运用多媒体进行流体力学教学的体会

本文介绍北京大学力学系在本科生流体力学课程中运用多媒体进行教学的情况和学生的反映．作者体会到：多媒体教学应该是常规教学的一种精彩的补充，但是不应该、也不能够完全代替常规教学．那些难以用语言描述的动态物理图像，采用多媒体演示的效果最好；播放的内容一定要严格精选，灵活使用，力求紧密配合教学大纲；要把多媒体教学与其它教学手段有机地结合起来，取长补短，相辅相成     

把小微元分析法的教学贯彻流体力学课程的始终

 小微元分析法是流体力学最重要的基本功之一, 用该法求解流体 力学问题具有概念清晰、 过程简洁等优点. 因此, 在教学中应将该方 法贯彻全课程的始终, 并不断加以深化, 使学生学会从物理本质上简化 问题, 建立合理的力学模型.     

Solution for the oscillation of a newtonian fluid in a co-axial viscometer

When one cup of a co-axial viscometer oscillates,the measured moment on theother(stationary)cup shows a phase lag,partly due to the inertial effect of the fluidwithin the gap between the cups.In this paper such an effect is illustrated by a newexact solution of the Navier-Stokes equation,which is derived herein by a scheme ofreducing it to a two-point boundary value problem for ODEs,Our numerical resultsindicate that,as the Womersley number a or the dimensionless gap widthδincreases,the fluid velocity profile within the gap gradually deviates from the linear one andtransits to that of the boundary layer type,with the result that the moment decreasesin the magnitude and lags behind in the phase.With the advantage of high accuracyand excellent stability,the scheme proposed herein can readily be extended to solveother linear periodic problems.     

Lubrication analysis of a cell sliding into a circular pore

The resistance to the blood cells at the entrance to capillaries and membrane pores contributes considerably to the peripheral resistance in the blood circulation. This paper proposes, for the first time, a simplified mechanical model in an attempt to treat the axisymmetric motion of a cell sliding into a circular pore. In this model, the shape of the cell is taken as given according to the microvideograph and the cell membrane is assumed to slide over its surface. The lubrication theory is applied to the thin layers of plasma between the membrane and the pore wall, yielding the pressure and shear stress distributions over the membrane as well as the resultant drag exerted on the cell. Our computations have simulated the process of the cell entering the pore, which is in qualitative agreement with the microvideographic observations.The Project Supported by National Natural Science Foundation of China.The authors wish to express their thanks to Professor S. Weinbaum of The City University of New York for his enlightening suggestions on the mechanical model of this problem during his visit to Peking University. The authors are also grateful to Professor Li Gui-shan of Institute of blood. The Chinese Academy of Medical Sciences, for providing the relevant microvideographes.     

脑动静脉畸形供血动脉内压力测量准确性的分析

对脑动静脉畸形供血动脉内压力测量的准确性进行了定量的分析,分析结果认为,以介入导管方法测量脑动脉畸形患者供血动脉内压力时,导管的影响可以导致测量结果偏低,这一结论支持了脑动静脉畸形患者低压灌注的程度一般不易于导致部分脑组织缺血的观点。     

我怎样讲授边界层概念

本概述作在本科生流体力学课程中讲授边界层概念的体会：一方面通过实例反复阐明雷诺数极限下在物面附近引入边界层概念的必要性;另一方面通过反复练习培养学生掌握量阶分析方法。     

Theoretical analysis of using airflow to purge residual water in an inclined pipe

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气流排除倾斜管道积水的理论分析

运用作者推导的动量积分关系式,分析了向有积水的斜置管道中分别吹入轴向气流和螺旋气流时积水的运动情况。结果表明:在大多数情况下,螺旋气流能除去斜置管道中积水;而轴向气流不能除去积水,一段时间后会出现逆流。这一结果与Horii和赵耀华等人在这个问题上所做的实验结果一致。此外,还讨论了不同的初始条件对排水情况的影响。     

三维斯托克斯流动在扁球坐标系中的基本解及其应用

通过把Lamb基本解中的调和函数转换为扁球坐标系下的表达式,这项研究成功地得到了一个新的Stokes流动三维基本解.此基本解可用于解决任意多个扁椭球处于任意位置和方向时的流动问题.应用最小二乘法,三维流动问题中常遇到的收敛性差的困难在此得以完全克服.结果表明该方法具有准确度高,收敛性好和计算量小的特点.由于扁球可用于模拟从圆盘到圆球的多种物体形状,此基本解被用于系统地分析了各种几何因素对两个扁球所受力和力矩的影响.为了显示此方法的通用性,该基本解还用于研究了两例三个扁球的问题.     

跨膜渗透的流体力学分析

当两种浓度不同的溶液被一个多孔屏障(例如膜)分开的时候,溶剂(例如水)会由浓度较低的一侧流向另一侧,这种流动叫做渗透流。这时如要完全恢复两侧溶液间的平衡,可在浓度较高的一侧加上一定的压力,使得渗透流量变为零。这一压力的大小叫做此二溶液间的渗透压差。一种溶液与纯溶剂之间的渗透压差定义为它的渗透压。渗透现象不仅在化工等部门中有所应用,而且对于人和各种动植物的生命活动具有特别重要的意义。例如,跨越所有活体细胞的原生质膜,以及通过人体或动物许多器官(如肾小管、毛细血管、小肠、膀胱和角膜)的内外皮细胞间隙,都有渗透流。又如,人造器官的合成膜以及植物细胞与组织间的水交换等,都与渗透有关。因此,近三十年来,生物物理、生理学和流体力学工作者从不同角度对于渗透现象的宏观描述和微观机理进行了广泛的探索。