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1.
Real‐time pseudodynamic (PSD) and hybrid PSD test methods are experimental techniques to obtain the response of structures, where restoring force feedback is used by an integration algorithm to generate command displacements. Time delays in the restoring force feedback from the physical test structure and/or the analytical substructure cause inaccuracies and can potentially destabilize the system. In this paper a method for investigating the stability of structural systems involved in real‐time PSD and hybrid PSD tests with multiple sources of delay is presented. The method involves the use of the pseudodelay technique to perform an exact mapping of fixed delay terms to determine the stability boundary. The approach described here is intended to be a practical one that enables the requirements for a real‐time testing system to be established in terms of system parameters when multiple sources of delay exist. Several real‐time testing scenarios with delay that include single degree of freedom (SDOF) and multi‐degree of freedom (MDOF) real‐time PSD/hybrid PSD tests are analyzed to illustrate the method. From the stability analysis of the real‐time hybrid testing of an SDOF test structure, delay‐independent stability with respect to either experimental or analytical substructure delay is shown to exist. The conditions that the structural properties must satisfy in order for delay‐independent stability to exist are derived. Real‐time hybrid PSD testing of an MDOF structure equipped with a passive damper is also investigated, where observations from six different cases related to the stability plane behavior are summarized. Throughout this study, root locus plots are used to provide insight and explanation of the behavior of the stability boundaries. Copyright © 2008 John Wiley & Sons, Ltd. 相似文献
2.
Izuru Takewaki 《地震工程与结构动力学》2001,30(4):519-535
Since earthquake ground motions are very uncertain even with the present knowledge, it is desirable to develop a robust structural design method taking into account these uncertainties. Critical excitation approaches are promising and a new non‐stationary random critical excitation method is proposed. In contrast to the conventional critical excitation methods, a stochastic response index is treated as the objective function to be maximized. The power (area of power spectral density (PSD) function) and the intensity (magnitude of PSD function) are fixed and the critical excitation is found under these restrictions. It is shown that the original idea for stationary random inputs can be utilized effectively in the procedure for finding a critical excitation for non‐stationary random inputs. The key for finding the new non‐stationary random critical excitation is the exchange of the order of the double maximization procedures with respect to time and to the power spectral density function. Copyright © 2001 John Wiley & Sons, Ltd. 相似文献
3.
In aeolian saltation, the sand bed is a mixture of sand particle with a wide range of particle sizes. Generally, the particle size distribution (PSD) of saltating particles is ignored by previous aeolian transport models, which will result in differences between predictions and observations. To better understand the saltation process, a prediction method of the PSD of saltating particles was proposed in this article. The probability of contact between incident sand and bed sand was introduced into the particle-bed collision process. An artificial PSD of the incident saltating particles was set as the initial condition. A stochastic particle-bed collision model considering contact probability was then used in each iteration step to calculate a new PSD of saltating particles. Finally, the PSD of saltating particles can be determined when aeolian saltation reaches a steady state (saltation is in a steady state when its primary characteristics, such as horizontal mass flux and the concentration of saltating particles, remain approximately constant over time and distance). Meanwhile, according to the experimental results, a calculation formula for the contact parameter n is given, which characterizes the shielding effect of particles on each other. That is, if soil PSD and friction velocity were given, the PSD of saltating particles can be determined. Our results do not depend on the initial conditions, and the predicted results are consistent with the experimental results. It indicated that our method can be used to determine the PSD of saltating particles. © 2020 John Wiley & Sons, Ltd. 相似文献
4.
