共查询到19条相似文献,搜索用时 209 毫秒
1.
2.
3.
摄动有限体积法重构近似高精度的意义 总被引:3,自引:0,他引:3
研讨有限体积(FV)方法重构近似高精度的作用问题.FV方法中积分近似采用中点规则为二阶精度时,重构近似高精度(精度高于二阶)的意义和作用是一个有争议的问题.利用数值摄动技术[1,2]构造了标量输运方程的积分近似为二阶精度、重构近似为任意阶精度的迎风型和中心型摄动有限体积(PFV)格式.迎风PFV格式无条件满足对流有界准则(CBC),中心型PFV格式为正型格式,两者均不会产生数值振荡解.利用PFV格式求解模型方程的数值结果表明:与一阶迎风和二阶中心格式相比,PFV格式精度高、对解的间断分辨率高、稳定性好、雷诺数的适用范围大,数值地"证实"重构近似高精度和PFV格式的实际意义和好处. 相似文献
4.
第二类边界积分方程Nystrom解的高精度组合方法 总被引:3,自引:1,他引:2
第二类边界积分方程常用配置法或Galerkin法计算,主要困难有:计算积分耗去大量机时;离散方程是满阵且不对称,计算量随剖分精细而急剧增加。本文提出Nystrom近似解的高精度组合法能有效克服上述困难。组合方法是并行地解m个具有n个不同结点的方程组,对得到的m个内点值取算术平均就得到了组合近似,本文证明组合近似精度几乎与解mn个结点近似方程达到精度同阶,数值结果表明本文方法简单、有效、并且算法高度 相似文献
5.
用Navier-Stokes方程直接数值模拟平板边界层流动中湍斑的形成和演化过程.发展了模拟湍斑的高精度、高分辨率的高效计算方法,包括推出四阶时间分裂法以提高精度;提出三维耦合差分方法,用于关于压力的泊松方程和关于速度的亥姆霍兹方程的空间离散,建立其四阶三维耦合中心差分格式;并采用四阶紧致迎风差分格式,避免了一般四阶中心差分格式不适用于边界邻域的困难和提高了分辨率;精心地处理各种边界条件,以保持精度和稳定.该方法适用于包含边界邻域的整个区域内的湍斑模拟.通过模拟平板边界层流动中湍斑的复杂演化过程,显示了湍斑的基本特征. 相似文献
6.
7.
迎风紧致格式求解Hamilton-Jacobi方程 总被引:1,自引:1,他引:0
基于Hamilton-Jacobi(H-J)方程和双曲型守恒律之间的关系,将三阶和五阶迎风紧致格式推广应用于求解H-J方程,建立了高精度的H-J方程求解方法.给出了一维和二维典型数值算例的计算结果,其中包括一个平面激波作用下的Richtmyer Meshkov界面不稳定性问题.数值试验表明,在解的光滑区域该方法具有高精度,而在导数不连续的不光滑区域也获得了比较好的分辨效果.相比于同阶精度的WENO格式,本方法具有更小的数值耗散,从而有利于多尺度复杂流动的模拟中H-J方程的求解. 相似文献
8.
构造基于界面修正的迭代并行方法的一般途径是:将物理空间区域剖分成若干不重叠的块;在分块子区域的内边界上,采用某种显式格式计算出界面值作为预估值;然后采用某种隐式格式并行求解各个子块区域上的解,这里的隐式格式通常需要进行迭代求解(称为内迭代);可在每一迭代步或几次迭代步结束时,利用已计算出的分块子区域内的(近似)解,在分块子区域内边界处利用隐式格式计算出在内边界处的校正值;随后再转入各个子块区域上的求解,该过程称为外迭代。与以往的并行差分格式不同,在求解的子区域上的定解问题时,可以仅仅在第一个(初始)迭代步求解时所需边界条件使用子区域内界面处的某种显式格式的解,在随后的迭代步中即可改用子区域内界面处的隐式修正格式的解。由此,至少可区分如下3类性质不完全相同的迭代并行格式。 相似文献
9.
