ON A NEW KIND OF METHODS TO SOLVE THE PLANE PROBLEMS OF TWO-PHASE FLOW THROUGH POROUS MEDIA

This paper presents a new kind of method for solving the planeproblems of two-phase flow in porous media.The ellipticalpartial differential equation for pressure distribution is sol-ved by the finite element method,and then the semi-analyticalsolution for pressure gradient is used to determine the new sa-turation field according to the existing exact formula describ-ing the saturation propagation along the streamlines.The maindistinguishing feature and advantage of this kind of method arethe ability to overcome the numerical dispersion which is inhe-rent in the ordinary numerical simulation methods.and thereby,to give a precise and clear-cut position of the saturation dis-continuity in the water-oil displacement front.moreover.thesaturation equation,which should commonly be solved simultan-eously or alternatively with the pressure equation,is complete-ly avoided,so that the computing time is greatly reduced.     

A NUMERICAL STUDY OF THE STRESS DISTRIBUTION IN HOPPER FLOW

The stress distributions of granular flow in a cylindrical hopper with fiat bottom are investigated by means of a combined approach of discrete element method (DEM) and averaging method. The filling and discharge of the hopper flow are first simulated at a particle level by means of a modified DEM. The results are then used to determine the velocity and stress profiles of the hopper flow by means of an averaging method. The analysis is focused on a central section plane of the hopper due to the relatively perfect axial symmetry. The velocity profiles are illustrated to be consistent with those obtained by the previous experiments, confirming the validity of the proposed approach. The distributions of four components of the planar stress tensor at different heights are quantified. It is shown that the vertical normal stress increases with increasing the height near the central axis, the horizontal normal stress varies more slowly at a higher level and is almost constant when the height is equal to or greater than about 12 particle diameter, and the magnitudes of two shear stresses are equal at the central zone of the hopper but not so at the points near the walls. The dependence of stress distributions on the wall mechanical properties such as sliding resistance and rolling resistance is also discussed.     

PROPAGATION BEHAVIORS OF SHEAR HORIZONTAL WAVES IN PIEZOELECTRIC-PIEZOMAGNETIC PERIODICALLY LAYERED STRUCTURES

This paper investigates shear horizontal （SH） waves propagating in a periodically layered structure that consists of piezoelectric （PE） layers perfectly bonded with piezomagnetic （PM） layers alternately. The explicit dispersion relations are derived for the two cases when the propagation directions of SH waves are normal to the interface and parallel to the interface, respectively. The asymptotic expressions for dispersion relations are also given when the wave number is extremely small. Numerical results for stop band effect and phase velocity are presented for a periodic system of alternating BaTiO3 and Terfenol-D layers. The influence of volume fraction on stop band effect and dispersion behaviors is discussed and revealed.     

THE DISTRIBUTION OF THE SPECIFIC PRESSURE IN ROLLING STRIPS

The principle of the distribution of the specific pressure in rol-ling strips is used not only for calculating the total rolling pres-sure but also for providing the basis in calculating the widening andin designing the rational roll profile.Hitherto,the results of an-alysis on this subject in the references are expressed as a functionof one dimension,and they cannot reflect the variation of the speci-fic pressure along the width of the contact surface.This paper dealswith the two-dimensional expression of the principle.of the distribu-tion of the specific pressure with the help of the calculus of varia-tions.     

Effect of the size and pressure on the modified viscosity of water in microchannels

The phenomenon that flow resistances are higher in micro scale flow than in normal flow is clarified through the liquid viscosity. Based on the experimental results of deionized water flow in fused silica microtubes with the inner radii of 2.5 μm, 5 μm, 7.5 μm, and 10 μm, respectively,the relationship between water flow velocity and pressure gradient along the axis of tube is analyzed, which gradually becomes nonlinear as the radius of the microtube decreases.From the correlation, a viscosity model of water flow derived from the radius of microtube and the pressure gradient is proposed. The flow results modified by the viscosity model are in accordance with those of experiments, which are verified by numerical simulation software and the Hagen–Poiseuille equation. The experimental water flow velocity in a fused silica microtube with diameter of 5.03 μm, which has not been used in the fitting and derivation of the viscosity model,is proved to be comsistent with the viscosity model, showing a rather good match with a relative difference of 5.56%.     

