共查询到19条相似文献,搜索用时 171 毫秒
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运用基于最大Lyapunov指数的混沌预测方法对摇摆条件下自然循环系统的流量脉动进行了预测. 对不规则复合型脉动的流量脉动实验数据进行相空间重构, 计算关联维数、二阶Kolmogorov熵和最大Lyapunov指数等几何不变量, 在说明不规则复合型脉动是混沌运动的基础上, 根据最大Lyapunov指数对不规则复合型脉动进行了预测. 通过预测结果和实验结果对比发现: 对于复杂的两相自然循环流动不稳定性, 预测结果具有较高的精度, 说明预测方法的可行性. 同时, 确定了混沌系统可预测的尺度, 提出用动态预测的方式监测系统流量脉动. 本文的研究方法为两相流复杂的流动不稳定性研究提供了新的思路.
关键词:
混沌时间序列
实时预测
最大Lyapunov指数
两相流动不稳定性 相似文献
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利用替代数据法检验了摇摆条件下自然循环系统不规则复合型脉动的混沌特性, 并在此基础上进行混沌预测. 关联维数、最大Lyapunov指数等几何不变量计算结果表明不规则复合型脉动具有混沌特性, 但是由于计算结果受实验时间序列长度的限制和噪声的影响, 可能会出现错误的判断结果. 为了避免出现误判, 在提取流量脉动的非线性特征的同时, 需要用替代数据法进一步检验混沌特性是否来自于确定性的非线性系统. 本文用迭代的幅度调节Fourier 算法进行混沌检验, 在此基础上用加权一阶局域法进行混沌脉动的预测. 计算结果表明: 不规则复合型脉动是来自于确定性系统的混沌脉动, 加权一阶局域法对流量脉动进行混沌预测效果较好, 并提出动态预测方法.
关键词:
混沌时间序列
替代数据法
实时预测
两相流动不稳定性 相似文献
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数值模拟圆柱绕流旋涡运动及尾流不稳定性分析 总被引:5,自引:1,他引:4
1引言流体绕过圆柱所产生的非定常旋涡运动以及由此引起的流动不稳定性在理论和实践上都具有重要的意义。数值模拟圆柱绕流旋涡产生及演化过程,探讨圆柱尾流涡街产生的机制,控制尾迹不同速度型以抑制涡街的产生,避免涡激振动在工程上造成破坏作用具有重大实际意义。为使问题简化,本文以二维圆柱绕流作为研究对象。该流动涉及到非定常分离,旋涡的形成、运动及发展,流动不稳定性质改变等许多未完全解决的问题。B。had等山对圆柱突然起动问题作了一系列实验研究。文献门对二维圆柱绕流问题作了系统数值研究。本文采用文献门提出的差分格… 相似文献
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根据混沌序列产生的确定性和非线性机制,基于Volterra级数展式和混沌序列高阶奇异谱特征,提出了一种高阶非线性傅里叶红外(HONFIR)滤波预测模型用于混沌时间序列的自适应预测.其自适应算法采用时域正交算法来自适应地跟踪混沌的运动轨迹,而不是重构混沌系统 的全局或局部运动轨迹.实验研究表明:(1)这种HONFIR自适应滤波器能够有效地预测一些超 混沌序列.(2)预测混沌序列的性能与预测模型的非线性拟合能力有关,但并非非线性程度越 高,预测性能就越好.(3)当HONFIR滤波器对混沌序列的非线性拟合精度高时,其自适应预测 的性能与其输入维数的关系不受Takens嵌入定理的约束.(4)HONFIR自适应滤波器具有一定的 抗噪能力.
