Centroid index: Cluster level similarity measure

In clustering algorithm, one of the main challenges is to solve the global allocation of the clusters instead of just local tuning of the partition borders. Despite this, all external cluster validity indexes calculate only point-level differences of two partitions without any direct information about how similar their cluster-level structures are. In this paper, we introduce a cluster level index called centroid index. The measure is intuitive, simple to implement, fast to compute and applicable in case of model mismatch as well. To a certain extent, we expect it to generalize other clustering models beyond the centroid-based k-means as well.     

EXTRUSION AND LUBRICATION FLOWS OF VISCOPLASTIC FLUIDS WITH WALL SLIP

The simplest model flow which approximates the extrusion (shallow screw channels) and lubrication flow is the steady, laminar flow occurring between two infinitely long parallel plates i.e., the generalized plane Couette flow. Here we develop an analytical model of the generalized plane Couette flow of viscoplastic fluids. The deformation and flow behavior of viscoplastic fluids can be realistically represented with the Herschel-Bulkley constitutive equation, which we have utilized as the basis for the development of our analytical model. Furthermore, as also demonstrated here, the deformation behavior of viscoplastic fluids is generally complicated by the presence of wall slip at solid walls, which occurs as a function of the wall shear stress. The wall slip versus the wall shear stress behavior of viscoplastic fluids can be experimentally characterized using viscomelric flows, including steady torsional and capillary flows. Thus determined Navier's wall slip coefficient can then be utilized in modeling of processing flows. In our analytical model of the generalized plane Couette flow of viscoplastic fluids the Navier's wall slip boundary condition was included. This model should be an important engineering tool, which provides design expressions for the extrusion and lubrication flows of viscoplastic fluids, with or without wall slip occurring at the walls. @KEYWORDS:Extrusion, lubrication, flow, viscoplastic, slip.     

Friction and adsorption properties of normal and high-oleic soybean oils

The steel/steel boundary friction properties of soybean oil (SBO) and high-oleic soybean oil (HOSBO) are compared. HOSBO is significantly more saturated than SBO and more oxidatively stable. Changes in degree of unsaturation affect lateral interactions of adsorbate molecules, which in turn affects their adsorption and, hence, their boundary lubrication properties. To investigate this possibility, the free energies of adsorption (ΔG _ads) of SBO, HOSBO, and methyl laurate (ML) were determined from the analysis of friction-derived adsorption isotherms using the Langmuir and Temkin adsorption models. The results showed a stronger adsorption for the vegetable oils than for ML, an indication of multiple interactions between the ester groups of the triglycerides and the steel surface. The result also showed no difference in the ΔG _ads values of SBO and HOSBO obtained using either the Langmuir or Temkin models. This was interpreted as an indication of the lack of appreciable net lateral interaction between triglyceride adsorbates.     

基于带约束人工蜂群算法和平均Hausdorff距离的重力匹配方法

重力匹配算法是实现重力辅助惯性导航系统的关键技术之一。但是,传统重力匹配方法存在复杂度高、应用范围小等缺陷,一般很难实现精确、快速匹配的效果。将人工蜂群算法用于重力匹配的搜索过程,并将多普勒测速仪提供的速度信息作为限制条件对蜂群搜索过程进行约束。在此基础上,利用平均Hausdorff距离对匹配结果进行筛选,在重力数据库中重力异常精度一定的条件下,可降低误配率。仿真结果表明,该匹配算法在重力特征显著的区域具有较高的匹配率,可以达到精确、快速的匹配定位,从而实现重力辅助导航。     

YZ-84润滑减阻剂在金刚石钻探、绳索取心中的应用

YZ-84润滑减阻剂是以腐植酸盐为y型原料,用造纸废液为Z型原料,以及其他原料制成。它具有润滑、减阻性能好,清洗能力强,性能稳定,可复配使用,不结垢、不粘管,使用方便,成本低等特点,完全能满足新型小口径金刚石钻机高速钻进、绳索取心的技术要求。     

紧固件表面锰系磷化膜的制备及摩擦磨损性能

为了提高核主泵紧固件的摩擦磨损性能,采用三种磷化工艺在40Ni Cr Mo7钢表面制备了锰系磷化膜.采用多功能材料表面性能测试仪进行了往复摩擦磨损试验,并研究了在有无润滑条件下,不同工艺对磷化膜摩擦磨损性能的影响.采用扫描电子显微镜和能谱仪表征了磨损前后磷化膜表面的组织形貌和化学成分,并分析了其磨损失效机制.结果表明,通过工艺Ⅱ制备的磷化膜具有最优的摩擦磨损性能.磷化膜特有的孔隙结构具有储油能力,有利于改善其摩擦学性能.随着法向载荷的增加,磷化膜的塑性变形增大,抗剪切强度降低,且摩擦系数呈先缓慢下降后急剧上升的趋势.     

