快速傅里叶变换FFT及其应用

利用快速傅里叶变换FFT将图像信号从空间域转换到频域进行分析,使快速卷积、目标识别等许多算法易于实现;然后根据图像信号的灰度结构特征和频谱分布,用Butterworth带通滤波器和二维维纳滤波器进行滤波处理,去除图像信号中的低频干扰和噪声信号;再利用傅里叶反变换将信号还原。结果显示,处理后的模拟远程高空卫星照片轮廓清晰可见。     

基于小波降噪和短时傅里叶变换的主轴突加不平衡非平稳信号分析

针对主轴运行过程中突加不平衡而产生的非平稳信号无法采用传统的傅里叶变换对信号进行分析处理的问题,提出一种采用小波降噪与短时傅里叶变换相结合对主轴振动特征信息进行准确提取的方法,该方法利用小波降噪技术对非平稳信号进行滤波处理,再对滤波处理后的信号进行重构,最后通过短时傅里叶变换精确获取主轴振动幅值,通过仿真和实验验证了该方法的有效性。     

基于卡尔曼滤波的STFT域回声抵消算法

提出了一种低复杂度的短时傅里叶变换域卡尔曼滤波算法来解决声学回声抵消问题。首先在短时傅里叶变换域建立了基于频域卷积传递函数的观测方程,并利用一阶马尔科夫模型对频域回声路径进行建模,给出了精确的卡尔曼滤波方程,并讨论了过程噪声和观测噪声的估计问题。为降低算法计算复杂度,提出了低复杂度卡尔曼滤波算法。另外,在更新滤波器时加入远端信号邻近频点的信息来进一步提高回声抵消性能。实验结果表明,所提算法对近端干扰不敏感,不需要额外的双端对讲检测算法,且比传统的频域自适应滤波算法具有更快的收敛速度。     

用于分数傅里叶域滤波位相元件设计新算法

基于部分相干成像和分数傅里叶变换理论,建立成像系统的分数傅里叶域滤波模型,提出了可快速设计分数域位相型滤波片的 FrPI 算法。此算法将逆向设计预设初位相与分数傅里叶迭代技术相结合,针对成像系统中不同的设计要求可快速设计出所需的分数域滤波片结构。模拟结果表明,对数值孔径有限的部分相干成像系统,使用新算法设计的分数域滤波片,可有效补偿由于高频损失带来的图像失真,从而使局部线宽偏差和面积偏差分别由滤波前的 36.548nm 和 39.09%下降到了 15.234nm 和 7.72%,明显减少了空间像畸变。     

基于曲线特征分段的多阶FRFT滤波提取齿轮早期故障特征

对于变速器齿轮早期微弱故障特征难以提取的问题,提出了一种基于曲线特征进行分段的多阶分数阶傅里叶变换(Fractional Fourier Transform,FRFT)滤波方法。首先,依据振动信号频率曲线的特征将目标档位的啮合频率曲线分成若干频率近似线性变化的信号段,然后通过计算确定相应信号段的分数阶傅里叶变换的滤波最佳阶次,再逐段进行滤波,从而分离出包含故障特征信息的目标阶比分量,进而进行故障特征提取。通过采用该方法分析变速器变加速工况振动信号,结果表明,基于曲线特征进行分段的多阶FRFT滤波能够有效分离出啮合频率分量,对分离出的分量进行阶次包络解调分析,能准确提取出齿轮微弱故障特征。     

差分吸收光谱测量臭氧浓度信号去噪的实验研究

对差分吸收光谱测量臭氧浓度信号去噪进行了实验研究。首先利用常用的小波变换、Savitzky-Golay滤波和傅里叶变换滤波这3种方法对臭氧的吸收光谱分别进行去噪处理,得到各自去噪后的吸收光谱,发现小波变换与Savitzky-Golay滤波可以很好地拟合特征吸收,傅里叶变换滤波稍差;然后,利用信噪比与均方根误差对所得光谱进行分析评价。实验结果表明:Savitzky-Golay滤波对信号去噪的效果最好,可优先应用于臭氧的光谱计量分析。     

一种新颖的科氏流量计数字信号处理方法

利用矩形自卷积窗对谐波和白噪声的抑制作用,加窗进行短时傅里叶变换能很好的跟踪测量信号频率,而且加窗后的信号能直接用于滑动Goertzel算法测量相位差的特性,提出了一种新的科氏流量计信号处理方法.仿真结果表明整个信号处理算法的测量精度高,实时性好,便于系统实现.     

飞机颤振试飞试验信号的广义时频滤波

针对飞机颤振试飞试验信号噪声过大的问题,提出了一种广义时频域滤波算法。算法采用分数阶傅里叶变换对线性扫频激励及其响应信号进行广义时频分析,利用该类信号在分数阶傅里叶域内的聚焦特性,有效提取真实响应信号,达到信噪分离的目的。给出了具体的滤波算法,并将其应用于仿真算例和实际试飞数据,结果表明该方法可显著提高信号的信噪比。     

龙洗三维液体表面重力波的动态测量

在龙洗的强迫振动实验中,当龙洗壳壁受到一定频率激振力作用时,液面出现不同形态的大幅重力波现象.由于重力波液面变形幅度较大、水花飞溅,为了满足测试要求,根据交叉光轴的光学原理设计了实验测试系统,采用数字条纹光栅投影图像,利用高速图像采集系统连续采集.并进行中值滤波、傅里叶变换、频域滤波、傅里叶反变换等处理,最终可得到第一阶及第二阶大幅重力波任意时刻的三维形貌及大幅重力波任意点的时间历程.这是对壳液耦合系统中自由表面波进行实验测试的新尝试,为今后的理论研究提供了可靠的实验数据.     

