某航空用扭转弹簧失效分析(英文)

某型扭转弹簧零件主要用于航空机构中,在装配过程中出现裂纹和发生断裂。通过视频显微镜、扫描电镜、金相显微镜等分析方法,对断裂弹簧裂纹、断口特征及其附近损伤形貌进行了宏、微观观察和覆盖物的能谱分析。在试验结果和数据的基础上,结合加工工艺综合分析失效的性质和原因。金相组织检查未发现材质异常,失效与材质无关。弹簧裂纹和断裂都起始于内表面,因此裂纹的萌生发生在弹簧绕制后镀镉前。裂纹张开方向与弹簧内表面的残余拉应力方向一致,而且绕制后、镀镉前接触氢介质。弹簧失效的原因是残余拉应力和氢共同作用下发生氢致延迟开裂。     

直升机变距拉杆杆端自润滑关节轴承的力学分析和损伤特性

以R44直升机主旋翼变距拉杆杆端自润滑关节轴承为研究对象,用三维建模软件Solidworks建立其旋转摆动的有限元模型并导入到有限元分析软件Ansys Workbench中,分析计算其在径向正弦载荷下衬垫的等效应力、位移、接触应力和等效剪切应力的变化特性;并结合实际服役工况下R44直升机失效的自润滑关节轴承衬垫进行分析。结果表明：在整个周期内,衬垫的边缘因为被挤压而发生变形,衬垫的等效应力和等效变形最大值均出现在外圈的边缘上,接触应力最大值所在的区域始终出现在衬垫的顶部和底部,并且接触应力分布区域的移动与内圈的转动方向一致,切应力最集中的地方在径向载荷施加点的左上方、左下方、右上方、右下方以及左右两侧;由于实际服役工况中载荷的变化,导致衬垫的损伤上半部分是以接触应力引起的疲劳损伤为主,下半部分是以切应力导致的转移膜形成为主。     

一种基于证据距离的多分类器差异性度量

 多分类器系统因其能够显著提升分类精度而引发了广泛关注。多分类器系统中各子分类器间的差异性是提升融合分类精度的先决条件。提出了一种基于证据距离的分类器系统差异性度量,同时基于该度量提出一种多分类器系统构造方法。综合了既有差异性度量、所提新差异性度量以及在训练样本集上的分类性能等多个指标,实现了多分类器系统的有效构造。实验结果表明,所提差异性度量及多分类器系统构造方法是合理的,能有效提升融合分类精度。     

民机复合材料目视检查中的眼动与疲劳检测

疲劳是导致民机复合材料结构目视检查差错的重要诱因，疲劳检测对于减少人的差错，保障飞行安全具有重要意义。对基于眼动行为的疲劳度量与检测方法进行了研究，建立了民机复合材料结构目视检查实验场景，利用Tobii眼动仪提取了正常状态和疲劳状态下的目视检查眼动数据，分析了瞳孔直径、平均注视时间、平均注视频率、平均眼跳时间、平均眼跳频率、注视热点与轨迹和扫视速度等眼动行为与疲劳的关系，进而提取了能表征疲劳的瞳孔直径、平均注视时间和扫视速度3种眼动指标，以该指标构建特征向量，利用支持向量机（SVM）方法构建了目视检查疲劳检测模型。研究发现疲劳状态下的目视检查平均注视时间更长，扫视速度更慢、瞳孔直径减小，右瞳孔减小程度更大，核函数为径向基函数和高斯函数的SVM方法对疲劳的检测效果好。研究结果表明，利用SVM方法训练由瞳孔直径、平均注视时间和扫视速度构成的眼动特征向量能有效检测目视检查中的疲劳状态。     

Space Debris Reentry Analysis Methods and Tools

The reentry of uncontrolled spacecraft may be broken into many pieces of debris at an altitude in the range of 75-85 km. The surviving fragments could pose great hazard and risk to ground and people. In recent years, methods and tools for predicting and analyzing debris reentry and ground risk assessment have been studied and developed in National Aeronautics and Space Ad-ministration (NASA), European Space Agency (ESA) and other organizations, including the group of the present authors. This paper reviews the current progress on this topic of debris reentry briefly. We outline the Monte Carlo method for uncertainty analysis, breakup prediction, and parameters affecting survivability of debris. The existing analysis tools can be classified into two categories, i.e. the object-oriented and the spacecraft-oriented methods, the latter being more accurate than the first one. The past object-oriented tools include objects of only simple shapes. For more realistic simulation, here we present an object-oriented tool debris reentry and ablation prediction system (DRAPS) developed by the present authors, which introduces new object shapes to 15 types, as well as 51 predefined motions and relevant aerodynamic and aerothermal models. The aerodynamic and aerothermal models in DRAPS are validated using direct simulation Monte Carlo (DSMC) method.     

