Elliptical Particles Research Articles

DEM and dual-probability-Brownian motion scheme for thermal conductivity of multiphase granular materials with densely packed non-spherical particles and soft interphase networks

Shape-anisotropic granules and their surrounding interphase networks are significant constituents in granular materials. Structural and physical configurations of these constituents significantly affect the overall thermal performance of granular materials, specifically microstructure-dependent thermal conductive properties. It has been a key but unresolved issue how to quantitatively understand the microstructure evolution of conductive interphase interacted by densely packed non-spherical particles triggering the change of thermal conductivity of granular materials. In this work, we devise a powerful scheme by using the discrete element method (DEM) and the dual-probability-Brownian motion simulation (DP-BMS) to accurately and efficiently predict the effective thermal conductivity of granular materials composed of homogeneous matrix, conductive (soft) interphase around randomly-dispersed elliptical particles over a broad range of aspect ratios with widespread applications, such as cracks, pores, fibers, cellulose whiskers, silicate nanorods, and aggregates. Comparison against extensive numerical and theoretical data validates that such the scheme can well predict the effective thermal conductivity of multiphase granular materials with densely packed non-spherical particles that is just the intrinsic limitation of the classical micromechanical homogenization theories. In this scheme, the DEM provides a direct means of investigating the time-dependent microstructure evolution of granular materials with elliptical particles from a loose parking state to a dense packing state. The DP-BMS provides an effective technique for predicting the effective thermal conductive transport properties of multiphase granular materials. By comparing with traditional numerical strategies like the finite element method (FEM) and random walk model (RWM), the DP-BMS is more user-friendly and efficient to accurately predict the effective thermal conductivity. This scheme can be regarded as a general procedure that is readily applicable to predictions of other transport properties of two-dimensional or three-dimensional multiphase granular materials. Furthermore, we use the scheme to probe the influences of the shape and high packing density of particles and the thickness and fraction of soft interphase on the effective thermal conductivity of granular materials. The results elucidate rigorous component-structure–property relations, which can provide sound guidance for composite design and microstructure optimization.

Numerical simulation of elliptical particles sedimentation in power-law fluid using the improved smoothed profile-lattice Boltzmann method

Simulation of non-circular particles movement in the power-law fluid has not been considered in detail because of the challenges existing in the identification of particles. Accordingly, the present work has numerically considered the elliptical particles sedimentation in a two-dimensional box filled with the power-law fluid by using the improved smoothed profile-lattice Boltzmann method (iSPM-LBM). The SPM was applied to assign the fluid–solid interaction. Furthermore, the effects of orientation, density ratio and aspect ratio on the flow patterns during the sedimentation of the single ellipse were considered. The results showed that decreasing the power-law index and increasing the aspect ratio and also, density ratio caused the stability of the particles to disappear, such that they started oscillation. The oscillation in the shear-thinning fluid was more than that observed in others. In the next case, the dynamics of two identical ellipses was investigated in different initial inclinations. It was observed that the sedimentation of particles in the shear-thinning fluid happened more quickly in comparison to the other two ones. Also, the kissing phenomenon did not occur for all cases considered. The results of the present study were then compared with those obtained from the previously published works on the Newtonian fluid, showing a good agreement.

Rotation of an elliptical dielectric particle in the focus of a circularly polarized Gaussian beam

A force and a torque exerted on an elliptical dielectric particle in the focus of a spherical circularly polarized laser beam are considered. The numerical simulation is conducted using a diffraction field obtained by an FDTD method, with the force and torque derived using a Maxwell’s stress tensor. It is shown that an optical torque is exerted on the center of an elliptical particle put in the focus of a circularly polarized spherical wave, making it rotate around the optical axis. The rotation occurs when the elliptical microparticle is situated in a transverse plane to the optical axis. When shifting the ellipsoid from the optical axis, an optical trapping force appears that prevents its displacement, meaning that the particle finds itself in an optical trap on the optical axis.

