Design Of Elastic Wave Emission Signal Based On Continuous Sources For Coal Seam Detection

The subject is supported by National Natural Science Foundation of"The theoretical research on the fine detection of reflective channel wave in coal seam based on continuous source".The aim is to design a continuous seismic signal that can replace the explosive sources and has a good detection effect,and to analyze the propagation characteristics of the channel waves generated by the excitation of different seismic sources in the coal seam.The main work of the dissertation are summarized as follows:(1)According to the propagation characteristics of the channel waves in the coal seam,the main influencing factors of the signal for coal seam detection are proposed,including upper limit frequency,lower limit frequency,time and energy of emission,which provide a theoretical basis for the design of the emission signal.(2)Combining with the influencing factors of the coal seam detection signal,the linear sweep signal is selected as the most basic continuous source,and the frequency band is determined from the detectability of the channel waves and the attenuation of the Airy phase,then the appropriate scanning time and energy is determined.In order to obtain a higher-frequency Airy phase and improve the resolution,a high-frequency energy compensation signal is designed according to the high-pass filter characteristics of the coal trough.Comparing with the frequency spectrum and the emission energy of the Ricker wavelet,linear sweep signal and high-frequency energy compensation signal,the high-frequency energy compensation characteristics of the designed signal are verified.(3)In Comsol Multiphysics,a three-layer model of coal-bearing formations and a model with a small fault were established.The Ricker wavelets with a frequency of 200 Hz were excited in two models to simulate the explosive sources,and the vibration signals of the line points were obtained.The signal was exported to Matlab R2012b,and the propagation characteristics of channel waves in the two models were compared from the waveform,spectrum and dispersion curves.Then the linear sweep signal and the high-frequency energy compensation signal are used to excite,and then the same analysis is performed.The obtained result is compared with the simulation effects of the Ricker wavelets.The results prove that the continuous source can obtain the detection effect consistent with the explosive source.Under the premise of the same excitation energy,the energy of the channel waves formed by the high-frequency energy compensation signal is stronger,the dispersion curve of the channel wave is clearer,and the signal characteristics change after the fault is more obvious.It is helpful to increase the detection distance.(4)By using the time-frequency analysis method of the generalized S-transform in Matlab R2012b,the time-frequency spectrum of the channel waves in the two models excited by three signals was obtained,which demonstrated the energy distribution of the signal in the time-frequency domain.The results prove that the channel waves formed by the high-frequency energy compensation signal are more powerful on the reflected wave generated by the fault,and the Airy phase frequency is higher,which can effectively improve the detection accuracy.