Transmission fluctuation method for particle analysis in multiphase flow

The transmission fluctuations can be used for measurements on particle size and particle concentration in multiphase flows. In Gregory’s method, the beam diameter is required to be much larger than the particle diameter, which limits the application seriously. In this work, we introduce a new method of the transmission fluctuation measurement, in which the beam diameter can be less, equal to and larger than the particle diameter. The theoretical analysis proves that, when the beam-to-particle diameter ratio is within the range of 0.05 and 10, the new method is able to achieve satisfying measurement results. However, Gregory’s method is only suitable in the range of 5 and 10. Therefore, this new method enhances the transmission fluctuation measurements greatly.     

Measuring particle size distribution using LED-illumination

A particle/droplet image analysis (PDIA) system employing LED-illumination was designed. Freezing the moving droplets using high speed camera instead of stroboscopic illumination, the system had no requirement to synchronize the backlight and the camera. It featured low cost, low power consumption and simple optical configuration in comparison to laser-based systems. Only focused droplets in images were counted. Given the sample size of the system was relatively small, an upper-limit lognormal distribution was used to fit the actual data to represent the spray patterns. The accuracy of the diameter measurement was verified using precisely manufactured balls. Comparisons with two laser-based systems were given and the system’s capacity to distinct spray patterns were demonstrated in nozzle classification experiments.     

On-line full scan inspection of particle size and shape using digital image processing

An on-line full scan inspection system is developed for particle size analysis.A particle image is first obtained through optical line scan technology and is then analyzed using digital image processing.The system is composed of a particle separation module,an image acquisition module,an image processing module,and an electric control module.Experiments are carried out using non-uniform 0.1 mm particles.The main advantage of this system consists of a full analysis of particles without any overlap or miss,thus improving the Area Scan Charge Coupled Device(CCD)acquisition problems.Particle size distribution,roundness,and sphericity can be obtained using the system with a deviation of repeated precision of around ±1%.The developed system is shown to be also convenient and versatile for any particle size and shape for academic and industrial users.     

旋转矢量算法系数优化的参数解析法的适用性

参数解析法是一种简单直观的旋转矢量算法系数优化方法,但在子样数为4的情况下,该方法却不能得到最优系数。对此,在采用参数解析法详细推导5子样算法的基础上,结合其他学者的研究成果分析了该方法的适用性。研究表明,参数解析法仅适用于子样数不大于3的旋转矢量算法系数优化。     

Determination of the relaxation time spectrum from dynamic moduli using an edge preserving regularization method

For the numerical determination of a continuous relaxation time spectrum from rheological data so-called regularization methods are necessary. The regularization method based on Tikhonov regularization and commonly used in rheology assumes the relaxation time spectrum to be smooth. Accordingly, this method is not able to properly resolve spectra containing edges or at least large curvatures as proposed in the literature. In order to reconstruct such spectra a novel edge preserving regularization (EPR) method was developed which extends the properties of the commonly used method. In order to demonstrate the efficiency of EPR it is compared with the commonly used regularization method by means of simulated and experimental data. This reveals that EPR is able to prove whether or not the theoretically predicted edge containing spectra for high-molecular-weight, monodisperse polymers are compatible with experimental data. Received: 11 June 1999/Accepted: 1 September 1999     

用同伦方法反演非饱和土中溶质迁移参数

非饱和土中溶质迁移参数反演问题可以归结为非线性算子方程的求解问题. 将同伦方法 引入该问题的求解，通过构造线性同伦将原问题转化为求解同伦函数最小值的无约束优化问 题. 同时在分析了同伦参数正则化效应的基础上，提出一种两段同伦参数修正方法. 即在求 解的初始阶段，根据拟Sigmoid函数调整同伦参数，以追踪同伦路径，保证计算稳定地进行； 在迭代的后期，采用与残差相关的同伦参数修正方法，以抵抗观测噪声对求解的影响. 数值 算例为求解带有平衡及非平衡吸附效应的一维非饱和土中溶质迁移模型参数反演问题，计算 结果表明了该方法的大范围收敛性及较强的抵抗观测噪声的能力.     

A method for assessing nanomaterial dispersion quality based on principal component analysis of particle size distribution data

Seemingly contradictory findings between studies are a major issue in nanoecotoxicological research and have been explained as a result of the lack of comparability between assay methods, with dispersion of nanomaterials being identified as a key factor. Here we show the use of a multivariate method, principal component analysis (PCA), as a tool in protocol development and categorization of dispersion quality. Results show the significance of particle concentration within a protocol, and its effect on repeatability. Our results suggest that future studies should involve the use of PCA as a powerful data exploration tool to facilitate method development, comparability and integration of data across different laboratories.     

