电弧喷涂的喷嘴射流研究（英文）

紧邻电弧喷涂枪喷嘴产生的喷射尾流对生成涂层的性质有着显著的影响.采用计算流体力学(CFD)和纹影摄影技术阐明了喷射尾流的性质.纹影图像的检查结果显示,尾流的性质和宽度取决于用于热喷涂的丝材的方向.通过CFD方法,观察到激波在喷嘴孔口之后迅即形成,然后在下游尾流中衰减.     

车身非光滑表面凹坑排布对气动性能的影响

受仿生学非光滑旋成体减阻启发,以SAE(美国机动车工程师协会)标准模型为研究对象,采用CFD(计算流体力学)数值模拟方法,在SAE模型顶部布置不同排布形式和不同排布密度的凹坑单元,研究其对车身气动性能的影响.通过比较各模型的尾流、气流速度、压力场、湍流动能等流场性能指标,分析非光滑表面减阻机理以及造成各模型流场性质差异的原因.计算结果显示:当凹坑型非光滑单元以矩形排布时模型具有最小的气动阻力,且气动阻力随着凹坑密度的增加而减小,减阻率最高达到4.1%.     

基于谐波平衡法的尾流激励的叶片振动降阶模型方法

在航空发动机中下游叶片在上游尾流的作用下易发生受迫振动,严重影响叶片的颤振和疲劳性能.对于这种尾流作用下复杂的流固耦合情况需要一种有效的方法来分析.针对这一问题,提出了基于谐波平衡法的尾流激励的叶片振动降阶模型方法.该方法首先将上游尾流Fourier(傅立叶)分解为若干尾流谐波,并计算各尾流谐波下叶片气动力谐波的振幅,得到尾流引起的叶片气动力;再通过叶片的结构运动方程和气动力降阶模型的耦合分析尾流激励下叶片的振动.算例结果表明,该方法可以快速准确地分析尾流激励下叶片的振动特性.     

线导+尾流自导鱼雷的有效射击可行域

基于线导+尾流自导鱼雷的弹道特点和末端尾流进入角的使用限制,选用Runge-Kutta方法,得出线导+尾流自导鱼雷在不同尾流进入角和不同射距时的弹道轨迹,进而分析并解算出线导+尾流自导鱼雷有效射击可行域.方法对自导鱼雷有效射击可行域解算方法进行了较大改进,能更好地满足线导+尾流自导鱼雷作战使用时射击阵位点选择需求.     

计算流体力学在大型风力机空气动力学的应用进展北大核心CSCD

针对大型风力机设计中的关键空气动力学问题,比较系统地介绍了计算流体力学(computational fluid dynamics,CFD)方法的主要应用,特别是在大型风力机翼型气动分析、风力机流动的数值模拟、风轮空气动力特性的数值计算以及大型风力机叶片的多目标气动优化设计方面的进展.基于CFD方法分别实现了风力机翼型与叶片二维/三维气动特性的准确预测,风力机尾流场涡系结构的准确捕捉;并结合多目标遗传算法对1.5 MW风力机叶片进行了优化,获得了具有高风能利用效率的叶片方案.     

集值Markov链及其随机集落影性质

提出了一种集值Markov链,该模型是对基于随机变量的Markov链推广,将随机变量提升到随机集上.模型继承了经典Markov链的诸多良好性质,而且可以退化为经典的Markov链模型.为了进一步分析该模型,引入随机集落影理论,提出转移落影、落影分布等概念,并给出了部分结论和性质.最后,给出一个应用实例.     

双激励超音速气体雾化喷嘴共振特性的数值研究

超音速气体雾化(ultra-sonic gas atomization,USGA) 喷嘴是实现喷射雾化的重要装置,它能够产生脉动的超音速气流,获得较小的平均粒径和集中的粒径分布.在USGA喷嘴的共振管端部引入了主动的激励信号,组成双激励式超音速气体雾化器,并对超音速气体雾化器内部Hartmann腔体气体流场在无激励/有激励情况下所产生的气体振动特性进行了数值研究.结果表明在主动激励器的作用下,超音速气体雾化器内气流的振动效果如振幅和起振特性等都得到了有效的加强.研究发现超音速气体雾化器存在多个气体受激振动的共振频率,其对应于两类不同的共振模式,“Hartmann模式”和“全局模式”.双激励器信号的频率、激励幅度及相位差改变都能够有效地改变超音速气流的振动特性.研究同时阐明了Hartmann共振管和二次共振管在USGA喷嘴腔体内产生气体脉动时的联动特点.     

单叶双曲面和双曲抛物面直母线的几何作图

在二次曲面中,唯有单叶双曲面和双曲抛物面是直纹面。这两种直纹面都有两族直母线(u族和v族),两族直母线有很多有益的性质,掌握这些有益的性质并运用这些性质便可在两个曲面上将这些直母线一条一条地作出来,这     

具有H_2引燃的CH_4、煤油超声速混合的三维数值研究

用双流体模型和分区算法 ,气相多组分N_S方程和液相Euler方程分别用迎风TVD格式和NND格式进行数值求解 ,相间相互作用项方程用二阶Runge_Kutta法求解·　并首次对H2 引燃的CH4 和煤油横向喷射、混合问题进行了数值研究·　结果表明 :与喷射加碘空气的PLIF结果相比 ,本文和实验结果符合得很好·　对直通道 ,后面喷嘴的穿透深度大 ,煤油较气态燃料的穿透深度大 ,但难以被卷吸到喷嘴前的回流区内 ,流场出现无煤油区·　H2 和CH4 均可扩散到回流区内 ,CH4 和煤油引燃机理不同·　对后台阶直通道 ,存在两个回流区 ,H2 可扩散到这两个回流区 ,但CH4 只能被卷吸到其喷嘴前的回流区·　后台阶直通道增强混合的效果和引燃点火的可靠性更好     

直纹二次曲面在现实生活中的应用分析

直纹二次曲面中有两种性质独特的曲面:单叶双曲面和双曲抛物面,它们在现实生活中多个领域都有特殊的用途.从理论角度对单叶双曲面和双曲抛物面在建筑、机械以及水利工程中的典型应用给予详细总结和分析,并结合它们自身的数学性质对其实际应用效果给予评析.     

