水下目标低频散射特性研究

本文主要研究了水下复杂目标的低频散射特性,应用边界元理论,采用SYSNOISE软件计算了刚性球、标准刚性潜艇模型及弹性球壳的低频散射特性,并分别与经典理论解、标准解进行对比,结果显示SYSNOISE的计算结果与理论解具有较好的吻合.通过上述验证,说明使用SYSNOISE软件计算能有效地预测大型水下复杂目标的声散射情况.     

水下气泡幕激光后向散射功率衰减特性实验研究

针对水下气泡幕的激光后向散射功率衰减特性,设计了实验系统,采用不同波长、不同发射功率的激光对不同密度、不同厚度、不同距离的气泡幕进行照射,采用激光功率计对后向散射光功率进行测量,并对数据进行了分析。结果表明：蓝绿光的后向散射特性较好;后向散射光功率与发射光功率及气泡幕厚度呈正比;水下气泡幕的激光后向散射特性与气泡密度、气泡幕距离关系密切。     

基于FEKO与MATLAB的扩展目标回波平台构建

为了在教学科研中形象化的展示扩展目标的回波以及一维距离像信息,构建一个基于电磁仿真软件FEKO与MATLAB图形用户界面(GUI)仿真的雷达扩展目标回波模拟平台.利用该平台可以完成不同带宽、不同入射方向以及不同极化条件下电磁散射特性数据的获取以及扩展目标回波的模拟,并通过对模拟的扩展目标回波信号进行脉冲压缩处理,得到目...     

并行计算水下大尺度弹性壳体的低频声散射

有限元与边界元耦合模型是研究水下弹性壳体目标低频声散射常用的数值方法。应用该模型计算大尺度弹性目标的声散射时需要大量的计算时间与存储空间,采用并行数值的方式可以解决这一问题。首先并行计算生成有限元矩阵和边界元矩阵,然后应用并行化的广义极小残差(GMRES)迭代算法求解大型非对称线性方程组。详细叙述了并行GMRES(m)迭代算法的执行过程,并以球壳的声散射计算为例分析了迭代步数对算法收敛情况的影响。最后计算了Benchmark目标模型的低频散射声场,分析了其收发分置散射目标强度以及表面声场的分布。     

藕节形耐压壳体强度与稳定性有限元分析

研究无入水下航行器壳体强度优化问题,由于随着下潜深度的增加,水下航行器受到的压力不断增大,传统水下航行器采用的壳体结构已不能满足强度要求.藕节形耐压壳体则结合了球形壳体和圆柱形壳体的优点,弥补了传统耐压壳体结构的不足.针对藕节形耐压壳体强度设计,利用有限元软件对不同厚度、不同切弧角下的强度和稳定性进行了分析,给出了最大应力和稳定性系数随厚度和切弧角的变化规律并分析了其原因,为大深度水下航行器的壳体结构设计提供了一定的参考依据.     

多个同频振动散射点雷达回波理论分析与仿真研究

基于雷达后向散射理论和散射点模型,针对雷达目标的同频振动散射点,详细推导并建立了雷达回波通用模型,对其幅度调制函数和相位调制函数的周期性进行了详细的讨论.最后对两个同频振动散射点合成雷达回波进行了计算机仿真研究,理论分析和仿真结果表明,该模型是有效的,并且随着同频振动散射点数的增加,其幅度调制函数和相位调制函数的周期性不发生变化,只是它们的值会随着振动点数的增加而改变.     

导弹目标逆合成孔径雷达成像的仿真

该文应用物理光学法仿真出平面波以任意角度、不同频率入射时某型导弹的电磁散射回波矩阵,并利用快速傅立叶变换成像处理算法得出目标的像。导弹目标利用部件分解法进行了近似,并引进了散射矩阵的概念而简化了导弹目标回波相关数值计算复杂度,从而提高逆合成孔径雷达成像(ISAR)的实时性。文中运用信号处理相关理论对平面波在不同的入射角下逆合成孔径雷达对导弹目标所成的像进行了分析,所成像能精确地反映出目标地镜像散射区域及目标的旋转情况。此仿真结果表明物理光学法能够简单有效地计算出导弹目标的散射回波并对其进行逆合成孔径雷达成像。     

