顶部开口条件下油罐油气爆炸数值模拟

根据油罐油气爆炸特性,基于RNG k-ε湍流模型、Finate-Rate/Eddy-Dissipation化学反应模型和相应的控制方程,采用SIMPLE算法对顶部开口条件下油气爆炸发生与发展过程进行了数值模拟。基于数值模拟结果分析了顶部开口条件下油罐油气爆炸罐外超压和火焰特征,与实验结果吻合良好,该模型可以用来预测顶部开口条件下油罐油气爆炸强度。     

基于开放环境的P2P网络主动型蠕虫传播模型

P2P网络主动型蠕虫采用主动扫描邻居节点信息的策略,能在短时间内破坏整个P2P网络,成为网络信息系统最为严重的安全威胁。结合主动型蠕虫的传播特点,考虑开放的P2P网络环境对蠕虫传播的影响,弥补现有模型忽略P2P网络动态性的不足,建立了基于开放环境的P2P网络蠕虫传播模型。与双因素模型相比较,该模型能更客观地反映现实网络中蠕虫的传播情况,在此基础上从初始已感染主机数、感染率、免疫率3方面定量分析了蠕虫的传播规律。仿真结果表明,感染率和免疫率是影响蠕虫传播的关键因素。     

希尔伯特-黄变换在脉冲涡流信号消噪与识别中的应用

针对传统方法无法有效识别不同尺寸细小裂纹所产生的脉冲涡流信号,提出一种基于希尔伯特-黄变换的脉冲涡流信号消噪与识别算法。对脉冲涡流信号进行集成经验模态分解并通过归一化自相关函数及其方差特性分选出含有噪声的本征模态函数;对含噪声的本征模态函数进行阈值消噪并与未做处理的本征模态函数重构成无噪声信号;对无噪声信号进行希尔伯特-黄变换并计算出希尔伯特边际谱;根据希尔伯特边际谱的差异识别出不同细小尺寸的表面与下表面裂纹。实验结果表明了所提方法的有效性,经过集成经验模态分解消噪,消除了噪声对脉冲涡流信号的干扰;而基于希尔伯特-黄变换的方法则能够有效识别出不同尺寸的裂纹。     

舰船装备远程维修支援体系研究

借用20世纪90年代初期中国学者提出的开放的复杂巨系统理论,以及处理开放的复杂巨系统的方法论——从定性到定量的综合集成法,揭示了舰船装备远程维修支援体系的本质是一个人机共栖的开放的复杂巨系统;给出了描述系统的基于Agent的一般框架和在巨系统理论指导下研究远程故障诊断问题的思路;最后提出了需要进一步研究的几个问题。     

Minimizing the makespan in open‐shop scheduling problems with a convex resource consumption function

We consider open‐shop scheduling problems where operation‐processing times are a convex decreasing function of a common limited nonrenewable resource. The scheduler's objective is to determine the optimal job sequence on each machine and the optimal resource allocation for each operation in order to minimize the makespan. We prove that this problem is NP‐hard, but for the special case of the two‐machine problem we provide an efficient optimization algorithm. We also provide a fully polynomial approximation scheme for solving the preemptive case. © 2006 Wiley Periodicals, Inc. Naval Research Logistics, 2006     

基于TRM的美海军火力控制系统开发框架研究

分析美海军在提出"从海到陆"的战略转移之后,为实现其战略目标开展了海军水面火力支援项目的专项研究,其关键任务系统之一是海军火力控制系统,介绍了美国防部推荐使用的技术参考模型(TRM),描述了美海军基于TRM开展的海军火力控制系统研发过程和结构框架.分析认为,美海军火力控制系统的开发工作提供了一种系统顶层开发的有效技术途径,值得参考与借鉴.     

