Structural response reconstruction with transmissibility concept in frequency domain

This paper presents a method for structural response reconstruction in the full structure or in a substructure, using the generalized transmissibility concept in frequency domain. The response reconstruction is based on transforming the measured responses into responses at other selected locations with the transmissibility matrix. The use of transmissibility concept in a substructure for response reconstruction is introduced by taking the interface forces at the interface degrees-of-freedom as input excitations. The First-Order-Hold input approximation is used in the forward response calculation to improve the accuracy of the dynamic response analysis. Numerical studies on a seven-storey plane frame structure are conducted to investigate the accuracy and efficiency of the proposed method and the effects of influencing parameters, such as the system sampling duration, sampling rate, sensor numbers and measurement noise are studied. Accurate reconstruction is achieved in all studies when there is significant vibration in the measured responses.     

Fast reconstruction of computerized tomography images based on the cross-entropy method

Computerized tomography (CT) has been applied to multi-phase flow measurement in recent years. Image reconstruction of CT often involves repeatedly solving large-dimensional matrix equations, which are computationally expensive, especially for the case of on-line flow regime identification. In this paper, a minimum cross-entropy (MCE) reconstruction based on wavelet multi-resolution processing, i.e., an MRMCE method, is proposed for fast reconstruction of CT images. Each row of the system’s matrix is transformed by 1-D wavelet decomposition. A regularized MCE solution is obtained using the simultaneous multiplicative algebraic reconstruction technique (SMART) at a coarse resolution level, where important information of the reconstructed image is contained. Then the solution in the finest resolution is obtained by inverse fast wavelet transformation (IFWT). Both computer simulation and experimental work were carried out for oil-gas two-phase flow regimes. Results obtained indicate that the MRMCE method improves the resolution of the reconstructed images and dramatically reduces the computation time compared with the traditional linear back-projection (LBP), MCE and algebraic reconstruction technique (ART) methods. Furthermore, the new method can also be used to accurately estimate the local time-averaged void fraction of dynamic two-phase flow. It is suitable for on-line multi-phase flow measurement.     

Trend extraction based on separations of consecutive empirical mode decomposition components in Hilbert marginal spectrum

Extracting the underlying trends is an important tool for the analysis of signals. This paper presents a novel methodology for extracting the underlying trends of signals based on the separations of consecutive empirical mode decomposition (EMD) components in the Hilbert marginal spectrum. A signal is initially represented as a sum of intrinsic mode functions (IMFs) obtained via the EMD. The Hilbert marginal spectrum of each IMF is then calculated. The separations of two consecutive IMFs in the Hilbert marginal spectrum are estimated based on their correlation coefficients. The group of the last several IMFs in which the IMFs are close to each other in the Hilbert marginal spectrum will be used for the representation of the underlying trend of the signal. Extensive experimental results are presented to illustrate the rationale and the effectiveness of the proposed method.     

基于独立分量分析的EMD模态混叠消除方法研究

针对经验模态分解(empirical mode decomposition,EMD)算法中存在的模态混叠现象,提出一种应用独立分量分析进行模态混叠消除的新方法.首先应用形态学滤波方法将信号中的噪声予以消除,减少由于噪声因素造成的模态混叠现象.然后将信号进行EMD分解,获得不同的IMF分量,将存在模态混叠成分的IMF分量进行相空间重构,利用基于峭度最大化的独立分量分解算法实现混叠成分的分离,仿真分析和工程应用的结果表明,所提方法能有效地消除EMD分解过程中的模态混叠现象.     

An improvement EMD method based on the optimized rational Hermite interpolation approach and its application to gear fault diagnosis

A demodulation technique based on improvement empirical mode decomposition (EMD) is investigated in this paper. Firstly, the problem of the envelope line in EMD is introduced and the drawbacks of two classic interpolation methods, cubic spline interpolation method and cubic Hermite interpolation method are discussed; then a new envelope interpolation method called optimized rational Hermite interpolation method (O-EMD) is proposed, which has a shape controlling parameter compared with the cubic Hermite interpolation algorithm. At the same time, in order to improve the envelope approximation accuracy of local mean, the parameter determining criterion is put forward and an optimization with Genetic Algorithm (GA) is applied to automatic select the suitable shape controlling parameter in each sifting process. The effectiveness of O-EMD method is validated by the numerical simulations and an application to gear fault diagnosis. Results demonstrate that O-EMD method can improve the reliability and accuracy significantly compared with traditional EMD method.     

基于EMD自相关的表面肌电信号消噪方法

为了更好地消除混杂在表面肌电信号(sEMG)中的噪声,提出一种基于噪声统计特性的EMD自相关消噪方法。首先,对含噪sEMG信号进行EMD分解,并根据噪声统计特性降低低信噪比的高频IMF分量的能量后重组信号。其次,对重组后的信号进行自相关函数特性的EMD分解,并对自相关函数方差低于阈值的高频IMF分量进行小波去噪。最后,把处理后的高频IMF分量和低频IMF分量重构,得到的信号即为消噪信号。实验结果表明,该方法不仅能更好的消除噪声,而且在低信噪比情况下有良好表现。     

A revised Hilbert–Huang transformation based on the neural networks and its application in vibration signal analysis of a deployable structure

