Motion Of Relativistic Particle Research Articles

Gauss Principle of Least Compulsion for Relative Motion Dynamics and Differential Equations of Motion

This paper focuses on Gauss principle of least compulsion for relative motion dynamics and derives differential equations of motion from it. Firstly, starting from the dynamic equation of the relative motion of particles, we give the Gauss principle of relative motion dynamics. By constructing a compulsion function of relative motion, we prove that at any instant, its real motion minimizes the compulsion function under Gaussian variation, compared with the possible motions with the same configuration and velocity but different accelerations. Secondly, the formula of acceleration energy and the formula of compulsion function for relative motion are derived because the carried body is rigid and moving in a plane. Thirdly, the Gauss principle we obtained is expressed as Appell, Lagrange, and Nielsen forms in generalized coordinates. Utilizing Gauss principle, the dynamical equations of relative motion are established. Finally, two relative motion examples also verify the results' correctness.

Quantifying the role of submesoscale Lagrangian transport features in the concentration of phytoplankton in a coastal system

Abstract Food resources in the ocean are often found in low densities, and need to be concentrated for efficient consumption. This is done in part by oceanographic features transporting and locally concentrating plankton, creating a highly patchy resource. Lagrangian approaches applied to ocean dynamics can identify these transport features, linking Lagrangian transport and spatial ecology. However, little is known about how Lagrangian approaches perform in ageostrophic coastal flows. This study evaluates two Lagrangian Coherent Structure metrics against the distribution of phytoplankton; Finite Time Lyapunov Exponents (FTLE) and Relative Particle Density (RPD). FTLE and RPD are applied to High Frequency Radar (HFR) observed surface currents within a biological hotspot, Palmer Deep Canyon Antarctica. FTLE and RPD identify different transport patterns, with RPD mapping single particle trajectories and FTLE tracking relative motion of paired particles. Simultaneous measurements of circulation and phytoplankton were gathered through the integration of vessel and autonomous glider surveys within the HFR footprint. Results show FTLE better defined phytoplankton patches compared to RPD, with the strongest associations occurring in stratified conditions, suggesting that phytoplankton congregate along FTLE ridges in coastal flows. This quantified relationship between circulation and phytoplankton patches emphasizes the role of transport in the maintenance of coastal food webs.

Construction of mathematical model of particle movement by an inclined screw rotating in a fixed casing

Screw conveyors are used to move bulk materials vertically upwards, horizontally, and at an angle to the horizon. The processes that take place when particles are moved by a screw conveyor in vertical and horizontal directions have been studied. There is a significant difference between them: for transportation in the vertical direction, the necessary conditions must be ensured (sufficient angular speed of rotation of the screw), and for horizontal transportation, the movement of the particle occurs at any angular speed of rotation of the screw. Therefore, when changing the inclination of the axis of the screw, there comes a moment when transportation becomes possible, while it was impossible in the vertical direction. This paper considers the movement of a particle under the condition that it simultaneously contacts two surfaces: the moving surface of the screw and the stationary surface of the cylindrical casing in which the screw rotates. Their common line along which the particle slides is a helical line – the periphery of the screw. The particle slides along the helical line of the rotating screw, i.e., it is in relative motion with respect to it. At the same time, it slides along the surface of the casing, relative to which it is in absolute motion. The trajectory of the particle's absolute motion is its sliding track on the casing surface. When constructing differential equations of the relative motion of particles, the forces applied to the particle were taken into account. The initial position was taken to be the vertical direction of the screw to transport the particle upwards. If an auger in a cylindrical casing is tilted from the vertical direction to a certain angle, then all applied forces (except the force of weight) will also tilt to this angle. On the basis of this, generalized differential equations of the relative motion of a particle during its transportation by an inclined screw were built. They made it possible to derive a generalized mathematical model of the movement of a particle by an inclined screw that rotates inside a fixed casing

Lagrangian and Hamiltonian Formalisms for Relativistic Mechanics with Lorentz-Invariant Evolution Parameters in 1 + 1 Dimensions

