纵肋或铺板衔接有限长圆柱壳声散射特性研究

The cylindrical shell reinforced by circumference or lengthwise ribs and plates is one of the main structural forms of underwater vehicles. With the improvement of the role played by underwater vehicles in the deep sea resources development, underwater acoustic scattering characteristics of these cylindrical shells are concerned significantly which act as the preconditions of active acoustic detection and identification on these objects. Both circumferential coupling and axial coupling are occurred in the case of lengthwise ribs and plates, while only axial coupling is occurred in the case of circumference ribs and plates. Consequently, acoustic scattering characteristics and formation mechanism aroused by lengthwise ribs and walls are more complicated than those of circumference ribs and plates. The project is implemented on insight of fine acoustic scattering characteristics and formation mechanism of finite cylindrical shells reinforced by lengthwise ribs and walls. By means of building the scattering model of finite cylindrical shells reinforced by lengthwise ribs or plate, rules of excitation, coupling and propagation of elastic waves in shells will be put forward, as well as the formation mechanism of fine acoustic scattering characteristics aroused by lengthwise ribs or plates. Broadband echo frequency spectrum with respect to the angle of incident wave will be studied. The method of extracting the circumference period of ribs and the location of walls will be established. Theoretical basis will be provided for active acoustic detection and recognition on underwater vehicles.

随着水下航行器在深海资源开发中发挥作用的日益显著，作为大多数水下航行器主体结构的环肋/舱壁、纵肋/铺板衔接圆柱壳的水下声学特性备受关注，掌握其声散射特性是对其主动声探测与识别的前提条件。由于纵肋/铺板衔接有限长圆柱壳周向、轴向同时耦合，而环肋/舱壁衔接有限长圆柱壳仅轴向耦合，因此纵肋/铺板引起的声散射特征及其形成机理的复杂程度更大、开展的研究较少。本项目以掌握纵肋或铺板衔接有限长圆柱壳体声散射精细特征及其形成机理为目标，通过建立纵肋或铺板衔接有限长圆柱壳体声散射理论模型，归纳纵肋或铺板衔接情况下壳体中弹性波激发、耦合和传播规律，揭示纵肋或铺板引起的声散射精细特征形成机理，掌握宽带声波激励下壳体回波频率谱随声波入射方位的变化规律，建立纵肋周期性、铺板衔接位置等特征提取方法，为水下航行器主动声探测与识别提供理论依据。

加环肋和纵肋以及铺板圆柱壳结构是大多数水下潜器主体结构的简化模型，纵肋或铺板对圆柱壳的振动与声学特性具有不可忽视的作用，掌握其声学特性可以为主动声呐探测与识别水下潜器提供新的依据。采用理论预报和实验验证的思路，深入研究了周期性纵肋或多层铺板对圆柱壳振动和声学特征的影响，主要包括如下几个方面：.1..采用二维弹性薄壳理论导出了加多层刚性铺板圆柱壳散射声场的解析解。基于背向散射声场形态函数频率-角度谱中的精细特性，着重分析了铺板与圆柱壳衔接点对入射声波的反射以及亚音速弯曲波的再辐射作用。研究表明亮区处铺板与圆柱壳衔接点不但对入射声波具有反射作用，还能够激发并再辐射亚音速的弯曲波，衔接点处的反射波与再辐射的弯曲波都能与镜反射回波发生干涉，在背向散射声场形态函数频率-角度谱中形成干涉条纹。此外，再辐射的亚音速弯曲波能量远小于铺板与圆柱壳衔接点处反射波的能量，若多个铺板与圆柱壳衔接点同时处于亮区，衔接点反射波的特征将掩盖其再辐射弯曲波的特征。.2..建立了水中加纵肋圆柱壳在平面波激励下的声散射数学模型。将周向模态数与圆柱壳半径之比看作离散周向波数，并基于离散周向波数频率谱研究了平面波激励时周期性纵肋对壳体振动的影响。研究表明，平面波无法直接激发亚音速的弯曲波，但在平面波的激励下，壳体振动带动了纵肋的振动，而纵肋对壳体的反力激发了壳体中亚音速的弯曲波。加周期纵肋圆柱壳的周向同样存在多阶次的Bloch弯曲波，不同阶次的Bloch弯曲波也能在对应的分波形态函数中形成共振峰，叠加在背向散射声场形态函数中形成复杂的共振峰。此外，满足一定关系的不同阶分波形态函数还具有相同的共振频率，也就是说周期性纵肋的共振存在简并现象。.3..设计了加单层铺板与加双层铺板圆柱壳声散射的水池实验，分别使用短脉冲入射和长脉冲入射波获得了目标背向散射的瞬态信息和稳态信息，并画出了瞬态的时间-角度谱和稳态的频率-角度谱。由于短脉冲的入射波能量较小，时间-角度谱中只观察到了明显的铺板与圆柱壳衔接点反射波的轨迹。长脉冲入射时，稳态的频率-角度中则同时观察到了较明显的衔接点反射波和再辐射弯曲波的轨迹。铺板与圆柱壳衔接点反射波的轨迹能准确预报。. 重点分析了纵肋或铺板对壳体中弹性波的激发、传播以及辐射作用以及由于纵肋周期性而产生的Bloch弯曲波对声场的贡献，为实际工程提供了新思路和理论依据。