Numerical simulation on fluid mixing by effects of geometry in staggered oriented ridges micromixers

Owing to the enhancement of surface effects at the micro-scale, patterned grooves on a microchannel remain a powerful method to induce chaotic advection within a pressure driven system. Since the staggered oriented ridges static micromixers are presented, there are few results in the literature about the geometric effects of such micromixer on the fluid mixing. This paper presents simulations within the micromixer and identifies geometric factors that affect the generation of advection flow over staggered oriented ridges. By varying the inflow directions, the ridge height ratio and the ridge asymmetry index, the modes of fluid motion and the pressure drops are studied respectively. Furthermore, through a set of numerical simulations, the relation expression between a mixing index to evaluate the mixing performance and the mentioned geometric parameters is obtained and the value of this mixing index could be calculated continuously. It indicates that the mixing performance of every staggered oriented ridges static micromixer could be estimated.     

On multi-objective optimization of geometry of staggered herringbone micromixer

A design methodology for micromixers is presented which systematically integrates computational fluid dynamics (CFD) with an optimization methodology based on the use of design of experiments (DOE), function approximation technique (FA) and multi-objective genetic algorithm (MOGA). The methodology allows the simultaneous investigation of the effect of geometric parameters on the mixing performance of micromixers whose design strategy is based fundamentally on the generation of chaotic advection. The methodology has been applied on a Staggered Herringbone Micromixer (SHM) at several Reynolds numbers. The geometric features of the SHM are optimized and their effects on mixing are evaluated. The degree of mixing and the pressure drop are the performance criteria to define the efficiency of the micromixer for different design requirements.     

基于混沌理论的交通量实时预测

分析了城市交通的混沌性，根据复杂的城市交通特点，引入了误差反馈系数，改进了混沌时间序列预测方法中的加权一阶局域法和基于最大Lyapunov指数的预测法，并将其成功应用于实时交通量预测．预测结果表明：这两种改进的方法都能较准确地预测交通量，但后者比前者更适合交通量预测，后者的预测误差一般可以控制在5％以下．     

采用LS-SVM计算时间序列的Lyapunov指数谱

为了计算未知系统的Lyapunov指数谱,首先,对一维观测数据序列进行相空间重构,然后,利用最小二乘支持向量机（LS-SVM）逼近重构系统的动力学方程,再通过雅克比矩阵计算Lyapunov指数谱。采用提出的方法计算Henon映射的Lyapunov指数谱,可以得到精确的计算结果且需要的序列步长小于1 000。计算了实测不同状态的交通流时间序列的Lyapunov指数谱。结果表明：在拥挤状态下,有多个Lyapunov指数大于零,说明系统是超混沌的;在同步状态下,有一个或多个Lyapunov指数大于零,说明系统是混沌的或超混沌的;在堵塞状态下,Lyapunov指数全小于零,说明系统不是混沌的。     

Micromixing and flow manipulation with polymer microactuators

Polymer actuators based on Gold/PolyPyrrole bilayers were microfabricated and their properties tested for flow promoting in the microdomain. When implemented in microchannels these actuators behaved as efficient micromixers for both, flow-through and stagnant conditions. Particle tracking experiments and numerical simulations of cross-sectional domains verified the capacity of these devices to promote complex, high velocity flows with chaotic advection properties in microscopic environments. Thinner devices could be actuated at higher frequencies than thicker devices, up to 10 Hz for 10 nm thick Gold layers with voltages not over 0.6 V (vs. Ag/AgCl), which led to enhanced flow generation properties. The results herein demonstrate that these actuators are practical candidates for fluid manipulation in the microdomain (for applications such as micromixing and pumping, and possibly even for propelling of swimming microdevices).     

Milliseconds microfluidic chaotic bubble mixer

In this study, we report a rapid microfluidic mixing device based on chaotic advection induced by microbubble–fluid interactions. The device includes inlets for to-be-mixed fluids and nitrogen gas. A side-by-side laminar flow segmented by monodisperse microbubbles is generated when the fluids and the nitrogen are co-injected through a flow focusing micro-orifice. The flow subsequently enters a series of hexagonal expansion chambers, in which the hydrodynamic interaction among the microbubbles results in the stretch and fold of segmented fluid volumes and rapid mixing and homogenization. We characterize the performance of the microfluidic mixer and demonstrate rapid mixing within 20 ms. We further show that bubbles can be conveniently removed from the mixed fluids using a microfluidic comb structure on completion of the mixing.     