This article presents alternative Hamiltonian and Lagrangian formalisms for relativistic mechanics using proper time and proper Lagrangian coordinates in 1 + 1 dimensions as parameters of evolution. The Lagrangian and Hamiltonian formalisms for a hypothetical particle with and without charge are considered based on the relativistic equation for the dynamics and integrals of particle motion. A relativistic invariant law for the conservation of energy and momentum in the Lorentz representation is given. To select various generalized coordinates and momenta, it is possible to modify the Lagrange equations of the second kind due to the relativistic laws of conservation of energy and momentum. An action function is obtained with an explicit dependence on the velocity of the relativistic particles. The angular integral of the particle motion is derived from Hamiltonian mechanics, and the displacement Hamiltonian is obtained from the Hamilton–Jacobi equation. The angular integral of the particle motion θ is an invariant form of the conservation law. It appears only at relativistic intensities and is constant only in a specific case. The Hamilton–Jacobi–Lagrange equation is derived from the Hamilton–Jacobi equation and the Lagrange equation of the second kind. Using relativistic Hamiltonian mechanics, the Euler–Hamilton equation is obtained by expressing the energy balance through the angular integral of the particle motion θ. The given conservation laws show that the angular integral of the particle motion reflects the relativistic Doppler effect for particles in 1 + 1 dimensions. The connection between the integrals of the particle motion and the doubly special theory of relativity is shown. As an example of the applicability of the proposed invariant method, analyses of the motion of relativistic particles in circularly polarized, monochromatic, spatially modulated electromagnetic plane waves and plane laser pulses are given, and comparisons are made with calculations based on the Landau and Lifshitz method. To allow for the analysis of the oscillation of a particle in various fields, a phase-plane method is presented.

Persistent nonequilibrium effects in generalized Langevin dynamics of nonrelativistic and relativistic particles.

Persistent nonequilibrium effects such as the memory of the initial state, the ballistic diffusion, and the break of the equipartition theorem and the ergodicity in Brownian motions are investigated by analytically solving the generalized Langevin equationof nonrelativistic Brownian particles with colored noise. These effects can also be observed in the Brownian motion of relativistic particles by numerically solving the generalized Langevin equationfor specially chosen memory kernels. Our analyses give rise to think about the possible anomalous motion of heavy quarks in relativistic heavy-ion collisions.

Multi-scale investigation on the stability of soil–gravel mixture slopes using imaging analyses

Gravel soil slopes are not only prevalent in nature but also are widely used in engineering. Understanding the damage characteristics of gravel soil slopes and preventing slope hazards requires a thorough investigation of the stability and deformation of gravel soil slopes. In this study, the stability and macroscopic deformation of slopes with varying gravel content (GC) were examined using laboratory tests and digital image correlation techniques, and the rock-winding motion on the shear zone was investigated in detail by capturing the relative motion of soil particles and gravels from a micro-scale perspective. In addition, the effects of loading location and slope angle were considered. The results indicated that there are two thresholds of 20 and 70% for the effect of GC on slope ultimate bearing capacity. Gravel soil slope shear damage was primarily caused by the gravel rotation at critical locations. There were at least five rock-inclusive movement patterns in the shear zone, and the primary cause of irregular damage on gravelly soil slopes was the difference in the relative movement of soil particles and gravels. High GC slopes were less sensitive to changes in loading location and slope angle than slopes with low GC.

A method for characterizing the deformation localization in granular materials using the relative particle motion

The failure location identification of granular materials can be solved by capturing the deformation localization. Considering the relative translation and rotation among particles, a new concept named the relative particle motion (RPM) is proposed to describe the deformation localization of the granular materials. An approach is developed to realize the selection of particles that are used to calculate RPM. The number of particles involved in RPM calculation is controlled by two key parameters, i.e., grid spacing (U) and domain radius (R). Combining the proposed concept and the selection approach of particles, the method that can capture the region of the deformation localization in the granular material is established and implemented in PFC2D.The simulation of a uniaxial compression test is conducted to analyze the effect of parameters U and R on the calculation results of the RPM field, and a reasonable range of U and R is given. Three typical conditions, including the biaxial compression, trapdoor, and particle flow tests, are taken as examples to validate the proposed method under different loading conditions. Regions of the deformation localization characterized by RPM have a good agreement with the shear band presented in the published literature.

