临界剪切应力系数曲线适用性研究

曲板的屈曲问题与材料的弹性模量和泊松比有关,对于机身蒙皮材料2060-T8E30,曲板临界剪切应力系数曲线的适用性有待研究。基于Abaqus的线性静力分析中的Buckle算法,以机身蒙皮材料2060-T8E30建立了多种构型曲板,对比有限元分析值和曲板临界剪切应力系数曲线,通过分析误差,得出结论:对于2060-T8E30材料,可以认为d/h=1.5的ks(曲板临界剪切应力系数)曲线相比有限元分析值偏高,误差不大于15%;d/h=2的ks曲线相比有限元分析值偏高,误差不大于20%;d/h=3.5的ks曲线相比有限元分析值偏高,误差不大于35%。在飞机机身结构常用的参数,即d/h=3.5,Z≤20的情况下,当Z10时,ks曲线的适用性较好,误差不大于10%;当10Z≤20时,ks曲线相比有限元分析值偏高,误差不大于20%。     

A different view of the ionospheric winter anomaly

The Winter Anomaly (WA) is an ionospheric phenomenon, particularly related to the F2-layer, that is classically defined as the situation in which the ionization level during winter is higher than during summer for a certain location. This situation is anomalous because it contradicts what would be naturally expected with summer’s ionization levels higher than winter ones. This phenomenon has been a matter of study since the early decades of the XX century.This contribution tackles the study of the WA based on long time series (up to two solar cycles) of Total Electron Content (TEC) measurements over a globally distributed network of stations. The work done relies on a threefold strategy including: a classical approach based on the comparison of the winter and summer maximum TEC values, that confirmed the results previously documented; an intermediate approach with maximum TEC values modelled as linear functions of the solar radiation level, that allowed to identify stations where the WA is likely to be observed (and at what solar radiation level) and where is not; a final original approach where the maximum TEC values are modelled using Chapman’s function for the seasonal variations, linear regressions for the solar activity dependence and the introduction of site and month dependent equivalent ionization coefficients for the remaining effects. The main conclusions are that the coefficients for winter months seem to depend mainly on geomagnetic latitude, to increase towards high latitudes and to be asymmetric between hemisphere. In accordance to these findings, the occurrences of WA effects would be regulated by proper combinations of these three effects.     

基于加速度频响函数小波分解的模型修正方法

为提高模型修正效率，满足修正方法对于实测环境噪声的鲁棒性，将Kriging模型和小波分解引入加速度频响函数模型修正。首先，将加速度频响函数进行小波分解，用得到的第1层幅值较大的小波系数来表征原频响函数。其次，采用拉丁超立方抽样对初选待修正参数进行设计，根据设计结果对各参数进行灵敏度分析，从而确定模型修正的待修正参数，以待修正参数作为Kriging模型输入，所对应的小波系数作为Kriging模型输出，通过混合灰狼算法寻得最优Kriging模型相关系数，建立精确有效的Kriging模型。最后，以目标加速度频响函数小波分解的小波系数与Kriging模型输出的小波系数差值最小为目标，通过水循环算法求解模型待修正参数。数值算例表明，所提模型修正方法具有良好的修正效果，即使在加速度频响函数中加入信噪比为5 dB的高斯白噪声时，修正误差也低于4%，证明了该方法对于随机噪声的鲁棒性。     

覆冰四分裂导线静态气动力特性试验

覆冰四分裂导线的空气动力特性,由于覆冰子导线尾流的相互干扰可能不同于覆冰单导线。针对两种不同冰型制作覆冰四分裂导线模型,通过风洞试验测试获得不同冰厚和不同风速下覆冰四分裂导线静态空气动力系数随攻角的变化曲线。结果表明,在一定的攻角下,子导线尾流相互干扰对空气动力系数有明显影响。所得试验结果为覆冰四分裂导线的舞动及其防止技术的研究提供必要的数据。     

A double integral method for quantitative evaluation of influence on thin-walled casing response caused by bearing uncertainties

Bearings in a gas turbine engine are the key connecting components transmitting force and motion between rotors and thin-walled flexible casing. The bearing stiffness and damping of squeeze film damper (SFD) nearby bearings are easily affected by many factors, such as assembly process, load condition and temperature variation, resulting in uncertainties. The uncertainties may influence the response of the measuring point on the casing. Hence, it is difficult to carry out the fault diagnosis, whole machine balancing and other related works. In this paper, a double integral quantitative evaluation method is proposed to simultaneously analyze the influence of two uncertain dynamic coefficients on the response amplitude and phase of casing measuring points. Meanwhile, the coupling influence of stiffness and damping accompanied by dramatic changes with rotational speeds are essentially discussed. As an example, a typical engine bearing-casing system with complex dynamic characteristics is analyzed. The impact of uncertain dynamic coefficients on the unbalance response is quantitatively evaluated.     