针对工程中常见的非平稳地震动激励,进一步建立了时变功率谱估计的理论框架。首先,在多个样本情形下,采用信号处理中的时频分析方法对非平稳激励的时变谱估计理论进行了讨论。当激励样本数量有限时,对Priestley提出的估计方法进行了介绍。其次,以地震工程中常用的Kanai-Tajimi谱模型为目标,分别对均匀调制与一般调制谱的估计结果以及不同估计方法的精度与收敛性进行评价后,提出了能够方便工程应用的建议。最后,针对SMART-Ⅰ(Strong Motion Array in Taiwan,Phase Ⅰ)密集台阵第45次地震记录的多组三维样本,揭示了EW、NS、UD三个方向时变谱的典型特征以及各方向间的时变相干性。结果表明:与短时Fourier变换相比,复Morlet小波与广义谐和小波估计谱具有较好的精度与收敛性,Priestley方法估计单个样本具有优势;SMART-Ⅰ台阵地震动具有强度和频率的双重非平稳性,三个方向具有弱相干性。研究结论可为拓展谱估计理论的工程应用以及后续大跨结构多维多点非平稳地震响应的分析提供参考。 相似文献
5.
ELECTROMAGNETIC ANOMALOUS PULSES BEFORE AND AFTER EARTHQUAKES(M>6.0) IN CHINA CONTINENT IN 2008 
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下载免费PDF全文 In this paper,we provided the electromagnetic anomaly phenomena prior to five earthquakes with magnitude MW>6.0 occurring in China continent in 2008.The electromagnetic data in frequency bands 800~0.1Hz are recorded at two stations located in Urumqi,Xinjiang Uygur Autonomous Region (URQ) and Tonghai,Yunnan Province (TH).The time series of four horizontal components of the electromagnetic field at the stations are converted to the spectra using Fast Fourier Transform.The relationship between the electromagnetic anomalous phenomena and the earthquake events is studied through analyzing the temporal variation of electromagnetic spectra and comparing them with earthquake events.This study provides the new examples for electromagnetic anomaly phenomena before the earthquakes.The following features can be found.①The obvious anomalous power spectrum density (PSD) of electromagnetic fields in frequency band of 128~0.5Hz appeared before earthquakes.The anomalous PSD is related to the earthquake magnitude and the epicenter distance.The anomaly size of magnetic PSD is about 1-3 orders of magnitude bigger than the background field before Wenchuan MS8.0 earthquake.② The changes of parameters are also related with frequency of the signal;The ELF signal strength observed at seismic stations is significantly related with distance between the stations or the measured magnetic and electrical field components and the source of earthquake.We also found that the field strength attenuated faster in area closer to the source than in far area.It is clear that the magnetic signals have higher signal noise ratio than the electric data.③ The amplitudes are also related with the azimuth of the earthquake to station and with the frequency of the data.④ The anomalous pulses showed cluster phenomenon in time. 相似文献
6.
By analysing long- and short-term seismological measurements at wind farms close to the town of Landau, SW Germany, we present new insights into ground motion signals from wind turbines (WTs) at local seismic stations. Because of their need to be located in similar regions with sparsely anthropogenic activities, wind turbines impact seismic stations and their recordings in a way that is not yet fully understood by researchers. To ensure the undisturbed recording tasks of a regional seismic array or a single station by a protected area around those endangered stations, it is very important to investigate the behavior of WTs as a seismic source. For that reason, we calculate averaged one-hour long spectra of the power spectral density (PSD) before and after the installation of a new wind farm within the investigated area. These PSD are ordered according to the rotation speed. We observe a clear increase of the PSD level after the WT installation in a frequency range of 0.5 to 10 Hz up to a distance of 5.5 km away from the WT. By analysing seismic borehole data, we also observe a decrease of the PSD of wind dependent signals with depth. The impact of wind-dependent signals is found to be much more pronounced for the shallower station (150 m depth) than for the deeper one (305 m depth). Using short-term profile measurements, we fit a power-law decay proportional to 1/r b to the main WT-induced PSD peaks and differentiate between near-field and far-field effects of ground motions. For low frequencies in the range from 1 to 4 Hz, we determine a b value of 0.78 to 0.85 for the far field, which is consistent with surface waves. The b value increases (up to 1.59) with increasing frequencies (up to 5.5 Hz), which is obviously due to attenuating effects like scattering or anelasticity. These results give a better understanding of the seismic wavefield interactions between wind turbines (or wind farms) with nearby seismic stations, including borehole installations, in a sedimentary setting. 相似文献
7.
