渗碳气氛的热力学及动力学分析

本文对渗碳气氛进行热力学及动力学分析,给出炉气各组分间反应速率的测试方法及测试数据。结果表明,渗碳气氛的独立反应数为4,自由度为3,甲烷的渗碳作用不可忽略,控制甲烷这一碳源有利于提高碳势控制精度.     

舰载火箭子母弹最优火力分配

舰载火箭子母弹对岸上目标实施火力压制射击时,火力分配方式直接影响毁伤效果和火力支援任务的完成.针对舰载火箭子母弹的射击特点,首先分析了海上射击误差,然后探讨了集群目标的简化处理方法,最后给出了最优火力分配时表尺差计算公式,并进行了举例分析.利用最优火力分配方法来计算舰载火箭子母弹效力射表尺差,避免了指挥员战场射击指挥的盲目性,可以在相同弹药消耗量情况下取得最佳射击效果,对未来舰载火箭子母弹的火力运用具有较高的现实意义.     

退化速率跟踪粒子滤波在剩余使用寿命预测中的应用

毋庸置疑,剩余使用寿命预测对于设备的健康管理越来越重要。近年来粒子滤波方法被越来越多地应用到设备寿命预测技术当中,这是因为粒子滤波方法能更好地解决非线性非高斯系统滤波问题,而且能够获得不确定度信息。但该方法的预测性能却过度依赖于预测模型,并且对于模型参数的初始分布也比较敏感,这在一定程度上限制了粒子滤波预测方法的进一步发展。针对基本粒子滤波预测方法的不足,提出了一种基于退化速率跟踪粒子滤波的通用预测框架,以历史观测数据的退化速率统计规律作为指导来跟踪目标数据的退化速率,实现对粒子滤波预测方法的简化,并将该方法用于轴承和锂离子电池的剩余使用寿命预测,验证了方法的有效性。     

On lifetimes in random environments

For a component operating in random environment, whose hazard rate is assumed to be the realization of a suitable increasing stochastic process, conditions are found such that its lifetime is increasing in likelihood ratio (ILR). For the lifetimes of two components of the same kind some comparisons based on partial stochastic orders are presented. Some applications to the case of repairable components are finally provided. © 1998 John Wiley & Sons, Inc. Naval Research Logistics 45: 365–375, 1998     

可靠度限制下相控阵雷达天线阵面T/R单元维修模型

为了描述维修活动对相控阵雷达天线阵面系统的影响,构建了以可靠度为基础的“修旧不如新”定期维修优化模型。对相控阵雷达T/R单元失效下的天线性能参数进行分析,根据指标确定系统不能正常工作的失效T/R单元阈值; 针对大部分维修活动都难以使T/R单元修复如新的事实,引入失效率递增因子,在系统一定的可靠度水平上,以相控阵雷达系统的使用可用度和维修费用率为优化决策参数,建立了系统的维修优化模型,并运用边际效能算法对系统的最佳预防换件维修周期和换件维修组数量进行求解。实例运算结果表明,该模型突破了已有模型“修旧如新”的限制条件,更符合实际,能为维修策略的制定提供理论依据。     

Some new results on the preservation of the NBUE and NWUE aging classes under the formation of coherent systems

We consider the classical problem of whether certain classes of lifetime distributions are preserved under the formation of coherent systems. Under the assumption of independent and identically distributed (i.i.d.) component lifetimes, we consider the NBUE (new better than used in expectation) and NWUE (new worse than used in expectation) classes. First, a necessary condition for a coherent system to preserve the NBUE class is given. Sufficient conditions are then obtained for systems satisfying this necessary condition. The sufficient conditions are satisfied for a collection of systems which includes all parallel systems, but the collection is shown to be strictly larger. We also prove that no coherent system preserves the NWUE class. As byproducts of our study, we obtain the following results for the case of i.i.d. component lifetimes: (a) the DFR (decreasing failure rate) class is preserved by no coherent systems other than series systems, and (b) the IMRL (increasing mean residual life) class is not preserved by any coherent systems. Generalizations to the case of dependent component lifetimes are briefly discussed.     

基于故障树分析的航空装备体系结构贡献率评估方法

针对航空装备体系构成复杂的特点,将故障树分析引入航空装备体系结构贡献率评估问题,提出基于故障树分析的评估方法.从作战装备、信息支援装备和保障装备三个方面构建航空装备体系结构,建造航空装备体系结构故障树;采用底事件的关键重要度指标来计算航空装备的体系结构贡献率,建立基于关键重要度的航空装备体系结构贡献率评估模型;以某航空...     

Phenomenological modelling of flow behaviour of 20MnMoNi55 reactor pressure vessel steel at cryogenic temperature with different strain rates

In the present study a phenomenological constitutive model is developed to describe the flow behaviour of 20MnMoNi55 low carbon reactor pressure vessel (RPV) steel at sub-zero temperature under different strain rates. A set of uniaxial tensile tests is done with the variation of strain rates and temperature ranging from 10⁻⁴ s⁻¹ to 10⁻¹ s⁻¹ and -80 °C to −140 °C respectively. From the experimental data, family of flow curves at different temperatures and strain rates are generated and fitted exponentially. The strain rate and temperature dependence of the coefficients of the exponential flow curves are extracted from these curves and characterised through a general phenomenological constitutive coupled equation. The coefficients of this coupled equation are optimised using genetic algorithm. Finite element simulation of tensile tests at different strain rates and temperatures are done using this coupled equation in material model of Abaqus FEA software and validated with experimental results. The novelties of proposed model are: (a) it can predict precisely the flow behaviour of tensile tests (b) it is a simple form of equation where fitting parameters are both function of strain rate ratio and temperature ratio, (c) it has ability to characterize flow behaviour with decreasing subzero temperatures and increasing strain rates.     

越肩发射原理仿真

作为当今最新的火控攻击方式 ,越肩发射包括前射和后射两种发射方式。首先建立了前射的数学模型 ,然后进行了仿真 ,最后在总结前面工作的基础上得出了一些有益的结论     

反直升机智能雷战斗部研制费用/效能分析

给出了反直升机智能雷战斗部总体效能的评价体系。对各种评价方法进行了分析 ,提出了适用于智能雷战斗部总体效能评价的层次 TOPSIS法。应用灰色系统预测理论解决智能雷战斗部研制费用估计问题 ,建立了灰色系统 GM模型。采用费效比值准则能较好地反映智能雷战斗部综合能力。通过实例计算可以看出 ,该方法能广泛地应用于弹箭系统