Expressions for pressure-velocity-gradient correlations

The term for pressure-velocity-gradient correlation was initiated by Rott’srewriting the correlation between the pressure fluctuation gradient and velocity fluctuation.However,it is very difficult to consider the effect of this term.Since Rotta’s work,Launderet al.has made some estimates of this term.In this paper according to the equations forvelocity fluctuation,the pressure fluctuation is solved so that the average value of theproduct of the pressure fluctuation and the velocity fluctuation gradient is obtained.Thus,the whole expressions for the pressure-velocity-gradient correlation are derived.The resultexplains that the limited expressions by Rotta and Launder are reasonable to a certaindegree.The whole expressions in this paper are discussed respectively in two situations:oneis without a separate consideration of large and small vortexes;the other is with a separateconsideration of three kinds of vortexes.Therefore,the paper gives the whole expressions forpressure-velocity-gradient correlation     

MEASUREMENT OF ADHESION FORCES IN AIR WITH THE VIBRATION METHOD

The vibration method represents a practical method for the measurement of adhesion forces and adhesion force distributions. This method causes sinusoidally alternating stresses and yields detachment and contact forces between particles and substrate of the same order of magnitude. Alternating contact forces of the vibration method can cause an adhesion force intensification through flattening of asperities. The measuring principle of the vibration method and the analysis of experimental results are described in the article. Normal adhesion forces (pull-off forces) are measured using the vibration method and the colloidal probe technique. The results of both methods show good agreement for small particle sizes. The influence of the detachment force direction is shown by comparing tangential and normal adhesion forces measured using particle reentrainment in a turbulent air flow and the vibration method, respectively. The surface roughness of the substrate and the relative humidity are shown to significantly influence the measured adhesion forces. For the calculation of the adhesion forces, an approach by Rabinovich was combined with approximations of plastic micro asperity flattening. The Rabinovich approach accounts for roughness effects on the van der Waals force by incorporating the rms roughness of the interacting surfaces, rms-values of the particles and substrates were measured with atomic force microscopy at different scanning areas.     

Time-optimal rendezvous transfer trajectory for restricted cone-angle range solar sails

The advantage of solar sails in deep space exploration is that no fuel consumption is required. The heliocentric distance is one factor influencing the solar radiation pressure force exerted on solar sails. In addition, the solar radiation pressure force is also related to the solar sail orientation with respect to the sunlight direction. For an ideal flat solar sail, the cone angle between the sail normal and the sunlight direction determines the magnitude and direction of solar radiation pressure force. In general, the cone angle can change from 0° to 90°. However, in practical applications, a large cone angle may reduce the efficiency of solar radiation pressure force and there is a strict requirement on the attitude control. Usually, the cone angle range is restricted less more than an acute angle （for example, not more than 40°） in engineering practice. In this paper, the time-optimal transfer trajectory is designed over a restricted range of the cone angle, and an indirect method is used to solve the two point boundary value problem associated to the optimal control problem. Relevant numerical examples are provided to compare with the case of an unrestricted case, and the effects of different maximum restricted cone angles are discussed. The results indicate that （1） for the condition of a restricted cone-angle range the transfer time is longer than that for the unrestricted case and （2） the optimal transfer time increases as the maximum restricted cone angle decreases.     

Effect of rotation in generalized thermoelastic solid under the influence of gravity with an overlying infinite thermoelastic fluid

The present problem is concerned with the study of deformation of a rotating generalized thermoelastic solid with an overlying infinite thermoelastic fluid due to different forces acting along the interface under the influence of gravity.The components of displacement,force stress,and temperature distribution are first obtained in Laplace and Fourier domains by applying integral transforms,and then obtained in the physical domain by applying a numerical inversion method.Some particular cases are also discussed in the context of the problem.The results are also presented graphically to show the effect of rotation and gravity in the medium.     

