基于小波变换的大型输电铁塔损伤位置识别

利用空间域信息进行小波变换的结构损伤位置识别方法。采用双正交小波bior6.8对结构的位移曲线进行一个尺度的小波分解,精确地识别了等截面和渐变截面悬臂梁的损伤位置,验证了空间域信息小波变换方法对结构损伤位置识别的有效性。针对土木工程结构的复杂性、输入不完备性等特点,提出了利用环境激励下的结构振动曲线进行小波变换的结构损伤位置识别方法,并将该方法应用于大型输电铁塔的损伤位置识别。结果表明,该方法能有效地识别沿高度刚度均匀分布或渐变的高耸格构式塔架的损伤位置,但对存在刚度突变的塔架,则无法有效地识别刚度突变处的损伤。     

Vorticity evolution mechanism in near‐field of a transverse jet

Abstract

Flow structure and vorticity evolution processes in the near field of an elevated jet in a crossflow are experimentally studied in a wind tunnel. The instantaneous and time‐averaged flow field characteristics are observed and measured by using a flow visualization technique and a high‐speed Particle Image Velocimeter (PIV). Time histories of the instantaneous velocity of the vortical flows in the shear‐layer are recorded by a hot‐wire anemometer and a high‐speed data acquisition system in order to analyze the frequency characteristics of the traveling coherent structure in the shear‐layer. Experiments are performed between two different jet‐to‐crossflow momentum flux ratios R = 0.08 and 0.56, which are selected from two regimes with different kinds of flow patterns at a fixed crossflow Reynolds number 2051. The behaviors and mechanisms of the vortical flow structure and the vorticity evolution mechanisms appear to be distinct in different flow regimes. By analyzing the pictures of the smoke flow visualization and the instantaneous vorticity contour maps, two kinds of vorticity evolution mechanisms, “shear‐induced vortices” and “swing‐induced vortices”, can be identified in the shear‐layer evolving from the jet exit. The time‐averaged velocity field and vorticity properties are also discussed in this paper.     

Continuous two-dimensional on-axis optical wavelet transformer and wavelet processor with white-light illumination

The wavelet transform can be expressed mathematically as a convolution between the input function and a continuous set of scaled wavelet mother functions. Optics has managed to implement only the hybrid wavelet transform in which the set of scaled wavelet mother functions is discrete but the shift is continuous. White-light illumination is used to obtain a two-dimensional, fully continuous, on-axis wavelet transformer. When the illumination source is also spatially incoherent, a complete wavelet processor may be constructed.     

H型断面渐近发散振动气动力特征的数值模拟研究

基于计算流体动力学(CFD)数值模拟和连续小波变换的方法研究了渐近发散振动条件下H型断面的非线性气动力。采用二维非定常不可压缩雷诺平均N-S方程结合重整化群(RNG)k-湍流模型计算纯扭转或竖向渐近发散振动条件下的气动力。采用复Morlet小波对气动力进行连续小波变换,结合蛇形罚函数方法提取小波脊。由小波脊识别气动力的各瞬时频率及对应的瞬时振幅。研究表明:H型断面在大振幅振动条件下的气动力存在多倍于强迫振动频率的高次谐波,各频率成份的瞬时振幅与激励瞬时振幅间存在复杂的非线性关系。     

舰船地震波场分析

简述舰船地震波场的产生机理,并研究小波谱用于舰船地震波信号的处理方法.对湖试数据做了传统谱及小波谱的分析对比,得到舰船地震波信号的时频特征.说明舰船海底地震波技术应用于舰船目标探测和定位的可行性及其应用前景.     

