准周期加隔板有限长圆柱壳声散射

研究准周期加隔板有限长圆柱壳在水中的声散射特性,隔板位置存在小的随机偏差.首先给出理论推导,通过计算周期加隔板情况验证理论公式的正确性.然后以角度-频率谱形式给出准周期加隔板圆柱壳声散射计算结果.计算表明隔板的准周期性导致Bloch-Floquet弯曲波和散射声场背景出现扩散和增强现象,而近乎平行于横轴的由隔板共振引起的亮条纹被散射声场背景所掩盖.最后讨论了随机因子、隔板个数以及隔板间距对Bragg散射的影响.计算表明随机因子越大Bragg散射条纹的频率范围越宽扩散越明显,隔板个数越多Bragg散射条纹的频率范围越窄能量越集中,隔板间距变大时Bragg散射条纹增多而且越高阶次的Bragg散射条纹扩散越严重.根据Bragg散射的几何特征导出的近似估算公式可以较准确预报Bragg散射在频谱图上的位置,也可以大致预报隔板准周期排列时Bragg散射的扩散现象.

Acoustic scattering from a finite quasi-periodic bulkhead cylindrical shell

Research on sound scattering from a finite quasi-periodic bulkhead cylindrical shell is conducted. The small deviation of bulkhead array exists. Firsts some applications are given to investigate the problem of backscattering from a periodic bulkhead cylindrical shell in order to verify the theory. Then the angle-frequency spectrum of the backscattering from quasi-periodic bulkhead cylindrical shell is calculated, and the angle-frequency spectrum shows that the quasi-periodic array of bulkhead results in the diffusion of Bloch-Floquet wave and background field. However, the resonance of bulkheads is covered by background field. Finally, the influences of the array random variable of bulkheads, the number of bulkheads and the spacing between bulkheads are discussed. The calculations show that the diffusion of Bragg waves is more evident with array random variable increasing; the power of Bragg waves is concentrated with the number of bulkheads increasing; with the spacing between bulkheads becoming broad, the number of Bragg waves increases and the diffusion of high modes Bragg waves becomes more serious. Based on the geometric characteristics of Bragg waves, the approximate calculation formula of the Bragg wave position on the angle-frequency spectrum is presented. The formula can forecast the position of Bragg wave on the angle-frequency spectrum exactly and the diffusion of Bragg waves roughly when the bulkheads array quasi-periodic.