Particle Displacement Research Articles

Thermal contraction coordination behavior between unbound aggregate layer and asphalt mixture overlay based on the finite difference and discrete element coupling method

AbstractThe constraint action of the unbound aggregate layer underneath plays an important role in affecting the temperature strains in the top asphalt layer. The focus of the present paper is to investigate the interactive thermal contraction mechanisms between the asphalt mixture and granular base layers to offer a new perspective in promoting the understanding of the thermal cracking disease. In this paper, both experiments and simulations were conducted for the thermal contraction tests. A novel numerical modeling of virtual composite structures was proposed using wall‐zone coupling operation based on the finite difference and discrete element coupling method. The experimental composite structures containing three types of asphalt mixture overlays and five types of unbound aggregate base layers were developed for verification. The thermal contraction and restraint mechanism were revealed from both macro and microscopic scales. The proposed numerical modeling shows a 94% high accuracy. The particle displacement vector and contact force chain could explain the thermal contraction behavior of composite structures. Smaller particle motion displacement or stronger contact force chain result in a higher restraint strain of the asphalt overlay. The thermal contraction behavior can be coordinated through the compaction and loosening of unbound aggregates. The material parameters and cooling temperature differences in the asphalt overlay have slight effects on the constraint action of a base layer, while the gradation and mechanical parameters of the unbound aggregate layer show significant impaction. The parameters, cohesion C and friction angle φ, show a quadratic function with the restraint coefficient. This work has significant guidance on the selection of pavement structure and materials to improve the thermal cracking problem and lay the basis for the mechanical theoretical calculation to predict thermal cracking.

Flame suppression due to acoustic streaming by using time reversal

Using high amplitude time reversal focusing to extinguish small flames is a novel demonstration of transient acoustic streaming. Typically, others have placed a low frequency acoustic source near the flame in order to generate a high enough particle displacement to extinguish it. In this study, we move the sources far from the flame and demonstrate that the time reversal method can focus transient waves to the flame. The peak acoustic overpressure level needed to extinguish a candle flame in free space is 191 dB peak when using a frequency range of 300 to 15000 Hz. This momentary focus causes acoustic streaming at the flame location after the focusing, which extinguishes the flame. By tracking the flame in high-speed video, we show the displacement of the flame due to the passing acoustic wave and subsequently due to the acoustic streaming. We further show that acoustic streaming extinguishes the flame, not the acoustic particle displacement.

Modeling of anomalous thermal conduction in thermoelectric magnetohydrodynamics: Couette formulation with a multiphase pressure gradient

A metal/liquid-metal junction is a practical thermoelectric cell causing heat absorption or release according to the direction of electric current and temperature gradient. During thermoelectric processes, the possibility of activating the anomalous heat transfer is considered in this work based on adopting a fractional version of Jeffreys equation with three fractional parameters. Because of the connection between the mean-squared displacement of diffusive hot particles and the thermal conductivity, the fractional Jeffreys law is employed to simulate the low thermal conductivity with crossovers; accelerated or retarded transition, and the transition from high (superconductivity—above the Fourier heat conduction) to low (subconductivity—below the Fourier heat conduction) thermal conductivity. The Couette formulation describing a pressure-driven flow of a viscous thick liquid-metal layer bounded by two similar metallic plates, in the presence of a constant transverse magnetic field, is investigated. A triple-phase pressure gradient, consisting of the phases: (i) ramp-up, (ii) dwell, and (iii) exponential decay, is applied as a real-life flow cause and compared with the classical constant pressure gradient and the impulsive pressure gradient case. The velocity and temperature are obtained in the Laplace domain, and then a suitable numerical technique based on the Fourier series approximation is used to recover the solutions in the real domain. It is found that the retarded crossover of low thermal conduction shows “ultraslow” temperature propagation within the thick layer, which indicates to a case of ultralow heat conduction. As well as the strong correlation between the pressure gradient type (constant, impulsive, or three-phase) and direction (favorable or adverse) and its induced velocity, the temperature gradient between the two plates plays a key role in the determination of the velocity direction and magnitude.