基于最大坡度法提取非平稳信号小波脊线和瞬时频率

提出一种基于最大坡度法的非平稳信号小波脊线提取和瞬时频率识别新方法。该方法首先对非平稳响应信号进行连续复Morlet小波变换,其时间轴、小波尺度轴及小波系数模值构成一个三维坐标系（x, y, z）;其次从预先设定的小波脊线初始点出发,在一定范围内进行搜索,并分别计算其在时间-尺度平面（x-y）的距离、z方向的距离及小波脊线的坡度值。最后,求解位于最大坡度方向上的各空间点并将其连接成线即为所求的小波脊线。采用三个非平稳信号数值算例和一个拉力时变的拉索试验验证了最大坡度法的有效性,并与基于小波系数模局部极大值的脊线提取方法、动态规划法及瞬时频率理论值进行比较。数值模拟和试验结果表明,该方法能够有效提取非平稳响应信号的瞬时频率,且识别精度优于基于小波系数模局部极大值和基于动态规划的小波脊线提取方法。     

Wavelet transform-based strain estimator for elastography

A new signal processing algorithm based on a wavelet transform (WT) is proposed for instantaneous strain estimation in acoustic elastography. The proposed estimator locally weighs ultrasonic echo signals acquired before tissue compression by a Gaussian window function and uses the resulting waveform as a mother wavelet to calculate the WT of the postcompression signal. From the location of the WT peak, strain is estimated in the time-frequency domain. Because of the additive noise in signals and the discrete sampling, errors are commonly made in estimating the strain. Statistics of these errors are analyzed theoretically to evaluate the performance of the proposed estimator. The strain estimates are found to be unbiased, but error variances depend on the signal properties (echo signal-to-noise ratio and bandwidth), signal processing parameter (time-bandwidth product), and the applied strain. The results are compared with those obtained from the conventional strain estimator based on time-delay estimates. The proposed estimator is shown to offer strain estimates with greater precision and potentially higher spatial resolution, dynamic range, and sensitivity at the expense of increased computation time.     

利用小波逆变换模拟随机风场的脉动风

首先对洞庭湖大桥处的自然脉动风进行了小波分析，从分析结果可以看出．自然脉动风具有一定的间歇性和局部相似性。传统的谐波合成法（WAWS）和线性滤波器方法（ARMA）虽然可以模拟随机风场的脉动风，但是它们无法模拟脉动风的局部相似性和间歇性。针对这一点，采用Meyer小波基，利用小波逆变换，模拟随机风场的脉动风。最后，根据目标谱，模拟了随机风场的脉动风，模拟的脉动风具有和自然脉动风类似的间歇性和局部相似性，同时模拟脉动风的风谱与目标风谱基本吻合，说明了论文方法的有效性。     

Some aspects of aerodynamic flow control using synthetic-jet actuation

Aerodynamic flow control effected by interactions of surface-mounted synthetic (zero net mass flux) jet actuators with a local cross flow is reviewed. These jets are formed by the advection and interactions of trains of discrete vortical structures that are formed entirely from the fluid of the embedding flow system, and thus transfer momentum to the cross flow without net mass injection across the flow boundary. Traditional approaches to active flow control have focused, to a large extent, on control of separation on stalled aerofoils by means of quasi-steady actuation within two distinct regimes that are characterized by the actuation time scales. When the characteristic actuation period is commensurate with the time scale of the inherent instabilities of the base flow, the jets can effect significant quasi-steady global modifications on spatial scales that are one to two orders of magnitude larger than the scale of the jets. However, when the actuation frequency is sufficiently high to be decoupled from global instabilities of the base flow, changes in the aerodynamic forces are attained by leveraging the generation and regulation of 'trapped' vorticity concentrations near the surface to alter its aerodynamic shape. Some examples of the utility of this approach for aerodynamic flow control of separated flows on bluff bodies and fully attached flows on lifting surfaces are also discussed.     

