共查询到20条相似文献，搜索用时 31 毫秒
1.
The high-rise frame structure has become more and more widespread, like its damage from the complication of the environment. The traditional method of damage detection, which is only suitable for the stationary signal, does not apply to a high-rise frame structure because its damage signal is non-stationary. Thus, this paper presents an application of the short-time Fourier transform (STFT) to damage detection of high-rise frame structures. Compared with the fast Fourier transform, STFT is found to be able to express the frequency spectrum property of the time interval using the signal within this interval. Application of STFT to analyzing a Matlab model and the shaking table test with a twelve-story frame-structure model reveals that there is a positive correlation between the slope of the frequency versus time and the damage level. If the slope is equal to or greater than zero, the structure is not damaged. If the slope is smaller than zero, the structure is damaged, and the less the slope is, the more serious the damage is. The damage results from calculation based on the Matlab model are consistent with those from the shaking table test, demonstrating that STFT can be a reliable tool for the damage detection of high-rise frame structures. 相似文献
2.
3.
针对图像降噪过程中,傅立叶变换存在不能有效表示图像中突变部分的缺点,以及小波变换对图像中的纹理变化不能有效描述的缺点,通过对傅立叶图像降噪和小波图像降噪进行量化和对比研究,提出傅立叶一小波混合降噪技术。结果表明,该技术弥补了单独使用傅立叶图像降噪或小波降噪的缺点,综合了两种降噪技术的优点。 相似文献
4.
论述了从Fourier变换,Gabor变换,小波变换,到Hilbert-Huang变换的理论进展与工程应用,比较了Fourier频谱与HHT边际谱的差异,并对非平稳信号的稳定性度量提出了新的指标。最后,介绍和述评了HHT的研究进展和实际应用。 相似文献
5.
小波分析在各领域中的应用及展望 总被引：1，自引：0，他引：1
小波分析在当今各个领域都得到了广泛的应用,它弥补了傅立叶变换及窗口傅立叶变换的不足,本文根据国内外本领域的研究情况,综合研究了信号处理、图像压缩、通信处理、信息安全、医学、化学、石油地质勘探、机械工程等各领域中的应用。 相似文献
6.
为去除常出现在图像采集和日常摄影中的摩尔纹噪声,提出一种由样条小波生成的紧框架下的稀疏信号恢复算法。该算法利用摩尔纹噪声的频域特性确定受影响的傅里叶频谱区域;利用图像在给定紧框架下的稀疏性,根据压缩感知理论实现数据在傅里叶频谱上的非线性插值。实验结果表明,相比传统频域滤波算法,该算法恢复图像的峰值信噪比更高,更符合人的视觉审美,在去除摩尔纹噪声的同时,还可有效保留图像边缘信息。 相似文献
7.
In this study, ground vibrations due to dynamic loadings from trains moving in subway tunnels were investigated using a 2.5D finite element model of an underground tunnel and surrounding soil interactions. In our model, wave propagation in the infinitely extended ground is dealt with using a simple, yet efficient gradually damped artificial boundary. Based on the assumption of invariant geometry and material distribution in the tunnel??s direction, the Fourier transform of the spatial dimension in this direction is applied to represent the waves in terms of the wave-number. Finite element discretization is employed in the cross-section perpendicular to the tunnel direction and the governing equations are solved for every discrete wave-number. The 3D ground responses are calculated from the wave-number expansion by employing the inverse Fourier transform. The accuracy of the proposed analysis method is verified by a semi-analytical solution of a rectangular load moving inside a soil stratum. A case study of subway train induced ground vibration is presented and the dependency of wave attenuation at the ground surface on the vibration frequency of the moving load is discussed. 相似文献
8.
V. U. Reddy 《Resonance》1998,3(10):79-88
Fast Fourier transform (FFT) is an efficient algorithm for computing the discrete Fourier transform. The discovery of the
FFT algorithm paved the way for widespread use of digital methods of spectrum estimation which influenced the research in
almost every field of engineering and science. In this article, we will first introduce the continuous-time Fourier transform
(CFT), discretetime Fourier transform and discrete Fourier transform (DFT) and then present an example to illustrate the relation
between CFT and DFT. In particular, we bring out the fact that the DFT is a tool to estimate the samples of the CFT at uniformly
spaced frequencies. Next, we introduce the FFT algorithm giving certain key steps in its development. 相似文献
9.
基于图像分解的分层图像修复 总被引：1，自引：0，他引：1
We propose a layered image inpainting scheme based on image decomposition.The damaged image is first decomposed into three layers:cartoon,edge,and texture.The cartoon and edge layers are repaired using an adaptive offset operator that can fill-in damaged image blocks while preserving sharpness of edges.The missing information in the texture layer is generated with a texture synthesis method.By using discrete cosine transform(DCT)in image decomposition and trading between resolution and computation complexity in texture synthesis,the processing time is kept at a reasonable level. 相似文献
10.
推导出在高次谐波干扰下,PARK矢量模平方函数的数学表达式,消除直接进行定子电流分析时基波频率对特征频率的影响。但是新增的频率成分很容易被直流分量、2f分量和4f分量淹没,对PARK矢量模平方函数进行傅立叶变换效果很差。采用多分辨率小波分析,对其各层系数进行分解与重构,其中第7层高频系数和第8层高频系数重构后的波形在发生故障时幅值明显大于无故障时的波形,对电机故障有很高的辨识度,是一种有效的方法。 相似文献
11.
