掩埋目标声散射特性及其实验

基于变分原理建立2D-FE弱形式解模型,针对轴对称掩埋目标进行散射远场的快速、高精度数值计算。入射波垂直于对称轴,给出:掩埋深度不变,以1°为间隔,改变掠射角所得到目标散射声压级相对于垂直海底照射获得结果的差值随频率、掠射角变化的表达式;掠射角不变,以0.1m为间隔,改变掩埋深度得到的散射声压级相对于浅掩埋条件下获得结果的差值随频率、深度变化的表达式。实验结果表明:在回波最强的正横方向,掩埋弹性目标表现出的共振散射特性与在自由场空间中具有相似性,表明了掩埋条件下目标内填充的透射和表面环绕波理论的适用性,验证了大掠射角入射得到散射声压级差值的变化规律。研究成果对宽带、高频入射声波探测更深掩埋目标提供思路。

Acoustic scattering experiments and characteristics of targets buried in sediment

We use weak form solution of 2D-FE model to calculate the far field of axis-symmetric target buried under the floor based on the variational principle. Assumed that the incident acoustic wave is perpendicular to the symmetry axis of a target, we give: when buried depth remains unchanged and grazing angle changed by 1° interval, difference of scattering sound pressure level compared with that of normal incident is derived. The expression is related to frequency and grazing angle. In addition, if the grazing angle is constant and the buried depth changed with 0.1 m interval, difference of scattering sound pressure level compared with that of shallow burial condition is also given. The experimental results show that the transmitting property of inner fillings and circumferential waves around the surface are suitable for the buried targets, the strongest echo is obtained when the grazing angle equals 90°. Resonance scattering characteristics of buried elastic targets show similarity to that in free space. In the case of oblique incidence, change law of difference of sound pressure level is verified when the sound wave incident at large grazing angle. The results of this work can provide a way for detecting deeper buried targets when broadband and high-frequency sound waves incident.