Analysis Of Particle Dynamics Research Articles

Experimental analysis of particle dynamics influenced by cavitation bubbles near a rigid wall

This study utilized experimental methods involving high-speed cameras to observe the interaction between cavitation bubbles, generated by a low-voltage electric spark device, and particles near a rigid wall. The dynamic characteristics of the particles were analyzed under varying conditions, including different cavitation bubble sizes, particle sizes, and distances between the cavitation bubble and the wall. Two characteristic parameters were introduced: χ for the particle and cavitation bubble sizes, and λ for the cavitation bubble wall distance. Qualitative distinctions were made among types of particle–bubble interactions, and force analysis was conducted under conditions where χ exceeded the threshold χt. The findings reveal that when χ < χt, particle motion is primarily influenced by the jet effects produced by the cavitation bubble. Conversely, when χ > χt, particle motion is dominated by the radiation forces exerted by the cavitation bubble. Under jet-dominated conditions, particle trajectories were observed to be erratic and unpredictable. For cases where λ < 0, the high-speed jet directly impacts the particle. Conversely, for λ > 0, the jet's velocity decays rapidly upon reaching the particle. In scenarios dominated by radiation forces, the cavitation bubble drew particles away from the wall, followed by their free fall back toward it. The influence of gravity, buoyancy, bubble radiation force, fluid resistance, and virtual mass force on particles was studied when radiation forces prevailed. The acceleration formula for particles was derived through the application of the bubble dynamics equation and was refined based on experimental observations.

Examination of particle motion in fluidized bed flotation columns: Effect of particle shape

The critical analysis of particle dynamics within the flow field is vital for the optimization and enhancement of new fluidized bed flotation columns. Prior research has centered on the kinetic properties of auxiliary fluidized particles (glass spheres) in these columns [1]. However, in real-world applications, these particles undergo wear and transform into irregular shapes. This investigation seeks to explore the motion characteristics of particles of various geometries in a three- phase gas-liquid-solid environment. By quantifying the velocities of particles with different shapes, we aim to improve the evaluation of their dispersion and collision behavior with the column walls. First, the particle concentration distribution within the fluidized zone is continuously monitored through pressure sensors at various axial positions, allowing us to examine the concentration patterns of particles from different shape categories under various operational conditions. Second, the motion dynamics of particles within the fluidization zone are studied using high-speed camera techniques. Particle velocities are determined by correlating tracer particle velocities with black markers for precise measurement. To evaluate the frequency of particle-wall collisions, a modified collision model is applied to ascertain collision rates and to investigate the influence of shape parameters on such interactions. Lastly, the normal and tangential restitution coefficients are measured based on the trajectories of particles before and after collisions with the walls.

Wigner Analysis of Particle Dynamics and Decoherence in Wide Nonharmonic Potentials

We derive an analytical expression of a Wigner function that approximately describes the time evolution of the one-dimensional motion of a particle in a nonharmonic potential. Our method involves two exact frame transformations, accounting for both the classical dynamics of the centroid of the initial state and the rotation and squeezing about that trajectory. Subsequently, we employ two crucial approximations, namely the constant-angle and linearized-decoherence approximations, upon which our results rely. These approximations are effective in the regime of wide potentials and small fluctuations, namely potentials that enable spatial expansions orders of magnitude larger than the one of the initial state but that remain smaller compared to the relevant dynamical length scale (e.g., the distance between turning points). Our analytical result elucidates the interplay between classical and quantum physics and the impact of decoherence during nonlinear dynamics. This analytical result is instrumental to designing, optimizing, and understanding proposals using nonlinear dynamics to generate macroscopic quantum states of massive particles.