弹道靶中超高速发射弹的流场及空气动力特性研究

本文描述的是研究爆炸成型发射弹(EFP)模型的流场及超高速空气动力特性所用的弹道试验设备;简要报导了记录全尺寸干涉图形的技术;对径向密度分布再现的方法进行了讨论;在零攻角实验时不同模型的空气动力阻力是采用简化方法来计算的;对各种不同EFP型式的气动稳定性提出了定性估计的方法;并阐述了用于组合体超高速飞行特性研究的数值计算技术的基本原理.     

发动机故障方程的建立与故障因子的引入

本文提出了在建立发动机故障方程时应当引入故障因子的概念。文中指出，根据原封不动地保留着部件正常特性方程（即不引入故障因子）的数学模型所得到的线性模型仅仅是小偏差方程而不是故障方程。这种小偏差方程不能适用于故障诊断，并且还会导致用较少测量参数可以诊断出较多的同时发生的独立故障的错误结论。文中给出了建立故障方程的正确方法，并以不可压流的管口出流问题为例加以说明，并且对个别相当有影响的文献在这一问题上的错误观点进行了详细的分析。     

30°预旋进气旋转盘流动与换热特性的实验

用实验的方法对具有30°预旋进气的旋转盘附近冷气流动与换热特性进行了研究,得到了静 盘表面压力、转盘表面温度、局部努赛尔特数的分布及平均努赛尔特数的变化.结果显示静 止盘罩表面的压力随着半径的增加而增加,随转速的增加而增加.转盘表面的局部努赛尔特 数在r＜0.7R的区域基本不变, r＞0.7R的区域里, 局部努赛尔特数随r的增加而增大.该预旋 角情况下,进气雷诺数对盘面平均努赛尔特数的影响大于旋转雷诺数.     

基于异频扰动和CFD技术的滑动轴承动力特性系数识别方法

目前CFD技术已广泛应用于滑动轴承的数值仿真中,但还存在两个问题,相对于传统的通过求解Reynolds方程获得流体压力场和油膜力的方法,如何通过CFD计算结果来识别得到动力特性系数,以及CFD方法误差有多大。针对这些问题,本文基于同幅异频位移激励技术,同时充分考虑惯性力、刚度、阻尼交叉项等因素给出了一套适用于挤压油膜阻尼器、可倾瓦轴承、固定瓦轴承等多种模型的动力特性识别方法,应用该方法可以一次性识别出油膜的动力特性系数。通过滑动轴承算例与短圆瓦轴承刚度阻尼理论解进行对比,验证了该方法的准确性。     

Collisional excitation of vinylidene (H2CC)

Though H₂CO, H₂CS, H₂CCC, H₂CCCC, H₂CCO have been identified in cool interstellar molecular clouds, identification of H₂CC is still awaited. To analyze its spectrum, collisional rate coefficients are required. We have calculated collisional rate coefficients for rotational transitions between 23 levels of ortho and para H₂CC for kinetic temperatures 10, 20, 30, 40, and 50 K. The scattering problem is analyzed using the computer code MOLSCAT where the colliding partner is He atom. The interaction between H₂CC and He has been calculated with GAUSSIAN 2003. For the interaction potential obtained with GAUSSIAN 2003, MOLSCAT is used to derive the parameters q(L,M,M^′|E)$q(L\text{,}M\text{,}{M}^{\prime }|E)$ as a function of energy E   of the colliding partner. After averaging the parameters q(L,M,M^′|E)$q(L\text{,}M\text{,}{M}^{\prime }|E)$ over a Maxwellian distribution, the parameters Q(L,M,M^′|T)$Q(L\text{,}M\text{,}{M}^{\prime }|T)$ as a function of the kinetic temperature T in the cloud are obtained. Finally, the collisional rate coefficients have been calculated.