关键词:
混沌
非线性模型
滤波器 相似文献
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瞬时浓度场的激光片光测量研究 总被引:2,自引:2,他引:0
根据粒子的光散射、散斑成像理论,建立了两相流动粒子相对数量浓度与粒子散斑图像强度之间的线性关系, 通过数字图像分析和处理技术进行污染扩散相对瞬时全场浓度的测量。利用粒子散斑成像测量原理自行设计了大范围瞬时浓度场测量系统,并利用该系统对烟雾扩散的瞬时浓度场进行了实际测量。 相似文献
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1引言圆柱绕流是流动与传热领域的基本流动现象,也是历史悠久的研究课题。“经过多年的努力,人们已经获得了圆柱绕流的基本图象,积累了相当丰富的实验及分析资料,但有许多问题至今仍然是不解之谜[1]。在这些问题中,亚临界绕流时的绕流阻力具有重要的意义。在能源、化工、环保等工业领域大量存在的圆管外绕流,其绕流雷诺数大多在104数量级,为典型的亚临界绕流工况。在该雷诺数范围内,圆柱绕流阻力系数Cd≈1.2,处于较高水平。降低亚临界绕流圆柱的流动阻力将产生工业上量大面广的节能效益。为探索实用的流动减阻技术,必须对亚临界… 相似文献
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A simultaneous measurement system that can analyze the flow-structure interactions has been developed. This system consists
of four CCD cameras, two for capturing instantaneous flow fields and two for tracking a solid body. The three-dimensional
vector fields around a cylinder are measured while the motion of the cylinder forced by the flow field is measured simultaneously
with the constructed system. The cylinder is suspended in the circulating water channel and the surface of the working fluid
is forced sinusoidal to make the cylinder bounced. Reynolds number for the mean main stream is about 3500. The interaction
between the flow fields and the cylinder motion is examined quantitatively. 相似文献
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To analyze the complex three-dimensional flow structure of an axial flow fan and determine the validity of its application, PIV is used to provide detailed space and time resolved experimental data for understanding and control of flow field. The high resolution stereoscopic PIV system was successfully employed in this study for the investigation of flow structure around the axial flow fan. Using the once-per-revolution signal from the rotor, image fields were captured at a fixed position of the blades and hence provides the ability to do phase-averaging. The three-dimensional instantaneous velocity fields, phase-averaged velocity fields, instantaneous and mean vorticity distributions of the stereoscopic PIV measurement results were represented at typical planes of the flow field. Phaseaveraged velocity fields were calculated based on 200 frames of the instantaneous stereoscopic PIV measurement results. From the velocity distribution, the vorticity and turbulent intensity distribution, which are known to be major factors of fan noise, were calculated and its diffusion was discussed as they travel downstream. From the reconstructed three-dimensional velocity iso-surface at 8 cross planes of the outlet flow fields, the three-dimensional features can be seen clearly. 相似文献
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方柱绕流是典型的钝体绕流问题,蕴含了丰富的流体力学现象,对这类流动的准确预测面临着诸多挑战.采用自主发展的大涡模拟程序,对来流Mach数M=0.3,Reynolds数ReD=22 000的绕孤立方柱流动进行了细致模拟,亚格子模型使用动力涡黏模型.对计算结果的分析表明,大涡模拟所得的平均流场及Reynolds应力分布与已有实验数据和直接数值模拟结果均吻合较好,验证了预测结果的可靠性;在此基础上对瞬态流场进行了研究,展示了计算条件下方柱绕流分离转捩及尾迹区旋涡交替脱落形成Karman涡街的全过程,为更细致的流动机理探索奠定了基础. 相似文献
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单级高负荷向心透平三维黏性非定常计算 总被引:1,自引:0,他引:1
对一台单级高负荷向心透平进行了三维黏性定常和非定常计算,计算得到的动叶出口以及下游的周向平均流场与文献提供的实验结果符合良好。在此基础上对流动的非定常特性进行了分析,发现由于动叶转速较高,且动叶下游不存在下一级静叶的干涉,流动的非定常效应主要体现在叶片排之间的区域以及动叶通道进口,动叶出口以及下游流动的非定常特性并不明显。非定常计算结果透平的级效率随时间的波动幅度达到了1.3%。 相似文献
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D. I. Okhotnikov V. M. Molochnikov A. B. Mazo A. V. Malyukov A. E. Goltsman I. I. Saushin 《Thermophysics and Aeromechanics》2017,24(6):873-882
Here we present the results of experimental investigation of a cross flow around a circular cylinder mounted near the wall of a channel with rectangular cross section. The experiments were carried out in the range of Reynolds numbers corresponding to the transition to turbulence in a wake of the cylinder. Flow visualization and SIV-measurements of instantaneous velocity fields were carried out. Evolution of the flow pattern behind the cylinder and formation of the regular vortex structures were analyzed. It is shown that in the case of flow around the cylinder, there is no spiral motion of fluid from the side walls of the channel towards its symmetry plane, typical of the flow around a spanwise rib located on the channel wall. The laminar-turbulent transition in the wake of the cylinder is caused by the shear layer instability. 相似文献
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The flow characteristics around a rotating axial fan were experimentally investigated using a phase-averaged PTV velocity field measurement technique. The axial fan has 5 forward-swept blades with a radius of 25 mm. Measurements were carried out at 4 axial planes and 4 radial planes perpendicular to the axis of rotation. For the axial plane measurements, one fan blade was divided into 4 different phases in order to analyze the flow structure according to blade phase. For each case, 500 instantaneous velocity fields were measured and ensemble averaged to obtain phase-averaged velocity vector fields and vorticity contours. In addition, measurements were carried out at two planes around the blade surface. Phase averaged velocity fields show periodic variations with respect to the blade phase. The periodic shedding of the tip vortex at the blade tip is also observed. The phase averaged velocity fields measured in the radial planes show periodic variations according to the fan phase and the distance from the fan. These experimental results can be used to validate numerical calculations and to understand the flow characteristics of forward-swept axial fans. 相似文献