Research progress of chaotic mixing in stirred tank

Chaotic mixing is regarded as an effective method to improve the mixing effect in the laminar stirred tank.To generate chaos in flow field in stirred tank,many efforts including aperiodic movement,asystematic installation impeller,etc.,were made to save mixing time and energy consumption.The computational fluid dynamics of chaotic flow field and the hyperchaotic controlling method as well as macro-instability were reviewed.Multiple flow field coupling is important in the turbulent mixing region of stirred tank.The development trends of flow field coupling and hyperchaotic controlling in chaotic mixing were prospected in energy saving operation.

Markov transition probability-based network from time series for characterizing experimental two-phase flow

We generate a directed weighted complex network by a method based on Markov transition probability to represent an experimental two-phase flow. We first systematically carry out gas-liquid two-phase flow experiments for measuring the time series of flow signals. Then we construct directed weighted complex networks from various time series in terms of a network generation method based on Markov transition probability. We find that the generated network inherits the main features of the time series in the network structure. In particular, the networks from time series with different dynamics exhibit distinct topological properties. Finally, we construct two-phase flow directed weighted networks from experimental signals and associate the dynamic behavior of gas-liquid two-phase flow with the topological statistics of the generated networks. The results suggest that the topological statistics of two-phase flow networks allow quantitative characterization of the dynamic flow behavior in the transitions among different gas-liquid flow patterns.

Investigation of Flow Behavior of Joule-Heating Flow in a 2-D Model of a Reprocessing Glass Melter Cavity

Flow behavior was observed in a simplified model cavity of a multiphase High Level Liquid Waste (HLLW) reprocessing glass melter. Electrodes were set to generate Joule-heating flow in the cavity. A chaotic flow occurred because the lower part of the cavity was heated while the top surface of the cavity was cooled. Downflow and upflow occurred alternately in cavities. The shape of the cavity was a sloping bottom cavity, which was similar in shape to the real glass melter. To know the flow behavior in the cavity, 1-D flow behavior and 2-D flow behavior were measured in an experiment and simulated by an original CFD code. In the sloping bottom cavity, chaotic flow occurred in the upper part of the cavity. In the case of the sloping bottom cavity which had the same set of electrodes as the glass melter, the effect of the downflow near the electrodes decreased. The same phenomena could be predicted in the melter. The experimental results were also used to validate the CFD code, which will be helpful for developing a multiphase Joule-heating flow predicting.

A Micromixer Using the Taylor-Dean Flow: Effect of Inflow Conditions on the Mixing

Chaotic mixing in a curved-square channel flow is studied experimentally and numerically. Two walls of the channel (inner and top walls) rotate around the center of curvature and a pressure gradient is imposed in the direction toward the exit of the channel. This flow is a kind of Taylor-Dean flows. There are two parameters dominating the flow, the Dean number De (∝ the pressure gradient or the Reynolds number) and the Taylor number Tr (∝ the angular velocity of the wall rotation). In the present paper, we analyze the physical mechanism of chaotic mixing in the Taylor-Dean flow by comparing experimental and numerical results. We produced a micromixer model of the curved channel several centimeters long with square cross section of a few millimeters side. The secondary flow was measured using laser induced fluorescence (LIF) method to examine secondary flow characteristics. We also performed three-dimensional numerical simulations for the exactly same configuration as the experimental system to study the mechanism of chaotic mixing. It is found that good mixing performance is achieved for the case of De ≤ 0.1Tr, and that mixing efficiency changes according to the difference in inflow conditions. The flow is studied both experimentally and numerically, and both results agree with each other very well.

