The Applied Research Of Optical Fiber Acoustic Emission Detection Technology In Collapse Prediction In Coal Mine

Coal accounts for about two-thirds of China's energy use,and coal mine accidents occur from time to time.It is very important to use scientific methods to carry out accurate early warning in advance to reduce the incidence of coal mine safety accidents.As a new nondestructive testing technology,optical fiber acoustic emission testing plays an important role in the prediction of mine collapse.The fiber-optic acoustic emission sensor has the advantages of small volume,high frequency bandwidth,high sensitivity,high damage threshold and so on.It has no contact with the object under test and can adapt to different harsh environment.This paper analyzes the existing optical fiber acoustic emission sensor,designs the structure of optical fiber acoustic emission sensor suitable for the prediction of coal mine collapse,studies the methods to improve its sensitivity,and puts forward how to predict the location of coal mine collapse and collapse point.First of all,several typical fiber-optic acoustic emission sensors are analyzed to provide theoretical basis for accurate prediction of coal mine collapse.The Sagnac fiber-optic acoustic emission sensor with directionality and strong anti-interference ability is selected for the prediction of coal mine collapse.Secondly,according to the special environment and existing problems in coal mine,Sagnac fiber-optic acoustic emission sensor strain flower is designed as the strain element to be used in coal mine.Because there is a lot of noise in the coal mine and the acoustic emission signal is very weak,it is necessary to improve the sensitivity of the strain rosette.According to the structure and principle of the strain flower,the method of modulating the initial phase is proposed to improve its phase sensitivity.When the initial phase is modulated to 3?/2,the phase sensitivity increases about 6 times.The experimental results show that this method effectively improves the sensitivity of the optical fiber acoustic emission sensor.Thirdly,taking Wangjialing coal mine as the research background,according to the No.2 coal seam of Wangjialing coal mine,the uniaxial compression test is carried out to test its mechanical parameters,at the same time,the acoustic emission signal generated by it is detected,and the relationship of stress time acoustic emission signal energy count is calculated and simulated.According to the special environment of the coal mine,a new denoising method based on wavelet transform is proposed.The simulation results show that when the acoustic emission energy count is more than 23×10~5V,the roof of the coal mine will collapse.In order to ensure the safety of the miners,the warning signal should be sent out immediately.When the warning is started,there is about 30 seconds to avoid danger.Finally,the traditional acoustic emission source location algorithm is analyzed.Combined with the special environment of coal mine and the structural characteristics of Sagnac fiber-optic acoustic emission sensor,a new acoustic emission source spatial location algorithm is proposed.This method solves the problem of difficult spatial location when a large number of optical fibers are laid in the coal mine.Through the simulation experiment,it can be seen that compared with the traditional optical fiber acoustic emission algorithm,the new acoustic emission source spatial location algorithm is proposed In short distance location algorithm,the error is smaller and the position of AE source can be detected accurately.