基于无退化混沌系统的序列密码研究

针对连续时间混沌系统的退化问题,提出一种基于矩阵特征值配置的方法来构造具有多个正Lyapunov指数的连续时间混沌系统。提出一种基于特征值定义的特征值配置方法,通过设计一个线性反馈控制器,可以配置任何系统为以稳定焦点为原点的渐近稳定线性系统;通过设计一个非线性反馈控制器来配置多个正Lyapunov指数。相比于现有算法,对于任意受控系统,该方法都能系统地配置该受控系统的Lyapunov指数,使之成为无退化混沌系统。将该方法得到的无退化混沌系统转换为二进制序列,对得到的混沌序列进行分析后证明该序列具有良好的加密特性。     

离散动力系统混沌化——配置若干个Lyapunov指数

对确定性离散时间动力学系统,提出了一种配置Lyapunov指数为正的混沌化和超混沌化方法.得到的受控系统所有Lyapunov指数均不为零,而其中至少一个为正,并且受控系统满足Devaney的混沌定义.此外说明了算法可以配置至少两个或者更多个Lyapunov指数为正,并给出了证明和两个混沌化实例,仿真结果显示了算法的良好效果.     

Local and Global Lyapunov Exponents of Blood Flow

The Lyapunov exponents are calculated from numerically simulated and measured time series. The existing algorithms for the estimation of Lyapunov spectra have free parameters. Hence, their influence is analysed on various chaotic and quasi-periodic simulated signals. Furthermore, the exponents of a blood flow signal, measured on a healthy subject, are calculated over a wide range of parameter values. For the embedding dimension d 10, two typical spectra are observed for both the global and the local Lyapunov exponents. There are either 4 paired and 1 zero, or 5 paired exponents. At least one exponent equals zero within the calculation error.     

Surface tension driven and 3-D vortex enhanced rapid mixing microchamber

This paper proposes a novel passive micromixer design for mixing enhancement by forming a large three-dimensional (3-D) flow vortex in a counterflow microfluidic system. The counterflow fluids are self-driven by surface tension to perform mixing in an open chamber. The chamber design consists of two rectangular bars to house the chamber and to form two opening inlets from opposite directions. The best design is selected from various versions of mixing chambers. The mixing effectiveness is tremendously increased by folds of contacting surface between two fluids induced and enhanced due to the stretching of two fluid contacting interfaces by the formation of a 3-D large size vortex structure inside the mixing chamber itself with unaccountable numbers of fluid layers. Both numerical simulations and experiments are performed and compared to identify the design parameters for maximum utilization in this microfluidic system, such as the length of rectangular bar, microchannel wall height, and mixing chamber size. Compared to traditional micromixers operated by two-dimensional (2-D) vortex, this passive mixer can greatly enhance mixing efficiency and reduce mixing time by tenfold from around 10 s to less than 10 ms by 3-D effective chaotic flow structures in a more compact size. This mixing chamber is also suitable for an H-shape digital fluidic system for parallel mixing process in different mixing ratio simultaneously as a lab-on-a-chip system.     

级联混沌系统Lyapunov指数研究

在现有变参级联混沌通信系统中,系统密钥出现短周期态会导致密钥泄漏。针对该问题,分析级联混沌系统中Lyapunov指数随级联子系统参量变化的分布情况以及实时加解密系统的安全性,指出即使各独立子系统的Lyapunov指数均为正,其级联系统的Lyapunov指数也可能为负,负Lyapunov指数将导致密钥泄漏。为此,设计一个短程相关性线程对系统密钥进行实时监测,防止短周期态的发生,从而较好解决密钥泄漏问题。     

Passive micromixers for applications in the microreactor and μTAS fields

An overview is given of current developments in micromixing technology, where the emphasis is on liquid mixing in passive micromixers. The mixers presented are differentiated by the hydrodynamic principle employed, and four important principles are discussed in some detail: hydrodynamic focusing, flow separation, chaotic advection, and split-and-recombine flows. It is shown that these principles offer excellent mixing performance in various dynamical regimes. Hydrodynamic focusing is a concept working very much independently of the Reynolds number of the flow. Flow separation offers rich dynamical behavior over a Reynolds number scale of several hundred, with superior performance compared to purely diffusive mixing already found at low Reynolds numbers. For chaotic advection, different implementations tailor-made for low and comparatively high Reynolds numbers exist, both leading to an exponential increase of the interface between two fluids. Split-and-recombine flows can only be realized in a close-to-ideal form in the low Reynolds number regime. Corresponding mixers can be equipped with comparatively wide channels, enabling a favorable ratio of throughput to pressure drop. The overview given in this article should enable a potential user of micromixing technology to select the most favorable concept for the application envisaged, especially in the field of chemical process technology     

Analysis of passive microfluidic mixers incorporating 2D and 3D baffle geometries fabricated using an excimer laser

We present new passive microfluidic mixing structures based on 2D and 3D geometries. The primary mechanism of mixing in these devices is based on chaotic advection. The mixers which incorporate 3D structures introduce transverse flow rotation greatly enhancing performance. Simulations and experimental tests were performed over a Reynolds number (Re) range from 0.1 to 20 and showed good agreement. At an Re of 0.1, 90% mixing was achieved in a path length of 32 and 7 mm, for the 2D and 3D geometrical mixers, respectively. This represents an improvement in performance over a standard T-mixer of 20% for the 2D mixer and 82.5% for the 3D mixer. An inflection point in the mixing efficiency was observed for both mixer types around an Re of 1. The devices were fabricated on a polymethylmethacrylate (PMMA) substrate, using an excimer laser beam incorporating an intelligent pinhole mask. Initially, structures were developed off-line using a laser simulation tool. A design-of- experiments (DOE) approach along with computational fluid dynamic (CFD) analysis was used to optimise mixing element geometry. This precursor to the fabrication step greatly reduces the time between the design stage and device realisation.     

