沿垂等温平板的自然对流问题的近似解析解

本文用加权残值得到了沿垂等温平板的自然对流问题的近似解析解。和已有准确解的比较表明，在平板表面附近，近似解有很好的精度，而且速度场的精度比温度场更好一些。文末还对配域法的准收敛问题作了说明。     

液压技术中的流体力学

 介绍了流体静力学和流体动力学在液压工程技术中的应用，说明了流体力学理论在液压工程 中所起到的非常重要的作用. 用流体力学的原理来解释液压技术中出现的问题，而这些问题的 解决都离不开流体力学的发展.     

主喷管叶片中热壁面对分流管道流场特性的影响

 连续波化学激光器运转时,位于主喷管叶片内的副气流的分流管道壁面将被主喷管叶片加热而形成热壁面。通过3维的数值模拟,分析了单端、双端不同供气方式下,热壁面对分流管道流场特性的影响。热壁面将使总管气流总温沿着气流的流动方向逐渐升高,由此引起的支管入口总温的升高会降低支管的流量。无论是单端供气,还是双端供气,热壁面引起的管道流量波动幅度都要远大于绝热壁面的情况,最大波动幅度达2.16%。对进入总管的气流预热,适当增加供气总温,或将冷却管道与供气管道分开设计,气流总温变化引起的流量波动将会得到一定地抑制。     

关于粘滞流体层流流量公式的讨论

泊肃叶公式仅适用于水平圆管内层流，本文根据稳定流动和内摩擦力的概念推导管轴的取向为任意方向时粘滞流体在均匀圆管内层流的流量公式，从而，得到水平管、垂直管等不同情况下的流量公式．     

Oscillatory disturbance in force calibration of optical tweezers

In the calibration of the optical trap stiffness, it is found that there appears an attenuating oscillation as an oscillatory disturbance added to the trapped bead movement, when the scanner is driven by a triangular wave input.An equivalent oscillator model is put forward to explain the mechanism of the oscillatory disturbance. Both the measurements and calculations show that the attenuating oscillation comes from the oscillation of the scanner and the triangular wave drive causes this additional oscillation of the scanner. Furthermore, the analysis indicates that the oscillatory disturbance will become stronger, when the stiffness of the trap increases or the natural frequency of the scanner decreases. We adopt another driving way, i.e. a sinusoidal wave input is used instead of the triangular wave input. Our experiment has verified that in this case the oscillatory disturbance is eliminated completely.     

Using Digital Imaging to Characterize Threshold Dynamic Parameters in Porous Media Based on Lattice Boltzmann Method

Digital images (DI) and lattice Boltzmann method (LBM) are used to characterize the threshold dynamic parameters of porous media. Two-dimensional representations of the porous structure are reconstructed from segmentation of digital images obtained from a series of tiny samples. The threshold pressure gradients and threshold Péclet numbers are researched on seven test samples by using LBM. Numerical results are in agreement with that obtained by integrating Darcy’s law. The results also indicate that fluids can flow through porous media only if the fluid force is large enough to overcome threshold pressure gradient in porous media. One synthetic case is used to further illustrate the applicability of the proposed technique. In addition, the dynamical rules in our model are local, therefore it can be run on parallel computers with well computational efficiency.     

孔洞增长与汇合的数值模拟

在研究延性材料的层裂过程中，微孔洞的成核、增长与汇合是主要问题。在二维平面条件下，应用二维拉氏有限元弹塑性流体力学程序(LTZ-2D)，在动态拉伸作用下，对多种形状的孔洞增长、相互作用和汇合进行了数值模拟。结果表明，初始非圆形孔洞在动态拉伸作用下，经过了一定时间后，孔洞的增长均趋近于圆形。如果在孔洞周围允许材料损伤断裂的话，当孔洞继续长大到一定程度时，将产生破裂并且汇合。以铜材料为例，     

SIMULATION OF PARTICLE COATING IN THE SUPERCRITICAL FLUIDIZED BED

Fluidized bed technology using supercritical carbon dioxide both as a fluidizing gas and as a solvent for the coating material makes possible the production of thin, uniform and solvent-free coatings. But operation at low fluidizing velocities, which is favorable to facilitate gas cleaning under the high pressure conditions, may lead to uneven distribution of the coating in the fluidized bed and to unstable operation due to agglomeration. Therefore a model has been developed which describes local fluid dynamics within the high pressure fluidized bed. Based on this model, the coating process is described and the distribution of the coating inside the fluidized bed is calculated. Furthermore a submodel for the calculation of local concentrations of liquid paraffin has been set up, which may be used as a basis for the prediction of agglomeration and thus stability of operation.     

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     

等离子体断路开关的一维磁流体力学数值模拟

 采用磁流体力学的方法对等离子体端路开关进行了一维数值模拟，通过对给定的进入等离子体的电流波形模型的计算，给出了轴向上等离子体的运动及其不同时刻的密度分布，分析了磁场在等离子体内部的异常渗透过程，指出考虑Hall效应是产生这一异常现象的最为主要的因素。