Real-time pseudodynamic (PSD) and hybrid PSD testing methods are displacement controlled experimental techniques that are used to investigate the dynamic behaviour of complex and load rate-dependent structures. Because the imposed command displacements are not predefined but generated during the test based on measured feedback, these methods are inherently prone to error propagation, which can affect the accuracy and even the stability of the entire experiment. As a result, to have these experimental methods as reliable tools, the accuracy of the test results needs to be assessed by carefully monitoring, and if possible, quantifying the errors involved. In this paper, phase and amplitude error indices (PAEI) are introduced to identify the experimental errors through uncoupled closed-form equations. Unlike the indicators that have been previously introduced in the literature for error identification purposes, PAEI do not use test setup specific parameters in their formulation, and can quantify the errors independent of the amplitude of the command displacements. As such, PAEI can be used as standard tools for assessing the quality of the experiments performed in different laboratories or under different conditions. Additionally, because they can quantify the error, when implemented online, PAEI have the potential to be incorporated in the control law and thereby improve the actuator control during the tests. The formulation and implementation of PAEI are provided in this paper. The enhanced performance of the proposed indices is demonstrated by processing several different measured and command signals using PAEI and comparing the results with those revealed by the previous indicators. Copyright © 2011 John Wiley & Sons, Ltd. 相似文献
8.
Stochastic finite-fault modeling is an important tool for simulating moderate to large earthquakes. It has proven to be useful in applications that require a reliable estimation of ground motions, mostly in the spectral frequency range of 1 to 10 Hz, which is the range of most interest to engineers. However, since there can be little resemblance between the low-frequency spectra of large and small earthquakes, this portion can be difficult to simulate using stochastic finite-fault techniques. This paper introduces two different methods to scale low-frequency spectra for stochastic finite-fault modeling. One method multiplies the subfault source spectrum by an empirical function. This function has three parameters to scale the low-frequency spectra: the level of scaling and the start and end frequencies of the taper. This empirical function adjusts the earthquake spectra only between the desired frequencies, conserving seismic moment in the simulated spectra. The other method is an empirical low-frequency coefficient that is added to the subfault corner frequency. This new parameter changes the ratio between high and low frequencies. For each simulation, the entire earthquake spectra is adjusted, which may result in the seismic moment not being conserved for a simulated earthquake. These low-frequency scaling methods were used to reproduce recorded earthquake spectra from several earthquakes recorded in the Pacific Earthquake Engineering Research Center (PEER) Next Generation Attenuation Models (NGA) database. There were two methods of determining the stochastic parameters of best fit for each earthquake: a general residual analysis and an earthquake-specific residual analysis. Both methods resulted in comparable values for stress drop and the low-frequency scaling parameters; however, the earthquake-specific residual analysis obtained a more accurate distribution of the averaged residuals. 相似文献
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10.
A method is presented for stochastic modelling of a design earthquake by a power spectral density function for seismic analysis of structures. The method can be adopted with information currently available in the form of design response spectra for earthquake motion. Accurate seismic responses of structures can be easily obtained using such stochastic models. The methods for accurate response analysis of structures with closely spaced modes and for generation of floor response spectra of a building using a prescribed ground response spectrum directly are also presented. The hypothesis that a design earthquake can be modelled by a power spectral density function is used only implicitly in developing these methods. 相似文献
11.
This work investigates the application of two post-processing methods of extracting spectra from VLF signals in order to detect disturbances that could be attributed to seismic-ionospheric precursory phenomena. Although precursory phenomena have been investigated in detail in past studies, a different application of time–frequency analysis methods may produce distinct patterns, which reveal disturbances in the VLF spectra received from stations that are in the propagation path over preparation zones, and also pinpoint disturbances that could be attributed to seismic-ionospheric precursors.To this purpose, three different methods of post processing are compared. These are the Wavelet Transform as a benchmark method in the form of the Continuous Wavelet Transform, a noise-assisted variant of the Hilbert-Huang Transform and the Zhao-Atlas-Marks Distribution. Comparative diagrams are presented and the advantages and weaknesses of each method are presented. 相似文献
12.
