岩石样品中超声波传播数值模拟及分析

为了深入研究超声波速度测试中超声波在岩石样品中的传播规律,对岩石超声波速度实验采用交错网格有限差分算法进行了数值模拟.选取了适合于超声波震源的差分精度、稳定性条件和吸收边界.通过模拟波形与实验记录波形的对比分析,结果表明:激发器和接收器直接位于岩心与探头接触面时,接收到的波形中干扰波较少,合成记录波形特征明显,易于分析;使用雷克子波作为超声波数值模拟的震源子波,计算得到实际首波初至时间为21.55μs,而波形图中首波初至时间为23.90μs,这是由于子波自身的长度使得波初至时间比实际波初至的时间晚;相对于岩心与探头接触面的反射波,岩心柱体与空气接触面的反射波对有效波形信号的影响更大.

Numerical simulation and analysis of the ultrasonic wave propagation in rock sample

In order to deeply study the ultrasonic waves propagation of samples in ultrasonic velocity experiments,staggered grid finite difference algorithm was used to the numerical simulation of rock ultrasonic velocity experiments.The differential accuracy,stability conditions and absorption boundaries are selected so as to be suitable for the ultrasonic source.Through the comparison between the simulating waveform and the experimental waveform,the results show that when the trigger and the receiver are directly located at the contact surface of the core,the received waveform has fewer interference waves,and the synthetic recording waveform features are easier to analyze;using the Ricker wavelet as the source in the ultrasonic numerical simulation,and the first wave arrival time in the waveform is 23.90μs,but it is 21.55μs in the real ultrasonic velocity experiments.This difference is due to the length of the wavelet itself.The first arrival time of the identified wave is later than the initial arrival time of the actual wave;the reflected wave of the core cylinder and the air contact surface has a greater influence on the effective waveform signal than the reflected wave of the contact surface between the core and the probe.