表面粗糙度对轮轨黏着特性影响

水油介质下极易发生轮轨低黏着现象,结合轮轨黏着试验和根据二维滚动接触理论和部分弹流润滑理论建立轮轨黏着数值仿真模型,给出了水油介质下轮轨表面粗糙度对轮轨黏着系数和增黏的影响规律,验证了数值仿真模型的有效性.结果表明:水介质下随蠕滑率增加黏着系数呈先快速增加后小幅减小并稳定的变化;水、油介质下随表面粗糙度增加轮轨黏着系数呈增加趋势;水介质下轮轨表面粗糙度从1μm提高到50μm,黏着系数增加126.5%,油介质下轮轨表面粗糙度从5μm提高到20μm,黏着系数增加61.4%.     

红河油田空气泡沫驱实验

鄂尔多斯盆地南部红河油田长8油藏为典型的致密双重介质储层,注水采油时出现沿裂缝水窜现象,导致开发效果变差.为有效补充地层能量、提高采收率,开展红河油田长8储层空气泡沫驱实验.通过空气原油氧化实验,确定红河油田原油与空气在地层条件下可以发生低温氧化反应,反应速率为(0.025~0.110)×10-5 mol(O2)/(h·g)(oil);通过泡沫体系优选实验,优选阻力因子高、封堵能力强、可有效封堵储层裂缝的泡沫体系;通过长岩心空气泡沫驱油实验,认为空气泡沫驱的采收率比水驱的提高15%以上,气体突破时产出气体中O2的体积分数为1.34%~3.81%,满足空气驱的安全范围.结果表明:空气泡沫驱综合泡沫驱与空气驱的稳定、耐温、耐油和较强封堵能力等优点,在红河油田具有较好适用性,为红河油田提高采收率提供技术储备.     

TRIP steel retained austenite transformation under cyclic V-bending deformation

To investigate the transformation behavior of TRIP steel retained austenite under cyclic load, cyclic V-bending deformation of low carbon Si-Mn TRIP600 was studied by experiment and finite element in this paper. The results showed that, under cyclic V-bending deformation, retained austenite in TRIP steel transformed into martensite gradually with the increasing of bending times, and for the symmetrical characteristic, upper surface and lower surface presented the same transformation tendency. From the first to the fourth V-bending deformatiort, retained austenite volume fraction decreased nearly linearly and then attained saturation step by step. Compressive stress state was helpful for martensite transformation than tension stress state with V-bending deformation, and strain magnitude was the determining factor for retaining anstenite martensitic transformation. With the increasing of bending times effective stress increased and the relationship between maximum effective stress and bending times was nearly linear. Effective stress and effective strain distribution were non-uniform, the maximum effective stress and effective strain were present in the center of the samples. The relationships between retained austenite and V-bending times, and retained austenite with effective strain were set up as Eqs.（1）-（5）. The relationship was typical quadric function, decreased linearly for the initial deformation and attained saturation finally.     

不同温度下AZ31镁合金绝热剪切变形局域化

为了了解镁合金在不同温度高应变率载荷作用下发生变形局域化的特点,进而揭示镁合金在高速冲击载荷作用下发生绝热剪切的特殊规律,采用分离式Hopkinson压杆对挤压态AZ31镁合金进行了常温及高温的高速冲击压缩试验,而后对不同温度冲击后的试样通过光学显微镜、扫描电镜和透射电镜进行变形机制的分析.结果表明:常温下试样在受到剪切力后,在剪切区的裂纹周围产生了大量的孪晶;高温下试样的剪切区内产生了明显的绝热剪切带,并且在剪切带周围发现了大量平行的孪晶.在TEM下观察到剪切带内为等轴晶晶粒,在剪切区内发生了动态再结晶过程.     