Large Eddy Simulation of turbulent nonpremixed sooting flames: Presumed subfilter PDF model for finite-rate oxidation of soot

Modeling soot evolution in turbulent reacting flows using Large Eddy Simulation (LES) is challenging due to the complex subfilter soot-turbulence-chemistry interactions. Soot particles form at fuel-rich mixtures and are subsequently oxidized as they are transported toward fuel-lean mixtures. In previous work, this phenomenology was explicitly encoded into a presumed subfilter PDF model for soot by confining soot strictly to mixtures where growth rates exceed oxidation rates. However, this model implicitly assumed that oxidation is infinitely fast. In this work, a new presumed subfilter PDF model for soot is proposed to account for finite-rate soot oxidation. The distribution of soot with respect to the flame structure (mixture fraction) is modeled by comparing the local relative motion of diffusionless soot particles with respect to mixture fraction iso-contours with the local oxidation rate. When the oxidation rate is suppressed or the transport rate is very fast, soot is allowed to penetrate further into fuel-lean mixtures. This model can allow for soot leakage across the flame, a critical phenomenon in smoking flames. The new model is validated a priori against Direct Numerical Simulation (DNS) databases of turbulent nonpremixed jet flames and then a posteriori against experimental measurements in a laboratory-scale turbulent jet flame. A priori results show remarkably good agreement with filtered DNS data and are shown to correctly allow for soot leakage at low Damköhler number. Finally, LES results of the turbulent sooting jet flame show an improvement of soot prediction using the new soot subfilter model compared to previous works. In this flame, as in experiments, evidence of soot leakage is found near the beginning of the sooting region, and this soot leakage cannot be predicted with previous subfilter models that presume infinitely fast oxidation.

A novel vortex flocculation reactor for efficient water treatment: Kinetic modeling and experimental verification

We designed a novel vortex flocculation reactor with column-cone-column structure by adding vortex generators to form the micro-vortices to improve the flocculation efficiency. The vortex generators, actually wedge-shaped baffles, act as turbulence components to generate large flow resistance, thus reducing the size of the vortex to approach that of the floc. The inverted cone-cone-inverted cone structure in small-vortex flow flocculation zone prompts the fluid to form boundary layer dissociation phenomenon, thereby enhancing the relative motion of floc particles. The numerical simulation results of flow field structure indicated that the fluid presented a multiphase flow of “swirl flow-vortex flow-plug flow”; hence the fluid characteristic changed step by step. Moreover, the multistage velocity gradient of the fluid in different flow layers enhanced the probability of floc particles collision, thus strengthening the flocculation. Then the lab-scale vortex flocculation reactor was manufactured to conduct flocculation tests. The results revealed that the vortex flocculation reactor took the reaction time of only 10 s to achieve a superior chemical oxygen demand removal rate of 93.7%. The vortex flocculation reactor, based on the multiphase flow and multistage velocity gradient reinforcement flocculation strategy, can offer an effective way to improve the flocculation efficiency.

Numerical Study of Supra-Wavelength Axial Motion Compensation in Contact-Mode Optical Coherence Angiography Using Fourier-Shift Procedures

