Ultrasonic wave stimulation shows potential in enhancing the permeability and production rate of low-permeability coal seam gas (CSG) reservoirs, however, the mechanisms of mechanical vibration induced by ultrasonic waves in coal is still unclear. In this paper, the effects of physical attributes of ultrasonic wave signals, including the incident angles and frequencies, on the propagation/attenuation of wave energy and cleat width variation are numerically analyzed. In the numerical modelling, the propagation direction of ultrasonic waves to the orientation of cleats varies from 0° to 90° by an 10° increasing range, and the frequency range of signals varies between 2 and 10 MHz with an increment of 2 MHz. To evaluate the changes of mechanical vibration near coal-cleats induced by the changes of physical attributes of ultrasonic waves, four parameters are discussed, including shear wave energy (SE), accumulation of wave energy (WE), cleat-width variation at each moment (D₁(t)), and accumulation of cleat-width variation during a certain period (D₂). Numerical simulation results show that: (1) wave signals with larger incident angles to the orientation of cleats contribute to larger SE, longer SE accumulation near cleat interfaces, and larger D₁(t) and D₂; (2) the ultrasonic waves at higher frequencies contribute to larger SE near cleat interfaces, which attenuates more easily during propagation. Meanwhile, the D₁(t) becomes larger during the initial period when waves firstly arrive at the cleat. However, in the case of smaller frequencies, comparatively larger D₁(t) lasts longer after waves leave from cleat, and D₂ is larger during the overall stimulation.

超声波刺激显示出提高低渗透煤层气（CSG）储层渗透率和生产率的潜力，但是，煤中超声波引起的机械振动机理仍不清楚。本文分析了超声波信号的物理属性，包括入射角和频率，对波能量的传播/衰减和楔形宽度变化的影响。在数值建模中，超声波向楔子方向的传播方向从0°到90°变化了10°，并且信号的频率范围在2到10 MHz之间变化，并以2 MHz的增量变化。为了评估由于超声波物理属性的变化而引起的煤层附近机械振动的变化，SE），波能的累积（WE），每个时刻的楔形宽度变化（D ₁ （t））和一定时期内（D ₂）的楔形宽度变化的累积。数值模拟结果表明：（1）相对于楔子方向具有较大入射角的波信号会导致更大的SE，在楔子界面附近的SE积累时间更长，D ₁ （t）和D ₂更大；（2）较高频率的超声波会导致楔形界面附近的SE增大，从而在传播过程中更容易衰减。同时，D在波浪首先到达防滑钉的初始阶段，图₁ （t）变大。但是，在频率较小的情况下，较大的D ₁ （t）在波浪从楔子离开后持续的时间更长，而D ₂在整个刺激过程中都较大。