中低负荷下脉动热管壁温信号的分形特性分析

运用功率谱、小波分解、相空间重构、关联维数计算等非线性分析方法对脉动热管壁面温度波动信号分析。表明:功率谱呈现连续谱线,时间序列存在自相似性,展现温度波动信号的混沌行为;小波分解表现出温度波动的分形特性;重构吸引子展现出4种不同的空间分形结构,说明温度信号波动属于分形下的混沌行为。计算分形维数与传热性能的关系,发现系统存在3~6个分形维;随嵌入维数的增加,分形速度关系为R134a大于丙酮大于去离子水,基本表现为分形维数越大,传热性能越好。并发现关联维和热阻成负相关关系。     

沸腾管内汽液两相流动压力波动信号的分析

研究了竖直管内沸腾两相流动时压力波动信号的特性,采用功率谱密度函数、分维数、关联维数及Kolmogorov熵等非线性分析方法对压力波动时间序列进行了定性及定量分析,考察了热流密度及液速对压力波动的影响规律。结果表明,此类系统具有非线性混沌特性。定量计算结果表明,分维数小于1.5,系统存在1个关联维。K熵的变化也具有同样的趋势,且为有限正值;沸腾流动的汽液两相流型和非线性特征量之间有一定的关系。     

湍流状况下的管式反应器中的速度时间序列关联维数分析

通过激光多谱勒测速仪(LDA）测得管式反应器中不同流点的速度时间序列，提出了关联维数在分析湍流场的速度时间序列的应用方法，并且得到关联维数在管式反应器中的径向和轴向的变化范围大约在1．5-2．5之间。随雷诺数Re的变化，关联维数的变化范围在1．0-2．5之间，由此可以推测关联维数为2．5有可能是湍流变化的一个临界值。提出关联维数可以用来判断涡漩的能量随时间的衰变阶数。通过使用这一方法扩展了研究湍流的思路，并且提出使用关联维数来判断湍流的可能性。     

基于测井数据小波变换的基准面旋回划分方法研究

测井数据的小波变换为地层基准面旋回的识别提供了可靠信息.本文基于连续小波变换和离散小波变换的特点,提出了一种在大尺度旋回划分中应用连续小波变换,小尺度旋回划分中应用离散小波变换的新方法,对GR测井信号进行小波分解,利用小波变换后的小波系数曲线进行基准面旋回的划分,最终结果表明该方法合理有效,具有可行性.这些研究是对小波变换应用于基准面旋回划分的一次有意义的探索.     

流化床压力波动混沌预测

基于混沌理论 ,通过建立重构相空间轨迹演化的离散动力学映射方程 ,提出了流化床压力波动预测方法 ,以流化床压力波动时间序列反演系统动力学行为 .对比了模型产生的压力波动时间序列和实验测得的压力波动时间序列的混沌特征参数 :关联维、Kolmogorov熵和Lyapunov指数谱 ,两组非线性混沌特征参数趋于一致 ,说明该模型能捕获系统的非线性动力学特征 .并研究了压力波动预测指数分离过程的长期不可预测性 .     

CHAOS PREDICTION OF PRESSURE FLUCTUATION IN FLUIDIZED BED

基于混沌理论 ,通过建立重构相空间轨迹演化的离散动力学映射方程 ,提出了流化床压力波动预测方法 ,以流化床压力波动时间序列反演系统动力学行为 .对比了模型产生的压力波动时间序列和实验测得的压力波动时间序列的混沌特征参数 :关联维、Kolmogorov熵和Lyapunov指数谱 ,两组非线性混沌特征参数趋于一致 ,说明该模型能捕获系统的非线性动力学特征 .并研究了压力波动预测指数分离过程的长期不可预测性 .     

汽-液流动沸腾蒸发系统的混沌分析及预测

应用功率谱、自相关系数、吸引子相图、关联维数等分析工具,对汽-液两相流动沸腾蒸发系统的传热系数时间序列进行了定性和定量混沌研究.研究结果为:时间序列的功率谱在半对数坐标下呈指数下降趋势;自相关系数随时间的推移而减小;吸引子相图呈现精细结构;关联维数随嵌入维数的增大而趋于一个稳定的分数值.这说明汽-液两相流动沸腾蒸发系统呈现混沌特性.在此基础上,应用临近点相似混沌预测法对不同加热蒸汽压力(0.11 MPa、0.13 MPa、0.15 MPa)下的传热系数时间序列进行了混沌预测.结果表明:预测值和实验值在有限时间长度内吻合程度较好;预测的平均相对误差随加热蒸汽压力的增加而增大;高精度预测时间长度随加热蒸汽压力增加而减小.这表明该系统具有短期可预测性.     

