Propagation Simulation of Ultrasonic Wave in Coal and Rock Medium

To identify coal-rock interface, ultrasonic detection technology is used to measure coal seam thickness based on acoustic impedance contrast between coal and rock. Kelvin-Voigt viscoelastic model and anisotropy theory is used to established the coal-rock interface identification model including water, coal and rock layer. A staggered-grid infinite difference in time domain (FDTD) scheme is used to simulate the ultrasonic wave propagation in this model. To solve the problem of false reflection caused by artificial boundary in numerical simulation, three PML implementations including split-field perfectly matched layer (S-PML), multi-axial perfectly matched layer (M-PML) and complex frequency-shifted perfectly matched layer (CFS-PML) are compared. The simulation shows that CFS-PML has a better result and calculation stability. The results provide a theoretical basis for ultrasonic identification of coal-rock interface.