Particle Trajectory Calculations Research Articles

The 540° Magnetic Buncher

Generation of short electron bunches with high peak current is of great importance for different research and technological applications. Such generation requires a special bunching magnetic system. The paper is an overview of the development of a new magnetic buncher. It consists of the buncher scheme description, the results of magnetic field modeling and reference particle trajectory calculation for the relativistic electrons, and of the description of bending magnets. The buncher provides a strong dependence of the time of flight on the particle energy and thus is capable to bunch relatively long bunches to short ones. Another feature of the buncher is that all electron-optical elements has been made of permanent magnets.

The impact of particle deposition on collection efficiency of electret fibers

This study presents a microscale simulation method that allows one to study the impact of particle loading on the aerosol capture efficiency of an electrostatically charged filter. This was done by considering a bipolarly charged fiber loaded with different amounts of neutral and charged particles with a diameter of 300 nm. The simulations predicted the deposition pattern of the aerosol particles as well as their impact on the electrostatic field of the bipolar fiber. The particle-loaded fiber was then challenged with aerosol particles in the range of 50 nm to 1 μm and with different charge polarities to study how the electrostatic field of the deposited particles interacts with that of the fiber to attract or repel the incoming airborne particles. More specifically, our simulations revealed that particle deposition can enhance the capture efficiency of a bipolar fiber when it is challenged with small particles (smaller than about 400 nm) regardless of the charge polarity of the airborne or deposited particles. The numerical simulations reported in this paper were conducted using the ANSYS CFD code enhanced with in-house subroutines to superimpose the electrostatic field of the deposited particles to that of the bipolar fiber and to include Brownian, polarization, and Coulomb forces in particle trajectory calculations.

Microscale modelling of electret filters using disordered 2-D domains

This paper reports on a computational study about the impact of fiber dipole orientation on particle collection efficiency of a bipolarly charged filter. The simulations were carried out using ANSYS software in a series of 2-D geometries comprised of randomly distributed fibers. The simulations were enhanced with in-house subroutines to incorporate Coulomb and dielectrophoretic forces in calculating particle trajectories and thereby simulating filter efficiency. The highest and lowest efficiencies were observed for dipole orientations that were perpendicular and parallel to the airflow direction, respectively. The simulation results were also compared with the predictions of the popular semi-empirical correlations from the literature and good general agreement was observed, without the need for any empirical correction factors. In addition, it was observed that the predictions of the semi-empirical correlations better agreed with the simulation results obtained for media comprised of fibers with random dipole orientations when challenged with neutralized particles.

Experimental investigations and three-dimensional computational fluid dynamics modeling of sediment transport in tanks influenced by cavities

Sediment transport is a very complex process in urban water systems, and sediment movement mechanisms are poorly understood. However, it is necessary to comprehend sediment transport to optimize stormwater and sewer tank designs for better performance in trapping particulate pollutants. This work focuses on the numerical simulation and experimental investigation of tank sediment transport. In the numerical simulation, a discrete phase model is applied to calculate particle trajectories, and the particle tracking calculation is coupled with the steady-state flow calculation. A user-defined function is developed in the Fluent computational fluid dynamics (CFD) code to implement the settling condition and improve the particle motion predictions. In the experimental work, a back-scattered ultrasonic method is used to measure the velocity field, and the accumulation of particles at the bottom is reproduced by transforming the raw experimental data. The sediment deposition is also recorded photographically, and the trap efficiency is calculated. The CFD and experimental results are compared to estimate the accuracy of the modified settling boundary condition, showing an improvement in the trap efficiency and deposition zone predictions. High water level in the tank corresponds to higher sediment trap efficiency, and sediment deposition type is strongly affected by the water level. Tank length and the presence of cavity alter the sediment deposition zone, and the presence of cavity increases the trap efficiency of tank.