Shaping photonic hook via well-controlled illumination of finite-size graded-index micro-ellipsoid

In this work, we present an investigation of the process of photonic hook generation using mesoscale finite-size graded-index elliptical particle under illumination of limited space. The combination of illuminating beamwidth and polarization allows efficient beam shaping and directionality control of photonic hook. The switching of photonic hook is achieved by changing the graded-index of the elliptical particle with index grading type parameter g. The finite-different time-domain simulations demonstrate that the long photonic hook could be obtained by low g, whereas the narrow photonic hook could be obtained by high g. Moreover, the bending direction of photonic hook could be controlled by the polarization state of incident beam. The adjustable graded-index and illumination of the elliptical particle open up a route for simple and versatile control of photonic hook generation.

An improved immersed moving boundary for hydrodynamic force calculation in lattice Boltzmann method

SummaryParticles suspension is considerably prevalent in petroleum industry and chemical engineering. The efficient and accurate simulation of such a process is always a challenge for both the traditional computational fluid dynamics and lattice Boltzmann method. Immersed moving boundary (IMB) method is promising to resolve this issue by introducing a particle‐fluid interaction term in the standard lattice Boltzmann equation, which allows for the smooth hydrodynamic force calculation even for a large grid size relative to the solid particle. Although the IMB method was proved good for stationary particles, the deviation of hydrodynamic force on moving particles exists. In this work, we reveal the physical origin of this problem first and figure out that the internal fluid effect on the hydrodynamic force calculation is not counted in the previous IMB. An improved immersed moving boundary method is therefore proposed by considering the internal fluid correction, which is easy to implement with the little extra computation cost. A 2D single elliptical particle and a 3D sphere sedimentation in Newtonian fluid is simulated directly for the validation of the corrected model by excellent agreements with the standard data.

Oscillation spectrum of ferroelectric inclusions in the ferroelectric-dielectric nanocomposite

The spectrum of oscillation of ferroelectric nanoparticles of different shapes was analyzed by the method of finding eigenvalues and eigenfunctions. The oscillation spectrum for elliptical particles obtained by an exact solution using numerical methods. The spectrum of eigenvalues of a particle of elliptic shape better coincides with the spectrum of a particle in the form of a parallelepiped of similar size. The obtained results provide a fundamental opportunity to construct the Green’s function and to evaluate the contribution of the ferroelectric component to the thermodynamic properties of the sample, to the dispersion of light and X-ray waves, etc.

Field monitoring of the ground vibrations adjacent to an onshore wind turbine foundation

Investigations of the soil–foundation interaction behaviour of wind turbine foundations and transfer of energy from the wind to the ground have not been reported in Canada. Indeed, very few vibration monitoring studies have been conducted globally around wind farms. It has been found that turbines predominantly produce vibrations related to structural resonances and blade-passing frequencies. Energy is found to be modified with distance and is dominated by surface waves. This paper describes a study of the effect of wind–structure interaction on the behaviour of a turbine foundation and the generation of ground-based vibrations around a working commercial wind turbine in Ontario. The field monitoring system and meteorological instrumentation are described in this paper and the responses of the structure and surrounding ground due to the fluctuating wind-field are discussed. The spectral analysis shows that the higher frequency vibrations attenuate more rapidly than the lower frequency vibrations. The tilted elliptical particle motions are found to be non-Gaussian because of the non-Gaussian wind conditions. The response attenuation with distance indicates that both geometric and material attenuation may dominate the vibration attenuation in the near field and only geometric attenuation occurs in the far field.

