基于WIM的钢桥面板轴重频值谱推导

依据钢桥面板的受力特点,分析了它的疲劳特性,在原有的荷载频谱值的基础上,提出了更为精确的基于轴重频值谱的疲劳寿命评估方法。以压电式动态称重获取的贵州坝陵河大桥一周的车辆数据为样本,根据轴组类型对所测的车辆车轴进行分类,将车辆分为7种车型形式,并建立了3种轴型的轴载谱。依据所监测的数据,并结合正交异型钢桥面板的疲劳特性,推导得到了适宜分析钢桥面板疲劳的随机轴重谱。以面板与U肋连接处的疲劳细节为例,将轴重频值谱以及随机轴重频值谱作为输入,计算得到该细节处的应力谱以及剩余使用寿命。这一研究为钢桥面板的疲劳验算提供了更加准确的方法。

天津市公路桥梁疲劳荷载谱初探

通过对天津市外环线典型路段进行的24h交通量观测调查,统计出了包含5种车型的车辆荷载频值谱并根据等效疲劳损伤原理,将其简化成为只含有2种标准车型的实用疲劳荷载频值谱,该实用疲劳荷载频值谱可以用于天津市公路桥梁的疲劳分析和疲劳设计。

城市桥梁汽车荷载调查与疲劳荷载模型研究

以成都市城市快速路三环路的汽车荷载为研究对象,在道路的东、南、西、北4个方向各全天候不间断地连续测试7 d,采集车辆信息共计122万余辆,信息包括交通流量、轴重、轴距、总重、车速和车牌等。最后以成都市三环路北段的测试数据为基础,根据299 439条汽车荷载信息,统计出成都市三环路的汽车荷载频值谱。依据基于损伤应变的疲劳等效原则和英国BS5400规范的计算方法,以实测的车辆荷载频值谱为基础,制定出符合成都市三环路的汽车疲劳荷载模型。对于其他交通组成相同的道路,该汽车荷载模型可为道路桥梁的疲劳损伤验算提供有价值的参考。

莲城大桥疲劳荷载车辆模型研究

为了确定莲城大桥合适的疲劳荷载车辆频值谱,基于无人机和人工现场实测交通量并且通过对莲城大桥交通量分析,得到了6种车辆荷载频值谱.基于等效损伤原理将得到的6种车型的荷载频值谱转化为3种标准的疲劳荷载车辆模型的频值谱,这3种标准疲劳荷载车辆模型分别为M1、M2和M3,其中M1为2轴车辆模型,总重为135 kN,轴距为3.6 m;M2为3轴车辆模型,总重为250 kN,轴距分别为4.1和1.36 m;M3为4轴车辆模型,轴距分别为1.86、3.56和1.35 m,总重为310 kN,这3种标准车辆荷载可以用于以后的此类桥梁疲劳设计中。

高速铁路桥梁疲劳荷载研究

高铁桥梁疲劳荷载是桥梁设计的重要依据,与高铁线路通行量与运行车辆密切相关。基于对京沪、沪宁、沪杭、杭深、合武、合宁等6条高速铁路与客运专线连续3年的营运数据收集,按春运、节假日、休息日、工作日等4类运营模式随机取12天作为全年样本,根据通行量和载重量对各条线路的运行列车车型、轴重、运行图、运行列车统计表和客座利用率等运营资料进行了统计分析,采用概率统计方法得到了不同通行量的6种运营荷载频值谱。依据疲劳损伤等效原理和Miner线性准则公式对运营荷载频值谱进行计算分析,提出了标准疲劳荷载车。建议高速铁路桥梁疲劳验算可根据线路的运量、本文提出的运营荷载频值谱和标准疲劳荷载车进行。

Generation of artificial earthquakes for matching target response unsmooth spectrum via wavelet package transform

The seismic records of target response spectrum used in the time-history analysis should be allowed to meet the norms. However, the previous fitting methods of target spectrum are mostly for the situations that the target spectrum is a smooth curve. In many cases, it needs to match unsmooth target spectrum for single determined response spectrum. An adjustment of time history via wavelet packet transform was presented, which is able to fit unsmooth target spectrum. It was found that there is a certain bias between the band center frequency of the component of seismic record after wavelet packet decomposition and the peak frequency of response spectra of wavelet packet components. For this reason, five strategies were presented to select iteration points, and the effects of the five strategies were compared with two calculation examples. It was turned out that the peak frequency of the response spectrum of wavelet packet component can lead to good fitting effect when it is selected as the iteration point. In the iteration process, it shows great promise in fitting non-smooth target spectrum and has a trend of converge.