基于相空间重构的计算机网络的动力学特性分析

文章利用相空间重构理论对网络流量数据进行研究分析,用单变量的网络流量时间序列重构与网络动力系统等距同构的相空间,进而计算网络的关联维数、Kolmogorov熵和最大Lyapunov指数,研究网络系统的这三个参数随时间的变化特性。从而指出了网络流量具有的混沌动力学行为,并为进一步利用混沌动力学理论对网络行为的控制和建模奠定了基础。     

基于李雅普诺夫指数的离散混沌系统的控制研究

讨论了通过改变离散混沌系统的李雅普诺夫指数对离散混沌系统进行控制的一种方法。离散混沌系统的李雅普诺夫指数可按需要配置为负值，从而使系统收敛到任意的期望点上，仿真和实验结果表明，该控制方法是有效的，可以实现系统的快速稳定。     

A chaotic mixer for magnetic bead-based micro cell sorter

An efficient magnetic force driven mixer with simple configuration is designed, fabricated, and tested. It is designed to facilitate the mixing of magnetic beads and biomolecules in a microchannel, where mixing is unavoidably inefficient due to its low Reynolds number. With appropriate temporal variations of the force field, chaotic mixing is achieved, hence the mixing becomes effective. The mixing device consists of embedded microconductors as a magnetic field source and a microchannel that guides the streams of working fluid. It is demonstrated that a pair of integrated micro conductors provides a local magnetic field strong enough to attract nearby magnetic beads. Mixing of magnetic beads is accomplished by applying a time-dependent control signal to a row of conductors, at the Reynolds number of as low as 10/sup -2/. Two-dimensional numerical simulation has been performed to design the configuration of the channel and electrodes, which creates chaotic motion of beads. It is found that a simple two-dimensional serpentine channel geometry with the transverse electrodes is able to create the stretching and folding of material lines, which is a manifestation of chaos. The mixing pattern predicted by the simulation has been confirmed by both flow visualization and PTV (particle tracking velocimetry) in the chaotic mixer fabricated, which should greatly increase the attachment of beads onto the target biomolecules. The optimum frequency of applied control signal is searched by evaluating the Lyapunov exponent in both numerical and experimental particle tracking. It is found that the range of optimum Strouhal number is 5相似文献   

Chen’s混沌吸引子及其特征量

计算了Chen’s混沌吸引子的Lyapunov指数, 关联维数, Kolmogorov熵等混沌特征量. 采用两种不同的计算方法得到了一致的Lyapunov指数. 这从数值实验上有力地证实了Chen’s吸引子是一个与Lorenz系统和Rossler系统均不拓扑等价的新的混沌吸引子.     

The mapping method as a toolbox to analyze,design, and optimize micromixers

The mapping method is employed as an efficient toolbox to analyze, design, and optimize micromixers. A new and simplified formulation of this technique is introduced here and applied to three micromixers: the staggered herringbone micromixer (SHM), the barrier-embedded micromixer (BEM), and the three-dimensional serpentine channel (3D-SC). The mapping method computes a distribution matrix that maps the color concentration distribution from inlet to outlet of a micromixer to characterize mixing in a quantitative way. Once the necessary distribution matrices are obtained, computations are fast and numerous layouts of the mixer are easily evaluated, resulting in an optimal design. This approach is demonstrated using the SHM and the BEM as typical examples. Mixing analysis in the 3D-SC illustrates that also complex flows, for example in the presence of back-flows, can be efficiently dealt with by using the new formulation of the mapping method.     

基于脉冲耦合神经网络的混沌控制

根据脉冲耦合神经网络(PCNN)能产生混沌现象,研究了对配置混沌PCNN系统的李雅普诺夫指数使其稳定于期望点的方法。根据特定期望点的情况,按需要配置负的李雅普诺夫指数,产生不同的控制序列来改变混沌PCNN系统,达到稳定控制的要求。仿真和实验结果证明了该算法的有效性,实现了混沌PCNN系统从混沌状态到稳定期望点的控制。     

利用Lyapunov指数和容量维分析永磁同步电机仿真中的混沌现象

给出了一种适合于一般混沌系统Lyapunov指数和容量维计算的数值算法,并首次应用感动永磁同步电机混沌现象的分析,在给定的几种典型运行条件下,计算了永磁同步电机混沌模型的Lyapunov指数和容量维,结果表明戾 磁同步电机运行呈现混沌行为,从而通过特征指数验证了永磁同步电机混沌现象的存在性。