Acoustic streaming in the Cochlea resulting from periodic excitation

This paper presents a model describing acoustic streaming in the scala vestibuli and the scala tympani of the cochlea. The magnitude and spatial features of the acoustic streaming are a function of the vibration of the cochlear partition. Hence, spatial adjustment of the acoustic streaming field can be accomplished by suitable harmonic adjustment of the excitation. It is shown that the dynamic behavior of the fluid is a function of the values of two nondimensional parameters S and R. The Strouhal number S is the ratio of the typical length to the oscillatory particle displacement and the oscillatory Reynolds number R is the ratio of typical length to the oscillatory boundary layer thickness. The method of matched asymptotic expansions is used to obtain a solution that is valid in the limit as 1/S tends to zero. The solution is shown for the slow streaming R/S = O(1) and moderate streaming R/S2 = O(1) cases.

Shear Resistance Evolution of Geogrid-Aggregate Interfaces under Direct Shear: Insights from 3D DEM Simulations

This paper presents a mesoscopic evaluation of the shear resistance evolution of geogrid-aggregate interfaces subjected to direct shear loading. A three-dimensional discrete element method (DEM) model was developed based on experimental data. The tensile response of geogrid were simulated through a series of calibration tests. Aggregate with complex particle shapes were simulated to accurately capture the interlocking effect among aggregates based on the real particle surface. The individual shear resistance components were quantified based on particle displacement field and contact distribution characteristics. The influences of aperture-aggregate size ratio and geogrid stiffness on the shear resistance components are discussed. The results indicate that the peak value of shear resistance component follows a descending order from frictional resistance of aggregate, to passive resistance of transverse rib, and to geogrid-aggregate interface frictional resistance. During the shear process, the frictional resistance of aggregate becomes active first, followed by the geogrid-aggregate interface frictional resistance, and then the development of passive resistance of transverse ribs starts with a certain lag. Optimizing the geogrid-aggregate size ratio and utilizing geogrids with higher rib stiffness could enhance the passive resistance of transverse ribs but would not significantly affect the geogrid-aggregate interface frictional resistance and frictional resistance of aggregate.

A numerical investigation on the effect of rotation on the cone penetration test

The cone penetration test (CPT) is one of the most popular in situ soil characterization tools. However, the test is often difficult to conduct in soils with high penetration resistance. To resolve the problem, a rotary CPT device has recently been adopted in practice by rotating the rod to increase the penetrability, particularly in deep dense sand. This study investigates the underlying mechanism of the rotation effects from a micromechanical perspective using models based on the discrete element method. With rotation, the cone penetration resistance ( qc) decreases by up to 50%, while the cone torque resistance ( tc) increases gradually. These results are also used to successfully assess existing theoretical solutions. The mechanical work required during penetration is observed to keep rising as the rotational velocity increases. Microscopic variables including particle displacement and velocity field show that rotation reduces the volume of disturbed soil during penetration and drives particles to rotate horizontally, while contact force chain and contact fabric indicate that rotation increases the number of radial and tangential contacts and the corresponding contact forces, forming a lateral stable structure around the shaft, which can reduce the force transmitted to the particles below the cone, thus decreasing the vertical penetration resistance.

Non-Gaussian Displacements in Active Transport on a Carpet of Motile Cells.

We study the dynamics of micron-sized particles on a layer of motile cells. This cell carpet acts as an active bath that propels passive tracer particles via direct mechanical contact. The resulting nonequilibrium transport shows a crossover from superdiffusive to normal-diffusive dynamics. The particle displacement distribution is distinctly non-Gaussian even at macroscopic timescales exceeding the measurement time. We obtain the distribution of diffusion coefficients from the experimental data and introduce a model for the displacement distribution that matches the experimentally observed non-Gaussian statistics. We argue why similar transport properties are expected for many composite active matter systems.

