采用遗传算法的自适应随机共振系统弱信号检测方法研究

针对传统自适应随机共振系统只能实现单参数优化的缺点,提出了一种基于遗传算法的多参数同步优化自适应随机共振算法.该算法选用由双稳系统输出的信噪比作为遗传算法的适应度函数,能够实现随机共振系统中多个参数的自适应选取,从而最优地检测出原始信号中的微弱周期成分.同时,将该优化算法和移频变尺度随机共振相结合,可以实现大参数条件下的随机共振.仿真数据和滚动轴承外环故障数据的分析表明,该算法收敛速度快,简单易行,在采样点数较少的条件下能从强噪声背景中检测出微弱的高频周期成分,因此具有良好的工程应用前景.     

随机共振结合RobustICA的两阶段结构损伤定位方法

为实现强噪声背景低信噪比环境下的结构损伤识别,提出一种基于非线性随机共振降噪与鲁棒性独立分量分析(RobustICA)的两阶段损伤定位方法.第一阶段,运用非线性随机共振系统对强噪声低信噪比的测量响应进行预处理,以降低背景噪声的干扰并增强结构响应;第二阶段,结合RobustICA提取包含损伤信息的特征分量对结构响应异常进行识别,之后计算归一化的源分布向量(NSDV)的最大值对结构损伤异常进行定位.框架数值算例结果表明,所提出的算法能够较精确实现信噪比为5dB下的结构损伤异常识别与定位.     

自适应移频变尺度随机共振在故障诊断中的应用

针对移频变尺度随机共振系统参数选择困难的问题,提出了一种基于时频指标的自适应移频变尺度随机共振算法.该算法选用了最高谱峰位置(频域)及过零间距方差(时域)作为优化目标函数,避开了以信噪比等为目标函数时需要预先知道目标信号确切频率的不足,能够自适应地获取最优系统参数,以最大信噪比检测出微弱周期信号.同时,由于移频变尺度随机共振的选用,该自适应算法突破了传统随机共振系统的限制,因此可以检测实际工程中的高频信号.仿真和故障诊断的工程应用结果表明,该自适应算法简单、易于理解,能有效地从强背景噪声中检测出高频微弱周期信号,具有较强的工程实用价值.     

基于改进随机减量法和小波变换的

基于改进随机减量法和小波变换提出了一种新的结构模态参数统计识别方法.随机减量法改进后可直接处理零均值非平稳响应信号,得到自由衰减响应,小波变换的时频域特性可解耦密频、低阻尼系统,自助分布的统计估计能力考虑和降低模态参数识别的不确定性.对提出的方法进行了完整的理论推导,并通过一个四自由度系统的数值算例验证了该方法可靠性.相比较传统的时域方法和直接小波变换方法,该方法具有更高的识别精度,尤其是阻尼比系数.随后的抗噪能力验证结果表明该方法在15dB噪声干扰下仍能够稳定、准确地识别出系统的模态参数,可适用于环境激励下模态参数识别.     

基于改进随机减量法和小波变换的结构模态参数识别

基于改进随机减量法和小波变换提出了一种新的结构模态参数统计识别方法.随机减量法改进后可直接处理零均值非平稳响应信号,得到自由衰减响应,小波变换的时频域特性可解耦密频、低阻尼系统,自助分布的统计估计能力考虑和降低模态参数识别的不确定性.对提出的方法进行了完整的理论推导,并通过一个四自由度系统的数值算例验证了该方法可靠性.相比较传统的时域方法和直接小波变换方法,该方法具有更高的识别精度,尤其是阻尼比系数.随后的抗噪能力验证结果表明该方法在15dB噪声干扰下仍能够稳定、准确地识别出系统的模态参数,可适用于环境激励下模态参数识别.     

水电站厂房结构模态参数的遗传识别方法

环境激励下结构模态参数的时域识别方法是近年来的研究热点,水电站厂房结构一般规模巨大,常规的激励方式会对结构产生不良影响．此外,由于噪声的干扰往往产生众多虚假模态．由于机组停机过程中环境激励响应较易获得,提出一种基于遗传算法的结构模态参数识别方法,采用多信号分类法进行信号定阶．运用该方法通过模拟信号对其进行验证．并将其应用到水电站厂房结构的模态参数识别中．结果表明,该方法能够有效准确地识别出结构的自振频率和阻尼比．     

联合经验模态分解与二次时频分布的参数识别方法

提出了联合经验模态分解和二次时频分布进行模态参数识别的方法.将多自由度系统的响应信号用经验模态分解法分解为单频率响应的振动信号,进而计算模态频率和阻尼;由单频率响应信号的二次时频分布及其与其它质点响应信号的互二次时频分布的比值来识别模态振型,并对一多自由度的线性系统进行了计算,结果表明该方法能较好地识别结构的模态参数,且抗噪声强.     

基于动力特性灵敏度解析代数算法的结构损伤识别:理论与数值分析

基于结构动力特性灵敏度解析解,建立了结构损伤方程组代数表达式,该损伤方程组通过矩阵运算实现,简洁紧凑,有效地避免模态截断问题.同时,基于经典的随机子空间模态算法(stochastic subspace method,SSI)实现结构损伤前与损伤后的模态参数识别.将结构损伤前后模态参数识别结果代入损伤方程组,可以检测出桥梁结构损伤的位置和损伤的程度,该方法无需迭代.利用简支梁桥算例对该模态参数识别方法和损伤识别方法进行了验证和分析.数值计算结果表明,在噪声水平较低地工况下,本文提出的方法对单损伤梁和多损伤梁均能实现损伤定位和损伤程度的判别,计算效率较高.     