Parameterization modeling for wind drift factor in oil spill drift trajectory simulation based on machine learning

Marine oil spill simulations typically employ the oil particle method to calculate particle trajectories, considering various factors such as wind, current, and turbulence. The wind drift factor (WDF), a random element determining the proportion of wind’s effect on oil particles, is often empirically set as a constant in traditional oil spill models, introducing limitations. This study proposes a support vector regression-based parameterization modeling (SVR-PM) for the WDF. Using extensive buoy data and ocean hydrodynamic reanalysis data, we trained an SVR model to compute the WDF in real-time based on real-time wind speed. The SVR-PM was integrated into an oil spill model to enhance the computation of the wind-induced velocity term. We validated the model using satellite images of two significant oil spills, resulting in an excellent average agreement. The SVR-PM’s advantage lies in enhancing the accuracy of wind-induced velocity term in oil spill simulations and demonstrating strong adaptability and generalizability over time and space. This advancement holds significant implications for maritime departments and emergency disaster response units.

Numerical Simulation of Ice Crystal Supercooled Droplet Mixed Phase Icing Based on the Improved Messinger Model

The ice crystal supercooled droplet mixed phase icing problem is an important research direction in aircraft icing and has received more attention in recent years. The thermodynamic process of the water film after the ice crystals impact on the surface determines the final ice shape, which is an important part of the accurate prediction of aircraft icing. In this paper, a thermodynamic model of ice crystal supercooled droplet mixed phase icing is proposed based on the extended Messinger model, according to the results of flow field and particle trajectory calculations. In this model, the mass and energy conservation equations of ice crystals, supercooled droplets, and liquid water are considered. The equations take the process of ice crystal adhesion and erosion into account, and the solution method of the equations is given. Ice shapes are calculated under various ice crystal supercooled droplet mixed phase conditions and compared with experimental results to demonstrate the validity of the numerical method. The effects of ice crystal erosion rate, melting ratio, and adhesion coefficient on the calculation results are analyzed by a numerical method. The results show that the ice crystal erosion rate has little effect on the ice shape, while a larger melting ratio and adhesion coefficient lead to more ice accretion.

Structural Improvement of Differential Motion Assembly in In Situ Pressure-Preserved Coring System Using CFD Simulation

In situ pressure-preserved coring (IPP-Coring) is one of the most efficient methods for identifying the scale of the oil and gas content. However, the differential motion assembly of the IPP-Coring system often undergoes ball and ball seat seal failure and sticking due to surface erosion, and a greater pressure drop may unexpectedly trigger the assembly. This paper addresses these issues by improving the hydraulic structure of an assembly based on a deep understanding of the flow characteristics in the assembly, thus increasing the success rate of the IPP-Coring. Computational fluid dynamics (CFD) was employed to investigate flows in a differential motion assembly. The effects of the diameter and outlet structure of the ball seat on the fluid status, velocity, and pressure distribution were thoroughly analyzed. When the ball seat diameter increased from 30 to 40 mm, the maximum velocity and pressure drop decreased to 0.55 and 0.2 times their original values, respectively. There was a severe vortex area in the differential motion assembly due to the presence of the ball seat, but changing the outlet structure in the ball seat to an arc structure decreased the length of the vortex area and the fluid velocity near the wall to 0.7 and 0.4 times, respectively, compared with those with the original right-angled structure. In addition, the pressure drop decreased to 0.33 times the original value. Thus, the hydraulic structure of the assembly was improved, and a 40 mm diameter ball seat and an arc-shaped ball seat outlet were selected. Particle trajectory and erosion calculation results showed that the improved structure has a lower particle velocity and less impact on the wall, and the average erosion rate is only 0.42 times the value of the original structure. Due to the better erosion resistance and smaller pressure drop, the improved structure shows promise for field performance.

Removal of Iron Oxide Scale From Boiler Feed-Water in Thermal Power Plant by Magnetic Separation-Scale Removal at High-Temperature

The removal of scale by high gradient magnetic separation (HGMS) has been investigated utilizing the magnetic properties of the scale. This study focuses on a thermal power plant with oxygen treatment (OT), which has been applied in many new power plants with large generation capacity in recent years. At high-temperature conditions where the HGMS system is expected to be installed, the viscosity of the fluid will be lower than that of at room temperature, which makes the separation ratio higher. In this study, the scale capture rate at room temperature (25°C) and 80°C was investigated by particle trajectory calculation and experiment, in order to design magnetic separation conditions suitable for the high-temperature environment of the chemical cleaning line of the thermal power plant adopting OT.

