依托学科优势建设有特色的流体力学教学实验体系

介绍北京航空航天大学流体力学教学实验体系及其课程建设,包括：从基础演示实验、流体力学基本方程实验到综合、扩展、学生自主的设计创新实验的3个层次的教学实验体系,理论学习、计算机虚拟实验、实际动手操作实验有机结合的教学方式,与国内外高校的切磋交流以及在中央电视台、北京电视台相关栏目演播等内容.     

数字流体力学教学系统——————力学课程的教学改革

 数字工程流体力学智能化教学系统是在多年实践的基础上提出的新概念，它以超媒体教 学资源数据库为核心，并在数字系统中心的指挥管理下，把教与学用几大模块有机地组 合在一起. 这一教学改革成果大大提高了该门力学课程的整体教学水平和质量.     

An intelligent data acquisition system for fluid mechanics research

Conclusions A new approach to experimental data acquisition has been demonstrated. The results of the proof-of-concept experiment show that by incorporating a degree of specific fluid dynamics knowledge to the data acquisition process, it is possible to increase the resolution of the experiment, or alternately, reduce the total number of data points required to achieve parity with the results of most conventional data acquisition approaches.     

Artificial intelligence in fluid mechanics

Acta Mechanica Sinica - Recent progress in machine learning and big data not only forms a new research paradigm, but also provides opportunity to solve grand challenges in fluid mechanics....     

Galilean relativistic fluid mechanics

Single-component nonrelativistic dissipative fluids are treated independently of reference frames and flow-frames. First the basic fields and their balances are derived, then the related thermodynamic relations and the entropy production are calculated and the linear constitutive relations are given. The usual basic fields of mass, momentum, energy and their current densities, the heat flux, pressure tensor and diffusion flux are the time- and spacelike components of the third-order mass–momentum–energy density-flux four-tensor. The corresponding Galilean transformation rules of the physical quantities are derived. It is proved that the non-equilibrium thermodynamic frame theory, including the thermostatic Gibbs relation and extensivity condition and also the entropy production, is independent of the reference frame and also the flow-frame of the fluid. The continuity-Fourier–Navier–Stokes equations are obtained almost in the traditional form if the flow of the fluid is fixed to the temperature. This choice of the flow-frame is the thermo-flow. A simple consequence of the theory is that the relation between the total, kinetic and internal energies is a Galilean transformation rule.     

Joseph Boussinesq's legacy in fluid mechanics

Joseph Boussinesq was the most prolific of all French contributors to nineteenth-century fluid mechanics. His scientific production included a novel theory of solitary waves, the KdV equation for finite deformations of the water surface in an open channel, a systematic study of open channel and pipe flow based on the concept of effective viscosity, pioneering derivations of boundary layers and entrance effects, new exact solutions of the Navier–Stokes equation under geometrically simple boundary conditions, and the ‘Boussinesq approximation’ for heat convection in a moving fluid under gravity. Although his extraordinary skills were quickly recognized and rewarded, other experts in the field were often unaware even of his most important results and they ended up rediscovering some of them. Boussinesq's unusual background and the resulting peculiarities of his style explain this problematic diffusion. They also account for the richness of his legacy.     

Some problems in metallurgical fluid mechanics

Application of computational fluid mechanics in two areas of metallurgy is considered: solidification of liquid alloys and MHD turbulence. In the first class of problems, where the technical issue is to obtain a reasonably homogeneous composition of the cast, one has to consider not only the completely molten and solidified regions but also the “mushy zone” that is made up of small-scale dendrites, which appear between the first two regions. In the completely molten region, the composition is practically constant and the fluid is set into motion due to the inhomogeneous temperature field. In the mushy zone, on the other hand, solutal convection often dominates strongly over thermal convection. It is shown that laminar convection is of prime importance for the composition of the solidified alloy. In the second class of problems, two cases of turbulent MHD flows in cylindrical containers are considered: an electromagnetic furnace and an electromagnetic stirrer. In the electromagnetic furnace, the mean flow consists of two toroidal vortices. The mean motion in the electromagnetic stirrer is a swirling motion that is accompanied by a weak meridional circulation, which is reminiscent of that occuring in spin down phenomena. The MHD flows are computed by using large eddy simulation methodology with a new subgrid model of the Smagorinsky type that accounts for a variable mesh. Predictions from the all model computations are compared with experimental observations. In general, the agreement between theory and experiments is satisfactory.     

Dynamic behaviors of the breather solutions for the AB system in fluid mechanics

Under investigation in this paper is the AB system, which describes marginally unstable baroclinic wave packets in geophysical fluids. Through symbolic computation, Lax pair and conservation laws are derived and the Darboux transformation is constructed for this system. Furthermore, three types of breathers on the continuous wave (cw) background are generated via the obtained Darboux transformation. The following contents are mainly discussed by figures plotted: (1) Modulation instability processes of the Akhmediev breathers in the presence of small perturbations; (2) Propagations characteristics of Ma solitons; (3) Dynamic features of the breathers evolving periodically along the straight line with a certain angle of z-axis and t-axis.     

