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嵌套网格技术中的Collar网格和虚拟网格方法 总被引:3,自引:0,他引:3
针对嵌套网格技术中的结合部问题,提出了Collar网格和虚拟网格方法.用双曲型微分方程生成的处于结合部的有两个边界分别处于不同固定曲面上的Collar网格,在保证计算网格的生成方便快捷而且网格质量高的前提下,解决了为物体结合部的内外边界点提供有效插值单元的问题.虚拟网格为紧贴物面的面网格,它的作用是将物面边界条件传递给其它网格的边界面,而其本身不作流场计算.计算实践表明,将Collar网格和虚拟网格结合起来应用在嵌套网格技术中能保证几何外形不发生变化,有效地处理各种复杂组合体外形的结合部问题. 相似文献
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在对流体力学方程进行数值求解时,需要应用到网格,当在物理区域上生成网格时,为了克服不同物理区域所带来的求解问题的复杂性,可以把物理区域转换为一个简单的逻辑区域,此时物理区域上的一组网格可以看作由逻辑区域内的一组点通过一个变换得到,这一变换通常要求是保边界的,同时变换的Jacobian也要求是非零的。如何选取这样的变换,使得通过变换在物理区域中生成均匀、光滑并尽可能正交的网格,是网格生成的主要目标之一。 相似文献
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利用基于多边形网格的有限容积法计算程序,考察了由三角形网格生成的三种多边形网格用于求解层流N-S方程组的数值特征.结果表明,收敛特性与多边形的构造方法无关,但计算结果的精度与网格类型有关,满足局部正交的PEBI网格精度最高,而由三角形形心相连构成的多边形精度较差.就方腔自然对流问题而言,在边界附近铺几层正交网格有利于提高努谢尔特数的精度. 相似文献
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在多维流体动力学计算中,流体运动和计算网格的关系可以分为两种情况。一是Lagrangian方法,即网格跟随流体运动;二是Eulerian方法,即流体流过固定;下动的网格。一般计算网格的运动是任意的。这就对应于任意Lagrangian—Eulerian(ALE)方法。ALE方法的核心是通过调整网格运动,使得数值模拟的精度、效率有所提高。它的主要步骤是:显式Lagrangian步;网格重分,即得到新的计算网格;物理量重映,即将Lagrangian步的计算结果变换到新网格上。在这3步中,较少研究网格重分。数值模拟和网格重分的一个基本前提是网格是合理的,或者说网格不能发生翻转,网格应当是凸的。而Lagrangian步数值模拟会造成网格扭曲,因此在网格重分前进行网格解扭是十分必要的。文中描述了通用的网格解扭、重分算法,使得解扭、重分后的网格有较好的几何品质,同时尽可能接近Lagrangian网格。 相似文献
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BNCT蒙特卡罗剂量计算中网格构造和材料确定的一种简便方法 总被引:2,自引:1,他引:1
BNCT国际基准问题分别推出了16 mm,8 mm和4 mm三种标准化网格模型,用MCNP蒙特卡罗程序模拟了这些模型,并与Snyder解析模型进行了比较.在此基础上,给出了一种质量守恒好,网格逼近程度高,且基于4种基本材料成份的BNCT网格构造方法.计算结果表明,在4 mm网格尺寸上,新方法采用基本材料模型可以达到采用混合材料模型的精度;用这种方法进一步产生了5 mm网格模型,把模拟结果和解析模型进行了比较,发现5 mm网格模型大脑内剂量计算误差较小,质量守恒好,并且能大大节省计算机模拟的时间,是一种很好的优化网格. 相似文献
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The accuracy of transmission line models of two-dimensional freestanding capacitive grids is studied on a very wide frequency band. The grids are of infinite extent in the transverse directions and are illuminated by a linearly polarized normally incident plane wave. Comparison with reference results deduced from Finite-Difference Time-Domain (FDTD) simulations allows determining the range of validity of commonly used equivalent circuits It is shown that their accuracy strongly depends on the dimensions of the grids and the operating wavelength. Although very convenient, their implementation for calculating the frequency response of multi-layer systems could lead to unreliable results. Two closed-form new models are thus proposed. The first one results from an optimized expression of the well-known Marcuvitz's impedance, and the second one involves a series resonant LC circuit shunted by an additional capacitance. Both formulations are very accurate for a wide range of grid geometries and over the whole visible region (wavelength > grid constant). 相似文献
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Stability Analysis of a Fully Coupled Implicit Scheme for Inviscid Chemical Non-Equilibrium Flows 下载免费PDF全文
Von Neumann stability theory is applied to analyze the stability of a fully
coupled implicit (FCI) scheme based on the lower-upper symmetric Gauss-Seidel (LU-SGS)
method for inviscid chemical non-equilibrium flows. The FCI scheme shows excellent
stability except the case of the flows involving strong recombination reactions,
and can weaken or even eliminate the instability resulting from the stiffness problem,
which occurs in the subsonic high-temperature region of the hypersonic flow field. In
addition, when the full Jacobian of chemical source term is diagonalized, the stability
of the FCI scheme relies heavily on the flow conditions. Especially in the case of high
temperature and subsonic state, the CFL number satisfying the stability is very small.