Label-free angiographic methods based on optical coherence tomography (OCT) visualize blood vessels utilizing detection of red blood cells motion against surrounding static tissue. However, in practice, the surrounding tissue is never still due to natural motions of living organisms (e.g., breathing or heart beating). To mitigate large scale motions of the tissue relatively to the OCT probe the tissue examination can be made in contact mode. In such a case, however, the OCT probe inevitably exerts some pressure onto the tissue, so that bulk motions lead to interframe deformations and depth-dependent tissue displacements which have to be numerically compensated prior to angiographic visualization. Usually, sufficiently small deformations primarily affect pixel phases in OCT images rather than pixel amplitudes, and, therefore, phase-only compensation of the masking motions may be fairly sufficient. However, in case of larger strains and supra-wavelength displacements, larger inter-scan phase variations of the order of several periods lead to the appearance of pronounced “decorrelation noise” in which variations in pixel amplitudes and phases are combined. This effect significantly degrades the quality of the final OCT-angiography images. In this paper, we present a new method allowing to a significant degree to compensate this phase-amplitude decorrelation caused by spatially-inhomogeneous supra-wavelengths displacements. This compensation is based on the Fourier-shift theorem which allows one to back-shift fragments of the deformed OCT-scans to their initial positions before deformation. At the same time variations of pixels due to the motion of blood particles within smaller-in-size vessel cross sections are retained. Although such backshifts do not compensate relative motions of sub-resolution particles, this procedure efficiently reduces decorrelation even for fairly big spatially-inhomogeneous displacements and leads to much lower signal variability outside blood vessels while preserving high variability inside. The proposed compensation method is compared to the earlier proposed phase-only compensation using simulated data. Pronouncedly lower strain-induced artefacts and much higher contrast between blood vessels and background are demonstrated.

Deep learning method for the super-resolution reconstruction of small-scale motions in large-eddy simulation

A super-resolution reconstruction model for the subgrid scale (SGS) turbulent flow field in large-eddy simulation (LES) is proposed, and it is called the meta-learning deep convolutional neural network (MLDCNN). Direct numerical simulation (DNS) data of isotropic turbulence are used as the dataset of the model. The MLDCNN is an unsupervised learning model, which only includes high-resolution DNS data without manually inputting preprocessed low-resolution data. In this model, the training process adopts the meta-learning method. First, in the a priori test, the SGS turbulent flow motions in the filtered DNS (FDNS) flow field are reconstructed, and the energy spectrum and probability density function of the velocity gradient of the DNS flow field are reconstructed with high accuracy. Then, in the a posteriori test, the super-resolution reconstruction of the LES flow field is carried out. The difficulty of LES flow field reconstruction is that it contains filtering loss and subgrid model errors relative to the DNS flow field. The super-resolution reconstruction of the LES flow field achieves good results through this unsupervised learning model. The proposed model makes a good prediction of small-scale motions in the LES flow field. This work improves the prediction accuracy of LES, which is crucial for the phenomena dominated by small-scale motions, such as relative motions of particles suspended in turbulent flows.

Micromechanics of granulated rubber–soil mixtures as a cost-effective substitute for geotechnical fillings

Rubber–soil mixtures (RSM), formed by mixing two types of granules with vastly different mechanical properties, has the potential for serving as a cost-effective substitute for geotechnical fillings. Its micromechanical behavior at a microscopic scale, however, is not yet well understood. In this study, a numerical model of granulated RSM under biaxial compression conditions is established based on the discrete element theory and two-dimensional particle flow code. Microparameters of a particular RSM are studied and calibrated by comparison with triaxial consolidated drained shear tests. The volumetric fraction of sand is assigned as the index of the mixture, and the deviatoric stress–axial strain curves of RSM with different sand fractions are analyzed. Particle rotation, average coordination number, force chain structure, and energy dissipation with axial strains are further investigated to better understand the microscopic mechanisms of RSM. The main findings of the study include: (1) Rubber particles are highly deformable and fill the voids more easily than stiffer sand particles. This contributes to the high friction of sand–rubber interfaces, which delays or even inhibits the relative motion and tumbling of sand particles; (2) The force chains of sand particles are either braced from buckling until large axial strains by rubber particles occupying the intergranular voids or distributed by increased rubber–rubber contacts depending on the rubber content; and (3) RSM with a rubber volumetric content of 30–40% are optimal in that the force chain increases monotonically with axial strain with a stable load-deformation relationship. In addition, the sensitivity analysis of the effect of microparameters on the macroscopic behavior of RSM is presented, which can provide theoretical support for exploring the mechanical properties of similar mixed granular materials subjected to external loading.