基于颜色矩的改进尺度不变特征变换的移动机器人定位算法

针对基于图像外观的移动机器人定位中图像特征提取与匹配实时性和准确性差的问题,提出基于颜色矩的改进尺度不变特征变换分级图像匹配算法。该算法先由颜色矩来排序图像序列,再由改进尺度不变特征变换特征与排序后图像序列精确匹配实现定位。其中,改进的尺度不变特征变换算法以基于采样的迭代搜索算法检测极值点,由Sobel算子计算特征点的梯度方向和幅值,提高尺度不变特征变换算法速度及匹配精度。实验结果表明:改进的尺度不变特征变换算法降低误匹配率约9.2%,特征提取与匹配耗时减少约25.8%;分级图像匹配算法减少尺度不变特征变换特征计算代价约70%,减少总体耗时约43.3%。     

离心-温度复合装置的自学习切换控制方法研究

针对惯性仪表的复合校准问题,设计了基于离心-温度复合装置的自学习切换控制方法,实现了高精度、高均匀性的温度场控制。根据离心机不同工况下的温度箱控制系统结构不同,切换控制方案可满足系统在高低温下的精度要求,自学习PID控制算法解决了控制过程中存在的温度波动问题。离心机旋转状态下和非旋转状态下的实验结果表明：该控制系统性能良好,在-55～80℃内的温度控制误差在±0.1℃之内。     

小波多分辨率分析在激光扫描回波信号处理中的应用

小波变换具有表征信号局部特征的能力，适于分析信号中的瞬态和奇异现象，并可展示其成份，所以采用小波多分辨率分析方法对激光回波弱信号进行处理。利用这种方法，可以有效消除噪声，提取有用的信号。结果证明小波多分辨率分析对于激光回波信号处理十分有效，提高了信号分析的准确性。     

Wavelet-enhanced bayesian classification of surface nanostructures observed in pentacene thin films

In recent years, the wavelet transform has proven to be an extremely powerful image-processing tool. Here, we have developed a wavelet-enhanced Bayesian methodology to analyze the AFM images of organic crystals, such as pentacene, using the Haar wavelet transform. This methodology segments and identifies structures in AFM data and extracts quantitative information such as grain size, perimeter, and orientation. This methodology relies on a Naïve Bayesian classification system, which determines whether each data point corresponds to a peak or a valley with a finite statistical probability based on analysis of a synthetic teaching image. In this work, we apply this technique to AFM images of organic crystal films deposited on three different substrates.     

Elementary Vortex Processes in Thermal Superfluid Turbulence

By solving pertinent mathematical models with numerical and computational methods, we analyze the formation of superfluid vorticity structures in a turbulent normal fluid with an inertial range exhibiting Kolmogorov scaling. We demonstrate that mutual friction forcing causes quantum vortex instabilities whose signature is spiral vortical configurations. The spirals expand until they accidentally meet metastable, intense normal fluid vorticity tubes of similar curvature and vorticity orientation that trap them by driving them towards low mutual friction sites where superfluid bundles are formed. The bundle formation sites are located within the tube cores, but, due to tube curvature and many-tube interaction effects, are displaced by variable distances from the tube centerlines as they follow the contours of the latter. We analyze possible implications of these processes in fully developed thermal superfluid turbulence dynamics.     

Multiscale windowed Fourier transform for phase extraction of fringe patterns

A multiscale windowed Fourier transform for phase extraction of fringe patterns is presented. A local stationary length of signal is used to control the window width of a windowed Fourier transform automatically, which is measured by an instantaneous frequency gradient. The instantaneous frequency of the fringe pattern is obtained by detecting the ridge of the wavelet transform. The numerical simulation and experiment have proved the validity of this method. The combination of the windowed Fourier transform and the wavelet transform makes the extracted phase more precise than other methods.     