振动流化床中流动结构的混沌分析

在内径90mm、静床高800mm的高床层流化床中,用动态压力传感器检测了不同气速条件下普通流化床和振动流化床中沿轴向的压力脉动信号,通过小波变换对信号除噪后,用混沌理论对信号进行了分析.通过关联维数和Kolmogorov熵定量表征振动流化床中的流动结构特征.结果表明:压力脉动信号的关联维数和Kolmogorov熵能够描述振动流化床中的流化状态;振动流化床中床层的流动结构存在两个区,在近分布板区域为射流区,床层主体部分为均匀流化区.     

蓝宝石表面形貌的功率谱与分形特征分析

运用二维功率谱和分形理论的关联维数分析了蓝宝石晶片的表面形貌特征。介绍了利用二维快速傅立叶变换计算二维功率谱在蓝宝石表面形貌中的应用方法;通过时间延迟技术重构相空间,利用GP算法计算了蓝宝石表面形貌的关联维数。分别利用二维功率谱和关联维数对蓝宝石的原始表面、加工后表面和单个取样长度的形貌特征进行了实验分析。结果表明:二维功率谱和关联维数能够表征蓝宝石表面形貌,且克服了传统的表征参数只包含有垂直方向上的信息而不能准确表征整个蓝宝石晶片表面形貌特征的缺点,它比传统的表面形貌表征方法具有准确、便捷和信息量大等优势。     

循环流化床压力波动信号的小波多分形特征

循环流化床压力波动信号是研究床内流体动力学的重要线索.本文在150 mm×150mm×2000 mm的循环流化床上进行试验,测量了不同工况下床壁的静压力波动信号.对获得的压力波动信号进行连续小波变换,利用小波变换模极大计算所得的全局分解函数来计算具有相同正则性的点集的分形维数.所取得的小波多分形谱能够很好地描述压力波动信号的几何特征和局部尺度行为.本文提取的最大多分形谱、最大多分形谱对应的Lipschitz指数、Lipschitz指数宽度三个特征对描述循环流化床中的流态转变,具有很好的作用.     

Chaotic forecasting of time series of heat-transfer coefficient for an evaporator with a two-phase flow

The time series of heat-transfer film coefficient for an evaporator with a vapor-liquid two-phase boiling flow were forecasted by the chaotic prediction or the local nonlinear short-term prediction. The forecasting method was based on the phase space reconstruction theory and a mathematic model in the form of datum driving had been developed to carry out the prediction. The signals of heat-transfer film coefficients predicted by this method were compared with those obtained from the experimental measurements. Different from the previous work, the comparisons in this work were done both from the point of view of the time trajectory and from the point of view of macroscopic or general characters. Besides the time-averaged statistics characteristics, such as the average value, average deviation and standard deviation, the power spectrum, phase plane map and chaotic invariants including the correlation dimension and Kolmogorov entropy had been calculated and been compared for the time series obtained both from the experimental measurement and from the forecast. The comparison for each parameter between the value calculated from the time series measured and that estimated from the time series forecasted by the chaotic forecast method shows satisfactory agreement. The limited length in time with an accuracy prediction indicates that the system is chaotic. The agreement of the comparison of the general parameter indicates that the chaotic prediction is effective for the estimations of the heat transfer characteristics of the two-phase flow boiling system and that the chaotic prediction method may be a potential tool for the effective thermo-fluid control for such evaporators.     