断层岩的粒度分布包含岩石破裂机制、摩擦性质和地震能量分配等重要信息。筛分-称重和激光测量是分析断层岩三维粒度的2种有效方法,但每一种方法的测量范围仅有3个量级,难以全面反映断层岩的粒度分布特征。利用上述2种方法对汶川地震断层滑动带上的断层岩（简称断层岩）的粒度分布进行了测量,粒径测量范围从0.2μm至16mm,跨度达到5个数量级。结果显示：1）存在临界粒径dc（0.95～1.90μm）。粒度大于和小于dc的颗粒满足不同的颗粒数（Nd）-粒径（d）分布关系,表明该断层岩的粒径分布不具有自相似性特征。2）利用粒度大于dc的颗粒计算出的分形维数与断层岩类型有很好的相关性,即断层带边缘的角砾岩的平均分形维数为2.6,核部压碎角砾岩的平均分形维数约为3.0,中心断层泥的分形维数约为3.5。粒径小于dc的颗粒的分形维数为1.7～2.1。分形维数的突变反映出断层破裂机制的复杂性,即在不同的粒度域,岩石的破裂机制不尽相同。3）依据粒度分析结果,估算出汶川地震断层泥的单位破裂能（Es）为0.63MJ/m2。 相似文献
13.
Paul C. Jennings 《地震工程与结构动力学》1973,2(3):281-293
A method is presented for calculating single or, by repeated use, selected ordinates of Fourier spectra rapidly and efficiently. The approach differs from standard methods in that any frequency consistent with the interval of digitization may be chosen and records of arbitrary length may be analysed. The method is based on the relation between Fourier spectra of an accelerogram and the final response of an undamped oscillator to the same accelerogram. This relation is reviewed and extended to aid the development of the computing method and to assist in the interpretation of Fourier spectrum techniques in earthquake engineering. Because only the terminal values of the response of an undamped oscillator are required to define the Fourier spectra, repeated application of superposition is used to form equivalent excitations with durations of only one-quarter of the period of the oscillator. 相似文献
14.
基于位移的概率极限状态设计 总被引：1，自引：0，他引：1
尽管近年来国内外学者提出了多种基于位移的抗震设计方法，但采用的与位移相关的反应谱大多是平均谱，设计过程可以看作是确定性的。基于位移的抗震设计应该建立在可靠度理论基础之上。利用作者在概率延性需求谱方面已有的研究成果和可靠度分析方法——验算点法，本文提出了根据基于位移的目标可靠指标直接进行结构设计的方法，并给出了设计流程图。为便于工程应用，在进行了大量分析计算之后，本文建议了基于位移的概率极限状态分项系数设计表达式，并确定了其中的分项系数。最后，本文对一8层框架结构采用建议的分项系数设计表达式进行了设计，并对有待于进一步研究的问题进行了简要分析。 相似文献
15.
本文首先分析了地震波在黏弹介质的传播规律,基于黏弹介质地震波动方程总结了时变子波振幅谱和相位谱的关系,从而得出结论,准确估计子波相位谱初值和不同时刻的子波振幅谱是实现时变子波准确提取的必要条件.在此基础上,针对传统方法限制子波振幅谱形态且受限于分段平稳假设的问题,提出了一种利用EMD(Empirical Mode Decomposition)和子波振幅谱与相位谱关系的时变子波提取方法,根据子波对数振幅谱光滑连续而反射系数对数振幅谱振荡剧烈的特点,采用EMD方法将不同时刻地震记录的对数振幅谱分解为一组具有不同振荡尺度的模态分量,通过滤除振荡剧烈分量、重构光滑连续分量提取时变子波振幅谱;再应用子波振幅谱和相位谱的关系提取时变子波相位谱,将分别提取的振幅谱和相位谱逐点进行合成,最终实现时变子波的准确提取.本文方法不需要求取Q值,适用于变Q值的情况,具有良好的抗噪性能.数值仿真和叠后实际资料处理结果表明,相比传统的分段提取方法,利用本文方法提取的时变子波准确度更高,研究成果对提高地震资料分辨率具有重要意义. 相似文献
16.