A Blackman-Harris windowed triple-spectrum-line interpolation method for measuring SNR of ADCs

In the practical measurement of signal to noise ratio(SNR)of analog-to-digital converters(ADCs)by using fast Fourier transformation(FFT)method,the non-coherent sampling is inevitable,leading to spectral leakage which in turn affects the calculation accuracy and final measurement results.In this paper,a new method based on the Blackman-Harris windowed triple-spectrum-line interpolation is presented for the measurement of ADCs SNR by FFT.The simulation platform is built based on MATLAB and the behavioral dynamic models of the high-speed ADC products of Analog Devices Inc.(ADI)are simulated.The simulation results show that,even in the case of the maximum non-coherent degree,the SNR error is less than0.23dB and reaches the testing standards provided by ADI,confirming that the proposed method is effective for suppressing the spectral leakage effects and improving the SNR test accuracy.

Ultrasonic attenuation estimation based on time-frequency analysis

The quality factor(or Q value)is an important parameter for characterizing the inelastic properties of rock.Achieving a Q value estimation with high accuracy and stability is still challenging.In this study,a new method for estimating ultrasonic attenuation using a spectral ratio based on an S transform(SR-ST)is presented to improve the stability and accuracy of Q estimation.The variable window of ST is used to solve the time window problem.We add two window factors to the Gaussian window function in the ST.The window factors can adjust the scale of the Gaussian window function to the ultrasonic signal,which reduces the calculation error attributed to the conventional Gaussian window function.Meanwhile,the frequency bandwidth selection rules for the linear regression of the amplitude ratio are given to further improve stability and accuracy.First,the feasibility and influencing factors of the SR-ST method are studied through numerical testing and standard sample experiments.Second,artificial samples with different Q values are used to study the adaptability and stability of the SR-ST method.Finally,a further comparison between the new method and the conventional spectral ratio method(SR)is conducted using rock field samples,again addressing stability and accuracy.The experimental results show that this method will yield an error of approximately 36%using the conventional Gaussian window function.This problem can be solved by adding the time window factors to the Gaussian window function.The frequency bandwidth selection rules and mean slope value of the amplitude ratio used in the SR-ST method can ensure that the maximum error of different Q values estimation(Q>15)is less than 10%.

基于NHHT的谐振接地系统单相接地故障特征分析

归一化的希尔伯特-黄变换是一种改进的希尔伯特-黄变换,NHHT可以更好地从非平稳非线性的故障电流信号中提取丰富的时频信息。建立了谐振接地系统单相接地故障暂态等值模型,从理论上分析了系统暂态接地电流特征,使用EMTP-ATP仿真谐振接地系统单相接地故障。NHHT分析结果表明,该仿真故障接地电流特征频带为200 Hz至400 Hz,且在250 Hz处到达最大值。联合时-频幅值谱显示了故障信号的时频信息,希尔伯特边际谱则动态地反应了故障信号的幅频特性。研究表明,不同故障初相角对故障接地电流有较大影响。

Determination of Threshold for Energy Detection in Cognitive Radio Sensor Networks

The Internet of Things （loT） is called the world＇ s third wave of the information industry. As the core technology of IoT, Cognitive Radio Sensor Networks （CRSN） technology can improve spectrum utilization efficiency and lay a sofid foundation for large-scale application of IoT. Reliable spectrum sensing is a crucial task of the CR. For energy de- tection, threshold will determine the probability of detection （Pd） and the probability of false alarm Pf at the same time. While the threshold increases, Pd and Pf will both decrease. In this paper we focus on the maximum of the difference of Pd and Pf, and try to find out how to determine the threshold with this precondition. Simulation results show that the proposed method can effectively approach the ideal optimal result.