自适应扫频随机共振方法的研究

针对大参数信号二次采样随机共振应用的局限性,提出了自适应扫频随机共振方法.该方法根据信号、噪声和系统三者协调作用发生随机共振时的关系,自动调整采样频率和双稳系统的结构参数,从而自动获取随机共振状态.将此方法应用于实际噪声下弱信号的提取,取得了较好的结果.     

非平稳背景噪声下微弱高频CW信号的自适应检测

在强噪声背景下,基于时频联合分析的高频CW信号检测算法性能严重下降,同时标准Kalman滤波器对非平稳背景噪声下微弱高频CW信号也失效.针对此问题,本文提出了一种基于ARMA新息模型的自适应Kalman滤波器检测方法.该方法避免了标准Kalman滤波检测CW信号时需要确定系统噪声统计特性的问题.论文根据CW信号的状态空间随机信号模型,构造了ARMA新息模型,通过在线辨识MA模型参数来估计Kalman滤波增益,从而实现了CW信号的自适应跟踪滤波.仿真结果表明,该方法能够在强噪声背景下动态跟踪CW信号时域波形,且算法简单,实时性强,可用于指导高频CW电报自动接收设备的研制.     

Markedness and its Interpretation in Language Use

Language markedness is a common phenomenon in languages, and is reflected from hearing, vision and sense, i.e. the variation in the three aspects such as phonology, morphology and semantics. This paper focuses on the interpretation of markedness in language use following the three perspectives, i.e. pragmatic interpretation, psychological interpretation and cognitive interpretation, with an aim to define the function of markedness.     

低渗透非均质砂岩油藏启动压力梯度研究

理论推导与室内实验相结合,建立了低渗透非均质砂岩油藏启动压力梯度确定方法。首先借助油藏流场与电场相似的原理,推导了非均质砂岩油藏启动压力梯度计算公式。其次基于稳定流实验方法,建立了非均质砂岩油藏启动压力梯度测试方法。结果表明:低渗透非均质砂岩油藏的启动压力梯度确定遵循两个等效原则。平面非均质油藏的启动压力梯度等于各级渗透率段的启动压力梯度关于长度的加权平均;纵向非均质油藏的启动压力梯度等于各渗透率层的启动压力梯度关于渗透率与渗流面积乘积的加权平均。研究成果可用于有效指导低渗透非均质砂岩油藏的合理井距确定,促进该类油藏的高效开发。     

On Tragic Consciousness In The Works By Ernest Hemingway

As an American modern novelist who were famous in the literary world, Hemingway was not a person who always followed the trend but a sharp observer. At the same time, he was a tragedy maestro, he paid great attention on existence, fate and end-result. The dramatis personae's tragedy of his works was an extreme limit by all means tragedy on the meaning of fearless challenge that failed. The beauty of tragedy was not produced on the destruction of life, but now this kind of value was in the impact activity. They performed for the reader about the tragedy on challenging for the limit and the death.     

Achieving Unusual States of Matter Under High Pressure

正The periodicity of the elements and the non-reactivity of the inner-shell electrons are two related principles of chemistry,rooted in the atomic shell structure.Within compounds,Group I elements,for example,invariably assume the+1 oxidation state,and their chemical properties differ completely from those of the p-block elements.These general rules govern our understanding of chemical structures and reactions.Using first principles calcula-     

Exchange-Correlation and Electronic Excitation Energies from Pairing Matrix Fluctuations

We have developed an adiabatic connection to formulate the ground-state exchange-correlation energy in terms of pairing matrix linear fluctuations.This formulation of the exchange-correlation energy opens a new channel for density functional approximations based on the many-body perturbation theory.We illustrate the potential of such approaches with an approximation based on the particle-particle Random Phase Approximation(pp-RPA).This re-     

Density Functional Theory for the Response of Periodic Systems to Electric Fields Based on the Vector Potential Approach

正The electronic and nuclear(structural/vibrational)response of 1D-3D nanoscale systems to electric fields gives rise to a host of optical,mechanical,spectral,etc.properties that are of high theoretical and applied interest.Due to the computational difficulty of treating such large systems it is convenient to model them as infinite and periodic(at least,in first approximation).The fundamental theoretical/computational problem in doing so is that     

On the Thermodynamic Limit for Responses to Static Electromagnetic Fields

For molecular systems,the quantum-mechanical treatment of their responses to static electromagnetic fields usually employs a scalar-potential treatment of the electric field and a vector-potential treatment of the magnetic field.Although the potential for each field separately is associated with the choice of an(unphysical)origin,the precise choice of the origin for the electrostatic field has little consequences for the results.This is different for the     

An affordable accurate evaluation of the binding conformations predicted by molecular docking studies in bio-system

Franck-Condon factors bridge the gap between theoretical modeling and experimental observations for molecular electronic spectroscopy and electron transfer.Under the displaced harmonic oscillator approximation,multidimensional Franck-Condon factors are decomposed into a product of many one-dimensional(1D)Franck-Condon(FC)factors,and each 1D-FC factor is associated with one Huang-Rhys factor that determines the leading contribution of     

Call for Papers

<正>"The Journal of Shanghai Normal University:Mathematics"is published by Shanghai Normal University as regular issues of The Journal of Shanghai Normal University each year from 2014 in English.The editors-in-chief of the issues are professors Yuhao Cong and Maoan Han.The Journal of Shanghai Normal University was started in 1958 with     

Journal of Donghua University ( English Edition) Contents of Volume 31

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