考虑气动不确定性的气动弹性系统模型确认

研究了机翼气动弹性系统的不确定性建模及其模型确认问题。结构的不确定性考虑为参数形式,气动力的不确定性分为未建模动力学和参数不确定性两种形式进行讨论。建立不确定气动弹性系统的线性分式变换（LFT）模型,给出了频域的模型有效性检验方法,对有效模型集进行参数化并将不确定性幅值最小的模型集求解归结为优化问题。在建模中计入了实际存在的、未知但能量有界的外扰和噪声的影响,降低了结果的保守性。最后,根据模型确认的结果,使用结构奇异值μ 分析方法进行不确定系统的鲁棒颤振分析。仿真计算结果表明了模型确认方法的有效性。     

AEKF在姿态确定中的应用研究

设计了加性扩展Kalman滤波器(AEKF),对卫星姿态进行了准确估计。针对四元数法描述卫星姿态所引起的信息冗余能使滤波误差协方差阵产生奇异,并导致滤波发散,为此提出了用协方差阵降维法解决该问题。仿真结果表明,应用本文设计的滤波器,能有效克服姿态敏感器的量测噪声,准确估计出卫星的姿态。     

轨道要素奇异问题的改进四元数方法

运用四元数方法可以在一定范围内解决描绘飞行器轨道运动时轨道要素的奇异问题。但四元数固有的双值性使得在对运动方程进行积分时,其正负选取很困难。为了解决这一问题,采用了改进约束方程的四元数方法,并用该方法描述了拉格朗日行星摄动方程,然后研究了地球扁率摄动对地球同步卫星轨道的影响。仿真结果表明：当偏心率小于1时,四元数可以很好地解决轨道要素奇异性问题。与改进的春分点轨道要素相比,四元数的方法有着更加明确的物理意义和几何意义,用四元数表示的运动变量方程的计算更为简单,积分计算效率更高,而且其计算误差也能达到精度要求。     

HIGH CYCLE FATIGUE RELIABILITY ANALYSIS ON ROTOR HUB BASED ON APPROXIMATION TECHNIQUE

A high cycle fatigue reliability analysis approach to helicopter rotor hub is proposed under working load spectrum. Automatic calculation for the approach is implemented through writing the calculating programs. In the system, the modification of geometric model of rotor hub is controlled by several parameters, and finite element method and S-N curve method are then employed to solve the fatigue life by automatically assigned parameters. A database between assigned parameters and fatigue life is obtained via Latin Hypercube Sampling （LHS） on toler- ance zone of rotor hub. Different data-fitting technologies are used and compared to determine a highest-precision approximation for this database. The parameters are assumed to he independent of each other and follow normal distributions. Fatigue reliability is then computed by the Monte Carlo （MC） method and the mean-value first order second moment （MFOSM） method. Results show that the approach has high efficiency and precision, and is suit- able for engineering application.     

一组新的四元数轨道要素建模方法

针对传统以欧拉角为参数的轨道要素的奇异性、不确定性以及计算效率低等问题,提出了一种新的四元数轨道要素。建立了新轨道要素与经典轨道要素,以及新轨道要素与惯性系下位置、速度的相互转换关系,推导了基于新轨道要素的高斯摄动方程。以J₂项摄动下的轨道推演为例进行仿真验证,结果表明新轨道要素不仅在圆轨道与赤道平面轨道处不存在奇异性和不确定性,而且由于新轨道要素不涉及三角函数运算,新高斯摄动方程积分效率和计算精度明显提高。     

Installation error calibration for MEMS angular measurement system in hypersonic wind tunnel

The accuracy of model attitude measurement has an important impact on wind tunnel test results. Microelectromechanical System Inertial Measurement Unit (MEMS IMU) provides a feasible way to measure model attitudes with high accuracy. However, the installation error between MEMS IMU coordinate system and the body coordinate system of test models can make the accuracy of the model attitude measurement decrease. In wind tunnel tests, the installation error depends on the relationship between the IMU and the model mechanism before tests. Therefore, in-field calibration in wind tunnel tests is necessary to reduce installation errors. To improve attitude measurement accuracy, the least squares quaternion calibration method based on MEMS IMU and six-position calibration procedure are proposed. High-precision three-axis turntable tests are performed. The pitch accuracy after calibration is higher than that before calibration in the angle of attack sweeping tests. The Root-Mean-Square Errors (RMSE) in the roll and yaw are within 0.01°, which are smaller than those before calibration. In the roll sweeping tests, RMSE of three attitude angles decrease significantly. In hypersonic wind tunnel tests, the pitch errors before and after calibration are within 0.05° and 0.02° in the angle of attack sweeping tests without wind. In five angle of attack sweeping tests with wind, the deviation between the mean of the pitch and the pitch after the elastic angle correction is within 0.03° and the standard deviation of five tests is within 0.01°. The proposed method is confirmed to enhance the accuracy of attitude measurement effectively, which is convenient for engineering applications.