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采用有限元素法 ,分别数值计算了平底孔道、台阶式孔道和尖劈状孔道等 3种孔眼模型中不同中心频率 (10 0 k Hz、5 0 0 k Hz、1MHz)的散射超声脉冲波。计算结果表明 ,无论选用哪一种孔底模型 ,均可以得到较为明显的对应于孔底的声波信号。但是 ,孔道越不规则 ,使用的超声信号的主频越高 ,则孔底信号越差。为了兼顾孔底信号质量和信号采集、传输的代价 ,在未来的检测仪器中应采用尽可能低的测量频率 (低于 5 0 0 k Hz)
By using the finite element method, the scattered ultrasonic pulse waves with different center frequencies (10 0 k Hz, 500 k Hz, 1 MHz) were calculated numerically for three kinds of perforation models, such as flat-bottom tunnel, stepped tunnel and wedge-shaped tunnel. The calculation results show that no matter which hole bottom model is selected, the acoustic signal corresponding to the hole bottom can be obtained obviously. However, the more irregular the channels, the higher the dominant frequency of the ultrasonic signal used, the worse the bottom hole signal. In order to balance the hole bottom signal quality and signal acquisition and transmission costs, the lowest possible measurement frequency (below 500 k Hz) should be used in future detection equipment.