity analysis of the meso-mechanical parameters of sand-pebble is carried out. The results show that the effective modulus of the particles has a significant effect on the macroscopic elastic modulus of the material, and the increase in the macroscopic elastic modulus of the material has an approximately linear relationship with the increase in the effective modulus. The effect of the particle stiffness ratio on the macro-mechanical properties of the material is insignificant. The increase in the friction coefficient is roughly linearly related to the increase in the peak stress. The increase in the interparticle porosity has a negative correlation with the decrease in the peak stress, and the particle diameter ratio affects both the number of particles produced and the peak stress. This paper provides a reference for the theoretical basis for subsequent research on the physical and mechanical characteristics of sand-pebble geology.

A numerical study on elliptical particle deposition with an immersed boundary-lattice Boltzmann method

This paper presents a numerical study on elliptic particle deposition in a Newtonian fluid at low Reynolds numbers. The effects of inflow condition, Reynolds number, aspect ratio, initial angle, and density ratio on the dynamic characteristics of the particle are investigated. The results show that the absolute deposition velocity of the particle increases with the decrease of Reynolds number for all flow conditions. Although there is a slight difference between the uniform and the Poiseuille flows, the absolute deposition and angular velocities of the particle are enhanced by the shear flow. Moreover, the deposition, horizontal and angular velocities exhibit a periodic fluctuation with the dependent frequency of the inflow conditions and the Reynolds numbers. The relationship between the time-averaged deposition velocity and the aspect ratio presents a closing quadratic curve. The initial angle of the particle only affects the phase difference of motion but not changes the dynamic characteristics of the particle. Furthermore, the time-averaged deposition velocity of the particle is proportional to the density ratio.

Full-Scale Simulation of the Fluid–Particle Interaction Under Magnetic Field Based on IIM–IBM–LBM Coupling Method

In this article, a full-scale computational model for fluid–particle interaction under a magnetic field is developed. In this model, the fluid field is solved by the lattice Boltzmann method, and the hydrodynamic force acting on the particle is computed by the immersed boundary method . The numerical solutions of the magnetic field in the fluid–solid domain are achieved by the immersed interface method with a finite difference scheme, in which the normal and tangential jump conditions of the magnetic field intensity are applied to modify the standard finite difference scheme. The magnetic stress tensor along the fluid–particle interface can be calculated accurately. Unlike the widely used point–dipole model, the magnetic force acting on the particle is determined by the stress integration method. Numerical simulation of several numerical tests are carried out to validate the proposed model. The numerical results demonstrate the validity of the present model. Moreover, the magnetoviscous effect is studied by simulating the motion of elliptical particles under the uniform magnetic field in shear flow.

Active control of particle position by boundary slip in inertial microfluidics

Inertial microfluidic is able to focus and separate particles in microchannels based on the characteristic geometry and intrinsic hydrodynamic effect. Yet, the vertical position of suspended particles in the microchannel cannot be manipulated in real time. In this study, we utilize the boundary slip effect to regulate the parabolic velocity distribution of fluid in the microchannel and present a scheme to active control the vertical position of particles in inertial microfluidics. The flow field of a microchannel with a unilateral slip boundary is equivalent to that of the microchannel widened by the relevant slip length, and the particle equilibrium positions in the two microchannels are consistent consequently. Then, we simulate the lateral migrations of three kinds of typical particles, namely circle, ellipse, and rectangle in the microchannel. Unlike the smooth trajectories of circular particles, the motions of the elliptical and rectangular particles are accompanied by regular fluctuations and non-uniform rotations due to their non-circular geometries. The results demonstrate that the unilateral slip boundary can effectively control the vertical equilibrium position of particles. Thus, the present scheme enables to active manipulate the particles positions in vertical direction and can promote more accurate focusing, separating, and transport in inertial microfluidics.

