纳米通道内气体剪切流动的分子动力学模拟

采用分子动力学模拟方法研究了表面力场对纳米通道内气体剪切流动的影响规律.结果显示通道内的气体流动分为两个区域:受壁面力场影响的近壁区域和不受壁面力场影响的主流区域.近壁区域内,气体流动特性和气体动力学理论预测差别很大,密度和速度急剧增大并出现峰值,正应力变化剧烈且各向异性,剪切应力在距壁面一个分子直径处出现突变.主流区域的气体流动特性与气体动力学理论预测相符合,该区域内的密度、正应力与剪切应力均为恒定值,速度分布亦符合应力-应变的线性响应关系.不同通道高度及密度下,近壁区域的归一化密度、速度及应力分布一致,表明近壁区域的气体流动特性仅由壁面力场所决定.随着壁面对气体分子势能作用的增强,气体分子在近壁区域的密度和速度随之增大,直至形成吸附层,导致速度滑移消失.通过剪切应力与切向动量适应系数(TMAC)的关系,得到不同壁面势能作用下的TMAC值,结果表明壁面对气体分子的势能作用越强,气体分子越容易在壁面发生漫反射.

基于微观弹流润滑的滚动轴承相对疲劳寿命分析

为了研究微观弹流润滑条件下粗糙表面的表征参数对滚动轴承相对疲劳寿命的影响,采用二维数字滤波方法生成了三维的随机粗糙表面,使用多重网格法求解了考虑三维随机粗糙表面的等温弹流润滑的表面力场,使用ANSYS求解了次表面应力场,以滚动轴承的单个接触副为研究对象,基于Zaresky的应力寿命模型,在弹流润滑的工况下,研究了粗糙表面的均方根值,偏度,峰度及纹理对滚动轴承相对疲劳寿命的影响。研究得到了在弹流润滑工况下均方根值、偏度、峰度及纹理与滚动轴承相对疲劳寿命的关系曲线,可为考虑粗糙表面特性时滚动轴承寿命的修正提供参考。

Experimental study on preferential solution flow during dump leaching of low-grade ores

The phenomenon of preferential solution flow during dump leaching of low-grade ores was studied.The formative mechanism of preferential solution flow was investigated through analyzing the relationship between permeability and ore diameter,and the relationship between surface tension and ore diameter.The preferential solution flow happened within the fine ore area when the dump was unsaturated.And it could happen within the coarse ore area when the dump became saturated.The results of experiment show that the outflow of coarse ore area increases sharply with higher applied rate.The outflow of fine ore area is greater than that of coarse ore area when the applied rate is below 3.2 L/min,and the preferential solution flow happens in fine ore area.But the preferential solution flow happens in coarse ore area when the applied rate is higher than 3.2 L/min.The result of the experiment is consistent with the mechanism analyzing.

A DYNAMICAL INTERPRETATION OF THE WIND FIELD IN TROPICAL CYCLONES

Based on the primitive equations in polar coordinates and with the supposition that parcel velocity in tropical cyclones is in linear variation and that the distribution of surface pressure agrees with the Fujita formula, a set of equations are derived, which describe the impact of perturbations of central pressure, position of tropical cyclones, direction and velocity of movement of tropical cyclones on the wind field. It is proved that the second order approximation of the kinetic energy of tropical cyclones can be described by the equations under linear approximation. Typhoon Wipha (2007) is selected to verify the above interpretation method, and the results show that the interpretation method of the wind field could give very good results before the landfall of tropical cyclones, while making no apparent improvement after the landfall. The dynamical interpretation method in this paper is applicable to improving the forecasts of the wind field of tropical cyclones close to the coast.

Simulation of droplet topography on superhydrophobic surface

We established a novel droplet model (with-gravity model) to show the gravity effect of the droplet in the contact angle experiment.By using with-gravity model, we obtained a three-dimensional topography of the droplet including the height of the droplet, the shape of the baseline and the circumference of the baseline.Comparing the with-gravity model with the ideal spherical model, our model considered the measurement error caused by gravity effect in the contact angle experiment which is a key point to influence the three-dimension topography of the droplet.From the calculation of our model, we found that there were two important points to enhance the measurement error: the size of the droplet and the contact angle.With the droplet and the contact angle became larger, measurement error was obviously increased.

Increase in Probability of the Correct Forecast of Tsunami Formation

The presented paper exhibits theory of the ＂gravitational＂ waves propagation near the Earth surface and in the ocean. There was determined an expression ＂gravitational＂ wave which was registered by the gravimeters being placed in several points of the Earth globe. Alteration of gravitational field was accompanied by alteration of the ＂gravitational＂ wave which has the velocity differing from the velocity of seismic waves. The theoretical model was proved by many experiments realized under registration of the underwater earthquake core by tens of gravimeters being placed in the Earth globe different points. The ＂gravitational＂ waves assist to increase the right forecast probability of the beginning tsunami to 50%.