A K-means clustering based blind multiband spectrum sensing algorithm for cognitive radio

In this paper,a blind multiband spectrum sensing(BMSS)method requiring no knowledge of noise power,primary signal and wireless channel is proposed based on the K-means clustering(KMC).In this approach,the KMC algorithm is used to identify the occupied subband set(OSS)and the idle subband set(ISS),and then the location and number information of the occupied channels are obtained according to the elements in the OSS.Compared with the classical BMSS methods based on the information theoretic criteria(ITC),the new method shows more excellent performance especially in the low signal-to-noise ratio(SNR)and the small sampling number scenarios,and more robust detection performance in noise uncertainty or unequal noise variance applications.Meanwhile,the new method performs more stablely than the ITC-based methods when the occupied subband number increases or the primary signals suffer multi-path fading.Simulation result verifies the effectiveness of the proposed method.

Study on the Interaction Between Tangerine Peel and Beer by Absorption Spectrum

This paper presents a new method to study the interaction between tangerine peel and beer by absorption spectrum.The author explores the change laws and the differences of the absorbance on some wave band from the absorption spectrums of tangerine peel and the mixture of tangerine peel and beer. The results show that there is an obvious difference around 323 nm though the absorbance values of the two samples are almost similar in the most bands. The absorbance value of the mixture is obviously greater than that of tangerine peel at 276 nm in the spectrums, and there is a shift of the peak position in the absorption spectrum of the mixture, which shows the differences of the absorbance values and the peak positions of the two samples. Through comparing the characteristics of the two samples' absorption spectrums, a new method for researching new pharmacological action of tangerine peel is presented in this paper. The result indicates that the technology of spectrum analysis will play an important role in the research and development of Chinese herbal pharmacology and new pharmacology.

Effect of Initial Frequency Chirp on Supercontinuum Generation in Dispersion-flattened Fibers

Supercontinuum generation in dispersion-flattened fibers is studied theoretically. It is found that the flat spectral width of the supereontinuum generation in normal dispersion-flattened fiber can be increased from 66 nm to over 100 nm when the absolute value of the initial frequency chirps is increased from zero to 10. It is further found that initial frequency chirps are adverse to flat and wideband supercontinuum generation in anomalous dispersion-flattened fiber, and when the absolute value of the frequency chirps is increased to a certain degree, supercontinuum spectrum even can not be achieved.

福州市城市桥梁疲劳荷载研究

通过对福州市城市桥梁交通荷载和运营车辆的装载情况调查,得到由32类日常典型的运营车辆组成的荷载频值谱,以及货运车辆的空载率.根据等效疲劳损伤原理将所得到的荷载频值谱简化为由6辆疲劳荷载模型组成的具有实用性的荷载频值谱.进一步分析得到一辆适宜验算桥面系构件的标准疲劳车辆荷载模型.所得到的疲劳荷载频值谱和疲劳车辆荷载模型,可以供城市钢桥疲劳损伤验算参考.

Numerical analysis of intermodal delay in few-mode fibers for mode division multiplexing in optical fiber communication systems

In order to achieve higher spectral efficiency, mode division multiplexing (MDM) in few-mode fibers is a new research area. The idea faces lots of technical issues including intermodal delay and mode coupling which limit the achievable length of the system. This paper is designated to complete the analysis of intermodal delay in step-index few-mode fibers. We analyze numerically all the parameters of fiber, which could impact intermodal delay in few-mode fibers and identify the conditions which can increase the number of multiplex modes without significant increase in maximum intermodal delay.

Application of wavelet transform in-ray spectra analysis

The frequency distribution of different ingredients in-ray spectra,e.g.,photo-peak,fluctuations of counts and Compton region,is separately analyzed.After wavelet transform of-ray spectra,the wavelet coefficients of a photo-peak increase with transforming scales and these coefficients show direct proportion with intensity of peak at determinate scale.A novel algorithm based on wavelet transform is proposed and studied.The results indicate that most of the photo-peaks in multi-spectra can be determined accurately,the-rays energy and intensity of the peak can also be determined.This method has the prospect of being applied in on-line multi-spectra analysis in such fields as radioprotection and nuclear safety monitoring.