10.
11.
对随机Ginzburg-Landau方程进行数值研究,构造一个非线性差分格式和一个线性化差分格式.通过对确定性和随机Ginzburg-Landau方程的计算,表明所构造的格式具有较高的精度和较快的计算效率.对随机Ginzburg-Landau方程就噪声振幅的不同取值进行了数值模拟,并对由此引发的各种行为进行了描述. 相似文献
12.
13.
Direct numerical simulation of the turbulent boundary layer over a sharp cone with 20° cone angle (or 10° half-cone angle)
is performed by using the mixed seventh-order up-wind biased finite difference scheme and sixth-order central difference scheme.
The free stream Mach number is 0.7 and free stream unit Reynolds number is 250000/inch. The characteristics of transition
and turbulence of the sharp cone boundary layer are compared with those of the flat plate boundary layer. Statistics of fully
developed turbulent flow agree well with the experimental and theoretical data for the turbulent flat-plate boundary layer
flow. The near wall streak-like structure is shown and the average space between streaks (normalized by the local wall unit)
keeps approximately invariable at different streamwise locations. The turbulent energy equation in the cylindrical coordinate
is given and turbulent energy budget is studied. The computed results show that the effect of circumferential curvature on
turbulence characteristics is not obvious. 相似文献
14.
J. R. Norris 《Communications in Mathematical Physics》2000,209(2):407-435
We introduce a general class of coagulation models, where clusters of given types may coagulate in more than one way and where the rate at which this happens may depend on the cluster types. In the continuum version of these models there is a generalization of Smoluchowski's coagulation equation. We introduce a notion of strong solution for this equation and prove the existence of a maximal strong solution, which while it persists is the only solution. When the total rate of coagulation for particles is bounded above and below by constant multiples of the product of their masses, we show that the maximal strong solution coincides with the maximal mass-conserving solution and does not persist for all time. Thus, for these models, loss of mass (to infinity) coincides with divergence of the second moment of the mass distribution and takes place in a finite time. When the total rate of coagulation of large particles is proportional to their masses, we establish the existence and uniqueness of solutions for all time. In a restricted class of "polymer" models, we allow coagulation of weighted shapes in a finite number of ways. For this class we establish a discrete approximation scheme for the continuum dynamics. For each continuum coagulation model, there is a corresponding finite-particle-number stochastic model. We show that, in the polymer case, which includes the case of simple mass coalescence, as the number of particles becomes large, the stochastic model converges weakly to the deterministic continuum model, at an exponential rate. 相似文献
15.
16.
17.
P. Kubíček 《Czechoslovak Journal of Physics》1973,23(10):1118-1132
This method eliminates some shortcomings encountered with other methods currently used for determination of the diffusion coefficients in melts. There are, with reasonable accuracy, fulfilled the starting and boundary conditions of a diffusion equation, and the diffusion process is not disturbed by melt flowing. This method considers a diffusion source at the boundary of a diffusion range and, when fulfilling certain conditions, both the solution of the diffustion equation and the evaluation of the diffusion coefficients is very simple. The required diffusion source, having a constant power, can be simulated by contacting the saturated gases of a substance, the diffusion of which is being investigated, with melt surface in which the diffusion takes place. The method takes into account application of radionuclides and this article brings about some criteria for application of that method. Simplicity is the main feature of the experimental arrangement.This work has been carried out in the scope of the State Research Task III-5-8 Equilibrium States of Metallurgical Systems. 相似文献
18.
19.
An asymptotic solving method for the periodic solution of a class of disturbed nonlinear evolution equation 下载免费PDF全文
<正>A class of disturbed evolution equation is considered using a simple and valid technique.We first introduce the periodic traveling-wave solution of a corresponding typical evolution equation.Then the approximate solution for an original disturbed evolution equation is obtained using the asymptotic method.We point out that the series of approximate solution is convergent and the accuracy of the asymptotic solution is studied using the fixed point theorem for the functional analysis. 相似文献