水下结构弹性体的声散射
文献类型：学位论文
| 作者 | 孙阳 |
| 学位类别 | 博士 |
| 答辩日期 | 2009-05-27 |
| 授予单位 | 中国科学院声学研究所 |
| 授予地点 | 声学研究所 |
| 关键词 | 目标散射 弹性体 微分方程 积分方程 声覆盖层 谐振散射 |
| 其他题名 | Sound Scattering by Submerged Elastic Structures |
| 学位专业 | 声学 |
| 中文摘要 | 水下目标多为结构弹性体，入射波能够激发结构弹性体的谐振，特别是在低频段，结构弹性体的谐振散射明显，散射频谱出现谐振峰，这种弹性谐振是低频主动声纳识别弹性体的重要特征量。对水下结构弹性体散射声场的研究，主要目的是获得弹性体的声散射特性和声传播机理，为低频主动声纳的目标探测、识别及声特性控制提供理论依据。 论文主要研究水中弹性体的声散射特性。物理模型由规则几何体的球壳模型到结构复杂的短柱壳体模型，以及最后的复杂潜艇模型。由于结构弹性体的散射声场一般不存在解析解，采用数值方法进行研究，数学模型分别应用求解微分方程的Rayleigh简正级数解、有限元－边界元数值解和求解积分方程的迭代解法；计算内容包括不同线形、不同结构目标的散射形态函数、目标强度、振动模态、内部和外部的声场等物理量；并研究了声覆盖层与壳体复合结构的声学响应。 对规则弹性球壳声散射特性与子波声散射机理的研究表明，弹性球壳的散射声场是受激辐射迭加刚性边界散射背景形成的；在受激辐射的频率曲线中存在大量弹性谐振峰值，每个谐振峰都是由某阶子波的谐振产生；加声覆盖层后，散射频谱减少了谐振峰数量、降低了散射强度；目标的声散射特性与声覆盖层的厚度、弹性壳的厚度及频率有关。这些结论为分析复杂结构弹性体的声特性提供理论依据。 在充水结构弹性球壳声散射特性的研究中，充入的水介质和隔板都增加了子谐振系统，散射频响曲线比无水、无隔板时的谐振峰增多；无隔板的弹性球壳在充入部分水时，内部水与空气介质交界面越大，其谐振峰幅度越高；有隔板球壳在充入部分水时，内部水对球壳声散射特性的影响较小，散射特性主要由球壳和隔板决定；当隔板一侧充满水时，内部水介质形成剧烈分布的驻波场，对球壳声散射特性的影响明显。 研究了中间充水双层短柱壳加声覆盖层前后的声散射特性。加声覆盖层后，瑞利散射区内，覆盖前后的声散射特性变化不明显；随频率升高，在谐振散射区，声覆盖层减少了短柱壳的谐振峰个数，增加了谐振峰值的宽度，降低了谐振幅度，并且声覆盖层越厚，谐振区越窄，频响曲线幅度越低；在物理声学区，有声覆盖层的短柱壳频响曲线逐渐趋于平滑。声覆盖层对内部结构的谐振有很好的抑制作用，减少了子系统中弯曲波引起的谐振，也减弱了水层的驻波场分布强度。 采用局部边界等效声阻抗的积分方程模型研究了声覆盖层潜艇的回波特性，通过边界等效声阻抗与声覆盖层反射系数的关系，建立了声覆盖层的局部声阻抗的求解公式。研究结果表明，对假定的声覆盖层，在1kHz以上的频段内，潜艇的目标强度相对于刚性边界约降低4～10dB；声覆盖层的反射系数越小，目标强度越小；覆盖相同声特性的声覆盖层，在低频段，单层壳体与双层壳体潜艇的目标强度不同，而在高频段，两种壳体结构潜艇的目标强度近似于相同。 |
| 英文摘要 | Underwater targets are mostly structural elastic solid. The resonance of elastic solid can be excited by incident wave. Especially in lower frequency, the resonance scattering characteristic is obviously and there are resonance peaks on the scattering spectrum. This elastic resonance is the important characteristic of low-frequency active sonar identifying target. Study of scattering sound field of underwater target is mainly for achieving its sound scattering characteristic and mechanism of transmission, and for providing theoretical evidence for target detection, identification of low-frequency active sonar and sound characteristic control. In this paper, the sound scattering characteristics of underwater elastic solid are presented. Studied physical models include spherical shell, finite cylindrical shell and submarine. As there is generally not exist analytic solution for the scattering sound field of structured target, numerical methods are used in which Rayleigh normal series solution and the finite element and boundary element method applied to solve differential equation, iterative solution solving integral equation are respectively employed. The computation contains scattering form function, target strength, vibration mode and interior-exterior fluid medium sound field distribution with different shape and structure. The study of sound scattering characteristic of elastic spherical shell and scattering mechanism of partial-wave indicates that the scattering sound field of elastic spherical shell is generated by excited radiation superposing scattering of rigid boundary. There exist many elastic resonance peaks in the spectrum curve of excited radiation. Every peak is formed by resonance of partial-waves. The number of resonance peaks and scattering strength in spectrum are reduced after coated with anechoic layer. Sound scattering characteristic of target is related to the thickness of coating and elastic shell, and frequency. These conclusions provide theoretical evidence for analyzing the sound scattering characteristics of elastic body with complex structure. In the study of sound scattering of water-filled elastic spherical shell, the filled water and embedding plate increase resonance sub-systems and the number of resonance peaks increase. When the spherical shell without the plate is filled water, the growing size of the water/air interface within the shell, the resonance peak amplitude is larger. When the spherical shell with the plate is filled water, the interior water has weak effect on the resonance characteristic and the basic vibration characteristic of the partially water-filled shell with inner plate is decided mainly by the structure of shell, but when one-half of the shell is full of water, the intensive standing wave field is formed in interior water and affects the scattering properties obviously. The sound scattering characteristics of double layer cylindrical shell with/without coating are investigated. After coated with anechoic layer, the scattering characteristics are almost not changed in Rayleigh scattering region. As frequency increases, in resonance scattering region, coating reduces the number of resonance peaks and resonance amplitude, increases the width of peaks. Moreover, the coating is thicker, the resonance region is narrower and the amplitude of resonance is lower. The coating has suppression of interior structured resonance, and reduces the resonance generated by flexural wave in sub-systems, and weakens the distributing intensity of water-layer’s standing wave field. In physical acoustics region, the spectrum line of cylindrical shell with coating gradually drives to smooth. Finally, the echoing characteristics of submarine with coating via the integral equation model of local equivalent acoustic impedance are presented. Using the relation of equivalent acoustic impedance and reflection coefficient of coating, the local acoustic impedance solution formula of coating is established. The result shows that for assumed coating, the target strength of submarine reduces about 4 to 10dB relative to rigid boundary upward of 1 kHz. The reflection coefficient of coating is smaller, the target strength is smaller. Coated with identical sound characteristic anechoic layer, in lower frequency, the target strength of one-layer and two-layer’s shelled submarine is different. In higher frequency, the both target strengths are similar. |
| 语种 | 中文 |
| 公开日期 | 2011-05-07 |
| 页码 | 95 |
| 源URL | [http://159.226.59.140/handle/311008/456]  |
| 专题 | 声学研究所_声学所博硕士学位论文_1981-2009博硕士学位论文 |
| 推荐引用方式 GB/T 7714 | 孙阳. 水下结构弹性体的声散射[D]. 声学研究所. 中国科学院声学研究所. 2009. |
入库方式： OAI收割
来源：声学研究所
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