基于AMESim的直升机液压助力器建模与仿真

介绍了直升机飞行操纵系统典型液压助力器的组成和工作原理,对助力器静动态性能分析方法进行了研究。综合考虑不可忽视液压刚度、结构刚度、摩擦、泄漏等非线性因素对系统的影响,建立了基于AMESim的助力器模型。利用该模型对直升机飞行操纵系统样例液压助力器进行仿真分析,将仿真结果和试验结果进行验证对比,结果表明仿真数据和试验数据基本吻合,较好地反映了实际系统的性能。因此仿真结果可以为直升机飞行操纵系统液压助力器打样设计和结构优化提供理论分析依据。     

微型飞行器桨翼气动干扰的数值模拟

对某一固定翼微型飞行器进行了桨翼气动干扰数值模拟研究,采用作用盘理论模拟真实桨盘的工作状态,通过时间平均稳态处理将非定常流场简化为准定常流场计算。利用FLUENT的用户自定义函数UDF实现作用盘前后压力、速度的变化。通过与无滑流影响下单独机身数值计算结果的比较,结果显示螺旋桨滑流延缓了机体上表面的气流分离,增强气流再附着能力,飞机的失速迎角增加2°,升力、阻力、俯仰力矩系数增加2%～5%,升阻比减小2%～3%。     

Experimental Investigation of the Effects of Various Plasma Actuator Configurations on Lift and Drag Coefficients of a Circular Cylinder Including the Effects of Electrodes

In this paper, the effects of the existence of plasma actuator electrodes and also various configurations of the actuator for controlling the flow field around a circular cylinder are experimentally investigated. The cylinder is made of PVC (Polyvinyl Chloride) and considered as a dielectric barrier. Two electrodes are flush-mounted on the surface of the cylinder and are connected to a DC high voltage power supply for generation of electrical discharge. Pressure distribution results show that the existence of the electrodes and also the plasma are able to change the pressure distribution around the cylinder and consequently the lift and drag coefficients. It is found that the effect of the existence of the electrodes is comparable with the effect of plasma actuator in controlling the flow field around the cylinder and this effect is not reported by other researchers. Eventually it is concluded that the existence of the electrodes or any extra objects on the cylinder and also the existence of the plasma are capable of changing the flow field structure around the cylinder so that the behavior of the lift and drag coefficients of the cylinder will be changed significantly.     

浅谈A320系列主起落架外筒难加工点的加工方法

A320系列飞机主起落架外筒是形状不规则零部件,材料为超高强度钢,为难切削加工材料,一些孔径或者孔径的端面出现腐蚀后,需要镗削去除以满足CMM规定的修理要求。为解决此类难加工问题,本文设计了一种通用性强的T型非标BT-50铣刀,操作简单,成本效益高,大大提高了起落架维修能力。     

薄壁管壳高速正撞击穿孔特性的数值研究

受径向曲率的影响,薄壁管壳遭受高速弹丸撞击产生的局部穿孔毁伤与薄板结构并不相同。本文利用LS-DYNA3D动力学程序,采用光滑粒子流体动力学和有限元法相耦合的方法(SPH-FEM),对球形弹丸高速正撞击不同直径薄壁钢管的穿孔毁伤特性进行数值研究。根据小弹丸高速撞击薄板的物理力学性质,可把穿孔过程简化为初始流动扩孔和随后的惯性扩孔两个阶段,提出一种圆柱管壳高速正撞击穿孔的简化物理模型,并分析圆管直径对轴向孔径和径向孔径尺寸差值比的影响。数值模拟结果表明,撞击速度为2~3 km/s时,薄壁钢管的正撞击穿孔略呈椭圆状,其轴向孔径尺寸稍大于径向孔径尺寸;随着薄壁钢管直径的增加,两个方向的孔径尺寸差值比减小。另外,薄壁钢管遭受小弹丸撞击穿孔后产生碎片云的分布形态受径向直径影响明显,相同撞击条件时,钢管直径越大,则产生碎片云的膨胀角和残余速度也较大。     

