涵道螺旋桨气动特性数值模拟

以某涵道螺旋桨为研究对象,利用动量理论分析了孤立螺旋桨和涵道螺旋桨产生不同拉力的原因;同时利用SST k-ω湍流模型,采用三维Navier-Stokes方程,利用滑移网格模型,通过数值模拟分别计算了孤立螺旋桨与涵道螺旋桨的复杂流动,分析它们在不同转速下,拉力系数、功率系数和效率的差异。分析表明,加上涵道以后,有效抑制了螺旋桨桨尖涡,减少了能量损失。在相同转速下,总拉力系数增加23%,涵道螺旋桨的拉力系数与功率系数的比值比孤立螺旋桨的高出40%,效率显著提高,同时需用功率系数也略有增加,约0.05,结果与理论分析相吻合。     

三维超声速开式空腔振荡特性研究

采用时间3阶、空间5阶的高精度、高分辨率格式,对稳态来流条件下超声速开式空腔的非定常振荡特性进行数值研究。通过二维和三维空腔压力变化、声压级、振荡频率等参数的计算和分析表明:空腔内存在典型的压力振荡,振荡有近似的周期性,且变化规律较复杂,三维空腔对主振荡频率影响较小,但振荡强度有较大的不同。     

The open shop scheduling problem with a given sequence of jobs on one machine

The paper considers the open shop scheduling problem to minimize the make-span, provided that one of the machines has to process the jobs according to a given sequence. We show that in the preemptive case the problem is polynomially solvable for an arbitrary number of machines. If preemption is not allowed, the problem is NP-hard in the strong sense if the number of machines is variable, and is NP-hard in the ordinary sense in the case of two machines. For the latter case we give a heuristic algorithm that runs in linear time and produces a schedule with the makespan that is at most 5/4 times the optimal value. We also show that the two-machine problem in the nonpreemptive case is solvable in pseudopolynomial time by a dynamic programming algorithm, and that the algorithm can be converted into a fully polynomial approximation scheme. © 1998 John Wiley & Sons, Inc. Naval Research Logistics 45: 705–731, 1998     

Open shop scheduling to minimize the number of late jobs

We develop polynomial algorithms for several cases of the NP-hard open shop scheduling problem of minimizing the number of late jobs by utilizing some recent results for the open shop makespan problem. For the two machine common due date problem, we assume that either the machines or the jobs are ordered. For the m machine common due date problem, we assume that one machine is maximal and impose a restriction on its load. © 1998 John Wiley & Sons, Inc. Naval Research Logistics 45: 525–532, 1998     

导管螺旋桨敞水性能的预报和比较

借助于计算流体力学软件,对导管螺旋桨的敞水性能进行了数值模拟,得到了在不同网格模型和湍流模型下导管螺旋桨的正车敞水性能曲线,通过与试验图谱的对比分析,发现Wilcoxk-ω模型更适合于导管螺旋桨的敞水性能计算,并且采用结构化网格和非结构化网格相结合的计算方法能够满足导管螺旋桨敞水性能预报的工程精度要求。同时,当网格中存在少量高度倾斜的网格单元时,在不影响计算收敛的情况下,仍能将计算误差控制在10%以内。此外,如果要获得更为精确的计算结果,应提高网格质量,尽量使用结构化网格,并将近壁面网格加密,合理控制壁面附近的Y+值。虽然网格数量的增加并不总是意味着计算误差的减少,但合理控制网格细密度能够获得更为可信的计算结果。     

Twittering for talent: Private military and security companies between business and military branding

Private military and security companies (PMSCs) play an increasingly important role in the provision of security-related services. In their attempts to win new clients and find suitable personnel, they take on different identities by presenting themselves as conventional businesses, military actors, and humanitarians. In this article, we examine how PMSCs deploy these identities when they recruit new personnel through social media. Our computer-assisted content analysis of Twitter messages posted by two major United States-based companies—CACI and DynCorp International—shows that while both PMSCs amplify their business and military identities to attract the most talented personnel, they construct and communicate these identities in different ways with CACI branding itself as a sophisticated, modern, and patriotic business and DynCorp as a home-grown, traditional military provider. In addition, our analysis lends force to scholars suggesting that state militaries and the private security sector compete increasingly for prospective employees using similar strategies.     

‘What is in a Name?’: The Role of (Different) Identities in the Multiple Proxy Wars in Syria

Abstract

Post-uprisings Middle East politics is frequently described as a ‘regional cold war’ involving proxy warfare that emphasises the role of shared identities linking external and local actors. But does the ‘content’ of identities impact proxy war dynamics? This article considers the present ‘battle for Syria’, a local conflict that became a theatre for multiple proxy wars involving actors emphasising identities on various levels, most notably national, religious/ sect and ethnic. It suggests that identity content does matter, with global powers more reluctant than regional players to back groups identifying at sub-national level, while foreign non-state actors are enthusiastic backers of sub-national identity.     

基于CA的雷达情报传输安全认证系统的设计与实现*

介绍了基于CA的雷达情报传输安全认证系统的整体结构及工作流程,设计了CA中心各个模块的组成和功能;使用VisualC 6.0开发工具与OpenSSL-0.9.8e开源包,实现了一个原型系统,研究了生成根钥证书,用户证书、证书吊销列表的方法和流程,为所有通信实体提供了密钥长度2048bit并遵从X.509v3标准的RSA数字证书;利用AES算法加密用户证书,结合SQLServer数据库,保证了证书的安全存储;最后探讨了USBKey智能钥匙在证书分发中的应用思路。     

3D SRAM中TSV开路测试算法研究与实现

基于三维集成电路技术实现的三维静态随机存储器,其电路中使用了大量的过硅通孔。目前过硅通孔制造工艺尚未成熟,使得过硅通孔容易出现开路或短路故障,从而给三维静态随机存储器的测试带来新的挑战。现有的过硅通孔专用测试方式虽然能够探测出过硅通孔的故障,但需要特定的测试电路来实现,这就增加了额外的面积开销,同时加大了电路设计的复杂度。因此,提出一种使用测试算法来探测过硅通孔开路故障的方法。在不增加额外面积开销的情况下,通过内建自测试电路解决三维静态随机存储器中过硅通孔的开路故障检测问题。结果显示,该过硅通孔测试算法功能正确,能够准确探测到过硅通孔的开路故障,并快速定位过硅通孔的开路位置。     

From the ESS to the EU Global Strategy: external policy,internal purpose

Security strategies are important sites for narrating the EU into existence as a security actor. The unveiling of a new global strategy on foreign and security policy for the EU immediately post-Brexit could be conceived as a pledge to remain together as a Union for the purposes of contributing to global security in a particular way. This paper offers a brief stock-taking of the EU’s way of writing security from the European Security Strategy (2003) to the EU Global Strategy (2016). A concise exegesis of these documents exposes an interesting dynamic: as exercises in ordering the world, both strategic guidelines have turned out to be major exercises in ordering the self. The comparative snapshot shows the EU as increasingly anxious to prove its relevance for its own citizens, yet notably less confident about its actual convincingness as an ontological security framework for the EU’s constituent members over time.