正态分布定时无失效寿命分散系数

针对现有分散系数计算公式只适用于完全数据,以及近年来在寿命试验中大量出现的无失效数据并不适用的情况,将完全数据的寿命分散系数的概念推广到定时无失效寿命数据,提出定时无失效数据寿命分散系数方法,给出了相应的寿命分散系数计算公式.理论分析和结算结果表明,定时无失效数据寿命分散系数L_f*明显小于完全数据寿命分散系数L_f,从而能有效提高被完全数据寿命分散系数过分压低的安全使用寿命.      

非定常条件下喷嘴结构对燃油流量脉动的影响

假设油路处于小脉动条件下,燃油流量连续,以流量数为中间变量,推导了燃油流量脉动关于喷嘴结构的关系模型.得出结论:当外部激励一定时,燃油流量脉动与流量数成正比,与平均燃油压降的0.5次方成反比.通过喷嘴标定得出了减小流量数进而减小燃油流量脉动的方法:增加节流级数、减小节流面积,并用脉动试验证明了此方法的正确性,为喷嘴设计者在面对不稳定性问题时提供了一般的设计步骤.      

M-FSVM在可靠性寿命分布模式识别中的应用CSCD

在产品的可靠性研究中,准确、有效地识别产品所属的寿命分布,是可靠性建模成败的关键。针对传统支持向量机(SVM)在解决多分类问题时存在不可分区域等缺陷,提出了一种基于多分类模糊支持向量机(M-FSVM)的可靠性寿命分布模式识别方法,建立了包括指数分布、正态分布、对数正态分布和威布尔分布四种常用寿命分布模式识别的模糊支持向量机模型,并进行了仿真试验研究。仿真试验结果表明,该模型能够克服传统支持向量机中存在的不足,能够对常用的寿命分布模式进行智能识别,识别率高,便于工程应用。     

Simulation of temperature distribution and discharge crater of SiCp/Al composites in a single-pulsed arc discharge

SiC_p/Al composites are difficult-to-cut materials. In recent years, electrical arc discharge machining has been developed to improve the machinability of these materials. However, there is a big challenge to build a satisfactory heat transfer model of SiC_p/Al composites in the arc machining. This is not only because of the material property difference between the reinforcement and matrix material but also because of the micro-dimension SiC reinforcements. This paper established a new heat conduction simulation model considering the SiC particle-Al matrix interface and the phase change effects in a single-pulsed arc discharge of SiC_p/Al composites. A novel SiC particle-Al matrix cell geometric model was designed firstly. Then, the temperature distribution at a different depth from the workpiece surface was analyzed, the influence of sic volume fraction on temperature field was studied, and the contribution of the interface thermal resistance and latent heat were explained. To demonstrate the validity of the new numerical model, comparisons and verifications were employed. Finally, the method of improving the model was proposed and the machining mechanism of arc discharge of SiC_p/Al matrix materials was discussed. It was found that high temperature is prone to concentrate on the surface layers of the workpiece especially when the SiC fraction is high, also, the temperature fluctuates respectively at the evaporation point of aluminum and SiC, and the SiC-Al resistance has less influence on temperature distribution compared to latent heat, etc. The model build in this work improves the simulation accuracy observably compared to the previous model, and the simulation work will help to acquire a detailed mechanism of material removal of SiC_p/Al composites in the arc discharge machining.     

一类带液体晃动航天器的姿态控制

针对一类带液体晃动的航天器,在建立系统数学模型的基础上,利用一种分层滑模的设计方法来设计控制器．将系统状态变量分成可自行到达平衡位置和需要施加控制才能到达平衡位置两部分,对于需要施加控制达到预定平衡位置的状态变量,用分层滑模控制来设计控制律,将其分解成两个子系统,分别构造滑动平面,采用Lyapunov方法求取总控制量．当系统接近平衡位置时,双层滑模控制器退化成单层控制器,保证系统能够稳定在最终的平衡位置上．仿真结果表明,该方法能很好地达到控制效果．     

喷管分离流动及其侧向载荷

利用商业软件CFX对某液体火箭大面积比喷管地面条件下的分离流动进行了三维数值模拟.计算获得了喷管入口总压从8MPa减小到1MPa时的流场参数分布和侧向力载荷情况.结果表明,随着入口总压的降低,喷管内流场会依次经历自由激波分离和受限激波分离两种分离激波模态.受限激波分离模态下喷管壁面压强具有较大波动,再附着点压强甚至高于环境压强.流动分离情况下,喷管将受到一定侧向载荷作用,载荷方向随机分布.入口总压为4MPa时计算得到的侧向载荷最大,实际侧向载荷峰值可能出现在自由激波分离与受限激波分离转换瞬间.     

复合材料板壳任意位置处载荷识别

提出了一种受载单元判别法,根据遗传算法生成的染色体所对应的载荷作用点的横、纵坐标和每个单元四条边间的几何关系,判断出集中载荷作用的单元,再根据力的等效分配原则,把载荷等效分配到所在单元的节点上,进而基于有限元分析和遗传算法自身优越的全局搜索能力实现作用于复合材料结构网格节点或单元内部任意位置处的载荷识别.与现有的神经网络识别法和有限元反分析法相比,该方法具有能够识别非网格节点处的载荷的优点,且仿真算例表明其识别精度更高.      

运输机襟翼压力分布飞行试验测量

为了飞行试验测量运输机襟翼压力分布,国内首次研制了测压带。提供了直接打孔法与测压带法的飞行试验比对测量结果,表明测压带法是准确适用的。在飞行试验中采用测压带测得了某后退双开缝襟翼起飞、着陆构型的压力分布,结果表明襟翼起飞构型的气动设计有待改进,襟翼着陆构型气动效率较高。测压带法适用于飞行试验空气动力学研究和飞机气动特性的演示验证。     

Dominant Factors of Metal Jet Breakup in Micro Droplet Deposition Manufacturing Technique

For the solutions of random variations of metal jet breakup and difficulties in controlling and predicting the process parameters (e.g. jet length) in micro droplet deposition manufacturing technique, experimental methods combining with theoretical analyses have been developed. The jet formation, jet length and their dominant factors (oxygen concentration and disturbance frequency, etc.) are discussed. The statistical law of jet length is found that the probability density function (PDF) of jet length is a log-normal distribution. The results show that the formation and size accuracy of metal jet breakup are improved by adjusting the gas pressure and optimizing the disturbance frequency. Under this circumstance, the jet length and morphological deviation can be minimized, which provides a stable droplet stream for the subsequent manufacturing process.     

航班旅客的二氧化碳补偿算法研究

研究了航空旅客的碳排放分摊问题,即碳补偿问题,通过算法说明按照业载分摊与按照总重分摊哪种适于旅客。二氧化碳排放数量与燃油消耗数量对应。以A320—200为例,计算说明了在标准情况下飞机燃油消耗数量与二氧化碳补偿的定量关系,从而确定碳补偿方案。在算法基础上,设计了通用计算程序,对输出结果进行了分析。