Moreover, we also consider the effect of the space step, and demonstrate that the stability
of the FCI scheme with the diagonalized Jacobian can be improved by reducing
the space step. Therefore, we propose an improved method on the grid distribution
according to the flow conditions. Numerical tests validate sufficiently the foregoing
analyses. Based on the improved grid, the CFL number can be quickly ramped up to
large values for convergence acceleration. 相似文献
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Martin Rheinländer 《Journal of statistical physics》2005,121(1-2):49-74
A method of coupling grids of different mesh size is developed for classical Lattice-Boltzmann (LB) algorithms on uniform
grids. The approach is based on an asymptotic analysis revealing suitable quantities equalized along the grid interfaces for
exchanging information between the subgrids. In contrast to other couplings the method works without overlap zones. Moreover
the grid velocity (Mach number) is not kept constant, as the time step depends not linearly but quadratically on the grid
spacing. To illustrate the basic idea we use a simple LB algorithm solving the advection-diffusion equation. The proposed
grid coupling is validated by numerical convergence studies indicating, that the coupling does not affect the second-order
convergence behavior of the LB algorithm which is observed on uniform grids. In order to demonstrate its principal applicability
to other LB models, the coupling is generalized to the standard D2P9 model for (Navier-)Stokes flow and tested numerically.
As we use analytic tools different from the Chapman-Enskog expansion, the theoretical background material is given in two
appendices. In particular, the results of numerical experiments are confirmed with a consistency analysis. 相似文献
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Construction of large aperture free-standing metal wire grids is demonstrated for the lower end of the millimeter wave spectral region. For the constructed two grids the co-polarized and cross-polarized components of transmitted power were measured at 45° oblique incidence. The measurements were performed as a function of wire orientation angle and in more detail at selected angles. The results are in good agreement with the theoretical results presented in the literature. In order to save time and costs the construction apparatus was simplified from those reported previously by other authors. It was shown that for this frequency range the grid characteristics are not degraded when such an apparatus is applied. One of the constructed grids will be used in a calibration system of the Helsinki University of Technology (HUT) polarimetric radiometer. 相似文献
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针对运动间断拟合中需频繁更新网格点位置的特点,提出一种基于LU-SGS(lower-upper symmetricGauss-Seidel)迭代方法的非结构弹簧网格运动算法.根据弹簧网格原理构建与网格拓扑关系相对应的稀疏系数矩阵,将LU-SGS思想成功引入动网格迭代算法,并辅以合理的网格运动管理策略,实现动网格的快速迭代.研究表明,在非结构网格下,LU-SGS算法可以满足运动间断拟合的需求,在流场隐式时间推进时,仍能保证获得稳定解;与传统的SOR方法相比,计算时耗减少20%以上. 相似文献
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研究如何在非结构网格上进行Navier Stokes(N-S)方程湍流计算.采用格心有限体积方法离散N-S方程.为了适应非结构网格,计算所用的湍流模型特别选用Baldwin Barth(B-B)单方程模型.此模型由一个单一的具有源项的对流扩散方程组成.为了能在非结构网格上求解B B单方程模型,提出一显式有限体积格式,并直接对带源项的格式进行稳定性分析,得到了相应的时间步长限制条件.最后以平板、RAE 2822翼型、多段翼型绕流等数值算例验证了计算方法的有效性. 相似文献
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对于粘性绕流的数值模拟,在自适应直角网格基础上,结合三角形非结构网格和结构化网格,利用其各自的优势和特点,提出一种生成混合杂交网格的思路和方法.在物面附近生成适合粘性流计算的大长宽比结构化网格,在远场分布自适应直角网格,快速离散计算空间.对于复杂的多体问题,采用三角形网格来连接各体网格,并运用网格合并的方法,保证各网格之间的光滑过渡与连接,提高网格质量.针对一些二维、三维外形的绕流问题,在上述网格基础上,采用B-L代数湍流模型和中心有限体积法,完成Navier-Stokes和Euler方程数值模拟的对比计算,结果表明网格生成和流场计算是正确的. 相似文献
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多块对接网格技术在电磁场散射问题中的应用 总被引:2,自引:0,他引:2
采用多块对接网格技术和时域有限体积法(FVTD)研究了典型目标和多体的电磁场散射问题.控制方程采用三维一般曲线坐标系下的时变麦克斯韦方程组.时间方向采用四步Runge-Kutta方法,空间离散采用基于通量雅可比矩阵特征结构的通矢量差分分裂,依赖变量采用MUSCL插值.时间方向的计算精度为2阶,空间方向的计算精度可达3阶.典型算例的雷达散射截面(RCS)的计算结果与理论解吻合很好.对于多体问题计算与文献结果相当一致,说明该算法具有对复杂拓扑结构外形(包括多体问题)进行数值模拟的能力. 相似文献