共查询到18条相似文献,搜索用时 640 毫秒
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半透明梯度折射率介质内辐射熵传递方程及其数值模拟 总被引:1,自引:0,他引:1
在非相干辐射条件下,基于Planck光谱辐射熵强度定义,导出半透明梯度折射率介质内光谱辐射熵传递方程,以及局部辐射熵产率理论表达式.基于离散坐标法对辐射熵传递方程进行数值求解.以一维半透明梯度介质平板为例,对辐射熵方程及其算法进行验证.平板整体无因次辐射熵产的计算结果与宏观热力学定律的结果一致. 相似文献
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《工程热物理学报》2017,(4)
采用间断有限元法(Discontinuous finite element method,DFEM)求解一维散射性介质内矢量辐射传输问题。推导了散射性介质内矢量辐射传输方程的间断有限元离散格式,空间离散采用间断有限元离散将求解域划分为相互独立的单元,角度离散在传统的均匀分段光滑近似(Piecewise Constant Approximation,PCA)角度离散基础上进行局部加密以得到关键方向上的数值解。采用两个稳态矢量辐射传输算例对间断有限元法求解矢量辐射传输方程的正确性和计算效率进行了验证,在此基础上拓展间断有限元法应用于求解散射性介质内瞬态矢量辐射传输方程,将随着时间推移过程中的瞬态辐射信息和最终的稳态结果相比较验证了本文方法的正确性。 相似文献
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求解辐射传递的非结构混合有限体积/有限元法 总被引:1,自引:0,他引:1
本文给了一种适用于任意非结构网格的有限体积/有限元法的混合算法用于求解多维半透明吸收、发射、散射性灰矩形介质内的辐射传递.该方法使用有限元法进行角度离散,有限体积法进行空间离散.与基于辐射传递离散坐标方程的方法不同的是,该方法在迭代求解的过程中,针对每一个空间体元,所有角度方向的辐射强度同时耦合求出.通过两个算例验证了该解法的正确性. 相似文献
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矢量辐射传输方程定量描述了辐射在地表-大气耦合介质中的传输过程,是定量遥感的基础.在处理辐射和离散介质相互作用时,如何处理多次散射、辐射偏振效应和耦合地表模型是研究的重点,直接影响定量化遥感反演的精度.文中基于逐次散射近似法求解了矢量辐射传输方程,求解过程中耦合典型地表的非偏双向反射(BRDF)模型和偏振双面反射(BPDF)模型.采用相对误差因子定量分析了地表双向反射效应和大气偏振效应对天基矢量辐射的影响.为进一步研究地表-大气耦合介质系统的偏振特性及地表大气参数的定量遥感反演提供理论支持.
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矢量辐射传输方程
逐次散射近似
定量遥感
偏振遥感 相似文献
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To avoid the complicated and time-consuming computation of curved ray trajectories, a discontinuous finite element method based on discrete ordinate equation is extended to solve the radiative transfer problem in a multi-dimensional semitransparent graded index medium. Two cases of radiative heat transfer in two-dimensional rectangular gray semitransparent graded index medium enclosed by opaque boundary are examined to verify this discontinuous finite element method. Special layered and radial graded index distributions are considered. The predicted dimensionless net radiative heat fluxes and dimensionless temperature distributions are determined by the discontinuous finite element method and compared with the results obtained by the curved Monte Carlo method in references. The results show that the discontinuous finite element method has a good accuracy in solving the multi-dimensional radiative transfer problem in a semitransparent graded index medium. 相似文献
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L.H. Liu 《Journal of Quantitative Spectroscopy & Radiative Transfer》2007,103(3):536-544
To avoid the complicated and time-consuming computation of curved ray trajectories, a least-squares finite element method based on discrete ordinate equation is extended to solve the radiative transfer problem in a multi-dimensional semitransparent graded index medium. Four cases of radiative heat transfer are examined to verify this least-squares finite element method. Linear and nonlinear graded index are considered. The predicted dimensionless net radiative heat fluxes are determined by the least-squares finite element method and compared with the results obtained by other methods. The results show that the least-squares finite element method is stable and has a good accuracy in solving the multi-dimensional radiative transfer problem in a semitransparent graded index medium, while the Galerkin finite element method sometimes suffers from nonphysical oscillations. 相似文献
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L.H. Liu 《Journal of Quantitative Spectroscopy & Radiative Transfer》2006,102(2):293-303
In graded index media, the ray goes along a curved path determined by Fermat principle. Generally, the curved ray trajectory in graded index media is a complex implicit function, and the curved ray tracing is very difficult and complex. Only for some special refractive index distributions, the curved ray trajectory can be expressed as a simple explicit function. Two important examples are the layered and the radial graded index distributions. In this paper, the radiative heat transfer problems in two-dimensional square semitransparent with layered and radial graded index distributions are analyzed. After deduction of the ray trajectory, the radiative heat transfer problems are solved by using the Monte Carlo curved ray-tracing method. Some numerical solutions of dimensionless net radiative heat flux and medium temperature are tabulated as the benchmark solutions for the future development of approximation techniques for multi-dimensional radiative heat transfer in graded index media. 相似文献
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L.H. Liu L. Zhang H.P. Tan 《Journal of Quantitative Spectroscopy & Radiative Transfer》2006,97(3):436-445
In graded index medium, ray goes along a curved path determined by Fermat principle, and curved ray-tracing is very difficult and complex. To avoid the complicated and time-consuming computation of curved ray trajectories, a finite element method based on discrete ordinate equation is developed to solve the radiative transfer problem in a multi-dimensional semitransparent graded index medium. Two particular test problems of radiative transfer are taken as examples to verify this finite element method. The predicted dimensionless net radiative heat fluxes are determined by the proposed method and compared with the results obtained by finite volume method. The results show that the finite element method presented in this paper has a good accuracy in solving the multi-dimensional radiative transfer problem in semitransparent graded index medium. 相似文献
