Chebyshev谱方法在声散射数值计算中的应用

基于声学边界元基本理论,并结合Chebyshev谱方法进行了声散射数值计算研究.采用2阶边界单元,谱点离散选用不包含边界的CG(Chebyshev-Gauss)配点法,克服了传统边界元在表面单元节点处出现的法向及法向导数不连续的现象;应用CHIEF(Combined Helmholtz Integral Equation Fomulation)方法进行了数值非唯一性处理,提高了计算的精度.与传统边界元方法进行了精度和效率的对比分析,证明该方法具有计算快速、精度高的特点.     

Comment: On the different approaches of Rayleigh optical depth determination

Srivastava et al. (2009) presented Rayleigh scattering cross-sections and optical depths for Earth’s atmosphere that are approximately 3% smaller than previously accepted. Their analysis was based on quantum-mechanical theory for anisotropic scattering in the Cabannes line published in papers that seem to have introduced some confusion about determining the anisotropy and King factors. This comment clarifies these factors and shows that including the frequency-shifted rotational Raman lines gives the traditional King factor and the correct Rayleigh scattering for the optical depth.     

增强飞行器角闪烁的方法—一种新的飞行器隐身技术

本文建立了任意截面缝隙加载理想导体柱电磁散射的一般数学模型,获得对缩比模型的理论计算与测量数据较好的一致性。在谐振频率区内对实际模型测量分析表明,利用多背接腔缝隙加载,可以实现较大姿态角范围内后向雷达散射戴面的减缩,并同时产生目标角闪烁线偏差有强烈增强,这是一种新的飞行器隐身技术措施。     

Studies on the imaging characteristics of Yohkoh Soft X-ray Telescope: Optical aberration and scattering

In order to better understand the characteristics of Yohkoh Soft X-ray Telescope (SXT) mirror, we have analyzed the in-flight overexposed image (the starburst image) obtained during the solar flare observation. It has been revealed from our study that the intensity distribution inside the shadows shown in the scattering difference image contains little of the scattered component of the PSF and matches almost correctly the extension of the PSF core profile. Also it is found that the scattering wing of the SXT PSF is connected smoothly to the PSF core within the distance of about 100–200 arcsec from the peak. With numerical simulations we have shown that an increase in energy affects not only the level of scattering wing, but also both the shape and the absolute level of the PSF core. The results have revealed, however, that the energy dependence for the SXT PSF cannot be easily estimated with the data obtained from one filter alone, which implies that the data analysis using multiple filters will enable us to determine the absolute amount of scattered component as well as the energy dependence of the SXT PSF. Details on the analysis of starburst image and the results from numerical simulations will be introduced and discussed thoroughly.     

C-R样条用于低散射目标爬行波求解

C-R(Catmull-Rom)样条具有直观、稳定、灵活、不需反求控制顶点等优点,特别适用于具有复杂外形的飞行器进行几何描述. 利用 (G¹,k=1) Catmull-Rom样条及其张量积曲面对低散射目标进行几何建模,并求解低散射目标爬行波RCS贡献,通过计算结果与实验结果比较,获得令人满意的结果.     

基于远场模式的散射体形状成像

对线性抽样法的电磁场逆散射求解进行了研究。为避免迭代和优化法的正问题求解,用积分算子将散射物边界数据映射到散射场的远场模式,针对第一类积分方程的不适定性,用Tikhonov正则化法求解,并用高阶收敛算法确定正则化参数以快速数值实现。数值计算结果表明：线性抽样法＋确定正则化参数的高阶收敛算法可较好地滤除噪声,减少了确定正则化参数的计算量。     

高斯粗糙表面电磁散射的曲率修正双尺度法

在传统双尺度法分析粗糙表面电磁散射特性的基础上，通过对大尺度切平面的曲率修正。给出了小入射角时改进双尺度法的计算模型。采用传统微扰法和基于圆柱曲面修正的微扰法，计算了实际粗糙面掠入射时的后向散射系数，并与有关测量值进行了比较。结果表明，在中、小入射角及掠入射条件下，基于曲率修正双尺度法的计算结果与实际值均较为相近，证明该方法有效。     

MRTD方法的色散特性分析和电磁散射应用

将基于Daubechies尺度函数的时域多分辨(Multiresolution time-domain,MRTD)方法应用于三维目标的电磁散射和雷达目标特性分析中,并对其Courant稳定性条件和色散特性进行了分析.在入射波引入方面,提出应用总场/散射场技术,在连接边界周围定义一些\"修正区域\",并推导出一系列\"修正区域\"内的迭代公式,把入射场作为\"连接边界条件\"引入到计算区域.理论分析和实验结果表明,基于Daubechies尺度函数的MRTD方法和入射波引入方法是有效的,且与传统的FDTD方法相比,MRTD方法在保持计算精度的前提下能够节省计算资源.     

近场微波成像的实验研究

本文针对转台模式的近场微波成像进行了实验研究。首先介绍了近场微波成像的实验系统，然后考虑到宽频带天线的非理想特性，提出一种近场微波成像系统的实验修正模型。最后基于该模型，给出了利用理想导体长方柱、理想导体圆柱、理想导体正方体盒以及四尾翼导弹模型的实测数据的重建图像。重建图像基本反映了目标的轮廊。     

回路线栅法分析目标散射场

提出了求解复杂飞行器目标谐振区散射场的回路线栅法.回路线栅法的基本思想是以其上流动着感应电流的三维线栅回路网格来模拟在入射波激励下的连续金属表面,与以往单独分段的线栅模型不同,本文利用构成闭合回路的线栅构造每一个金属面元,而不采用单独分段线栅电流表示面元的被激电流,从而使得基尔霍夫定律在每个节点处能够得到自动满足.通过分析目标几何特性建立相应的回路线栅电磁模型,并利用共轭梯度快速傅利叶变换法(CGFFT),给出谐振区复杂飞行器目标的雷达散射截面(RCS)结果.