Improved detection of particle displacement in optical traps using back focal plane interferometry and image processing

Optical tweezers play a crucial role in particle manipulation and force measurement. Therefore, it is essential to calibrate the force measurement parameters, such as the optical trap stiffness and the conversion factor of the sensor deflection signal to the actual displacement of the trapped particle. This calibration is necessary to achieve accurate and efficient parameter calibration. In this study, we employed a suitable image processing method, based on a low-frequency CMOS camera, to calibrate the Displacement Conversion Factor (DCF) of the optical tweezers system. The high accuracy of this image processing method makes it ideal for analyzing the actual displacement of optically trapped microspheres. Interestingly, we discovered that the normalized deflection signal captured by the quadrant photodiode (QPD) through back focal plane interferometry is primarily correlated with the axial height of the trapped microspheres, and is relatively unaffected by laser power variations. Building on this finding, we also examined the linear detection range of the trapped microspheres at different heights. These results address certain limitations associated with the use of optical tweezer systems and provide valuable guidance for utilizing this tool effectively.

Variability in the displacement of solute particles in heterogeneous confined aquifers

In this work, the variability of regional-scale transport of inert solutes in heterogeneous confined aquifers of variable thickness is quantified by the variance of the displacement of a solute particle. In the traditional stochastic approach to solute transport at the regional scale, the variability of solute displacement is attributed to the variability of the transmissivity fields. In this work, however, variability in solute displacement is attributed to variability in hydraulic conductivity and aquifer thickness fields. A general stochastic methodology for deriving the variance of the displacement of a solute particle based on the convection velocity of solute particles, developed from the relationship between the two-dimensional depth-averaged solute mass conservation equation and the Fokker-Planck equation, is given. Assuming that the fluctuations in log hydraulic conductivity and log thickness of the confined aquifer are second-order stationary processes, a closed-form expression for the solute displacement variance in the mean flow direction is obtained for the case of advection-dominated solute transport. The results show that variation in hydraulic conductivity and aquifer thickness can lead to nonstationarity in the covariance of flow velocity, making longitudinal macrodispersion anomalous and increasing linearly with travel time at large distances.

Diffusion in multicomponent granular mixtures.

We investigate diffusion in polydisperse granular media. We derive the mean-squared displacement of granular particles in a polydisperse granular gas in a homogeneous cooling state, containing an arbitrary amount of species of different sizes and masses. We investigate both models of constant and time-dependent restitution coefficients and obtain a universal law for the size dependence of the mean-squared displacement for steep size distributions.

Development of calculation model for designing temperature characteristics of double-layered thickness-shear resonator

A calculation model for predicting the temperature characteristics of the double-layered resonator (DRL) was developed by using the total strain ratio including the influence of the waves reflected at the bonding boundary. The validity of the model proposed was examined from the comparison between the measured and calculated results for a DRL specimen consisting of 129.55°Y- and 0°Y-quartz substrates. The calculation results of the model proposed demonstrated that it is possible to predict the trends of changes in experimental values of temperature characteristics not only in the 1st-order mode but also in the higher-order modes. In addition, the changes in the particle displacement distribution and temperature characteristics of the DLR obtained by the model proposed were also in good agreement with the results of finite element method analysis. The proposed model is expected to greatly contribute to the design of DLRs with high excitation efficiency and excellent temperature characteristics.

Investigation of renal calculi fragmented tracer particles in lithotripsy model by laser speckle technique

We have developed a laser sheet method to evaluate micro-sized fragmented calcium oxalate granular particles created kidney stones suspended in a Newtonian fluid in an in vitro model. These tracer particles are examined by laser optical techniques. An optical setup is configured with a laser sheet to conduct image velocimetry on these calcium oxalate seed particles in the urine environment. The experimental setup involves the application of ultrasonic waves to fragment the calcium oxalate tiny stones of varying sizes and disperse them in random directions in the fluid. The data acquisition process employs double frame-single exposure imaging, which captures images at specified time intervals using a high-resolution CCD camera. This provides information regarding particle displacement and track the flow path within the Newtonian fluid. In addition, the bigger fragmented particles are identified, and their sizes are also measured.

