曲线片型加筋壁板的稳定性优化设计

加筋板作为一种典型结构被广泛应用于航空航天领域,为进一步拓展直筋加筋板的设计空间,提出了一套基于ModelCenter设计优化环境、Catia和Abaqus的曲线片型加筋板优化设计框架.一方面,筋条曲线采用参数数目可变的等距剖分三次B样条插值函数,为曲筋加筋板提供了足够大的优化空间.另一方面,采用筋条加载端相聚和筋条垂直于板边2种方式来解决曲线片型加筋板的筋条加载问题,从而产生了一些新的曲筋加筋板布局形式.优化结果表明,对于单向载荷主导的加筋板,曲筋加筋板相对于直筋加筋板稳定性改善不大.但对于复杂组合载荷,曲筋加筋板获得了比直筋加筋板更好的稳定性.      

非对称转捩对横向偏离稳定的影响

为研究非对称转捩对横向偏离稳定的影响,采用指定位置的强制转捩方法,对典型升力体外形进行非对称转捩的的数值模拟,包含全层流、全湍流及斜线转捩情况的计算与分析,得到非对称转捩对横向偏离稳定性影响的结论。结果表明：极端转捩会使飞行器航向稳定性变差,斜线转捩甚至会使飞行器航向稳定性的极性发生改变。     

抛物化稳定性方程在曲面边界层中的应用

为了研究抛物化稳定性方程在曲面边界层中的应用,选取了等曲率圆环管道、等曲率板和NACA0012翼型3种典型的曲面边界层.通过计算小幅值扰动波的演化,抛物化稳定性方程的计算结果和线性稳定性理论、数值模拟扰动方程结果相符,说明可以使用抛物化稳定性方程研究曲面边界层的小幅值扰动波的演化和稳定性分析;通过计算有限幅值扰动波的演化,线性阶段抛物化稳定性方程计算结果和扰动方程相符,在非线性很强的阶段,抛物化稳定性方程计算发散,发散的位置可作为转捩位置.      

运输飞机非常态俯仰振荡分析

对某运输飞机在大襟翼偏度下的非常态俯仰振荡原因进行了分析。研究结果表明,该运输飞机在大襟翼偏度下飞行时因平尾受机翼的强下洗作用导致平尾下翼面发生局部分离,该分离未达到失速分离,从而引起飞机非常态的俯仰振荡。分离的主要原因是机身与平尾融合处抗流场逆压梯度能力下降,导致在大襟翼偏度飞行时出现局部分离,使得飞机出现纵向非常态俯仰振荡。该结论在风洞试验及该运输飞机试飞中得到验证。     

Experimental study on impact of roller imbalance on cage stability

This study presents a method for measuring the imbalance in a small-sized cylindrical roller. The roller imbalance was calibrated on the built static-pressure-air flotation measurement machine. The impact of the roller imbalance on the dynamic characteristics of a cage were then studied on the aero-bearing test rig. The displacement spectrums with different roller imbalance of the obtained cage orbits under various bearing speed and radial load were used to evaluate the cage stability. The results show that the cage cannot form a stable operating state at a lower bearing speed with or without the unbalanced rollers. The cage with balanced rollers gradually develops stable motion with the increase of the bearing speed. The existence of a small roller imbalance causes the stability of the cage to deteriorate. With an increase in the bearing speed and radial load, the cage with the unbalanced rollers runs unsteadily accompanied by a high-frequency vibration when the roller imbalance is large enough. The vibration amplitude of the cage in the horizontal direction is greater than that in the vertical direction during an unstable operation, which is similar in the stable status.     

Medium Earth Orbit dynamical survey and its use in passive debris removal

The Medium Earth Orbit (MEO) region hosts satellites for navigation, communication, and geodetic/space environmental science, among which are the Global Navigation Satellites Systems (GNSS). Safe and efficient removal of debris from MEO is problematic due to the high cost for maneuvers needed to directly reach the Earth (reentry orbits) and the relatively crowded GNSS neighborhood (graveyard orbits). Recent studies have highlighted the complicated secular dynamics in the MEO region, but also the possibility of exploiting these dynamics, for designing removal strategies. In this paper, we present our numerical exploration of the long-term dynamics in MEO, performed with the purpose of unveiling the set of reentry and graveyard solutions that could be reached with maneuvers of reasonable $\mathrm{\Delta }V$ cost. We simulated the dynamics over 120–200?years for an extended grid of millions of fictitious MEO satellites that covered all inclinations from 0 to 90°, using non-averaged equations of motion and a suitable dynamical model that accounted for the principal geopotential terms, 3rd-body perturbations and solar radiation pressure (SRP). We found a sizeable set of usable solutions with reentry times that exceed $～40$ years, mainly around three specific inclination values: 46°, 56°, and 68°; a result compatible with our understanding of MEO secular dynamics. For $\mathrm{\Delta }V?300$ m/s (i.e., achieved if you start from a typical GNSS orbit and target a disposal orbit with $e<0.3$), reentry times from GNSS altitudes exceed $～70$ years, while low-cost ($\mathrm{\Delta }V?5–35$ m/s) graveyard orbits, stable for at lest 200?years, are found for eccentricities up to $e\approx 0.018$. This investigation was carried out in the framework of the EC-funded “ReDSHIFT” project.     

微小卫星三轴稳定磁控算法工程应用

为降低微小卫星的成本和提高卫星可靠性,研究采用磁力矩器作为唯一执行机构对卫星进行三轴姿态稳定的问题。利用线性二次型调节器（LinearQuadraticRegulator,LQR）最优控制理论分别设计无限时间状态调节器和定常增益状态调节器,实现纯磁控下的微小卫星对地三轴稳定控制。同时结合卫星实际工程应用,以在轨飞行的“开拓一号”卫星为研究对象,分析卫星惯量积、轨道倾角、剩磁干扰、气动干扰等因素对控制精度的影响。仿真结果表明LQR控制器具有稳定性和实用性,在小干扰情况下,控制精度较高。     

星敏感器光轴热稳定性仿真分析方法

热稳定性用来衡量星敏感器光轴指向抵抗温度变化影响的能力,常用试验及仿真的方法进行分析验证.仿真方法因其高效率、低成本、可贯穿产品设计全周期等优点,已成为热稳定性分析验证的重要手段.开发了一种热 力 光联合仿真分析的方法进行星敏感器热稳定性计算.该方法集合了热分析、变形分析、成像仿真及热漂移计算等多项仿真分析过程.以某高精度星敏感器为例,进行了热稳定性计算,结果表明了该仿真方法的有效性.