共查询到15条相似文献,搜索用时 156 毫秒
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采用蒙特卡罗方法根据团簇-团簇凝聚(CCA)模型对由球形原始微粒凝聚而成的烟幕凝聚粒子进行模拟,用离散偶极子近似(DDA)方法研究随机取向烟幕凝聚粒子的消光特性.结果表明,凝聚粒子的消光特性受到原始微粒数量以及粒径的影响,粒子的凝聚将减弱烟幕的消光性能;当凝聚结构中原始微粒的数目一定时,存在使烟幕消光性能达到最大的原始微粒粒径. 相似文献
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基于分形理论,采用团簇—团簇凝聚模型对随机分布烟尘团簇粒子的分形结构进行了模拟.利用离散偶极子近似方法研究了不同类型的随机分布烟尘团簇粒子的单次散射特性.利用蒙特卡罗方法研究了激光信号在随机分布烟尘团簇粒子中的传输衰减特性.讨论了入射角、激光波长、烟尘粒子数密度以及组成单个烟尘团簇粒子的原始微粒粒径和数目等参量对激光衰减特性的影响.研究结果对激光在复杂随机介质中的传输衰减特性分析提供了理论依据. 相似文献
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基于分形理论,采用蒙特卡罗方法对随机分布的烟尘团簇粒子结构进行了仿真模拟,利用离散偶极子近似(discrete dipole approximation, DDA)方法研究了随机分布的烟尘团簇粒子的辐射特性,分析讨论了分形维数、原始微粒粒径和数量以及复折射率对随机分布烟尘团簇粒子辐射特性的影响.研究表明,在给定分形维数的情况下,烟尘团簇粒子的辐射特性取决于原始微粒粒径、数量及复折射率;原始微粒较小的团簇粒子,当分形维数较小时,吸收截面变化不明显,但当分形维数大于2时,吸收截面骤然增大,然而,对于具有比较大的原始微粒粒径、数量及复折射率的烟尘团簇粒子,吸收截面随着分形维数的增大而单调递减;随着分形维数的增大,团簇粒子的散射截面、消光截面及单次散射反照率均单调递增;从整体上来讲,团簇粒子的辐射特性与等效球形粒子的辐射特性存在着比较大的差别,并且这种差别随着分形维数的增大而减小.该工作对研究气溶胶粒子的辐射及气候效应具有重要的科学价值.
关键词:
烟尘团簇粒子
辐射特性
离散偶极子近似方法 相似文献
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利用蒙特卡罗方法根据团簇-团簇凝聚(CCA)模型对由球形原始粒子凝聚而成的烟尘簇团粒子进行了模拟,用离散偶极子近似(DDA)方法对随机分布的烟尘簇团粒子的缪勒矩阵元素进行了数值计算,给出了不同入射波长情况下随机分布烟尘簇团粒子的缪勒矩阵元素与组成簇团粒子的基本粒子的粒径和数目的数值关系,为进一步研究随机分布簇团粒子的形成机理、形态特性、散射特性提供了一种理论方法.
关键词:
烟尘簇团粒子
缪勒矩阵
离散偶极子近似方法 相似文献
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分形结构对随机取向烟尘团簇粒子光散射特性的影响 总被引:1,自引:0,他引:1
利用蒙特卡罗方法对不同分形维数和分形前向因子的随机取向烟尘团簇粒子的分形结构进行了仿真,采用离散偶极子近似(DDA)方法对随机取向烟尘团簇粒子的缪勒矩阵元进行了数值计算,并与球形粒子模型进行了比较,深入探讨了烟尘团簇粒子的分形维数和分形前因子对其散射特性的影响。研究表明,等效球形粒子的光散射特性与随机取向烟尘团簇粒子的光散射特性存在很大差别,并且此差别随着团簇粒子的分形维数以及分形前向因子的增大而减小;分形维数对表征团簇粒子散射特性的缪勒矩阵元的影响在一定散射角范围内均比较明显,分形前向因子对团簇粒子的缪勒矩阵元角分布的影响与分形维数的影响类似,不过其影响相对分形维数较弱。 相似文献
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采用Monte-Carlo方法,对气溶胶凝聚粒子进行了模拟,讨论了凝聚粒子的孔隙特性,分析了空间结构、原始粒子数目对凝聚粒子孔隙率和等效折射率的影响。结合物质的电结构,将气溶胶凝聚粒子离散为一系列偶极子,利用离散偶极子近似方法,数值计算了不同孔隙率气溶胶凝聚粒子的散射、吸收和消光截面各种取向的统计平均值。结果表明,气溶胶凝聚粒子的孔隙率明显取决于其空间形状和所含原始微粒的数目;气溶胶凝聚粒子的等效折射率、吸收、散射和消光截面则随孔隙率的增加而减小。研究结果可为全面理解气溶胶粒子光学特性提供参考;也可为某些涂层材料光学性能的改变提供参考,通过改变涂层材料中凝聚粒子的孔隙率来改变涂层材料的等效折射率,进而改变涂层材料对光的散射和吸收。 相似文献
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随机取向气溶胶凝聚粒子光学特性研究 总被引:1,自引:0,他引:1
利用Cluster-cluster aggregation (CCA)模型,模拟了由64个球形原始微粒凝聚而成的四种随机取向气溶胶凝聚粒子。结合离散偶极子近似方法,分别得到了不同入射角和不同尺寸参数情况下气溶胶凝聚粒子的吸收、散射、消光效率因子和不对称因子的数值结果,并比较分析了四种形状气溶胶凝聚粒子吸收、散射、消光效率因子和不对称因子的差异。结果显示:对于相同数目原始微粒的气溶胶凝聚粒子,其光学特性明显依赖于入射光的入射角度和气溶胶凝聚粒子的形状;对于不同尺寸参数的气溶胶凝聚粒子,当入射光波长给定时,吸收、散射和消光效率因子最初随尺寸参数增大而快速增大,随后又随尺寸参数增大缓慢变小,但在尺寸参数变化过程中存在一个极大值;不对称因子则随尺寸参数的增大一直呈增大趋势,且随尺寸参数的增大趋近于1。 相似文献
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Optical characteristics, namely, dispersion and absorption spectra of an ensemble of spherical particles randomly oriented inside an optical cavity are investigated. The study is based on the self-consistent matching of new data from the inhomogeneous optical cavity with data from the scattering of an ensemble of spherical particles of different size, randomly oriented in free space. As a result, a new model, which self-consistently accounts for multiple scattering in the optical cavity, has been developed to predict absorption and dispersion of ensembles of spherical particles. This model is supposed to enhance potentiality of the intracavity method for plotting wavelength dependences of optical characteristics of media. A specific calculation of dispersion and absorption dependences on the wavelength shows that this method can be used for investigation of biological media consisting of spherical particles, in particular, erythrocyte suspension. 相似文献
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V. EymetA.M. Brasil M.El HafiT.L. Farias P.J. Coelho 《Journal of Quantitative Spectroscopy & Radiative Transfer》2002,74(6):697-718
