概念设计时影响涡轮转子叶片强度的关键因素

基于总体结构参数对后期详细设计的重要性这一事实,探讨了航空发动机叶片概念设计中可能出现的强度问题,研究了涡轮叶片的 AN2值、轮缘切线速度、叶片稠度和材料性能等重要设计参数对强度和寿命的影响.结果表明:目前先进民用大涵道比涡扇发动机的 AN2值在25m2·(r/min)2以内,轮缘切线速度应当使得涡轮盘的形状因子控制在2以内,叶片稠度则应满足叶片能被榫连结构包容的要求,材料蠕变和低循环疲劳性能的限制要求高压涡轮叶片根部平均应力控制在250MPa左右.这些结果将为先进航空发动机和燃气轮机涡轮叶片的设计提供重要的参考依据.      

飞行器RCS控制力矩辨识方法研究

对于依靠RCS(反作用控制系统)进行控制的返回舱等跨大气层飞行器,如何获得其在真实飞行条件下RCS的控制力矩一直是一个难题。本文提出了采用系统辨识技术得到RCS控制力矩的思路,研究建立了基于最大似然准则和牛顿-拉夫逊迭代算法的参数辨识算法模型。仿真辨识及对某飞船返回舱实际飞行数据的辨识结果表明,本文建立的方法是有效的,利用其能够对飞行器的气动力矩和RCS控制力矩同时进行有效辨识。     

含共线分布多裂纹板的剩余强度

采用各向异性体平面弹性理论中的复势方法，应用保角映射技术和Faber级数展开，导出在任意载荷作用下多裂纹板应力场的级数解，引入当量屈服应力修正裂尖塑性区，并利用Swift韧带屈服准则建立舍共线分布多裂纹结构的剩余强度分析模型，计算结果与试验结果吻合较好。文中还讨论了各裂纹参数对结构剩余强度的影响。计算结果表明，本文以当量屈服应力代替材料屈服应力，避免了复杂的弹塑性分析，思路简单有效。便于工程应用。     

A forced ignition probability analysis method using kernel formation analysis with turbulent transport and Lagrangian flame particle tracking

A forced ignition probability analysis method is developed for turbulent combustion, in which kernel formation is analyzed with local kernel formation criteria, and flame propagation and stabilization are simulated with Lagrangian flame particle tracking. For kernel formation, the effect of turbulent scalar transport on flammability is modelled through the incorporation of turbulence-induced diffusion in a spherically outwardly propagating flame kernel model. The dependence of flammability limits on turbulent intensities is tabulated and serves as the flammability criterion for kernel formation. For Lagrangian flame particle tracking, flame particles are tracked in a structured grid with flow fields being interpolated from a Computational Fluid Dynamics (CFD) solution. The particle velocity follows a Langevin model consisting of a linear drift and an isotropic diffusion term. The Karlovitz number is employed for the extinction criterion, which compares chemical and turbulent timescales. The integration of the above two-step analysis approach with non-reacting CFD is achieved through a general interpolation interface suitable for general unstructured CFD grids. The method is demonstrated for a methane/air bluff-body flame, in which flow and fuel/air mixing characteristics are extracted from a non-reacting simulation. Results show that the computed ignition probability map agrees qualitatively with experimental results. A reduction of the ignition probability in the recirculation zone and a high ignition probability on the shear layer of the recirculation zone near the mean stoichiometric surface are well captured. The tools can facilitate optimization of spark placement and offer insights into ignition processes.     

充气机翼承载能力和气动特性分析

应用结构力学和材料力学的相关理论分析了一种充气机翼的承载能力,基于充气机翼特性和工程要求分析,确定了充气机翼失效的条件,建立了充气机翼弯曲变形的力学模型,并通过试验验证了该模型的合理性;然后,利用FLUENT 6.3对该种充气机翼翼型进行了气动特性仿真分析,并与相应的标准翼型进行了对比.最后,将三维充气机翼的气动载荷仿真数据导入Patran,对充气机翼在飞行状态下的应力和变形进行了有限元分析.      

基于谱分割的视频镜头聚类方法

针对现有镜头聚类算法中选择最优化分类个数复杂度较高、分类结果准确性较低的问题,提出了一种基于谱分割理论的镜头聚类算法.通过对每个镜头集构造球状高斯模型SGM(Spherical Gaussian Model),最优化地拟合镜头数据集,提高镜头分割的准确性;在镜头迭代分类过程中采用谱分割算法以提高最终分类结果的准确性;在迭代分类过程中,采用贝叶斯信息准则BIC(Bayesian Information Criterion)作为分类停止的评判标准;最后根据BIC准则计算每两类融合前后的匹配值,判断比较后对分类结果进行融合,矫正在分类过程中同一类被割裂的错误.通过3类体育视频样本对算法的有效性进行了验证、比较和分析.     

Stability and chaos of a damped satellite partially filled with liquid

The stability and chaotic motions of a damped satellite partially filled with liquid which is subjected to external disturbance are investigated in this paper. With linearization analysis, the stability of the two non-trivial equilibrium points is studied. The homoclinic and heteroclinic orbits are found by using the undetermined coefficient method, and the convergence of the series expansions of these two types of orbits is proved. It analytically demonstrates that there exist homoclinic orbits of the Si’lnikov type that join the two non-trivial equilibrium points to themselves, and therefore smale horseshoes and the horseshoe chaos occur for this system via the Si’lnikov criterion. In addition, there also exists a heteroclinic orbit connecting the two non-trivial equilibrium points. Numerical simulations are also given, which verify the analytical results. The system can be chaotic through period-doubling bifurcations as the amplitude of the external disturbance varies, and backward period-doubling bifurcations as the angular momentum of the rotor varies.     

成形极限预测韧性断裂准则及屈服准则的影响

将韧性断裂准则用于预测板材成形极限,通过数值模拟HS钢、IF钢和6111-T4铝合金3种板材在单向拉伸、平面应变和双向等拉等不同应变路径下的变形过程,获得试件中心区域主应变最大单元的应变历史,结合成形极限实验数据计算韧性断裂准则的材料常数;通过对接近平面应变变形路径下的模拟结果与实验获得的网格应变相比较分析了Hill48,Hill90和Barlat89 3种各向异性屈服准则对模拟获得的应变路径的影响.结果表明,Barlat89屈服准则可以较好地描述单元的应变路径;在此基础上比较了几种韧性断裂准则用于预测板材断裂成形极限的计算结果, Cockcroft-Latham准则和总塑性功准则的计算结果比较理想,材料常数的确定也较为简单.      

上下文无关文法测试充分性

讨论了文法测试的基本概念,分析了文法测试的特点、应用场景及其与一般软件测试的异同.形式化地定义了上下文无关文法的测试充分性准则,提出了一个上下文无关文法的测试充分性准则族.分析了该准则族中各准则之间的包含关系,以及这种包含关系与揭示文法所特有的2类缺陷的能力之间的关系. 计算和比较了准则族中各准则的测试集规模复杂性.为了评价文法的测试开销,定义了一个上下文无关文法的测试复杂性度量,该度量能够从测试充分性的角度反映测试一个文法的难易程度和测试开销的大小.      

韧性断裂准则中材料参数的特征和估算方法

对经过球化处理的20号钢进行一步加裁和两步加载实验,研究了作者提出的韧性断裂准则中材料参数的统计特征,并导出该参数的估算公式。结果表明,该参数服从正态分布,所建立的估算公式是合理的。所提出的韧性断裂准则可以揭示塑性加工过程中工件内部损伤演化规律和预测材料加工性。