Linear stability analysis on a spherical particle growing from a binary melt under the far-field flow

The solutions of temperature and solute fields around a spherical crystal growing from a binary melt under the far-field flow are obtained.Based on the results,a linear stability analysis on the spherical interface growing from the binary melt under the far-field flow is performed.It is found that the constitutional supercooling effect ahead of the spherical crystal interface under the far-field flow is enhanced compared with that without the flow.The growth rate of the perturbation amplitude at the up-wind side of the spherical crystal interface is larger than that at the down-wind side.The critical stability radius of the crystal interface decreases with the increasing far-field flow velocity.Under the far-field flow,the whole spherical interface becomes more unstable compared with that without the flow.

Calculation of terminal velocity in transitional flow for spherical particle

The terminal velocity has been widely used in extensive fields,but the complexity of drag coefficient expression leads to the calculation of terminal velocity in transitional flow e1 < Re 6 1000 T with much more difficulty than those in laminar flow eRe 6 1T and turbulent flow eRe P 1000 T.This paper summarized and compared 24 drag coefficient correlations,and developed an expression for calculating the terminal velocity in transitional flow,and also analyzed the effects of particle density and size,fluid density and viscosity on terminal velocity.The results show that 19 of 24 previously published correlations for drag coefficient have good prediction performance and can be used for calculating the terminal velocity in the entire transitional flow with higher accuracy.Adapting two dimensionless parameters(w*,d*),a proposed explicit correlation,w*=-25:68654 exp(-d*/77:02069)+24:89826,is attained in transitional flow with good performance,which is helpful in calculating the terminal velocity.

THE MOTION OF A SPHERICAL PARTICLE IN THE STOKES FLOW OUTSIDE A CIRCULAR ORIFICE

For any study ofa suspension entering a pore, the knowledge of the force and moment exerted on a solute particle in an arbitrary position outside the pore is essential, 'This paper for the first lime presents approximate analytical expressions (in closed form) of all the twelve force and moment coefficienis for a sphere outsied a circular orifice, on the basis of a number of discrete data computed by Yan et al(1987).These coefficients are then applied to calculate the trajectory and angular velocity of a spherical particle approaching the pore at zero Reynolds number. The trajectory is in excellent agreement with the available experimental results. An analysis of the relative importance of the coefficients shows that the rotation effect cannot be neglected near the pore opening or near the wall, and that the lateral force effect must be taken into account in the neighborhood of the edge of the pore opening. It is due to neglecting these factors that previous theoretical results deviate from the experimental ones near the pore opening. The effects of the ratio of the particle to pore radii as well as the influences of the graritytbuoyance on the particle trajectory, velocity distribution and rotation are discnssed in detail. It is pointed out that in the experiments of neutrally-buoyant suspensions, the restriction on the density of the particle is most demanding for a large particle size.The expressions of forces and moments presenled herein are complete, relatively accurate and convenient, thus providing a good prerequisite for further studies of any problems involving the entrance of particles to a pare.

Flow Behaviors of Non-spherical Granules in Rectangular Hopper

Flow behaviors of four kinds of granular particles(i.e. sphere,ellipsoid,hexahedron and binary mixture of sphere and hexahedron) in rectangular hoppers were experimentally studied. The effects of granular shape and hopper structure on flow pattern,discharge fraction,mean particle residence time and tracer concentration distribu-tion were tested based on the visual observation and particle tracer technique. The results show that particle shape affects significantly the flow pattern. The flow patterns of sphere,ellipsoid and binary mixture are all parabolic shape,and the flow pattern shows no significant difference with the change of wedge angle. The flowing zone be-comes more sharp-angled with the increasing outlet size. The flow pattern of hexahedron is featured with straight lines. The discharge rates are in increasing order from hexahedron,sphere,binary mixture to ellipsoid. The dis-charge rate also increases with the wedge angle and outlet size. The mean particle residence time becomes shorter when the outlet size increases. The difference of mean particle residence time between the maximum and minimum values decreases as the wedge angle increases. The residence time of hexahedron is the shortest. The tracer concen-tration distribution of hexahedron at any height is more uniform than that of binary mixture. The tracer concentra-tion of sphere in the middle is lower than that near the wall,and the contrary tendency is found for ellipsoid particles.

