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。     

重装空投动力学分析与控制方案研究

针对重装空投任务,基于拉格朗日分析力学,建立了货物在机舱内滑行阶段飞机-货物两体系统的动力学模型.给出了一种控制补偿方案,用以抵消或削弱货物运动对飞机的影响.通过数值仿真,观察货物运动和飞机运动之间的耦合关系,分析了牵引伞尺寸对飞机和货物运动参数的影响.仿真结果表明,所给出的控制补偿方案能够有效改善飞机飞行品质,提高飞...     

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.     

Optimal station-keeping near Earth–Moon collinear libration points using continuous and impulsive maneuvers

In this study the gravitational perturbations of the Sun and other planets are modeled on the dynamics near the Earth–Moon Lagrange points and optimal continuous and discrete station-keeping maneuvers are found to maintain spacecraft about these points. The most critical perturbation effect near the L₁ and L₂ Lagrange points of the Earth–Moon is the ellipticity of the Moon’s orbit and the Sun’s gravity, respectively. These perturbations deviate the spacecraft from its nominal orbit and have been modeled through a restricted five-body problem (R5BP) formulation compatible with circular restricted three-body problem (CR3BP). The continuous control or impulsive maneuvers can compensate the deviation and keep the spacecraft on the closed orbit about the Lagrange point. The continuous control has been computed using linear quadratic regulator (LQR) and is compared with nonlinear programming (NP). The multiple shooting (MS) has been used for the computation of impulsive maneuvers to keep the trajectory closed and subsequently an optimized MS (OMS) method and multiple impulses optimization (MIO) method have been introduced, which minimize the summation of multiple impulses. In these two methods the spacecraft is allowed to deviate from the nominal orbit; however, the spacecraft trajectory should close itself. In this manner, some closed or nearly closed trajectories around the Earth–Moon Lagrange points are found that need almost zero station-keeping maneuver.     

一种考虑截面任意变形模式梁的有限元模型

提出了一种考虑截面完整变形的截面插值梁模型,并用于机翼结构的建模与分析。首先引入截面插值函数——拉格朗日函数描述截面形状,以位移向量为未知变量描述截面位移,在此基础上依据插值理论构造梁单元位移场。不同于传统梁单元通过假定的中性轴的挠度和转角来确定梁截面各点位移,该梁模型摒弃了中性轴假设与平截面假设,通过截面插值函数得到梁截面面内、面外变形;然后通过有限元理论推导了梁单元刚度矩阵与质量矩阵;最后利用截面插值梁单元对机翼各部件进行有限元建模,并展开典型工况下的静力学分析以及动力学分析,与Nastran实体单元计算结果进行了对比分析,验证了该梁模型的有效性,为机翼的结构设计和强度分析提供了一种新的简化建模方法。     

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。