Sidewall flow stability in the MHD channel flows

The velocity distribution between two sidewalls is; M-shaped for the MHD channel flows with rectangular cross section and thin conducting walls in a strong transverse magnetic field. Assume that the dimensionless numbers R(m) much less than 1, M, N much greater than 1, and sigma

Concentration distribution in crystallization from solution under microgravity

Concentration distribution in crystallization from solution under microgravity is numerically studied. A quasi-steady state growth and dissolution in a 2D rectangular enclosure filled with sodium chlorate (NaClO3) aqueous solution, in which one wall is the growth surface of the crystal and the opposite one is the dissolution surface, is considered. The solute transport process at the growth surface is described by the diffusion-reaction theory with finite interface kinetics coefficient. The results show that the concentration at the growth surface is supersaturated and the supersaturation distribution is of non-uniformity, i.e. the supersaturation in a region facing an incoming flow is high. On the other hand, the non-uniformity of supersaturation at the growth surface is closely related to the gravity level even under microgravity, it exponentially increases as the thermal Rayleigh number on behalf of the gravity level rises.

Saturation impulses for dynamically loaded structures with finite-deflections

The concept of ''Saturation Impulse'' for rigid, perfectly plastic structures with finite-deflections subjected to dynamic loading was put forward by Zhao, Yu and Fang (1994a). This paper extends the concept of Saturation Impulse to the analysis of structures such as simply supported circular plates, simply supported and fully clamped square plates, and cylindrical shells subjected to rectangular pressure pulses in the medium load range. Both upper and lower bounds of nondimensional saturation impulses are presented.

A finite-element analysis of viscoelastically damped sandwich plates

A finite element analysis associated with an asymptotic solution method for the harmonic flexural vibration of viscoelastically damped unsymmetrical sandwich plates is given. The element formulation is based on generalization of the discrete Kirchhoff theory (DKT) element formulation. The results obtained with the first order approximation of the asymptotic solution presented here are the same as those obtained by means of the modal strain energy (MSE) method. By taking more terms of the asymptotic solution, with successive calculations and use of the Padé approximants method, accuracy can be improved. The finite element computation has been verified by comparison with an analytical exact solution for rectangular plates with simply supported edges. Results for the same plates with clamped edges are also presented.

Slightly slanting impact on an elastic cantilever column-an experimental study

Experiments concerning slightly slanting impact between a flat-ended rigid body and a flat-ended elastic cantilever column with a rectangular cross-section have been performed. The experimental results are compared with the theoretical ones. The small angle of incidence was measured by using an optical method. The impact process was studied by using a split disc for the rigid body, with the two halves bonded together and electrically insulated from each other. The disc and the column were parts of an electric circuit. Different contact states could be distinguished according to different voltage levels. Reasonably good agreement between theory and experiment was found. Thus, the impact duration has its minimum under perfectly axial impact as predicted by the theory. Also, the predicted process of alternating line and surface contact was observed. Furthermore, the existence of a small critical angle of incidence was verified. This critical angle of incidence divides the impact processes into two categories: (1) The rigid body and the column end come into surface contact before separation. (2) They separate without surface contact. Comparison of axial strains between theory and experiment shows good agreement.

Dynamic-response of a laminated plate with friction damping

Static equilibrium of horizontal ring prominence

In 1980 the Beijing Observatory had successively observed sevesal rare completely closed ring prominences whose ring plane was approximately parallel to the solar surface with a characteristic life about 1—2 days. In this paper we discuss the static equilibrium of this kind of horizontal ring plasma under the simultaneous actions of magnetic force, gravity and pressure gradients. Assuming ring plasma with axisymmetry and rectangular plasma cross-section and adopting closed magnetic field boundary condition from the basic equations we obtain the exact zero order general solutions for magnetic field (force-free field) and density (pressure). We further obtain an eigen-solution for the zero order magnetic field and density as well as the first order magnetic field, thus giving a kind of the possible distribution of magnetic field and density for the horizontal closed ring prominence. The closed magnetic structure of ring prominence as presented in this paper, has no link with the force lines of the outside corona magnetic field. This is helpful to explain the great temperature difference between prominenee and corona.

矩形微槽道气体流动的速度分布

矩形微槽道的各个流向截面可以局部近似为平面Poiseuille流动，应用信息保存（IP）方法和直接模拟Monte Carlo（DSMC）方法计算了从连续介质区到自由分子流区的平面Poiseuille流动，利用其结果对Beskok-Karniadakis公式和质量流率动理论因子进行修正和重新拟合，给出在整个稀薄气体流动领域都适用的微槽道气体流动速度分布.

Experimental Study on Bénard-Marangoni Convection in Double Immiscible Liquid Layer

An experimental investigation of Bénard-Marangoni convection has been performed in double immiscible liquid layers of rectangular configuration on the ground. The two kinds of liquid are 10cst silicon oil and FC-70 respectively. The size of rectangular chamber is 100mm×40mm in horizontal cross-section. The evolution processes of convection are observed in the differential thickness ratio of two liquid layers. The critical temperature difference was measured via the detections of fluid convection by a particle image velocimetry (PIV) in the vertical cross-section of the liquid layer. The critical temperature difference or the critical Marangoni number was given. And the influence of the thickness ratio of two liquid layers on the convection instability was discussed. The evolution processes of patterns and temperature distributions on the interface are displayed by using thermal liquid crystal. The velocity distributions on the interface were also obtained. In comparison with the thermocapillary effect, the effect of buoyancy convection will relatively increase when the depth of the liquid layer increases. Because of the coupling of buoyancy and thermocapillary effect, the convection instability is much more complex than that in the microgravity environment. And the critical convection depends on the change of the thickness of liquid layers and also the change of thickness ratio of two liquid layers.

