Computation of nonlinear functionals in particle methods

We consider the numerical computation of nonlinear functionals of distribution functions approximated by point measures. Two methods are described and estimates for the speed of convergence as the number of points tends to infinity are given. Moreover, numerical results for the entropy functional are presented.     

Homotopy perturbation method for motion of a spherical solid particle in plane couette fluid flow

He’s homotopy perturbation method is applied to obtain exact analytical solutions for the motion of a spherical particle in a plane couette flow. It is demonstrated that the applied analytical method is very straightforward in comparison with existing techniques. Furthermore, it is decidedly effectual in terms of accuracy and rapid convergence. The formulation of the problem is presented in the text as well as the analytical and numerical procedures. The current results can be used in different areas of particulate flows.     

Patterning of flow and mixing in rotating radial microchannels

We demonstrate how the speed of mixing under laminar conditions can be appreciably enhanced in concurrent centrifugal flows through straight, low-aspect-ratio microchannels pointing in radial direction in the plane of rotation. The convective mixing is driven by the inhomogeneous distribution of the velocity-dependent Coriolis pseudo force and the interaction of the so-induced transverse currents with the side walls. By investigating the key impact parameters, which are the geometry of the channels and the speed of rotation, it is shown that the contact surface between two laminar flows can be folded to shorten mixing times by up to two orders of magnitude!     

Computation and visualization of discrete particle systems on gLite-based grid

Three-dimensional simulation of discrete particle systems is performed by the discrete element method (DEM) software on the gLite-based BalticGrid infrastructure. The performance of a parallel algorithm for particles exchanging processors is investigated by using a number of benchmarks. Polydispersed particle systems are visualized by a novel grid e-service VizLitG designed for convenient access and interactive visualization of remote data files located on the grid. Partial dataset transfer from the storage element is implemented in the visualization e-service. The efficiency tests of VizLitG are performed on the datasets of different sizes. Two granular problems associated with triaxial compaction and hopper discharge are solved.     

Computation of global geometric properties of solid objects

A computational scheme for determining global geometric properties of solid object models is presented. The method operates directly on the boundary representation of the model. The scheme is tested on a number of models produced by an experimental modelling system. Primitive objects combined for the tests are all represented in terms of parametric bicubic patches.     

Computation of unsteady viscous flow and aeroacoustic noise of cross flow fans

Time-accurate viscous flow solutions are sought for the prediction of unsteady flow characteristics and associated aeroacoustic blade tonal noise of a cross flow fan. The two-dimensional incompressible Navier-Stokes equations in a moving coordinate are time-accurately solved by an unstructured finite-volume method on triangular meshes, and a sliding mesh technique is utilized at the interface between the domain rotating with blades and the stationary one for allowing the unsteady interactions. An accuracy assessment of the present method is made by comparing the fan performances with experimental data for a rotational speed at 1000 rpm and the Reynolds number 5300 based on blade tip speed and chord length. With the computed unsteady viscous flow solutions, sound pressure is predicted using Curle’s equation and narrow-band noise characteristics of three impellers with a uniform and two random pitch (type-A and -B) blades are compared by their sound pressure level spectra. Also, the frequency modulations of the blade passing frequency noise by random pitch fans are discussed.     

Computing the velocity of a rotating flow

To compute the time-dependent flow of a rotating incompressible fluid we consider the velocity–vorticity formulation of the Navier–Stokes equations in cylindrical coordinates. In the numerical method employed the velocity field at each time-step is found as the least squares solution of an overdetermined system of linear equations, Ax=b. We consider how to compute x using the preconditioned conjugate gradient algorithm for least squares (PCGLS) on a distributed parallel computer. The various aspects of using a parallel computer are discussed, and results for a wide range of parallel computers are presented. The parallel speed-up depends on the architecture but is typically about 80% of the number of processors used.     

Dynamics of rotating paramagnetic particle chains simulated by particle dynamics,Stokesian dynamics and lattice Boltzmann methods

Paramagnetic particles, when subjected to external unidirectional rotating magnetic fields, form chains which rotate along with the magnetic field. In this paper three simulation methods, particle dynamics (PD), Stokesian dynamics (SD) and lattice Boltzmann (LB) methods, are used to study the dynamics of these rotating chains. SD simulations with two different levels of approximations—additivity of forces (AF) and additivity of velocities (AV)—for hydrodynamic interactions have been carried out. The effect of hydrodynamic interactions between paramagnetic particles under the effect of a rotating magnetic field is analyzed by comparing the LB and SD simulations, both of which include hydrodynamic interactions, with PD simulations in which hydrodynamic interactions are neglected. It was determined that for macroscopically observable properties like average chain length as a function of Mason number, reasonable agreement is found between all the three methods. For microscopic properties like the force distribution on each particle along the chain, inclusion of hydrodynamic interaction becomes important to understand the underlying physics of chain formation. Any opinion, findings and conclusions or recommendations expressed in this material are those of the authors and do not necessarily reflect the views of the National Science Foundation.     

