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排序方式: 共有3653条查询结果,搜索用时 15 毫秒
31.
Asymmetric horizontal thermal profiles can change the flow field structure in the physical vapor transport (PVT)of Hg2Cl2. It is found that for the ratios of horizontal to vertical thermal Rayleigh numbers RaH/Ra ≥ 1·5, the convetive flow structure changes from multicellular to unicellular for the base parametric state of Ra = 2·79 × 104, Pr = 0·91, Le=l·01. Pe = 4·60, Ar= 0·2 and Cr = 1·01. The unicellular flow structure obtained by increasing ∇*H(RaH) is not likely to support the conjecture of the presence of unicellular convective mode in the laser Doppler velocimetry (LDV) experiments for PVT process of Hg2Cl2 (Kim el al., 1996). When the six parameters of Ra, Pr, Le, Pe, Ar and Cr are fixed, the dimensional maximum magnitude of the velocity vector |U|max is proportional to √∇T*H. 相似文献
32.
自适应布谷鸟搜索算法 总被引:1,自引:0,他引:1
为了使布谷鸟搜索算法(Cuckoo Search,CS)在保持强大的全局搜索能力的同时,尽可能地提高局部搜索能力,在深入分析CS算法机理的基础上,将CS算法中影响布谷鸟搜索路径步长的参数β和布谷鸟蛋被发现(淘汰)的概率p_a由固定值改为随搜索过程自适应变化的动态参数,将越界的鸟窝折返回边界内、在当前代最优鸟窝附近的区域随机建立1个新的鸟窝、而非折返回边界上重新建立鸟窝,以提高算法的局部搜索能力和收敛速度。改进后的CS算法称为自适应布谷鸟搜索算法(Adaptive Cuckoo Search,ACS)。通过8个标准测试函数分别测试了CS算法和ACS算法的性能,结果表明,无论是简单的单峰函数还是复杂的多峰函数,无论是小型的低维函数还是大型的高维函数,ACS算法的寻优性能均超过CS算法。 相似文献
33.
The inverse problem approach by conjugate gradient with adjoint equations is adapted to the context of a non-isothermal bioprocess, controlled by internal heat generation from microbial oxidation, as could be found in a composting reactor for instance, to determine the heat source from internal temperature measurements. The volumetric heat source is assumed proportional to the rate of consumption of a substrate by a biomass, as described by a Monod model. Computations are performed for Rayleigh numbers equal to 0.25 and 25, for a representative biochemical reaction under typical boundary conditions, for constant and temperature-dependent model parameters. The influence of noisy input data is also considered. It is found that good solutions can be obtained when heat release and diffusion occur over very different time scales. The variation of the model parameters with temperature must be taken into account, but single sensor solutions are possible at relatively small Rayleigh numbers when convection is present. 相似文献
34.
Boundary layer equations for free convection heat transfer along a semi-infinite horizontal plate are derived by giving more importance to the energy equation. The equations are obtained for low Prandtl number and two separate polynomials are used to approximate the temperature and velocity profiles in these regions. The rate of heat transfer is compared with the available analytical and numerical results based on conventional boundary layer equations. 相似文献
35.
王成伟 《北京电子科技学院学报》2010,18(2):46-54
利用一个对称的调配函数,结合NURBS曲线中权的思想,在曲线控制顶点处引进调配参数,将三次Bézier曲线进行扩展,得到的新曲线比原来的曲线有更强的描述能力,并且包含了原曲线形式。讨论了扩展曲线的基表示及曲线的性质,调配参数可以用来控制曲线的局部形状,特别适用于自由曲线曲面的设计,在CAD/CAM中具有很好的应用前景。 相似文献
36.
王成伟 《北京电子科技学院学报》2010,18(4):30-33
描述了一种与给定多边形相切的五次Bézier曲线的算法。在算法中,所有的五次Bézier曲线的控制点可以通过对多边形的顶点简单计算产生。所构造的曲线对多边形具有保形性,曲线可以局部修改,最后给出了一个算例。 相似文献
37.
刘颖 《哈尔滨理工大学学报》2009,14(2):44-46
考察了具有分布时滞的Liénard型方程,利用重合度理论研究其周期解问题,得到了该方程周期解存在的充分条件,结论丰富了现有文献的结果. 相似文献
38.
39.
A numerical study is presented for magnetohydrodynamic free convection of an electrically conducting fluid in a shallow cavity heated from below and cooled from above. The side walls are maintained adiabatic. A uniform magnetic field, inclined with an angle 0 with respect to the horizontal plane, is externally imposed. The investigation covers the range of the Rayleigh number, Ra, from 1.8 × 103 to 3 x 104the Hartmann number, Ha, from 0 to 35, the Prandtl number, Pr, from 0.005 to 1 and aspect ratio of the cavity, A = 6. The effect of the magnetic field on the flow structure is presented. For supercritical convection it is found that, upon increasing Ha, the number of roll cells in the cavity increases when it is perpendicular to it. The imposition of an inclined magnetic field gives rise to new flow patterns with tilted lateral cell walls. The effect of both strength and orientation of the magnetic field on the overall heat transfer is found to be significant. 相似文献
40.
Wei-Mon Yan 《加拿大化工杂志》1993,71(1):54-62
Numerical results are presented for effects of latent heat transport associated with film vaporization on laminar mixed convection heat and mass transfer in a vertical channel with a half channel width b = 0.01 m. The influences of the inlet liquid mass flowrate and wall temperature on the film vaporization and the associated heat and mass transfer characteristics are examined for air-water and air-ethanol systems with gas Reynolds number Reg = 2000. Predicted results obtained by including transport in the liquid film are contrasted with those where liquid film transport is neglected, showing that the assumption of an extremely thin film made in Lin et al. (1988) and Yan and Lin (1989) is only valid for systems having small liquid mass flow rates. Additionally, it is found that the interfacial heat flux is predominantly determined by latent heat transfer connected with film evaporation. 相似文献