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- 저자 : Chengjun Tan (검색결과 2 건)
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Hilbert transform based approach to improve extraction of “drive-by” bridge frequency
Chengjun Tan,Nasim Uddin 국제구조공학회 2020 Smart Structures and Systems, An International Jou Vol.25 No.3
Recently, the concept of"drive-by" bridge monitoring system using indirect measurements from a passing vehicle to extract key parameters of a bridge has been rapidly developed. As one of the most key parameters of a bridge, the natural frequency has been successfully extracted theoretically and in practice using indirect measurements. The frequency of bridge is generally calculated applying Fast Fourier Transform (FFT) directly. However, it has been demonstrated that with the increase in vehicle velocity, the estimated frequency resolution of FFT will be very low causing a great extracted error. Moreover, because of the low frequency resolution, it is hard to detect the frequency drop caused by any damages or degradation of the bridge structural integrity. This paper will introduce a new technique of bridge frequency extraction based on Hilbert Transform (HT) that is not restricted to frequency resolution and can, therefore, improve identification accuracy. In this paper, deriving from the vehicle response, the closed-form solution associated with bridge frequency removing the effect of vehicle velocity is discussed in the analy tical study. Then a numerical Vehicle-Bridge Interaction (VBI) model with a quarter car model is adopted to demonstrate the proposedapproach. Finally, factors that affect the proposed approach are studied, including vehicle velocity, signal noise, and road roughness profile.
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Study on the Energy Spectrum Response of a CdZnTe Detector
Yuandong Li,Liangquan Ge,Kun Sun,Shangqing Sun,Guoqiang Zeng,Chengjun Tan 한국물리학회 2020 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.76 No.9
In order to study the energy spectrum response of a CdZnTe detector, we firstly measured the temperature dependence and the bias dependence of the main characteristic parameters for both a quasi-hemispherical detector and a CAPtureTM plus detector. Secondly, we designed a low-noise readout circuit for the CdZnTe detector and measured the noise. Finally, we evaluated the energy spectrum response of the detector to different radioactive sources at different temperatures by connecting the detector to the readout circuit. The research showed that both detectors had low leakage current and junction capacitance, as well as good stability in temperature and bias; the quasi-hemispheric detector had a smaller leakage current and junction capacitance compared to the CAPtureTM plus detector; under zero input capacitor, the noise of the readout circuit was 612e, with the noise slope being 5.44e/pF; at room temperature(20 °C), the energy resolutions of the detector reached 3.84% and 1.36% for X-rays from 241Am (59.5 keV) and gamma-rays from 137Cs (662 keV), respectively; the signal-noise ratio of the output signal reached 31:1 with the rise time being 90 ns; at low temperature, the energy resolution reached 3.41% for the X-rays from 241Am (59.5 keV); the detector achieved an excellent spectrum response and was able to distinguish clearly the energy peaks of 152Eu and 226Ra.
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