Investigation of Multidimensional Fractionation in Microchannels Combining a Numerical DEM-LBM Approach with Optical Measurements

The fractionation in microchannels is a promising approach for the delivery of microparticles in narrow property distributions. The underlying mechanisms of the channels are however often not completely understood and are therefore subject to current research. These investigations are done using different numerical and experimental methods. In this work, we present and evaluate our method of combining a numerical Discrete Element Method (DEM)-Lattice Boltzmann Method (LBM) approach with experimental long-exposure fluorescence microscopy, micro-Particle Image Velocimetry (µPIV) and Astigmatism Particle Tracking Velocimetry (APTV) measurements. The suitability of the single approaches and their synergies are evaluated using the exemplary investigation of multidimensional fractionation in different channel geometries. It shows that both, numerical and experimental method are well suited to evaluate particle dynamics in microchannels. As they furthermore show strengths canceling out weaknesses of the respective other method, the combined method is very well suited for the comprehensive analysis of particle dynamics in microchannels.

Modified stochastic diffusion particle tracking model driven by skew Brownian motion: Analysis of sediment particle motion in turbulent flow under the effects of ejection and sweep.

Turbulent bursting events have been classified into outward interactions (Q1), ejections (Q2), inward interactions (Q3), and sweeps (Q4) in various studies. Ejections (Q2) and sweeps (Q4) have been identified as significant contributors to time consumption, momentum flux, and sediment flux. Additionally, research has shown that the distribution of these events varies nonuniformly at different bed elevations. Despite extensive investigations into the nonuniform distribution of turbulent bursting events, their impact on sediment transport has been rarely explored. In this work, we developed a modified stochastic diffusion particle tracking model (SD-PTM) driven by skew Brownian motion (SBM) using the stochastic Lagrangian approach to scrutinize sediment particle movement in turbulent flows. The model incorporates turbulent characteristics derived from a direct numerical simulation dataset, allowing for a comprehensive analysis of sediment particle dynamics. Moreover, the proposed model accounts for the nonuniform spatial distribution of ejection and sweep events, as well as the particle movement direction during these events. Numerical simulations of the model were conducted to trace sediment particle trajectories in the streamwise and vertical directions. The analysis of sediment transport involved calculating the variance of particle trajectories to examine anomalous diffusion. The model's performance was evaluated by comparing it with flow velocity and sediment concentration profiles obtained from measurements in previous studies. In conclusion, our study suggests that the motion of sediment particles in turbulent flow can be thoroughly investigated under extreme flow conditions using the modified SD-PTM driven by SBM.

Effects of Shape on Interaction Dynamics of Tetrahedral Nanoplastics and the Cell Membrane.

Cellular uptake of nanoplastics is instrumental in their environmental accumulation and transfer to humans through the food chain. Despite extensive studies using spherical plastic nanoparticles, the influence of the morphological characteristics of environmentally released nanoplastics is understudied. Using dissipative particle dynamics simulations, we modeled the interactions between a cell membrane and hydrophobic nanotetrahedra, which feature high shape anisotropy and large surface curvature seen for environmental nanoplastics. We observe robust uptake of nanotetrahedra with sharp vertices and edges by the lipid membrane. Two local energy minimum configurations of nanotetrahedra embedded in the membrane bilayer were identified for particles of large sizes. Further analysis of particle dynamics within the membrane shows that the two interaction states exhibit distinct translational and rotational dynamics in the directions normal and parallel to the plane of the membrane. The membrane confinement significantly arrests the out-of-plane motion, resulting in caged translation and subdiffusive rotation. While the in-plane diffusion remains Brownian, we find that the translational and rotational modes decouple from each other as the particle size increases. The rotational diffusion decreases by a greater extent compared to the translational diffusion, deviating from the continuum theory predictions. These results provide fundamental insights into the shape effect on the nanoparticle dynamics in crowded lipid membranes.

Experimental and numerical study on the performance and mechanism of a vortex-broken electrocyclone