基于Abaqus和Isight的水下壳体声散射优化

针对水下椭圆壳的声散射优化问题，以壳体声散射强度最小为优化目标，以截面特征参数为设计变量建立模型。采用有限元与无限元耦合的混合优化方法，利用Python和Abaqus二次开发求解远场声散射强度，并结合Isight对水下壳体声散射进行优化。根据优化结果改进椭圆壳截面几何参数，可有效降低其声散射强度。     

复合材料结构水下振动噪声仿真研究

开展复合材料夹芯板的损耗特性测试试验,获得了复合材料夹芯板结构内损耗因子,并以此作为数值计算的基础参数输入;采用声固耦合有限元分析法,对水下航行器上层建筑采用复合材料夹芯板后的振动声辐射特性进行分析;探索了壳板厚度参数对水下航行器上层建筑振动声辐射特性的影响规律,提出了复合材料上层建筑结构声学优化设计方案,旨在为上层建筑结构声学设计提供参考.     

基于稀疏分解的水下目标回波信号处理方法

针对超低信噪比的水下弱信号处理问题,基于稀疏分解理论,重点关注入射信号和回波模型等先验信息如何融入稀疏字典（过完备原子库）的构造,并结合匹配追踪方法,提出基于稀疏分解的水下回波信号处理方法。首先建立水下回波信号亮点模型,得到回波模型和入射 信号的关系,对已知的发射信号进行离散化、能量归一化以及移位处理,构造适合回波信号自身特性的过完备原子库;然后基于匹配追踪算法实现水下回波信号的稀疏分解,并将处理结果与常用的匹配滤波方法进行对比分析。仿真结果表明,本文方法不仅能精确重构出原始回波信号,而且在处理超低信噪比水下回波信号时较匹配滤波方法具有明显的优势。     

基于Abaqus的水下结构声辐射仿真方法

提出一种在Abaqus中直接完成辐射声场仿真的方法,该方法可大大减少流场网格层数.利用无限元的计算结果求解任意远处球形声场的声压;结合弹性球壳的解析解算例验证该方法的正确性,并将该方法拓展到细长型结构中.结果表明：基于Abaqus无限元的水下结构声辐射的计算方法简单、可行;采用有限元与无限元相结合的方法可以大幅度缩小流场区域.     

Postbuckling of multilayer cylindrical and spherical shell panels reinforced with graphene platelet by isogeometric analysis

The present work fills a gap on the postbuckling behavior of multilayer functionally graded graphene platelet reinforced composite (FG-GPLRC) cylindrical and spherical shell panels resting on elastic foundations subjected to central pinching forces and pressure loadings. Based on a higher-order shear deformation theory and the von Kármán’s nonlinear strain–displacement relations, the governing equations of the FG-GPLRC cylindrical and spherical shell panels are established by the principle of virtual work. The non-uniform rational B-spline (NURBS) based isogeometric analysis (IGA), the modified arc-length method and the Newton’s iteration method are employed synthetically to obtain nonlinear load–deflection curves for the panels numerically. Several comparative examples are performed to test reliability and accuracy of IGA and arc-length method in present formulation and programming implementation. Parametric investigations are carried out to illustrate the effects of dispersion type of the graphene platelet (GPL), weight fraction of the GPL, thickness of the panel, radius of the panel and parameters of elastic foundation on the load–deflection curves of the FG-GPLRC shell panels. Some complex load–deflection curves of the FG-GPLRC cylindrical and spherical shell panels resting on elastic foundations may be useful for future references.

     

Underwater polarization‐based single pixel imaging

This paper extends single pixel imaging (SPI) to underwater scenario. Backscattering, which is a limiting factor for underwater imaging, is analyzed for the SPI, and the forward model of SPI under backscattering is formulated. Inspired by the polarization‐based descattering technique, we propose the two cross‐polarization SPI detection scheme to eliminate the backscattering light. The descattered image is reconstructed from the cross‐polarization data. Experimentally, we construct the underwater polarization‐based single‐pixel imaging system. And we test our scheme under different turbidity water. It is shown in experiments that our method can provide a clear image at turbid water of 32FTU, where the classical SPI has been severely contaminated by the backscattering, even under the best the polarization state.     