Substantiation of the main design parameters of the separation chamber of the pneumatic separator using various methods for calculating particle trajectories in the pneumoseparating channel

The article presents a study of the influence of methods for calculating particle trajectories in the pneumatic separation channel (PSC) on the design parameters of the separation chamber (length and height of the exit window), completed in 2013-2021. The field of air flow velocities and trajectories of spring wheat seed material components in the separation chamber of fractioning pneumatic seed separator was constructed. The initial data for the calculation were the information obtained earlier when calculating the trajectories of particles in the PSC by various methods. The location at the outlet of the channel, the value and direction of the particle velocity vectors were determined by computer modelling using the Solidworks Flow Simulation software package and two experimental and theoretical methods. They took into account the real velocity field of the air flow with and without grain load. The obtained values of the design parameters are compared with the results of experimental studies of the separation chamber. It should be noted that the methods of calculating the trajectories of grain impurity particles have a significant impact on the length of the separation chamber and the height of the exit window. The maximum length of the separation chamber of 0.75 m will be required for computer modelling of the velocity field in the PSC. Much smaller values of 0.50 m and 0.45 m will be required when calculating the trajectories of particles in the PSC using the velocity field obtained by experimental and theoretical methods. During the experimental study of the separation chamber during the cleaning of wheat seeds, the optimal length of the separation chamber was determined to be 0.55 m with an exit window height of 0.30 m. Thus, the values of the design parameters of the separation chamber obtained by experimental and theoretical methods are the closest to experimental data, which makes it possible to recommend them for use at the design stage of pneumatic separators.

A hybrid particle model with advanced conversion parameters and dynamic drag model applied for the CFD modeling of an entrained-flow gasifier

The main focus of the current work is to establish a hybrid particle model to depict the char conversion process, taking into account the influence of pore diffusion on the carbon consumption rate. Compared to existing char conversion models, the new hybrid model uses advanced correlations for conversion parameters such as the density and diameter exponents α and β and the Random Pore Model correction factor γ, which are functions of char conversion and effectiveness factor. CFD simulation results for a Pressurized Entrained-Flow Reactor (PEFR) using the hybrid particle model are in good agreement with experimental data. In addition, the current work also introduces dynamic drag models based on the development of the shape of spherical and non-spherical particles during the char conversion process. The dynamic drag models, which up to now has been missed in calculation of particle trajectories, are examined to evaluate their influences on the total carbon conversion of the PEFR. Furthermore, the performance of ideal particle sub-models such as the Uniform Conversion Model and Shrinking Unreacted Particle Model are also studied and compared with that of the hybrid particle model. PEFR CFD simulation results illustrate considerable differences between the carbon conversion profiles obtained with these sub-models and those profiles obtained using the hybrid particle model.

Test particle acceleration in resistive torsional fan magnetic reconnection using laboratory plasma parameters

Particle acceleration via magnetic reconnection is a fundamental process in astrophysical plasmas. Experimental architectures are able to confirm a wide variety of particle dynamics following the two-dimensional Sweet–Parker model, but are limited in their reproduction of the fan-spine magnetic field topology about three-dimensional (3-D) null points. Specifically, there is not yet an experiment featuring driven 3-D torsional magnetic reconnection. To move in this direction, this paper expands on recent work toward the design of an experimental infrastructure for inducing 3-D torsional fan reconnection by predicting feasible particle acceleration profiles. Solutions to the steady-state, kinematic, resistive magnetohydrodynamic equations are used to numerically calculate particle trajectories from a localized resistivity profile using well-understood laboratory plasma parameters. We confine a thin, 10 eV helium sheath following the snowplough model into the region of this localized resistivity and find that it is accelerated to energies of ${\approx }2$ keV. This sheath is rapidly accelerated and focused along the spine axis propagating a few centimetres from the reconnection region. These dynamics suggest a novel architecture that may hold promise for future experiments studying solar coronal particle acceleration and for technology applications such as spacecraft propulsion.