Experimental Study on Surface Deformation and Surface Wave of Fluid Convection with Free Surface

An optical diagnostic system consisting of Michelson interferometer with image processor has been developed for study of the kinetics of thermal capillary convection and buoyancy convection. This optical interferometer has been used to observe and measure surface deformation and surface wave of capillary convection and buoyancy convection in a rectangular cavity with different temperature’s sidewalls. Fourier transformation is used to image processing. The quantitative results of surface deformation and surface wave have been calculated from the interference fringe pattern. With the increasing of temperature gradient, the liquid surface slant gradually. It’s deformation has been calculated, which is related directly with temperature gradient. This is one of the characters introducing convection. Another interesting phenomenon is the inclining direction, which is different when the liquid layer is thin or thick. When the liquid layer is thin, convection is mainly controlled by thermocapillary effect. However, When the liquid layer is thick, convection is mainly controlled by buoyancy effect. Surface deformation in the present experiment are more and more declining in this process. The present experiment proved that surface deformation appears before the appearance of surface wave on fluid convection, it is related with temperature gradient, and the height of liquid layer, and lies on capillary convection and buoyancy convection. The present experiment also demonstrates that the amplitude of surface wave of thermocapillary-buoyancy convection is much smaller than surface deformation, the wave is covered by deformation.

Characteristics of Wake Flow in Long Bluff Bodies

Vortex shedding is the main characteristics of bluff bodies, which will cause the bluff bodies to vibrate and sometimes result in the structures failure. In this paper the wake flow characteristics of 21 bluff bodies with rectangular, rounded and angular profiles and the length-to-width ratio in the range of 4~12 were deeply studied by Micro ADV. Two parameters, namely the relative intensity of the load due to Karman vortices and the large scale vortex intensity, were introduced to measure the wake flow intensity. Generally, the values of these parameters for different bluff bodies are consistent with each other. The experiment results showed that the key factor affecting the wake flow characteristics is the bluff edge, especially the leading edge geometry. The wake flow in bluff bodies with rounded edge profiles has more regular vortices and becomes more periodic than that in bluff bodies with rectangular ones. A bluff body with angular edged profile was witnessed to have not only small wake loading but small hydraulic resistance also.

Experimental Study the Flow Pattern in Thermal Capillary Convection

In the present research work, the thermal capillary convection has been investigated and measured by particle image velocimetry (PIV) technique. There is one liquid layer in a rectangular cavity with different temperature’s sidewalls. The cavity is 52mm,42mm,20mm, 4mm in height of the silicon oil liquid layer. A sidewall of the cavity is heated by electro-thermal film, another sidewall is cooled by the semiconductor cooling sheet. The velocity field and the stream lines in cross section in liquid layer have been obtained at different temperature difference. The present experiment demonstrates that the pattern of the convection mainly relates with temperature difference.

Experimental Observation on Surface Wave Phenomena in Thermal Capillary Convection

An optical diagnostic system consisting of the Michelson interferometer with the image processor has been developed for studying of the surface wave in the thermal capillary convection in a rectangular cavity. In this paper, the capillary convection, surface deformation and surface wave due to the different temperature between the two sidewalls have been investigated. The cavity is 52mm?42mm in horizontal cross section and 4mm in height. The temperature difference is increased gradually and flow in liquid layer will change from steady convection to unstable convection. The optical interference method measures the surface deformation and the surface wave of the convection. The deformation of the interference fringes, which produced by the meeting of the reflected light from the liquid surface and the reference light has been captured, and the surface deformation appears when the steady convection is developed. The surface deformation is enhanced with the increasing of the temperature difference, and then several knaggy peeks in the interference fringes appear and move from the heated side to the cooled side, it demonstrates that the surface wave is existed. The surface deformation, the wavelength, the frequency, and the wave amplitude of the surface wave have been calculated.

Two-phase Flow in Fuel Cells in Short-term Microgravity Condition

A visual observation of liquid-gas two-phase flow in anode channels of a direct methanol proton exchange membrane fuel cells in microgravity has been carried out in a drop tower. The anode flow bed consisted of 2 manifolds and 11 parallel straight channels. The length, width and depth of single channel with rectangular cross section was 48.0 mm, 2.5 mm and 2.0 mm, respectively. The experimental results indicated that the size of bubbles in microgravity condition is bigger than that in normal gravity. The longer the time, the bigger the bubbles. The velocity of bubbles rising is slower than that in normal gravity because buoyancy lift is very weak in microgravity. The flow pattern in anode channels could change from bubbly flow in normal gravity to slug flow in microgravity. The gas slugs blocked supply of reactants from channels to anode catalyst layer through gas diffusion layer. When the weakened mass transfer causes concentration polarization, the output performance of fuel cells declines.

Effects of geometric shape on the hydrodynamics of a self-propelled flapping foil

The hydrodynamics of a free flapping foil is studied numerically. The foil undergoes a forced vertical oscillation and is free to move horizontally. The effect of chord-thickness ratio is investigated by varying this parameter while fixing other ones such as the Reynolds number, the density ratio, and the flapping amplitude. Three different flow regimes have been identified when we increase the chord-thickness ratio, i.e., left-right symmetry, back-and-forth chaotic motion, and unidirectional motion with staggered vortex street. It is observed that the chord-thickness ratio can affect the symmetry-breaking bifurcation, the arrangement of vortices in the wake, and the terminal velocity of the foil. The similarity in the symmetry-breaking bifurcation of the present problem to that of a flapping body under constraint is discussed. A comparison between the dynamic behaviors of an elliptic foil and a rectangular foil at various chord-thickness ratios is also presented.