Experimental investigation and numerical simulation for chloride diffusivity of cement paste with elliptical cement particles

The shape of cement particle affects the hydration process of cement through its specific surface area and dispersion morphology, and then exerts great effects on the pore structure characteristic and the chloride ingression of cement paste, while it is generally simplified as the sphere in most of the vector models of cement hydration. To reveal the influence of cement particle shape on chloride diffusivity, a numerical method for quantitative analysis was proposed in this work. According to the size distribution curve and periodic distributions of cement particles, a representative fresh cement paste with elliptical inclusions was firstly constructed. According to the regulations of uniform increase of the thickness of hydration layer around the surface of quasi-ellipse and the interference effects induced by hydration layer overlapping, a vector-based model of cement hydration was established and the influence of aspect ratio of cement particles on the hydration degree was discussed. By considering the diffusion properties of the multi-phase composite cement paste, the first-passage theory suited to two-dimensional pixel model was proposed, and the corresponding Brownian motion algorithm was applied. Using high power microscope, the average aspect ratio of cement particles was calculated. By full comparison of eight groups of experimental results, the effectiveness of this estimation method was verified. At last, the influence of the aspect ratio of elliptical cement particles on chloride diffusivity was drawn.

Characteristics, relationships and precision of direct acoustic-to-seismic coupling measurements from local explosions

SUMMARY Acoustic energy originating from explosions, sonic booms, bolides and thunderclaps have been recorded on seismometers since the 1950s. Direct pressure loading from the passing acoustic wave has been modelled and consistently observed to produce ground deformations of the near surface that have retrograde elliptical particle motions. In the past decade, increased deployments of colocated seismometers and infrasound sensors have driven efforts to use the transfer function between direct acoustic-to-seismic coupling to infer near-surface material properties including seismic velocity structure and elastic moduli. In this study, we use a small aperture (≈600 m) array of broadband seismometers installed in different manners and depths in both granite and sedimentary overburden to understand the fundamental nature and repeatability of seismic excitation from 1 to 15 Hz using horizontally propagating acoustic waves generated by 97 local (2–10 km) explosions. In agreement with modelling, we find that the ground motions induced by acoustic-to-seismic coupling attenuate rapidly with depth. We confirm the modelled relation between acoustic and ground motion amplitudes, but show that within one acoustic wavelength, the uncertainty in the transfer coefficient between seismic and acoustic energy at a given seismic station increases linearly with separation distance between the seismic and acoustic sensor. We attribute this observation to the rapid decorrelation of the infrasonic wavefield across small spatial scales and recommend colocating seismic and infrasound sensors for use in studies seeking to invert for near-surface material properties. Additionally, contrary to acoustic-to-seismic coupling theory and prior observations, we find that seismometers emplaced in granite do not record retrograde elliptical particle motions in response to direct pressure loading. We rule out seismometer tilt effects as a likely source of this observations and suggest that existing models of acoustic-to-seismic excitation may be too simplistic for seismometers placed in high rigidity materials.

Elliptical particle suspensions in Couette flow

The roles of inertia (Re) and particle aspect ratio (Ar) on the rheology of elliptical particle suspensions are investigated. Scaling trends are found between the viscosity and the particle alignment for any Re considered here. Different mechanisms of stress are calculated. Besides the major contribution of stresslet, Reynolds stress contributes more as Ar and Re increase.

Extinguishing capability of novel ultra-fine dry chemical agents loaded with iron hydroxide oxide

This study aimed to develop high-efficiency fire extinguishing agents that is halogen-free and phosphorus-free, natural clinoptilolite (CP) was used as a carrier to adsorb iron, and iron-loaded functional clinoptilolite (ICP) was prepared. The structure and morphology of the samples were characterized by Fourier transform infrared spectrometer, X-ray diffractometer, X-ray photoelectron spectroscopy, and scanning electron microscopy. The results showed that a layer of FeOOH is attached to the surface of the functionalized ICP, forming elliptical particles with a length of 100–500 nm, and the iron content can reach 4.99%. The suppression experiment involving pool fires indicated that the fire extinguishing performance of ICP is better than CP and commercial ABC dry powders fire extinguishing agents. The average extinguishing time and usage of ICP were reduced by 41.4% and 40.1%, respectively, compared with ABC powders. The improvement of the fire-extinguishing performance of ICP was mainly since the loaded iron ions are converted into active iron atoms during high-temperature combustion and participate in the catalytic reaction of capturing combustion radicals.

