相互碰撞的圆粒子在竖直通道中沉降的数值研究

采用格子Boltzmann方法,数值模拟了考虑相互碰撞的两圆粒子的沉降,分析了Re数、初始相对位移及通道宽度对粒子沉降的影响.结果表明,在0.1<Re<20范围内,粒子沉降具有周期性.Re数越大,两圆粒子的相互作用越强,粒子横向位移的幅度也越大.在大Re数时,沉降的过程是两个粒子交替领先;在较小Re数时,当后面的粒子接近的时候,领先的粒子被向右侧推了一段后仍会继续领先;对中等Re数,原先在后面的粒子在第一次加速后将取得领先位置并一直保持下去.粒子的初始分布位置对沉降的形态影响不大.管道宽度变化时,粒子总的沉降特性不变,而周期改变,管道越宽,周期越长.

圆环上自由运动粒子的路径积分解法

用路径积分的方法求解了圆环上自由运动粒子的传播子,并和演化算符的方法进行了比较,发现使用Feynman路径积分的方法更加简便.

基于粒子群圆检测的无人机目标定位算法

无人机在室内等复杂环境中飞行时,存在GPS信号较弱、惯性传感器累计误差较大等问题,导致无法实现室内的精准定位。本文提出一种基于粒子群圆检测算法的无人机目标定位方法,该方法通过OpenCV视觉模组进行图像预处理,并通过增量式PID(Proportion Integration Differentiation)与图像滤波相结合的粒子群圆检测算法获得目标标靶的核心坐标与半径等参数,通过对运动的实时控制、增加判断条件等提高无人机的标定效率与准确率。实验结果表明,该方法能够将无人机的位置调整时间控制在4 s以内,且将标定准确率提高到了90%,极大地缩短了无人机的标定时间,提升了无人机的位置标定准确率。

Nanoparticle Transport and Coagulation in Bends of Circular Cross Section via a New Moment Method

Transport of nanoparticles and coagulation is simulated with the combination of CFD in a circular bend. The Taylor-expansion moment method(TEMOM)is employed to study dynamics of nanoparticles with Brownian motion,based on the flow field from numerical simulation.A fully developed flow pattern in the present simulation is compared with previous numerical results for validating the model and computational code.It is found that for the simulated particulate flow system,the particle mass concentration,number concentration,particle polydispersity, mean particle diameter and geometric standard deviation over cross-section increase with time.The distribution of particle mass concentration at different time is independent of the initial particle size.More particles are concen-trated at outer edge of the bend.Coagulation plays more important role at initial stage than that in the subsequent period.The increase of Reynolds number and initial particle size leads to the increase of particle number concentration.The particle polydispersity,mean particle diameter and geometric standard deviation increase with decreasing Reynolds number and initial particle size.

Phase—Locking Dynamics in Coupled Circle—Map Lattices

The phase-locking dynamics in 1D and 2D lattices of non-identical coupled circle maps is explored. Aglobal phase locking can be attained via a cascade of clustering processes with the increase of the coupling strength.Collective spatiotemporal dynamics is observed when a global phase locking is reached. Crisis-induced desynchronizationis found, and its consequent spatiotemporal chaos is studied.

Coupled 3D discrete-continuum numerical modeling of pile penetration in sand

A coupled discrete-continuum simulation incorporating a 3D aspect and non-circular particles was performed to analyze soil-pile interactions during pile penetration in sand.A self-developed non-circular particle numerical simulation program was used which considered sand near the pile as interacted particles using a discrete element method;the sand away from the pile was simulated as a continuous medium exhibiting linear elastic behaviors.The domain analyzed was divided into two zones.Contact forces at the interface between the two zones were obtained from a discrete zone and applied to the continuum boundaries as nodal forces,while the interface velocities were obtained from the continuum zone and applied to the discrete boundaries.We show that the coupled discrete-continuum simulation can give a microscopic description of the pile penetration process without losing the discrete nature of the zone concerned,and may significantly improve computational efficiency.