A Micromixer Using the Taylor-Dean Flow: Effects of Aspect Ratio and Inflow Condition on the Mixing

Chaotic mixing in three different types of curved-rectangular channels flow has been studied experimentally and numerically. Two walls of the channel (inner and top walls) rotate around the center of curvature and a pressure gradient are imposed in the direction toward the exit of the channel. This flow is a kind of Taylor-Dean flow. There are two parameters dominating the flow, the Dean number De (∝ the pressure gradient or the Reynolds number) and the Taylor number Tr (∝ the angular velocity of the wall rotation). In this paper, we analyze the physical mechanism of chaotic mixing in the Taylor-Dean flow by comparing experimental results and numerical ones. We produced three micromixer models of the curved channel, several centimeters long, with rectangular cross-section of a few millimeters side. The secondary flow is measured using laser induced fluorescence (LIF) method to examine secondary flow characteristics. Also we performed three-dimensional numerical simulations with the open source CFD solver, OpenFOAM, for the same configuration as the experimental system to study the mechanism of chaotic mixing. It is found that good mixing performance is obtained in the case of De ≤ 0.1 Tr, and it becomes more remarkable when the aspect ratio tends to large. And it is found that the mixing efficiency changes according to the aspect ratio and inflow condition.

ON THE BELTRAMI FLOWS

To illustrate the general properties of the Beltrami flows,a new sufficient and necessary condi- tion of the general solution of the Beltrami flows has been given,on whose basis some sufficient and necessary conditions and sufficient conditions in literature are unified.The advantages of the new expressions are that one may get solutions of Beltrami flows with constant proportional factors which satisfy some given asymptotic decaying conditions at infinity.Finally,we find a class of spherical vortices of Beltrami flows,where the mo- tion trajectories of the fluid particles are confined within a sphere or two adjacent concentric spherical shells.We find that the superpositions of the spherical vortices of the same order with different polar axes may produce chaotic trajectories.

融入智能网联汽车的混行交通流混沌特性

为了研究混行交通流混沌特性、辨析影响混行车队混沌程度的因素,在传统交通流理论基础上,利用Cao方法和改进的Cao方法确定混行交通流延迟时间和嵌入维数,对混行交通流序列进行相空间重构并通过计算最大Lyapunov指数判定其混沌特性.对混行交通流中智能网联汽车(intelligent connected vehicle,ICV)协同自适应巡航(cooperative adaptive cruise control,CACC)车辆比例及延迟时间关键参数进行影响分析.结果表明:在跟驰过程中车头间距序列的最大Lyapunov指数小于0时,混行交通流存在混沌;CACC车辆比例增加能够减弱混沌的时间区域,比如当CACC车辆比例达到0.6时,跟驰系统趋于稳定;CACC车辆的延迟时间对混沌的影响显著,保持低通信延迟才能发挥CACC车辆的作用,从而有效抑制混沌.

THE GENERAL PROPERTIES OF THE SPHERICAL VORTICES（SV）OF n－TH ORDER AND THE CHAOTIC PHENOMENA AND OF THE ORDERED STRUCTURES OF THE SV OF 3RD ORDER

The general properties of the spherical vortices(SV)of n-th order are discussedin this paper Numerical calculations are carried out in the case of n=3.We find outsome interesting phenomena concerning the chaotic regions and ordered islands on the Poincare sections. Interpretations of these phenomena are also given.

两端固定输流管振动实验研究

通过实验的方法对简谐激励和脉动流作用下的两端固定输流管的动力学行为进行振动测试分析.设计并制作了两端固定输流管的振动实验装置,为确保实验结果翔实可靠,选取三种不同材料的管分别进行了三次实验,研究了管内流体流速、激振力振幅和脉动流频率对两端固定输流管振动特性的影响.结果表明,流体流速和激振力幅值对两端固定输流管的一阶共振特性和振动幅值有着显著影响,在脉动流作用下,两端固定输流管存在混沌运动,并且随着脉动频率的增大,管道平均振幅减小.