Experimental Investigation and CFD Modelling of Settling Efficiency in a Cylindrical Tank

Evaluating the performance of a settling tank is an important issue for wastewater system managers. The relevance of a CFD approach for determining the settling efficiency of a tank has already been demonstrated from experimental data obtained from scale models of basins. The CFD modelling strategy is based on the resolution of Navier-Stokes equations to calculate the flow (Eulerian approach), and then on a Newton equation to calculate particle trajectories (Lagrangian approach). In this study, experimental data on settling efficiency are collected in a 1 scale cylindrical settling tank constructed in the laboratory. Eighteen experiments were carried out to collect data (settling efficiency) for a range of flow rates (between 5 and 30 l/s) and three materials representative of the sediments encountered in sewage networks. These data were then compared with the results obtained by CFD modelling to assess the relevance of the numerical approach for a full-scale structure.

Software for Numerical Calculations of Particle Trajectories in the Earth’s Magnetosphere and Its Use in Processing PAMELA Experimental Data

Software for Numerical Calculations of Particle Trajectories in the Earth’s Magnetosphere and Its Use in Processing PAMELA Experimental Data

Measurement-driven Large Eddy Simulation of dispersion in street canyons of variable building height

The ventilation efficiency of three periodic building patterns of equal total volume and packing density is investigated: street canyons bounded by H uniform and 0.5H/1.5H variable height buildings, via wind tunnel measurements and Large Eddy Simulation. The numerical model utilizes the Transient Wind Forcing method to take the effect of eddies larger than the domain size into account, and a special Lagrangian dispersion model, which allows for the calculation of particle trajectories exceeding the periodic boundaries of the LES domain. The spatial and temporal characteristics of the concentration responses of both pulse-like and steady point sources located at the street surfaces are analyzed. It is shown that the variable building height has a favorable effect on urban ventilation in densely built areas: the average near-ground concentration can be reduced by up to 70% for the variable height buildings in a staggered arrangement. In terms of velocity, turbulence and concentration distributions, the model results are consistent with the experiments, verifying the applicability of the model for comparative air quality studies. Since the presented dispersion model is capable of handling dynamic changes in wind direction and magnitude, the accuracy of the TWF model can potentially overcome the limitations of wind tunnel tests.

World grid of cosmic ray vertical cut-off rigidity for the last decade

Cosmic ray cut-off rigidity tables and maps over the world concerning the epochs 2010, 2015 and the current one 2020 have been constructed. These maps display the effective cut-off rigidity in every five degrees in latitude and in longitude at the altitude of 20 km above the surface of the international reference ellipsoid. The values of the geomagnetic cut-off rigidity were calculated in every 5° in latitude and in every 15° in longitude applying the well-known method of particle trajectory calculations resulted from the theory of the particle motion in the Earth's magnetic field. The applied software employed the 12th Generation of the International Geomagnetic Reference Field (IGRF 12) and trajectories were calculated at 0.01 GV intervals in order to determine the vertical cut-off rigidity for each location. Beyond the use of the calculated cut-off rigidity values as a basic reference of charged particle access to different geographical locations during quiet and/or more intense geomagnetic periods, these results can be used for a long- term forecasting of the geomagnetic conditions variations.

A study of droplet evaporation coupling model based on Eulerian method

Research on engine icing is a hot topic among the world. Different from the aircraft wing or airframe icing, the evaporation phenomenon in the internal flow field has a great influence on the engine icing. Moreover, the thermodynamic coupling between droplets and flow field is not available in current particle trajectory calculations, or only for one-dimensional situation. Therefore, a three-dimensional droplet trajectory calculation model based on Eulerian method is used to demonstrate the thermodynamic coupling between droplets and flow field. The model was verified by NRC small engine icing wind tunnel test data and the flow field evolution is obtained which cannot be obtained by the one-dimensional coupling model. In the meanwhile, the effects of different initial LWC, relative humidity and MVD on the internal flow evaporation were studied, and the trends of droplets and flow field affected by evaporation were obtained. The numerical method in this paper can provide guidance for the subsequent research on engine icing