本文分析了现行的最大似然法速度谱估计的基本运算过程。结果表明,各记录道间的幅度差异将严重降低方法的分辨率,对此,文中提出两种改进方法,并用人工合成记录方式进行了方法的可行性试验。 相似文献
17.
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
18.
本文利用云南地区永胜台观测的地磁南北和东西分量开展舒曼谐振的背景变化特征分析.通过提取舒曼谐振各阶频率和功率谱密度的小时均值,分析了前三阶舒曼谐振频率和功率谱密度在分点和至点前后的周日变化特征.舒曼谐振功率谱密度的周日变化与亚洲、非洲和美洲三大闪电活动中心的活跃时段以及观测站相对于三大闪电活动中心的方位密切相关.舒曼谐振频率的周日变化特征更复杂.各阶功率谱密度和频率在夏至和秋分前后的变化幅度比春分和冬至前后大.从2011年舒曼谐振频率和功率谱密度日中值的年变化图中发现,谐振频率随季节变化的特征不明显,而功率谱密度的年度变化曲线呈半周期正弦波形态,以7月份为轴对称分布.功率谱密度的季节变化特征与闪电活动的季节变化特征相一致.南北和东西分量得到的前三阶谐振频率,第一阶约稳定在7.5 Hz.而随着阶数增加,南北分量得到的谐振频率比东西分量约大0.5 Hz.高阶谐振频率发生偏移的原因目前还不清楚. 相似文献
19.
《Journal of Atmospheric and Solar》2007,69(6):707-720
This paper presents direct measurements of narrowband 10 MHz HF radiation from so-called “chaotic leaders” associated with subsequent return strokes. Although the term is controversial and poorly defined, we find that more than 30% of subsequent strokes in close lightning flashes contain electric field characteristics that are best described as “chaotic”. In earlier studies, return strokes have consistently been observed to be the strongest sources of HF radiation, but the results for leader processes are less consistent. We also observe return strokes to be the main HF emitter, and the leaders before the first return stroke in a flash sequence also emit HF though somewhat less intensely. The leaders preceding subsequent strokes typically emit little or no HF radiation, whether they are dart or dart-stepped leaders.However, it was observed that the presence of a chaotic component increases the leader HF intensity dramatically Defining the HF intensity unequivocally can be problematic for processes like chaotic leaders which have a combination of continuous and impulsive phenomena. Two time-domain methods were used to measure the HF intensity, the peak energy and the RMS energy. In the frequency domain these correspond to the energy spectral density (ESD) and power spectral density (PSD), respectively.It was found that the methods are not necessarily compatible. Thus, it is suggested that to clarify future work, leader processes should be characterized by the PSD rather than the ESD. 相似文献
20.
图像增强技术在重磁图像中的应用 总被引：2，自引：0，他引：2
本文综述了图像增强技术在位场数据中的应用现状，并介绍了两种改进的图像增强技术，用于增强重磁图像特征。一种方法借鉴了直方图平滑化的思想，应用于位场彩色影像的色谱的自动确定。该方法的应用能够使色彩合理地配置，从而保证了图像的视觉效果和分辨率。另一种方法基于改进的Radon变化和梯度计算，用于重磁图像中线性特征的检测和增强。该方法能在变化域中突出显示线性特征，从而有利于线性特征的检测和增强。通过对简单图像和实际资料的应用，表明了两种方法在增强特征中的有效性。 相似文献