Numerical simulation of flow and heat transfer in radially rotating microchannels

Investigation of fluid flow and heat transfer in rotating microchannels is important for centrifugal microfluidics, which has emerged as an advanced technique in biomedical applications and chemical separations. The centrifugal force and Coriolis force, arising as a consequence of the microchannel rotation, change the flow pattern significantly from the symmetric profile of a non-rotating channel. Successful design of microfluidic devices in centrifugal microfluidics depends on effectively regulating these forces in rotating microchannels. In this work, we have numerically investigated the flow and heat transfer in rotating rectangular microchannel with continuum assumption. A pressure-based finite-volume technique with a staggered grid was applied to solve the steady incompressible Navier–Stokes and energy equations. It was observed that the effect of Coriolis force was determined by the value of the non-dimensional rotational Reynolds number (Re _ω ). By comparing the root mean square deviation of the axial velocity profiles with the approximate analytical results of purely centrifugal flow for different aspect ratios (AR = width/height), a critical rotational Reynolds number (Re _ω,cr) was computed. Above this value of (Re _ω,cr), the effect of secondary flow becomes dominant. For aspect ratios of 0.25, 0.5, 1.0, 2.0, 4.0 and 9.09, this critical rotational Reynolds number (Re _ω,cr) was found to be 14.0, 5.5, 3.8, 4.7, 6.5 and 10.0, respectively.     

High-gain feedback control of rotating stall in axial flow compressors

High gain feedback is used to improve the performance of bifurcation control designs for the mitigation of stall in axial flow compressors. The maximum steady-state pressure rise is maintained for a range of operating conditions beyond the stall/surge line. Analysis and numerical results are presented to support the conclusions.     

Computation of MHD flow due to moving boundaries

A non-iterative numerical scheme is presented which computes in a single iteration the steady, laminar flow of a viscous, incompressible, electrically conducting fluid caused by moving boundaries in the presence of a transverse magnetic field. It also eliminates the possible error induced by taking the value of numerical infinity (representing the unbounded domain of the flow) as a finite number. The scheme is based on implicit use of infinite series of exponentials for velocity components. The issue of convergence of these series is also discussed. An asymptotic solution valid for large values of M, the Hartmann number, and an approximate solution valid for any value of M are further developed. In particular, the case of axisymmetric magnetohydrodynamic (MHD) flow due to a stretching sheet has been dealt with in some detail. A comparison has been made of the merits of various techniques used in the paper and appropriate conclusions are drawn.     

移动边缘计算中基于粒子群优化的计算卸载策略

计算卸载作为移动边缘计算（MEC）中降低时延与能耗的手段之一,通过合理的卸载决策能够降低工业成本。针对工业生产线中部署MEC服务器后时延变长和能耗增高的问题,提出了一种基于粒子群优化（PSO）算法的计算卸载策略PSAO。首先,将实际问题建模为时延模型与能耗模型。由于是针对时延敏感型的应用,因此将模型转化为在能耗约束条件下的最小化时延问题,使用惩罚函数来平衡时延与能耗。其次,根据PSO算法优化后得到计算卸载决策向量,通过集中控制的方式使每一个计算任务合理分配到对应的MEC服务器。最后,通过仿真实验,对比分析了本地卸载策略、MEC基准卸载策略、基于人工鱼群算法（AFSA）的卸载策略以及PSAO的时延数据,PSAO的平均总时延远远低于其他三种卸载策略,PSAO比原来系统总代价降低了20%。实验结果表明,PSAO策略能够降低MEC中的时延,均衡MEC服务器的负载。     

Three-dimensional hydrodynamic flow and particle focusing using four vortices Dean flow

We present a three-dimensional (3D) hydrodynamic focusing device built on a single-layer platform using single sheath flow. Despite the simple structure and operation, the device not only achieves narrow focusing of a sample fluid or particles but also switches the cross-sectional size and lateral position of the sample stream. The focusing mechanism utilizes four Dean vortices generated in a high-speed flow through a curved channel. Theoretical calculations, numerical simulations, and an experimental study demonstrated that the device could focus microparticles that resemble human platelets in terms of particle size and density in a single-stream manner. Further simulation study suggested that the device could focus most cell sizes used in flow cytometry with a throughput of 200,000 cells s^?1. In addition, the device can function as a 3D liquid-core/liquid-cladding (L2) optical waveguide by introducing a core liquid with a refractive index higher than that of the cladding.     

