考虑喷注流强分布的纵向稳定性建模与分析

喷注器流强分布是除声学阻尼装置以外使液体火箭发动机稳定工作的重要措施,通过控制喷注流强分布使推进剂的燃烧尽量远离主要振型的波腹区,减少热声耦合振荡的能量源,从而达到抑制高频振荡的效果。因此,建立喷注流强分布与稳定性之间的综合分析模型,研究流强分布的不稳定性抑制特性具有重要实际意义。针对采用自击式喷嘴器、液滴蒸发作为燃烧速率控制过程的某自燃推进剂缩尺燃烧室高频纵向燃烧不稳定问题,近似采用蒸发速率峰值区代替集中燃烧释热区,引入燃烧室三维声学控制方程以考虑多喷嘴条件下燃烧响应空间分布,建立了针对喷注器流强分布条件下的高频纵向燃烧稳定性分析模型,并对喷注流强的稳定性抑制特性进行了分析,给出了不同分布流强下燃烧室一阶纵向信号的增长率变化规律。研究表明,喷注流强分布有利于燃烧室稳定,"驼峰区"喷注孔径的增大对改善高频纵向不稳定性更为显著,"驼峰区"流强增加30%,相应的增长率降低15%。     

Quality variation of GPS satellite clocks on-orbit using IGS clock products

Over 60% clocks on board of the GPS satellites are working longer than their designed life. Therefore realizing their stabilities in a long time scales is essential to GPS navigation and positioning plus IGS time scale maintaining. IGS clock products from 2001 to 2010 are used to analyze the GPS satellite clock qualities such as frequency stabilities and clock noise level. We find out that for the clocks of Block IIA satellites the frequency stabilities and clock noise are 10 times worse than that of the Block IIR and IIR-M satellites. Moreover, the linear relationships between frequency stabilities and clock residuals have been deduced with an accuracy of better than 0.02 ns. Specially, it is noticed that the clock of the PRN27 is instable and the relationship between the frequency stability and residuals is at least a quadratic curve. Therefore, we suggested that GPS satellite clocks should be weighted by their quality levels in application, and the observations of the Block IIA should not be used for real-time positioning which required precision better than one meter.     

复合材料帽形加筋结构稳定性研究

建立了复合材料帽形加筋结构的参数化有限元模型,给出了两种进行层板结合处的模拟计算方法,通过计算得到了模型的屈曲载荷并总结了加筋结构几何参数对结构稳定性的影响,给出了模型的收敛性分析,对比了模型网格密度对于计算结果的影响,找到最佳的网格密度,提高了模型计算的效率和准确性,为实际的结构设计提供了重要参考,为结构分析提供了依据。     

航空发动机多路模糊切换控制系统设计

针对航空发动机在不同控制通路切换过程中出现的转速等参数发生大幅度跳变以及系统不稳定的问题,提出了一种模糊切换控制方法,设计了基于不同结构控制通路的模糊切换控制器,基于无源性概念对航空发动机多路模糊切换控制系统进行了稳定性分析,得到了多路模糊切换控制系统稳定的充分条件。航空发动机模糊切换系统与直接切换系统仿真结果表明了航空发动机多路模糊切换控制方法的有效性。     

Investigation on Thermal and Dimensional Stability of Epoxy Resin In-Situ Modified by Cyanate Ester Resin and Polydimethylsiloxane

The thermal and dimensional stability of epoxy resin (EP) in-situ modified by cyanate ester (CE) and polydimethylsiloxane (PDMS) are investigated by means of experiments and numerical simulation. Thermal gravimetric analysis (TGA) and differential scanning calorimeter (DSC) are used to analyze the heat resistance of the modified EP. The dimensional stability is characterized by the volume shrinkage of the series PDMS/CE/EP obtained by the density method. The chemical structure of the PDMS/CE/EP is analyzed by Fourier transform infrared spectroscopy (FTIR). The results of TGA and DSC indicate that the thermal stability of PDMS/CE/EP decreases firstly and then increases with the increase in the amount of CE. The addition of PDMS shows a slight effect on the thermal stability. The 40% CE makes the blending system exhibit the lowest initial decomposition temperature, which reduces by 15.5% and 40.8% compared with pure EP and CE, respectively. The FTIR results suggested that the influence of CE on the thermal stability of the modified EP is mainly ascribed to the generation of oxazolidinone ring with low thermal stability and the increase in the triazine ring with high thermal stability. The volume shrinkage measurement results show that the introduction of CE and PDMS are both beneficial to the improvement of the dimensional stability of the blending systems. The in-situ addition of 80% CE shows the lowest volume shrinkage of 6.11%. The thermal stress distribution of PDMS/CE/EP generated during the solidification process is simulated by the finite element analysis. The results suggested that the introduction of 80% CE into EP results in the lowest thermal stress in the blending system, which indicates that the system has the lowest volume shrinkage, which agrees well with the experimental results.     

总压畸变在三级轴流压气机中的传递性能研究

介绍了一种计算进气畸变的方法.通过求解非稳态三维欧拉方程,计算压气机各截面气流参数分布.以74A三级压气机为例,进行了周向总压畸变传递特性计算,得到了压气机进口存在总压畸变时总压、静压、总温和流量系数在各截面上的分布规律,得出了畸变强度、畸变范围和畸变位置在轴向上的分布规律.      

气体减压阀的稳定性分析

针对逆向卸荷式气体减压阀,采用线性化分析方法,对其工作稳定性进行分析．得到了主要参数对减压阀稳定性的影响规律。研究结果表明阻尼和低压腔体积是影响减压阀稳定性的主要因素,并给出了提高减压阀稳定性设计的主要措施。     

基于线性稳定性理论的转捩控制试验

 使用线化稳定性理论研究了某后掠机翼试验模型在风洞试验条件下可能的试验结果。在当前试验条件下,三维边界层中横流驻波的不同波长扰动发展趋势不同,根据理论分析和数值计算给出了最大放大率波长为4.0 mm。通过升华法试验验证了理论分析与数值计算结果。在试验中使用丝网印刷技术在后掠机翼前缘添加粗糙带,成功地引入了理论计算的最大放大率波长。根据预期影响了三维边界层的转捩。     

无铰旋翼变截面盒型梁桨叶气弹动力学多目标优化

基于有限元法建立了无铰旋翼变截面盒型梁桨叶的挥舞/摆振气弹稳定性优化分析模型,提出了多目标、多约束条件下的灵敏度分析方法,采用遗传优化算法(Non-dominated sorting geneti calgorithm-NSGA-Ⅱ),实现了盒型梁桨叶气弹稳定性条件下多约束、多目标优化.最后完成了实例模型旋翼桨叶的优化与对比验证,结果表明,在气弹稳定性、自转惯量和振动固有频率等多约束条件下,实现自转惯量提高到原来的1.147倍,桨叶重量减少5.74%～8.6%,应力减少29.6%～30.1%的多目标优化,优化性能良好.      

碟形飞行器横航向飞行品质

碟形飞行器是一种新颖的,采用翼身融合布局的飞行器。应用经典飞行动力学理论的线性化小扰动方法对碟形飞行器在低速条件下的横航向稳定特性进行了仿真计算,采用时域分析的方法对横航向模态进行了分析,得到了碟形飞行器的横航向飞行品质状况.同时将碟形飞行器同常规布局飞机和飞翼飞机的特性做了简要的对比,分析了碟形飞行器同二者的异同之处和产生的原因.研究结果表明,碟型飞行器具有良好的横航向飞行品质和综合性能.