A new steering approach for VSCMGs with high precision

A new variable speed control moment gyro (VSCMG) steering law is proposed in order to achieve higher torque precision. The dynamics of VSCMGs is established, and two work modes are then designed according to command torque:control momentum gyro (CMG)/reaction wheel (RW) hybrid mode for the large torque case and RW single mode for the small. When working in the CMG/RW hybrid mode, the steering law deals with the gimbal dead-zone nonlinearity through compensation by RW sub-mode. This is in contrast to the conventional CMG singularity avoidance and wheel speed equalization, as well as the proof of definitely hyperbolic singular property of the CMG sub-mode. When working in the RW single mode, the motion of gimbals will be locked. Both the transition from CMG/RW hybrid mode to RW single mode and the reverse are studied. During the transition, wheel speed equalization and singularity avoidance of both the CMG and RW sub-modes are considered. A steering law for the RWs with locked gimbals is presented. It is shown by simulations that the VSCMGs with this new steering law could reach a better torque precision than the normal CMGs in the case of both large and small torques.     

Design and implementation of rigid-flexible coupling for a half-flexible single jack nozzle

The aerodynamic design of a rigid-flexible coupling profile is the decisive factor for the flow-field quality of a supersonic free jet wind tunnel nozzle, and its mechanic dynamic features are the key for engineering implementation of continuous Mach number regulations. To fulfill the requirements of a free jet inlet/engine compatibility test within a wide simulation envelop, both uni-form flow-fields of continuous acceleration and deceleration are necessary. In this paper, the aero-dynamic design methods of an expansion wall and machinery implementation plan for the half-flexible single jack nozzle were researched. The profile control in nozzle flexible plate design was studied with a rigid-flexible coupling method. Design and calculations were performed with the help of numerical simulation. The technique of axial free stretching of the flexible plate was used to improve the matching performance between the designed elasticity profile and the theoretical one, and the rigid-flexible coupling structure was calibrated by wind tunnel tests. Results indicate that the flexible plate aerodynamic design method used here is effective and feasible. Via rigid-flexible coupling design, the flexible plate agrees with the rigid body very well, and continuous Mach number changes can be achieved during the tests. The nozzle’s exit flow-field uniformity meets the requirements of China Military Standard (GJB).     

2219铝合金变截面结构搅拌摩擦焊接工艺及组织特性

针对变截面结构产品,提出了一种变截面搭接结构搅拌摩擦焊接方法,通过加装辅助板将整条焊缝焊接方向上补偿为等厚度。焊接采用一次定位焊接+二次定位焊接+正式焊接的工艺方式,一次定位焊为预定位,二次定位焊保证辅助板与试片主体结构之间形成有效连接,正式焊保证形成完整的焊缝。焊缝表面成形良好,超声相控阵检测无超标缺陷。通过对力学性能的分析,变截面搭接结构处焊缝与非搭接处焊缝和常规对接焊缝的力学性能基本相同,平均抗拉强度均达到母材的70%以上,平均延伸率均在5.8%以上。变截面搭接焊缝焊核处晶粒形态为细小的等轴晶,靠近轴肩影响区部分的晶粒尺寸大于靠近焊缝根部的晶粒尺寸,受再结晶影响,焊缝两侧热机影响区处辅助板搭接界面消失。     

Stationary flow fields prediction of variable physical domain based on proper orthogonal decomposition and kriging surrogate model

In this paper a new flow field prediction method which is independent of the governing equations, is developed to predict stationary flow fields of variable physical domain. Predicted flow fields come from linear superposition of selected basis modes generated by proper orthogonal decomposition(POD). Instead of traditional projection methods, kriging surrogate model is used to calculate the superposition coefficients through building approximate function relationships between profile geometry parameters of physical domain and these coefficients. In this context,the problem which troubles the traditional POD-projection method due to viscosity and compressibility has been avoided in the whole process. Moreover, there are no constraints for the inner product form, so two forms of simple ones are applied to improving computational efficiency and cope with variable physical domain problem. An iterative algorithm is developed to determine how many basis modes ranking front should be used in the prediction. Testing results prove the feasibility of this new method for subsonic flow field, but also prove that it is not proper for transonic flow field because of the poor predicted shock waves.     