Computation of the integrated flow of particles between polygons

To quantify the flow of particles over a heterogeneous area, some models require the integration of a pointwise dispersal function over source and target polygons. This calculation is a non-trivial task and may require a great deal of computing time. In this paper, an efficient and accurate algorithm is presented to integrate general individual dispersal functions between pairs of convex or non-convex polygons. Geometric calculations are performed using standard tools from computational geometry. Numerical integration is then performed either by a grid method or by an adaptive cubature method. The procedure is illustrated with a case study. It is shown that the cubature method is much more efficient than the grid method and that its error estimates are accurate. The algorithm is implemented in a C++ program, Califlopp.     

Non-coaxial rotating flow of viscous fluid with heat and mass transfer

Heat and mass transfer in unsteady non-coaxial rotating flow of viscous fluid over an infinite vertical disk is investigated. The motion in the fluid is induced due to two sources. Firstly, due to the buoyancy force which is caused because of temperature and concentration gradients. Secondly, because of non-coaxial rotation of a disk such that the disk executes cosine or since oscillation in its plane and the fluid is at infinity. The problem is modeled in terms of coupled partial differential equations with some physical boundary and initial conditions. The dimensionless form of the problem is solved via Laplace transform method for exact solutions. Expressions for velocity field, temperature and concentration distributions are obtained, satisfying all the initial and boundary conditions. Skin friction, Nusselt number and Sherwood number are also evaluated. The physical significance of the mathematical results is shown in various plots and is discussed for several embedded parameters. It is found that magnitude of primary velocity is less than secondary velocity. In limiting sense, the present solutions are found identical with published results.

     

Computation of discontinuous optical flow by domain decomposition and shape optimization

A well-known method for the reconstruction of motion fields from noisy image data is to determine flow fields by the minimization of a quadratic functional. The first approach of this class has been proposed by Horn and Schunck (1981). A drawback of such approaches is that an explicit representation of the discontinuities of the motion field is lacking and that, in general, the resulting flow fields approximate the motion fields only badly at the corresponding locations in the image plane. In this article, we discuss the possibility to improve the results by hypothesizing the qualitative structure of the motion field in terms of certain parameters. We decompose the image plane into disjoint sets, restrict the domain of definition of the functionals to these sets, and use the hypotheses to deform and to move the boundaries of the sets within the image plane. We discuss the range of applicability of this new technique and illustrate the algorithm by numerical examples. This article is a revised and extended version of Schnörr (1990).This work has been supported by the PROMETHEUS programme while the author was with the Fraunhofer-Institut (IITB) at Karlsruhe.     

虚拟战场环境中的态势标绘与表现

针对军事指挥所现状,设计并实现了一个态势标绘系统,能提供在电子地图上的二维标绘和在虚拟战场环境中的三维标绘两种标绘手段。重点讨论了三维态势标绘中涉及到的地形高程匹配、碰撞检测与碰撞响应、特殊信息和特殊效果的表现等关键技术,并提出了一种二维标绘和三维标绘的实时转换方法,从而实现了二维态势与三维态势的联动表现。     

Superparamagnetic particle dynamics and mixing in a rotating capillary tube with a stationary magnetic field

The dynamics of superparamagnetic particles subject to competing magnetic and viscous drag forces have been examined with a uniform, stationary, external magnetic field. In this approach, competing drag and magnetic forces were created in a fluid suspension of superparamagnetic particles that was confined in a capillary tube; competing viscous drag and magnetic forces were established by rotating the tube. A critical Mason number was determined for conditions under which the rotation of the capillary prevents the formation of chains from individual particles. The statistics of chain length was investigated by image analysis while varying parameters such as the rotation speed and the viscosity of the liquid. The measurements showed that the rate of particle chain formation was decreased with increased viscosity and rotation speed; the particle dynamics could be quantified by the same dimensionless Mason number that has been demonstrated for rotating magnetic fields. The potential for enhancement of mixing in a bioassay was assessed using a fast chemical reaction that was diffusion-limited. Reducing the Mason number below the critical value, so that chains were formed in the fluid, gave rise to a modest improvement in the time to completion of the reaction.     

GIS中Jpg图形的地图绘制

利用ArcGIS软件中的ArcMap模块对Jpg图形进行地理图像配准,对Jpg图形加控制点并进行点的地理位置设置,可直接进行地图设置,也可根据这些控制点的信息与该软件中的数据文件进行叠加,这样就可将该图形作为一个图层,并与数据文件一起,运用GIS中的一些特性对Jpg图片进行处理,如加入经纬度设置,加入站点信息等。通过这种方法,在面对精细的地理数据文件短缺的情况下,可以利用扫描地图或网络截屏等方式,与GIS软件结合,为初学者处理图片提供方便。