Estimation of particle dynamics in 2-D fluidized beds using particle tracking velocimetry

The experimental characterization of particle dynamics in fluidized beds is of great importance in fostering an understanding of solid phase motion and its effect on particle properties in granulation processes. Commonly used techniques such as particle image velocimetry rely on the cross-correlation of illumination intensity and averaging procedures. It is not possible to obtain single particle velocities with such techniques. Moreover, the estimated velocities may not accurately represent the local particle velocities in regions with high velocity gradients. Consequently, there is a need for devices and methods that are capable of acquiring individual particle velocities. This paper describes how particle tracking velocimetry can be adapted to dense particulate flows. The approach presented in this paper couples high-speed imaging with an innovative segmentation algorithm for particle detection, and employs the Voronoi method to solve the assignment problem usually encountered in densely seeded flows. Lagrangian particle tracks are obtained as primary information, and these serve as the basis for calculating sophisticated quantities such as the solid-phase flow field, granular temperature, and solid volume fraction. We show that the consistency of individual trajectories is sufficient to recognize collision events.     

Crack identification method in beam-like structures using changes in experimentally measured frequencies and Particle Swarm Optimization

In this paper, a technique is presented for the detection and localization of an open crack in beam-like structures using experimentally measured natural frequencies and the Particle Swarm Optimization (PSO) method. The technique considers the variation in local flexibility near the crack. The natural frequencies of a cracked beam are determined experimentally and numerically using the Finite Element Method (FEM). The optimization algorithm is programmed in MATLAB. The algorithm is used to estimate the location and severity of a crack by minimizing the differences between measured and calculated frequencies. The method is verified using experimentally measured data on a cantilever steel beam. The Fourier transform is adopted to improve the frequency resolution. The results demonstrate the good accuracy of the proposed technique.     

Influence of intrinsic parameters on the particle size of magnetic spinel nanoparticles synthesized by wet chemical methods

The synthesis of magnetic spinel ferrites at the nanoscale is a field of intense study, because the mesoscopic properties enable their novel applications. Spinel nanoparticles have a promising role because of their extraordinary properties compared with those of micro and macro scale particles. Several colloidal chemical synthetic procedures have been developed to produce monodisperse nanoparticles of spinel ferrites and other materials using sol–gel, co-precipitation, hydrothermal, and microemulsion techniques. To improve the synthesis method and conditions, quality and productivity of these nanoparticles, understanding the effect of extrinsic (pH, temperature, and molecular concentration) and intrinsic parameters (site preferences, latent heat, lattice parameters, electronic configuration, and bonding energy) on the particle size during synthesis is crucial. In this review, we discuss the effect of the intrinsic parameters on particle size of spinel ferrites to provide an insight to control their particle size more precisely.     

基于移动粒子半隐式法的表面张力模拟

采用移动粒子半隐式法(MPS)模拟了受表面张力影响的自由面流动。表面张力的计算采取了一种较适合于MPS方法的表面自由能模型。方形液滴振荡和射流断裂的模拟结果分别与理论分析和试验结果一致,同时进行了三维射流注水模拟,从而验证了MPS方法结合该表面张力模型可以有效、方便地进行自由面流动中表面张力现象的模拟。     

Development and validation of SuperDEM for non-spherical particulate systems using a superquadric particle method

This article presents the development and validation of the Superquadric Discrete Element Method (SuperDEM) for non-spherical particle simulation using a superquadric particle method in open-source CFD suite MFiX. A superquadric particle–particle contact algorithm with accelerating and stabilizing strategy was developed. A superquadric particle–arbitrary wall contact algorithm was developed, which enables the simulation in complex geometry. The solver was validated by comparing with experimental data generated in this study or available in the literature. Tests include cylinder contacting with a wall, static packing of M&M chocolate candies in a cylindrical container, static packing of cylinders in a cylindrical container, dynamic angle of repose of cylinders in a rotating drum, and discharging of chocolate candies from a hopper. Besides, MPI parallelization of the solver was implemented and the parallel performance of the solver using MPI was assessed through large-scale simulations of 1 million, 10 million, and 100 million particles on up to 6800 cores, which demonstrates that the SuperDEM solver has great potential for industrial-scale systems simulation.     

一种基于复变量求导法的岩土体抗剪强度参数反演新方法

边坡稳定性分析中,岩土体(含结构面)抗剪强度参数的确定至为重要.工程实践中利用边坡上实测的位移数据反演岩土参数是一种理想的参数确定方法.当前采用的位移反分析方法在反演弹性模量、泊松比及地应力等参数时已经取得了较好的成果,但在反演抗剪强度参数时仍未获得理想的结果.本文针对岩土体抗剪强度参数反演中所存在的困难,将复变量求导法、优化方法以及岩土弹塑性有限元法结合起来,提出一种适用于岩土体抗剪强度参数的反演分析新方法,通过测点实测位移反演计算出岩土体的抗剪强度参数.算例结果表明,该方法具有较高的计算精度和搜索效率,是一种值得推广的位移反分析方法.     