Preferential orientation of tracer spheroids in turbulent channel flow

Axis-symmetric spheroids, such as rod-like and disk-like particles, have been found to orient preferentially in near-wall turbulence by both experiment and numerical simulation. In current work we examined the orientation of inertialess spheroids in a turbulent channel flow at medium friction Reynolds number Reτ=100 given based on the half of channel height. Both elongated prolate spheroid and flat oblate spheroid are considered and further compared with the reference case of spherical particle. The statistical results show that in near wall region the prolate spheroids tend to align in the streamwise direction while the oblate spheroids prefer to orient in the wallnormal direction, which are consistent with earlier observation in low Reynolds number (Reτ=180)wall turbulence. Around the channel center we found that the orientation of spheroids is not fully isotropic, even though the fluid vorticity are almost isotropic. The mechanism that gives rise to such particle orientations in wall-turbulence has been found to be related to fluid Lagrangian stretching and compression (Zhao and Andersson 2016). Therefore, we computed the left Cauchy-Green strain tensor along Lagrangian trajectories of tracer spheroids in current flow field and analyzed the fluid Lagrangian stretching and compression. The results indicated that, similar to the earlier observations, the directions of the Lagrangian stretching and compression in near-wall region are in the streamwise and wall-normal directions, respectively. Furthermore, cross over the channel the prolate spheroids aligned with the direction of Lagrangian stretching but oblate spheroids oriented with the direction of Lagrangian compression. The weak anisotropy of orientations of fluid Lagrangian stretching and compression observed at the channel center could be the reason for the aforementioned modest anisotropic orientation of spheroids in channel central region.

Global Static Solutions of the Spherically Symmetric Vlasov-Einstein-Maxwell (VEM) System for Low Charge

We consider the VEM system in the context of spherical symmetry and we try to establish a global static solutions with isotropic pressure that approaches Minkowski spacetime at infinity and have a regular center. To be in accordance with numerical investigation we take here low charge particles.

A New Method of the Production of the THZ Electromagnetic Wave and Electromagnetic Paticle’s Flows and Other Application

This paper reveals that a new method of the production of the THZ electromagnetic wave and electromagnetic particle’s flows is using a solid-consisted body, and the solid-consisted body is formed of the polylayer’s parallel nonferromagnetic knitted conductance’s nets: when a large powered (around 1000 W) microwave (2.45 G) once comes into the solid-consisted body, a change from microwave to electromagnetic particle’s flows takes place and it does not have a place-phase of the wave by its reflection and transmission between net and other net limitless times;and when the surface-induction’s current produces the electron’s transition in the net-holes, the THZ electro-magnetic wave is produced, and the THZ electromagnetic wave is divided into two parts: single frequency and continuous spectrum. When the THZ electromagnetic wave and the electromagnetic particle’s flows illuminate the living beings, the living beings will live better.

改进的粒子群算法优化TSFNN的交通流预测

为提高T-S模糊神经网络在交通流量预测的准确性,提出了一种改进的粒子群算法优化T-S模糊神经网络预测交通流量的算法。该算法利用改进粒子群算法通过群体极值进行t分布变异,使算法跳出局部收敛,使用改进的粒子群算法优化T-S模糊神经网络,能够优化网络参数配置,进而提高网络的预测精度。利用优化后的T-S模糊神经网络对实测交通流量进行预测,实验仿真表明优化的T-S模糊神经网络可有效提高交通流量预测精度,减小预测误差。

改进粒子群优化Takagi-Sugeno模糊径向基函数神经网络的非线性系统建模

针对复杂非线性系统建模的难点问题,提出了一种基于改进的粒子群优化算法(PSO)优化的T-S模糊径向基函数(RBF)神经网络的新型系统建模算法。该算法将T-S模糊模型良好的可解释性及RBF神经网络的自学习能力相结合,构成T-S模糊RBF神经网络用于系统建模,并采用动态调整惯性权重的改进的PSO算法结合递推最小二乘算法实现网络参数的优化调整。首先,利用所提算法进行了非线性多维函数的逼近仿真,仿真结果均方差(MSE)为0.00017,绝对值误差不大于0.04,逼近精度较高;又将该算法用于建立动态流量软测量模型,并进行了相关的实验研究,动态流量测量结果平均绝对误差小于0.15 L/min,相对误差为1.97%,基本满足测量要求,并优于已有算法。上述仿真及实验研究结果表明,所提算法对于复杂非线性系统具有较高的建模精度和良好的自适应性。

Ray tracing particle image velocimetry-Challenges in the application to a packed bed

Ray tracing Particle Image Velocimetry(RT-PIV)is an optical technique for high resolution velocity measurements in challenging optical systems,such as transparent packed beds,that uses ray tracing to correct for distortions introduced by transparent geometries in the light paths.The ray tracing based correction is a post processing step applied to the raw PIV particle images before classical PIV evaluation.In this study,RT-PIV is performed in the top layer of a body centred cubic(bcc)sphere packing with gaseous flow,where optical access is obtained by the use of transparent N-BK7 glass balls with a diameter of d=40 mm.RT-PIV introduces new experimental and numerical challenges,for example a limited field of view,illumination difficulties,a very large required depth of field and high sensitivity to geometric parameters used in the ray tracing correction.These challenges and their implications are the main scope and discussed in the present work.Further,the validation of the ray tracing reconstruction step is presented and examples for the obtained corrected vector fields in a packed bed are given.The results show the strength of the method in reconstructing velocity fields behind transparent spheres that would not have been accessible by optical measurement techniques without the ray tracing correction.

