光线跟踪生成三维真实感景物

将全局光照模型和球冠光源模型结合起来,利用光线跟踪算法实现了由CSG树定义的任意复杂物体的真实感图形生成,模拟了阴影、透明、反射等多种效果,生成的画面具有很强的真实感,并利用包围框大大减少了计算量。     

Light scattering by a spherical particle with multiple densely packed inclusions

This paper calculates light scattering by a spherical water particle containing densely packed inclusions at a visible wavelength 0.55 \mum by a combination of ray-tracing and Monte Carlo techniques. While the individual reflection and refraction events at the outer boundary of a sphere particle are considered by a ray-tracing program, the Monte Carlo routine simulates internal scattering processes. The main advantage of this method is that the shape of the particle can be arbitrary, and multiple scattering can be considered in the internal scattering processes. A dense-medium light-scattering theory based on the introduction of the static structure factor is used to calculate the phase function and asymmetry parameters for densely packed inclusions. Numerical results of the single scattering characteristics for a sphere containing multiple densely packed inclusions are given.     

激光等离子体产生X射线数值模拟的两个问题

对激光等离子体产生X射线的数值模拟中的光路方程组,提出了采用Runge-Kutta求解的思路。对计算X射线发射中需要求解的束缚电子占据概率方程组,讨论了采用显式求解的可能性。得到的计算结果初步表明,我们提出的方法是可行的。     

Comparison of ray-tracing methods for semitransparent slab with variable spatial refractive index

The ray-tracing technique has the main difficulty in solving radiative transfer in the medium with variable spatial refractive index. Recently, three methods have been developed for the application of the ray-tracing technique in those medium. To compare and discuss the numerical characteristics of those methods, a semitransparent slab with variable spatial refractive index is taken as an example, and the reflectivity and the transmissivity of the slab are computed by the curved ray-tracing method, the multi-layer approach, and the discrete curved ray-tracing method, respectively. As the result, it is shown that, the discrete curved ray-tracing method gives the result with good accuracy and convergence characteristics than the multi-layer approach. Due to accounting physically inexistent reflection on the interface between sublayers, the multi-layer approach converges slowly.     

Monte Carlo discrete curved ray-tracing method for radiative transfer in an absorbing-emitting semitransparent slab with variable spatial refractive index

A Monte Carlo discrete curved ray-tracing method is developed to analyze the radiative transfer in one-dimensional absorbing-emitting semitransparent slab with variable spatial refractive index, in which the Monte Carlo method is combined with the discrete curved ray-tracing method. A problem of radiative equilibrium with linear variable spatial refractive index is taken as an example to examine the accuracy of the proposed method. The temperature distributions and the dimensionless radiative heat flux are determined by the proposed method and compared with the data in references, which are obtained by other different methods. The results show that the Monte Carlo discrete curved ray-tracing method has a good accuracy in solving the radiative transfer in one-dimensional semitransparent slab with variable spatial refractive index.     

Analysis of cylindrical microlenses simultaneously implementing beam-splitting and focusing based on rigorous electromagnetic theory

A cylindrical microlens for implementing both functions of beam-splitting and focusing on the preset positions is proposed. Phase functions of the microlenses are determined by the ray-tracing method. The performance of the microlenses is investigated based on rigorous electromagnetic theory and the boundary element method. Numerical results show that the designed microlenses basically can realize beam-splitting and focusing on the preassigned positions simultaneously. Dual and triple beam-splitting and focusing on the expected positions by the designed microlenses are demonstrated. Diffraction efficiency of the the beam-splitting and focusing is evaluated.     

地震波旅行时非线性/线性联合插值法

地震波旅行时计算是射线追踪方法的核心问题,其精度直接影响着路径的精度和正演模拟的准确程度.为了提高地震波旅行时的计算精度,基于Asakawa的旅行时线性插值法(LTI)提出了一种改进的射线追踪法--非线性/线性联合插值法,即在震源的近场采用非线性插值计算旅行时,在远场仍用LTI算法.非线性/线性联合插值法提高了近场旅行时的计算精度,进而提高了全场(尤其是远场)旅行时的计算精度.数值模拟和模型试算的结果表明,本文提出的非线性/线性联合插值法较传统的LTI算法更为精确.     

不同光线入射角度下超声速湍流边界层气动光学效应的实验研究

利用基于纳米粒子的平面激光散射技术获取超声速(Ma=3.0)湍流边界层的密度分布,采用光线追迹方法计算其对应的光程差分布,并结合边界层气动光学相似律验证实验结果的可靠性.着重研究了光线入射角度对超声速湍流边界层气动光学效应的影响,并对其内在机理进行了分析.研究表明,气动光学效应对光线入射角度的依赖性源于光线在流场中的传输路径,传输路径的不同导致了光线在流场中的传输距离以及对应密度脉动互相关结果的差异.光线倾斜入射导致其在流场中传输距离增长,进而气动光学效应出现恶化.光线入射方向与壁面垂直方向之间的夹角越大,气动光学效应越显著,而且不同时刻的差异性增加,气动光学效应校正的难度增加.超声速湍流边界层中大量具有特定方向的涡结构导致了湍流边界层气动光学效应的各向异性.当光线倾斜向下游入射时,光线传播方向与流场中的涡结构具有较好的一致性,体现为此方向上密度脉动互相关系数较大,故气动光学效应比较严重.而当光线倾斜向上游入射时,相关系数较小,故气动光学效应较弱.     

含有密集随机分布内核的椭球粒子光散射特性研究

给出了一种结合射线追踪和蒙特卡罗方法计算含核粒子光散射的方法,内核粒子可以为稀疏分布也可为浓密分布.粒子外边界的反射和折射由射线追踪方法计算,而粒子内部的多次散射过程由蒙特卡罗方法模拟;当内核粒子为浓密随机分布时,其单次散射特性由基于静态结构因子（static structure factor）的浓密介质光散射理论计算.最后讨论了含核椭球粒子模型的单次散射特性. 关键词： 射线追踪技术 蒙特卡洛方法 光散射 椭球粒子     

闭域空间泄漏同轴电缆和单极天线辐射场的比较

从泄漏同轴电缆和天线的辐射理论出发，利用射线追踪法，以屏蔽良好的室内空间为例分析了其中由泄漏同轴电缆和单极天线产生的辐射场．通过比较，体现出了泄漏同轴电缆的场强在这种特定环境下具有分布均匀的优越性．该理论和结果可以扩展到其他场所，对于进一步研究闭域空间中的无线通信问题具有较强的参考价值．