基于压力控制的常分离式双离合器膜片弹簧设计与仿真

为了保证干式双离合器在摩擦片磨损后仍能可靠传递扭矩,首先利用解析法对常分离式膜片弹簧载荷-变形特性进行理论分析,提出了基于压力控制的膜片弹簧磨损后压力保持方法,其次通过优化设计对膜片弹簧的结构参数进行了优化,并利用MSC.Patran/Marc软件对优化后常分离式离合器膜片弹簧工作过程进行了有限元接触仿真,最终得到了更符合实际工况的膜片弹簧载荷-变形特性曲线。结果表明：经过优化后的膜片弹簧,采用压力控制方法,摩擦片磨损后无需机械补偿,仍能保证扭矩的可靠传递。     

基于开路分支线加载双模谐振器的微带带通滤波器设计

文章设计了一款基于开路分支线加载双模谐振器的微带带通滤波器。通过对开路分支线加载双模谐振器的奇偶模特性及固有传输零点分析,利用调节分支线的长度可以灵活地调整谐振器的固有传输零点位置这一特性,采用了两个具有不同分支线长度的谐振器实现了一个高选择性滤波器的设计与测试,测试结果与仿真结果基本一致。所设计的滤波器中心频率为2.45 GHz,通带宽度为150 MHz,通带内插损小于1.5 dB,具有两个位于2.27 GHz和2.57 GHz的传输零点,在2.0 GHz与2.95 GHz处的衰减分别达到41 dB和29.8 dB。此外,该滤波器尺寸小巧,设计加工方便,具有一定的实用价值。     

Investigation on the process parameters of TIG-welded aluminum alloy through mechanical and microstructural characterization

Multi-pass TIG welding was conducted on plates (15×300×180 mm3) of aluminum alloy Al-5083 that usually serves as the component material in structural applications such as cryogenics and chemical processing industries. Porosity formation and solidification cracking are the most common defects when TIG welding Al-5083 alloy, which is sensitive to the welding heat input. In the experiment, the heat input was varied from 0.89 kJ/mm to 5 kJ/mm designed by the combination of welding torch travel speed and welding current. Tensile, micro-Vicker hardness and Charpy impact tests were executed to witness the impetus response of heat input on the mechanical properties of the joints. Radiographic inspection was performed to assess the joint's quality and welding defects. The results show that all the specimens displayed inferior mechanical properties as compared to the base alloy. It was established that porosity was progressively abridged by the increase of heat input. The results also clinched that the use of me-dium heat input (1-2 kJ/mm) offered the best mechanical properties by eradicating welding defects, in which only about 18.26% of strength was lost. The yield strength of all the welded specimens remained unaffected indicated no influence of heat input. Partially melted zone (PMZ) width also affected by heat input, which became widened with the increase of heat input. The grain size of PMZ was found to be coarser than the respective grain size in the fusion zone. Charpy impact testing revealed that the absorbed energy by low heat input specimen (welded at high speed) was greater than that of high heat input (welded at low speed) because of low porosity and the formation of equiaxed grains which induce better impact toughness. Cryogenic (-196 C) impact testing was also performed and the results corroborate that impact properties under the cryogenic environment revealed no appreciable change after welding at designated heat input. Finally, Macro and micro fractured surfaces of tensile and impact specimens were analyzed using Stereo and Scanning Electron Microscopy (SEM), which have supported the experimental findings.     

Scheduling and lot streaming in two‐machine open shops with no‐wait in process

We study the problem of minimizing the makespan in no‐wait two‐machine open shops producing multiple products using lot streaming. In no‐wait open shop scheduling, sublot sizes are necessarily consistent; i.e., they remain the same over all machines. This intractable problem requires finding sublot sizes, a product sequence for each machine, and a machine sequence for each product. We develop a dynamic programming algorithm to generate all the dominant schedule profiles for each product that are required to formulate the open shop problem as a generalized traveling salesman problem. This problem is equivalent to a classical traveling salesman problem with a pseudopolynomial number of cities. We develop and test a computationally efficient heuristic for the open shop problem. Our results indicate that solutions can quickly be found for two machine open shops with up to 50 products. © 2005 Wiley Periodicals, Inc. Naval Research Logistics, 2005