The solid-fluid transmission problem

We study microlocally the transmission problem at the interface between an isotropic linear elastic solid and a linear inviscid fluid. We set up a system of evolution equations describing the particle displacement and velocity in the solid, and pressure and velocity in the fluid, coupled by suitable transmission conditions at the interface. We show well-posedness for the coupled system and study the problem microlocally, constructing a parametrix for it using geometric optics. This construction describes the reflected and transmitted waves, including mode converted ones, related to incoming waves from either side. We also study formation of surface Scholte waves. Finally, we prove that under suitable assumptions, we can recover the s- and the p-speeds, as well as the speed of the liquid, from boundary measurements.

Modelling and simulation study on dynamic pollution accumulation process of composite insulator

AbstractWith the widespread application of composite insulators in transmission lines, exploring the accumulation mechanism of pollution particles on composite insulator surfaces is of importance to ensure the safe and steady operation of the power system. Addressing the current theoretical shortcomings, this study categorises the accumulation process of particles on the insulator surface into three stages, namely ‘spatial motion’, ‘surface collision’, and ‘surface motion’. The motion and rotation velocities in a multi‐physics field are calculated in the spatial motion stage. In the surface collision stage, a parameter called ‘neck height’ is introduced to determine the optimum mechanics theory, and the normal deposition criterion is established. For the surface motion stage, the sliding displacement and rolling displacement on the surface are calculated based on the rotation speed of the particles. A dynamic pollution accumulation model of the composite insulator is established based on the normal deposition criterion and tangential displacement. Finally, numerical simulations are performed by using the finite element method. Simulation results show that the proposed model agrees with the actual insulator pollution accumulation, and the deposition model is still applicable for various types of composite insulators operating in different applied voltages. The deposition probability of particles increases with the increasing particle size. In the surface motion stage, particle displacement increases with particle size and wind velocity.

Active Regulation of Elastic Waves in a Type of Two-Dimensional Periodic Structures With Piezoelectric Springs

Abstract Wave propagations exhibit direction and frequency selectivity in two-dimensional (2D) periodic structures, which provides possibilities to regulate wave dispersion and bandgap properties. Most of current researches focus on regulations of 1D waves, and there are few works about active regulations of 2D waves, especially in the structures with strong nonlinearities that have remarkable influences on dispersions. In this work, two types of 2D periodic nonlinear lattice structures with piezoelectric springs, which include a monatomic and a diatomic structure, are designed to implement controllable dispersion and propagation direction of 2D waves. Considering the strong nonlinearities caused by the cubic spring, dynamic models of the wave propagations in the two kinds of periodic structures are established, and an improved incremental harmonic balance (IHB) method is developed to implement efficient and accurate calculations of the 2D wave propagation. Influences of active and structural parameters on dispersion and bandgap properties are comprehensively studied, and the regulation ability of the piezoelectric springs is demonstrated where the proportional voltage constant is the active control parameter with particle displacements as the feedback. Results also show that a piezoelectric modulated bandgap and a critical wave vector region are created by positive and negative proportional constants, respectively, which indicate that the structures can be used to filter a wide range of low-frequency long-wavelength noises and waves at particular directions. The properties predicted by the improved IHB method are verified by numerical experiments.

Exploring Controlled Passive Particle Motion Driven by Point Vortices on a Sphere

This work focuses on optimizing the displacement of a passive particle interacting with vortices located on the surface of a sphere. The goal is to minimize the energy expended during the displacement within a fixed time. The modeling of particle dynamics, whether in Cartesian or spherical coordinates, gives rise to alternative formulations of the identical problem. Thanks to these two versions of the same problem, we can assert that the algorithm, employed to transform the optimal control problem into an optimization problem, is effective, as evidenced by the obtained controls. The numerical resolution of these formulations through a direct approach consistently produces optimal solutions, regardless of the selected coordinate system.

Water-Wave Vortices and Skyrmions.

Topological wave structures-phase vortices, skyrmions, merons, etc.-are attracting enormous attention in a variety of quantum and classical wave fields. Surprisingly, these structures have never been properly explored in the most obvious example of classical waves: water-surface (gravity-capillary) waves. Here, we fill this gap and describe (i)water-wave vortices of different orders carrying quantized angular momentum with orbital and spin contributions, (ii)skyrmion lattices formed by the instantaneous displacements of the water-surface particles in wave interference, and (iii)meron (half-skyrmion) lattices formed by the spin-density vectors, as well as (iv)spatiotemporal water-wave vortices and skyrmions. We show that all these topological entities can be readily generated in linear water-wave interference experiments. Our findings can find applications in microfluidics and show that water waves can be employed as an attainable playground for emulating universal topological wave phenomena.

