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Journal of Hydrodynamics 1992年第4期4卷 21-26页

作者： Ding Zhuo-yi Yangtze River Scientific Research Institute,Wuhan Hubei 430010,P.R.China Yangtze River Scientific Research Inst Wuhan China

Using four types of stilling basin models,this paper studies frequency characteris- tics of the fluctuating pressure acting on the stilling basin apron when Froude number is not greater than *** testing results show that the frequency of fluctuating pressure,f_s in the ranges of 0. 4Hz≤f_s≤1.1Hz.0.2Hz≤f_s≤2.5Hz and 0.4Hz≤f_s≤*** be used as the design frequency corresponding to three patterns of hydraulic *** reliability of f_s for three jump patterns is all nearly equal to 90%.

关键词： frequency characteristics fluctuating pressure stilling basin apron

Prediction of characteristic blast-induced vibration frequency during underground excavation by using wavelet transform

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Frontiers of Structural and Civil Engineering 2022年第8期16卷 1029-1039页

作者： Tae Un PAK Guk Rae JO Un Chol HAN Faculty of Mining Engineering Kim Chaek University of TechnologyPyongyang 999093Democratic People’s Republic of Korea School of Science and Engineering Kim Chaek University of TechnologyPyongyang 999093Democratic People’s Republic of Korea

Blast-induced vibration produces a very complex signal,and it is very important to work out environmental problems induced by *** this study,blasting vibration signals were measured during underground excavation in carbonaceous shale by using vibration pickup CB-30 and FFT analyzer ***,wavelet analysis on the measured results was carried out to identify frequency bands reflecting changes of blasting vibration parameters such as vibration velocity and energy in different frequency *** characteristics are then discussed in view of blast source distance and charge weight per *** analysis of results,it can be found that peak velocity and energy of blasting vibration in frequency band of 62.5–125 Hz were larger than ones in other bands,indicating the similarity to characteristics in the distribution band(31–130 Hz)of main vibration *** frequency bands were affected by blasting source distance,and the frequency band of 0–62.5 Hz reflected the change of charge weight per *** presenting a simplified method to predict main vibration frequency,this research may provide significant reference for future blasting engineering.

关键词： wavelet analysis blast-induced vibration frequency characteristics underground excavation

Numerical Investigation of the Transient Flow and frequency Characteristic in a Centrifugal Pump with Splitter Blades

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Journal of Thermal Science 2021年第2期30卷 562-573页

作者： LI Guidong ZHANG Jinfeng MAO Jieyun YUAN Shouqi JIA Jing National Research Center of Pumps Jiangsu UniversityZhenjiang 212013China

To analyze the internal flow characteristics of each subchannel in a low-specific-speed centrifugal pump with splitter blades,the time histories and frequency spectra of pressure fluctuations and the distributions of the corresponding flow states in one impeller channel were investigated through the numerical *** experiments and particle image velocimetry (PIV) tests were carried out to verify the results of the numerical *** results suggested that the simulation analysis agreed well with the test *** time histories and frequency spectra of pressure fluctuations depending on its location (close to or away from the volute tongue) present different *** predominant frequency of each monitor point equals to five or ten times shaft *** jet-wake flow pattern at each subchannel separated by splitter blade in one impeller channel is not circumferentially *** the channel away from volute tongue,the magnitude of turbulence kinetic energy in pressure side subchannel is well larger than that in suction side *** the increase in flow rate,the region close to the elbow of the volute outlet emerges a large-scale vortex.