Resistance and mobility functions for the near-contact motion of permeable particles

A lubrication analysis is presented for the resistances between permeable spherical particles in near contact,$h_0/a\ll 1$, where$h_0$is the minimum separation between the particles, and$a=a_1 a_2/(a_1+a_2)$is the reduced radius. Darcy's law is used to describe the flow inside the permeable particles and no-slip boundary conditions are applied at the particle surfaces. The weak permeability regime$K=k/a^{2} \ll 1$is considered, where$k=\frac {1}{2}(k_1+k_2)$is the mean permeability. Particle permeability enters the lubrication resistances through two functions of$q=K^{-2/5}h_0/a$, one describing axisymmetric motions, the other transverse. These functions are obtained by solving an integral equation for the pressure in the near-contact region. The set of resistance functions thus obtained provide the complete set of near-contact resistance functions for permeable spheres and match asymptotically to the standard hard-sphere resistances that describe pairwise hydrodynamic interactions away from the near-contact region. The results show that permeability removes the contact singularity for non-shearing particle motions, allowing rolling without slip and finite separation velocities between touching particles. Axisymmetric and transverse mobility functions are presented that describe relative particle motion under the action of prescribed forces and in linear flows. At contact, the axisymmetric mobility under the action of oppositely directed forces is$U/U_0=d_0K^{2/5}$, where$U$is the relative velocity,$U_0$is the velocity in the absence of hydrodynamic interactions and$d_0=1.332$. Under the action of a constant tangential force, a particle in contact with a permeable half-space rolls without slipping with velocity$U/U_0=d_1(d_2+\log K^{-1})^{-1}$, where$d_1=3.125$and$d_2=6.666$; in shear flow, the same expression holds with$d_1=7.280$.

Effect of microstructure and relative hardness on slurry abrasion response of heat treated En24 steel

The slurry handling industrial pumps, pipes carrying minerals, and slurry processing equipment are prone to worn out by particulate flow. The relative motion of abrasive particles suspended in slurries induces the wear of mining components in such applications. Wear by slurry abrasion is dependent on several parameters such as hardness of abrasive and the surface and service conditions. The work reported here aims at the effect of these parameters on the slurry abrasion of hardened and tempered En 24 steel. The microstructural characterization of specimens was carried out by Scanning electron microscopy, and X-ray diffraction analysis. A slurry abrasion test rig was used to evaluate the wear rate, in which slurries of silica sand, iron ore, and limestone were used as a slurry medium. The wear loss increased with the trend with an increase in abrasive hardness. The observations of worn surfaces have been explained using electron scanning electron microscopy.

Establishing the conditions for the formation of a near-wall layer of solid granular fill of a rotating drum

This paper reports the assessment of the influence of dynamic motion parameters on the formation and disappearance at the cylindrical surface of the chamber of the rotating drum of the near-wall layer of non-loose granular fill. Based on the results of experimental visualization of the flow, the effect of solidity on the behavior of granular fill was revealed. The hydrodynamic effect of fill quasi-liquefaction under the action of solidity has been established, which involves the occurrence of a connecting interaction between adjacent layers and the surface of the chamber. Conversion of shear circulation flow to homogeneous dense clustered stream with slipping and rolling without relative movement of particles was detected. The hydrodynamic characteristics of circulation flow transition to the near-wall layer mode during rotation acceleration have been defined. Such a transition is implemented by smoothly increasing the thickness of the layer when the rest of the fill is circulated at the bottom of the chamber. The effect of the rheological hysteresis of the movement of the rotating chamber fill, caused by quasi-liquefaction of non-loose granular environment, has been established. The effect implies exceeding the speed limit ωfl in the formation of a near-wall layer, at rotation acceleration, above the boundary ωdl of the layer disappearance when the rotation slows down. The manifestation of hysteresis mainly increases with an increase in Reynolds number. The intensity of increased hysteresis manifestation increases with a decrease in the degree of filling the chamber. The value of the Froud number for the ωfl and ωdl boundaries increases with the increase in Re. It has been established that at the relative particle size of the dispersed fill ψdc≈(0.065–1.04)·10‑3 and Re=30–500, Fr=1–2.9, for the ωfl boundary, and Fr=0.5–1.4, for the ωdl boundary. The Fr value for the ωfl limit was found to exceed this value for the ωdl boundary by 1.6–2.1 times. The established effects make it possible to substantiate the rational parameters for the grinding process in drum-roll mills

