Physical Model Building And Study In Acoustic Test Method Of Gas-bearing Sediment In Hangzhou Bay

Shallow gas is widespread in Hangzhou Bay, Yangtze River Delta, Pearl River Delta andother coastal regions. Construction on these areas often lead to accidents. The release of shallowgas also cause environment pollution. Therefore, it’s important to implement non-destructivedetection of shallow gas before construction in these areas. However, there is no high-precisionnon-destructive detection methods and equipment put into use.In this thesis, according to actual engineering survey, a laboratory gas-bearing model isdesigned. It can simulate different type of gas sediment. The section used to fill sediment isdesigned as a cylinder,100mm diameter,200mm height,60mm stroke, the maximum pressure is10MPa. It can be equipped with temperature, pressure, displacement sensors and ultrasonictransducers.A system based on PXI virtual instrument platform which could measure ultrasonic signal,temperature, pressure, displacement has been designed. The circuit for ultrasonic signaltransmitting and receiving has been designed. Output pulse through virtual instrument interface,the pulse frequency, duty cycle, and number is adjustable. After through excitation circuit,ultrasonic transonic is excited to emit ultrasonic waves. Ultrasonic wave is received by thereceiving transducer, it output a weak alternating voltage signal, the signal through0~80dBgain amplifier circuit which is cascaded by two AD603chips. After the amplifier circuit, thesignal meet acquisition card’s demand which input voltage range is±10V. Finally, clearultrasonic waveform is acquired by digitizer. Virtual instrument software to collect ultrasonic,temperature, pressure and displacement data has been designed, the ultrasonic waveform isanalyzed in time and frequency domain, sound speed and sound attenuation is measured byrecording the come time of first wave and the ratio of voltage amplitude.Based on the current samples we have, a comparative experiment has been designed,ultrasonic testing on samples is experimented by using PXI virtual instrument system and RS-ST10C. Ultrasonic testing result is similar, the comparative experiment verify the feasibilityof the ultrasonic measurement of PXI virtual instrument system.