用渐近变分法对复合材料层合板简化数值建模及仿真

为有效分析三维复合材料层合板非线性、单向耦合弹性问题,基于渐近变分方法构建单斜对称的复合材料层合板的简化模型。推导了基于旋转张量分解概念的复合材料层合板能量表达式;利用渐近变分法将三维层合板严格拆分为二维板分析和沿法线方向的一维非线性分析;进行了降维后近似能量推导及reissner形式转换;提供了三维场重构关系以得到沿厚度方向的准确应力分布。通过对一具有四层复合层合板的柱形弯曲算例表明:基于该理论和重构过程开发的渐近变分程序VAPAS重构生成的三维应力场精确性较古典层合理论更好,与三维有限元精确解相一致。     

Nd~(3+)的稳定能与晶场参数及磁交换作用的关系

基于单离子模型,通过对Nd3+磁晶各向异性哈密顿数值的求解,研究了温度趋于0 K时,Nd3+离子稳定能与晶场参数及磁交换作用的关系.结果表明,对于强磁物质(如NdCo5,Nd2Co17,Nd2Fe14B等),Nd3+贡献的稳定能与晶场参数B20近似成正比,而对磁交换作用的变化不敏感.     

Parametric effects on the combustion flow field of a typical strut-based scramjet combustor

The flame-holding mechanism in hypersonic propulsion technology is the most important factor in prolonging the duration time of hypersonic vehicles.The two-dimensional coupled implicit Reynolds-averaged Navier-Stokes equations,the shear-stress transport k-ω turbulence model and the finite-rate/eddy-dissipation reaction models were used to simulate the combustion flow field of a typical strut-based scramjet combustor.We investigated the effects of the hydrogen-air reaction mechanism and fuel injection temperature and pressure on the parametric distributions in the combustor.The numerical results show qualitative agreement with the experimental data.The hydrogen-air reaction mechanism makes only a slight difference in parametric distributions along the walls of the combustor,and the expansion waves and shock waves exist in the combustor simultaneously.Furthermore,the expansion wave is formed ahead of the shock wave.A transition occurs from the shock wave to the normal shock wave when the injection pressure or temperature increases,and the reaction zone becomes broader.When the injection pressure and temperature both increase,the waves are pushed out of the combustor with subsonic flows.When the waves are generated ahead of the strut,the separation zone is formed in double near the walls of the combustor because of the interaction of the shock wave and the boundary layer.The separation zone becomes smaller and disappears with the disappearance of the shock wave.Because of the horizontal fuel injection,the vorticity is generated near the base face of the strut,and this region is the main origin for turbulent combustion.     

Enhanced anti-sunward flow near local noon during a period of horizontal IMF and high solar wind velocity <Emphasis Type="Italic">V</Emphasis><Subscript><Emphasis Type="Italic">Y</Emphasis></Subscript>

It is believed that a southward interplanetary magnetic field (IMF) is mainly responsible for the energy input from solar wind into the magnetosphere. This paper presents an unusual case of strong anti-sunward plasma flow (up to 2 km/s) in the polar cap ionosphere and large cross-polar cap potential (CPCP) during a period of horizontal IMF (|B _Z | < 2 nT) observed by both ACE (at the L1 point) and Geotail (on the dusk flank of the magnetosheath). The CPCP is even higher than that under preceding B _Z ≈ −23 nT. Furthermore, GOES8 observed that the magnetosheath field turns northward as the anti-sunward plasma flow and CPCP start to increase, which implies that the magnetosheath field interacting with the Earth’s magnetopause has significantly rotated and differs from the IMF observed by ACE and Geotail. In accordance with previous theoretical work, we suggest that the magnetic field line draping produces a southward magnetosheath field and enhances anti-sunward plasma flow and the CPCP.     