Sedimentation of general shaped particles using a multigrid fictitious boundary method

In this paper, a direct numerical simulation technique, the Finite Element Fictitious Boundary Method (FBM), is used to simulate fluid–solid two-phase flows of different general shaped particles. The momentum interactions between solid and fluid phases are handled by using the FBM. The continuity and momentum equations are solved on a fixed Eulerian grid that is independent of flow features by using a discrete projection scheme inside a multi-grid finite element approach. A detailed description is presented for the geometric representation and modeling of two-dimensional particles of different general shapes, i.e., circular, elliptical, square, rectangular, triangular, and pentagonal shapes inside the fluid. We discussed the effects of particle shapes and the influences on the settling behavior of the particles. A comparison of the settling trajectories of the particles of the same mass but with different shapes is presented. Moreover, depending upon the particle’s shape, some interesting facts are discovered, which have a great influence on the particles’ trajectory and settling velocity. Some very important correlations between the drag force coefficient and particle’s Reynolds numbers with different density ratios of particles are obtained. Furthermore, we also studied the settling behavior of elliptical and rectangular particles with different axis ratios and a boomerang particle with different concave angles. The authors of the article agree to the retraction of the article effective AUGUST 20, 2021.

Using multicomponent ambient seismic noise cross-correlations to identify higher mode Rayleigh waves and improve dispersion measurements

SUMMARYAmbient seismic noise cross-correlation with three-component sensors yields a nine-component empirical Green's tensor, in which four components of the radial–vertical plane contain Rayleigh waves. We exploit the retrograde elliptical nature of particle motion of the fundamental mode Rayleigh wave to correct the phase of the four radial–vertical components and stack them to obtain an average fundamental mode Rayleigh-wave time-series. This technique can suppress incoherent noise and wave packets that do not follow the targeted elliptical particle motion. The same technique can be used to isolate the first higher mode Rayleigh wave that follows prograde elliptical particle motion. We first demonstrate the effectiveness of the method on synthetic waveforms and then apply it on noise cross-correlations computed in Central California. Using this method, we isolate 1st higher mode Rayleigh waves on noise cross-correlations in the Great Valley, California, which provides new phase velocity constraints for estimating velocity structure in the sedimentary basin. We also obtain improved estimates of fundamental mode Rayleigh-wave dispersion for surface-wave tomography. The waveforms stacked assuming retrograde particle motion return at least ∼20 per cent more group velocity dispersion measurements satisfying a minimum signal-to-noise ratio (SNR) criterion than the individual components for periods ∼4–18 s. For equivalent group velocity measurements, SNR for the stacked estimate of the fundamental mode Rayleigh wave is on average 40 per cent greater than that measured on the individual components at periods less than 10 s. The technique also provides an easy way to detect large errors in sensor orientation.

Asymmetric Effective Medium Approximation for Describing the Optical Characteristics of Randomly Inhomogeneous Media with Discrete Inclusions.

The symmetric Bruggeman approximation, also known as the Effective Medium Approximation (EMA), is widely used in applications including the description of light scattering on inhomogeneous structures containing discrete inclusions. However, in the latter case, the natural asymmetry of the fillers topology, where discrete inclusions are mostly surrounded by the material of a simply connected matrix, is not taken into account. In this paper, two versions of asymmetric EMA are proposed for the case of a statistically isotropic medium containing discrete inclusions based on the difference in the structure of the fields inside and outside the inclusions. One of them does not differ too much from the usual EMA and leads to the same percolation threshold. For the second, the threshold value differs from the usual one even in the case of spherical particles. Expressions are given for the corresponding percolation thresholds in the model of randomly oriented elliptical particles. The proposed approximations are compared with the standard Maxwell Garnett and Bruggeman approximations for the case of silver particles in a dielectric matrix.

Preparation of Novel Mesoporous Silica Using a Self-Assembled Graphene Oxide Template

Novel mesoporous silicas rolled with silica sheets with 2D regular spacing were prepared using a self-assembled graphene oxide (GO) template formed by mixing GO with Pluronic123 (P123). Self-assembled GO templated mesoporous silicas (SGT-PMS) showed well-developed X-ray diffraction peaks with d-spacings of 9.8–10.8 nm depending on the amount of GO, indicating mesoporous structures. The specific surface areas increased from 603.8 to 861.2 m2g−1 on adding GO. The pore size distribution was in the range 5.1–5.8 nm and pore volume in the range 0.80–0.99 m3g−1. The SEM images of SGT-PMS showed irregular elliptical particles with various sizes. TEM images showed that the cross section of SGT-PMS particles comprises a roll of silica sheets with 2D regular spacing. The pore walls of SGT-PMS are firmer and thicker than those for PMS without GO as indicated by the corresponding intensities of Q3 and Q4 signals. These results were explained well by the self-assembled GO templating mechanism.

