A constrained‐optimization methodology for the detection phase in contact mechanics simulations

The detection phase in computational contact mechanics can be subdivided into a global search and a local detection. When potential contact is detected by the former, a rigorous local detection determines which surface elements come or may come in contact in the current increment. We first introduce a rigorous definition of the closest point for non‐differentiable lower‐dimensional manifolds. We then simplify the detection by formulating an optimization problem subject to inequality constraints. The formulation is then solved using different techniques from the field of mathematical optimization, for both linear and quadratic finite element meshes. The resulting general and robust detection scheme is tested on a set of problems and compared with other techniques commonly used in computational geometry. Copyright © 2013 John Wiley & Sons, Ltd.     

一个深海能源土的温度-水压-力学二维微观胶结模型

天然气水合物以胶结形式赋存时,对深海能源土的强度和变形特性影响显著,且其影响程度与所处温度、水压与力学环境密切相关。旨在建立可考虑温（温度）-压（水压）-力（力-位移与胶结破坏准则）耦合影响的深海能源土微观胶结模型。首先,依据能源土中水合物胶结可发生于两种接触形式（直接接触与有间距）的土颗粒间,提出适用于两种胶结模式的力-位移准则和胶结破坏准则。其次,提出温压距离参数L（表示在无量纲化处理后的温度-水压坐标平面,土体所处温度与水压点到水合物相平衡线的最小距离）,并依据文献资料分析,建立水合物胶结强度、刚度与参数L间的关系。最后,建立由水合物饱和度确定的粒间水合物胶结尺寸计算方法,并据此进一步建立了胶结强度与刚度同水合物饱和度间的关系。该模型可以方便地植入离散元程序,从而用于深海能源土的宏微观力学分析。     

Influence of Na2 CO3 as Additive on Direct Reduction of Boron-bearing Magnetite Concentrate

Boron-bearing magnetite concentrate is typically characterized by low grade of iron and boron (wTFe=51%-54%,wB2 O3=6%-8%),as well as the close intergrowth of ascharite phase and magnetite phase.A promising technology was proposed to separate iron and boron by coupling the direct reduction of iron oxides and Na activation of boron minerals together.The influence of Na2 CO3 as additive on the direct reduction of boron-bearing magnetite was studied by chemical analysis,kinetic analysis,XRD analysis and SEM analysis.The results showed that the ad-dition of Na2 CO3 not only activated boron minerals,but also reduced the activation energy of the reaction and pro-moted the reduction of iron oxides.Besides,the addition of Na2 CO3 changed the composition and melting point of non-ferrous phase,and then promoted the growth and aggregation of iron grains,which was conducive to the subse-quent magnetic separation.Thus,the coupling of the two processes is advantageous.     

冷梁系统在办公类建筑中的应用探讨

本文简单介绍了冷梁的分类、优缺点、气流组织、水系统匹配,并分析了冷梁在办公类建筑中应用时遇到的主要产湿因素及防结露控制等内容。     

控制设备和线间连接案例分析与预控措施研讨

发电厂控制系统部件连接与电缆接线松动导致的接触不良,引起机组参数与控制异常现象时有发生,影响了机组的安全运行.本文通过连接故障案例的分析与处理,结合DL/T261规程要求,提出避免控制设备部件和线间连接故障发生的预控措施建议.     

主动密封旋转防喷器胶心油压响应规律研究

确定主动密封旋转防喷器胶心的油压响应对整个装备的研制至关重要。运用有限元软件建立了胶心模型,在内胶心上、下两端全约束的情况下计算胶心的Von Mises应力分布,对胶心内置铁块的数量、形状及安放位置进行计算和设计,得到了注油压力与最大接触压力的估算式,通过样机的密封压力试验对估算式进行验证。研究结果表明,主动密封胶心完全采用橡胶材料其刚度无法满足设计要求;主动密封胶心需要内置8块铁块,铁块外弧10°,内弧13°,径向长度确定为105 mm,轴向高度为90 mm;胶心与钻杆的接触压力比施加在胶心上的油压小5 MPa。     

Improved tooth trajectory model for prediction of milled surface geometry

The prediction on surface roughness and surface geometry in peripheral milling operation is a crucial but tedious task. The current researches concerned are almost based on circular tooth trajectory assumption to simplify analysis and modeling, and some models derived from true tooth trajectory are not concise enough or have certain limitation when put into practice. A novel idea on account of the principle of curvature circle approximation to true tooth path curve in cutting contact point nearby is presented, and the relevant mathematical theory is established. Then by means of specific curvature circles, mathematical models and analysis methods of surface roughness are discussed systematically, which cover two situations—cutting with and without runout effect. The validity and superiority of the models are demonstrated by experimental studies and numerical simulations. Finally, based on the suggested models and analytical methods, the effects of runout, feed rate, and cutter geometry on surface roughness and geometry are studied in depth, and several significant mathematical formulas and quantitative conclusions are reached, which would contribute to the theory of milled surface studies.     

