Correlation analysis of PCB and comparison of test-analysis model reduction methods

The validity of correlation analysis between finite element model（FEM） and modal test data is strongly affected by three factors, i.e., quality of excitation and measurement points in modal test,FEM reduction methods, and correlation check techniques. A new criterion based on modified mode participation（MMP） for choosing the best excitation point is presented. Comparison between this new criterion and mode participation（MP） criterion is made by using Case 1 with a simple printed circuit board（PCB）. The result indicates that this new criterion produces better results. In Case 2, 35 measurement points are selected to perform modal test and correlation analysis while 9 selected in Case 3.System equivalent reduction expansion process（SEREP）, modal assurance criteria（MAC）, coordinate modal assurance criteria（CoMAC）, pseudo orthogonality check（POC） and coordinate orthogonality check（CORTHOG） are used to show the error introduced by modal test in Cases 2 and 3. Case 2 shows that additional errors which cannot be identified by using CoMAC can be found by using CORTHOG.In both Cases 2 and 3, Guyan reduction, improved reduced system（IRS） method, SEREP and Hybrid reduction are compared for accuracy and robustness. The results suggest that the quality of the reduction process is problem dependent. However, the IRS method is an improvement over the Guyan reduction, and the Hybrid reduction is an improvement over the SEREP reduction.     

导流板对25°倾角Ahmed类车体尾流与气动阻力的影响

在雷诺数8．7×10^5的条件下,运用眼镜蛇探针、压力扫描阀和表面油膜流动可视化技术对倾角为25°的Ahmed类车体尾流与尾部压力分布进行了研究。对比了模型尾部斜面上边缘和两侧不同宽度导流板对模型尾流与气动阻力的影响规律。实验发现模型尾流中存在一对对称的拖曳涡,其在尾流中心线附近形成强烈的下扫流。拖曳涡强度与模型尾部压力分布和气动阻力有直接关系,较强的拖曳涡对应的模型尾部负压以及气动阻力均较大。斜面两侧导流板宽度为1％模型长度时,不仅无减阻效果,反而会使气动阻力增加约3．0％。当导流板宽度增加为2％和3％模型长度时,能够明显削弱斜面上的分离泡,对应的减阻效果分别为3．5％和7．2％。斜面上边缘导流板可有效地抑制分离流在斜面上的再附,并消除斜面上的分离泡,其抑制拖曳涡强度和降低气动阻力的效果明显优于同等宽度的斜面两侧导流板。上边缘导流板宽度为模型长度的1％,2％和3％时,减阻率分别可达9．3％,10．7％和10．9％。     

航空发动机转子振动的“热模态”和减振设计

为适应航空发动机变转速变工况下转子动力学设计,提出了航空发动机转子"热模态"的概念.利用两种模型解释了"热模态"的含义,并建立了"热模态"下转子动力学设计的方法.利用支承弹性转子(弹支转子)的临界转速与支承刚性转子(刚支转子)的临界转速之比作为优化参数,对转子进行优化设计,既包含了刚度的作用,也计及了质量的影响.结果表明:若所有"热模态"均在刚支转子的第1阶模态之下,则转子临界转速应尽量小于刚支转子的第1阶临界转速.若第1阶"热模态"在刚支转子第1阶模态之下,而第2阶"热模态"在刚支转子第1阶模态之上,但在刚支转子第2阶模态之下,则转子第2阶临界转速应取刚支转子第2阶临界转速和刚支转子第1阶临界转速之方均根值.除此之外,转子剩余不平衡量的分布应与刚支转子的模态正交.      