Multi-particle FEM modeling on hot isostatic pressing of Ti6Al4V powders

The hot isostatic pressing (HIP) of Ti6Al4V powders was systematically simulated in two dimensions by using multi-particle finite element method (MPFEM) from particulate scale. Different initial packing structures formed by three kinds of powders (i.e. mono-sized powder, binary powder, and powder with normal size distribution) were firstly constructed. Subsequently, the effects of capsule shape, HIP procedure, temperature, pressure, as well as the powder type on the densification behavior of different Ti6Al4V compacts were investigated and discussed. The macroscopic property like relative density and various microscopic properties such as coordination number, stress/strain distributions of capsule and particles, deformation degree, pore filling behavior, densification mechanism and so on were quantitatively characterized. The results indicate that a larger aspect ratio (AR) is more likely to induce local order packing structure during particle rearrangement, and the proportion of powder particles with more regular deformation of Ti6Al4V compact increases after HIP. The total strain energy and deformation mechanisms of Ti6Al4V compacts are quite different with different HIP procedures. With the rise of temperature, the equivalent total strain of both the capsule and the particles became larger and the equivalent Von Mises stress decreased after HIP. In addition, Ti6Al4V powders with different size ratios will affect the performance of the compact in HIP process. The larger the particle size, the smaller the strain acting on the particle, the closer the roundness of the particle to 1. The Ti6Al4V compacts with different particle size distributions were found to exhibit different densification mechanisms. For packing of mono-sized powder, particle rearrangement destroyed bridging structure and large pores so as to accelerate the densification process. While for the Ti6Al4V compacts formed by binary powder or the powder with normal size distribution, the densification mechanism can be inferred to the extreme deformation of small particles promoting relative rigid motion of large particles.

Optimisation design of process control strategy for biomass cracking reaction

Cone pyrolysis liquefaction reactor is the key core device of biomass energy production equipment. The study of the dynamics of the cone is of great significance to the bioenergy conversion technology. Proper control of the movement time of the heat carrier in the cone can prevent it. Biomass superheated carbonisation can increase the ratio of gas and liquid formation. It is a difficult and key technology in the design of the cone pyrolysis liquefaction reactor. The kinetic differential equation of the relative motion of heat carrier particles can be obtained by kinetic analysis and calculation. It can play a key role in the in-depth study of the structural size design of the cone and the optimisation of the structural size parameters. This study conducts a dynamic simulation of the physical simplification model of biomass energy production equipment. The computer simulation software was used to simulate the running process of the simplified cone mechanism model. A reasonable physical prototype that meets the process parameters is designed. In view of the above complex dynamic phenomena, it is necessary to comprehensively analyse various methods of dynamics, and use appropriate numerical analysis and computer-aided design methods to carry out system equipment research and design.

ПРОЦЕССЫ ТРАНСПОРТА ШЛАМА ПРИ ОЧИСТКЕ СКВАЖИН С ПРОИЗВОЛЬНОЙ ОРИЕНТАЦИЕЙ БУРОВЫХ ТРУБ, СОДЕРЖАЩИХ ЭКСЦЕНТРИЧНО РАСПОЛОЖЕННОЕ КРУГЛОЕ ЯДРО С ПОДВИЖНОЙ СТЕНКОЙ: ПРОБЛЕМЫ, РЕЗУЛЬТАТЫ, ПЕРСПЕКТИВЫ (ОБЗОР)