A generalized Boltzmann kinetic theory for strongly magnetized plasmas with application to friction

Coulomb collisions in plasmas are typically modeled using the Boltzmann collision operator, or its variants, which apply to weakly magnetized plasmas in which the typical gyroradius of particles significantly exceeds the Debye length. Conversely, O'Neil has developed a kinetic theory to treat plasmas that are so strongly magnetized that the typical gyroradius of particles is much smaller than the distance of the closest approach in a binary collision. Here, we develop a generalized collision operator that applies across the full range of magnetization strength. Since there is no closed-form solution for the scattering cross section when plasma is strongly magnetized, the input to the collision operator is obtained by numerically calculating particle trajectories. To demonstrate novel physics associated with strong magnetization, it is used to compute the friction force on a massive test charge. In addition to the traditional stopping power component, this is found to exhibit a transverse component that is perpendicular to both the velocity and Lorentz force vectors in the strongly magnetized regime, as was predicted recently using linear response theory. Good agreement is found between the collision theory and linear response theory in the regime in which both apply, but the new collision theory also applies to stronger magnetization strength regimes than the linear response theory is expected to apply in.

Two-dimensional leapfrog scheme for trajectories of relativistic charged particles in static axisymmetric electric and magnetic field

A method for the calculation of two-dimensional particle trajectories is proposed in this work. It makes use of the cylindrical symmetry and the simplification of the static electric field, so that there should be no systematic error for the centered large-orbit rotations nor for the acceleration or deceleration in a uniform electric field. The method also shows a lower error level than the standard Boris method in many cases. Typical applications of this method are for example, electron microscopes, electron guns and collectors of gyro-devices as well as of other vacuum tubes, which can be described in axisymmetric cylindrical coordinates. Besides, the proposed method enforces the conservation of canonical angular momentum by construction, which is expected to show its advantages in the simulation of cusp electron guns and other components relying on non-adiabatic transitions in the externally applied static magnetic field.

Slow Decay Processes of Electrostatically Trapped Rydberg NO Molecules.

Nitric oxide (NO) molecules initially traveling at 795 m/s in pulsed supersonic beams have been photoexcited to long-lived hydrogenic Rydberg-Stark states, decelerated and electrostatically trapped in a cryogenically cooled, chip-based transmission-line Rydberg-Stark decelerator. The decelerated and trapped molecules were detected insitu by pulsed electric field ionization. The operation of the decelerator was validated by comparison of the experimental data with the results of numerical calculations of particle trajectories. Studies of the decay of the trapped molecules on timescales up to 1ms provide new insights into the lifetimes of, and effects of blackbody radiation on, Rydberg states of NO.

Measurement and calculation of particle trajectory of liquefied soil under wave action

In offshore areas, the silty soil seabed can be liquefied under cyclic wave loads, and the liquefied soil fluctuates with the upper water body with the same period. Similar to the movement of water, the fluctuation orbit of liquefied soil particles is elliptical with a horizontal major axis, and the orbit radius gradually decreases with depth. Although some researchers have constructed theories to describe the fluctuation of liquefied soils, no corresponding data have been verified in wave flume tests on silty soils under visual conditions. In this paper, the particle trajectory of liquefied soil is observed to be elliptical under the condition of small-amplitude waves in shallow water by wave flume tests. The vertical displacement of liquefied soil particle motion is measured by the falling ball method, which provides validation data for the theoretical calculation results. In addition, the results of the double-layer fluid wave theory are compared with the experimental data. For engineering applications, an analytical solution for particle motion and the displacement of liquefied silty soil under wave action is given by using the small-amplitude wave theory and the method of setting a reference surface of fluid wave depth. The vertical displacement of liquefied soil particles calculated by the analytical solution is smaller than that calculated by the double-layer fluid wave theory and larger than that calculated from the experimental results.