Chemo-thermomechanical ageing of elastomers based on multiphase continuum mechanics

This article concerns the constitutive representation of one of the chemical ageing processes that occur in elastomers, chemo-thermomechanical ageing, which takes place as an irreversible, time-delayed chemical reaction when a medium diffuses into an unlike solid. This process is inhomogeneous in component parts of finite thickness, and as it can be thermally activated, ageing is accelerated on an increase in temperature. The application of multiphase continuum mechanics to these basic characteristics enables a thermodynamically coupled material model to be formulated, which is able to describe not only the viscoelasticity, but also the chemical decomposition and reformation processes that occur in the polymer network. The evolution principle of Liu-Müller is used to evaluate the thermomechanical consistency of the model obtained. Subsequent to this, the finite element method is applied to solve the resulting set of partial equations, which corresponds to a coupled multifield problem. The article closes with convincing simulations of illustrative examples.     

Free surface problems in rheological fluid mechanics

Summary In this paper we review our work on the theory of domain perturbations of the rest state of a viscoelastic fluid and its applications to the science of rheometry. To explain the principle behind the domain perturbation analysis we begin the paper with a discussion of a model problem, free of rheological complications, in which the principles involved may be clearly demonstrated. In Chapter two we formulate the analysis for rheological problems and we present some new, previously unpublished, simplifications of the theory. The canonical forms for stress tensors which perturb the state of rest are given in Chapter three. Chapter four is devoted to the problem of steady rod climbing. There we discuss the main physical features of the motion, the phenomenon of the critical radius, the effects of surface tension and temperature, secondary motions, the applicability of theory and experiment for rheological measurements, and an interesting new normal stress anplifier. Unsteady problems of rod climbing are considered in Chapter five. We review recent results on the free surface induced by torsional oscillations of a rod, and we show how to use these results to find the form of the material functions in the canonical forms of the stress. The breathing instability of steady axisymmetric rod climbing (aHopf bifurcation) and the flower instability of time-periodic climb induced by the oscillating rod (a symmetry-breakingPoincaré bifurcation) are also described in Chapter five. In Chapter six we consider other free surface problems: the free surface on a fluid between oscillating planes, die swell and edge effects in rheometers.

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Zusammenfassung Es wird ein Überblick über die Untersuchungen der Verfasser zum Thema Gebietsstörungen des Ruhezustandes (domain perturbations of the rest state) einer viskoelastischen Flüssigkeit und ihre Anwendung auf die Rheometrie gegeben. Zur Erläuterung der Grundlagen der Gebietsstörungs-Analyse wird in Kap. 1 die Diskussion eines Modellproblems vorangestellt, das keinerlei rheologische Komplikationen enthält, so daß die betreffenden Prinzipien in einfacher Weise erläutert werden können. In Kap. 2 wird die Analyse auf rheologische Probleme angewendet, und es werden einige bisher unveröffentlichte Vereinfachungen der Theorie vorgestellt. In Kap. 3 werden die kanonischen Formen der die Störung des Ruhezustandes hervorrufenden Spannungstensoren angegeben. In Kap. 4 wird das Problem des Hochkletterns einer Flüssigkeit am stationär rotierenden Zylinder behandelt. Dabei werden die Hauptmerkmale der Bewegung, das Phänomen des kritischen Radius, die Wirkung von Oberflächenspannung und Temperatur, Sekundärbewegungen, die Anwendbarkeit von Theorie und Experiment auf rheologische Messungen, sowie ein interessanter neuer Normalspannungs-Verstärker diskutiert. In Kap. 5 wird das Problem des Hochkletterns bei instationärer Bewegung des Zylinders betrachtet. Es werden neuere Ergebnisse über die durch eine Torsionsschwingung erzeugte freie Oberfläche referiert, und es wird gezeigt, wie diese Ergebnisse zur Bestimmung der Stoff-Funktionen in der kanonischen Darstellung der Spannungen verwendet werden können. Die atmende Instabilität beim stationären Hochklettern (eine Verzweigungslösung vomHopfschen Typ) und die blütenförmige Instabilität beim zeitlich-periodischen Hochklettern infolge der Zylinder-Oszillation (eine die Symmetrie brechende Verzweigungslösung vomPoincaréschen Typ) werden hier ebenfalls beschrieben. In Kap. 6 schließlich werden weitere an freien Oberflächen auftretende Probleme behandelt: nämlich die freie Oberfläche einer Flüssigkeit zwischen oszillierenden Platten, die Strahlaufweitung und die Randeffekte in Rheometern.

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With 13 figures     

运用多媒体进行流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.     

智能物面对非定常分离流的最优自适应控制

以低雷诺数二维大攻角翼型绕流为研究对象, 将非定常动边界计算流体力学方法与 最优控制方法有机结合, 研究二维不可压非定常流智能物面最优自适应流 动控制的理论与算法, 并将其用于固定攻角和俯仰振荡翼型绕流. 结果表明: 在给定合适的最优控制目标函数下, 智能物面可最优地实时改变形状, 得到能显著提高翼型性能的最优翼型. 最优翼型在非设计工况下的气动性能也比对照翼型有 所提高.     

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.     

The use of images in fluid mechanics

Still images, photographs and drawings, as well as movies are widely used in fluid mechanics and this has been true since the very early developments of this discipline. The intrinsic geometrical complexity of fluid flows, in particular when they are turbulent, explains this necessity of using visual representations to gain a physical understanding of the phenomena involved. The aesthetic appeal of images in fluid mechanics research is another reason why their use is more prevalent than in other fields of the physical sciences.     

流体力学在选矿中的应用

分析了一些典型的选矿设备中流体的运动,阐述了流体力学对选矿发展的重要性,说明了选矿中流体力学的特点及选矿中面临的流体力学问题.