As the synthesis unit of a gas cyclone and electrostatic precipitator, electrocyclone has advantages in particle collection efficiency, capital outlay, and space occupation. This paper proposes a better combination of the gas cyclone and electric field based on the self-designed vortex-broken wing. The performances of the vortex-broken electrocyclone with different inlet velocities and working voltages were investigated by both experiments and numerical simulations. The flow field and electric field in the electrocyclone were obtained by large eddy simulation and solving the potential equation, respectively. The particles were modeled by the Lagrangian particle tracking model and the dynamic behavior of a representative particle was analyzed. The experimental results show that the vortex-broken electrocyclone can reduce the pressure drop and improve the collection efficiency simultaneously. However, the reduction in pressure drop is obvious at high inlet velocity, while the increment in collection efficiency is just the opposite. On the one hand, the simulated flow field reveals that the mechanism for the reduction in pressure drop is that the vortex-broken wing breaks up the inner vortex core, thereby yielding a static pressure recovery. On the other hand, the electric intensity and velocity have opposite directions in the key flow regions, thus affecting the force balance and changing particle trajectories. Further analysis of particle dynamics demonstrates that although the electric field force is far less than the drag force, the particle trajectory can be significantly changed over time. These findings can provide guidance for optimizing the technologies that incorporate electric fields and gas cyclones.

Analysis of particle dynamics in a rotating dish

Although the rotating dishes are widely used in industrial processes, there are not many studies regarding the behavior of granular flow in this type of device. It is reported that the particle dynamics directly influences the dish performance in relation to its applications, e.g., in the granulation process. This work provides an experimental study about the effect of the main variables (rotational speed, angle of inclination, and physical properties of particles) on the behavior of particle dynamics in a rotating dish. The conditions, under which transitions between the flows regimes (rolling, cascading, cataracting, and centrifuging) occurred, were identified and the effects of the studied variables were quantified. The increase in the rotational speed and filling degree and the decrease in the angle of inclination caused a decrease in the angle of departure of the particles and anticipated the transition between flow regimes, demonstrating that both responses are correlated. Correlations proposed in the literature for predictions of the critical rotational speed related to the centrifuging regime were analyzed. A new equation was proposed, which reduced the average percentage deviation from 52.83% to 14.27% when compared to experimental data. • The particle dynamic behavior in a dish granulator was investigated. • The influence of relevant variables was quantified. • The transitions between the characteristic flow regimes were identified. • A new equation to predict the critical rotational speed was proposed.

Merlin++, a flexible and feature-rich accelerator physics and particle tracking library

Merlin++ is a C++ charged-particle tracking library developed for the simulation and analysis of complex beam dynamics within high energy particle accelerators. Accurate simulation and analysis of particle dynamics is an essential part of the design of new particle accelerators, and for the optimization of existing ones. Merlin++ is a feature-full library with focus on long-term tracking studies. A user may simulate distributions of protons or electrons in either single particle or sliced macro-particle bunches. The tracking code includes both straight and curvilinear coordinate systems allowing for the simulation of either linear or circular accelerator lattice designs, and uses a fast and accurate explicit symplectic integrator. Physics processes for common design studies have been implemented, including RF cavity acceleration, synchrotron radiation damping, on-line physical aperture checks and collimation, proton scattering, wakefield simulation, and spin-tracking. Merlin++ was written using C++ object orientated design practices and has been optimized for speed using multicore processors. This article presents an account of the program, including its functionality and guidance for use. Program summaryProgram Title: Merlin++CPC Library link to program files:https://doi.org/10.17632/4x4nsbhz37.1Developer's repository link: 10.5281/zenodo.3700155Licensing provisions: GPLv2+Programming language: C++Nature of problem: Complexity of particle accelerators beam dynamics over extensive tracking distances.Solution method: Long-term particle accelerator and tracking simulations utilizing explicit symplectic integrators.Additional comments including restrictions and unusual features: For further information see github.com/Merlin-Collaboration

Analysis of particle dynamics in a pin mill by Discrete Element Method

Milling is an important process for tailoring the particle size distribution for enhanced attributes, such as dissolution, content uniformity, tableting, etc., especially for active pharmaceutical ingredients and excipients in pharmaceutical industries. Milling performance of particulate solids depends on the equipment operating conditions (geometry, process conditions and input energy etc.) as well as material properties (particle size, shape, and mechanical properties, such as Young’s modulus, hardness and fracture toughness). In this paper the particle dynamics in a pin mill is analysed using Discrete Element Method (DEM), combined with a novel approach for assessing particle breakability by single particle impact testing. A sensitivity analysis is carried out addressing the effect of the milling conditions (rotational speed and feed particle flow rate), accounting for feed mechanical properties on the breakage behaviour of the particles. Particle collision energy spectra are calculated and shown to have a distribution with the upper tail end being close to the maximum energy associated with the collision with the rings. Breakage is primarily due to collisions with the rings, except for large particles that are comparable in size with the gap between the rings, nipping is also a contributory breakage mechanism.