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L.H. Liu J.Y. Tan B.X. Li 《Journal of Quantitative Spectroscopy & Radiative Transfer》2006,101(2):237-248
A meshless local Petrov-Galerkin (MLPG) approach is employed for solving the coupled radiative and conductive heat transfer in a one-dimensional slab with graded index media. The angular distribution term in discrete ordinate equation of radiative transfer within a one-dimensional graded index slab is discretized by a step scheme, and the meshless approach for radiative transfer is based on the discrete ordinate equation. A moving least-squares approximation is used to construct the shape function. Two particular test cases for coupled radiative and conductive heat transfer within a one-dimensional graded index slab are examined to verify this new approximate method. The temperatures and the radiative heat fluxes are obtained. The results are compared with the other benchmark approximate solutions. By comparison, the results show that the MLPG approach has a good accuracy in solving the coupled radiative and conductive heat transfer in one-dimensional graded index media. 相似文献
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Under various interface reflecting modes, different transient thermal responses will occur in the media. Combined radiative-conductive heat transfer is investigated within a participating, anisotropic scattering gray planar slab. The two interfaces of the slab are considered to be diffuse and semitransparent. Using the ray tracing method, an anisotropic scattering radiative transfer model for diffuse reflection at boundaries is set up, and with the help of direct radiative transfer coefficients, corresponding radiative transfer coefficients (RTCs) are deduced. RTCs are used to calculate the radiative source term in energy equation. Transient energy equation is solved by the full implicit control-volume method under the external radiative-convective boundary conditions. The influences of two reflecting modes including both specular reflection and diffuse reflection on transient temperature fields and steady heat flux are examined. According to numerical results obtained in this paper, it is found that there exits great difference in thermal behavior between slabs with diffuse interfaces and that with specular interfaces for slabs with big refractive index. 相似文献
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The spectral collocation method (SCM) is employed to solve the radiative transfer in multi-layer semitransparent medium with graded index. A new flexible angular discretization scheme is employed to discretize the solid angle domain freely to overcome the limit of the number of discrete radiative direction when adopting traditional SN discrete ordinate scheme. Three radial basis function interpolation approaches, named as multi-quadric (MQ), inverse multi-quadric (IMQ) and inverse quadratic (IQ) interpolation, are employed to couple the radiative intensity at the interface between two adjacent layers and numerical experiments show that MQ interpolation has the highest accuracy and best stability. Variable radiative transfer problems in double-layer semitransparent media with different thermophysical properties are investigated and the influence of these thermophysical properties on the radiative transfer procedure in double-layer semitransparent media is also analyzed. All the simulated results show that the present SCM with the new angular discretization scheme can predict the radiative transfer in multi-layer semitransparent medium with graded index efficiently and accurately. 相似文献
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L. Zhang 《Journal of Quantitative Spectroscopy & Radiative Transfer》2009,110(13):1085-1096
Both Galerkin finite element method (GFEM) and least squares finite element method (LSFEM) are developed and their performances are compared for solving the radiative transfer equation of graded index medium in cylindrical coordinate system (RTEGC). The angular redistribution term of the RTEGC is discretized by finite difference approach and after angular discretization the RTEGC is formulated into a discrete-ordinates form, which is then discretized based on Galerkin or least squares finite element approach. To overcome the RTEGC-led numerical singularity at the origin of cylindrical coordinate system, a pole condition is proposed as a special mathematical boundary condition. Compared with the GFEM, the LSFEM has very good numerical properties and can effectively mitigate the nonphysical oscillation appeared in the GFEM solutions. Various problems of both axisymmetry and nonaxisymmetry, and with medium of uniform refractive index distribution or graded refractive index distribution are tested. The results show that both the finite element approaches have good accuracy to predict the radiative heat transfer in semitransparent graded index cylindrical medium, while the LSFEM has better numerical stability. 相似文献