一种基于FFT功率谱的全隐框玻璃幕墙结构胶脱粘长度检测方法

针对全隐框玻璃幕墙结构胶脱粘长度检测问题,率先提出了基于瞬态脉冲动力响应信号的FFT功率谱脱粘长度检测方法.通过对4个测点进行动力响应实验信号的采集,采用FFT功率谱对实验信号进行了分析评判,并提取功率谱主峰频率对信号总功率的贡献比重η<,i>作为结构胶损伤长度α的因变量.采用Gaussian函数和Lorentzian函数对实验数据进行了拟合,建立了η关于α的函数关系式,并对小损伤的α值进行了检测识别.研究成果表明,该方法有助于全隐框玻璃幕墙结构胶脱粘长度检测技术的推广和应用.     

基于希尔伯特-黄转换的变压力下航空发动机液压管路振动特性研究

以经验模态分解法(empirical mode decomposition,EMD)与希尔伯特黄转换(Hilbert-Huang transform,HHT)作为信号分解与振动频率分析的方法,针对压力突变情况下航空发动机液压管路的振动信号进行HHT分析。对某航空发动机液压管路压力突变时振动信号的分析结果表明,HHT分析方法能够反映航空液压管路在压力突变时所表现的振动特性,而且随着压力的增大,压力突变会导致管路的振动加剧。该方法克服了传统傅里叶变换(fast Fourier transformation,FFT)分析方法无法得到的瞬时频率信息,为分析航空发动机液压管路在压力突变时的非平稳振动信息提供了一种新思路。     

基于谱单元方法的杆件导波数值模拟与损伤检测的时频分析

相比于传统的有限元方法,谱单元法是一种基于FFT算法的频域数值方法,它能够大大降低求解问题的阶数,在模拟高频导波在结构中传播、捕捉结构微小损伤方面尤为高效。以弯曲弹簧模型作为裂纹的数学模型,建立了裂纹杆件谱单元模型,求解高频导波激励下裂纹杆件的波动解。以短时傅里叶变换与Choi-Williams两种时频方法分析裂纹杆件的导波信号的能量时频分布。结果表明:短时傅里叶谱与ChoiWilliams谱均能够准确反映导波信号的时频分布特点,可以实现结构微小损伤的定位与定量分析;短时傅里叶变换的时域分辨率比Choi-Williams法低,但是其能量分布在时域上与导波信号的时域波形吻合更好;随着裂纹的加深,这两种时频分析方法对频域的分辨率更高。     

基于HHT和AE主频统计的岩石破坏进程分析

岩石的AE波形主频已被证明与内部微破裂模式有着紧密的联系。目前对于岩石声发射波形的主要频谱分析方法以快速傅里叶变换(FFT)和小波变换为主,两者都存在时-频测不准和针对非平稳信号的自适应性不强的问题。目前对于岩石内部破坏过程的研究缺乏宏观定量化的分析工具。本文以自适应性强,可以直接求得时-频分布的希尔伯特-黄变换(HHT)及其边际谱为基础,提出了一套新的波形频谱处理和主频统计方法。利用岩石直接拉伸试验的声发射信号验证,本文方法的统计结果与FFT方法统计得到的主频成分分布特征基本相同,但更加稳定。结合主频统计结果,本文对试件全试验过程的微破裂成分与岩石破坏进程的快慢之间的关系进行了定量的统计分析。通过对定量分析结果的讨论,笔者认为直接拉伸加载模式下微观剪破坏对受力方向上摩擦阻力的破坏效应不可忽略,其会造成强度的大幅下降。     

不同方法提取信号模态特征的影响

为了分析非稳态、非线性信号，采用HHT、STFT、小波及小波包来提取信号的特征，较好地验证了HHT的有效性，研究发现，HHT是一种适合非线性、非稳态信号瞬时特征提取的良好方法。     

爆破震动信号的时频分析

针对具体的爆破震动信号,基于短时Fourier变换(STFT)、连续小波变换(CWT)、离散小波变换(DWT)和Hilbert-Huang变换(HHT)进行时频分析比较研究。结果表明:STFT使用的窗函数固定,分辨率单一,其分析结果只能大致反映信号能量随时间的变化;小波变换(WT)以小波基为变换基础,具有多分辨率特点,其分析结果较详细地反映了质点震动强度随时间的衰减起伏变化,但小波谱的能量在频率范围内分布较宽;HHT自适应性强、高效,Hilbert能量谱能清晰地表明能量随时频的具体分布,并且大部分能量都集中在有限的能量谱线上。分析认为HHT是一种全新而更优越的分析与处理爆破震动信号的时频方法。     