A revised Hilbert–Huang method is proposed to deal with the non-linear and non-stationary signals generated from any kinds of the sensors, in order to overcome shortcomings of the Hilbert–Huang method, such as the end swings problem and the undesired intrinsic mode functions (IMFs) at the low-frequency range. Firstly, a radial basis function neural network is used as a pre-processor to extend the length of the signal at the both ends. Secondly, the empirical mode decomposition is applied to obtain IMFs. Thirdly, the selection process is employed to select the optimal IMFs. Finally, an energy–frequency–time distribution can be gained after the Hilbert transformation. Two simulated signals are analyzed to explain the pre- and the post-processor, respectively, by using the above two techniques. The efficiencies of the different bases are compared, and the length of signal extended is analyzed. The correlation coefficients between the analyzed signal and the IMFs are introduced to eliminate the undesired IMFs. In this paper, the revised HHT method has been applied to analyze vibration signals of a deployable structure. A simulated solar array setup is built, which contains six parts: the basal body, a locked mechanism, the synchronism mechanism, the connection joints, the driven parts, and two simulated panels. Vibration signals of the solar array setup in the deployed case that is knocked by a single impulse on the middle of the second panel are estimated, and the results show that the revised Hilbert–Huang method is efficient for non-linear and non-stationary signal analysis.     

基于改进EMD的微机械陀螺随机误差建模方法

为了降低微机械(MEMS)陀螺仪的随机误差,提出一种将改进的经验模态分解法(EMD)与传统建模滤波方法相结合的新方法对随机误差进行处理。首先采用传统EMD算法将信号分解为有限个本征模态函数(IMF),并根据皮尔逊相关系数准则和噪声统计特性提出一种筛选机制,将IMF分为噪声IMFs、混叠IMFs和信号IMFs 3类;其次,对混叠IMFs进行时间序列建模,建模完成后进行卡尔曼滤波拟合;最后,将建模滤波后的混叠IMFs与信号IMFs进行重构,得到最终去噪信号。实验分析结果表明,本文方法在抑制随机误差的效果上有明显的优势,极大地改善了信号的质量,提高了惯导的解算精度。     

基于VMD和互谱分析的供水管道泄漏定位方法

针对低信噪比(SNR)下的供水管道泄漏振动信号用于时延估计泄漏定位误差大的问题,提出基于变分模态分解(VMD)和互谱分析结合的供水管道泄漏定位方法。首先,利用VMD将管道泄漏信号分解为若干个本征模态函数(IMF),对供水管道泄漏信号进行互谱分析确定特征频带;然后,利用IMF分量在特征频带内的能量比例作为选取准则来确定有效IMF分量,并对选取的有效IMF分量进行重构;最后,对重构信号进行时延估计来确定泄漏点位置。为了验证所提泄漏定位算法的有效性,通过仿真和实验分别对互谱与VMD结合、互相关及VMD与相关系数结合3种方法进行研究。实验结果表明,以上3种定位算法的平均相对定位误差分别为2. 53%,8. 62%和16. 86%。     

基于像散原理的并行共焦检测的微形貌参数的可视化测量

为实现对微结构表面轮廓参数的精确测量,用基于像散原理的并行共焦检测系统获取微结构表面的三维信息,进而实现对微结构表面参数的可视化测量。考虑到微结构表面特点,采用累加弦长双三次样条插值曲面对其表面进行重构。并选择高的插值细分倍率获得连续光顺廓形表面,通过拾取拟合曲面上的点而不是廓形局部三角面片上的点实现三维廓形参数评定。由重构曲面模拟结果显示:累加弦长双三次样条重构微结构表面可以有效地实现对微结构表面参数的精确测量。     

钢轨中超声导波激励响应计算方法研究

为了在钢轨中激励出特定模态的导波信号,需确定导波发射探头在钢轨上的安装位置和激励方向,导波激励响应计算方法可通过仿真和计算来研究激励位置、激励方向与响应结果的关系,替代传统的试验验证方法。计算时通过半解析有限元方法建立钢轨中超声导波传播的一般均质波动方程,求解方程得到波数和振型矢量,建立钢轨的系统函数模型,在钢轨指定位置和方向施加激励信号,结合傅里叶变换与反变换计算得到最终的激励响应结果。已知激励位置和方向,结合计算结果可以研究分析各导波模态的激励方法。在西宝高速铁路现场试验表明,激励响应计算结果与实际测试结果误差为0.4%,具有较好的一致性。     

3-D reconstruction of the atomic positions in a simulated gold nanocrystal based on discrete tomography: prospects of atomic resolution electron tomography

A novel reconstruction procedure is proposed to achieve atomic resolution in electron tomography. The method exploits the fact that crystals are discrete assemblies of atoms (atomicity). This constraint enables us to obtain a three-dimensional (3-D) reconstruction of test structures from less than 10 projections even in the presence of noise and defects. Phase contrast transmission electron microscopy (TEM) images of a gold nanocrystal were simulated in six different zone axes. The discrete number of atoms in every column is determined by application of the channelling theory to reconstructed electron exit waves. The procedure is experimentally validated by experiments with gold samples. Our results show that discrete tomography recovers the shape of the particle as well as the position of its 309 atoms from only three projections.

Experiments on a nanocrystal that contains several missing atoms, both on the surface and in the core of the nanocrystal, while considering a high noise level in each simulated image were performed to prove the stability of the approach to reconstruct defects. The algorithm is well capable of handling structural defects in a highly noisy environment, even if this causes atom count “errors” in the projection data.