Orientation distribution of fibers and rheological property in fiber suspensions flowing in a turbulent boundary layer

A model relating the translational and rotational transport of orientation distribution function （ODF） of fibers to the gradient of mean ODF and the dispersion coefficients is proposed to derive the mean equation for the ODE Then the ODF of fibers is predicted by numerically solving the mean equation for the ODF together with the equations of turbulent boundary layer flow. Finally the shear stress and first normal stress difference of fiber suspensions are obtained. The results, some of which agree with the available relevant experimental data, show that the most fibers tend to orient to the flow direction. The fiber aspect ratio and Reynolds number have significant and negligible effects on the orientation dis- tribution of fibers, respectively. The additional normal stress due to the presence of fibers is anisotropic. The shear stress of fiber suspension is larger than that of Newtonian solvent, and the first normal stress difference is much less than the shear stress. Both the additional shear stress and the first normal stress difference increase with increasing the fiber concentration and decreasing fiber aspect ratio.     

On the dynamical structure of the wind field of Jupiter's Great Red Spot

Based on the geographic approximation the two-dimensional dynamical structure of the wind fields of Jupiter's Great Red Spot and White Oval BC is obtained. The results of calculation are in good agreement with the observations. Thus, an explanation of the observed dispersion of the velocities along the horizontal streamline is given. The major physical mechanism of this dispersion is as follwos: The distance between two adjacent elliptical streamlines varies along the elliptical streamline, leading to the variance of the normal pressure gradient. Thus, the horizontal velocity V_t has to vary correspondingly so that the Coriolis force can approximately balance the normal pressure gradient Another less important factor, i. e., the change of the Coriolis force parameter with the latitude, is also taken into account.The distributions of the vorticities of GRS and White Oval BC are also calculated.     

考虑边界层影响时溢流坝动水压强分布规律的研究

根据溢流坝反弧段水流运动的基本方程,考虑水流边界层的影响,在流线曲率同心圆假设条件下,得到了溢流坝反弧段水流压强计算的表达式。通过引入近壁薄流层要领和缓和过渡流线假设,在水工模型试验的基础上,得到了溢流坝反弧段水流流线曲率半径的计算公式,使反弧段离心力影响范围内的水流流线曲率光滑连续,从而得到反弧段水流压强分布规律的统一表达式,该表达式能够反映水流压强沿反弧法线方向及切线方向的变化规律。     

The pressure melting of ice around a horizontal elliptical cylinder

The pressure melting processes of a block of ice around a moving, horizontal, elliptical cylinder are investigated. The film thickness of liquid and the relation between the force exerted on the elliptical cylinder and the melting velocity are obtained analytically. The results include those of pressure melting around a horizontal cylinder, and are discussed and compared with that of ΔT-driven melting around an elliptical cylinder. The basic differences between Δp-driven and ΔT-driven melting are obtained. Some important conclusions are drawn.     

涡识别技术及其在船用螺旋桨伴流场中的应用

涡识别是很重要的流体问题, 为了在船用螺旋桨伴流场中寻找一种合理的涡识别方法, 本文结合实践, 研究了六种涡识别技术理论, 其中使用Burgers涡流和Lamb-Oseen涡流作了必要的解释, 讨论了各种识别方法的优缺点. 局部低压标准比较直观, 但深究其黏性和非定常影响后, 明显不足; 迹线或流线显然不能满足伽利略不变性, 会使辨别变得混乱; 涡度大小需要规定其阈值, 具有一定不确定性, 且也会识别不是涡的涡片; 速度梯度张量的复特征值也会有识别不出的区域; 速度梯度张量的第二不变量标准和对称张量的第二特征值标准能更好地识别涡核, 这两种标准有时等效. 螺旋桨伴流场的数值模拟是在开源软件OpenFOAM平台上实现的, 湍流大涡模型由一种局部动态方程建模, 此模型优于动态Smagorinsky模型. 最终的结果显示: 对于船用螺旋桨伴流场中的涡, 采用速度梯度张量的第二不变量和对称张量的第二特征值的结果基本一致, 而最小压力标准、流线或迹线标准、涡度值标准和速度张量的复特征值标准都存在一定的缺陷, 不适用于船用螺旋桨伴流场中的涡识别.      

