An efficient SPH methodology for modelling mechanical characteristics of particulate composites

Particulate composites are one of the widely used materials in producing numerous state-of-the-art components in biomedical, automobile, aerospace including defence technology. Variety of modelling techniques have been adopted in the past to model mechanical behaviour of particulate composites. Due to their favourable properties, particle-based methods provide a convenient platform to model failure or fracture of these composites. Smooth particle hydrodynamics (SPH) is one of such methods which demonstrate excellent potential for modelling failure or fracture of particulate composites in a Lagrangian setting. One of the major challenges in using SPH method for modelling composite materials depends on accurate and efficient way to treat interface and boundary conditions. In this paper, a master-slave method based multi-freedom constraints is proposed to impose essential boundary conditions and interfacial displacement constraints in modelling mechanical behaviour of composite materials using SPH method. The proposed methodology enforces the above constraints more accurately and requires only smaller condition number for system stiffness matrix than the procedures based on typical penalty function approach. A minimum cut-off value-based error criteria is employed to improve the compu-tational efficiency of the proposed methodology. In addition, the proposed method is further enhanced by adopting a modified numerical interpolation scheme along the boundary to increase the accuracy and computational efficiency. The numerical examples demonstrate that the proposed master-slave approach yields better accuracy in enforcing displacement constraints and requires approximately the same computational time as that of penalty method.     

Shock-induced reaction behaviors of functionally graded reactive material

In this paper, the ballistic impact experiments, including impact test chamber and impact double-spaced plates, were conducted to study the reaction behaviors of a novel functionally graded reactive material (FGRM), which was composed of polytetrafluoroethylene/aluminum (PTFE/Al) and PTFE/Al/bismuth trioxide (Bi₂O₃). The experiments showed that the impact direction of the FGRM had a significant effect on the reaction. With the same impact velocity, when the first impact material was PTFE/Al/Bi₂O₃, compared with first impact material PTFE/Al, the FGRM induced higher overpressure in the test chamber and larger damaged area of double-spaced plates. The theoretical model, which considered the shock wave generation and propagation, the effect of the shock wave on reaction efficiency, and penetration behaviors, was developed to analyze the reaction behaviors of the FGRM. The model predicted first impact material of the FGRM with a higher shock impedance was conducive to the reaction of reactive materials. The conclusion of this study provides significant information about the design and application of reactive materials.     

Influence of a liquid-filled compartment structure on the incoming shaped charge jet stability

Liquid-filled compartment structure consists of a bulk steel plate with matrix blind holes which are filled with liquid and a steel front plate to seal up the liquid with rings and bolts.The liquid-filled compart-ment structure can resist the shaped charge warhead effectively.This paper presents experimental and theoretical investigations of the penetration ability of the residual shaped charge jet emerging from the liquid-filled compartment structure after the penetration process at different impact angles.On the basis of shock wave propagation theory,the influence of the liquid-filled compartment structure on jet sta-bility is analysed.The interferences of the liquid backflow caused by a reflected shock wave and a back plate on jet stability under different impact angles are also examined.In addition,the range of the disturbed velocity segments of the jet at different impact angles and the penetration ability of the re-sidual jet are obtained.A theoretical model is validated against the experimental penetration depths.     

设备健康状态评估指标体系约简方法

针对设备健康状态评估涉及指标多、指标间关系复杂的问题,提出基于粗糙集和遗传算法的设备健康状态评估指标体系约简方法.将粗糙集理论和遗传算法相结合,对设备健康状态评估指标进行约简的同时,提高约简效率.某燃气轮机健康状态评估指标体系约简案例显示,该方法能够在不失代表性、系统性的前提下,将复杂指标体系约简为较为简洁、明了的指标体系,保持评估结果准确的同时减少信息收集工作量.     

批量独立可修件的备件需求预测仿真算法

利用Monte Carlo随机仿真技术,采用事件调度法的仿真策略对可修件的使用与维修过程进行仿真,给出了在给定备件和维修分队数量下批量独立可修件的备件保障概率仿真算法,并用一系列计算实例证明了算法的可行性和正确性,该算法能有效解决安装在不同装备上,具有不同已工作时间、不同故障间隔时间分布、不同修复时间分布的可修件的备件保障概率计算问题,为备件的科学储备提供了有力的决策依据。     

军工企业转型问题中的三个不等式

在当前鼓励民营资本进入军品市场,参与军工企业的改组改造这一政策背景下,分析了当前军工企业转型中的竞争与管制、姓"军"与姓"民"、法制与法治等三对辩证关系,澄清了对民营资本参与军工企业改组改造这一举措的模糊认识,对更好地推进优质民营企业参与军工建设有现实意义。     

国外经典核爆炸放射性沉降模式概述

介绍了国外经典的核爆炸放射性沉降模式,包含了DELFIC、WSEG系列、KDFOC系列、SEER系列、DNAF系列和EM-1。同时列举了各种模式在主要物理过程中的区别,包括了云的初始化、粒子分布、沉降机制,放射性活度和剂量率的转化、放射性衰变和传输过程。最后简述了目前核爆炸放射性沉降模式研究的发展趋势。     

Optimal joint preventive maintenance and production policies

We study joint preventive maintenance (PM) and production policies for an unreliable production‐inventory system in which maintenance/repair times are non‐negligible and stochastic. A joint policy decides (a) whether or not to perform PM and (b) if PM is not performed, then how much to produce. We consider a discrete‐time system, formulating the problem as a Markov decision process (MDP) model. The focus of the work is on the structural properties of optimal joint policies, given the system state comprised of the system's age and the inventory level. Although our analysis indicates that the structure of optimal joint policies is very complex in general, we are able to characterize several properties regarding PM and production, including optimal production/maintenance actions under backlogging and high inventory levels, and conditions under which the PM portion of the joint policy has a control‐limit structure. In further special cases, such as when PM set‐up costs are negligible compared to PM times, we are able to establish some additional structural properties. © 2005 Wiley Periodicals, Inc. Naval Research Logistics, 2005.     

北洋海军在甲午战争中的后路保障

北洋海军作为一支近代化的海上武装,其“前路”舰队的一切行动均离不开“后路”保障,在某种程度上甚至后者还对前者作战胜负具有决定性的影响。本文主要考察甲午战争期间对北洋海军机动力、续航力、战斗力及其恢复影响较大的煤炭补给、弹药供应、装备维修等三个方面的保障需求与能力,并兼及其他相关内容,通过厘清具体保障过程和基本史实,评估后路各项保障与综合保障的效能及其对北洋海军作战的实际影响,进而揭示北洋海军前路失败与后路保障的关系。     

《中华人民共和国军事史要》评价

中华人民共和国已经走过了55年的光辉历程,人民解放军与祖国同行,这半个多世纪的历程是一部光辉的篇章。由中国人民解放军军事科学院军事历史研究所《中华人民共和国军事史要》编写组撰写的《中华人民共和国军事史要》(军事科学出版社出版)一书,以丰富的史料,真实客观地记录了50多年军事斗争、国防和军队现代化建设的伟大历史,热情讴歌了新中国军事建设所取得的巨大成就,对了解与研究中华人民共和国的国防建设和军队建设的历史与成就、经验与教训,探索建设有中国特色的国防和军队现代化建设的规律,具有十分重要的意义。一《中华人民共和国军…