基于表面阻抗测量的声学覆盖层吸声系数测试及修正

Sound absorption coefficient measurement and correction of acoustic coating based on impedance experiment

[目的]鉴于采用传统的水声管试验方法测量潜艇声学覆盖层的表面阻抗要求较高,提出一种可简化试验的基于阻抗测量的吸声系数测试方法,并解决阻抗测量中非平面波反射的修正问题。[方法]首先,将覆盖层简化为阻抗率矩阵边界和结合流体边界条件,推导出覆盖层表面不同半径处的速度;然后,通过汉克尔积分变换建立非平面反射波压力与轴向速度的关系,得到修正非平面波反射的吸声系数公式;最后,对模型样品进行数值计算和表面阻抗测量,分别与理论计算和传统的水声管测试方法所得结果相互比较,以验证所提方法的有效性。[结果]数值计算结果表明:实心覆盖层得到的结果与理论结果一致;圆柱空腔结果与理论结果有明显差异。阻抗测量的结果经平面波处理后与水声管试验结果有较大误差,经修正后与水声管试验结果较为吻合。[结论]覆盖层空腔易引起非平面波反射,在阻抗测量中需要予以修正;经修正后的阻抗测量方法得到的吸声系数与传统的水声管试验方法在所关注的频段内一致,且简化了试验,具有一定实践价值。

[Objective]As specific and demanding requirements are imposed by measuring the impedance of the anechoic coatings on the hull surface of an underwater vehicle using the traditional water-filled tube experiment,a method of sound absorption coefficient measurement based on a simplified impedance experiment is proposed,and the correction of non-planar wave reflection in the measurement is achieved.[Methods]The velocity at different radii on the surface of the coating is deduced by simplifying the coating as the impedance matrix boundary and combining the fluid boundary conditions.The relationship between the pressure of the non-planar reflected wave and axial velocity is established via the Hankel transformation,and the formula of the sound absorption coefficient of the modified non-planar reflection wave is obtained.Numerical calculation and the impedance experiment are compared with theoretical calculation and the traditional acoustic tube experiment to validate the validity of the proposed method.[Results]The numerical calculation shows that the results of solid coating are consistent with the theoretical results,but the results of coating with cylindrical cavities are obviously different from the theoretical results.The impedance experiment results have a large error compared with the acoustic tube results after planar wave processing,and are consistent with the acoustic tube results after correction.[Conclusions]Cavities are among the causes of the reflection of the non-planar wave from the coating,and this needs to be corrected in impedance measurement.The sound absorption coefficient obtained by the modified impedance measurement method is consistent with that obtained by the acoustic tube experiment in the frequency range of interest,and the experiment is simplified,giving the proposed method a certain practical value.