Efficient approaches of determining the motion of a spherical particle in a swirling fluid flow using weighted residual methods

The motion of a spherical particle released in a swirling fluid flow is studied employing the least-squares method and method of moments. The governing equations are obtained and solved employing the two methods. The accuracy of the results is examined against the results of a fourth-order Runge-Kutta numer- ical method. The effects of various parameters, namely the initial radius, initial radial velocity, initial angular velocity, and drag-to-inertia ratio, on the non-dimensional velocity profiles and particle position distribution are considered. The results show that the radial velocity increases over time while the angular velocity decreases, and that an increase in the initial radial velocity increases the particle radial distance and angular velocity but decreases the radial velocity profile.

EFFECT OF NON-SPHERICAL PARTICLES ON THE FLUID TURBULENCE IN A PARTICULATE PIPE FLOW

In the non-spherical particulate turbulent flows, a set of new fluidfluctuating velocity equations with the non-spherical particle source term were derived, then a newmethod, which treats the slowly varying functions and rapidly varying functions separately, wasproposed to solve the equations, and finally the turbulent intensity and the Reynolds stress of theflu-id were obtained by calculating the fluctuating velocity statlsti-cally. The equations andmethod were used to a paniculate tur-bulent pipe flow. The results show that the turbulent intensityand the Reynolds stress are decreased almost inverse proportion-ally to the fluctuating velocityratio of particle to fluid. Non-spherical particles have a greater suppressing effect on thetur-bulence than the spherical particles. The particles with short re-laxation time reduce theturbulence intensity of fluid, while the particles with long relaxation time increase the turbulenceinten-sity of fluid. For fixed particle and fluid, the small particles sup-press the turbulence andthe large particles increase the turbu-ience.

Flow-regime transitions in fluidized beds of non-spherical particles

Fluidized beds frequently involve non-spherical particles, especially if biomass is present. For spheri- cal particles, numerous experimental investigations have been reported in the literature. In contrast, complex-shaped particles have received much less attention. There is a lack of understanding of how par- ticle shape influences flow-regime transitions. In this study, differently shaped Geldart group D particles are experimentally examined. Bed height, pressure drop, and their respective fluctuations are analyzed. With increasing deviation of particle shape from spheres, differences in flow-regime transitions occur with a tendency for the bed to form channels instead of undergoing smooth fluidization. The correlations available in the literature for spherical particles are limited in their applicability when used to predict regime changes for complex-shaped particles. Hence, based on existing correlations, improvements are derived.

Behaviors of Spherical and Nonspherical Particles in a Square Pipe Flow

The lattice Boltzmann method(LBM)for multicomponent immiscible fluids is applied to the simulations of solid-fluid mixture flows including spherical or nonspherical particles in a square pipe at Reynolds numbers of about 100.A spherical solid particle is modeled by a droplet with strong interfacial tension and large viscosity,and consequently there is no need to track the moving solid-liquid boundary explicitly.Nonspherical(discoid,flat discoid,and biconcave discoid)solid particles are made by applying artificial forces to the spherical droplet.It is found that the spherical particle moves straightly along a stable position between the wall and the center of the pipe(the Segr´e-Silberberg effect).On the other hand,the biconcave discoid particle moves along a periodic helical path around the center of the pipe with changing its orientation,and the radius of the helical path and the polar angle of the orientation increase as the hollow of the concave becomes large.

Standard Model Masses Explained

The Standard Model of particle physics requires nine lepton and quark masses as inputs, but does not incorporate neutrino masses required by neutrino oscillation observations. This analysis addresses these problems, explaining Standard Model particle masses by describing fundamental particles as solutions of Einstein’s equations, with radii 1/4 their Compton wavelength and half of any charge on rotating particles located on the surface at each end of the axis of rotation. The analysis relates quark and lepton masses to electron charge and mass, and identifies neutrino masses consistent with neutrino oscillation observations.

