Singular formalism and admissible control of spacecraft with rotating flexible solar array

This paper is concerned with the attitude control of a three-axis-stabilized spacecraft which consists of a central rigid body and a flexible sun-tracking solar array driven by a solar array drive assembly. Based on the linearization of the dynamics of the spacecraft and the modal identi- ties about the flexible and rigid coupling matrices, the spacecraft attitude dynamics is reduced to a formally singular system with periodically varying parameters, which is quite different from a space- craft with fixed appendages. In the framework of the singular control theory, the regularity and impulse-freeness of the singular system is analyzed and then admissible attitude controllers are designed by Lyapunov＇s method. To improve the robustness against system uncertainties, an H∞ optimal control is designed by optimizing the H∞ norm of the system transfer function matrix. Comparative numerical experiments are performed to verify the theoretical results.     

Sliding mode control based guidance law with impact angle constraint

The terminal guidance problem for an unpowered lifting reentry vehicle against a sta- tionary target is considered. In addition to attacking the target with high accuracy, the vehicle is also expected to achieve a desired impact angle. In this paper, a sliding mode control （SMC）-based guidance law is developed to satisfy the terminal angle constraint. Firstly, a specific sliding mode function is designed, and the terminal requirements can be achieved by enforcing both the sliding mode function and its derivative to zero at the end of the flight. Then, a backstepping approach is used to ensure the finite-time reaching phase of the sliding mode and the analytic expression of the control effort can be obtained. The trajectories generated by this method only depend on the initial and terminal conditions of the terminal phase and the instantaneous states of the vehicle. In order to test the performance of the proposed guidance law in practical application, numerical simulations are carried out by taking all the aerodynamic parameters into consideration. The effec- tiveness of the proposed guidance law is verified by the simulation results in various scenarios.     

Aeroelastic two-level optimization for preliminary design of wing structures considering robust constraints

An aeroelastic two-level optimization methodology for preliminary design of wing struc- tures is presented, in which the parameters for structural layout and sizes are taken as design vari- ables in the first-level optimization, and robust constraints in conjunction with conventional aeroelastic constraints are considered in the second-level optimization. A low-order panel method is used for aerodynamic analysis in the first-level optimization, and a high-order panel method is employed in the second-level optimization. It is concluded that the design of the abovementioned structural parameters of a wing can be improved using the present method with high efficiency. An improvement is seen in aeroelastic performance of the wing obtained with the present method when compared to the initial wing. Since these optimized structures are obtained after consideration of aerodynamic and structural uncertainties, they are well suited to encounter these uncertainties when they occur in reality.     

肋角度对气膜冷却特性的影响

在光滑二次流通道的基础上,分析对比了两种带肋通道(135°肋和45°肋)对气膜冷却特性的影响.采用瞬态液晶测试技术获得了气膜孔下游表面传热系数比与气膜冷却效率分布.使用Fluent软件RANS数值方法对相应结构进行了数值模拟,并使用了realizable k-ε湍流模型.光滑二次流通道模型中,气膜孔内流线呈螺旋状分布,导致较大的孔内速度分离与流动损失.冷气射流分成两部分,其中一股形成一对偏斜的对转涡.135°肋结构中,二次流通道上部分的旋转涡为顺时针方向,使得气流易于流入气膜孔,气膜孔内流线呈直线分布.45°肋结构中,二次流通道上部分旋转涡为逆时针方向,增强了气膜孔内旋转涡.45°肋结构中冷气流入气膜孔之后的流动结构与光滑二次流通道结构相似.135°肋结构气膜冷却效率最大而表面传热系数比最低.     

端壁附面层抽吸对对转压气机性能的影响

以双级对转压气机为研究对象,通过在两排转子机匣处开设抽吸孔,采用数值方法研究了不同抽吸流量下端壁附面层抽吸对压气机性能的影响,为吸附式压气机优化设计提供参考。计算结果表明:在级环境下端壁附面层抽吸可以提升压气机失速裕度,但抽吸流量过大会对效率造成一定损失,当抽吸1.6%流量时失速裕度提升了3.8%,压气机性能达到最佳;失速主要由间隙泄漏涡引起并首先在第二排转子叶尖发生,抽吸削弱了泄漏涡的强度推迟失速发生;端壁附面层抽吸增大了叶尖流通能力,使转子叶尖效率和压比得到提升,并有效改善了出口导叶流场。     

转子-支承耦合结构的模型修正研究

在转子-支承耦合结构的动力学分析过程中,结构模态参数计算结果与实验测试结果往往存在较大差异。针对此问题,应用优化算法对结构动力学模型进行修正,使计算模型能更准确地反映结构特性。建立由梁单元、盘单元、弹性支承单元组成的结构动力学有限元模型;选择优化目标函数、设计参数,并对各参数进行灵敏度分析。应用粒子群算法对选取的设计参数进行优化,得到最优模型。利用转子-滚动轴承实验器进行验证,结果表明,方法能够有效地实现转子-支承耦合结构的动力学模型修正,修正后模型更接近实际结构。     

基于ANSYS的机翼动力学分析

针对无人机在挂载导弹飞行和发射导弹时,无人机机翼由于受到多种载荷影响所产生的应力应变,应用ANSYS软件动力学分析,计算模拟了机翼在受到多种载荷影响时所产生的应力分布和应变量。分析结果表明,由于外挂物重量和机翼周围气动流场的影响,机翼会产生不同程度的颤振和扭转,其研究结果对合理设计机翼结构具有一定的参考意义。     

低碳硅锰系结构钢中相变诱发塑性的研究

在低碳硅锰系结构钢中，也可获得ＴＲＩＰ效应，使其力学性能尤其是延伸率大幅度提高。本研究硅含量较高的Ｂ钢残余奥氏体稳定性增强，ＴＲＩＰ效应显著。     

利用混合遗传算法的线性飞机动力学最大似然辨识

本文论述了利用混合遗传算法于线性飞机动力学特性的最大似然辨识。这种方法与其它最小化方法进行了比较，并且发现这种方法明显地优于简单的遗传算法。这种方法也与传统的ＭＮＲ（Ｍｏｄｉｆｉｅｄ Ｎｅｗｔｏｎ－Ｒａｐｈｓｏｎ）方法和单一方法进行了比较。与ＭＮＲ方法相比，该方法的优点是没有必要说明初始参数估计，即不必给定参数边界。也不会遇到以最佳化技术为基础的梯度有时明显引起的数值问题。如果适用时，结合初始参数估计也是简单的。