Self-similarity of density and velocity profiles in a 2D hopper flow of elliptical particles: Discrete element simulation

Two-dimensional discharge flow of elliptical particles with different aspect ratios from a silo is investigated by using discrete element simulation. The measured flow rate of the particles is well fitted via Beverloo's law. The flow rate shows a monotonic decrease with increasing aspect ratio. The density and velocity profiles of particles at the outlet were systematically measured. At an identical outlet size, the speed of particles through the aperture decreases with increasing aspect ratio. The velocity profiles in all cases follow the same definite self-similar law and are in good agreement with the reported experimental results, thereby showing compatibility with the free fall arch postulation. The density profiles show obvious self-similar feature and can be fitted conveniently by using a fractional power law. Based on these observations and the results of the previous work, the flow rate for elliptical particles is calculated and is in agreement with the simulated results.

Inertial focusing and rotating characteristics of elliptical and rectangular particle pairs in channel flow

The lattice Boltzmann method is used to study the inertial focusing and rotating characteristics of two-dimensional elliptical particles and rectangular particles in channel flow. The results show that both elliptical particles and rectangular particles initially located on one side and two sides of channel centerline migrate first towards the equilibrium position. Then, the single-line particle train with an increasing spacing and the staggered particle train with stable spacing are formed. The axial spacing of the staggered particle pair increases with aspect ratio and Reynolds number increasing. The staggered elliptical or rectangular particle pairs form perpendicular orientation angles, which will be more obvious at larger aspect ratio and lower Reynolds number. The single-line particle trains with different shapes seldom form the perpendicular orientation angle.

Low-frequency ultrasound-assisted esterification of Bixa orellana L. seed starch with octenyl succinic anhydride

This study aimed to evaluate the impact of the ultrasound intensity (0, 5, 10, and 20 W/cm2) on the esterification of annatto (Bixa orellana L.) seed starch with octenyl succinic anhydride (OSA) employing a short processing time (5 min) to produce a novel emulsifier. OSA-esterified annatto seed starches were examined according to their degree of substitution (DS), amylose content, granule size distribution, microstructure, and X-ray diffractogram. Also, the performance of the OSA-modified annatto seed starch to stabilize colloidal systems was compared to commercial samples of OSA-modified starches. For this, annatto seed oil-in-water emulsions were produced and characterized according to their droplet size distribution, microstructure, and kinetic stability. Increasing ultrasound intensity from 5 W/cm2 to 20 W/cm2, DS values reached up to 0.139 ± 0.031. Likewise, these treatments yielded approximately 1.24–1.36 times more amylose content than the sample without ultrasound application. Most of the starch granules presented smooth surfaces without visible fissures. The higher ultrasound intensity hindered the aggregation of starch granules, thus forming well-defined elliptical particles. On the other hand, the increase of the ultrasound intensity did not change Brouckere mean diameter of the starch granules. No significant qualitative differences were seen in the X-ray diffractograms in terms of diffraction angle and peak intensity, indicating that the main functional characteristics of starches were not altered with ultrasound treatment. Furthermore, modified annatto starch was able to stabilize annatto seed oil-in-water emulsions. When compared to two commercial modified starches, OSA-esterified annatto starch produced a colloidal system with a larger Sauter mean diameter (14 ± 2 μm). However, the emulsion stabilized with modified annatto starch was more kinetically stable during the storage time in comparison to those stabilized with commercial starches.

Study on the edge defects of high volume fraction 70% SiCp/Al composites in ultrasonic-assisted milling

Directing at the hard machinability of high volume fraction 70% SiCp/Al composites, a longitudinal and torsional ultrasonic-assisted milling (LTUAM) method is proposed to improve the edge quality and machining efficiency. By observing the metallographic structure of the material, a three-dimensional (3D) finite element model of random distribution of spherical, elliptical and polygonal SiC particles is established and analyzed by ABAQUS simulation software. The formation mechanism of edge defects, stress distribution, defect characteristics and the effect of machining parameters on milling forces are investigated during ultrasonic-assisted milling. The results show that the edge defects appear at the inlet, outlet and middle edge position, especially is more serious at the outlet position. The SiC particles failure modes mainly include particle pullout, particle shearing, and crushing, moreover, the edge defects mainly include matrix tearing, edge breakage, burrs, bulges and pits. Ultrasonic-assisted milling (UAM) with a certain range of ultrasonic amplitude could effectively reduce the surface fragmentation rate and milling force, and it not only could slow down the expansion of cracks, but also increase the plastic flow of material, and obtain better edge quality compared with the traditional machining method. Comparing the results of finite element analysis and experimental tests, it shows that the simulation results are in good agreement with that of tests.