Oxidation Kinetics of Aluminum Powders in a Gas Fluidized Bed Reactor in the Potential Application of Surge Arresting Materials

In this technical paper, the oxidation mechanism and kinetics of aluminum powders are discussed in great details. The potential applications of spherical aluminum powders after oxidation to be part of the surging arresting materials are discussed. Theoretical calculations of oxidation of spherical aluminum powders in a typical gas fluidization bed are demonstrated. Computer software written by the author is used to carry out the basic calculations of important parameters of a gas fluidization bed at different temperatures. A mathematical model of the dynamic system in a gas fluidization bed is developed and the analytical solution is obtained. The mathematical model can be used to estimate aluminum oxide thickness at a defined temperature. The mathematical model created in this study is evaluated and confirmed consistently with the experimental results on a gas fluidization bed. Detail technical discussion of the oxidation mechanism of aluminum is carried out. The mathematical deviations of the mathematical modeling have demonstrated in great details. This mathematical model developed in this study and validated with experimental results can bring a great value for the quantitative analysis of a gas fluidization bed in general from a theoretical point of view. It can be applied for the oxidation not only for aluminum spherical powders, but also for other spherical metal powders. The mathematical model developed can further enhance the applications of gas fluidization technology. In addition to the development of mathematical modeling of a gas fluidization bed reactor, the formation of oxide film through diffusion on both planar and spherical aluminum surfaces is analyzed through a thorough mathematical deviation using diffusion theory and Laplace transformation. The dominant defects and their impact to oxidation of aluminum are also discussed in detail. The well-controlled oxidation film on spherical metal powders such as aluminum and other metal spherical powders can potentially become an important part of switch devices of surge arresting materials, in general.

基于DEM的滑坡碎屑流运动堆积特性研究

滑坡碎屑流灾害往往具有瞬时性和极强的破坏性,传统监测方法很难对滑坡碎屑流的运动过程进行观察和研究,故根据滑坡碎屑流的堆积形态研究滑坡碎屑流灾害演变规律,为滑坡碎屑流的灾害防护提供理论支持。通过运用离散元的方法,定量地研究场地偏转α和分形维数D对滑坡碎屑流运动堆积特性及滑坡碎屑流堆积体颗粒反序结构特征的影响规律。研究结果表明:滑坡碎屑流颗粒的堆积宽度、冲程和堆积面积随着分形维数的增大而减少,分形维数对堆积体的堆积形态影响较小,颗粒反序结构特征的显著性随着分形维数的增大而减弱;滑坡碎屑流颗粒的堆积宽度、冲程和堆积面积随着偏转角增大而增大,并且冲程与场地偏转角关系模型为二次抛物线模型,堆积体最大厚度随着场地偏转角度的增大而逐渐减小,颗粒反序结构特征的显著性随分形维数的增大而减弱;根据滑坡碎屑流颗粒间的接触特性验证了颗粒间的剪切作用是影响颗粒反序结构的主要因素。

非球形颗粒沉降动力学研究进展

固体颗粒在流体中的流动行为在自然界和工业生产中都是普遍存在的。对于固体颗粒在流体中的沉降运动的研究大多局限于球形颗粒。对于球形颗粒运动特征的研究,科学家们已经取得了丰硕的成果。但是,对于非球形颗粒在流体中的运动特性的研究则相对较少。事实上,实际工业应用中的颗粒很少是球形。回顾了近年来关于颗粒沉降的相关研究,对颗粒沉降在实验研究、理论以及数值模拟的研究成果进行了综述。以理论为基础,实验工作与数值模拟相辅相成;一旦得到实验数据的验证,模拟就可以更深入地了解时间尺度和流体结构,这些流体结构是导致非球形颗粒在沉降时发生方向演变的原因。最后,提出非球形颗粒沉降未来的研究方向。

几何参数对非对称球形弯头气力输运颗粒流动的影响

气力输送在工业生产中的应用越来越广泛,减少输送过程中的能量损耗、提高颗粒运送效率变得尤为重要。以90°气力输送管道弯头为研究对象,设计了一种非对称球形弯头,以改善弯头内颗粒流动及分布特性,提高输送效率。采用CFD-DEM耦合方法,讨论了弯头球体半径和进出口管道偏心距对颗粒流动分布特性的影响。结果表明:进、出口偏心距增大,旋流增强,弯头内部颗粒堆积减少,颗粒分布更均匀,气体能量转化效率提高;球体半径增大,颗粒能量损耗增加,气体能量转化效率降低,更容易产生堆积。

Modelling incompressible flows and fluid-structure interaction problems with smoothed particle hydrodynamics:Briefing on the 2017 SPHERIC Beijing International Workshop

The 2017 SPHERIC Beijing International Workshop（or SPHERIC Beijing 2017） was held at Peking University, in China,on October 17-20, 2017. This is the first time that the SPHERIC Workshop was held out of Europe. We are delighted to present nine contributions in this Special Column of the Journal of Hydrodynamics, and take this opportunity to announce that the 13 th SPHERIC Workshop（or SPHERIC 2018） will be held in Galway, Ireland in 2018 by the National University of Ireland, and the SPHERIC International Workshop in Harbin, China in 2019 by the Harbin Engineering University.