Brownian Particle in a Poisson‐Shot‐Noise Active Bath: Exact Statistics, Effective Temperature, and Inference

AbstractThe dynamics of an overdamped Brownian particle in a thermal bath that contains a dilute solution of active particles is studied. The particle moves in a harmonic potential and experiences Poisson shot‐noise kicks with specified amplitude distribution due to moving active particles in the bath. From the Fokker–Planck equation for the particle dynamics, the stationary solution for the displacement distribution is derived along with the moments characterizing mean, variance, skewness, and kurtosis, as well as finite‐time first and second moments. An effective temperature is also computed through the fluctuation–dissipation theorem and show that equipartition theorem holds for all zero‐mean kick distributions, including those leading to non‐Gaussian stationary statistics. For the case of Gaussian‐distributed active kicks, a re‐entrant behavior from non‐Gaussian to Gaussian stationary states and a heavy‐tailed leptokurtic distribution across a wide range of parameters are found as seen in recent experimental studies. Further analysis reveals statistical signatures of the irreversible dynamics of the particle displacement in terms of the time asymmetry of cross‐correlation functions. Fruits of the work is the development of an compact inference scheme that may allow experimentalists to extract the rate and moments of underlying shot‐noise solely from the statistics the particle position.

Towards an enhanced understanding of the particle size effect on conversion/alloying lithium-ion anodes

Conversion/alloying materials (CAMs) represent a potential alternative to graphite as a Li-ion anode active material, especially for high-power applications. So far, however, essentially all studies on CAMs have been dealing with nano-sized particles, leaving the question of how the performance (and the de-/lithiation mechanism in general) is affected by the particle size. Herein, we comparatively investigate four different samples of Zn0.9Co0.1O with a particle size ranging from about 30 nm to a few micrometers. The results show that electrodes made of larger particles are more susceptible to fading due to particle displacement and particle cracking. The results also show that the conversion-type reaction in particular is affected by an increasing particle size, becoming less reversible due to the formation of relatively large transition metal (TM) and alloying metal nanograins upon lithiation, thus hindering an efficient electron transport within the initial particle, while the alloying contribution remains essentially unaffected. The generality of these findings is confirmed by also investigating Sn0.9Fe0.1O2 as a second CAM with a substantially greater contribution of the alloying reaction and employing Fe instead of Co as a TM dopant.

The distinguishable-particle lattice model of glasses in three dimensions.

The nature of glassy states in realistic finite dimensions is still under fierce debate. Lattice models can offer valuable insights and facilitate deeper theoretical understanding. Recently, a disordered-interacting lattice model with distinguishable particles in two dimensions (2D) has been shown to produce a wide range of dynamical properties of structural glasses, including the slow and heterogeneous characteristics of the glassy dynamics, various fragility behaviors of glasses, and so on. These findings support the usefulness of this model for modeling structural glasses. An important question is whether such properties still hold in the more realistic three dimensions. In this study, we aim to extend the distinguishable-particle lattice model (DPLM) to three dimensions (3D) and explore the corresponding glassy dynamics. Through extensive kinetic Monte Carlo simulations, we found that the 3D DPLM exhibits many typical glassy behaviors, such as plateaus in the mean square displacement of particles and the self-intermediate scattering function, dynamic heterogeneity, variability of glass fragilities, and so on, validating the effectiveness of the DPLM in a broader realistic setting. The observed glassy behaviors of the 3D DPLM appear similar to those of its 2D counterpart, in accordance with recent findings in molecular models of glasses. We further investigate the role of void-induced motions in dynamical relaxations and discuss their relation to dynamic facilitation. As lattice models tend to keep the minimal but important modeling elements, they are typically much more amenable to analysis. Therefore, we envisage that the DPLM will benefit future theoretical developments, such as the configuration tree theory, towards a more comprehensive understanding of structural glasses.