Application of Active Flow Control Technique for Gust Load Alleviation

A new gust load alleviation technique is presented in this paper based on active flow control. Numerical studies are conducted to investigate the beneficial effects on the aerodynamic characteristics of the quasi "Global Hawk" airfoil using arrays of jets during the gust process. Based on unsteady Navier-Stokes equations, the grid-velocity method is introduced to simulate the gust influence, and dynamic response in vertical gust flow perturbation is investigated for the airfoil as well. An unsteady surface transpiration boundary condition is enforced over a user specified portion of the airfoil’s surface to emulate the time dependent velocity boundary conditions. Firstly, after applying this method to simulate typical NACA0006 airfoil gust response to a step change in the angle of attack, it shows that the indicial responses of the airfoil make good agreement with the exact theoretical values and the calculated values in references. Furthermore, gust response characteristic for the quasi "Global Hawk" airfoil is analyzed. Five kinds of flow control techniques are introduced as steady blowing, steady suction, unsteady blowing, unsteady suction and synthetic jets. The physical analysis of the influence on the effects of gust load alleviation is proposed to provide some guidelines for practice. Numerical results have indicated that active flow control technique,as a new technology of gust load alleviation, can affect and suppress the fluid disturbances caused by gust so as to achieve the purpose of gust load alleviation.     

运输机空投控制器设计(英文)

重物空投过程中,飞行器各飞行参数随着货物舱内移动发生连续的变化,当货物投放瞬间则发生突变。随着空投货物重量的增加,这一过程将严重恶化飞行器飞行品质和操控特性。本文在简化的空投飞行方程基础上,研究反演和切换控制方法以解决这一过程中的飞行状态保持和扰动抑制(包括大范围飞行状态,飞行员操纵误差和系统量测延迟等)问题,所得控制策略也可用于驾驶员空投操纵的指令参考。利用反演理论,推导了自适应控制器以稳定运输机飞行状态,并提出了协调的切换控制方法解决飞机在货物离机过程中出现的状态跳变问题。仿真结果表明所提控制方法在不仅能有效保持系统状态,并能在较大飞行范围内具有较好的鲁棒性。     

A novel approximation of basic probability assignment based on rank-level fusion

Belief functions theory is an important tool in the field of information fusion. However, when the cardinality of the frame of discernment becomes large, the high computational cost of evidence combination will become the bottleneck of belief functions theory in real applications. The basic probability assignment (BPA) approximations, which can reduce the complexity of the BPAs, are always used to reduce the computational cost of evidence combination. In this paper, both the cardinalities and the mass assignment values of focal elements are used as the criteria of reduction. The two criteria are jointly used by using rank-level fusion. Some experiments and related analyses are provided to illustrate and justify the proposed new BPA approximation approach.     

基于Viterbi算法的扩频码与信息序列联合估计

针对短码DSSS（Direct Sequence Spread Spectrum,直接序列扩频）信号扩频码MLE（Maximum Likelihood Estimation,最大似然估计）问题,提出了一种基于Viterbi算法的扩频码搜索方法,并将其应用到同步CDMA（Code Division Multiple Access,码分多址）信号的扩频码估计中.该算法利用了扩频码码元为±1的先验知识,以向量的2-范数平方或1-范数作为度量值;每次判决扩频码码元时,计算2条可能路径的度量值,并选择使度量值最大的那条路径作为幸存路径,最终的幸存路径即为估计的扩频码;所提算法不仅计算复杂度低,而且能同时估计扩频信号的扩频码和信息序列.仿真实验表明,本算法在低信噪比时同样具有较好的性能.     

Effects of Staged Injection on Supersonic Mixing and Combustion

The three-dimensional (3D) reacting flow in a staged supersonic combustor is examined numerically. In order to obtain the optimum stream-wise vortices, a swept ramp injector is chosen as the second-stage wall injection combined with the first-stage central strut injection. The performance of the two-staged injection is compared with that of a one-staged injection, while the strut is kept installed in both cases. The two-staged injections can make full use of the residual oxygen near the wall and release more heat. The second-stage injection further downstream avoids the strong shock waves in the isolator and results in a rising wall pressure and good burning effects after the wall injection. Therefore, it allows more fuel to be injected into the supersonic combustor without causing thermal choking. Parallel injection from the second-stage swept ramp shows low total pressure loss and the best burning efficiency, compared with the other injection angles.