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41.
Decoupled two‐grid finite element method for the time‐dependent natural convection problem I: Spatial discretization
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Tong Zhang JinYun Yuan ZhiYong Si 《Numerical Methods for Partial Differential Equations》2015,31(6):2135-2168
In this article, a decoupled two grid finite element method (FEM) is proposed and analyzed for the nonsteady natural convection problem using the coarse grid numerical solutions to decouple the nonlinear coupled terms, and the corresponding optimal error estimates are derived. Compared with the standard Galerkin FEM and the usual two‐grid FEM, our algorithm not only keeps good accuracy but also saves a lot of computational cost. Some numerical examples are provided to verify the performances of the decoupled two‐grid FEM. Both theoretical analysis and numerical experiments show the efficiency and effectiveness of the decoupled two‐grid FEM for the nonsteady natural convection problem. © 2015 Wiley Periodicals, Inc. Numer Methods Partial Differential Eq 31: 2135–2168, 2015 相似文献
42.
S. V. Nizhankovskyi A. V. Tan'ko N. S. Sidelnikova G. T. Adonkin 《Crystal Research and Technology》2015,50(3):223-229
It is shown that the formation of longitudinal aggregation of inclusions in bulk sapphire and yttrium‐aluminum garnet (YAG) grown by the method of HDC is caused by local accumulation of impurities, disturbance of morphological stability of the crystallization front and capture of inclusions and impurities in the nodal region of the melt two‐vortex convection. Studied is the influence of thermal and geometrical parameters of the melt and the shape of the crystallization front on the conditions of the formation of the capture of inclusions. 相似文献
43.
统一的对流扩散型可压缩流体力学方程与解法 总被引:1,自引:1,他引:0
流体力学的动量方程、能量方程、湍动能方程和耗散方程都具有对流扩散方程的形式,但连续方程却不是对流扩散型的。对于可压缩问题,本文通过合理的数学推导,不作任何近似、假定与简化,得到一个全新的连续方程形式.该连续方程以压力为未知变量,并具有对流扩散型形式,使得所有的流体动力学方程组都具有完全统一的方程形式,给出了这种三维对流扩散方程组的有限精确差分计算格式。对流体力学的进一步发展具有一定意义. 相似文献
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The generation of friction drag in turbulent duct flows has direct connection with statistical quantities and corresponding turbulence dynamics in the duct cross-section. In this study, we generalize the RD identity (Renard and Deck, 2016) to a ‘two-dimensional’ form which we exploit to decompose the mean friction drag in turbulent square-duct flows into contributions associated with viscosity, turbulence and cross-stream convection. The friction Reynolds number of the duct flows ranges from 220 to 2000. The scaling, spatial distribution and local normalization of the contributions to friction are investigated and compared with those in pipe and channel flows. As in other canonical flows, we find logarithmic growth of the turbulent contribution in contrast to the viscous one, the former thus becoming dominant at high enough Reynolds numbers. Whereas cross-stream convection has no net effect on friction, its contribution may be locally comparable to the other two, hence may be responsible for redistribution of friction along the duct perimeter. 相似文献
47.
Yifeng Xiang Xi Tang Changjun Min Guanghao Rui Yan Kuai Fengya Lu Pei Wang Hai Ming Qiwen Zhan Xiaocong Yuan Joseph R. Lakowicz Douguo Zhang 《Annalen der Physik》2020,532(4):1900497
Near-field optical trapping can be realized with focused evanescent waves that are excited at the water–glass interface due to the total internal reflection, or with focused plasmonic waves excited on the water–gold interface. Herein, the performance of these two kinds of near-field optical trapping techniques is compared using the same optical microscope configuration. Experimental results show that only a single-micron polystyrene bead can be trapped by the focused evanescent waves, whereas many beads are simultaneously attracted to the center of the excited region by focused plasmonic waves. This difference in trapping behavior is analyzed from the electric field intensity distributions of these two kinds of focused surface waves and the difference in trapping behavior is attributed to photothermal effects due to the light absorption by the gold film. 相似文献
48.
In this article,three-dimensional mixed convection flow over an exponentially stretching sheet is investigated.Energy equation is modelled in the presence of viscous dissipation and variable thermal conductivity.Temperature of the sheet is varying exponentially and is chosen in a form that facilitates the similarity transformations to obtain self-similar equations.Resulting nonlinear ordinary differential equations are solved numerically employing the Runge-Kutta shooting method.In order to check the accuracy of the method,these equations are also solved using bvp4c built-in routine in Matlab.Both solutions are in excellent agreement.The effects of physical parameters on the dimensionless velocity field and temperature are demonstrated through various graphs.The novelty of this analysis is the self-similar solution of the threedimensional boundary layer flow in the presence of mixed convection,viscous dissipation and variable thermal conductivity. 相似文献
49.
The problem of phase change in the presence of natural convection has been investigated. A model has been proposed based on the treatment of the release/absorption of latent heat as a heat source/sink in combination with the standard Galerkin finite element method with a primitive variable formulation on a fixed grid. To demonstrate the capabilities of the model, three cases of phase change of an aluminium alloy in the presence of natural convection arc considered, i.e. solidification, melting and combined solidification and melting. The solidification of water in a square cavity is modelled as another example, taking into account the density extremum, and the results are compared with a previously published work. 相似文献
50.
针对流固耦合传热问题,本文提出了一种基于浸没边界-简化热格子玻尔兹曼方法(immersed boundary method-simplified thermal lattice Boltzmann method,IB-STLBM)的耦合模型.不同于传统的格子玻尔兹曼方法使用分布函数演化流场和温度场,简化热格子玻尔兹曼方法(simplified thermal lattice Boltzmann method,STLBM)的演化过程不需要依赖分布函数,只涉及平衡态分布函数和非平衡态分布函数,能够直接演化宏观量,极大减小了计算过程中所占用的虚拟内存,简化了边界条件的实现方式,同时具有较高的稳定性.传统的浸没边界法对流场的计算采用欧拉网格,对固体边界采用拉格朗日网格,认为固体边界是对流场产生某种体积力.在应用浸没边界法时,汲取介观的思想,把固体的介入看作是对流场的干扰,打破了固体附近流体介观微团颗粒原始的平衡状态,这种干扰可以看作是在耦合边界上产生的一个非平衡项,可用非平衡态分布函数来表示.基于此,在模型中浸没边界法与简化热格子玻尔兹曼方法更紧密联系在一起,更大程度发挥二者的优点,整个计算过程更加简单直观,符合物理特性.通过对热圆柱绕流和内含热颗粒的封闭方腔自然对流问题的模拟以及对其结果的分析,验证了该算法在求解流固耦合传热问题的有效性和可行性. 相似文献