冷轧界面油膜厚度对表面形貌转印过程的影响

为研究冷连轧过程中接触界面润滑油膜厚度对表面形貌转印过程的影响,在跟踪实际生产中带钢表面形貌的基础上,结合轧辊表面磨损形貌以及润滑分析确定的界面油膜分布,建立真实表面接触的带钢形貌生成模型,用跟踪测量轧辊服役期内生产带钢表面的粗糙度对模型进行验证.利用模型分析在不同磨损状态下电火花毛化轧辊油膜厚度对转印形成带钢表面形貌的影响规律.结果表明:轧辊表面处于不同磨损状态时,带钢表面Ra的转印率随着油膜厚度的增加而减小;轧辊表面磨损后转印形成的带钢表面P_c的转印率在油膜厚度增加的初期基本保持不变,而后急剧减小.     

Numerical analysis of rainfall effects in external overburden dump

The effect of slope angle for external overburden dump in response to average and heavy rainfall has been analyzed using a two dimensional finite difference method of transient water flow through unsaturated–saturated soil. The external dump stability is evaluated for five geomaterial types on the basis of globally accepted safety factor analysis technique, based on shear strength reduction approach using finite difference method. The results obtained from the finite difference method of analysis indicate that the external dump with more than 30° slope angle is greatly influenced by the rainfall under the studied conditions for geomaterial 3, 4 and 5, whereas dumps with geomaterial 1 and 2 remain safe. The analysis shows that major slope failure is out of preview for the studied rainfall conditions.     

纳米间隙润滑剂季戊四醇四酯的压缩性能分子动力学模拟

季戊四醇四酯(Pentaerythritol tetra(2-ethylhexanoate),PETE)是良好的环境友好润滑剂。采用聚合物一致性力场(PCFF),分别在2种温度、3种初始油膜厚度和8种压力下对纳米间隙中PETE的压缩性能进行分子动力学模拟,研究润滑剂分子和密度的分布规律,并与经典宏观压缩试验得出的Tait方程计算值进行比较。结果表明,随着初始油膜厚度的增加,分子动力学模拟结果越接近Tait方程计算值,当初始油膜厚度为9.17 nm时,相对误差小于5%。在压缩过程中,油膜厚度和润滑剂的可压缩性能随着压力的增大而减小。对于不同初始油膜厚度的油膜,其压缩性能相近。由于PETE的分子结构中有较多且较长的支链,各方向尺度没有太大差异,受压缩后,除了接近固体壁面处有润滑剂原子聚集,其他地方不存在分层现象,且润滑剂与固体壁面之间不存在明显的空隙。     

不同工况下丁腈橡胶的摩擦磨损机理

为了合理选择螺杆泵定子橡胶材料以提高螺杆泵的使用寿命,分析了不同工况下丁腈橡胶与金属配副的摩擦磨损机理.采用MPV-600环块式摩擦磨损试验机对不同炭黑质量分数的丁腈橡胶在变载荷情况下进行摩擦磨损试验,利用体视显微镜观察橡胶磨损后的表面形貌,使用红外光谱仪分析表面官能团变化.试验结果表明:干摩擦情况下,磨损量在一定炭黑质量分数范围内随其增加而减小,磨损机制为黏着磨损和磨粒磨损;水润滑情况下,由于水的润滑及冷却作用,炭黑质量分数适中的橡胶耐磨性最好,磨损机制为磨粒磨损;原油润滑低载荷情况下,磨损量几乎不受炭黑质量分数的影响,而高载荷情况下,炭黑质量分数越高,磨损量越小,其磨损机制以腐蚀磨损为主.