基于Wolf的数字化变电站通信网异常流量检测系统

数字化变电站通信网异常流量检测过程中易陷入局部最优,导致检测结果不精准。为了解决这个问题,提出了基于Wolf的数字化变电站通信网异常流量检测系统。构建系统总体结构,分析通信网流量异常频域特征。通过采集异常流量模块解析目的物理地址,检查组件为系统提供信息交互引擎。使用Wolf算法将混沌序列映射到数字化变电站通信网异常流量多维相空间,设置控制收敛因子,避免检测结果陷入局部最优。计算异常流量特征值的熵,判断流量异常类型。实验结果表明,该系统一次设备异常流量检测结果与实际数据一致,二次设备异常流量检测结果与实际数据存在最大为2 Mb/s的误差,说明使用所设计系统检测结果精准。

基于LSTM-SVR的地铁客流量预测研究

在日常生活中,交通管理部门需要精准、及时地预测地铁客流量,以帮助出行者规划出行路线,节约出行时间,缓解交通拥堵问题。文中从组合不同模型的角度出发,尝试探索了更准确的数据预测。首先,时间序列数据特征适用于LSTM模型处理,借助该模型可以实现极强的特征提取功能;其次,支持向量回归(SVR)是一种基于SVM的回归算法,具有高维的表达能力,在数据拟合上具有显著优势。文中结合LSTM与SVR构建组合模型,并借助实际的仿真实验数据验证了组合模型的有效性。另外,为使结果更具说服力,文中还比较分析了最近邻回归(KNN)模型的实验数据。

自适应混沌竞争文化算法及在车间调度中的应用

针对传统文化算法初始种群多样性低、收敛效率低、易陷入局部最优解等问题,本工作对其进行优化设计,提出了一种自适应混沌竞争文化算法。该算法由上层信念空间和下层种群空间组成,种群空间为优化主体,信念空间控制种群空间的优化。首先,通过混沌立方映射产生初始种群,该方法提高了初始种群的遍历性、均匀性;其次,在种群空间引入将种群分为优势群体和劣势群体的双种群竞争机制,且不同群体采用不同进化方式,提高了算法的收敛效率;最后,将本工作提出的自适应变异方式引入双种群,避免了算法后期易陷入局部最优解的困惑。函数优化结果突出了该算法的高效性,将该算法应用于流水车间调度问题求解最小化最大完工时间优化目标,仿真结果显示,该算法在收敛速度、精度方面都有较大提升,验证了该算法的优越性。

旋流静态混合器内瞬态流动特性研究进展

首先概括了静态混合的技术特色;其次,重点综述了近年来旋流静态混合器内脉动压力与速度波动的统计特征、多尺度分形和混沌混合特性等方面的研究进展;实验研究发现Kenics静态混合器各点压力最大波动幅值与进口流量呈二次函数关系,脉动功率谱随着频率的增加呈幂函数关系衰减;轴截面内壁面自由涡和主体区强制涡相互耦合诱导混沌流的产生,同时提高速度与温度梯度的场协同程度。最后,总结了静态混合器内螺旋元件的切割分流、改变流向和径向混合等功能在强化CO2水合物形成过程中的作用。指出将计算流体力学、映射法等方法同LIF、PIV、PFS有机结合可有效地分析静态混合器内多相流动混合机理。

垂直上升管中气液两相流电导波动信号的混沌特性分析

首先以Lorenz混沌方程产生的非线性时间序列为例,讨论了在不同时间序列长度下各种延迟时间算法对噪声的适用性.研究发现,采用C_C算法计算延迟时间的鲁棒性强.在此基础上,给出了垂直上升管中气水两相流电导波动信号混沌表征结果,发现在较低水相表观速度时,随着气相表观速度增加,泡状流及混状流动力学特性变得愈加复杂,而段塞流动力学特性受液相表观速度影响较大;在较高水相表观速度时,随着气相表观速度增加,当流型从泡状流向段塞流转变时,气液两相流动力学特性变得相对简单.但是,由于受液相湍流作用影响,段塞流的动力学特性表现出了涨落现象,呈现不稳定性,当流型从段塞流向混状流转变时,气液两相流动力学特性则变得愈加复杂.研究结果表明:基于电导波动信号的混沌分析可以较好地表征气液两相流流型变化,是理解流型转变机理及其动力学演变特性的有用工具.