The effect of exposure to elevated temperatures on the microstructure and hardness of Mg–Ca–Zn alloy

Abstract The die cast Mg-5 wt.% Ca-6 wt.% Zn ternary alloy was exposed to 160 °C for different times of up to 40 days. Microstructural analysis and microhardness and hardness measurements of the samples after different exposure times enabled the thermal stability of the cast alloy to be monitored. The as-cast structure is composed mainly of α-Mg solid solution, elliptical grain boundary particles of CaMg2, and an intergranular eutectics of Mg and Ca2Mg6Zn3. The grain size of α-Mg and the structure of the alloy did not change during the treatment, but the amount of the intergranular phases increased slightly. Exposure to 160 °C resulted in a decrease in micro-hardness of the α-Mg grains, but no change in the overall hardness of the samples was observed. Microstructural analyses indicated diffusion of the solute elements from the α-Mg grains to the grain boundaries, resulting in a decrease in hardness of the α-Mg which is, however, compensated by an increase in hardness related to intergranular precipitates. Using a simple diffusion model, the diffusion coefficient of Ca atoms in Mg at 160 °C was estimated to be 2.1 · 10 –17 m2 s– 1, which is greater than that of Zn by two orders of magnitude.

Prediction of Failure Envelope of Calcified Aneurysmatic Tissue

The abdominal aortic aneurysm (AAA) may have a varying degree of calcification where calcium particles are found in different geometrical configurations. The impact of calcification on the failure of aneurysms is not very clear as literature shows contradictory results. This work is dedicated to investigating the impact of calcification on the failure strength of an aneurysmatic wall using micromechanical finite element simulations. A Representative Volume Elements (RVE) consisting of circular and elliptical particles are generated with different volume fractions, which is further extruded in the thickness direction. A two-fibre model is used for modeling anisotropic tissues. Calcium particles are assumed to be elastic. An anisotropic phase-field model is employed to model the failure in the tissue. A unique set of representative material parameters as well as phase-field parameters, like critical fracture energies for isotropic and anisotropic parts, are determined by fitting the model to experimental data, available in the literature. Finite element simulations are being performed on RVEs to generate a failure envelope of the calcified tissues under bi-axial loading conditions. This study will help in better understanding and better prediction of failure in aneurysms.

Dense packings of geodesic hard ellipses on a sphere.

Packing problems are abundant in nature and have been researched thoroughly both experimentally and in numerical models. In particular, packings of anisotropic, elliptical particles often emerge in models of liquid crystals, colloids, and granular and jammed matter. While most theoretical studies on anisotropic particles have thus far dealt with packings in Euclidean geometry, there are many experimental systems where anisotropically-shaped particles are confined to a curved surface, such as Pickering emulsions stabilized by ellipsoidal particles or protein adsorbates on lipid vesicles. Here, we study random close packing configurations in a two-dimensional model of spherical geodesic ellipses. We focus on the interplay between finite-size effects and curvature that is most prominent at smaller system sizes. We demonstrate that on a spherical surface, monodisperse ellipse packings are inherently disordered, with a non-monotonic dependence of both their packing fraction and the mean contact number on the ellipse aspect ratio, as has also been observed in packings of ellipsoids in both 2D and 3D flat space. We also point out some fundamental differences with previous Euclidean studies and discuss the effects of curvature on our results. Importantly, we show that the underlying spherical surface introduces frustration and results in disordered packing configurations even in systems of monodispersed particles, in contrast to the 2D Euclidean case of ellipse packing. This demonstrates that closed curved surfaces can be effective at introducing disorder in a system and could facilitate the study of monodispersed random packings.