基于HHT方法的微差爆破延期时间识别与应用

结合某爆破工程实例,运用HHT方法,首先,对实测爆破震动信号进行EMD分解,得到信号IMF分量;其次,通过IMF分量的Hilbert变换,识别出各段雷管实际的通过起爆时刻点,得到实际微差爆破工程中的延期时间,利用HHT方法的自适应性强和高效性的特点,为爆破延期参数设计提供了一定的分析手段。     

风速谱对大跨度屋盖风振系数的影响

本文基于随机振动理论,在频域内采用风力谱分析法,进行了大跨度梯形钢屋架双坡屋盖随机振动分析。采用6种水平脉动风速谱图,讨论了其对屋盖风振响应和风振系数的影响。同时,讨论了竖向脉动风速谱对所分析大跨屋盖风振响应的影响,以供工程设计及研究工作参考。     

基于HHT信号分析的GFRP锚杆锚固质量无损检测方法研究

为优化土遗址GFRP锚固体系无损检测信号反演分析过程,采用希尔伯特–黄等信号处理方法,对多种完整锚固和缺陷锚固模型的检测信号进行分析。分析过程中首先通过巴特沃斯滤波法消除检测信号中的噪声,然后对消噪后的信号依次进行傅里叶和希尔伯特–黄变换(HHT)分析。试验发现,该处理方法能较为清晰地识别缺陷和杆底反射信号,从而更精确地反演出缺陷位置和锚固长度。此外,利用完整模型和缺陷模型杆底反射的时间差反演出的空浆缺陷长度也与预设工况相近。研究结果为土遗址GFRP锚固长度和空浆缺陷的位置与大小的反演提供了较为系统的分析方案。     

Pushover能力谱方法的基本原理及应用

Pushover分析是一种基于位移的静力弹塑性分析方法,近几年在国内外得到了广泛的重视和应用.本文首先阐述了Pushover能力谱方法的原理及其在SAP2000N中的应用步骤,接着对偏心支撑钢框架算例进行了分析,根据Pushover曲线,对结构性能点进行了试算与逼近的理论计算.另外,算例分析还证明,Pushover能力谱方法能够对结构的屈服机制、薄弱层位置、结构的性能目标等做出评价.     

Modal identification of Di Wang Building under Typhoon York using the Hilbert–Huang transform method

The Di Wang Building is one of the tallest composite buildings in the world, located in downtown Shenzhen City of China about 2 km from the Hong Kong border. On 16 September 1999, Typhoon York – that is the strongest typhoon since 1983 and the typhoon of longest duration on record – attacked Hong Kong and Shenzhen. The wind and structural monitoring system installed in the Di Wang Building timely recorded wind and structural response data. The newly emerged Hilbert–Huang transform (HHT) method in conjunction with the random decrement technique (RDT) is applied to the measured data in this paper to identify dynamic characteristics of the building. A series of natural frequencies and modal damping ratios of the building under different wind speeds in different directions are identified and compared with those from the fast Fourier transform (FFT)‐based method. The variations of natural frequency, total modal damping ratio and net structural modal damping ratio with wind speed and vibration amplitude are also investigated. The results show that the natural frequencies identified by the HHT method are almost the same as those obtained by the FFT‐based method. The first two modal damping ratios given by the HHT method are, however, lower than those by the FFT‐based method, which may indicate that the FFT‐based method overestimates the modal damping ratios. Both the total and the net structural modal damping ratios increase with increasing wind speed and vibration amplitude but the situation is reversed for the natural frequency. Copyright © 2003 John Wiley & Sons, Ltd.     

Enhanced Hilbert–Huang transform and its application to modal identification

The well‐known Hilbert–Huang transform (HHT) consists of empirical mode decomposition to extract intrinsic mode functions (IMFs) and Hilbert spectral analysis to obtain time–frequency characteristics of IMFs through the Hilbert transform. There are two mathematical requirements that limit application of the Hilbert transform. Moreover, noise effects caused by the empirical mode decomposition procedure add a scatter to derivative‐based instantaneous frequency determined by the Hilbert transform. In this paper, a new enhanced HHT is proposed in which by avoiding mathematical limitations of the Hilbert spectral analysis, an additional parameter is employed to reduce the noise effects on the instantaneous frequencies of IMFs. To demonstrate the efficacy of the proposed method, two case studies associated with structural modal identification are selected. In the first case, through identification of a typical 3‐DOF structural model subjected to a random excitation, accuracy of the enhanced method is verified. In the second case, ambient response data recorded from a real 15‐story building are analyzed, and nine modal frequencies of the building are identified. The case studies indicate that the enhanced HHT provides more accurate and physically meaningful results than HHT and is capable to be an efficient tool in structural engineering applications. Copyright © 2012 John Wiley & Sons, Ltd.     

