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1.
碳纤维板与钢梁之间的界面连接情况影响着钢梁的加固效果以及承载性能的发挥,为更好地判别脱粘病害,探究出一种有效的界面脱粘位置定性识别方法。首先制作碳纤维板加固钢梁后的未脱粘试件和脱粘试件,然后通过采用局部敲击指定位置的方法来获取声音信号,并采用Welch功率谱密度(PSD)估计法和快速傅里叶变换(FFT)分析声音信号中的频谱特征。结果表明：从低阶振动频率范围0～500 Hz来看,PSD估计法的2条曲线峰值差别明显,存在脱粘损伤部位的PSD曲线峰值处频率较正常部位处峰值对应频率明显向0偏移,从工况1 PSD曲线中提取得到的平均一阶振动频率从定量的角度揭示出脱粘损伤部位与正常部位频率的变化,这与界面脱粘后局部刚度降低有关;与传统常用的FFT损伤定位方法相比,PSD曲线峰值相比FFT曲线峰值差异性更大,更容易判别出该位置是否发生了脱粘损伤。文章还探究不同属性锤头对试验结果的影响,为实际工程提供有效的参考。 相似文献
2.
N. R. Dalezios P. A. Tyraskis 《Stochastic Environmental Research and Risk Assessment (SERRA)》1990,4(1):43-53
The accuracy of an optimum interpolation technique in filling missing values in multichannel (or multisite) hydrologic series containing time-coincident data gaps is examined. The applied methodology is based on the maximum entropy method (MEM) of spectral estimation or multivariate autoregressive modeling and heavily depends upon the properties of multichannel prediction error filter (PEF). Six precipitation time series spatially located within a hydrologic basin are used and time-coincident artificial gaps are created in all six series. The performance of the technique is assessed by comparing the filled-in series to the observed and by employing spectral analysis. The results reveal the usefulness of the method in multichannel hydrologic analysis. 相似文献
3.
The accuracy of an optimum interpolation technique in filling missing values in multichannel (or multisite) hydrologic series containing time-coincident data gaps is examined. The applied methodology is based on the maximum entropy method (MEM) of spectral estimation or multivariate autoregressive modeling and heavily depends upon the properties of multichannel prediction error filter (PEF). Six precipitation time series spatially located within a hydrologic basin are used and time-coincident artificial gaps are created in all six series. The performance of the technique is assessed by comparing the filled-in series to the observed and by employing spectral analysis. The results reveal the usefulness of the method in multichannel hydrologic analysis. 相似文献
4.
The depth determination from the gravity data in frequency domain is carried out using the classical fast Fourier transform
(FFT) method utilizing scaling properties of ensemble of anomalous source. The problem of calculating power spectrum from
the FFT is well described in the literature. Here, the application of other high-resolution methods of power spectrum calculation,
such as maximum entropy method (MEM) and multi-taper method (MTM) are explored to estimate depth to anomalous sources. At
the outset, the FFT, the MEM and the MTM are tested on synthetic gravity data, generated for different types of synthetic
models and then all these methods are applied to the field gravity data of the Bengal basin. The MTM with scaling is found
to be superior for providing the detailed subsurface information rather than the MEM and the FFT methods in the case of synthetic
as well as field examples. 相似文献
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6.
利用最大熵谱法和快速傅里叶变换分别对天祝地震序列频谱进行了分析,并对分析结果进行了比较,结果表明,上述２种方法对于提取地震波中的有用信息都是有效的,可靠的,最大熵谱法的分辨率较高,傅里叶变换分辨率较低,但使用简单、方便。 相似文献
7.
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8.
首都圈地区地震视应力的计算及空间分布 总被引：6，自引：0，他引：6
本文计算了首都圈地区2003年9月到2007年12月117个ML>2.5地震的视应力, 计算视应力的两个参数地震矩(M0)和地震辐射能量(Es)都是通过分析地震波形得到。 首先用多重窗FFT获得观测谱, 在扣除仪器响应后对其进行几何扩散和非弹性衰减校正。 几何扩散使用Gail提出的三分段几何模型, 非弹性衰减用随频率变化的Q值来表征。 之后通过遗传算法找到一组Brune圆盘模型下的低频水平(Ω0)和拐角频率(fc), 使得它们的理论震源谱和校正过的观测谱残差最小。 通过Ω0可以得到M0, 通过对校正过的观测谱求积分再加上有限仪器响应带宽补偿可以得到Es, 最后就能通过M0和Es获得视应力。 计算结果与先前的一些研究比较符合: 视应力随地震矩不存在系统变化; fc随着M0变化和定标率M0∝f-3c符合较好; M0和ML的关系与定标率lg(M0)=1.20ML+10.0符合较好。 最后给出了视应力的空间分布, 结果显示视应力在邢台、 唐山和晋冀蒙交界处的空间分布有不同的特征。 还显示在2006年7月发生M5.1地震的文安北东方向有一个较大的视应力值, 唐山地区视应力从南西到北东方向大体是增加的。 相似文献
9.
