翼型前缘变形对动态失速效应影响的数值计算

翼型或机翼的动态失速效应所引起的低头力矩和正气动阻尼限制了飞行器气动性能的提高,甚至可能诱导发生不稳定运动。应用于小尺寸机翼的前缘动态变形（DDLE）技术,通过实时改变前缘形状,能够改善翼型前缘区域的速度梯度,进而抑制动态失速效应。采用转捩剪切应力输运（SST）黏性模型结合分区混合动态网格技术,研究了这种前缘变形对机翼俯仰运动所引起的非定常流动的影响,得到通过小幅度前缘变形抑制和延迟动态失速的方法,从而提高翼型的气动性能。翼型NAC A0012的数值模拟结果与动态失速风洞试验结果比较表明：所使用的数值计算方法能够较为准确地模拟翼型在动态失速过程中升力系数与俯仰力矩系数的变化情况,可用于研究前缘变形对翼型俯仰运动所引起的非定常流动的影响。前缘动态变形翼型俯仰运动过程的非定常流场的数值模拟表明：在大迎角下不同幅度的前缘下垂运动能够抑制流动分离的发生,从而抑制动态失速,但在大迎角下小幅度高频率的前缘下垂变形能更高效地抑制动态失速;前缘变形幅度以及变形沿中弧线的分布对升力系数和俯仰力矩系数的影响并不明显。     

在制品管理中条码技术的应用

针对面向订单的单件、小批量生产制造企业,设计了一套条码数据采集系统,分析了主要运作流程和功能模块.在在制品的管理中提出了基于不同级别的工件生产状态定义,并给出了相应的加工、检验判定准则.经实际使用证明条码技术运用于工业现场是可行的.     

不确定参数结构特征值问题的概率统计方法和区间分析方法的比较

 基于区间数学理论、灵敏度分析理论、Kronecker代数理论,应用Taylor级数展开、概率摄动技术,提出了具有不确定参数结构的特征值问题的区间分析方法。结合工程实例与传统的概率分析方法进行比较,给出了两种方法的数值解法及各自解法的Kronecker代数形式。数值算例的结果显示了区间分析方法在具有不确定参数结构特征值问题分析中的价值和有效性。     

Design and analysis of a truss deployable antenna mechanism based on a 3UU-3URU unit

Space deployable structures with large calibers, high accuracy, and large folding ratios are indispensable equipment in the aerospace field. Given that the single-DOF 3RR-3RRR deployable unit cannot be fully folded, this study proposes a 3UU-3URU deployable unit with two kinds of DOF: folding movement and orientation adjustment. First, based on the G-K formula, the DOF of the 3UU-3URU unit is analyzed. Then, the 3UU-3URU unit is used to construct a deployable truss antenna with a curved surface, and the DOF of the whole deployable antenna containing multiple 3UU-3URU units is calculated. The structural design of a deployable antenna with two loops is carried out with specific parameters and geometric relations. Next, a DOF simulation of a basic combination unit composed of three 3UU-3URU units is performed. Finally, a prototype of the basic combination unit is manufactured, and the DOF of the mechanism is experimentally verified.     

A novel approach for predicting inlet pressure of aircraft hydraulic pumps under transient conditions

Cavitation caused by insufficient suction is a major factor that influences the life of aircraft pumps. Currently, pressurizing the tank can solve the cavitation problem under steady large-flow conditions. However, this method is not always effective under transient conditions (from zero flow to full flow in a very short time). Moreover, to apply and design other measures, such as a boost impeller, the suction dynamics during the transient period must be investigated. In this paper, a novel approach based on the pressure wave propagation theory is proposed for predicting the inlet pressure of an aircraft pump under transient conditions. First, a dynamic model of a typical aircraft pump is established in the form of differential equations. Then, the transient flow model of the inlet line is described using momentum and continuity equations, and the governing equations are discretized by the method of characteristics and the finite difference method. The simulated results are in good agreement with the results from verification tests. Further simulation analysis indicates that the wave velocity and transient time may influence the inlet and reservoir pressure as well as the size of the inlet line. Finally, solutions for upgrading the inlet pressure are discussed. These solutions provide guidelines for designing inlet installations.     

关于大容量高速立式电机加装大转动惯量飞轮的设计研究

电机在发生事故突然失电时,为确保系统安全,要求电机能拖动设备依靠自身惯量,继续运转2 min。由于电机自身惯量远小于系统惯量要求,因此需在电机本体上加装大直径、大重量飞轮,以提供足够的惯量。在大容量、高速立式电动机加装大转动惯量飞轮后,电机的稳定运行变得至关重要,因此对电机自身的刚度、轴系及结构设计的合理性需进行验证。针对电机的关键点结构设计及计算,并通过现场运行,对电机的可靠性进行了验证。这为电机的工程运用提供参考。     

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.     

光电自准直经纬仪水平角测量误差分析

针对光电自准直经纬仪的水平角测量原理和系统组成特点,全面分析了影响其水平角测量精度的各项误差分量,并对各种误差因素进行了定量计算,对系统误差提出补偿方法。通过分析和补偿,可将光电准直经纬仪水平角测量精度提高到0.5″,满足Ⅰ等电子经纬仪的测量精度指标。     

Alfvén gravity waves in viscous solar plasma: Effect of the background flow

We study the Propagation and damping properties of Alfvén gravity waves in the presence of the vertical magnetic field in the viscous solar plasma under influence of the background flow by deriving a fourth order dispersion relation in terms of the Doppler shifted frequency. We derive the dispersion relation under WKB and Boussinesq approximation. We study the damping of Alfvén gravity waves for the wave frequencies less than and greater than the Brunt-Väisälä frequency. We find that the Brunt-Väisälä frequency divides the frequency ranges where the weakly or strongly damped oscillations occur. The background flow exhibits a strong effect on weakly damped oscillations and a weak effect on the strongly damped oscillations. We also notice that the damping of both the strong and weakly damped oscillations depend on the Brunt-Väisälä frequency and wave number. The effect of the background flow is also being governed by the Brunt-Väisälä frequency and wave number. We also study the properties of gravity wave mode after filtering the Alfvén wave mode by minimizing the magnetic field and noticed that the background flow shows a very strong effect on the gravity wave mode.     

运动基航天飞行模拟器信号缩比策略

对于大幅值的输入信号,三阶多项式缩比法易产生信号畸变且参数配置复杂;而Hermite缩比函数法的触发速度较慢.提出两种改进的缩比方法:基于三阶多项式缩比法的最优参数配置法和加入线性缩比的非线性缩比法.前一种方法通过参数的优化配置最大化稳定区,以防止信号的畸变;后一种方法则利用线性缩比的特性将缩比度限制在稳定区内.仿真结果表明:线性缩比的加入可以防止三阶多项式缩比法信号的畸变;最优配置参数法应用方便且整体效果较好.为航天飞行模拟提供了更有效的缩比策略.