【作者】 孔祥东；

【导师】 李建龙；

【作者基本信息】 浙江大学 ， 信息与通信工程， 2012， 硕士

【摘要】 水下声学材料构件是水声工程中使用广泛且至关重要的水下部件,不同的应用背景对材料声学性能有特殊的要求。随着材料科学的进步,粘弹性高分子材料等高性能吸声新材料在吸声降噪等水声工程领域的应用日益广泛。因而,对该类材料在水声使用环境中的声学性能测量和研究是迫切需要解决的问题。水声无源材料的声学性能测量包括插入损失(透射系数)、回声降低(反射系数)、吸声系数等参数的测量。目前水声无源材料的声学性能测量在中高频段已经取得了重要进展,但随着主动声纳技术的发展,其探测信号频率逐渐向低频扩展,所以发展低频情况下水声无源材料声学性能的测量方法是目前水声测量领域的主要趋势。时间反转聚焦技术充分利用了波导环境中声传播的多径特性,将多径与直达波同相位叠加,使接收信号在时间上得到了压缩,增强了信号幅度,降低了混响效应,从而可提高低频情况下接收信号的信混比。同时,时间反转技术的空间聚焦特性使信号主瓣较基于平面波波束形成(直达波单路径)的常规阵发射窄,可减小声波衍射对测量结果的影响。本文通过理论仿真分析和现场试验对时间反转聚焦测量方法进行了研究。为了使时间反转技术能够在封闭圆柱形容器环境中得到最佳的聚焦效果,本文利用声射线的方法对该环境中的声场进行了分析,通过对主瓣分辨力和对旁瓣的抑制能力的分析,设计了最佳的接收阵和发射阵组合。由于时反测量方法利用了波导的多径效应,为使测量结果与自由场条件相一致,通过理论分析,提出了测量参数的修正方法。分别在波导水池和压力容器环境开展了无源材料声学性能常压测量试验,并且在压力容器环境中进行了2MPa、3MPa、4MPa压力条件下的声学性能测量。通过标准试样试验结果与自由场理论结果的比较,验证了时间反转聚焦技术应用于无源材料声学性能测量的可行性。更多还原

【Abstract】 Acoustic material components are widely used, and they are vital underwater parts in acoustic engineering. Different application backgrounds have different requirements on acoustic materials performance. With the development of material science, viscoelastic polymer materials and other high performance absorption new materials are applied widely in the absorption and noise reduction underwater acoustic engineering field. Therefore, researching the acoustic materials performance is the urgent problem.Acoustic passive materials performance parameters include insertion loss (transmission coefficient), echo reduction (reflection coefficient), sound absorption coefficient and others. At present acoustic passive materials’performance measurement has made important progress in high frequency band, but with the development of sonar technology, the acoustic performance measurement in low frequency band is needed.Time reversal focusing technique takes full advantage of multipath characteristics of sound propagation in the waveguide environment, summing all paths in the same phase. The temporal compression of the time-reversal focusing increases the signal strength, and improves signal reverberation ratio. The spatial compression of the time-reversal focusing makes the main lobe narrower than the plane wave beam-forming, reducing the influence of diffraction. This article researches the time reversal focus measurement method through the theory simulation analysis and field test.In order to have the best result of time reversal in a closed cylindrical vessel environment, the best receive array and transmitting array combination is designed after the analysis of the resolution of the main lobe.In order to make the measurement results are consistent with in free field conditions, the paper put forward the correction method of measuring parameters through the theoretical analysis. The passive materials are tested in the waveguide pool under normal pressure and the pressure vessel environment under normal,2MPa, 3MPa and 4MPa pressure. The experiment results are consistent with the theoretical value. This result proves that time reversal technology is another way to test the passive materials’ performance parameters.更多还原