干燥及饱和含水煤样超声波特征的实验研究

采用超声波透射法对无烟煤、焦煤和肥煤煤样在干燥及自然饱和吸水状态进行超声波测试实验，利用快速傅里叶变换对超声波信号进行了频谱分析，研究干燥及自然饱和吸水状态下煤样超声波特征。研究结果表明：在干燥或自然饱和吸水状态下，同种煤样的纵波波速相差较小；在干燥和自然饱和吸水两种状态下，无烟煤煤样纵波速度最大，肥煤纵波速度最小，焦煤介于两者之间，煤样纵波速度与其密度呈正相关、与孔隙率和变质程度呈负相关关系。焦煤和肥煤煤样在自然饱和吸水状态下纵波波速高于其在干燥状态下的纵波波速，无烟煤则相反；焦煤和肥煤煤样的纵波波速对水的敏感性大于无烟煤纵波波速对水的敏感性，这是由水分子在煤样孔隙中的运动形式决定的。煤样自然饱和吸水后，其主频率值有所下降，出现“频率漂移”的现象，使其能量多集中在低频部分；在煤样中传播的超声波信号的波速和主频率值能够反映煤样内部的孔隙、微裂隙等结构情况及其含水情况。

Experimental study on ultrasonic wave characteristics of coal samples under dry and water saturated conditions

Ultrasonic wave propagation tests of anthracite,fat coal and coking coal samples were carried out with ultrasonic transmission method under the condition of dry and water saturated states.A spectrum analysis was conducted for the ultrasonic signals using the fast Fourier transform.Also,ultrasonic wave characteristics in coal samples were studied under dry and water saturated states.The research results show that:Under the condition of dry or water saturated state,the longitudinal wave velocities of the homogeneous coal samples has little difference.Under the conditions of dry and water saturated states,the longitudinal wave velocities of anthracite coal samples are larger than that of cooking coal samples;the longitudinal wave velocities of fat-coal samples are the last.The longitudinal wave velocities of coal samples has positive correlation with apparent density,and negative correlation with their porosities and metamorphic grades.The longitudinal wave velocities of fat-coal and coking coal samples under dry state are slightly less than those under water saturated state,and the experiment result of the anthracite coal samples are opposite.The sensitivity of longitudinal wave velocity of fat-coal and coking coal samples to water is greater than that of the anthracite coal samples to water.This is due to the movement of water molecules in the pores of coal samples.After coal samples saturation for absorption,the main frequency values decrease and the “frequency drift” phenomenon appears,which makes the energy be concentrated in the low frequency part.The distribution of interior pores,micro-cracks and conditions of water contents in coal samples are reflected by the wave velocity and main frequency values of ultrasonic signal.