SK型静态混合器壁压脉动信号的多尺度多分形特性

为了探讨静态混合器内非线性、非均匀性和混沌特性机理,利用高速数据采集系统对SK型静态混合器管壁处脉动压力进行测量。结合小波变换模极大值理论,对采集的不同进口流量下壁压波动时间序列用Daubechies二阶小波提取1～7尺度下的特征信号,并分别对提取的信号进行R/S分析。通过对压力波动信号不同尺度下的细节信号与概貌信号研究,发现在不同尺度下其表现出不同的分形结构,且随着进口流量的增大,分形结构的变化趋势基本一致。此外,该系统不仅存在确定性非周期成分,而且不同尺度的旋涡之间的能量交换导致混沌的产生。各尺度信号的能量分布表明,压力波动信号主要体现了宏观尺度的旋涡级串的相互作用。     

Studies on the Hydrodynamics of Chaotic Bubbling in a Gas‐Liquid Bubble Column with a Single Nozzle

In this work, the chaotic bubbling mechanism in a gas‐liquid bubble column with a single nozzle was investigated. The signal for the analysis was the time series of pressure fluctuations measured from a pressure transducer probe placed in the bubble column close to the nozzle. In order to study the bubbling process, statistical analysis, qualitative and quantitative nonlinear analyses were carried out for the pressure fluctuations. Power spectra used as standard statistical measures provided preliminary evidence that bubbling in the middle values of gas flow rates may be chaotic in nature. Phase plots provided a qualitative means of analyzing the fine geometry structure of the attractor reconstructed from the bubbling time signal. Positive finite estimates of the Kolmogorov entropy provided a quantitative evidence of behavior consistent with chaos. Besides previous diagnostic tools, the local nonlinear short‐term prediction was also used as a supplement method. It was found that the bubbling process exhibits a deterministic chaotic behavior in a certain range of the gas flow rate. When increasing the gas flow rate, the sequence of periodic bubbling, primary and advanced chaotic bubbling, and jetting or random bubbling were successively observed. However, no clear period doubling sequence leading to chaotic behavior was observed. The sharp loss of the ability to predict the pressure signal successfully with the nonlinear prediction method provides the strongest evidence of the presence of the chaotic bubbling. The variations of the nonlinear invariants, such as the Kolmogorov entropy and the correlation dimension together with the plot of the correlation integral with the operation conditions, might be developed as potential and effective quantitative tools for flow regime identification of the bubbling process.     

High-velocity fluidization of solid particles in a liquid-solid circulating fluidized bed system

Particulate and aggregative fluidizations in a liquid-solid circulating fluidized bed system are characterized by chaotic time series analysis of local voidage and heat transfer fluctuations in terms of the correlation dimension and Kolmogorov entropy. Both correlation dimension and Komogorov entropy of the voidate fluctuation are found to decrease with decreasing bed voidage in both fluidization regimes, suggesting the suppression of chaotic motion of individual particles due to high solid concentration. The correlation dimension of the heat transfer fluctation in the aggregative fluidization regime is higher than that in the particulate fluidization regime. This reflects the complex convective motion of liquid and solid phases induced by the formation of the liquid streaks and aggregates of particles.     

Chaotic characteristics of local voidage fluctuation in a circulating fluidized bed

Local voidage fluctuations have been measured by using an optical transmittance probe at various axial and radial positions in a circulating fluidized bed riser with a 0.1 m i. d. and 10 m height. The chaotic time series analysis of the local voidage fluctuations has been adopted to characterize the nonlinear dynamics of the circulating fluidized bed riser. The variations of the correlation dimension and the Kolmogorov entropy of the voidage fluctuation were found to depend on the local time-average voidage. The axial and radial distributions of the correlation dimension and the Kolmogorov entropy were strongly affected by the solids flow structures (e.g. core-annulus flow) in various operating conditions. The correlation dimension of local voidage fluctuations increases along the riser, except the position near the distributor. Both, the correlation dimension and the Kolmogorov entropy of local voidage fluctuations near the wall, were found to be smaller than those at the center of the riser, independent of the solids circulation rate and the axial position.     

浸没循环撞击流反应器撞击区压力波动的混沌分析

浸没循环撞击流反应器撞击区的压力瞬态信号包含了该区域内流体的许多动态信息,为了分析这些动态信号,采用了一种新的非线性分析方法,即混沌分析.利用小波理论对信号进行过滤,采用重构相空间理论恢复已过滤信号的吸引子.利用数学方法计算刻画混沌吸引子的3个特征参数：关联维、K熵和最大Lyapunov指数.对不同螺旋桨转速及同一y平面上不同测量点位置上算得的特征参数值进行研究,研究结果显示浸没循环撞击流反应器撞击区流体具有混沌特性,而且3个特征参数在不同的螺旋桨转速下及不同的测量点位置具有相同的变化趋势.