一种研究逆向卸荷膜片式减压器稳定性的BP神经网络改进算法

为更好地研究多结构参数耦合变化下减压器PPR(pressure reducing regulator)的稳定性，使用BFGS (Broyden-Fletcher-Goldfarb-Shanno)拟牛顿法替换梯度下降法，实现了基于Wolfe条件的一维线搜索变步长BP(back propagation)算法.结果表明:改进的BP算法使迭代次数减少了1~2个数量级，且易于收敛到最小点.该算法用于逆向卸荷膜片式减压器时，能适应2~3个结构参数的耦合，可预测大于106个数据点的数据集.多结构参数同时变化时，更容易找到使得减压器稳定的结构参数组合.更重要的是这些结构参数同时变化时减压器的稳定性比仅其中一个参数变化时更好.      

一种可靠性增长试验抽样数Max-Min准则的反馈修正方法

对成败型航空发动机部件可靠性增长试验抽样数的确定问题进行了研究。推导出了初始故障数服从典型离散分布时的最小化最大准则(Max-Min准则),提出了一种逐次抽样样本估计值反馈修正方法。最后给出了一个应用实例,验证了该方法的有效性。     

直升机高置信度中值使用飞行谱编制方法

依据直升机使用寿命分布规律,在高置信度条件下,提出了飞行谱编制的最小样本容量准则。在此基础上,采用科目统计和飞行状态分解技术,基于单机10年统计分析的方法,研究了直升机高置信度中值使用飞行谱编制原理,以此编制的使用飞行谱具有一定的置信区间,能够真实地反映直升机单机短期执行任务的分散性和整个机群长期服役的规律性,为研究直升机关键动部件的损伤与直升机定寿提供依据。     

Numerical study on combustion efficiency of aluminum particles in solid rocket motor

The combustion of aluminum particles in solid rocket motor plays an important role in energy release of propellants. However, due to the limited residence time, aluminum particles may not be burned completely, thus hindering the improvement of specific impulse. This study aims to explore the characteristics of aluminum combustion efficiency and its influencing factors by experiments and numerical simulations, providing a guideline for engine performance improvement. As an input of simulation, the initial agglomerate size was measured by a high pressure system. Meanwhile, the size distribution of the particles in plume was measured by ground firing test to validate the numerical model. Then, a two-phase flow model coupling combustion of micro aluminum particle was developed, by which the detailed effects of particle size, detaching position and nozzle convergent section structure on aluminum combustion efficiency were explored. The results suggest that the average combustion temperature in the chamber drops with increasing initial particle size, while the maximum temperature increases slightly. In the tested motors, the aluminum particle burns completely as its diameter is smaller than 50 μm, and beyond 50 μm the combustion efficiency decreases obviously with the increase of initial size. As the diameter approaches to 75 μm, the combustion efficiency becomes more sensitive to particle size. The combustion efficiency of aluminum particle escaping from end-burning surfaces is significantly higher than that from internal burning surface, where the particle combustion efficiency decreases during approaching the convergent section. Furthermore, the combustion efficiency decreases slightly with increasing nozzle convergent section angle. And theoretically it is feasible to improve combustion efficiency of aluminum particles by designing the convergent profile of nozzle.     

电大尺寸平面数字相控阵外场通道校准测试方法

电大尺寸平面数字相控阵通道校准测试对暗室规模和质量要求极高，扫描架探针移动速度受限导致通道校准的暗室测试时间长达数小时，且长时间测试引起的温度变化会造成通道相位漂移从而导致测试结果不准确。针对存在的问题，提出了一种外场通道校准测试方法，整个阵面中所有通道单次校准测试仅需几分钟，可有效解决由于长时间测试引起的温度变化进而造成的通道相位漂移问题，并通过引入基准通道来解决外场通道校准测试中存在的收发不同源问题。测试方法可有效缩短电大尺寸平面数字相控阵的通道校准时间，提高测试准确性，降低天线测试过程中的时间成本和暗室硬件建造成本。最后，通过某Ka频段电大尺寸平面数字相控阵测控系统的外场测试，验证了方法的可行性和正确性。