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.     

Si(Al)C纤维先驱体聚铝碳硅烷的合成

采用低分子量固态聚碳硅烷和乙酰丙酮铝为原料,利用Si-H与乙酰丙酮铝之间的交联反应合成适于熔融纺丝的聚铝碳硅烷。研究了反应条件对产物数均分子量、软化点和组成结构的影响及交联反应程度与可纺性之间的关系。实验结果表明:随着反应温度的升高和反应时间的延长,反应程度提高,残余乙酰丙酮基减少,Si-O-Al交联支化结构增多,分子量和软化点增大,可纺性随之下降。当乙酰丙酮铝投料比为8%时,在370℃下反应4~6 h,可得到软化点为206~221℃,Al wt%=0.68%,具有良好可纺性的聚铝碳硅烷。     

储运过程反应失控型火灾爆炸事故的预测与防范

储运化学活泼性物质时易发生反应失控型火灾爆炸事故,其危险性随着容器的增大和储运时间的增长而增加.介绍一种储运容器中反应失控火灾爆炸事故危险性预测的方法,预测结果与实际情况具有良好的一致性,并对预防事故的冷却方法进行了实验研究.     

Fe~(3+)与S~(2-)反应的研究

Fe3+ 与S2 - 反应是一个典型的竞争反应 ,反应的生成物与反应条件有着非常密切的关系。通过理论研究和实验验证 ,确认在酸性介质中反应的生成物为Fe3+ 和单质S↓ ;在碱性介质中反应的生成物为黑色Fe2 S3↓。     

中学化学继续教育应强化实验研究

通过Ｚｎ与Ｃｕ（ＮＯ_３）_２溶液反应的实验分析,提出了研究和全面认识置换反应的思路。对中学化学教师继续教育中实验教学应解决的问题进行了讨论。     

溴酸盐体系中的化学波

本文对溴酸盐体系中的化学波进行了实验研究,得到了反应物的初始浓度与波速的关系,随 ＫＢｒＯ３和 Ｈ２ＳＯ４初始浓度的增加,波速具有增加的趋势,而随 ＭＡ的初始浓度的增加而变化不大。并给出了其反应机理的分析及数学模型。     

基于核主成分分析方法的水面舰艇空中目标威胁评估?

对来袭空中目标的威胁进行评估与排序是舰艇对空火力分配的重要一环。根据来袭空中目标的特点,在确定目标指标后进行相应量化,针对来袭目标各指标间非线性的特点,提出使用核主成分分析法对目标信息进行特征提取,随后依据核主成分方差贡献率对威胁目标进行评估与排序。通过仿真算例验证,所得结果较为准确、客观,有效地克服传统方法中主观性较强的问题,并且在对指标数据提取的过程中降低了相关信息维数,降低了计算复杂度,为舰艇防空作战威胁评估提供了新途径。