直接使用FFT由数字地震记录来恢复地面位移可能产生包括虚假的长周期分量在内的不正确结果.本文介绍了根据FFT和现代控制论所建立起来的迭代方法.对FFT和所介绍的迭代方法所给出的恢复结果进行比较表明,本文所提出的方法确实改善了地面位移的估计. 相似文献
10.
离散快速傅里叶变换算法在频谱分析中得到了广泛的应用,这种算法得到的计算结果是在整个频段上的频谱信息. 在一些应用中,需要了解的仅仅是某一窄带内的频谱精细结构,要求频谱的分辨率较高. 而要得到一个较高分辨率的频谱,直接采用快速傅里叶变换计算则会导致参加快速傅里叶变换运算的数据点数的增加,从而引起计算量和存储量的急剧增大,这样,快速傅里叶变换算法就不能满足要求了. 本文介绍了基于复调制的频率细化技术的原理及其在超低频/极低频电磁接收机研制中的应用,阐述了采用这种技术如何实现高分辨率频谱的计算,并给出了理论数据和实际观测数据的计算结果. 相似文献
11.
Introduction EM technique of artificial SLF/ELF (Super low frequency/extremely low frequency, their frequency ranges from 0.1 to 300 Hz) can be used to investigate crustal conductivity structure. The SLF/ELF artificial signal is very stable and transmitte… 相似文献
12.
本文基于电磁波频谱理论研究方法,对2008年四川汶川MS8.0地震前后金河、剑阁及郑州二砂三个电磁波台站的观测资料进行FFT和小波变换分析,研究了电磁辐射数据快速傅里叶频谱变化特征和在不同尺度下小波变化的分解,发现在汶川地震前确实有异常信息存在.结果表明:(1) FFT动态谱图像说明,地震前电磁波频谱变化特征较明显,在时间、频段上均显示了阶段性进程特征,且随着震中距的增大,辐射能量越小,异常出现的时间越晚;(2) 小波分解显示了地震前电磁波异常信号低频部分出现的时间较早;距震中较近的台站,异常信息在高频部分相对明显;距震中稍远的台站,异常信息在低频部分相对明显. 相似文献
13.
针对广域电磁法（WFEM）接收机各频组数字信号快速傅里叶变换（FFT）点数不统一、低频组点数大不适合现场可编程门阵列（FPGA）实时实现的技术难题,本文采用插值和抽取相结合的抽样率转换方法,提出了满足广域电磁法接收机要求的等长度FFT变换技术,将各频组FFT变换点数统一变换到1024点,并以广域电磁法接收机实际采集到的电场信号进行了测试,最终在EP2C35F484C8 FPGA芯片上实现了1024点FFT变换,最高响应频率达到了93.84 MHz,完成1024点广域电磁信号FFT运算最快只需34 μs,并且能够有效提取广域电磁信号的振幅和相位信息.结果表明：在对广域电磁法接收机信号进行FIR低通滤波后,能够通过插值和抽取相结合的方法,将各个频组FFT变换的长度统一变换成1024点,实现广域电磁信号的FFT实时变换.本文提出的等长度FFT变换技术能够满足新一代高性能广域电磁法接收机FFT实时变换的需求. 相似文献
14.
甚长周期VP型垂直摆倾斜仪对某些地球物理信号有特殊的敏感性,除了在观测小地震、慢地震等方面有优势之外,还可有效应用于低频地球自由振荡信号的探测.利用安置在武汉大学珞珈山的我国自行研制的VP型垂直摆倾斜仪在2011日本Mw9.0级大地震之后不同长度的观测数据,联合EEMD方法、自回归估计(AR)方法和bootstrap法,本文不仅检测到该地震激发的频率小于4.7 mHz的零阶球型振荡(0S2至0S38)和环型振荡(0T4至0T35)几乎所有振型以及15个谐频振型,还检测到5个其频率低于1mHz的低阶球型多线态(0S2、2S1、0S3、0S4和1S2)的部分或全部谱峰分裂现象,并给出了所有检测结果的精度评估.此外,本文分析了某些球型和环型振荡之间的耦合效应,结果表明耦合效应将显著影响地球自由振荡信号的相关参数. 相似文献
15.
We did a Study of Horizontal-to-Vertical Component Spectral Ratio in the Tehran seismic zone. Micro-earthquakes, microtremors and quarry blasts data were used as an estimation of the site response in the Tehran zone. Site effects were studied based on horizontal to vertical ratios by the Nakamura׳s technique. Also, we used the spectra of signals for three components with the lowest noise levels for spectral slope studies. The analysis used seismic events from a network of 13 seismic stations by the permanent local seismological network of the Tehran Disaster Mitigation and Management Organization (TDMMO) from 2004 to 2007. The number of events used were different for each station. Quarry blast events were with 1.2≤ML≤2.2 and micro-earthquakes were with 1.1≤ML≤4.1.By comparing results for earthquake, microtremor and quarry blast, we could see that there is a significant difference between them. The data showed clear observations, especially in high-frequencies. The H/V spectral ratios indicate dominant frequency for rock/soft site with a higher ratio level for quarry blast ratios, which are comparable to the earthquake results due to their difference sources. The results derived by spectral H/V ratios and spectral analysis may be used to distinguish between local earthquakes and quarry blasts. 相似文献
16.