Velocity Profiles between Two Baffles in a Horizontal Circular Tube

The shell and tube heat exchanger is an essential part of a power plant for recovering heat transfer between the feed water of a boiler and the wasted heat.The baffles are also an important element inside the heat exchanger.Internal materials influence the flow pattern in the bed.The influence of baffles in the velocity profiles was observed using a three-dimensional particle image velocimetry around baffles in a horizontal circular tube.The velocity of the particles was measured before the baffle and between them in the test tube.Results show that the flows near the front baffle flow were parallel to the vertical wall,and then concentrate on the upper opening of the front baffle.The flows circulate in the front and rear baffles.These flow profiles are related to the Reynolds number(Re) or the flow intensity.The velocity profiles at lower Re number showed a complicated mixing,concentrating on the lower opening of the rear baffle as front wall.Swirling flow was employed in this study,which was produced using tangential velocities at the inlet.At the entrance of the front baffle,the velocity vector profiles with swirl were much different from that without swirl.However,velocities between two baffles are not much different from those without swirl.

The effects of attached flexible tail length on the flow structure of an oscillating cylinder

Particle Imaging Velocimetry （PIV） is utilized to investigate the flow structures of an oscillating cylinder attached to a flexible tail. At the same oscillation frequency and amplitude, the mean streamwise velocity along the wake central-line and the mean vertical velocity around the trailing edge of the flexible tail can be greatly increased with the tail length. Meanwhile, the longer the flexible tail is, the larger its deformation is. In order to study the influence of flexible tail length on the wake pattern of the experimental model, the relationships between the swirling strength Aci of vortex structure near the tail end and the velocity of tail trailing edge have been revealed. Moreover, the convection tracks and the Aci of vortex cores for different flexible tails are discussed.

PIV measurements of turbulent jets issuing from triangular and circular orifice plates

The present study experimentally investigated the near-field flow mixing characteristics of two turbulent jets issuing from equilateral triangular and circular orifice plates into effectively unbounded surroundings,respectively.Planar particle image velocimetry(PIV) was applied to measure the velocity field at the same Reynolds number of Re=50,000,where Re = UeDe /with Ue being the exit bulk velocity and the kinematic viscosity of fluid,D e the equivalent diameters.The instantaneous velocity,mean velocity,Reynolds stresses were obtained.From the mean velocity field,the centreline velocity decay rate and half-velocity width were derived.Comparing the mixing characteristics of the two jets,it is found that the triangular jet has a faster mixing rate than the circular counterpart.The triangular jet entrainments with the ambient fluid at a higher rate in the near field.This is evidenced by a shorter unmixed core,faster Reynolds stress and centreline turbulence intensity growth.The primary coherent structures in the near field are found to break down more rapidly in the triangular jet as compared to the circular jet.Over the entire measurement region,the triangular jet maintained a higher rate of decay and spread.Moreover,all components of Reynolds stress of the triangular jet appear to reach their peaks earlier,and then decay more rapidly than those of the circular jet.In addition,the axis-switching phenomenon is observed in the triangular jet.

Comnutational Models for New Fiber Ootic Tweezers

This paper discusses the calculation of the trapping forces in optical tweezers using a combination of the finite differences time domain （FDTD） method and the Lorentz force on electric dipoles. The results of 2D simulations of the trapping of a circular particle by a waveguide with a circular tip are presented and discussed.

Diffusion-Limited Aggregation with Polygon Particles

Diffusion-limited aggregation （DLA） assumes that particles perform pure random walk at a finite tem- perature and aggregate when they come close enough and stick together. Although it is well known that DLA in two dimensions results in a ramified fractal structure, how the particle shape influences the formed morphology is still un- clear. In this work, we perform the off-lattice two-dimensional DLA simulations with different particle shapes of triangle, quadrangle, pentagon, hexagon, and octagon, respectively, and compare with the results for circular particles. Our results indicate that different particle shapes only change the local structure, but have no effects on the global structure of the formed fractal duster. The local compactness decreases as the number of polygon edges increases.