关键词： centrifugal pump splitter blades frequency characteristics transient analysis turbulence kinetic energy

characteristics of Oscillation in Cavity of Helmholtz Nozzle Generating Self‑excited Pulsed Waterjet

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Chinese Journal of Mechanical Engineering 2022年第3期35卷 264-274页

作者： Miao Yuan Deng Li Yong Kang Hanqing Shi Haizeng Pan Hubei Key Laboratory of Waterjet Theory and New Technology Wuhan UniversityWuhan 430072China School of Power and Mechanical Engineering Wuhan UniversityWuhan 430072China

Cavity flow oscillations in the axisymmetric cavity are critical to the operating efficiency of self-excited pulsed waterjets,which are widely employed in many practical *** this study,the behaviors of a turbulent flow in axisymmetric cavities causing cavity flow oscillations are investigated based on wall pressure *** are performed using four Helmholtz nozzles with varying length-to-radius ratios at flow velocities of 20–80 m/*** orders of hydrodynamic modes in axisymmetric cavity are obtained through the spectral analysis of wall *** on the experimental results,the empirical coefficient of Rossiter’s formula is modified,and the values of the parameter phase lag and the ratio of convection velocity to free stream velocity are obtained as 0.061 and 0.511,*** addition,the spectral peak with a relatively constant frequency shows that the flow-acoustic resonance is excited significantly.A modified model is introduced based on the fluidic networks to predict the lockon *** results obtained can provide a basis for the structural optimization of the nozzle to improve the performance of self-excited pulsed waterjets.

关键词： Self-excited cavitation waterjet Flow-excited oscillations frequency characteristics Vibration analysis

Acoustic emission characteristics of rock under impact loading

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Journal of Central South University 2015年第9期22卷 3571-3577页

作者：刘希灵李夕兵洪亮尹土兵饶蒙 School of Resources and Safety Engineering Central South University Norman B. Keevil Institute of Mining Engineering University of British Columbia School of Civil Engineering Hunan City University

Acoustic emission tests were performed using a split Hopkinson pressure bar system(SHPB) on 50-mm-diameter bars of granite, limestone, sandstone and skarn. The results show that the amplitude distribution of hits is not well centralized around 50 d B, and that some hits with large amplitudes, usually larger than 70 d B, occur in the early stages of each test, which is different from the findings from static and low-loading-rate tests. Furthermore, the dominant frequency range of the recorded acoustic emission waveforms is between 300 k Hz and 500 k Hz, and frequency components higher than 500 k Hz are not significant. The hit with the largest values of amplitude, counts, signal strength, and absolute energy in each test, displays a waveform with similar frequency characteristics and greater correlation with the waveform obtained from the elastic input bar of the split Hopkinson pressure bar system compared with the waveforms of the other hits. This indicates that the hit with the largest values of amplitude, counts, signal strength, and absolute energy is generated by elastic wave propagation instead of fracture within the rock specimen.

关键词： rock acoustic emission(AE) split Hopkinson pressure bar(SHPB) hit driven features frequency characteristics correlation analysis

Combined optical fiber interferometric sensors for the detection of acoustic emission

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Optoelectronics Letters 2008年第3期4卷 184-187页

作者： LIANG Yi-jun MU Lin-lin LIU Jun-feng YU Xiao-tao College of science Harbin Engineering University Harbin 150001 China

A type of combined optical fiber interferometric acoustic emission sensor is proposed. The sensor can be independent on the laser source and make light interference by matching the lengths of two arms,so it can be used to monitor the health of large structure. Theoretical analyses indicate that the system can be equivalent to the Michelson interferometer with two optical fiber loop reflectors,and its sensitivity has been remarkably increased because of the decrease of the losses of light energy. PZT is powered by DC regulator to control the operating point of the system,so the system can accurately detect feeble vibration which is generated by ultrasonic waves propagating on the surface of solid. The amplitude and the frequency of feeble vibration signal are obtained by detecting the output light intensity of interferometer and using Fourier transform technique. The results indicate that the system can be used to detect the acoustic emission signals by the frequency characteristics.