The effect of aggregation on soot radiative properties in the infrared region of the spectrum is numerically investigated using Rayleigh-Debye-Gans theory for fractal aggregates (RDG-FA). In order to use the RDG-FA theory for a wide range of aggregate sizes and wavelengths, the predicted phase functions, scattering and absorption coefficients are compared with a more accurate theory, the integral equation formulation for scattering—IEFS. The importance of scattering when compared with absorption is investigated, as well as the effect of aggregation on the phase function shape and on the scattering cross section. It is concluded that in the case of small aggregates formed with small primary particles the scattering coefficient is negligible compared with the absorption coefficient, and scattering and aggregation of primary particles can be ignored. Thus, the Rayleigh approximation can be used leading to isotropic scattering. In the case of large aggregates constituted by large primary particles, aggregation becomes important and the scattering cross section is of the same order of magnitude of the absorption cross section. Moreover, the phase function becomes highly peaked in the forward direction. Therefore, the Rayleigh and the equivalent volume Mie sphere approximations are not valid, and the RDG-FA method emerges as a good compromise between accuracy and simplicity of application. However, radiative transfer calculations between two infinite, parallel, black walls show that scattering may always be neglected in the calculation of total radiative heat source and heat fluxes to the walls. The minor influence of scattering on the accuracy of the predictions is explained by the shift between the spectral region where scattering is important and the region where the spectral radiative heat source is large. 相似文献
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N. G. Khlebtsov 《Optics and Spectroscopy》2001,90(3):408-415
Using the discrete dipole method, exact and approximate analytical solutions for orientation-averaged cross sections for extinction, absorption, and scattering of light are obtained. The analytical solutions can be applied to the calculation of integrated cross sections of fractal clusters formed by primary particles with different optical properties (soot in air and aqueous suspensions of aggregates of polystyrene, gold, and silver nanoparticles). It is shown that two models of aggregates that differ only in trajectories (ballistic or Brownian) of primary particles and intermediate clusters and in average fractal dimensions give close values of averaged extinction cross sections. 相似文献
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L. E. Paramonov 《Optics and Spectroscopy》2012,112(5):787-795
Light scattering by isotropic ensembles of ellipsoidal particles is considered in the Rayleigh-Gans-Debye approximation. It is proved that randomly oriented ellipsoidal particles are optically equivalent to polydisperse randomly oriented spheroidal particles and polydisperse spherical particles. Density functions of the shape and size distributions for equivalent ensembles of spheroidal and spherical particles are presented. In the anomalous diffraction approximation, equivalent ensembles of particles are shown to also have equal extinction, scattering, and absorption coefficients. Consequences of optical equivalence are considered. The results are illustrated by numerical calculations of the angular dependence of the scattering phase function using the T-matrix method and the Mie theory. 相似文献