Numerical study of the hydraulic tortuosity for fluid flow through elliptical particle packings

In this work, the hydraulic tortuosity (Th) specific for the binary-sized elliptical particle packings is studied using the Lattice Boltzmann method (LBM) and discrete element method (DEM). The model is validated by comparing with experimental and simulation data with an average deviation of 6% (Max 10%). Then the model is used to develop a reliable Th correlation to describe the fluid streamlines in elliptical particle packings. Firstly, a generalized Th correlation format is proposed, containing porosity (ε) and two empirical coefficients (a, b). Then the effects of ε and size ratio (r) on the Th are studied, and by curve-fitting the simulation results, the empirical coefficients (a, b) are formulated as a function of r. Meanwhile, the generalized Th correlation format is applicable for predicting the Th in porous media with different microstructures. The Th correlations provide a theoretical basis for macroscopic modelling of fluid flow through porous media of elliptical particles.

Further contributions to the dynamics of a freely rotating elliptical particle in shear flow

AbstractIn this study, the dynamic response of a neutrally buoyant elliptical cylinder is investigated for a two‐dimensional shear flow over a wide range of aspect ratios ( where, and are the major and minor axis radii, respectively). Parametric studies were carried out for confinement ratios () that vary the distance between the particle and the domain walls (H) for shear‐rate (G) based Reynolds number The simulations were performed using the signed distance field‐immersed boundary method (SDFIBM) algorithm implemented in OpenFOAM. The motion of the particle is limited to free rotation about the axis through the centroid without any translational freedom. This work demonstrates and affirms two distinct responses of the elliptical particle in shear flow: (1) a periodical rotating stage that exhibits a relaxation type of response and (2) a spontaneously locked stationary stage, where the net torque becomes zero. A critical Reynolds number () demarcates the transition between these two stages, and it depends on aspect ratio and confinement ratio. The prediction of was found to be in excellent agreement with the experimentally reported data in the literature, validating the SDFIBM for particles subjected to shear flows.

Machine‐learning‐enabled discrete element method: Contact detection and resolution of irregular‐shaped particles

AbstractThis paper presents a machine learning (ML)‐enabled discrete element method (DEM) for the computational mechanics of irregular‐shaped particles. ML‐enabled DEM, as with most conventional DEMs, encompasses four main steps in one typical calculation cycle, namely, (1) the detection and resolution of contacts, (2) the evaluation of contact behavior, (3) the calculation of particle motion, and (4) the updating of particle geometric descriptions. Unlike conventional DEMs, the proposed method constructs and employs neural networks to detect particle contacts and resolve contact geometric features. Neural networks take particle geometric descriptors as inputs and output the contact status and contact geometric features. Using two‐dimensional elliptical particles as an example, the performance of the ML‐enabled DEM is investigated through five numerical experiments and compared with analytical solutions or conventional DEM methods. A sixth numerical experiment involving irregular‐shaped particles is also presented to showcase the potential and applicability of the proposed method for other particle shapes. ML‐enabled DEM can accurately capture the trajectory and energy evolution of individual particles, the fabric characteristics of dense packing, and the mechanical behavior of packing under large loads, while demonstrating computational efficiency over conventional methods.

Orientational arrest in dense suspensions of elliptical particles under oscillatory shear flows

We study the rheological response of dense suspensions of elliptical particles, with an aspect ratio equal to 3, under oscillatory shear flows and imposed pressure by numerical simulations. Like for the isotropic particles, we find that the oscillatory shear flows respect the Cox-Merz rule at large oscillatory strains but differ at low strains, with a lower viscosity than the steady shear and higher shear jamming packing fractions. However, unlike the isotropic cases (i.e., discs and spheres), frictionless ellipses get dynamically arrested in their initial orientational configuration at small oscillatory strains. We illustrate this by starting at two different configurations with different nematic order parameters and the average orientation of the particles. Surprisingly, the overall orientation in the frictionless case is uncoupled to the rheological response close to jamming, and the rheology is only controlled by the average number of contacts and the oscillatory strain. Having larger oscillatory strains or adding friction does, however, help the system escape these orientational arrested states, which are evolving to a disordered state independent of the initial configuration at low strains and ordered ones at large strains.