二次流实现流体混沌混合的数值研究

在加权残余法与谱方法相结合的基础上,分析了扭转弯管中的二次层流,并说明了在某些情况下将诱发混沌现象.根据二次流的动力学特性,建立了扭管不同截面之间的非线性映射关系,用数值方法研究了流体微团在该映射下的混合特性,并进行了实验研究.结果表明,利用不同的单元弯管的组合与连续扭转,可以实现流体在层流状态下的高效无切割混合.

交通流实时预测的混沌时间序列模型

针对城市交通流普遍存在的混沌特性,介绍了一种改进的加权一阶局域预测模型,并将其应用于交通流实时预测中。为了进一步提高算法的精度与速度,对最优邻域的点数进行动态选择,通过改进,使之成为一种鲁棒性强、预测精度高的实时预测算法,并能有效地用于短时交通流的预测问题中。仿真结果表明:该算法完全满足实时交通流预测的需要,为交通信号智能控制和交通流诱导奠定了坚实的基础。

气液两相流中压力波动信号的混沌分析

对气液两相垂直向上并流中压力波动信号的混沌分析表明：外界噪声的干扰不可避免地会进入压力波动信号，从相空间内的吸引子图可明显地观察到噪声的存在，实验中采取多种手段，尽可能地把噪声的干扰降到最低极限，为提取反映系统特征的有效信息作前期准备。将预处理过的数据进行混沌分析得到，气液两相流的压力波动信号特征由两部分组成，低频部分（大气泡的运动或大尺度气液波动）和高频部分（如液体脉动、界面湍动等）。并且对应于不同操作条件下的流动体系，相关分维和Ｋｏｌｍ ｏｇｏｒｏｖ 熵均有较大变化，由此可区分流型。研究表明，对压力波动信号的混沌分析有助于深入理解系统的动力学特征。

三螺杆挤出机端面二维流场混沌混合拉格朗日拟序结构分析

三螺杆挤出机是一种新型的聚合物流体加工设备,其独有的中心区呈现出几何结构和受力状态的周期性变化,混合机理非常复杂。区别于传统的线性混合分析,从拉格朗日体系的新视角对三螺杆挤出机混沌混合进行拉格朗日拟序结构分析,利用有限时间Lyapunov指数(FTLE)、拉格朗日拟序结构(LCS),结合Poincaré截面和粒子可视化技术研究三螺杆挤出机二维流场的流体输运和混沌混合机理,讨论了中心区动态结构特性对FTLE和LCS分布的影响,并与单螺杆挤出机和双螺杆挤出机进行了对比分析。结果表明,LCS将三螺杆挤出机流域划分为近螺杆区、远螺杆区和中心区3个具有不同运动特性的区域,扭结是连接近螺杆区、远螺杆区和中心区物质交换的桥梁。随着混合时间的增加,扭结的弯曲和折叠程度逐渐增大,增强了3个区域的物质交换,强化了三螺杆流场的混沌混合。三螺杆挤出机啮合区附近存在3个双曲固定点,混合能力较好。Poincaré截面中椭圆周期点的出现说明在流域中心有非混沌区存在,因此三螺杆挤出机的中心区混合能力相对较弱。

应用混沌烟花算法求解置换流水车间问题

改进烟花算法求解置换流水车间问题。用最大位置法编码,将连续变量映射到离散空间。引入动态半径因子,平衡局部搜索与全局搜索。精英个体混沌搜索,进一步挖掘个体信息。用锦标赛策略替代原有的选择算子,群体中的优良个体被选择的概率增大。通过正交实验选择合适参数,求解Car类和Rec类基准问题。与基本烟花算法、萤火虫算法和粒子群算法的对比实验说明,改进后的混沌烟花算法在寻优率、寻优速度等上具有一定的优势,是求解置换流水车间问题的有效工具。

基于Lyapunov指数的交通量混沌预测方法

交通量预测分析已成为交通工程领域重点研究课题 ,智能运输系统的核心研究内容之一。在判定交通流量存在混沌的前提下 ,对交通量的实测数据进行相空间重构 ,而后在重构相空间上 ,利用基于Lyapunov指数的混沌预测方法预测交通量。