声辐射阻测量系统设计及测量精度影响因素分析*

在噪声控制领域,声辐射阻是一个重要的声学变量,在产品的设计阶段,可以通过改变结构表面形状来改变结构的声辐射阻抗,从而达到降噪的目的。本文基于集中参数模型,设计了测量设备,搭建了实验测量系统,并通过对无限大障板上圆形活塞声源的声辐射阻的测量对影响实验测量结果的因素进行了研究,之后对消音器入口处辐射阻进行了测量。测量结果表明:该实验测量系统具有操作简单,测量方便快捷,测量结果精度高等特点,可用于确定结构表面声辐射阻矩阵。     

螺桨盘转子轴头动刚度实验测量方法及技术处理

在螺桨盘转子系统的颤振涡动研究中,系统的安装刚度对转子的颤振涡动失稳有着重要的作用.对于飞机发动机,实际安装情况十分复杂,发动机短舱.安装节、机翼等对螺桨盘转子的运动均有影响.所以,在颤振涡动研究中,必须考虑轴头的动刚度.轴头的动刚度是通过动柔度转换而来的,而在动柔度的实验测量中必须解决几个技术问题,首先是提高信噪比.其次是消除工艺夹具带来的附加质量和附加转动惯量的影响,从而提高动刚度系数的测量精度.本文通过对模型转子以及某实际桨轴发动机转子轴头动刚度系数的测量及处理,阐述轴头动刚度矩阵的测量方法,以及有关技术问题的处理过程.     

弹性约束梁参数失稳分析的离散奇异卷积法

针对具有重要的学术价值和工程意义的弹性约束梁在动轴向载荷作用下的参数失稳问题,本文采用离散奇异卷积法对其进行研究。在离散奇异卷积法中,采用正则化的Shannon核进行空间离散,同时采用四阶龙格-库塔法进行时间离散。在采用界面与边界匹配技术处理弹性边界条件后,计算了四种不同弹性约束梁的参数失稳区。研究结果表明:计算结果和采用假定模态法得到的结果基本一致,从而说明了采用离散奇异卷积法求解弹性约束梁的参数失稳问题是可行和有效的;同时采用离散奇异卷积法可以更加准确地处理具有较大轴向力时的结构参数失稳问题。     

氧化镧掺杂对氧化锡粉体特性及气敏性的影响

利用高能球磨工艺,制备了不同氧化镧掺杂量的氧化锡粉体.研究了粉体的比表面积、微观形貌和物相结构,测试了镧掺杂前、后氧化锡粉体的本征电阻及其对乙醇的气敏性能.结果显示:随氧化镧掺杂量增加,氧化锡衍射峰沿2θ升高方向偏移,偏移程度先增大后恢复到原位置;对乙醇气体灵敏度先减小后增大.当氧化镧掺杂量为1.5;时,氧化锡衍射峰偏移最大,掺杂氧化锡粉体比表面积最大,掺杂氧化锡颗粒最小,电阻最低,对乙醇的灵敏度最低.说明氧化镧掺杂改善了氧化锡粉体对乙醇的气敏选择性.     

微极性流体在上下正交移动的渗透平行圆盘间的流动

分析了上下正交运动的两平行圆盘间的非稳态的不可压缩的二维微极性流体的流动．应用von Krmn类型的一个相似变换,偏微分方程组(PDEs)被转化成一组耦合的非线性常微分方程(ODEs)．应用同伦分析方法,得到方程的解析解,并且详细讨论了不同的物理参数,像膨胀率,渗透Reynolds数等,对流体的速度场的影响．     

Silica nano-rings and nano-hollows: Preparation and UV photoluminescence emission

By annealing fused silica coated with ultra-thin Ag film, silica nano-rings and nano-hollows were prepared on the substrate. The Ag nano-particles attached on the wall of nano-hollows or embedded in silica were confirmed with energy dispersive spectroscopy and transmission electron microscopy. Besides the well-known characteristic stretching bands of silica, three novel stretching bands around 1579, 1320 and 270 cm^?1 were found in the annealed Ag-coated silica by Raman scattering spectroscopy, which have been attributed to the O₂ in ground state, O–O and metal–oxygen stretching bands, respectively. The formation mechanism of nano-rings and nano-hollows has been discussed based on the experimental results. An ultraviolet photoluminescence emission of 360–370 nm from annealed Ag-coated silica was found when the excitations were 230 nm and 280 nm or longer. The possible photoluminescence emission mechanism has been discussed, which suggests that oxygen excess defects are responsible for the photoluminescence emission, and photoexcitation occurs in the silica as well as in Ag⁺ ions.     

Microstructure and field emission properties of the Si–TaSi2 eutectic in situ composites by electron beam floating zone melting technique

The directionally solidified Si–TaSi₂ eutectic in situ composites, which have highly aligned and uniformly distributed TaSi₂ fibers embedded in the Si continuous matrix, are obtained by electron beam floating zone melting (EBFZM) technique at the solidification rate range 0.3–9.0 mm/min. The preferential orientation of the Si–TaSi₂ eutectic is also studied by selected area electron diffraction (SAED), which is [0 1¯ 1¯]Si∥[0 0 0 1]TaSi₂ and (0 1¯ 1)Si∥(0 1¯ 1 1)TaSi₂. Moreover, field emission properties of the Si–TaSi₂ eutectic in situ composites are investigated by transparent anode imaging technology. Approximately straight F–N curves show that this material has excellent field emission properties.     

D301大孔树脂吸附钒(V)的性能研究

研究了D301大孔树脂对钒的吸附性能.结果表明,pH值对D301树脂吸附钒的影响很大,与钒在溶液中的赋存状态有关,且在pH=2时吸附效果最好:测得吸附热力学参数分别为:△H=8.97kJ/mol,△G_(313)=-5.69kJ/mol,△G_(303)=-5.2kJ/mol,△G_(293)=-4.9kJ/mol,△S=46.84J/mol·K.等温吸附服从Freundlich经验式;考察了溶液浓度、搅拌速率对交换过程的影响,并对实验数据运用相关理论模型进行拟合,结果显示钒(V)在D301树脂上吸附交换过程控制步骤为颗粒扩散控制,反应级数n为0.2391.     

最小二乘问题的稳定近似解

最小二乘法在实际中有着大量的应用,为解决其结果易受误差影响的问题,利用试验设计的思想,借助正交表得到了其稳定近似解的求解方法,使结果得以改进,并通过实例予以验证.     

Ag3PO4/ZnO复合粉体制备及其可见光催化性能

室温下,以ZnO粉体、Na2HPO4、AgNO3和聚乙烯吡咯烷酮为原料,成功制备出了系列Ag3PO4/ZnO复合粉体.采用X射线衍射仪、扫描电子显微镜和紫外-可见光谱仪分别对复合粉体的物相、形貌和可见光吸收性能进行了表征.研究了不同摩尔比的Ag3PO4/ZnO复合粉体的光催化性能.结果表明:当ZnO和Ag3PO4摩尔比约为1:1时,所得的Ag3PO4/ZnO复合粉体对罗丹明B染料的可见光催化效果最好,降解率达到99;.