Phase Field Simulation of Intragranular Microvoids Evolution Due to Surface Diffusion in Stress Field

Based on the bulk free energy density and the degenerate mobility constructed by the quartic double-well potential function,a phase field model is established to simulate the evolution of intragranular microvoids due to surface diffusion in a stress field.The corresponding phase field governing equations are derived.The evolution of elliptical microvoids with different stressesΛ,aspect ratiosβand linewidths hˉis calculated using the mesh adaptation finite element method and the reliability of the procedure is verified.The results show that there exist critical values of the stressΛc,the aspect ratioβc and the linewidth hˉc of intragranular microvoids under equivalent biaxial tensile stress.When Λ≥Λ_(c),β≥β_(c) or h≤h_(c),the elliptical microvoids are instable with an extending crack tip.WhenΛ<Λ_(c),β<β_(c) or hˉ>h_(c),the elliptical microvoids gradually cylindricalize and remain a stable shape.The instability time decreases with increasing the stress or the aspect ratio,while increases with increasing the linewidth.In addition,for the interconnects containing two elliptical voids not far apart,the stress will promote the merging of the voids.

Molecular dynamics simulation study on behaviors of liquid 1,2-dichloroethane under external electric fields

Molecular dynamics simulation was carried out to study the behavior of liquid 1,2-dichloroethane molecules under external electric fields including direct current field, alternating current field and positive-half-period cosin field. The maximum applied field strength was 10^8 V/m , the maximum frequency of the alternating current field and that of the positive-half-period cosine field was 10^12 Hz . The simulation revealed that the field type and field strength act on the population of the molecular configuration. In the strong direct current field, all trans forms converted completely into gauche forms. Order parameter and the correlation of the system torsion angle were also investigated. The results suggested that these two dynamical parameters depended also on the field type and the field strength. The maximum of order parameter was found to be at 0.6in the strong direct current field.

Surface Breakdown of Printed Circuit Board under Magnetic Field with Reduced Pressure

Epoxy resin laminate onto which a pair of copper foil was printed was employed as test samples.The samples were placed in an artificial atmospheric chamber, which was vacuumed by a rotary pump from 100 kPa to 5 kPa.The magnetic field was produced by permanent magnets that were assembled to make E×B drift away from, into and parallel to the sample surface, respectively.Magnetic flux density was adjusted at 120 mT, 180 mT and 240 mT respectively.By applying a negative bias voltage between the electrodes, the ...

Molecular Dynamics Study of Hydrogen Dissociation on Pd Surfaces using Reactive Force Fields

Developing a widely-used reactive force field is meaningful to explore the fundamental reaction mechanism on gas-surface chemical reaction dynamics due to its very high computational efficiency. We here present a study of hydrogen and its deuterated molecules dissociation on Pd surfaces based on a full-dimensional potential energy surface （PES） constructed by using a simple second moment approximation reactive force field （SMA RFF）. Although the descriptions of the adsorbate-substrate interaction contain only the dissociation reaction of H2/Pd（111） system, a good transferability of SMA potential energy surface （PES） is shown to investigate the hydrogen dissociation on Pd（100）. Our simulation results show that, the dissociation probabilities of H2 and its deuterated molecules on Pd（111） and Pd（100） surfaces keep non-monotonous variations with respect to the incident energy Ei, which is in good agreement with the previous ab initio molecular dynamics. Furthermore, for the oriented molecules, the dissociation probabilities of the oriented H2 （D2 and T2） molecule have the same orientation dependence behavior as those oriented HD （HT and DT） molecules.

Analysis of residual gas disturbance on the inner satellite of Inner Formation Flying System

The Inner Formation Flying System （IFFS） consisting of an freely flying in the shield cavity can construct a pure gravity outer satellite and an inner satellite which is a sphere proof mass orbit to precisely detect the earth gravity field. The residual gas in the cavity is a significant disturbance source due to the temperature inhomogeneity and relative motion of the inner satellite. The expressions of the disturbance forces were derived based on the property of rarefied gas, including the radiometer effect and the damping force. According to the current design of IFFS, heat transfer analysis of the cavity and the inner satellite was carried out, and the surface temperature distribution of the cavity and the inner satellite was given. The relative motion of the inner satellite was obtained from the formation control simulation of IFFS. Then the residual gas disturbance was calculated. The disturbance acceleration acting on the inner satellite due to the radiometer effect was on the order of 10^-11 m s^-2 and the damping acceleration was on the order of 10^-15 m s^-2.

Shape and gravitational field of the ellipsoidal satellites

The shape and gravitational field of ellipsoidal satellites are studied by using the tidal theory. For ellipsoidal satellites, the following conclusions were obtained: Firstly, in the early stage of the satellite formation, strong tidal friction allowed the satellites move in a synchronous orbit and evolve into a triaxial ellipsoidal shape. Because the tidal potential from the associated primary and the centrifugal potential from the satellite spin are nearly fixed at the surface, the early satellites are the viscoelastic celestial body, and their surfaces are nearly in the hydrostatic equilibrium state. The deformation is fixed in the surface of the satellite. By using the related parameters of primary and satellite, the tidal height and the theoretical lengths of three primary radii of the ellipsoidal satellite are calculated. Secondly, the current ellipsoidal satellites nearly maintain their ellipsoidal shape from solidification, which happened a few billion years ago. According to the satellite shape, we estimated the orbital period and spinning angular velocity, and then determined the evolution of the orbit. Lastly, assuming an ellipsoidal satellite originated in the hydrostatic equilibrium state, the surface shape could be determined by tidal, rotation, and additional potentials. However, the shape of the satellite's geoid differs from its surface shape. The relationship between these shapes is discussed and a formula for the gravitational harmonic coefficients is presented.