RECENT PROGRESS ON SPHERICAL HARMONIC APPROXIMATION MADE BY BNU RESEARCH GROUP ——In memory of Professor Sun Yongsheng

As early as in 1990, Professor Sun Yongsheng, suggested his students at Beijing Normal University to consider research problems on the unit sphere. Under his guidance and encouragement his students started the research on spherical harmonic analysis and approximation. In this paper, we incompletely introduce the main achievements in this area obtained by our group and relative researchers during recent 5 years （2001-2005）. The main topics are： convergence of Cesaro summability, a.e. and strong summability of Fourier-Laplace series; smoothness and K-functionals; Kolmogorov and linear widths.     

On a class of self-similar processes with stationary increments in higher order Wiener chaoses

We study a class of self-similar processes with stationary increments belonging to higher order Wiener chaoses which are similar to Hermite processes. We obtain an almost sure wavelet-like expansion of these processes. This allows us to compute the pointwise and local Hölder regularity of sample paths and to analyse their behaviour at infinity. We also provide some results on the Hausdorff dimension of the range and graphs of multidimensional anisotropic self-similar processes with stationary increments defined by multiple Wiener–Itô integrals.     

A REPRESENTATION FORMULA RELATED TO SCHR(O)DINGER OPERATORS

Schr(o)dinger operator is a central subject in the mathematical study of quantum mechanics.Consider the Schrodinger operator H = -△ V on R, where △ = d2/dx2 and the potential function V is real valued. In Fourier analysis, it is well-known that a square integrable function admits an expansion with exponentials as eigenfunctions of -△. A natural conjecture is that an L2 function admits a similar expansion in terms of "eigenfunctions" of H, a perturbation of the Laplacian (see [7], Ch. Ⅺ and the notes), under certain condition on V.     

On a class of Riemann surfaces

It is considered the class of Riemann surfaces with dimT1 = 0, where T1 is a subclass of exact harmonic forms which is one of the factors in the orthogonal decomposition of the spaceΩH of harmonic forms of the surface, namely The surfaces in the class OHD and the class of planar surfaces satisfy dimT1 = 0. A.Pfluger posed the question whether there might exist other surfaces outside those two classes. Here it is shown that in the case of finite genus g, we should look for a surface S with dimT1 = 0 among the surfaces of the form Sg\K , where Sg is a closed surface of genus g and K a compact set of positive harmonic measure with perfect components and very irregular boundary.     

CONTENTS OF VOLUME 30

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Instructions for contributions

正Applied Mathematics-A Journal of Chinese Universities,Series B(Appl.Math.J.Chinese Univ.,Ser.B)is a comprehensive applied mathematics journal jointly sponsored by Zhejiang University,China Society for Industrial and Applied Mathematics,and Springer-Verlag.It is a quarterly journal with     

Journal of Mathematical Research with Applications Guide for Authors

正Journal overview:Journal of Mathematical Research with Applications(JMRA),formerly Journal of Mathematical Research and Exposition(JMRE)created in 1981,one of the transactions of China Society for Industrial and Applied Mathematics,is a home for original research papers of the highest quality in all areas of mathematics with applications.The target audience comprises:pure and applied mathematicians,graduate students in broad fields of sciences and technology,scientists and engineers interested in mathematics.     

Staircase transportation problems with superadditive rewards and cumulative capacities

A cumulative-capacitated transportation problem is studied. The supply nodes and demand nodes are each chains. Shipments from a supply node to a demand node are possible only if the pair lies in a sublattice, or equivalently, in a staircase disjoint union of rectangles, of the product of the two chains. There are (lattice) superadditive upper bounds on the cumulative flows in all leading subrectangles of each rectangle. It is shown that there is a greatest cumulative flow formed by the natural generalization of the South-West Corner Rule that respects cumulative-flow capacities; it has maximum reward when the rewards are (lattice) superadditive; it is integer if the supplies, demands and capacities are integer; and it can be calculated myopically in linear time. The result is specialized to earlier work of Hoeffding (1940), Fréchet (1951), Lorentz (1953), Hoffman (1963) and Barnes and Hoffman (1985). Applications are given to extreme constrained bivariate distributions, optimal distribution with limited one-way product substitution and, generalizing results of Derman and Klein (1958), optimal sales with age-dependent rewards and capacities.To our friend, Philip Wolfe, with admiration and affection, on the occasion of his 65th birthday.Research was supported respectively by the IBM T.J. Watson and IBM Almaden Research Centers and is a minor revision of the IBM Research Report [6].     

Boundedness for commutators of multipliers on Hardy type spaces

In this paper, we study the commutators generalized by multipliers and a BMO function. Under some assumptions, we establish its boundedness properties from certain atomic Hardy space Hb^p（R^n） into the Lebesgue space L^p with p 〈 1.