A comparative study of three tool replacement/operation sequencing strategies in a flexible manufacturing system

This paper studies three tool replacement/operation sequencing strategies for a flexible manufacturing system over a finite time horizon: (1) failure replacement—replace the tool only upon failure, (2) optimal preventive tool replacement for a fixed sequence of operations, and (3) joint scheduling of the optimal preventive tool replacement times and the optimal sequence of operations. Stochastic dynamic decision models are used for strategies 2 and 3. The optimization criterion for strategies 2 and 3 is the minimization of the total expected cost over the finite time horizon. We will show through numerical studies that, with the same amount of information, the total expected costs can be reduced considerably by choosing an optimal strategy. Our conclusion is that in flexible manufacturing, optimal tool replacement and optimal operations sequencing are not separate issues. They should be considered jointly to minimize the expected total cost. © 2000 John Wiley & Sons, Inc. Naval Research Logistics 47: 479–499, 2000     

一种新的一体化压水型反应堆──热管输热核反应堆构想

本文提出了热管输热核动力反应堆的构想,即用热管代替现今压水堆的一回路管道、主泵和稳压器,并对热管输热反应堆进行了原理分析,提出了工程应用可行性等急需研究的问题。     

柱壳极限分析的广义变分原理

本文提供了适用于满足简化Mises屈服条件的刚塑性体柱壳极限分析的两类变量广义变分原理,并证明了它与柱壳极限分析的全套方程和条件等价。     

VCOHOR:一个面向复杂对象的版本模型

复杂(组合)对象的版本管理是工程数据库的重要组成部分,承担着工程DBMS定义、描述和操作同一对象的多个不同的表示或一致性状态、支持工程设计反复性和试探性过程的综合控制任务。而版本化复杂对象的数学模型、版本控制机制的逻辑设计以及版本对象的差分存贮等一直是工程数据库版本管理的重点和难点,笔者在以上诸方面进行了有益的探索。     

线膛火炮身管剩余寿命的神经网络模型研究

利用前馈式人工神经网络方法,根据试验数据,建立了某火炮身管剩余寿命(RL)模型;并用该模型研究了各特征截面内径改变量对弹丸初速改变量的影响,以及弹丸初速改变量与总内径改变量间的关系。     

过椭圆外一定点作其法线的求解分析及其几何逼近作图

对过椭圆外一定点的法线作图问题作了探讨,指出了几何作图法的不可解性。根据椭圆与其法线的几何特征关系建立了求解法线的解析方程,分析了法线问题解析求解的繁杂性。提出了一种几何逼近作图方法,并具体给出了该方法的几何作图步骤。     

装备综合保障大纲的制定

根据装备综合保障大纲要求达到的目的和所要完成的任务,提出了装备综合保障军用标准的体系表,建议并拟定了“大纲”的框架结构.     

Hypersonic impact flash characteristics of a long-rod projectile collision with a thin plate target

Impact flash occurs when objects collide at supersonic speeds and can be used for real-time damage assessment when weapons rely on kinetic energy to destroy targets.However,the mechanism of impact flash remains unclear.A series of impact flash experiments of flat-head long-rod projectiles impacting thin target plates were performed with a two-stage light gas gun.The impact flash spectra for 6061 aluminum at 1.3-3.2 km/s collision speeds were recorded with a high-speed camera,a photoelectric sensor,and a time-resolved spectrometer.The intensity of the impact flash exhibited a pulse charac-teristic with time.The intensity(I)increased with impact velocity(V0)according to I∝Vn0,where n = 4.41 for V0 ＞ 2 km/s.However,for V0 ＜ 2 km/s,n = 2.21,and the intense flash duration is an order of magnitude less than that of higher V0.When V0 ＞ 2 km/s,a continuous spectrum(thermal radiation background)was observed and increased in intensity with V0.However,for V0 ＜ 2 km/s,only atomic line spectra were detected.There was no aluminum spectral lines for V0 ＜ 2 km/s,which indicated that it had not been vaporized.The initial intense flash was emission from excited and ionized ambient gases near the impact surface,and had little relationship with shock temperature rise,indicating a new mechanism of impact flash.     

Research progress on advanced rail materials for electromagnetic railgun technology

Electromagnetic railgun attracts more and more attention due to its advantage in speed,cost,and obscurity.It is found that the rail should withstand huge mechanical and thermal shocks during the launching operation.The forms of rail failure are accompanied by gouge,grooving,transition,and arc ablation,etc.The service life of the rail has become a bottleneck restricting the development of elec-tromagnetic railgun technology.A series of researches are carried out to solve rail failure,including analysing the failure mechanism and using various advanced rail materials.This paper provides a comprehensive review of rail materials,including material composition,preparation,microstructure,and properties.We begin from a short background of the requirement of the rail material.Then a detailed investigation of rail materials is described,and the performances of those materials are introduced.Finally,further development prospect of rail material is discussed.     

Preparation and characterization of HMX/EVA/hBNNSs micro-composites with improved thermal stability and reduced sensitivity

Hexagonal boron nitride nanosheets(HBNNSs)have huge potential in the field of coating materials owing to their remarkable chemical stability,mechanical strength and thermal conductivity.Thin-layer hBNNSs were obtained by a liquid-phase exfoliation of h-BN powders and incorporated into EVA coatings for improving the safety performance of 1,3,5,7-tetranitro-1,3,5,7-tetrazocane(HMX).HBNNSs and ethylene-vinyl acetate copolymer(EVA)were introduced to HMX by a solvent-slurry process.For com-parison,the HMX/EVA and HMX/EVA/graphene(HMX/EVA/G)composites were also prepared by a similar process.The morphology,crystal form,surface element distribution,thermal decomposition property and impact sensitivity of HMX/EVA/hBNNSs composites were contrastively investigated.Results showed that as prepared HMX/EVA/hBNNSs composites were well coated with hBNNSs and EVA,and exhibited better thermal stability and lower impact sensitivity than that of HMX/EVA and HMX/EVA/G composites,suggesting superior performance of desensitization of hBNNSs in explosives.