The rotation of two-dimensional elliptical porous particles in a simple shear flow with fluid inertia

The motion of porous particles in fluid flow is of fundamental importance in both natural and industrial processes. Recent work shows that fluid inertia can essentially alter the rotation of spherical porous particles in a simple shear flow. In this contribution, we examined the influence of fluid inertia on the rotation of elliptical porous particles in shear flow by solving the volume-averaged macroscopic equations with a two-dimensional lattice Boltzmann model. It is confirmed that the Darcy number Da has only a minor effect on the rotation of elliptical porous particles if fluid inertia is neglected. At finite fluid inertia, the elliptical porous particles, however, manifested time-periodic rotation with a non-uniform angular rate. For particles with small to intermediate Da, the period of rotation increases with Reynolds number Re up to a critical Rec above which the particle would stop rotating. It is shown that the maximum and minimum angular rates, as well as the inclination angle at which the particle has a minimum angular rate, are significantly affected by Da. A scaling law for the period of rotation initially proposed for solid impermeable particles can be extended to elliptical porous particles at finite fluid inertia. For a highly permeable ellipse, however, Rec has not been observed, and thus, the scaling law breaks down. We calculated the relative viscosity and intrinsic viscosity for simple shear flow containing elliptical porous particles. A formula developed for suspensions with vanishing Re can also be extended to correlate the intrinsic viscosity to Da at finite Re.

From scalar to polar active matter: Connecting simulations with mean-field theory.

We study numerically the phase behavior of self-propelled elliptical particles interacting through the "hard" repulsive Gay-Berne potential at infinite Péclet number. Changing a single parameter, the aspect ratio, allows us to continuously go from discoid active Brownian particles to elongated polar rods. Discoids show phase separation, which changes to a cluster state of polar domains, which then form polar bands as the aspect ratio is increased. From the simulations, we identify and extract the two effective parameters entering the mean-field description: the force imbalance coefficient and the effective coupling to the local polarization. These two coefficients are sufficient to obtain a complete and consistent picture, unifying the paradigms of scalar and polar active matter.

Orientational order in dense suspensions of elliptical particles in the non-Stokesian regime.

Suspensions of neutrally buoyant elliptic particles are modeled in 2D using fully resolved simulations that provide two-way interaction between the particle and the fluid medium. Forces due to particle collisions are represented by a diffuse interface approach that allows the investigation of dense suspensions (up to 47% packing fraction). We focus on the role inertial forces play at low and high particle Reynolds numbers termed low Reynolds number and inertial regimes, respectively. The suspensions are characterized by the orientation distribution function (ODF) that reflects shear induced rotation of the particles at low Reynolds numbers, and nearly stationary (swaying) particles at high Reynolds numbers. In both cases, orientational ordering differs qualitatively from the behavior observed in the Stokesian-regime. The ODF becomes flatter with increasing packing fraction, as opposed to the sharpening previous work predicted in the Stokesian regime. The ODF at low particle concentrations differs significantly for the low Reynolds number and inertial regimes, whereas with increasing packing fraction convergence is observed. For dense suspensions, the particle-particle interactions dominate the particle motion.

Numerical Study of Paramagnetic Elliptical Microparticles in Curved Channels and Uniform Magnetic Fields.