Integration and calibration of a multi slit spectropolarimeter

Multi-slit spectropolarimeter is a next-generation spectropolarimeter to obtain vector magnetic field information at high spatial, spectral, and temporal resolution for studying the magnetic structures on the Sun. Once developed, it can be used as ground based instrument at solar observatories, also as a space payload for various solar missions. A high spectral resolution is invariably an important parameter for accurate vector magnetic field measurements and faster cadence is required for the study of dynamical evolution of structures (e.g., solar flares, sunspots etc.) on the Sun and hence better understanding on the physics behind their evolution.     

β Cep stars from a spectroscopic point of view

In this review we present the current status of line-profile-variation studies of β Cep stars. Such studies have been performed for 26 bright members of this class of pulsating stars in the past 25 years. We describe all these currently available data and summarize the interpretations based on them in terms of the excited pulsation modes. We emphasize that line-profile variations offer a much more detailed picture of the pulsational behaviour of pulsating stars compared to ground-based photometric data. The latter, however, remain necessary to unravel the often complex frequency pattern and to achieve unambiguous mode identification for multiperiodic β Cep stars and also to derive the pulsational properties of the faint members of the class. We highlight the statistical properties of the sample of 26 stars for which accurate spectroscopic studies are available and point out some future prospects. This revised version was published online in June 2006 with corrections to the Cover Date.     

A novel control method for turboshaft engine with variable rotor speed based on the Ngdot estimator through LQG/LTR and rotor predicted torque feedforward

In order to compensate for the disturbance of wide variation in rotor demanded torque on power turbine speed and realize the fast response control of turboshaft engine during variable rotor speed, a cascade PID control method based on the acceleration estimator of gas turbine speed (Ngdot) and rotor predicted torque feedforward is proposed. Firstly, a two-speed Dual Clutch Transmission (DCT) model is applied in the integrated rotor/turboshaft engine system to achieve variable rotor speed. Then, an online estimation method of Ngdot based on the Linear Quadratic Gaussian with Loop Transfer Recovery (LQG/LTR) is proposed for power turbine speed cascade control. Finally, according to the cascade PID controller based on Ngdot estimator, a rotor demanded torque predicted method based on the Min-batch Gradient Descent-Neural Network (MGD-NN) is put forward to compromise the influence of rotor torque interference. The simulation results show that compared with cascade PID controller based on Ngdot estimator and the one combined with collective pitch feedforward control, the novel control method proposed can reduce the overshoot of power turbine speed by more than 20%, which possesses faster response, superior dynamic effect and satisfactory robustness performance. The control method proposed can realize the fast response control of turboshaft engine with variable rotor speed better.     

基于重叠网格的唇口移动变几何进气道数值模拟研究

吸气式冲压发动机的进气道需要在比较宽广的马赫数范围内工作,而变几何进气道具有良好的气动性能,成为了最佳选择。重叠网格技术是解决存在复杂运动边界流动模拟问题的有效策略,在应用于变几何进气道非定常流动模拟时需要进一步完善。采用发展的重叠网格技术,对变几何平动方式的进气道开展了数值模拟研究。针对存在物面接触重叠网格的挖洞操作在执行时无法取得合理的插值模板问题,引入了虚拟单元赋值方法和“Collar”网格方法,实现了多体相交时重叠网格的计算。为了引入“Collar”型重叠网格,对其算法作了适当修改以适应本论文所建立的洞面优化方法。对平移过程中内收缩变化所造成的对启动过程的影响进行了研究。通过迎着来流方向平移唇口,增大了进气道的内收缩比,导致内压缩段出现边界层分离,分离泡随着唇口的前移而增大,当其移出内压缩段时,原本启动的进气道进入不启动状态,而后移唇口减小了内收缩比,使分离泡减小并向下游移动,辅以边界层排移,可以改善进气道的启动性能。此外,平移速度和振荡频率对启动过程的影响也进行了研究,进气道迟滞效应随平移速度和振荡频率增大而增大。     

K8V变稳飞机飞行试验验证系统

介绍了Ｋ８Ｖ变稳飞机飞行试验验证系统的组成及功能,分别阐述了该系统的飞控软件综合验证子系统、机上地面试验数据采集与处理子系统和飞行试验数据处理分析子系统等三部分的组成、工作原理、以及在飞行试验各个阶段的不同特点和作用。通过Ｋ８Ｖ变稳飞机飞行试验的应用,表明该系统能够满足变稳飞机的软件维护、系统验收试飞及后续的应用研究,具有实时,快速,准确,自动化等优点,可为Ｋ８Ｖ变稳飞机应用研究提供重要的支持手段