Research On Ultrasonic Signal Processing Method Based On Time-frequency Analysis

With the huge demand for natural gas in the world,the consumption of natural gas is accelerating,and the demand for natural gas in China,a populous country,is more urgent.However,due to regional differences,most of the natural gas energy is stored in the west,while China's main population is in the east.Therefore,China has put forward the policy of "west-east gas transmission".Salt cavern gas storage is widely used in natural gas storage due to its advantages of large storage capacity,small occupation area,high safety factor,fast operation rate and small impact on the ecological environment.Salt cavern storage is to drill through the salt rock layer by drilling technology,and then through the injection of fresh water for erosion,brine after the formation of dissolved cavity,gas storage.In order to ensure the stability of salt cavern storage,the cavity must be monitored in real time in the process of cavity building to ensure that the cavity form formed after dissolving salt rock meets the design requirements.The ultrasonic ranging technique was used to measure the radius of the salt cavity,and the horizontal profile and radius of the cavity with different depths were obtained by changing the position of the ultrasonic probe,which provided directional guidance for the cavity construction in the later stage.In this paper,a three-dimensional ultrasonic detection system of salt cavity shape was established for the stability detection of salt cavity gas storage reservoir,and the cavity shape was monitored during the cavity building process,so as to adjust the cavity building process and improve the stability of salt cavity building.Firstly,according to the nature of ultrasonic wave,the denoising effect of ultrasonic echo signal after digital filtering processing and wavelet threshold processing is compared.The experiment shows that the signal-to-noise ratio,anti-interference ability,measurement accuracy and accuracy of ultrasonic echo signal after digital filtering denoising are far lower than that of wavelet threshold denoising.In this paper,several delay estimation algorithms of ultrasonic ranging are also studied.The traditional threshold method,cross-correlation method and envelope peak method are analyzed by using the measurement data of ultrasonic ranging system.Then an improved correlation envelope ranging method is proposed.The experimental results show that the anti-noise capability of the improved ultrasonic signal processing method is obviously better than the previous methods,and the measurement of ultrasonic transmission time is only related to the position of the envelope peak.Compared with the traditional ultrasonic signal processing method,this method can not only determine the location of the unique envelope peak,but also improve the measurement accuracy,and is not easily affected by noise,the measurement result is stable,and the system measurement error is smaller.The signals collected by detecting the radius of salt cavity are nonlinear and non-stationary ultrasonic echo signals,which are generally processed by time-frequency analysis method.Therefore,several typical time-frequency analysismethods are studied in this paper: short-time Fourier transform,wavelet transform,Wigner-Ville distribution and Hilbert yellow transform.The four time-frequency analysis methods are compared and the Hilbert yellow transform is selected as the time-frequency processing method of the ultrasonic signal.The time spectrum of Hilbert yellow is obtained by feature extraction of echo signal.The change of frequency of ultrasonic signal with time is analyzed,and the corresponding time point of ultrasonic transmitting frequency is found according to the change of signal spectrum on the time axis.Finally,the radius of the cavity and the shape information of the cavity are obtained by the distance formula of ultrasonic ranging,and then the stability of the current cavity shape is analyzed.