We numerically investigated the dynamics of a paramagnetic elliptical particle immersed in a low Reynolds number Poiseuille flow in a curved channel and under a uniform magnetic field by direct numerical simulation. A finite element method, based on an arbitrary Lagrangian-Eulerian approach, analyzed how the channel geometry, the strength and direction of the magnetic field, and the particle shape affected the rotation and radial migration of the particle. The net radial migration of the particle was analyzed after executing a rotation and at the exit of the curved channel with and without a magnetic field. In the absence of a magnetic field, the rotation is symmetric, but the particle-wall distance remains the same. When a magnetic field is applied, the rotation of symmetry is broken, and the particle-wall distance increases as the magnetic field strength increases. The causation of the radial migration is due to the magnetic angular velocity caused by the magnetic torque that constantly changes directions during particle transportation. This research provides a method of magnetically manipulating non-spherical particles on lab-on-a-chip devices for industrial and biological applications.

Anisotropic Hollow Microgels That Can Adapt Their Size, Shape, and Softness.

The development of soft anisotropic building blocks is of great interest for various applications in soft matter. Furthermore, such systems would be important model systems for ordering phenomena in fundamental soft matter science. In this work, we address the challenge of creating hollow and anisotropically shaped thermoresponsive microgels, polymeric networks with a solvent filled cavity in their center that are swollen in a good solvent. Sacrificial elliptical hematite silica particles were utilized as a template for the synthesis of a cross-linked N-isopropylacrylamide (NIPAm) shell. By varying the amount of NIPAm, two anisotropic microgels were synthesized with either a thin or thick microgel shell. We characterized these precursor core-shell and the resulting hollow microgels using a combination of light, X-ray, and neutron scattering. New form factor models, accounting for the cavity, the polymer distribution and the anisotropy, have been developed for fitting the scattering data. With such models, we demonstrated the existence of the cavity and simultaneously the anisotropic character of the microgels. Furthermore, we show that the thickness of the shell has a major influence on the shape and the cavity dimension of the microgel after etching of the sacrificial core. Finally, the effect of temperature is investigated, showing that changes in size, softness, and aspect ratio are triggered by temperature.

Simulating anisotropic flows with isotropic lattice models via coordinate and velocity transformation

We propose a rectangular lattice Boltzmann model for anisotropic flows based on coordinate and velocity transformation. Unlike other existing rectangular models which tuned the lattice Boltzmann algorithm to fit the rectangular or cuboid lattice grids, here we apply the general lattice Boltzmann method to solve the transformed system over regular square lattice grids. The method is tested with simulations of representative anisotropic flows, including flows in narrow straight and wavy channels, the Taylor–Green vortex flow, and the flow through an elliptical particle array. These simulations show that in general our method produces satisfactory results; however, the aspect ratio [Formula: see text] is limited to relatively large values ([Formula: see text]). The effects of [Formula: see text] on simulation accuracy and stability have been carefully examined, and a possible remedy to improve these concerns has been proposed. The method and analysis could be useful for future development of more robust and practical anisotropic lattice Boltzmann models for realistic simulations.

Blue-light excitable La2Ce2O7:Eu3+ red phosphors for white light-emitting diodes

Inorganic phosphors which can be effectively excited with blue-light are highly desirable for white light-emitting diodes (WLEDs). Herein, Eu3+-activated La2Ce2O7 phosphors are prepared by a self-rising reaction using urea and glycine as leavening agents under hydrothermal conditions. The phosphors display a well-distributed round or elliptical particle shapes with an average diameter of about 55 ± 10 nm. The excitation spectrum is dominated by the 7F0→5D2 transition (∼465 nm) that overlaps the emission of efficient blue emitting LEDs, rendering these phosphors as very attractive as blue down converters. The luminescence performance can be effectively improved by optimizing the molar ratios of leavening agents and the content of Eu3+ concentration and, thus, the absolute quantum yield can reach 0.229 ± 0.023. By combining a commercial blue emitting LED chip (InGaN, 465 nm) and the phosphors, intriguing efficient pure red emission is achieved with International Commission on Illumination (CIE) color coordinates of (0.669,0.330). This pure red emission is used to tune the well-known poor correlated color temperature values of WLEDs based on YAG:Ce3+. WLEDs are fabricated by coating LED chips emitting in the blue with blends of YAG:Ce3+ and Eu3+-activated La2Ce2O7, yielding prototypes with enhanced color rendering index that is easily adjusted from 7119 to 3242 K, demonstrating that this strategy may use to complement the red component in WLEDs.