Analogies between growing dense active matter and soft driven glasses

We develop a minimal model to describe growing dense active matter such as biological tissues, bacterial colonies and biofilms, that are driven by a competition between particle division and steric repulsion. We provide a detailed numerical analysis of collective and single particle dynamics. We show that the microscopic dynamics can be understood as the superposition of an affine radial component due to the global growth, and of a more complex non-affine component which displays features typical of driven soft glassy materials, such as aging, compressed exponential decay of time correlation functions, and a crossover from superdiffusive behaviour at short scales to subdiffusive behaviour at larger scales. This analogy emerges because particle division at the microscale leads to a global expansion which then plays a role analogous to shear flow in soft driven glasses. We conclude that growing dense active matter and sheared dense suspensions can generically be described by the same underlying physics.

Investigation and validation of the dynamic response of an acoustically levitated particle using the lattice Boltzmann method

The stable levitation of an analyte sample in an acoustic levitator is a primary requirement for accurate x-ray characterization of its scientific structure. A rigid particle oscillates in an under-damped manner when introduced into the node of established standing acoustic waves. This investigation has employed the lattice Boltzmann method (LBM), a computational fluid dynamics technique, for the analysis of such rigid particle dynamics in acoustic levitation. The simulation uses the two dimensional and nine velocity (D2Q9) Bhatnagar–Gross–Krook formulation to levitate a rigid 1.6 mm diameter nylon (ρ = 1150 kg/m3) particle in the air at standard pressure and temperature conditions. The presented work is the first reported simulation of realistic acoustic levitator boundary conditions using the LBM. The simulation can capture the particle–fluid interactions that produce dynamic levitation at less than one-period timescale in the ultrasonic frequency regime. An experiment was conducted by levitating a 1.6 mm-diameter nylon sphere to estimate the oscillations, and the oscillating frequency was found to be 50 Hz. The dynamic simulation results are consistent with experimental results for particle oscillations within the same order of magnitude, indicating that LBM formulation can be successfully used to study acoustic levitation to understand and mitigate particle jitter. The distortion of the acoustic field due to a levitating particle’s presence was also analyzed to demonstrate how the presence of the particle can disrupt adjacent levitating nodes.

Mechanisms of two-step yielding in attractive colloidal glasses

A combination of experiments and Brownian Dynamics simulations is utilized to examine the mechanisms of yielding and flow in attractive colloidal glasses during start-up shear flow. In both experiments and simulations, the transient stress exhibits two stress peaks indicative of two-step yielding processes. The first yield depends largely on details of interparticle potential whereas the second yield is independent of the potential and takes place at strain (≃20%), at which a purely repulsive glass yields. The stress decomposition into repulsive (hard sphere, HS) and attractive contributions reveals that there are strong contributions of both types of stresses into the first stress peak whereas the second stress peak is mainly linked with HS stresses. The transient stress during start-up shear originates from the change in the averaged pair orientation. At the first stress peak, bonded particles (causing attractive stresses) show the maximum orientation along the extension axis with colliding particles (causing HS stresses) being locally oriented along the compression axis. However, at the second stress peak, collided particles show the maximum orientation along the compression axis with particles escaping their cages along the extension axis similar to a HS glass. Analysis of particle dynamics shows that yielding takes place through a two-step shear-activated hopping process in which first shear flow takes particles out of their attractive constraints. The length scale associated to this process is at the order of attraction range (bond length). Subsequently, cage escape of particles sets the second process which leads to a complete yielding and flow.