切削加工表面完整性建模现状与发展趋势

针对切削加工表面完整性建模方法种类繁多且相互关系揭示不明等问题,总结了各表面完整性指标,包括表面形貌、残余应力、加工硬化和相变的主要建模方法,并从各建模方法的应用范围以及主要成果的角度概括了表面完整性建模的研究现状.论述了解析建模与数值建模方法在预测表面完整性各指标时的优缺点及内在联系,重点分析了数值模拟技术在表面完整性建模中的作用.指出了国内外表面完整性研究体系的区别及联系,并对表面完整性建模的发展方向作了展望.     

一种应用于噪声点分布密集环境下的噪声点识别算法

为了提高DBSCAN及其改进算法在噪声点分布密集环境下的噪声点识别率,通过结合PageRank算法思想及噪声数据分布密集的特点,构造簇间投票映射函数,提出了簇间投票噪声点识别算法-NoiseRank 。实验结果表明,在噪声点分布密集环境下,NoiseRank算法比DBSCAN算法具有更高的噪声点识别率。     

细粒层厚度与法向应力对砂土强度影响的试验研究

以河北磁县境内的砂土为研究对象,利用环剪仪对砂土的强度特性进行了研究.主要考虑细粒层厚度、法向应力对其峰值强度和残余强度的影响.结果表明:法向应力对砂土的峰值强度和残余强度及强度损失率均有影响,法向应力增大,峰值强度和残余强度均增大,强度损失率也越大,细粒层厚度对砂土强度的影响亦是如此;法向应力为50~200 kPa,细粒层厚度为0.0~2.0 mm的情况下,强度损失率由10.0%增大到28.0%;剪切面上土的性质决定了剪应力-剪切位移关系曲线的形状.     

S －次仿紧空间

针对一些广义仿紧空间以及拓扑空间中半开集和半闭集的性质,本文将次仿紧空间的一些结论推广到半闭集的条件下,新定义并研究S －次仿紧空间的基本性质。首先给出一些基本的定义和定理,然后在此基础上定义S－次仿紧空间,最后得出一些主要结果：（1）空间X是S－次仿紧空间,则X的每一开覆盖U,存在半开加细覆盖序列｛Vn｝n∈N使对每一x∈X,存在n∈N,使ord（x,Vn）＝1,这里（ord（x,Vn）＝｜｛V：V∈Vn,x∈V｝｜）;（2）空间X是S－次仿紧空间,则X的每一开覆盖具有σ垫状加细覆盖;（3）如果（X,Fa）是S－次仿紧空间,则（X,F）也是S－次仿紧空间,并给出相应的证明。     

一种能量有效的无线医疗传感器网络动态分簇协议

在无线医疗传感器网络体系结构中,由于信息的采集是由大量医疗传感器节点合作完成的,因此采用分簇路由协议能够有效减少节点能量的消耗和方便节点的拓扑管理。在相关研究的基础上提出一种新的动态分簇协议WMDCP(dynamical clustering protocol in wireless medical sensor networks),以解决目前分簇协议中缺少对医疗传感器节点动态分布的支持问题。仿真实验表明,相对其它分簇协议,WMDCP不仅可以有效地改善无线传感器网络的性能,而且可以有效延长网络中传感器节点的生存时间。     

Multiple k-hop clusters based routing scheme to preserve source-location privacy in WSNs

Privacy is becoming one of the most notable challenges threatening wireless sensor networks （WSNs）. Adversaries may use RF （radio frequency） localization techniques to perform hop-by-hop trace back to the source sensor＇s location. A multiple k-hop clusters based routing strategy （MHCR） is proposed to preserve source-location privacy as well as enhance energy efficiency for WSNs. Owing to the inherent characteristics of intra-cluster data aggregation, each sensor of the interference clusters is able to act as a fake source to confuse the adversary. Moreover, dummy traffic could be filtered efficiently by the cluster heads during the data aggregation, ensuring no energy consumption be burdened in the hotspot of the network. Through careful analysis and calculation on the distribution and the number of interference clusters, energy efficiency is significantly enhanced without reducing the network lifetime. Finally, the security and delay performance of MHCR scheme are theoretically analyzed. Extensive analysis and simulation results demonstrate that MHCR scheme can improve both the location privacy security and energy efficiency markedly, especially in large-scale WSNs.