基于Hilbert-Huang变换的心率变异信号分析

提出一种基于Hilbert-Huang变换(HHT)的心率变异信号分析的新方法。心率变异分析被广泛应用于评估心脏自律功能以及疾病诊断领域。为获得更多心率信号内在特征,首先利用经验模态分解(Empirical Mode Decomposi-tion,EMD)方法将信号分解为一组固有模态函数(Intrinsic Mode Function,IMF),运用Hilbert变换计算并分析各层IMF的瞬时频率和瞬时幅值,从而获取信号所包含的内在信息、心率变异突发时刻和变化趋势。结合积分脉冲频率调制(Inte-gral Pulse Frequency Modulation,IPFM)模型模拟出的心率信号以及真实的心率信号,利用小波分析方法以及HHT方法对心率信号进行对比分析,实验结果证明了HHT方法的可行性,显示了该方法相对于小波分析方法的优势。     

Maximum likelihood principal components regression on wavelet-compressed data

Maximum likelihood principal component regression (MLPCR) is an errors-in-variables method used to accommodate measurement error information when building multivariate calibration models. A hindrance of MLPCR has been the substantial demand on computational resources sometimes made by the algorithm, especially for certain types of error structures. Operations on these large matrices are memory intensive and time consuming, especially when techniques such as cross-validation are used. This work describes the use of wavelet transforms (WT) as a data compression method for MLPCR. It is shown that the error covariance matrix in the wavelet and spectral domains are related through a two-dimensional WT. This allows the user to account for any effects of the wavelet transform on spectral and error structures. The wavelet transform can be applied to MLPCR when using either the full error covariance matrix or the smaller pooled error covariance matrix. Simulated and experimental near-infrared data sets are used to demonstrate the benefits of using wavelets with the MLPCR algorithm. In all cases, significant compression can be obtained while maintaining favorable predictive ability. Considerable time savings were also attained, with improvements ranging from a factor of 2 to a factor of 720. Using the WT-compressed data in MLPCR gave a reduction in prediction errors compared to using the raw data in MLPCR. An analogous reduction in prediction errors was not always seen when using PCR.     

Detection and characterization of transport barriers in complex flows via ridge extraction of the finite time Lyapunov exponent field

This paper proposes an algorithm to detect and characterize ridges in the finite time Lyapunov exponent (FTLE) field obtained from a continuous dynamical system or flow. These ridges represent time‐dependent separatrices of the flow and are also called Lagrangian coherent structures (LCS). LCS have been demonstrated to be an effective way to analyze realistic time‐chaotic flows, although they can be quite complex. Therefore, in order to exploit the information that LCS can provide it is important to locate and characterize these structures in a systematic way. This can be accomplished by interpreting the FTLE as a height field and detecting the LCS as ridges of this graph. Methodologies developed in the image processing framework are integrated with dynamical system inspired approaches in order to characterize ridge strength and location. The main novel contribution of the proposed algorithm is a scheme to connect sets of points into curves or surfaces (rather than distributions of points around a ridge axis) and classify these curves or surfaces using a dynamical systems measure of strength. This approach provides the capability to track ranked LCS in space and time. The results are presented for a simple analytical model and noisy LCS from realistic three‐dimensional geophysical fluid data. Copyright © 2010 John Wiley & Sons, Ltd.     

Damage detection of cracked beams based on wavelet transform

In this paper, a damage detection method based on a continuous wavelet transform is proposed and applied to analyze flexural wave in a cracked beam. For flexural waves obtained from FEM or experiments, some useful characters of the incident, reflected and transmitted waves at a certain frequency can be extracted by the Gabor wavelet to exactly identify the damage location and its extent. The orientation of an inclined crack is also discussed in the paper.     

基于iDDES的双三角翼大迎角非定常涡破裂特征分析

采用基于两方程k-ω-SST模型的iDDES方法对80°/65°双三角翼涡破裂流动进行了数值模拟,获得了迎角α=30°~40°范围内,涡破裂在双三角翼主翼面上方发生时的气动力、表面压力、空间涡结构、湍动能等流动信息,在与风洞实验充分比对的基础上,详细分析了涡破裂发生时的涡破裂形态,表面压力均方根值分布,非定常气动力、表面压力脉动等流动特征,对涡破裂与气动力频谱、表面压力/压力脉动、空间速度、湍动能分布之间的相互关系进行了阐述,并分析了以这些流动信息为判据得到的涡破裂位置之间的相关性。