Transient numerical analysis of thermophoresis and particle dynamics in a nanofluid – pool boiling conditions

This paper attempts to apply two different equations of thermophoresis (applicable to micro-fluids) to nanofluids. Three significant parameters namely thermophoretic diffusion coefficient, thermophoretic velocity and thermophoretic mobility are used to analyse thermophoresis in a nanofluid. Both experiments and CFD simulations (ANSYS Fluent) are performed for water-alumina nanofluid under transient pool boiling conditions. A hollow stainless steel/glass chamber with a brass heater is used to boil water-alumina nanofluid under sub-cooled conditions. Three different heater surface temperatures (60, 70 and 80°C) are investigated to realize thermophoresis phenomena of the nanofluid. Random variation of temperature measurements in experiments is justified using an uncertainty analysis. Although, volume fraction of nanoparticles (diameter 46 nm) dispersed in the fluid is only 2% by volume, they are featured to exist in every frame of the numerical model for better understanding. 2-D transient implicit pressure based Navier-Stokes solver with SIMPLE (Semi-implicit Method for Pressure Linked Equation) pressure correction technique is used to discretize the numerical grid. Gauss-Seidel iterative procedure is used to solve the discretized equations. Simulation results are validated using a sequence of investigation (thermal property variation of water-alumina nanofluid with respect to pure water under steady-state/transient conditions, thumb rule from literature and experiments). A thin line of differentiation is found to exist between viscosity induced particle migration and thermophoresis induced particle migration for the nanofluid. Implications of equations and parameters used for estimating thermophoresis of nanofluid are discussed.

Influence of surface tension on macroscopic erosion of castellated tungsten surfaces during repetitive transient plasma loads

This paper is focused on the analysis of surface tension contribution to the erosion features of tungsten resolidified surfaces and resulting material response to a large number of repetitive transient hydrogen plasma impacts. Experimental investigations of erosion processes on castellated tungsten surfaces in conditions relevant to uncontrolled ITER ELMs have been performed within powerful quasi-stationary plasma accelerator QSPA Kh-50. The surface energy load measured with a calorimeter was varied between melting (0.6 MJ/m2) and evaporation (1.1 MJ/m2) thresholds, the plasma pulse duration was 0.25 ms. Observations of plasma interactions with exposed W surfaces, analysis of dust particle dynamics and the droplets monitoring have been performed with a high-speed digital camera. Repetitive plasma loads above the melting threshold led to the formation of melted and resolidified surface layers. Networks both macro and intergranular cracks appeared on exposed surfaces. Cracks propagate to the bulk mainly transversely to the irradiated surface. The splashing of dust/liquid particles has been analyzed in the course of repetitive plasma pulses. It was revealed that mountains of displaced material at the edges of castellated units are the primary source of the splashed droplets due to the development of instabilities in a melted layer. The solid dust ejection dominates by cracking processes after the end of pulse and surface resolidification. Due to the continuously growing crack width (from value of sub-μm till tens μm) with the increasing number of pulses the initially uniform melt pool on the castellated units became disintegrated into a set of melt structures separated by cracks. After a large number of exposures the progressive corrugation of the surface occurred due to the capillary effects on exposed W surfaces. Results of simulation experiments for castellated targets and developed surface structures are compared with repetitive plasma exposures of flat tungsten surfaces.

Analysis of particle dynamics in a horizontal pneumatic conveying of the minimum pressure drop based on POD and wavelet transform

In order to study the characters of particle fluctuation velocity at the minimum pressure drop (MPD) velocity in the acceleration and fully developed regimes of a horizontal pneumatic conveying, the particle fluctuation velocities measured by the high-speed particle image velocimetry (PIV) are first analyzed by time-averaged particle velocity, fluctuating energy, power spectrum and autocorrelation. Then the proper orthogonal decomposition (POD) and continuous wavelet transform are developed to reveal the particle fluctuation velocities in terms of the contributions to the particle fluctuation energy, time-frequency distribution, as well as probability density function from POD modes. The energy distributions of POD modes suggest that the first two POD modes are most energetic and dominate the particle motion, and the dominance increases from the acceleration regime to fully-developed regime. The time-frequency characteristics of POD modes reveal that small-scale particle fluctuations are suppressed in the fully-developed regime. It implies that the suppression of small-scale particle fluctuations may result in lower pressure drop at MPD velocity. The PDF distributions of POD modes exhibit that the particle fluctuation of first two POD modes follows the Gaussian distribution in the acceleration and fully developed regimes. However, the PDF distributions of POD modes gradually deviate from Gaussian distribution as increasing mode number.

