非线性结构气动伺服弹性稳定性分析

真实的气动伺服弹性系统通常都含有各种非线性因素,它们会对系统的特性带来不可忽略的影响.为此采用一种频域方法对带有间隙的非线性结构进行气动伺服弹性稳定性分析.在气动伺服弹性运动方程中,非线性的结构刚度通过描述函数法转化为准线性的等效刚度,然后采用线性控制理论中的Nyquist方法来判断气动伺服弹性系统的稳定性并计算稳定裕度.以某一飞机的带有扑动和旋转间隙的受控翼面为例进行了数值计算.结果表明,旋转间隙对系统的稳定性影响是主要的;旋转间隙越大,系统稳定裕度越小.      

不同周向位置端壁翼刀对压气机叶栅损失影响的实验研究

在低速大尺寸叶栅风洞上通过详细测量叶栅流场,研究了叶栅端壁上不同周向位置处加装端壁翼刀对压气机叶栅损失和二次流的影响。实验结果表明,合理选择翼刀安装位置,可有效地控制压气机叶栅的二次流,降低叶栅的总损失。进一步对实验方案中叶栅总损失最小的翼刀位置的叶栅内流场进行了测量,分析了安装翼刀后流场内涡系结构的变化,探讨了翼刀涡的形成和发展变化。      

非线性动力学理论及其在机械系统中应用的若干进展

非线性动力学的理论及其工程应用是非线性科学研究的前沿和热点，应用非线性动力学的理论揭示事物动态过程现象的本质和机理，进行自主性原始创新，具有十分重大的理论和应用价值，在科学与工程中具有广阔的应用前景。综述非线性动力学基础理论方面的近期研究成果及其在机械系统中应用的研究进展。理论研究方面主要涉及揭示非线性动力系统周期分岔解与系统结构参数之间关系的C—L方法、高余维分岔的普适分类、高余维非对称分岔的普适开折、约束分岔的分类、计算非线性自治系统正规形的直接方法、计算非线性非自治系统正规形的复内积平均法以及高维非线性系统的降维方法等。应用方面主要涉及大型旋转机械非线性转子系统的失稳机理、分岔解与混沌运动、故障诊断及其综合治理技术；冲击振动机械的稳定性、Hopf分岔、亚谐分岔、余维二分岔和混沌运动；大型共振筛的非线性振动及其动力学设计方法等。     

航天器数据预测中的因果关系调整技术应用研究

在航天领域，预测参数不但受其自身时序变化的影响，也普遍受到关联因素的交叉影响。因果因素的影响也需要在时序预测过程中被考虑，该类问题被列入因果调整技术当中。为了更全面地反映航天器参数变化的实际情况，提出了一种基于层次分析法（AHP）的因果调整方法。该方法提供了因果因素的判断调整方法，并将调整系数应用于时序模型预测的修正。最终，建立了一个因果与时序预测有机结合的预测体系。     

Flutter control of a composite plate with piezoelectric multilayered actuators

Active flutter velocity enhancement scheme is presented for lifting surfaces, employing Linear Quadratic Gaussian based multi-input multi-output controller with multilayered piezoelectric actuators. To numerically test the developed concept, a composite plate wing, surface bonded with eight piezoelectric bender actuators and sensors has been considered. A modal flutter control model is formulated in state-space domain using coupled piezoelectric finite element procedures along with unsteady aerodynamics and optimal control theory. The bending – torsion flutter instability has been actively postponed from 44.13 to 55.5 m/s using the energy imparted by the multilayered piezoelectric actuators. As the power requirement by these actuators is comparatively very low with respect to stack actuators, they can be employed in an integrated form to develop active lifting surfaces for real time applications.     

Robust reliable control for autonomous spacecraft rendezvous with limited-thrust

This paper investigates the problem of robust reliable control for the spacecraft rendezvous with limited-thrust. Based on the Clohessy–Wiltshire (C–W) equations and by considering the uncertainties and the possible failures, the dynamic model for spacecraft rendezvous is proposed, and the orbital transfer control problem is transformed into a stabilization problem. Then, by a Lyapunov approach, the existence conditions for admissible controllers are formulated in the form of linear matrix inequalities (LMIs), and the controller design is cast into a convex feasibility problem subject to LMI constraints. With the obtained controllers, the rendezvous can be accomplished with the limited-thrust in spite of the possible thruster failures. The effectiveness of the proposed approach is illustrated by simulation examples.     

Coupling between structural deformation and attitude motion of large planar space structures suspended by multi-tethers

A planar space structure suspended by multi-tethers is one candidate for large and lightweight structures. For such flexible structures, coupling phenomena between structural deformation and attitude motion must be considered. In the present paper, the dynamic characteristics of a planar structure suspended by multi-tethers are investigated. Simulation results reveal that the coupling occurs for low tether stiffness. In addition, it is shown that the coupling can also occur if a number of the tethers become slack. Thermal deformation of the planar structure is one cause of tether slack. Thermal deformation and the induced attitude motion are also investigated. It is shown that roll and yaw motions become unstable due to thermal deformation. Finally, we modify the condition of the connection between sub-panels in order to reduce the overall thermal deformation, and it is confirmed that large deformation can be inhibited by the modification.     

Validation study of numerical simulations by comparison to measurements in piston-driven shock-tunnels

The simulation of high enthalpy flows, both experimentally and numerically, is a topic of international research efforts. It is important to understand and quantitatively describe the aerothermodynamic phenomena of high speed/high enthalpy flows in order to develop more capable reusable space transportation systems. A CFD-method is used here to model several piston driven shock tunnels used around the world to experimentally study re-entry and supersonic combustion phenomena. The results are compared to measured data (pressure and shock speed) of the various tunnels and shows that the approach is valid and is ideal for the development of new tunnel operating conditions and new tunnels. Using the numerical models, test facilities are compared to each other. For the medium enthalpy condition presented here, the tunnels produce similar test conditions, with the bigger ones having greater levels of nozzle supply pressure relative to the diaphragm rupture pressure, and greater test time.     

化学回热循环中工质热力性质的处理方法

采用VC和Matlab混合编程的方法,编制了CRGT循环中工质（水-水蒸气和空气-湿燃气）的热力性质计算程序。空气和干燃气的热力性质采用理想气体掺混模型,水和蒸汽的热力性质采用IAPWS-IF97标准模型,湿燃气的热力性质采用改进的工程计算方法进行处理。计算结果表明：该方法计算精度高、计算速度快。