反射激波作用下两种重气柱界面不稳定性实验研究

在水平方形激波管中对两种无膜重气柱界面(分别是SF6和氩气)在反射激波作用下的不稳定性发展进行了实验研究。气柱界面采用射流技术形成,实验采用连续激光片光源照射流场,乙二醇作为示踪粒子,并用高速摄像机对流场进行拍摄,获得了入射激波以及反射激波共同作用下,两种不同气柱界面的演化过程。实验结果表明,两种气柱的Atwood数不同,界面演化速率不同,反射激波到达前后的界面形态不同。SF6气柱在入射激波作用下会产生两个比较明显的反向的涡环结构,而氩气柱界面上由于产生的涡量较少,涡环结构并不明显。在反射激波作用下,SF6气柱界面会出现明显的次级涡对,而且次级涡对的旋转方向与初始涡环结构的旋转方向相反。对于氩气柱而言,在反射激波作用下虽然也产生了与初始涡环方向相反的次级涡对,但次级涡对始终未充分发展。这是因为反射激波作用时氩气柱界面的Atwood数较小导致氩气柱界面上产生的反向涡量较少。实验结果充分表明了气体Atwood数对界面不稳定性的发展起到了较大的影响。     

大口径长焦距相机主次镜支撑结构方案初步研究

随着航天技术的迅猛发展,为了实现高分辨率的对地观测,大口径、长焦距的空间相机已成为发展趋势。连接相机主镜和次镜的支撑结构,很大程度上影响相机的成像性能和稳定性,是光学系统的敏感环节。为了得到更好的成像品质,文章选择了筒式、三杆式与桁架式这3种支撑方案作为研究对象,通过工程分析软件对每种结构的设计参数进行优化并进行有限元分析,通过对结构的力学稳定性、热稳定性以及质量等因素的综合考虑,最终选择桁架式支撑结构为最优方案,更适合于大口径、长焦距相机的发展趋势,并提出了该种结构进一步优化的空间与方向。     

Energy-saving and accurate motion control of a hydraulic actuator with uncertain negative loads

Pump controlled hydraulic actuators are wildly used in the aerospace industry owing to the advantages of energy-saving and integrated configurations. Negative loads may occur to actuators due to external force loads or the inertial force when the actuator decelerates significantly. Uncertain negative load working conditions may cause cavitation, actuator vibration, and even instability to the motion control if the actuator is without sufficient meter-out damping. Various types of hydraulic configuration schemes have been proposed to deal with negative loads of hydraulic actuators. However, few of them can simultaneously achieve energy saving and high control accuracy. This study proposes an energy-saving and accurate motion tracking strategy for a hydraulic actuator with uncertain negative loads. The actuator’s motion is driven by a servomotor pump, which gives full play to the advantage of energy-saving. The meter-out pressure is controlled by proportional valves to provide the optimized meter-out damping. The nonlinear adaptive robust control law is designed, which guarantees the control stability and achieve high tracking accuracy. An integrated direct/indirect adaptation law obtains satisfactory parameter estimations and model compensation for asymptotic motion tracking. Comparative experiments under different working conditions were performed to validate the advantages of the proposed control strategy.     

基于非线性未知输入观测器的航天器故障诊断

针对一类满足Lipschitz条件的非线性系统,设计了一组非线性未知输入观测器,并依据故障解耦的思想,产生结构化的残差集,实现非线性系统执行器的故障隔离。研究考虑了未知扰动对非线性系统的影响,并利用Lyapunov理论证明了所设计观测器的稳定性。最后,以三轴稳定卫星的姿态控制系统为对象,仿真验证了所提方法对各种典型执行器故障诊断的有效性。     

A longitudinal & longitudinal-torsional vibration actuator for rotary-percussive ultrasonic planetary drills

Ultrasonic drills, which can sample rocks using a lower weight on bit and lower power, are more suitable for sampling on a minor planet than conventional drills. To remove cutting chips and improve drilling efficiency, rotary-percussive ultrasonic drills (RPUD) drive drill tools for rotary-percussive motion. This paper proposes a novel longitudinal & longitudinal-torsional (L-LT) actuator, which is composed of a stepped horn, a piezoelectric stack, and a longitudinal-torsional (LT) coupler, for the RPUD. The horn magnifies the longitudinal vibration on the front surface of the piezoelectric stack, which is clamped between the horn and the LT coupler, and impacts the drill tool. The LT coupler transforms the longitudinal vibration on the back surface into longitudinal-torsional vibration, which generates elliptical movements that drive the rotor to rotate. Then, the rotor drives the drill tool to rotate. A method of adjusting the displacement amplitudes of the horn and the driving tips is discussed. The prototype achieved a maximum speed and torque of 193?r/min and 0.065?N$·$m, respectively. The maximum drilling speed through sandstone under a weight on bit of 5?N was 13?mm/min.