On applicability of Hilbert–Huang transform for vibration analysis of a two-member truss

The Hilbert–Huang transform (HHT) proposed for treating the time history data of nonlinear dynamic systems comprises two parts: the empirical mode decomposition and the Hilbert transform. In this study, focus is placed on the physical interpretation of the HHT results for an elastic two-member truss, for which the nonlinear behaviour can be clearly interpreted at various stages of excitation, from nearly linear, nonlinear, period-doubling, to chaotic. The instantaneous frequency of the truss is computed using the HHT or derivative-based HHT. In each case, the result obtained by the fast Fourier transform is also presented for comparison. It is concluded that the enforcement by the HHT of the data set to be symmetric with respect to the local zero mean in extracting the intrinsic mode functions may result in frequencies that are not physically meaningful. Care needs to be taken when using HHT for interpreting the frequency contents of a nonlinear structure.     

频谱分析在建筑设备电机故障检测与诊断中的应用

本文以建筑设备电机为研究对象,总结了电机故障诊断的方法及特点,阐述了 FFT 频谱分析诊断电机故障机理。通过试验模拟电机故障,对电流信号进行了 FFT 频谱分析。分析结果表明,FFT频谱分析法可以实现电机故障的诊断。     

Time-frequency analysis of typhoon effects on a 79-storey tall building

Di Wang Tower located in Shenzhen, PR China, has a height of approximately 325 m and is a 79-storey tall building. This paper presents selected results of full-scale measurements of typhoon effects on Di Wang Tower. Wind speed, wind direction, wind-induced acceleration and displacement responses were simultaneously and continuously measured from the super tall building with anemometers, accelerometers and global position system (GPS) during a typhoon. The advanced data analysis method called Hilbert-Huang transform (HHT) was adopted in this study to analyze the non-stationary characteristics of wind speed and wind-induced responses of this building under typhoon condition. By using the empirical mode decomposition (EMD) method, the measured data were decomposed into several inherent intrinsic mode functions (IMFs). The probability density and power spectral density of fluctuating wind speed were obtained by traditional methods and were further analyzed by considering time-varying mean values of the measured data via the EMD method. The wind-induced responses with non-stationary features were studied by applying the HHT to each IMF for obtaining their instantaneous frequency and Hilbert-Huang composite spectrum. Meanwhile, the transient energy distributions of the wind-induced responses were analyzed in time-frequency domain, which were compared with the traditional power spectral densities obtained from the fast Fourier transform (FFT) method and those from the wavelet transform. Furthermore, the amplitude-dependent damping ratios were determined by combining the EMD and the random decrement technique (RDT) method. Through comprehensive analysis of the measured data, it was testified that the HHT method is a promising tool for the time-frequency analysis of random signal and can serve as a flexible and effective tool for analyzing field data of wind speed and wind-induced response with non-stationary features.     

非平稳地震激励下结构随机响应及动力可靠性研究

基于美国西部121条基岩强震加速度记录,采用Hilbert-Huang变换(HHT)生成能真实反映地震记录频率和强度双非平稳特性的非均匀调制演变功率谱,并用经验统计方法建立了根据地震矩震级、震源距预测演变谱的统计模型。运用虚拟激励法得到具有特定震级、震源距的演变功率谱作用下结构的非平稳随机响应特性,同时结合首次超越理论,分析了结构的动力可靠度问题,并且与仅具有强度非平稳特性的均匀调制地震随机激励作用进行比较,结果表明,在总能量相同的情况下,双非平稳功率谱的激励会使结构的响应更大,结构更容易失效。     

希尔伯特变换子波反褶积及其改进方案

详细推导和介绍了希尔伯特变换子波反褶积的基本原理与方法,并试图从平均振幅谱的角度对传统方法作出一定的改进,通过对实际地震资料的验证和比较,证明了该方法的正确性和有效性。