A Novel Amphibious Spherical Robot Equipped with Flywheel,Pendulum, and Propeller

The ability of amphibious movement is found widely among small animals such as frogs, tortoises, snakes, and crabs. They can move on land, in water, and even on the water bottom. Inspired by the animals’ moving capability, an amphibious spherical robot with flywheel, pendulum, and propeller has been developed. In this paper, the mechanical structure, motion performance, control architecture, and experimentation of the amphibious spherical robot are presented. The robot can show three outstanding advantages for underwater observation, which distinguish it from the other existing observing robots. First, it can resist great water pressure to protect the internal components that is based on the spherical shell. Second, the robot only requires a single propeller to achieve the flexible movement and control posture in water. Third, the robot can roll on land or on water bottom only through an internal motor that can reduce the energy consumption during the observation process. The robot has a wide range of applications such as underwater observation, search and rescue, sensor networks.     

基于板块元法的水下目标回波亮点仿真

针对传统亮点模型模拟水下目标回波亮点精确度不高的问题,给出了一种运用板块元法仿真实现目标回波亮点的方法。采用建模软件对潜艇模型进行精确几何建模,运用板块元法计算了潜艇目标的高频回波数据。仿真结果表明：该方法可以更真实地反应水下目标的回波亮点特性,为水下目标的探测与识别提供数据支持。     

声诱饵回波模拟器仿真研究

随着水声技术的发展，水下武器对抗也日趋复杂。能够模拟目标回波的主动式声诱饵的出现，为对抗主动自导鱼雷及主动声纳提供了非常重要的帮助。着重对声诱饵的回波模拟器的作用机理进行了分析，然后给出了脉冲宽度、多普勒频移、时延与展宽、目标强度：最大回波强度等回波特征参数的估计方法，并对可以同时对抗声自导鱼雷和主动声纳的某声诱饵回波模拟器进行了仿真研究，并给出了仿真结果，对水声对抗技术研究有着重要的参考价值。     

局部各向异性的薄壳收缩变形

基于位置动力学提出局部各向异性的薄壳收缩变形方法.首先针对基于位置动力学变形模拟方法的材质局限性的不足,提出薄壳收缩变形的弹性变形能,实现了多材质的弹性收缩变形.其次,针对薄壳收缩变形过程中的抖动问题,给出适当的弯曲能系数,实现了稳定的收缩变形.第三,针对薄壳局部类球面结构收缩变形缓慢且细微的不足,定义了局部各向异性ARAP变形能等,实现了薄壳局部类球结构的快速、显著、稳定的收缩变形.最后以轴向平行包围盒与非渗透滤波器作为碰撞检测的预处理,剔除不可能发生碰撞的图元对,提高了收缩变形过程中的碰撞检测效率.相关实验结果表明,提出的薄壳收缩变形算法适用于多种材质模型以及多种各向异性能量,且有效地解决了抖动及局部类球结构收缩变形缓慢且不显著等问题.     

Development and control of articulated amphibious spherical robot

In this paper, we proposed an amphibious spherical robot that can search and rescue from uneven terrain and also move in narrow underwater spaces. This paper presents three control methods for an articulated amphibious spherical robot. The first is a full-dimensional that is adapted the robot to the complex amphibious terrain, in this method, relying on a novel drive mode of mecanum wheels, the power required for the movement comes from the friction generated by mecanum wheels and the spherical shell. The second control method is modeling based on a unit quaternion motion control algorithm to realized 6 Degrees of Freedoms (DoFs) movement mode. The last control algorithm is according to Archimede Buoyancy Principle (ABP) and Fuzzy Control (FC) algorithm by controlling the air density of the spherical capsules in the lower hemispheres, the relationship between buoyancy and gravity is controlled to achieve the functions of floating and diving. Experiments are performed to demonstrate the effectiveness of the proposed methods and the developed robot.