电冰箱仿真计算研究概述

电冰箱仿真计算不仅可以缩短产品开发周期,而且也是提高系统效率和实现环保制冷剂替代研究的重要手段.本文概述了国内外冰箱仿真计算的研究进展,以及冰箱系统和各部件的仿真建模方法,并指出了目前冰箱仿真研究存在的问题和今后的发展方向.     

充液管路系统中阀门流噪声的研究

用二方程模型封闭的雷诺平均N-S方程组,对水管路系统中三种常见阀门的三维分离流动进行数值模拟.模拟结果表明,随着蝶阀、闸阀和球阀开度的减小,流体在蝶阀背面、球阀阀门内外分别形成两个方向相反的漩涡,闸阀的漩涡出现在挡板与管道的壁角处,并且漩涡在阀门下游逐渐消失.同时实验表明,阀门下游的流噪声大于阀门上游的流噪声,涡声是阀门噪声的主要来源.     

爆破振动信号的时频分析

爆破振动信号的研究方法已由单纯的频域分析过渡到时频联合分布分析。在讨论FOURIER变换(FT)和短时 FOURIER变换(STFT)不足的基础上,论述了基于连续小波变换(CWT)和离散小波变换(DWT)在爆破振动信号分析中的应用。作为一种严格的时频分析方法,论文尝试利用二次型时频分布来进行爆破振动信号的时频联合分析;通过几种二次型时频分布的对比分析,认为CWD在具有较强的时频聚集性的同时又较好的对交叉项进行了抑制,适合于进行爆破振动信号的时频分析。     

高能球磨制备15% SiC/2009 Al复合材料的微观组织与断裂行为

利用高能球磨法制备了15％SiC／2009 Al复合材料。结果表明，基体合金内具有明显的位错胞与亚结构，平均品粒尺寸约为3～4μm。对复合材料挤压棒材分别在25，150，200，315，400℃下测试了拉伸力学性能：复合材料在150℃下还能保持较高的拉伸强度-断口形貌表明，在低温下孔洞首先在界面附近的基体合金内形成，而高温下孔洞可以在整个基体合金区域形成。     

非化学计量一氧化钛的颜色研究

在确定非化学计量一氧化钛氧指数范围的基础上，研究了其颜色及其随氧指数的变化规律，并比较了其颜色与现用仿金材料之间的优劣。结果表明，在整个氧指数范围内一氧化钛均呈金黄色；随着氧指数的增大，在可见光作用下，对波长350．550nm范围内的紫、蓝和绿光反射逐渐减弱，对波长650-780nm范围内的红、橙光反射逐渐增强，其颜色从浅金黄色稍带白青色至纯正金黄色，最后至金黄色偏红；氧指数在1．14-1．16范围内其颜色最接近金黄，TiO1.15与24KAu色度差仅为0．0044，较仿金铜、TiN的颜色与24K黄金更为接近。     

百分百的设计，百分百的伦敦

九月中的伦敦，空气中充满了设计的气息，一年一度的伦敦设计艺术节如期进行，这个为期两周的设计节成为全球广大设计爱好者，专业人员，厂商的嘉年华会。他们繁忙地游走于遍布全球大大小小的展览会场，抢先观看新产品的发布，把握展出的机会 ，让自己的作品一鸣惊人，又或者能亲眼目睹明日之星的诞生……所有的一切都让人兴奋不已，乐此不疲地投入这个欢乐的设计盛宴。     

Multiscale Analysis of Fracture of Carbon Nanotubes Embedded in Composites

Due to the enormous difference in the scales involved in correlating the macroscopic properties with the micro- and nano-physical mechanisms of carbon nanotube-reinforced composites, multiscale mechanics analysis is of considerable interest. A hybrid atomistic/continuum mechanics method is established in the present paper to study the deformation and fracture behaviors of carbon nanotubes (CNTs) in composites. The unit cell containing a CNT embedded in a matrix is divided in three regions, which are simulated by the atomic-potential method, the continuum method based on the modified Cauchy–Born rule, and the classical continuum mechanics, respectively. The effect of CNT interaction is taken into account via the Mori–Tanaka effective field method of micromechanics. This method not only can predict the formation of Stone–Wales (5-7-7-5) defects, but also simulate the subsequent deformation and fracture process of CNTs. It is found that the critical strain of defect nucleation in a CNT is sensitive to its chiral angle but not to its diameter. The critical strain of Stone–Wales defect formation of zigzag CNTs is nearly twice that of armchair CNTs. Due to the constraint effect of matrix, the CNTs embedded in a composite are easier to fracture in comparison with those not embedded. With the increase in the Young’s modulus of the matrix, the critical breaking strain of CNTs decreases.     

Fabrication of transparent La2Hf2O7 ceramics from combustion synthesized powders

Transparent La₂Hf₂O₇ (LHO) ceramics were, for the first time, successfully fabricated from combustion-synthesized powders. Nanosized La₂Hf₂O₇ powders were obtained through combustion reaction, using glycine or EDTA as a fuel. The as-made powders were isostatically pressed at 180 MPa and then sintered at 1850 °C for 6 h in hydrogen atmosphere. The resulting ceramics have high optical transmittance.     

Effect of annealing ambient on structure and ferroelectric properties of Pb(Zr0.4Ti0.6)O3 thin films on LaNiO3 coated Si substrates

Pb(Zr_0.4Ti_0.6)O₃ [PZT(40/60)] thin films were deposited onto LaNiO₃ (LNO) coated Si substrates by sol-gel technique. Three kinds of gases, air, O₂ and N₂, were used as the annealing ambient. The effect of the annealing ambient on their structure and ferroelectric properties was investigated. The results showed that both the films annealed in air and O₂ were the complete perovskite phase with (1 0 0) preferential orientation, while those annealed in N₂ were random orientation including some pyrochlore phases. As compared with the air ambient, either too much O₂ or too much N₂ was detrimental to the ferroelectric properties of PZT films. The difference in structure and ferroelectric properties was mainly associated with the intermediate phases and the concentration of domain pinning centers in the films.     

Structural and ferroelectric properties of La modified Sr0.8Bi2.2Ta2O9 thin films

La modified SBT (Sr_0.8La_0.1Bi_2.1Ta₂O₉) thin films of different thickness were fabricated on Pt/Ti/SiO₂/Si substrates by the metalorganic decomposition technique. All the films were annealed layer-by-layer at 800 °C using a rapid thermal annealing furnace. X-ray diffraction analysis indicated that the relative intensity of the (2 0 0) diffraction peak [I(2 0 0)/I(1 1 5)] increased with the increase of the film thickness. Eventually, an a-axis preferentially oriented SLBT film was obtained. These results are discussed with respect to the anisotropy of the grain growth. The a-axis preferentially oriented SLBT film, whose relative intensity of the (2 0 0) peak [I(2 0 0)/I(1 1 5)] was 1.05, had a remanent polarization (2P_r) value of 21 μC/cm² and a coercive field (2E_c) value of 70 kV/cm under the electric field of 200 kV/cm.