融合CNN和ViT的声信号轴承故障诊断方法

针对轴承故障诊断任务数据量少、故障信号非平稳等特点,提出一种短时傅里叶变换、卷积神经网络和视觉转换器相结合的轴承故障诊断方法。首先,利用短时傅里叶变换将原始声信号转换为包含时序信息和频率信息的时频图像。其次,将时频图像作为卷积神经网络的输入,用于隐式提取图像的深层特征,其输出作为视觉转换器的输入。视觉转换器用于提取信号的时间序列信息。并在输出层利用Softmax函数实现故障模式的识别。试验结果表明,该方法对于轴承故障诊断准确率较高。为了更好解释和优化提出的轴承故障诊断方法,利用t-分布领域嵌入算法对分类特征进行了可视化展示。     

Estimation of Parameters of Universal Distribution of Moments of Failure of Products

A method is proposed for estimating the parameters of a mixture of exponential and Weibull distributions for which the accuracy of preliminary estimates obtained by graphical analysis is refined in accordance with the criterion of maximum likelihood. The efficiency of the proposed method is supported by the results of statistical modeling.     

Evaluation of optical properties of highly scattering media by moments of distributions of times of flight of photons

A novel method for the determination of the optical properties of tissue from time-domain measurements is presented. The data analysis is based on the evaluation of the first moment and the second centralized moment, i.e., the mean time of flight and the variance of the measured distribution of times of flight (DTOF) of photons injected by short (picosecond) laser pulses. Analytical expressions are derived for calculation of absorption and of reduced scattering coefficients from these moments by application of diffusion theory for infinite and semi-infinite homogeneous media. The proposed method was tested on experimental data obtained with phantoms, and results for absorption and reduced scattering coefficients obtained by the proposed method are compared with those obtained by fitting of the same data with analytical solutions of the diffusion equation. Furthermore, the accuracy of the moment analysis was investigated for a range of integration limits of the DTOF. The moment analysis may serve as a comparatively fast method for evaluating optical properties with sufficient accuracy and can be used, e.g., for on-line monitoring of optical properties of biological tissue.     

Analysis of the rate of propagation of the wave of change of boiling modes

An approximate analytical expression is derived for the velocity of the front of the wave of change of boiling modes on a rod and on a plate. The impact of the Thomson effect and of the heater orientation in the gravity field is included. Adequate agreement is demonstrated between the derived relations and experimental data.     

Estimation of potentialities of methods of summation of direct measurement errors

Conventional methods for summation of direct measurement errors are considered. Conditions under which these methods provide consistent results are stated. It is proposed to utilize for characteristic of the total error, its interval estimator or the half-sum of the value obtained by adding up its arithmetic and geometric random errors.Translated from Izmeritel'naya Tekhnika, No. 4, pp. 10–12, April, 1995.     

空压机轴承箱蜗壳温度探头油封改造

由于空压机进气侧轴承箱蜗壳温度探头密封效果不好,使空压机及其后续管道受到油污染。后将温度探头的O形圈密封改为骨架油封,杜绝了轴承箱漏油问题。文章简介空压机的结构和技术参数,详细介绍了骨架油封的制作和优点。     

Characteristics of mechanical properties of materials in studies of conditions of attainment of marginal states

It is shown that conditions of attainment of marginal states in the material of structural components are formulated on the basis of analysis of force and deformation criteria of formation and development of destruction. The parameters of these criteria are data on types of structural materials, standard and special characteristics of their mechanical properties, structural forms of considered elements of the equipment, and their operating stress loading. In this case, the construction of a system of state equations for describing interrelation of current damage, external actions, and responses to them is based on the concept of calculating variations in properties of materials at all stages of the design life cycle.     

Determination of parameters of microstructural inhomogeneity of deformation of metals by the method of modeling

The article suggests a method of evaluating the microstructural inhomogeneity of deformation of metals by modeling. The method includes the measurement of deformations of metal according to meshes of a dividing grid with small base and the calculation of the distribution parameters of microdeformations in model representation. It is shown that the modeling method makes it possible objectively to evaluate the microinhomogeneity of deformation of metals independently of the chosen mesh size of the dividing grid. New structural characteristics are introduced: the base and wave of variation expressing the degree of crumbling or amalgamation of metal grains by inhomogeneity of deformation.Translated from Problemy Prochnosti, No. 7, pp. 40–44, July, 1991.     

水三相点复现的不确定度评定

水三相点是开尔文热力学温度的唯一基准点，也是ITS-90国际温标重要的定义固定点。因此，水三相点不确定度分析对整个温标的建立、温度量值传递起着至关重要的作用。近3年来，中国计量科学研究院研制出一系列高质量的水三相点容器，加强了水三相点的研究，为不确定度的分析提供了更为可靠的实验依据。同时，不确定度的分析也是客观评价新研制容器性能的一个重要指标。因此，根据实验结果对新研制容器所复现的水三相点进行了不确定度评定。评定结果表明，其扩展不确定度为0．16mK(k=2．69，P=0．99)。