关键词： Acoustic emissions Acoustics Electric network analysis Fiber optics Fibers Fourier transforms Geodetic satellites Interferometers Interferometry Lattice vibrations Light sources Michelson interferometers Optical fibers Optical in Acoustic emission sensors Acoustic Emission signals Fiber loop reflectors Fourier frequency characteristics Interferometric sensors Laser sources Light energy Light intensities Operating points Optical Vibration signals

Application of a New Qeneration of Geophonesto Improve Seismic Acquisitionin Onshore-offshore Transition Areas

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Applied Geophysics 2005年第4期2卷 235-240页

作者：吕公河西安交通大学建筑与力学学院

In this paper, we review the differences between velocity geophones （VG） and acceleration geophones （AG） and their effect on seismic signals acquired in onshore-offshore transition areas. We present a new generation of Land Piezoelectric Geophone （LPG） and analyze its performance. Our field experiments demonstrate that our new LPG can be used to substitute for VGs in order to eliminate phase, frequency and energy differences between different geophone systems commonlv used in transition areas.

关键词： transition areas vibrate system land piezoelectric geophone frequency characteristics data acquisition

A 4H-SiC trench IGBT with controllable hole-extracting path for low loss

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Chinese Physics B 2023年第4期32卷 714-718页

作者：吴丽娟刘恒宋宣廷陈星曾金胜邱滔张帮会 Hunan Provincial Key Laboratory of Flexible Electronic Materials Genome Engineering Changsha University of Science&TechnologyChangsha 410114China

A novel 4H-Si C trench insulated gate bipolar transistor(IGBT)with a controllable hole-extracting(CHE)path is proposed and investigated in this *** CHE path is controlled by metal semiconductor gate(MES gate)and metal oxide semiconductor gate(MOS gate)in the p-shield *** grounded p-shield region can significantly suppress the high electric field around gate oxide in Si C devices,but it weakens the conductivity modulation in the Si C trench IGBT by rapidly sweeping out *** effect can be eliminated by introducing the CHE *** CHE path is pinched off by the high gate bias voltage at on-state to maintain high conductivity modulation and obtain a comparatively low on-state voltage(VON).During the turn-off transient,the CHE path is formed,which contributes to a decreased turn-off loss(EOFF).Based on numerical simulation,the EOFFof the proposed IGBT is reduced by 89%compared with the conventional IGBT at the same VONand the VONof the proposed IGBT is reduced by 50%compared to the grounded p-shield IGBT at the same *** addition,the average power reduction for the proposed device can be 51.0%to 81.7%and 58.2%to 72.1%with its counterparts at a wide frequency range of 500 Hz to 10 k Hz,revealing a great improvement of frequency characteristics.

关键词： controllable hole-extracting path energy loss frequency characteristics Si C insulated gate bipolar transistor(IGBT)

Nonlinear Tracking Differentiator Based on Feedforward and Arctangent Function

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Nonlinear Tracking Differentiator Based on Feedforward and A...

SIMULATION OF U-TYPE TUBE FOR MEASURING DIRECT MASSFLOW USING FINITE ELEMENT MODEL

第三十九届中国控制会议

作者： Yawen Kong Dapeng Tian Jihong Xiu Xin Che Key Laboratory of Airborne Optical Imaging and Measurement Changchun Institute of Optics Fine Mechanics and Physics Chinese Academy of Sciences University of Chinese Academy of Sciences

Nonlinear tracking differentiator（NTD） extracts the filtered continuous signals and differential signals from any noisy signals. Therefore, it is often used in several fields especially in high-precision motion control. In order to improve the tracking characteristics of NTD, this paper presents a design based on the arctangent function and feedforward. The arctangent function has the property of approximate saturation function and feedforward effectively solves the problem of phase lag that is common in differentiators. According to the simulation analysis of the proposal, it can be concluded that its tracking speed, differential characteristics and filtering ability are obviously improved.

关键词： Nonlinear tracking differentiator arctangent function feedforward phase lag frequency characteristics

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SIMULATION OF U-TYPE TUBE FOR MEASURING DIRECT MASSFLOW USIN...