图像融合是信息融合在图像处理领域的一个重要应用．由于小波分析在时域和频域同时具有趋好的局部化及多分辨特性，小波分析已成为图像融合领域的一种主流技术．近几年发展起来的多子带小波，更使小波图像融合进入了一个新的领域．从小波及多子带小波的分解与重建算法，以及对多子带小波的特性分析，得出基于多子带小波的图像融合具有明显的优点，同时也给出了小波融合系数算法．几个评价图像质量的指标，用于评定融合方法的优劣． 相似文献
12.
CHE Ai-lan IWATATE Takahiro ODA Yoshiya GE Xiu-run 《浙江大学学报(A卷英文版)》2006,7(11):1856-1863
INTRODUCTION It is well known that micro-tremor observation is one of the most convenient methods for investi- gating the dynamic characteristics of the surface ground and the affected structure (Bard, 1998; Dow- rick, 1997). Micro-tremor is a kind of geophysics information related to soil formation of site, corre- sponding to engineering geological condition. The frequency characteristics of micro-tremor can be obtained by spectral analyses of its signals, which can be used to probe into… 相似文献
13.
根据小波变换和噪声信号的能量分布特性,提出了一种先用小波变换对含噪图像进行多尺度分解,求出各尺度小波变换高频系数的噪声方差和阈值,利用各尺度的阈值对高频系数进行处理,然后利用小波变换系数重构图像,实现图像降噪的方法;实验结果说明该方法可以有效地降低噪声,又可以较好地保持图像细节。 相似文献
14.
融合小波多尺度分析方法及分形纹理提取方法在遥感影像信息提取方面的优势,提出高分辨率遥感影像小波域分形纹理特征计算方法,以获取地物多尺度分形纹理属性,为遥感影像地类识别提供更好的标识。首先对遥感影像进行小波多尺度分解,进而基于DBC、多重分形纹理计算方法在各个分解层上提取地物纹理特征,通过比较分析,从中选取更为有效的小波域分形纹理特征。基于该方法,利用福州市高空间分辨率QuickBird遥感影像进行试验,并对QuickBird影像进行三级小波分解及纹理提取,结果表明：小波第一、第二分解层粗影像（CA1、 CA2）及三方向平均细节影像（L1、 L2）的DBC空隙特征及多重分形分维数结果作为最终甄选的小波域分形纹理特征更为合适。 相似文献
15.
16.
首先对雷电流的波形进行分析,然后对雷电流的脉冲函数模型进行傅里叶变换,得出雷电流的频谱函数、雷电流峰值比率的频谱及雷电流峰值比率积累的频谱,在给定波形的条件下绘出雷电流的频谱图、雷电流峰值比率的频谱图及雷电流峰值比率积累的频谱图,然后找出雷电危害的重要波段所在。这对雷电防护装置的设计具有重要的指导意义。 相似文献
17.
基于样图的纹理合成基本思想是根据给定的小区域的纹理样本,拼合生成任意大小的纹理图像并且在视觉上与样本是相似而连续的。通过对基于样图的纹理合成算法进行研究,在待合成纹理块的搜索策略上,提出优先搜索前一个已合成纹理块在样图中的位置附近,快速定位下一个用于合成的纹理块。在纹理块的匹配策略中引入小波变换,结合小波变换后的小波系数和小泼变换后的低频域图像进行块的重叠区域匹配,最后使用最小路径法将待合成纹理块缝合到输出图像中。充分考虑了样图的结构信息并提高了合成速度,获得了较好的纹理合成效果。 相似文献
18.
The all-phase fast Fourier transform (apFFT) is proposed as a digital demodulation algorithm in place of the fast Fourier transform (FFT) for orthogonal frequency division multiplexing (OFDM) based multiple-input multiple-output (MIMO) communication systems. The amplitude spectrum of apFFT-demodulated symbols is the square of that of the FFT, which helps reduce the Gaussian noise to a great extent. Moreover, the phases of apFFT symbols are not affected by the frequency shift between the transmitter and receiver oscillators. These properties particularly appeal to MIMO systems over frequency-selective fading channels. The proposed MIMO-OFDM system employing the apFFT is validated using the spatial channel model (SCM) proposed by the third generation partnership project (3GPP). The simulation results demonstrate that the performance of the proposed system after compensating for the rate loss due to zero bits inserted in the space-frequency OFDM (SF-OFDM) coding scheme, still considerably outperforms the conventional system over 3GPP SCM channels, especially under poor channel conditions. 相似文献
19.
LI Mao-quan XU Zheng-quan 《浙江大学学报(A卷英文版)》2006,7(12):2057-2062
INTRODUCTION Currently, main video coding algorithms, such as H.26x and MPEG families are all based on block discrete cosine transform (BDCT). At low bit rate, all these BDCT-based algorithms suffer from visible blocking artifacts, which are easily noticeable as the discontinuities between neighboring blocks, particu- larly in flat and low activity homogeneous areas of the image because high frequency DCT coefficients are inclined to be quantizd to zeros due to the high quan- tizatio… 相似文献
20.
郑明辉 《实验室研究与探索》2008,27(11)
首先论述了基于小波变换的谐波检测的原理,根据目前小波变换在三相不对称系统谐波检测中存在的无法分离基波信号之不足,介绍了一种用于三相不对称系统的基于周期交错的测量方法。针对MRA算法既不能直接可靠地估算三相交流信号的基波成分(50 Hz),也不能精确地提取信号的谐波分量的缺点,探讨了将快速傅立叶变换和小波变换相结合的方法,利用小波变换的奇异信号检测能力和较好的时域分辨率,结合傅立叶变换准确的频域分辨能力对电网谐波信号模型进行了分析。文中归纳出基于小波变换的谐波监测方法。该方法的技术优势是可以实时跟踪谐波信号的变化。仿真实验结果表明了该方案能够满足电力系统中谐波检测的实时性要求。 相似文献