气压缓冲器非线性数学模型辨识

为了求得某涡喷发动机中气压缓冲器的高精度数学模型,利用机理建模的方法,建立了气压缓冲器非线性数学模型的基本结构,用模型辨识方法得到了模型的参数。通过时域仿真与实测结果的比较,证明非线性模型的最大误差比线性模型的小３倍。     

区域分裂的SIMPLE算法用于管路粘性流场计算

为了研究气动系统中节流管的特性和计算节流管内部及尾部射流区的粘性流场,利用ＳＩＭＰＬＥ算法对两端带有节流口的管路粘性流场进行了数值计算,根据管路的几何形状和流动特点,对计算区域共划分了５个区,并给出了相应的分区算法和各种边界条件的处理方法,通过计算得到节流管内各项参数。计算结果表明这种算法不仅可以计算出管路内部的流场,而且可以计算出管路尾部射流区的流场,并可以较好地描述通量的守恒性。     

低重环境下圆柱贮箱内液体晃动特性研究的一种解析法

考虑低重环境下圆柱贮箱内由于表面张力影响而呈现弯曲自由液面的情况,利用Fourier Bessel级数对贮箱受横向激励时的自由液面处的边界条件进行展开,得到液体晃动系统的广义状态方程,给出了固有频率、晃动波高、晃动力和晃动力矩等晃动特性的计算公式。通过数值算例与文献结果对比,在验证文中方法正确性的同时,具体研究了各晃动特性随充液深度、外激励频率和Bond数等参数变化的规律。     

空间机械臂自适应扩展雅克比零反作用控制

针对自由漂浮空间机械臂执行在轨服务(On Orbit Servicing, OOS)时对基座姿态的扰动问题,设计了一种基于扩展雅克比矩阵的自适应零反作用运动控制器。通过巧妙利用角动量守恒定律,解决了广义雅克比矩阵的非线性参数化问题。基于此,将运动学不确定性和动力学不确定性都考虑在内,采用李雅普诺夫稳定性分析工具,得到了自适应零反作用运动控制器,可以同时实现航天器姿态调节和机械臂末端执行器对任务空间中期望轨迹的跟踪,并且不需要测量机械臂末端执行器的速度。仿真结果表明了本文所提算法的有效性。     

Solar EUV flux variation and flare brightenings

On 2010 February 8, the Extreme ultraviolet (EUV) flux variation in 195 Å and flare brightening has been examined in different sizes of active regions by using SOHO/EIT, MDI and Hα$\alpha$ observational data. These three active regions represent a large active region with a sunspot group, a moderate active region without a sunspot and a small region with weak plage in Hα$\alpha$ band respectively. Our study shows that the main full disk EUV flux comes from active regions, especially from large active regions. The sudden increases of EUV flux are corresponding to the EUV flare brightenings. For the large active region, the local EUV 195 Å flux peaks are well correlated to that of the GOES X-ray flux. The EUV 195 Å flux peaking time of M-class flares delay GOES X-ray flux a few minutes. For the moderate active region, the local EUV 195 Å flux is not well correlated to GOES X-ray flux. The EUV 195 Å flare brightenings in the moderate active region appeared in the duration of sudden increase of its own local EUV flux. For the small active region, the local EUV 195  Å flux varied almost independently of the GOES X-ray flux. Our study suggests that for an active region its local EUV 195 Å flux is more closely correlated to the EUV flare brightening than the full disk GOES X-ray flux.     

飞翼布局气动方案优选和试验验证

提出综合考虑飞翼布局隐身性能和气动性能的平面形状特征参数,分析了方案优选中的约束关系.采用参数化方法构建了三维曲面模型,并将物面网格划分流程进行自动化封装,通过更改设计参数准确快速地得到新方案的物面网格.应用基于Euler方程的数值方法进行布局方案的气动性能计算分析,在重点方案的分析中加入黏性修正;应用高频近似方法估算方案的隐身性能.以巡航状态作为设计点,在隐身性能的约束下,应用分析-修正的方法完成了气动布局方案优选,并对最终选定的方案进行风洞试验验证,证明该方案有进一步研究的价值.     

UM L顺序图的形式化定义与特性分析

以统一建模语言(UML,Unified Modeling Language)规范为基础,给出UML顺序图及组合顺序图的形式化定义;并在此基础上,详细讨论了UML顺序图中对象的消息发送特性和消息接收特性,给出了发送消息集合和接收消息集合的形式化定义;同时进一步分析了对象消息发送和接收之间的一致性问题;最后,通过实例分析,对UML顺序图的特性作进一步的解释.该形式化定义与特性分析为基于UML顺序图的模型转换和模型验证提供了必要的前提条件,也为基于UML顺序图的测试用例的自动生成奠定了基础.UML顺序图的形式化描述可用于对软件结构的理解和构造可视化建模工具.     

声发射在微铣削过程中监测刀具破损的应用

应用声发射传感器对微铣削过程中的刀具状态进行监测。通过结合传声器传感器,利用小波分析,声发射传感器能更精确有效地监测刀具破损的现象。分别在几种不同的工件材料进行了声发射监测实验。通过该声发射监测刀具破损技术采集得到信号,再利用小波分析对实验数据分析。结果表明,在微铣削中利用声发射信号来监控刀具状态的可行性。     

Shape Modification by Beam Model in FEM

Shape modification and deformation play an important role in the filed of geometry modeling, computer graphics, conceptual design and so on. A novel physically based shape modification approach is presented in this article, with beam model in finite element method (FEM). By means of interactively creating a beam with circle cross section based on pre-defined local coordinate system, the primitive geometry model is embedded in the beam globally or locally. After imposing external loads, such as concentrated force or couple, on selected nodes, their displacement can be computed. Moreover, deflection, axial deformation and twist angle of beam model can also be interpolated using shape function matrix. As a result, object is modified as a part of beam. The proposed approach is linear, simple and fast, by which stretch, bending, taping and twist deformation can be accomplished. Finally, some experimental results are given to demonstrate that the presented method is potentially useful in geometry modeling and shape design.     

三层铝板结构高速撞击损伤与极限特性

利用二级轻气炮发射铝球弹丸,在真空环境下高速撞击双层铝板和三层铝板结构,研究撞击速度、板间距、铝板厚度对结构撞击损伤的影响。然后分析三层铝板结构的撞击极限速度,并与相同面密度的双层铝板结构的试验结果进行比较。结果表明,当面密度相同时,三层铝板结构比双层铝板结构具有更强的高速撞击防护能力,增加首层铝板厚度有助于提高三层铝板结构高速撞击防护性能,当第二层铝板位于首层铝板与舱壁中间位置时,三层铝板结构的高速撞击防护性能趋于最佳。