Development and Research of Flux-Cored Electrodes For Welding And Surfacing Of Parts From Aluminum And Titanium Alloys

Perpose of research was to study the properties of powder materials obtained from aluminum and titanium waste by the method of electroerosion dispersion for the development of electrodes suitable for welding and surfacing of parts from aluminum and titanium alloys. Methods . To obtain an aluminum powder material by electroerosion dispersion method, an aluminum wire GOST 14838-78 was used, pre-cut to 5-7 cm. the Wire was loaded into a reactor filled with a working liquid – distilled. The process was carried out at the following electrical parameters: discharge capacitor capacity 65 UF, voltage 100 V, pulse frequency 100 Hz. To obtain a titanium powder material by electroerosion dispersion method, shavings of VT6 grade were used. The chips were loaded into a reactor filled with a working liquid – distilled water. The process is carried out at the following electrical parameters: capacity of the bit capacitors 65 µf, a voltage of 150 V, pulse frequency of 250 Hz. The result of the local effects of intermittent electrical discharges between the electrodes was the destruction of the material with the formation of dispersed particles of powder. In order to study the shape and morphology of powder material particles obtained by electroerosion dispersion from aluminum waste, images were taken on a raster (scanning) electron microscope QUANTA 600 FEG. The study of granulometric composition of powder materials obtained by the method of electroerosion dispersion of aluminum and titanium waste was carried out on a laser analyzer particle size Analysette 22 NanoTec. Results. It is established that the most promising and not industrially used materials for the production of electrodes used in welding and surfacing of parts are powder materials obtained by electroerosion dispersion. It is experimentally established that the powder materials obtained by electroerosive dispersion of aluminum and titanium wastes consist of spherical and elliptical particles. The results of the study of the elemental composition of powder materials obtained by electroerosive dispersion of aluminum and titanium waste, it is shown that the main elements of the powders produced and aluminum waste are aluminum and oxygen, and the main elements of the powders produced and shavings of the VT6 BRAND are Ti, Al, O, V, Fe, W and K. Studies of the particle size distribution of powder materials obtained by electroerosion dispersion showed that the average particle size of powders obtained from aluminum waste is 19.08 microns, and the average particle size of powders obtained from titanium waste is 33.12 microns. It is established that the most promising method for the production of electrodes used for welding and surfacing of parts from aluminum and titanium alloys is the method of spark plasma sintering. Conclusion . The obtained results can be used to create resource-saving processes for processing metal alloys and composite materials.

Dynamics of a pair of ellipsoidal microparticles under a uniform magnetic field

Under a uniform magnetic field, magnetic particles tend to form chains, clusters or columns due to particle–particle interactions. Non-spherical magnetic particles dispersed in a liquid medium show different rheological properties. However, there is a lack of knowledge about the fundamental mechanism of particle–particle interactions of non-spherical particles under a uniform magnetic field. In this work, we numerically investigate the particle–particle interactions and relative motions of a pair of paramagnetic elliptical particles by using direct numerical simulations to create two-dimensional models that resolve the magnetic and flow fields around the finite-sized particles. The modeling is based on the finite element method and arbitrary Lagrangian–Eulerian approach with full consideration of particle–fluid–magnetic field interaction. The effects of initial position and aspect ratio of the particles are investigated. The results show that the particles spend much more time under global reorientation than local magneto-orientation. Larger initial relative angles and distances, and larger aspect ratios, tend to require more time to form a stable chain. The particle–particle interactions and relative motion of a pair of elliptical particles in this study provide insights into the particle alignment and chaining processes under uniform magnetic fields, which are closely related to the response of magneto-rheological fluids to magnetic fields.