Numerical analysis of breaking waves using the moving particle semi-implicit method

The numerical method used in this study is the moving particle semi-implicit (MPS) method, which is based on particles and their interactions. The particle number density is implicitly required to be constant to satisfy incompressibility. A semi-implicit algorithm is used for two-dimensional incompressible non-viscous flow analysis. The particles whose particle number densities are below a set point are considered as on the free surface. Grids are not necessary in any calculation steps. It is estimated that most of computation time is used in generation of the list of neighboring particles in a large problem. An algorithm to enhance the computation speed is proposed. The MPS method is applied to numerical simulation of breaking waves on slopes. Two types of breaking waves, plunging and spilling breakers, are observed in the calculation results. The breaker types are classified by using the minimum angular momentum at the wave front. The surf similarity parameter which separates the types agrees well with references. Breaking waves are also calculated with a passively moving float which is modelled by particles. Artificial friction due to the disturbed motion of particles causes errors in the flow velocity distribution which is shown in comparison with the theoretical solution of a cnoidal wave. © 1998 John Wiley & Sons, Ltd.     

Numerical simulation of solitary waves overtopping on a sloping sea dike using a particle method

Sea dikes, as a commonly used type of coastal protection structures, are often attacked or damaged by violent waves overtopping under tsunamis and storm surges. In this study, the behavior of solitary waves traveling on a sloping sea dike is simulated, and solitary wave overtopping characteristics are analyzed using a complete Lagrangian numerical method, the moving particle semi-implicit (MPS) method. To better describe the complicated fluid motions during the wave overtopping process, the original MPS method is modified by introducing a new free surface detection method, i.e., the area filling rate identification method, and a modified gradient operator to provide higher precision. Meanwhile, the approximation method for sloping boundaries in particle methods is enhanced, and a smooth slope approximation method is proposed and recommended. To verify the improved MPS method, a solitary wave traveling over a steep sloping bed is studied. The entire solitary wave run-up and run-down processes and exquisite water movements are reproduced well by the present method, and are consistent with the corresponding experimental results. Subsequently, the improved MPS method is applied to investigate the overtopping process of a single solitary wave over a sloping sea dike. The results show that the hydraulic jump phenomenon is also possible to occur during the run-down motion of the solitary wave overtopping. Finally, the characteristics of the propagation and overtopping of two successive solitary waves on a sloping sea dike are discussed. The result manifests that the interaction between adjacent solitary waves affects wave overtopping patterns and overtopping velocities.     

双相介质参数反演的混沌搜索方法

混沌运动能在一定的范围内按自身的规律不重复地遍历所有状态。利用这个特点 ,本文将混沌运动引入到双相介质参数反问题的研究中。首先利用边界元方法实现了由介质参数到地表位移的非线性映射 ,然后通过建立合成位移与实测位移的相关函数将参数识别问题归结为优化问题 ,最后利用混沌运动指导优化搜索求得介质参数。算例结果表明了混沌搜索方法用于双相介质参数反演问题的可行性和有效性     

Modal parameter identification of flexible spacecraft using the covariance-driven stochastic subspace identification (SSI-COV) method

In this paper, the on-orbit identification of modal parameters for a spacecraft is investigated. Firstly, the cou-pled dynamic equation of the system is established with the Lagrange method and the stochastic state-space model of the system is obtained. Then, the covariance-driven stochas-tic subspace identification (SSI-COV) algorithm is adopted to identify the modal parameters of the system. In this algo-rithm, it just needs the covariance of output data of the system under ambient excitation to construct a Toeplitz matrix, thus the system matrices are obtained by the singular value decom-position on the Toeplitz matrix and the modal parameters of the system can be found from the system matrices. Finally, numerical simulations are carried out to demonstrate the validity of the SSI-COV algorithm. Simulation results indi-cate that the SSI-COV algorithm is effective in identifying the modal parameters of the spacecraft only using the output data of the system under ambient excitation.     

Retrieval of aerosol size distribution using improved quantum-behaved particle swarm optimization on spectral extinction measurements

An improved quantum-behaved particle swarm optimization (IQPSO) algorithm is employed to determine aerosol size distribution (ASD). The direct problem is solved using the anomalous diffraction approximation and Lambert–Beer's Law. Compared with the standard particle swarm optimization algorithm, the stochastic particle size optimization algorithm and the original QPSO, our IQPSO has faster convergence speed and higher accuracy within a smaller number of generations. Optimization parameters for the IQPSO were also evaluated; we recommend using four measurement wavelengths and 50 particles. Size distributions of various aerosol types were estimated using the IQPSO under dependent and independent models. Finally, experimental ASDs at different locations in Harbin were recovered using the IQPSO. All our results confirm that the IQPSO algorithm is an effective and reliable technique for estimating ASD.