局部配置法求解TBC界面裂纹应力强度因子研究

主要探讨了应用局部配置法求解拉伸载荷下和热载荷下陶瓷隔热涂层界面裂纹的应力强度因子的方法.对于陶瓷隔热涂层,其陶瓷层与粘结层之间的界面裂纹的应力强度因子是复型的,它包括应力强度因子的模和相位角.其求解与传统均质材料的应力强度因子是不同的.     

Numerical investigation on jet interaction with a compression ramp

A numerical investigation on jet interaction in supersonic laminar flow with a compres- sion ramp is performed utilizing the AUSMDV scheme and a parallel solver. Several parameters dominating the interference flowfield are studied after defining the relative increment of normal force and the jet amplification factor as the evaluation criterion of jet control performance. The computational results show that most features of the interaction flowfield between the transverse jet and the ramp are similar to those between a jet and a flat plate, except that the flow structures are more complicated and the low-pressure region behind the jet is less extensive. The relative force increment and the jet amplification factor both increase with the distance between the jet and the ramp shortening till quintuple jet diameters. Inconspicuous difference is observed between the jet-before-ramp and jet-on-ramp cases. The variation of the injection angle changes the extent of the separation region, the plateau pressure, and the peak pressure near the jet. In the present computational conditions, 120 is indicated relatively optimal among all the injection angles studied. For cold gas simulations, although little influence of the jet temperature on the pressure distribution near the jet is observed under the computation model and the flow parameters studied, reducing jet temperature somehow benefits the improvement of the normal force and the jet efficiency. When the pressure ratio of jet to freestream is fixed, the relative force increment varies little when increasing the freestream Mach number, while the jet amplification factor increases.     

负载对超声加工声学系统特性的影响

以一维超声振动系统为研究对象,以点、线、面三种不同的加载方式对工件进行加载,研究了负载对超声加工声学系统特性的影响。实验表明,当以点、线的加载方式对工件进行加载时,载荷的变化对声学系统特性各参数的影响不大;而当加载方式为面接触时,机械品质因数Qm、谐振频率fs和动态电阻R随着载荷F的增大有明显的增大趋势,动态电容C和最大电导Gmax却随着载荷F的增大而减小。     

Software defect prevention based on human error theories

Software defect prevention is an important way to reduce the defect introduction rate.As the primary cause of software defects,human error can be the key to understanding and preventing software defects.This paper proposes a defect prevention approach based on human error mechanisms:DPeHE.The approach includes both knowledge and regulation training in human error prevention.Knowledge training provides programmers with explicit knowledge on why programmers commit errors,what kinds of errors tend to be committed under different circumstances,and how these errors can be prevented.Regulation training further helps programmers to promote the awareness and ability to prevent human errors through practice.The practice is facilitated by a problem solving checklist and a root cause identification checklist.This paper provides a systematic framework that integrates knowledge across disciplines,e.g.,cognitive science,software psychology and software engineering to defend against human errors in software development.Furthermore,we applied this approach in an international company at CMM Level 5 and a software development institution at CMM Level 1 in the Chinese Aviation Industry.The application cases show that the approach is feasible and effective in promoting developers' ability to prevent software defects,inde pendent of process maturity levels.     

Acceptance sampling plan of accelerated life testing for lognormal distribution under time-censoring

Lognormal distribution is commonly used in engineering.It is also a life distribution of important research values.For long-life products follow this distribution,it is necessary to apply accelerated testing techniques to product demonstration.This paper describes the development of accelerated life testing sampling plans(ALSPs)for lognormal distribution under time-censoring conditions.ALSPs take both producer and consumer risks into account,and they can be designed to work whether acceleration factor(AF)is known or unknown.When AF is known,life testing is assumed to be conducted under accelerated conditions with time-censoring.The producer and consumer risks are satisfied,and the size of test sample and the size of acceptance number are optimized.Then sensitivity analyses are conducted.When AF is unknown,two or more predetermined levels of accelerated stress are used.The sample sizes and sample proportion allocated to each stress level are optimized.The acceptance constant that satisfies producer and consumer risk is obtained by minimizing the generalized asymptotic variance of the test statistics.Finally,the properties of the two ALSPs(one for known-AF conditions and one for unknownAF conditions)are investigated to show that the proposed method is correct and usable through numerical examples.     

单轴拉伸和压缩镁合金各滑移系的Schmid因子计算

针对单轴拉伸和压缩条件下的镁合金,计算了不同滑移系（基面滑移、柱面滑移、锥面滑移、锥面滑移）在整个取向空间中的Schmid因子分布.计算结果表明,基面滑移、柱面滑移和锥面滑移系的Schmid因子在取向空间中都有0.5的极大值;而锥面滑移系的Schmid因子普遍较低,当θ在80°左右,ψ在70°左右时的最大值仅为0.383.计算结果为镁合金变形机制的分析提供基础.     

γ-Re_θ转捩模型在高超声速下的应用及分析

为了初步研究γ-Reθ转捩模型在高超声速领域的适用性,在自行开发的CFD程序中添加了该模型,利用T3系列平板算例对该模型的实现进行了验证;针对高超声速流动,选取压缩面绕流和双圆锥扰流等算例,分别利用该转捩模型、全层流模拟、以及传统的湍流模型进行了数值模拟计算,并与实验结果进行对比。计算结果表明,尽管该转捩模型是在低速流动的基础上发展的,它仍能准确预测高超声速流动下的转捩现象。     

卫星测控直扩信号安全性能评价体系研究

为了定量评估直扩信号的安全性能,在给出卫星测控直扩信号安全防护定义的基础上,对卫星测控直扩信号安全性能评价指标进行了研究.在深入分析直扩信号典型威胁的基础上,提出了等效码长、调制指数、码速率截获因数、等效码长截获因数、码序列截获因数、干扰因数等衍生指标,分析、仿真了它们的影响因素,得到了它们与基本指标的关系,初步建立了直扩信号安全性能评价体系,为后续安全性能评估打下基础.     

基于名义极限因子和降维方法的涡轮盘结构可靠性优化

结合名义极限因子方法完全实现了可靠性分析与优化过程的解耦,使可靠性分析成为进行优化之前的预分析过程,而在预分析中采用的基于降维的可靠性分析技术,在一阶可靠度方法(FORM)获得的计算结果的基础上进行适晕的数值计算就能够提高可靠性分析的结果.最后,以某涡轮盘结构优化为例对提出的方法可行性和效率进行了验证,结果表明:该方法...     

一种基于约束因子的超载迟滞模型

在常幅载荷中加入一个超载会明显影响后续一段时间裂纹扩展的速率.要准确预测结构在变幅载荷谱下的疲劳裂纹扩展寿命,必须研究超载对裂纹扩展的影响.现有的变幅疲劳裂纹扩展模型大致可分为屈服区模型、经验的裂纹闭合模型和条带屈服模型.条带屈服模型预测较准确但需要数值迭代求解,计算量大,且程序复杂,不利于工程应用;屈服区模型比较简单...