边坡岩体结构的三维失稳形式及稳定性分析研究

由两组结构面控制的四面体块体是岩体中最基本的结构体, 其稳定性取决于块体所受荷载及结构面上的摩阻力。正确判定边界面上摩阻力分布是评价块体稳定性的关键。本文提出的块体稳定性分析适用于岩体所受荷载为三维非共点力系。在不同外力作用下块体可产生平动、转动、翘扭及倾倒等各种三维失稳组合形式, 从而得到更为合理的块体稳定性评价。     

两种弹性损伤模型的基本方程与色散关系讨论

分析了传统连续介质损伤理论的控制方程在损伤过程中的变化特点,方程类型的改变导致错误预测波不能在损伤区域传播.二阶隐式应变梯度损伤理论是对传统理论的一种改进,严格证明了其控制方程在损伤过程中类型不变,这意味着损伤区域能传播波,同时有助于克服病态的网格相关性.色散分析结果表明:传统连续介质损伤理论不能反映色散现象,隐式梯度模型可以并对波长有上限截断作用.     

Comparative study of two corrective gradient models in the simulation of multiphase flows using moving particle semi-implicit method

In this study, two corrective gradient models (CGMs) are compared in the simulation of multiphase flows. Linear consistency of the gradient model of moving particle semi-implicit (MPS) method has been recovered by introducing corrective matrix. However, it is found that particles tend to disperse along the streamline while using the CGM proposed in a previous study. Particle shifting (PS) schemes are necessary to reduce the irregularity of particle distribution to stabilize the calculation. To enhance the accuracy and stability, another CGM with dummy particle (CGMD) was proposed in our previous study. This enhanced CGM is featured by linear consistency and purely repulsive pressure gradient force. In this study, this enhanced CGM is modified and applied to multiphase flow simulation. Comparative study suggests that the modified CGM with PS scheme is capable of calculating various multiphase flows and predicting the interface evolution both clearly and accurately.     

Effect of system rotating on turbulent boundary layer flow

This paper experimentally investigated the effect of rotating on the turbulent boundary layer flow using hot-wire. The experiments were completed in a rotating rig with a vertical axis and four measured positions along the streamwise direction in channel, which focuses on the flow flied in the rotating channel. The rotating effects on velocity profile, wall shear stress and semi-logarithmic mean velocity profile are discussed in this paper. The results indicated that: due to the Coriolis force induced by rotating, the phenomenon of velocity deficit happens near the leading side. The velocity deficit near the leading side, do not increase monotonically with the increase of Ro. The trend of the velocity deficit near the leading side is also affected by the normal component of pressure gradient, which is another important force in the cross-section of the rotating channel. The wall shear stress near the trailing side is larger than that on the leading side, and the semi-logarithmic mean velocity profile is also different under rotating effects. The phenomenon reveals that the effect of rotation penetrates into the logarithm region, and the flow near the leading side tends to turn into laminar under the effect of rotation. The rotation correction of logarithmic law is performed in current work, which can be used in the wall function of CFD to increase the simulating accuracy at rotating conditions.     

MOTION OF THE DAMPED FOUCAULT PENDULUM

本文建立运动方程,得到了阻尼傅科摆的解析解,并对解的性质进行了一些探究.文中建立的模型是在理想单摆的基础上增加了科里奥利力和与速度成正比的阻尼力.