摩擦电喷镀Ni-Co-MoS2复合镀层摩擦学性能研究

采用摩擦电喷镀技术制备Ni-Co-MoS2复合镀层,系统试验研究了复合镀层的摩擦学性能。结果表明,Ni-Co-MoS2复合镀层在滑动摩擦条件下,摩擦因数主要取决于镀层中MoS2微粒的含量、滑动速度和载荷;MoS2微粒的减磨作用,可有效改善镀层的耐磨性;在滑动摩擦条件下,Ni-Co-MoS2复合镀层的耐磨性能将随MoS2含量的提高而提高。     

分布式卫星系统相对运动的Hamilton力学建模及求解方法研究

介绍了地球扁率摄动下分布式卫星系统(DSS,Distributed Satellite System)相对运动的Hamilton动力学模型,给出DSS相对运动的Hamilton正则方程;针对地球扁率摄动下DSS相对运动的两点边值问题,提出了一种基于生成函数的打靶求解法,应用该方法对地球扁率摄动下DSS高精度构型调整问题进行了计算,结果表明该算法具有较高的计算效率,可有效避免维数灾难问题。     

横向扰动对超声速混合层被动标量混合影响分析

采用大涡模拟数值计算二维空间发展的超声速混合层,重点分析横向扰动对混合层的标量结构、标量厚度以及标量体积卷吸率的影响。采用理论模型验证了数值方法在计算标量混合特性方面的准确性。结果表明,横向扰动频率和振幅明显影响着混合层的标量增长率和卷吸率。高频扰动增大了混合层近场标量增长率和卷吸率,但是低频扰动改善了混合层远场标量增长率。大尺度涡卷吸过程对混合层标量卷吸率起决定作用。多频扰动有效地增强了超声速混合层的标量混合。     

高超声速飞行器中若干气动难题的实验研究

回顾了近几年本研究团队在高超声速飞行器若干气动难题方面的实验研究进展。在边界层转捩方面,测量了边界层转捩现象,研究了攻角效应对圆锥边界层转捩的影响,获得了边界层转捩的脉动特性以其对飞行器表面热流和摩阻的影响。在激波-边界层干扰方面,分析了突起物形状变化对流动特性的影响,研究了复杂外形的流动特性。     

SECURITY GOVERNANCE IN SOUTH AFRICA

In the ten years since the establishment of South Africa's first inclusive democratic government, an ambitious, extensive and systematic process of reform has been carried out in the governance of security. The process is widely regarded as having been successful and a model for other processes of ‘security sector reform’ in the context of transitions from authoritarian forms of governance to democratic ones.

That this been achieved with hardly a shot fired in anger is a remarkable achievement and a credit to visionary political leadership as well as organisational capacity, in other words to effective security governance.

At the same time, progress has been uneven and sometimes fragmentary, policy intentions and commitments have not always been translated into practice, the end results have not been to everyone's liking, and transformation has engendered its own pathologies. Thus several challenges remain in improving security governance.

This article provides a broad overview of the roles played by the various actors in the governance of the security sector, including the executive, parliament and civil society. It examines the main policy frameworks and touches on organisational transformation, because it is impossible to deal with governance in isolation from these issues. Policy processes and the frameworks they give rise to—in particular—are critical for effective governance. This article deals with the defence, safety and security and intelligence fields. A comprehensive overview would need to include the governance of criminal justice and foreign policy. The article does not seek to make an overall evaluation of governance, but to identify achievements, shortfalls and challenges.     

基于排队论的油料供给最优化分析

通过有限源排队系统的理论,分析油料供给工作中在满足一定的可靠性要求下的最优设计与最优分配问题,同时结合计算机技术,提出了求数值解的方法。     

几种固体润滑层的减摩抗磨性能与耐腐蚀性能研究

在MFT-R4000摩擦磨损试验机上考察了几种固体润滑层的减摩抗磨性能,并利用电化学工作站研究了其腐蚀电流和腐蚀电位的变化情况,分析了磨损表面的形貌和硫元素的化学价态变化。几种改性表面的耐腐蚀性能从好到坏的顺序为：NSL层〉SLD层〉离子渗硫〉基体;抗磨性能从好到坏的顺序为：NSL层〉SLD层〉离子渗硫〉基体;摩擦因数从大到小的顺序为：基体〉离子渗硫〉SLD层〉NSL层。NSL层的耐腐蚀性能和抗磨减摩性能最好,原因主要是基础油和纳米材料的润滑作用和屏蔽作用。     

一种基于区域标记的虹膜内边缘定位新算法

提出了一种新颖简单的虹膜内边缘(瞳孔)定位算法.首先,采用Soble边缘检测算子和形态学变换进行边缘检测;然后,利用区域标记法为边缘检测后形成的各连通成分赋予相应的灰度值,并利用直方图的方法分离出瞳孔区域;最后,采用投影的方法进行瞳孔的定位.实验结果表明,文中提出的方法能够准确地进行虹膜内边缘定位.     

二维超声速混合层的大涡模拟

对二维超声速混合层流动进行大涡模拟。采用五阶精度的WENO格式求解大尺度涡的控制方程,小尺度涡的作用采用Smagorinsky亚格子模型进行模拟。模拟结果再现了二维超声速混合层拟序结构,计算得到了涡组对、合并等现象。通过对流场不同位置压力振荡历程的频谱分析,对超声速混合层中的谐波变化规律作了初步探讨。计算得到的速度剖面的时均统计结果与实验结果相比,吻合程度较好。     

棱纹面与洛仑兹力对湍流边界层特性影响的比较

用氢气泡技术对棱纹面平板以及施加行波式洛仑兹力的平板水边界层开展流动显示实验研究,探讨棱纹面与行波式洛仑兹力影响湍流边界层相干结构的作用机理.实验结果表明,棱纹面与洛仑兹力促进了边界层由层流向湍流的转捩;而对于湍流边界层,在一定的无量纲参数范围内棱纹面与行波式洛仑兹力都能实现边界层的局部减阻,相应地湍流边界层粘性底层低速条带平均间距有所增加.