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;以某航空装备体系为例进行建模分析。分析结果表明:所提方法能够准确评估航空装备体系结构贡献率,为确定航空装备体系结构短板、优化航空装备体系结构等提供方法支撑。     

OFDM/OQAM系统信道估计改进方法

在基于导频的信道估计方法中,伪导频的功率决定了该信道估计方法的性能。为了提高OFDM/OQAM系统的信道估计精度,提高频谱效率,提出一种基于改进导频结构的信道估计方法。在原有导频结构的基础上,对其中功率最高的导频结构进行改进,并给出对应的信道估计方法。由于缺乏足够的接收信号先验知识,无法直接对信道进行估计。为了解决这一问题,提出一种预判决方法对接收信号进行估计,并通过迭代减小预判决引入的误差,提高估计精度。仿真结果表明,本文提出的导频结构具有更高的频谱效率和更好的信道估计性能。     

Numerical modelling of non-ideal detonation in ANFO explosives applying Wood-Kirkwood theory coupled with EXPLO5 thermochemical code

Ammonium nitrate and fuel oil (ANFO) based explosive is a classic example of non-ideal high explosives. Its detonation is characterized by a strong dependence of detonation parameters on explosive charge diameter, presence and characteristics of confinement, as well as incomplete consumption of explosive at the sonic point.In this work we propose a detonation model based on the Wood-Kirkwood (WK) theory coupled with the thermochemical code EXPLO5 and supplemented with reaction rate models. Our objective is to analyze the validity of the model for highly non-ideal ANFO explosives, with emphasis on effect of reaction rate models.It was found that both single-step and two-step pressure-based models can be calibrated to reproduce experimental detonation velocity-charge radius data of ANFO at radii significantly above the failure radius (i.e. for D/D_id > ∼0.6). Single-step pressure-based model, with the pressure exponent equal to 1.4, proved to be the most accurate, even in the vicinity of the failure radius. The impact of the rate models is most evident on temporal (and spatial) distribution of flow parameters in detonation driving zone, especially when it comes to the conversion and width of detonation driving zone.     

Increasing of photostability of HNS explosive in the presence of UV photostabilizers

The photostabilies of hexanitrostillbene(HNS)were studied at 1％wt.of photostabilizers.The photo-stabilizers of Chiguard BP-12(UV-531),ADK STAB LA-326(UV-326),ADK STAB LA-32(UV-P),Irganox 1010 and Everstab LS944 were used in this study.A photoreactor including a 30 W monochromatic UV lamp was used for investigation of photodegradations of solid HNS.The changes in surface area of HNS peak in HPLC chromatogram at time intervals of 2,4,6 and 8 h were used for calculation of kinetic rate constants of photodegradation process.The compound of UV-P photostabilizer was found to have the greatest effect on enhancing photostability for HNS among the investigated photostabilizers.The kinetic rate constants were obtained 6.2 × 10-2 and 4.1 × 10-2 h-1,respectively,for photodegradation process of HNS in absence and in presence of UV-P.     

Mechanical behavior and failure mechanism of polyurea nanocomposites under quasi-static and dynamic compressive loading

Polyurea is an elastomeric material that can be applied to enhance the protection ability of structures under blast and impact loading.In order to study the compressive mechanical properties of SiC/polyurea nanocomposites under quasi-static and dynamic loading,a universal testing machine and split Hop-kinson pressure bar(SHPB)apparatus were used respectively.The stress-strain curves were obtained on polyurea and its composites at strain rates of 0.001-8000 s-1.The results of the experiment suggested that increase in the strain rates led to the rise of the flow stress,compressive strength,strain rate sensitivity and strain energy.This indicates that all of the presented materials were dependent on strain rate.Moreover,these mechanical characters were enhanced by incorporating a small amount of SiC into polyurea matrix.The relation between yield stress and strain rates were established using the power law functions.Finally,in order to investigate the fracture surfaces and inside information of failed specimens,scanning electron microscopy(SEM)and micro X-ray computed tomography(micro-CT)were used respectively.Multiple voids,crazes,micro-cracks and cracking were observed in fracture surfaces.On the other hand,the cracking propagation was found in the micro-CT slice images.It is essential to understand the deformation and failure mechanisms in all the polyurea materials.     

初相未知信号联合检测与估计的序贯实现

在未知参数的充分统计量和再生概率密度函数的基础上,引入了联合检测与估计的序贯算法,给出了算法的实现框图,并将该算法应用于高斯噪声中初相位未知信号的联合检测与估计当中.仿真实验表明,新算法较传统算法有一定的性能改善.     

线性方程组二级迭代法的收敛速度

二级迭代法由内、外迭代和内迭代次数三部分组成。给出了线性方程组二级迭代法R1-收敛因子的一个上界,这个上界由内、外迭代的R1-收敛因子和内迭代次数所决定,其主部为外迭代的R1-收敛因子。在矩阵单调性条件下,对于任何内迭代方法和任意内迭代次数,证明了外迭代的R1-收敛因子也是二级迭代法R1-收敛因子的下界。所得结果反映了内、外迭代的收敛速度以及内迭代次数对于二级迭代法收敛速度的综合影响。     

Single machine scheduling with a restricted rate‐modifying activity

In this paper we consider the problem of scheduling a set of jobs on a single machine on which a rate‐modifying activity may be performed. The rate‐modifying activity is an activity that changes the production rate of the machine. So the processing time of a job is a variable, which depends on whether it is scheduled before or after the rate‐modifying activity. We assume that the rate‐modifying activity can take place only at certain predetermined time points, which is a constrained case of a similar problem discussed in the literature. The decisions under consideration are whether and when to schedule the rate‐modifying activity, and how to sequence the jobs in order to minimize some objectives. We study the problems of minimizing makespan and total completion time. We first analyze the computational complexity of both problems for most of the possible versions. The analysis shows that the problems are NP‐hard even for some special cases. Furthermore, for the NP‐hard cases of the makespan problem, we present a pseudo‐polynomial time optimal algorithm and a fully polynomial time approximation scheme. For the total completion time problem, we provide a pseudo‐polynomial time optimal algorithm for the case with agreeable modifying rates. © 2005 Wiley Periodicals, Inc. Naval Research Logistics, 2005     

海岛阵地环境下弹药贮存寿命评估

针对海岛高温、高湿的自然环境,建立了海岛阵地环境下弹药的可靠贮存寿命模型,并以某型号弹药为研究对象,对其试验数据进行了分析,得出了在一定置信度下弹药的贮存寿命。