水洞动态测力和流动显示一体化实验技术

研制能够用于低速水流中的三分量内式测力天平,结合氢气泡(或染色液)方法,在水洞(槽)中实现测力和流动显示实验同步进行的动态实验系统,克服了通常测力和流动显示分别在风洞和水洞中进行,实验条件不同给结果分析带来的困难。天平采用高精度位移传感器,避开传统的应变片技术应用于水中所遇到的技术困难。简易飞行器模型的静态和等速俯仰实验结果表明了测量系统的可靠性。     

A new dynamic pushback control method for reducing fuel-burn costs: Using predicted taxi-out time

Long departure-taxi-out time leads to significant airport surface congestion, fuel-burn costs, and excessive emissions of greenhouse gases. To reduce these undesirable effects, a Predicted taxi-out time-based Dynamic Pushback Control(PDPC) method is proposed. The implementation of this method requires two steps: first, the taxi-out times for aircraft are predicted by the leastsquares support-vector regression approach of which the parameters are optimized by an introduced improved Firefly algorithm. Then, a dynamic pushback control model equipped with a linear gate-hold penalty function is built, along with a proposed iterative taxiway queue-threshold optimization algorithm for solving the model. A case study with data obtained from Beijing International airport(PEK) is presented. The taxi-out time prediction model achieves predictive accuracy within 3 min and 5 min by 84.71% and 95.66%, respectively. The results of the proposed pushback method show that total operation cost and fuel-burn cost achieve a 14.0% and 21.1%reduction, respectively, as compared to the traditional K-control policy.(3) From the perspective of implementation, using PDPC policy can significantly reduce the queue length in taxiway and taxi-out time. The total operation cost and fuel-burn cost can be curtailed by 37.2% and 52.1%,respectively, as compared to the non-enforcement of any pushback control mechanism. These results show that the proposed pushback control model can reduce fuel-burn costs and airport surface congestion effectively.     

Geometric error analysis of an over-constrained parallel tracking mechanism using the screw theory

This paper deals with geometric error modeling and sensitivity analysis of an overconstrained parallel tracking mechanism. The main contribution is the consideration of overconstrained features that are usually ignored in previous research. The reciprocal property between a motion and a force is applied to tackle this problem in the framework of the screw theory. First of all, a nominal kinematic model of the parallel tracking mechanism is formulated. On this basis, the actual twist of the moving platform is computed through the superposition of the joint twist and geometric errors. The actuation and constrained wrenches of each limb are applied to exclude the joint displacement. After eliminating repeated errors brought by the multiplication of wrenches, a geometric error model of the parallel tracking mechanism is built. Furthermore,two sensitivity indices are defined to select essential geometric errors for future kinematic calibration. Finally, the geometric error model with minimum geometric errors is verified by simulation with SolidWorks software. Two typical poses of the parallel tracking mechanism are selected, and the differences between simulation and calculation results are very small. The results confirm the correctness and accuracy of the geometric error modeling method for over-constrained parallel mechanisms.     

发射脉冲载波泄漏抑制研究与实现

对发射端采用双平衡正交调制器产生线性调频造成载波泄漏的原因进行了详细分析,提出了采用直接数字合成(DDS)技术产生发射端线性调频信号的实现方法,从而很好地解决了载波泄漏的问题,并给出了试验结果。     

高温存储对Sn-Pb-Ni凸点界面金属间化合物生长的影响

倒装焊工艺由于具有信号处理速度快、封装密度高、可靠性高等特点,已广泛应用于高密度集成电路封装工艺中。高可靠倒装焊器件的互连焊点通常采用10Sn90Pb等高铅焊料,该焊料具有剪切强度高、可靠性高等优点,但其熔点高、回流工艺窗口窄等特性给封装工艺带来一定难度,此外该焊料在高温存储环境的可靠性有待进一步提高。本文采用Ni元素对10Sn90Pb焊料进行改性,研究高温存储下Sn-Pb-Ni体系凸点的力学性能以及金属间化合物（Intermetallic compound,IMC）的生长演变规律,以此评估Ni元素对10Sn90Pb凸点可靠性的影响。主要结果如下：适量添加Ni元素可以细化10Sn90Pb焊点界面处IMC晶粒,降低高温存储条件下的IMC生长速度,但在一定程度上会降低凸点的剪切强度。0.05%~0.1%含量的Ni元素添加对10Sn90Pb凸点综合性能提升较为显著。     

航空发动机性能差异问题的故障部件快速检验方法

提出了一种航空发动机性能差异问题的故障部件快速检验方法.该方法以部件特性曲线为基础,可以快速检测出航空发动机各部件的自身特性变化而排除由于其它部件性能变化引起的工作线变动带来的影响,从而快速判断出故障的部件.该方法特别适用于仿制发动机与原型发动机性能变化原因的查找.      

基于FMECA信息的测试性验证试验样本分配方法

针对目前国内外测试性验证试验中普遍采用的基于故障率的分层抽样方法考虑因素单一,可能导致样本分配不尽合理,而现有考虑多因素的样本分配方法代表性不足,难以实现工程上的应用的问题,对影响样本分配的因素与故障模式影响及危害性分析(FMECA)信息的关系进行了详细分析,提出了基于FMECA信息的样本分配方法。首先定义了单元影响系数和影响因子向量,提出了向量各元素赋值规则,解决了影响因素选取的问题;其次通过基于逼近理想解排序法(TOPSIS)优化的层次分析法确定了权值矩阵,实现了样本分配。最后通过实例验证表明该方法考虑因素全面,运用灵活,更具代表性和工程应用价值。     

碳化硅反射镜柔带磨削方案设计与验证

碳化硅材料比刚度高、导热性好、热稳定性好,是一种优良的反射镜材料,在空间光学遥感器是有着广泛的使用。同时,它具有硬度高、脆性大的特点,给反射镜加工带来困难,且加工周期长。本文比较了碳化硅材料不同加工技术的优缺点,选择了机器人柔性砂带磨削技术作为研究对象。针对某1550mm直径碳化硅反射镜坯加强筋的去除要求,设计了一套新型机器人柔带磨削系统,利用有限元方法对加工中的镜体应力进行了分析,并完成了某镜坯加强筋的去除,残余筋高度0.5mm～1mm。反射镜镜坯在完成镜面精磨、镀膜等处理后,利用干涉仪测试面形RMS 为0.0157λ（λ=632.8 nm）,满足使用需求。遥感器于2020年发射,反射镜在轨运行表现良好。     

仿生偏振光定向算法及误差分析

基于标准大气偏振模型,研究了仿生偏振光定向原理,推导了当载体倾斜时的航向角计算方法,分析了各项误差源对航向角估计误差的影响。结果表明：若已知载体的水平角,可根据偏振角解算出载体航向角;引起定向误差的主要因素来自于仿生偏振光传感器误差和载体的水平角误差,太阳位置误差的因素可以忽略;当太阳高度角小于50°、载体水平角小于20°时,仿生偏振光定向的精度约等于偏振角的测量精度,即定向精度约为0.2°。     

下颔式进气道实验研究

为了验证下颔式进气道 /前机身一体化设计方案的合理性及其进气道性能 ,对下颔式进气道 /前机身一体化设计方案进行了实验研究。测出了进气道总压恢复系数、畸变指数随流量系数、攻角、侧滑角的变化规律。结果表明 ,进气道性能较好 ,进气道 /发动机匹配良好。最后提出了下颔式进气道的进一步改进措施