复合材料环向缠绕飞轮轮体工艺应力研究

在平面应力微分方程中考虑温度影响,可以得到复合材料轮体在制造和使用过程中更真实的应力应变情况。计算结果表明常规固化降温过程产生的应力足以使厚壁圆筒开裂。为解决复合材料环向缠绕飞轮在固化以及旋转时径向强度不足的难题,文中提出采用纤维加力缠绕施加径向压预应力,配合及时在线电子束固化的新工艺方法。将新方法中的加力缠绕过程等效为薄层过盈配合,统一加力缠绕和过盈配合两种制造方法以及后续升降温和旋转等工况下的计算问题。最后编制Matlab程序,给出算例,结果表明新工艺方法对径向应力改善明显。     

用瞬时转速图诊断各缸工作不均匀性故障

本文研究了一种在内燃机与配套装置运行中诊断各缸工作不均匀性故障的方法,介绍了用瞬时转速图形诊断各缸工作不均匀性故障的原理,进行了理论分析与计算。作者在6102柴油机上实测了各缸工作正常及工作不均匀时的瞬时转速图,实测与计算的图形十分吻合,验证了这一方法的可用性。     

Study of the mechanisms of the flame propagation and stabilization in porous media

The CH4/air premixed gas combustion processes in porous media were numerically studied using the two-temperature reacting fluid model with dispersions and detailed chemical reaction mechanism GRI 3.0. The mechanisms of the propagation and stabilization of submerge flames and surface flames in porous media were illuminated distinctly by considering the magnitude of the terms in the two energy equations, analyzing the sensibility of flame propagation speed to flame location, heat exchange coefficient between gas and solid, thermal conductivity and radiative extinction coefficient of porous media. It was concluded that the propagation mechanism of a submerged flame is similar to that of a free flame with an additional preheat zone and that the surface-flame propagation mechanism in porous media is similar to that of a free flame with heat loss in reaction zone. Supported by the National Natural Science Foundation of China (Grant No. 50376060)     

Synthesis of zinc oxide nanocrystals by thermal decomposition of Zn-oleate in organic medium

We report the synthesis of uniform-sized hexagonal ZnO nanocrystals by the thermolysis of Zn-oleate complex, which was prepared from the reaction of inexpensive and environmentally friendly reagents such as zinc nitrate and sodium oleate. Two organic compounds with different boiling points, octadecene and octylether, were selected as the medium for thermolysis of Zn-oleate complex. Under optimized reaction conditions, we were able to synthesize ZnO nanoparticles with the size being about 10 nm. X-ray diffraction and transmission electron micrograph (TEM) images confirmed the high crystallinity of the nanocrystals.     

汽车主减速比的优化设计

本文在汽车发动机、整车参数、部分传动系参数等确定的基础上,建立了以汽车燃油经济性为目标函数、动力性为约束条件的优化选择主传动比的数学模型。采用随机试验优化方法编制了计算机程序,而后在微机上计算了几种常见的车型,得到比较满意的结果。     

Decorating multiwalled carbon nanotubes with zinc oxide nanoparticles by thermally decomposing Zn-oleate in an organic medium

Carbon nanotubes decorated with zinc oxide nanoparticles were produced by thermally decomposing a Zn-oleate complex in an octadecene medium. The structure of the ZnO decorating nanotube surfaces was characterized by transmission electron microscopy, scanning electron microscopy and X-ray diffraction. The surfaces were shown to be densely and homogeneously covered by ZnO nanoparticles with a size below 10 nm. The nanoparticles had the wurtzite hexagonal crystal structure and showed good adhesion to the nanotubes. The carbon nanotubes decorated by metal oxide nanoparticles were synthesized at relatively low temperature and non-oxidation environment. Moreover, the large-scale production with low cost can be realized.     

Numerical study of methane/air jet flame in vitiated co-flow using tabulated detailed chemistry

Two different combustion models, the autoignition (AI) model and flamelet/progress variable (FPV) model, have been applied to study the auto-ignition process of methane/air jet flame in vitiated co-flow. A priori study was conducted to test the validity of the two models. Results show that the different range of predicted reaction rates is mainly responsible for their different performances in large eddy simulation (LES) studies. In this paper, beta PDF was used to model the mixture fraction distribution, while two different shapes of PDF, delta function and beta function, were applied for the reaction progress. Compared to the FPV model, the AI model combined with beta function for reaction progress could capture the auto-ignition process and predict the exact lifted height. Also the results indicate that the variance of reaction progress plays an important role in predicting the flame lifted height.     

硫化氢环境中低周疲劳裂纹扩展速率的研究

针对高强钢在硫化氢环境中腐蚀疲劳数据极为缺乏的现状,研究高压气瓶材料4130X在硫化氢腐蚀介质中的疲劳裂纹扩展速率.结合气瓶实际运行的环境和应力状态,应用改进型WOL(wedge-opening-loading)试样,在自行改造的专用低周腐蚀疲劳试验机上,完成0.006 7 Hz超低频率下饱和H_2S溶液、中等浓度H2S溶液和空气三种环境下的腐蚀疲劳试验,并用Paris公式进行两段式拟合,得出da/dN-ΔK的数学表达式.将试样微观断口的变化与宏观应力强度因子K的变化进行对比研究,给出不同环境中三个阶段K值的定量结果.结果表明:相同条件下,H_2S环境中的疲劳裂纹扩展速率比空气环境中大20倍以上;但当H_2S浓度达到一定范围后,对da/dN影响并不按比例增长,浓度相差11倍时,da/dN相差2.4倍,H_2S腐蚀介质的存在加速了疲劳破坏.     

LTE自组织网络MRO功能浅析

随着LTE网络规模的不断扩大,网络中存在的异常切换次数也逐渐增多。本文主要针对SON中的MRO功能及其实现方法进行了详尽的论述,并通过现网验证,优化后网络KPI指标有所提升,异常切换比例下降。     

Large eddy simulation of unconfined turbulent swirling flow

Large eddy simulations(LES) were performed to study the non-reacting flow fields of a Cambridge swirl burner. The dynamic Smagorinsky eddy viscosity model is used as the sub-grid scale turbulence model. Comparisons of experimental data show that the LES results are capable of predicting mean and root-mean-square velocity profiles. The LES results show that the annular swirling flow has a minor impact on the formation of the bluff-body recirculation zone. The vortex structures near the shear layers, visualized by the iso-surface of Q-criterion, display ring structures in non-swirling flow and helical structures in swirling flow near the burner exit. Spectral analysis was employed to predict the occurrence of flow oscillations induced by vortex shedding and precessing vortex core(PVC). In order to extract accurately the unsteady large-scale structures in swirling flow, a three-dimensional proper orthogonal decomposition(POD) method was developed to reconstruct turbulent fluctuating velocity fields. POD analysis reveals that flow fields contain co-existing helical and toroidal shaped coherent structures. The helical structure associated with the PVC is the most energetic dynamic flow structure. The latter toroidal structure associated with vortex shedding has lower energy content which indicates that it is a secondary structure.