Актуальность работы вызвана необходимостью современной оценки решения проблем: моделирования течений смеси вязкой жидкости с твердыми частицами и взаимодействия ее со стенками устройств, предназначенных для бурения; очистки скважин с произвольной ориентацией буровых труб с эксцентрично расположенным вращающимся ядром. Цель: уяснение методов управления процессами транспорта шлама из скважин с участками вертикально-горизонтального сочленения в рамках комплексных численных и экспериментальных исследований; выдача рекомендаций в практику процессов очистки. Методы. Теоретические и практические методы исследований из смежных областей гидродинамики и тепломассопереноса реологически сложных вязких сред при решении задач о влиянии режимов течения, вращения стенок эксцентричного ядра на расположение и поведение частиц дисперсного потока, а также правомерность идеализаций явлений в смесях; методы исследований процессов, характеризующих перемещение частиц сквозь жидкость совместно, в общей массе, как это происходит при осаждении, а также в режимах: неподвижности частиц, соответствующих плотно упакованному слою; относительного движения частиц и жидкости, осложненного турбулентностью; движения частиц относительно друг друга при сложном сдвиговом течении несущей среды. Результаты. Представлен обзор результатов исследований процессов в скважинах и бурильных колоннах. Проанализированы достоинства отдельных критериальных связей поведения шлама. Уясняется правомерность допущений, возможностей ряда моделей турбулентности и их замыкающих связей в определении структуры, теплогидродинамических и диффузионных свойств смеси, условий и механизмов образования, накопления, осаждения, транспорта и отделения частиц шлама от жидкости, в которой они взвешены. Отмечается, что в приложениях очень популярны исследования транспорта шлама в полях действия центробежных, массовых сил (гравитации, вращения), вызывающих изменение плотности частиц в режимах сальтации, включающих серии отрывов/присоединений частиц, чередующихся с ударами о стенку трубного ядра. Наблюдения процесса взаимодействия твердых и жидких частиц бесконтактными средствами регистрации могут служить информацией для валидации и верификации современных RSS-моделей турбулентности (Reynolds Shear Stresses) с опорной базой из kL/kɛ-уравнений для кинетической энергии турбулентности (k) и ее интегрального масштаба (L)/скорости диссипации (ɛ). Они корректно предсказывают изменения в анизотропной неоднородной структуре сложного турбулентного течения смеси частиц шлама и жидкости. Отмечены достоинства разработок универсального алгоритма очистки скважин с выдачей сведений о: формировании шлама в произвольной точке затрубного пространства; получении минимальной скорости, обеспечивающей его образование и удаление. Сформулированы направления перспективных исследований; даны рекомендации по эффективной очистке отверстий.

Bidensity particle-laden exchange flows in a vertical duct

Buoyancy-driven exchange flow in a vertical duct is studied theoretically for a light pure fluid and a heavy fluid. The latter is a suspension composed of a Newtonian fluid and two populations of negatively buoyant particles of the same size but different densities (bidensity). In a previous study (Mirzaeian & Alba, J. Fluid Mech., vol. 847, 2018, pp. 134–160), the authors developed a lubrication model for monodensity suspension of particles of uniform size. The main observation of the monodensity study was the discovery of particle-enriched zones near heavy and light fluid fronts due to the relative motion of particles and the fluid. Distinct from the previous work, here, mismatched densities instigate a relative motion of lighter and heavier particles in addition to the movement of fluids. Other than the previously observed enrichment case, the bidensity case gives rise to a novel flow regime where there is enrichment of heavy particles but depletion of light particles near the interface. The transition to this regime is governed by a balance between the densities of heavy and light particles as well as those of light and carrying fluids for a given choice of initial volume fractions of particles. Such density balance is characterized by two dimensionless parameters comprising light and heavy particle-to-carrying-fluid density ratios. The transition mechanism is studied through additional simulations, revealing that the former increases with initial volume fraction of particles of either type, while the latter contrarily decreases. The effect of other parameters on the flow are discussed within the context of the paper.

Steering Zitterbewegung in driven Dirac systems: From persistent modes to echoes

Although zitterbewegung -- the jittery motion of relativistic particles -- is known since 1930 and was predicted in solid state systems long ago, it has been directly measured so far only in so-called quantum simulators, i.e. quantum systems under strong control such as trapped ions and Bose-Einstein condensates. A reason for the lack of further experimental evidence is the transient nature of wave packet zitterbewegung. Here we study how the jittery motion can be manipulated in Dirac systems via time-dependent potentials, with the goal of slowing down/preventing its decay, or of generating its revival. For the harmonic driving of a mass term, we find persistent zitterbewegung modes in pristine, i.e. scattering free, systems. Furthermore, an effective time-reversal protocol -- the "Dirac quantum time mirror" -- is shown to retrieve zitterbewegung through echoes.