Research On Dynamic Testing And Demodulation Technology Of Small And Micro High Speed Targets

Laser interference velocimetry technology can be used for non-contact dynamic measurement of the velocity of micro-sized flying pieces of pyrotechnics,which is widely used in scientific research in the fields of shock wave physics,blast physics,explosion mechanics,high-energy physics and nuclear physics.The measurement accuracy of all-fiber laser Doppler velocimetry system is high,but the velocity test and demodulation technology of micro-size flying piece explosion is difficult due to the small size of small flying piece,fast movement speed and weak carrying optical signal,etc.There is an urgent need to improve the test and demodulation technology of very weak signal.This thesis focuses on dynamic velocimetry and signal demodulation of micro-sized high-speed targets,and carries out research in four aspects,including all-fiber optical path construction,photonic Doppler system simulation,velocimetry experiments,and Doppler signal demodulation.This paper firstly introduces the background,significance and current development of Doppler velocimetry at home and abroad,then explains the basic principle of photonic Doppler velocimetry and builds the PDV test system.The Doppler velocity signal is simulated and the whole process of signal demodulation is carried out,and the advantages and disadvantages of streak method,fast Fourier transform and short-time Fourier transform are analyzed and compared.On this basis,the short-time Fourier transform is used to convert the Doppler signal from the time domain to the frequency domain,obtain the time-frequency curve,and calculate the velocity of the target object according to the time-frequency curve.A data processing program is designed on MATLAB platform to solve the velocity profile by analyzing the Doppler signal of the experimental data.Finally,the functional program was wrapped using MATLAB GUI.Based on the platform of the blast velocimetry device,the velocity profile of the small flying piece was driven and obtained in two ways:electric explosion and explosive explosion,and the corresponding results were obtained.In the process of electric explosion drive,when the drive voltage is 1500V,the peak speed of the flying piece can reach about 5000m/s;when the drive voltage increases to 2000V,the peak speed of the flying piece reaches 5379m/s.In the process of explosive explosion drive flying piece,the speed of the flying piece keeps around 2000m/s,and the phenomenon of breaking or shattering of the flying piece occurs.The results of this experiment were compared with the results of fast Fourier transform data processing,and the speed error was within 2%.When the received signal is weak and the noise is strong,the time-frequency plot after the short-time Fourier transform is obtained after grayscale conversion,binarization and denoising ossification to obtain the deburred image.The points of the frequency signal corresponding to the power spectral density are extracted from the boned time-frequency map,substituted into the Doppler velocity equation,the peak velocity is calculated,and the velocity profile is fitted.The reliability of the all-fiber system is experimentally verified,and the results show that the system designed in this paper is feasible and solves the problem of complicated signal demodulation process.It provides a reference for further simplification of the velocity demodulation algorithm and lays the foundation for subsequent engineering applications.