机身后体装置对阻力的影响

1.引言 切尾运输机的机身后体阻力在总阻力中所占的比例仅次于表面摩阻及诱导阻力。机身后体附近的绕流不仅影响飞机的阻力,而且对空中投放及空中加油也有很大的影响。过去的研究得出底部附加隔板(减阻片)可起到减阻作用。现除了对减阻片的几何尺寸和安装位置需进行优化外,还需探索平尾上附加隔板以及后体台阶的减阻效果,以扩展减阻方案。     

直升机双线摆桨毂吸振器参数影响分析

采用多体系统动力学建模方法,建立了圆曲线路径构型双线摆式吸振器的非线性动力学模型,采用Runge—Kutta法和Newmark法进行了时域响应的直接求解,并以桨毂中心的力传递率作为衡量指标,讨论了设计参数,诸如吸振器离心质量块质量、调谐、阻尼对吸振性能的影响以及桨毂中心纵横向加速度阻抗对吸振性能的影响。     

一种改进的运载火箭迭代制导方法

为提高运载火箭在大气层外当推力出现故障条件下制导算法的最优性、鲁棒性和适应性,提出了一种改进的迭代制导方法。该方法以基于最优控制理论推导的解析形式作为最优控制解,并推导出以5个轨道根数作为终端约束的横截条件,增强了算法的最优性;迭代过程中采用高斯-勒让德方法计算推力积分,并采用球极坐标系下泰勒多项式逼近方法计算引力积分,提高了故障模式下算法的积分精度;该算法采用降维迭代求解模式,并结合对控制变量的合理限幅,保障了推力故障条件下算法的实时性和收敛性。分别基于蒙特卡洛打靶和推力故障条件下进行仿真验证,结果验证了所提方法具有较强的最优性、鲁棒性和故障适应能力。     

Nondestructive acquisition of the micro-mechanical properties of high-speed-dry milled micro-thin walled structures based on surface traits

Requirements for the service performance of aeronautic microelectronic components are increasingly strict. However, sever issues, that the acquisition of the service performance such as micro-mechanical properties is destructive, limit the subsequent application of the tested components. Addressing this issue, this paper proposes a nondestructive acquisition method of the micro-mechanical properties of the accelerometer micro-components, based on analyzing surface traits. To select qualified components without damage, we firstly developed a quasi-static micro-tensile tester and then established a combination prediction model of mechanical properties based on micro-milled surface traits. The model works due to the thin-walled structure, which makes the machined surface traits have significant influences on the mechanical properties such as Young’s modulus, yield strength, tensile strength, and elongation at break. Surface roughness, surface structure, and surface anisotropy are extracted to comprehensively present surface traits from different aspects. For improving the practicability of the model, the principal component analysis (PCA) is adopted to reduce high-dimensional traits explanatory variable space into two dimensions, and regression analysis models are comparative established in predicting the mechanical properties. Residuals analysis and error analysis are carried out to show the prediction accuracy. The maximum prediction error is about 10.62%, but the significance levels in the t-test of the predicted Young’s modulus and yield strength are not ideal. Therefore, kernel support vector regression (SVR) is imported to improve the prediction ability of the combination prediction model. The residuals analysis result shows that SVR is effective in enhancing the prediction ability of this model.     

消除CMOS管内部噪声的方法

介绍了一种通过改进电路结构来消除CMOS管内部的噪声,最终达到降低总输出噪声的技术。首先从理论上证明了这种技术的原理,然后把这种技术应用到具体的低噪声放大器电路中,通过PSPICE软件模拟仿真,比较和分析了采用这种技术前后LNA电路的总输出噪声、输出信噪比和电压增益。     

一种航天器蜂窝夹层板发泡胶减重方法

针对航天器蜂窝夹层板发泡胶减重需求,以预埋件-发泡胶组合体等效半径为参数进行理论分析,给出蜂窝夹层板应力分布解析式,预测其破坏模式。据此提出两种发泡胶减重填充方案,并开展试件拉脱力测试、仿真,舱板组件性能评估和结构精度稳定性分析等验证工作。研究表明,方案1实现预埋件发泡胶减重25%,方案2实现减重50%。减重方案已成功应用于两型卫星,可为其它航天器研制提供有益的参考。     

直升机旋翼桨叶气弹优化减振设计方法

从振源着手通过设计参数的最优选择设计直升机旋翼桨叶,使传递到机身的交变载荷最小达到降低振动水平的目的是旋翼桨叶设计思想的进步。本文在简单概述该方法的基础上,以某4桨摆振柔软的无铰复合材料桨叶为研究对象,将其大梁模拟为一单闭室复合材料盒形梁,研究了通过铺层角的优化选择,降低4次/转的桨毂交变力与力矩的情况。数值算例表明方法效果良好。