超高效液相色谱⁃四极杆⁃飞行时间质谱对含PET食品接触材料中可迁移非挥发性物质的筛查研究

采用超高效液相色谱⁃四极杆⁃飞行时间高分辨质谱（UPLC⁃Q⁃TOF）对4类不同类型的含聚对苯二甲酸乙二醇酯（PET）材质的食品接触材料在4 %乙酸和50 %乙醇模拟物中的迁移出的非挥发性未知物进行筛查解析。结果表明，产品在4 %乙酸模拟物的迁移风险远小于50 %乙醇模拟物，主要迁移物质为聚合单体形成的寡聚物，抗氧剂、润滑剂、胶黏剂等加工助剂以及生产加工、迁移过程中形成的非有意添加物（NIAS）物质；纯PET材质的产品迁移物质较少，多层复合材料迁移物质较多。复合材质的产品中，PET材质可能在生产时添加了己二酸、癸二酸、新戊二醇等物质，进行了改性处理；此外，部分迁移物质会与模拟物中的乙醇发生反应，生成新的NIAS物质。     

Linear and cyclic oligomers in polybutylene terephthalate for food contact materials

Polybutylene terephthalate (PBT) is a polyester (PES) gaining more importance on the food contact material (FCM) market. However, little is known about the potential migration of PBT oligomers which are formed during polymer production. In this work, PBT pellets and a slotted spoon manufactured from this material by injection moulding were analysed on extractable oligomers and their migration potential into hydrophilic foods. Overall 27 oligomers (cycles and linears) could be identified in different extracts by HPLC-DAD/ESI-MS data, but without confirmation by reference substances. The oligomers were quantified by HPLC-DAD using bis(2-hydroxyethyl) terephthalate (BHET) as external standard and the total amount of oligomers isolated by reprecipitation from the pellets and the spoon were 0.69 and 0.71%, respectively. While cyclic oligomers made up for approximately 90% of the extractable oligomers, linear oligomers proved to be more relevant for migration into aqueous foodstuffs. Furthermore, it was shown that hydrolysis of oligomers can take place in water at elevated temperatures. Consequently, the qualitative and quantitative composition of PBT oligomers in aqueous foods from FCMs does not only depend on migration but also on hydrolysis. Migration testing of the PBT spoon under repeat use conditions with water at 100°C for 2 h resulted in 0.29 mg item^?1 of linear oligomers and 0.05 mg item^?1 of the cyclic PBT dimer in the third migrate.     

Effectiveness of UV light as a means to reduce Salmonella contamination on tomatoes and food contact surfaces

The effectiveness of ultraviolet light at a wavelength of 254 nm to reduce Salmonella contamination on tomatoes and food contact surfaces was evaluated. Inoculated tomatoes were exposed to UV-C light at doses ranging from 0 to 223.1 mJ/cm². All UV treatments significantly reduced Salmonella populations (p < 0.05). The effectiveness of UV-C light in reducing Salmonella contamination on different locations on tomato surfaces under various UV doses (0–117.2 mJ/cm²) was also explored. Results indicated that regardless of the locations, UV treatment was shown to be effective in decreasing Salmonella populations. Subsequent studies evaluated possible photoreactivation or dark repair of injured Salmonella post-UV treatment. Following UV light exposure at doses of 0, 22.3, 44.6, and 89.2 mJ/cm², tomatoes were either exposed to visible light for 0, 3, and 5 h or stored in the dark for the same amount of time. Photoreactivation was not detected, nor was dark repair. UV light was also evaluated for its effectiveness to reduce Salmonella contamination on food contact surfaces (stainless steel, HDPE, waxed cardboard and PVC). Contaminated coupons were exposed to UV-C light at 0, 3.3, and 19.7 mJ/cm². Significant differences were observed between coupons treated with UV light and the controls (p < 0.05). Coupons exposed for longer time had greater Salmonella population reductions, except for waxed cardboard coupons. Application of UV-C light to reduce Salmonella contamination in tomato handling facilities is feasible.