环状激光作用于薄管产生温度场的有限元模拟

Finite element simulation of temperature field of thin tubes irradiated by ring lasers

为了提高激光在管道中激发超声波的效率,基于激光超声的热弹激发理论,建立了环状激光源作用于薄管中的有限元模型,采用有限元方法,数值模拟了环状激光脉冲作用于铝管内壁时产生的瞬态温度场,得到了铝管内部温度随时间变化的曲线和不同时刻温度沿径向、轴向的变化曲线,并进一步分析了铝管内温度梯度的形成及随时间、沿径向的变化规律。结果表明,激光产生的瞬态温度场建立极其迅速,整个过程仅持续几十纳秒,该过程产生的温度梯度非常大,因此环状激光源可在铝管中激发很强的超声波;同时,由于温度梯度分布在整个圆周上,因而形成的导波衰减慢,可在周向、轴向上实现大范围超声检测。该结果对热弹条件下激光在管道中激发超声导波的研究有一定参考作用。

In order to improve the efficiency of ultrasound excited by pulsed laser in a thin tube, a laser-ultrasonic model of an aluminum tube irradiated by a ring laser was established based on thermo-elastic theory of laser-ultrasound. The transient temperature field of the interior surface of the aluminum tube irradiated by a pulse ring laser was simulated by means of finite element method. Then the evolution curves of the temperature with time, radial and axial variables were obtained. Furthermore, the formation and variation of temperature gradient in the interior of aluminum tubes was analyzed. Results show that transient temperature field can be set up in a few tens of nanoseconds under the irradiation of a pulsed ring laser. Enormous temperature gradient produces in this process and a very strong ultrasonic wave appears subsequently in the aluminum tube. Because temperature gradient distributes on the entire circle, the ultrasonic wave spreading in tube attenuates slowly, which is useful for ultrasonic detection on large region along circle and axis of the tube. The results may provide valuable reference for the laser- generated thermo-elastic ultrasonic guided wave pipeline.