集成化虚拟装配系统体系结构研究

针对虚拟装配系统中的信息孤岛问题,提出了与CAD系统集成的虚拟装配系统体系结构。通过信息双向传递的VA-CADPIM模型实现虚拟装配系统与CAD系统的设计集成;采用虚拟手和鼠标、键盘的混合交互模式使设计者在沉浸式虚拟环境与非沉浸式CAD环境中相互切换,充分发挥沉浸式与非沉浸式环境的优势;通过分析系统信息流、运行原理及工作流程描述了系统的集成工作过程。基于CATIA V5及其二次开发环境,Immersion Virtual Hand SDK和组件技术实现了虚拟装配原型系统IVADS。通过某飞机的实例验证,表明该体系结构能够实现虚拟装配系统和CAD系统的无缝集成,具有较好的可扩展性和易移植性。     

High Fidelity Simulation of Turbulent Jet and Identification of Acoustic Sources

A turbulent round jet at the Reynolds number of 7,290 is simulated by direct numerical simulation to study jet noise source and its propagation. A large domain of 60 diameters in the axial direction, 30 diameters in the radial direction, and full 360 degrees is chosen to minimize the effect of boundary conditions. The spatial statistics of the simulated flow and the peak amplitude of acoustic radiation at 45 degree angle agree well with existing literature, confirming the quality of the data. Motivated by Ffowcs Williams and Hawkings equation, acoustic source terms for the far field sound propagation were identified both in the time and the frequency domains. The spectra at three respective locations of the potential core, the shear layer, and the ambient indicate that the fluctuation magnitudes are highest in the shear layer, followed by the potential core and the ambient. The turbulent characteristics are isotropic in the potential core and the shear layer, and the ambient exhibits an intermittent behavior.     

章动目标接触消旋的特征模型控制

针对含有模型不确定性的章动非合作目标接触消旋问题，提出一种基于特征模型的双通道自适应控制方法。利用接触碰撞时的几何关系和线弹性接触力模型建立消旋系统动力学模型；分析目标自由运动特性，设计分离式消旋策略；构建描述章动目标消旋系统三轴角速度特性的特征模型，计算特征参数表达式；设计基于特征模型的双通道自适应控制器。仿真实验结果表明：所提方法通过在线估计特征参数，有效克服了消旋系统不确定性因素的影响，消旋后剩余角速度小且消旋速度快。