一种由横波激发的特殊非线性声现象

A special nonlinear phenomenon excited by transverse wave source

目前对非线性超声的研究多集中在纵波激发的谐波性质以及对材料微观结构变化的实验检测上,横波激发的非线性声波性质少有研究。对横波激发的一维非线性声波方程入手,利用摄动法求解该方程,并改写为一阶偏微分方程,然后利用交错网格的有限差分形式进行数值求解。结果表明:采用横波激发,能产生线性横波和非线性纵波,且纵波的高次谐波内有两个信号,分别以纵波和横波两种速度传播。若采用较长的激发信号,纵波谐波能形成"拍"现象,成为一种奇特的声传播现象。

Studies of nonlinear acoustics mostly concentrate on the problems relevant to the longitudinal harmonic waves generated by longitudinal waves at present. Nonlinear waves generated by transverse wave are seldom studied. In this paper, the nonlinear acoustic wave equation for the two dimensional oscillation propagating in one dimension direction is studied and solved by perturbation method. First the nonlinear acoustic wave equation is reformed into first order partial differential equation, and then the finite difference method in staggered grid style is performed to obtain the numerical solution. The results show that the linear transverse wave and nonlinear longitudinal wave can be observed with a transverse source; two signals in the longitudinal harmonic waves can propagate with longitudinal and transverse wave velocities respectively; and the clap phenomena of longitudinal harmonic waves can be seen in the nonlinear wave, which becomes a special acoustic propagation phenomenon. The results can provide a theoretical guidance for the basic study of nonlinear acoustic wave propagation.