地球物理信号处理的进展和今后方向 总被引：3，自引：0，他引：3
本文简要叙述了近年来我国地球物理信号处理的进展和国际动态.其中包括:强干扰背景下微弱地球物理信号的提取;非稳态地震前兆信息的处理;现代谱估计的进展;瞬态谱理论在地球物理资料处理中的应用;畸变信号恢复的研究以及其它有关信号处理的研究. 相似文献
17.
用数字测高仪漂移测量研究电离层声重波扰动 总被引：8，自引：1，他引：8
数字测高仪Digisonde中的漂移测量,常用来研究小尺度电离层扰动,如电离层小不均匀体的漂移。文中提出一种新的分析方法,利用漂移测量数据中多普勒频移和到达角参量的最大熵动态功率谱,估算声重波一类大尺度电离层扰动的水平传播速度和传播方向。作为实例,研究了Millstone Hill测高仪站的漂移观测资料,并对处理结果进行了初步分析。分析结果表明,从数字测高仪漂移测量数据中,可有效地提取声重波一类大尺度电离层扰动的传播参量,在电离层动力过程的研究中很有意义。 相似文献
18.
2D and 3D potential-field upward continuation using splines 总被引：1，自引：0，他引：1
Bingzhu Wang † 《Geophysical Prospecting》2006,54(2):199-209
The dominant upward‐continuation technique used in the potential‐field geophysics industry is the fast Fourier transform (FFT) technique. However, the spline‐based upward‐continuation technique presented in this paper has some advantages over the FFT technique. The spline technique can be used to carry out level‐to‐uneven surface 2D and 3D potential‐field upward continuation. An example of level‐to‐uneven surface upward continuation of 3D magnetic data using the spline technique is shown, and it is evident that the continued anomalies are very close to the theoretical values. The spacing can be irregular. Synthetic examples using the spline technique to continue noise‐contaminated gravity and magnetic data upward to an altitude of 15 km on irregular grids are shown. Gaussian noise with a zero mean and a standard deviation of 1% does not cause much error and can readily be tolerated. Through comparison with the FFT technique, it is found that for low‐altitude gravity and magnetic upward continuation, both the FFT technique and the spline technique are suitable; for high‐altitude upward continuation, the FFT technique is inaccurate, whereas the spline technique works very well. Also, upward continuation by the spline technique has a smaller edge effect than upward continuation by the FFT technique. The spline‐based upward continuation technique works fairly well even when the periphery of a grid is not quiet: it is rather robust in general. A real example shows that the spline technique can be employed to perform upward continuation of total‐field magnetic data and to de‐emphasize near‐surface noise. 相似文献
19.
-- During a multidisciplinary microzonation pilot project in the city of Heraklion (Crete, Greece), microtremor data were collected at the top of exploratory boreholes specifically designed for the purposes of the project, over a period of 5 days, for 4 h/day at 125 Hz (continuous recordings). The data were analysed with the SSR and H/V Ratio techniques, using the standard FFT (applied to long data series) and a Multi-variate Maximum Entropy (MV-MAXENT) spectral analysis method. Both techniques, implemented with both spectral analysis methods, identify the same major resonance frequency band, albeit with different amplification levels. The MV-MAXENT however is effective in handling short data lengths while yielding high resolution spectra and addressing several shortcomings of the conventional FFT (windowing, zero padding etc.). Thus, it yields competitively similar results, with only a fraction (a few minutes) of the data required by the lower resolution (FFT) method and appears to be a powerful tool for site effect investigations. Moreover, the results of both microtremor-based techniques are consistent and remarkably similar to the results of microzonation methods that require (expensive) borehole data. 相似文献
20.
Cigong Yu Zhihong Fu Huaiqing Zhang Heng‐Ming Tai Xuegui Zhu 《Geophysical Prospecting》2014,62(2):377-384
Distributed parameters of the receiver coils greatly affect transient electromagnetic signals over short time periods, causing a delay in the signal's effective sampling time and the loss of shallow exploration information. This paper investigates the influence of transient process on apparent resistivity calculation and analyses the relations between the error of apparent resistivity and receiver coil design. We find that, under the same effective area, different radii of the receiver coils lead to different levels of impact on the estimation of the apparent resistivity. An optimization model is proposed to determine the optimal receiver coil size that gives rise to the smallest estimation error of the apparent resistivity. The relationship between the optimal radius and the effective areas is developed, which serves as a guideline for the optimal receiver coil design. The results may provide a useful means for improving the accuracy of the small loop transient electromagnetic instrumentation for shallow‐depth mapping. 相似文献