Statistical models for intensity and phase fluctuation of laser light in a turbulent medium

The probability density function of irradiance fluctuations in a turbulent atmosphere remains an open topic of research.It is generally considered that the speckle field has an elliptical-Gaussian speckle distribution,but because of its complexity there is still no exact analytical solution.By introducing the concept of random fluctuation intensity and using an equiprobability density ellipse,exact models of the random fluctuation intensity and its phase are proposed.Through theoretical analysis and numerical simulation,it is concluded that the random fluctuation intensity and its corresponding phase are independent only under the circular-Gaussian approximation.     

Optimization of flue gas turbulent heat transfer with condensation in a tube

Conservation equations for sensible and latent entransy are established for flue gas turbulent heat transfer with condensation in a tube, and the entransy dissipation expression is deduced. The field synergy equation is obtained on the basis of the extremum entransy dissipation principle for flue gas turbulent heat transfer with condensation. The optimal velocity field is numerically obtained by solving the field synergy equation. The results show that the optimal velocity field contains multiple longitudinal vortices near the tube surface. These improve the synergy not only between the velocity and temperature fields but also between the velocity and vapor concentration fields. Therefore, the turbulent heat and mass transfers are significantly enhanced.     

Phase field simulation of interatomic potentials for double phase competition during early stage precipitation

Phase field model was employed to study the variations of interatomic potentials of Ni 3 Al (L1 2 phase) and Ni 3 V (DO 22 phase) as a function of temperature and concentration. The long-range order (LRO) parameter related interatomic potentials equations formulated by Khachaturyan were utilized to establish the inversion equations for L1 2 and DO 22 phases, with which interatomic potentials could be calculated. The interatomic potentials of Ni-Al and Ni-V exhibited approximately linear increases and decreases, individually, with enhanced Al concentration. Substituting the inverted interatomic potentials into the microscopic phase field equations led to three cases of precipitation sequence: the DO 22 phase preceded L1 2 phase precipitating at the interatomic potentials of Ni-V > Ni-Al; the vice cases; and two phases precipitated simultaneously at interatomic potentials of Ni-V and Ni-Al were equal.     

Mineralogical and geochemical features of sulfide chimneys from the 49°39′E hydrothermal field on the Southwest Indian Ridge and their geological inferences

During January–May in 2007,the Chinese research cruise DY115-19 discovered an active hydrothermal field at 49°39′E/37°47′S on the ultraslow spreading Southwest Indian Ridge (SWIR).This was also the first active hydrothermal field found along an ultraslow-spreading ridge.We analyzed mineralogical,textural and geochemical compositions of the sulfide chimneys obtained from the 49°39′E field.Chimney samples show a concentric mineral zone around the fluid channel.The mineral assemblages of the interiors consist ...     

基于扫描电子显微镜的单根一维纳米材料原位场发射性能研究

基于扫描电子显微镜和纳米探针技术,展示了一维纳米材料原位场发射的测量方法和实例。实验以钨针尖为接收极,纳米材料为发射极,通过结合扫描电子显微镜的实时成像功能,纳米探针的精确操纵及电学测量技术以及激光辐照功能,系统研究了极间距离D、形貌变化、吸附气体和激光注入对单根多壁碳纳米管和氧化锌纳米线场发射性能的影响。结果表明,当D远小于纳米材料长度L的3倍时,D越小,开启场强和阈值场强越大,场发射性能越弱。此外,纳米线尖端曲率半径越大,场增强因子越小,场发射性能越弱。研究还发现O2的脱附和激光辐照有助于纳米材料场发射性能的提高。     

厚圆盘基频振动声场指向性

 指向性是描述声场特性的一个重要指标.因中厚盘弯曲振动的解析解难以得到,数值计算了3种边界条件下弯振厚圆盘基频振动下的辐射声场指向性.计算结果表明,对几何尺寸相同的厚圆盘,在基频振动模式下,固定边界下弯振厚圆盘辐射声场指向性最尖锐,简支居中,自由边界盘的辐射声场只有旁瓣,没有主瓣,指向性不好.与线度相同的薄圆盘相比,厚圆盘的指向性更加尖锐.