Residual stresses in colloidal gels.

A combination of experiments and Brownian Dynamics (BD) simulations is utilized to examine internal stresses in colloidal gels brought to rest from steady shear at different shear rates. A model colloidal gel with intermediate volume fraction is chosen where attractions between particles are introduced by adding non-adsorbing linear polymer chains. After flow cessation, the gel releases the stress in two distinct patterns: at high shear rates, where shear forces dominate over attractive forces, the shear-melted gel behaves as a liquid and releases stresses to zero after flow cessation. After low shear rates, though, stresses relax only partially, similar to the response of hard sphere glasses and jammed soft particles. The balance between shear and attractive forces which determines the intensity of structural distortion controls the amplitude of the residual stresses through a universal scaling. Stress decomposition to repulsive and attractive contributions in BD simulations reveals that internal stresses mainly originate from attractive forces. Moreover, analysis of particle dynamics indicates that internal stresses are associated with sub-diffusive particle displacements on average smaller than the attraction range as such short-range displacements are not sufficient to completely erase structural anisotropy caused during the course of shear.

Directly Modifying the Nonbonded Potential Based on the Standard Iterative Boltzmann Inversion Method for Coarse-Grained Force Fields.

Effective potentials are of great importance for coarse-grained (CG) simulations, which can be obtained by the structure-based iterative Boltzmann inversion (IBI) method. However, the standard IBI method is incapable of maintaining the mechanical and thermodynamic properties of the CG model in agreement with those of the all-atom model. Unlike the existing techniques, such as introducing friction force as the dissipative force to reduce the superatom motion while keeping the conservative force arising from the CG potential intact, we directly modified the standard IBI nonbonded potential by adding an empirical function. According to an analysis of the dissipative particle dynamics, the additional function did compensate for the friction reduction of the standard IBI CG model. In this work, the thermal fluctuation information from the nonbonded radial distribution function was incorporated into the additional empirical function. As an illustration of the new CG force fields, we presented simulations of the stress-strain relation and thermodynamic properties in terms of cis-polyisoprene and compared the statistical structure information of the superatoms with those of the IBI CG model and the all-atom model. It should be emphasized that the additional empirical function contributed to compensating for the friction reduction, irrespective of the functional form it took. In this sense, the proposed method was easily operable.

Localized Excitations and the Morphology of Cooperatively Rearranging Regions in a Colloidal Glass-Forming Liquid.

We develop a scheme based on a real space microscopic analysis of particle dynamics to ascertain the relevance of dynamical facilitation as a mechanism of structural relaxation in glass-forming liquids. By analyzing the spatial organization of localized excitations within clusters of mobile particles in a colloidal glass former and examining their partitioning into shell-like and corelike regions, we establish the existence of a crossover from a facilitation-dominated regime at low area fractions to a collective activated hopping-dominated one close to the glass transition. This crossover occurs in the vicinity of the area fraction at which the peak of the mobility transfer function exhibits a maximum and the morphology of cooperatively rearranging regions changes from stringlike to a compact form. Collectively, our findings suggest that dynamical facilitation is dominated by collective hopping close to the glass transition, thereby constituting a crucial step towards identifying the correct theoretical scenario for glass formation.

Numerical solution of Sylvester matrix equations: Application to dynamical systems

Many problems of control theory specially dynamical system lead to Sylvester equations. In this paper, we employ an iterative method of optimization based on partial swarm theory to solve the Sylvester system. To this purpose we consider dynamical system with different construction of state observer which lead to Sylvester observer equation. Using Pso to optimize the solution, obtain the solution with high accuracy comparison with other numerical methods, since the stability analysis of particle dynamics of PSO associated with the best particle is based on nonlinear feedback systems. Finally, some examples demonstrate the efficiency of the proposed method.