鲤鱼钳毛坯楔横轧成形压力的工程计算

介绍了楔横轧成形过程的工艺参数及变形区参数,分析了楔横轧展宽区的金属变形情况及推导了变形区参数的工程计算公式。文末对鲤鱼钳毛坯进行了实例计算。     

基于粗糙集和K-均值聚类的概念设计实例检索方法研究

针对产品概念设计非常复杂、涉及内容多等特点,提出基于粗糙集的实例推理技术,并将其应用于实例检索.首先在分析了概念设计特征基础上,建立了基于粗糙集的概念设计实例知识表达系统模型,然后通过基于分层聚类的K-means聚类法离散化决策表中的连续属性,利用粗糙集对离散后的决策表进行实例特征属性约简,抽取重要的特征属性作为检索依据,通过权值计算方法得到各特征属性的权值,检索出最为接近的概念设计实例作为设计参考实例.最后以冲压模具实例检索为应用实例,说明了这种实例检索方法的可行性、有效性.     

换流变压器三相直流偏磁的计算研究

为研究相邻架设的交直流线路互感在换流变压器中产生的三相直流偏磁情况,在计算了单相变压器二次侧直流电流所产生的偏置磁通与励磁电流的基础上,对直流线路基波电流引起的换流变阀侧直流电流及其在换流变三相产生的直流偏磁进行了分析,讨论了△绕组的影响,并在Matlab中对换流变三相励磁电流做了仿真计算。其结果表明：交直流线路互感引起的换流变三相直流偏磁大小不等,且会因Y-△连接而发生变化,而由此产生的变压器接地中性点零序电流的直流分量为零。     

有限元法的基本思想与发展过程

有限元法是工程分析中广泛应用的数值计算方法,由于它的通用性和有效性,受到工程技术界的高度重视.文章论述了有限元法基本思想的发展过程、求解步骤、应用特点,并简单列举了几种基于有限元法的大型通用软件.     

骨架密实型沥青混合料集料的分形特征

为了分析和利用骨架密实型沥青混合料集料分形特征,基于分形几何的基本理论,推导出了集料的质量分布分形几何模型,并以SMA-16混合料为例,探讨了集料分维值(D)的最小计算粒径;结合SMA-16混合料体积参数的测试结果,研究了分形维数与体积参数的关系.结果表明:对于SMA-16混合料,分维值的最小计算粒径为0.6 mm;规范级配范围对应的分维值为2.355～2.457;分维值越大,混合料级配越细;分维值与空隙率、矿料间隙率、沥青饱和度等混合料体积参数有很好的线性相关性.     

Low temperature adsorption of ethylene and butadiene on platinum and palladium surfaces: A theoretical study of the diσ/π competition

The different low temperature coordination modes of ethylene and butadiene on a platinum (111) face, (110) face and on a palladium (111) face are compared on the basis of extended Hückel calculations. The nature of the chemical interaction between the olefin and the surface is detailed and the electronic factors that govern the coordination mode of the hydrocarbon are underlined. The different surfaces are modelled by a 49 or a 44 atoms cluster. A correction is applied in the calculation in order to minimize the artefact introduced by this cluster representation of an extended surface. For the adsorption, the respective importance of two electrons interactions and four electrons repulsions is the key point for the determination of the preferred mode. The di- coordination is more stable on platinum (111) but on the platinum (110) face the coordination yields the same adsorption energy than the di- one. This is roughly the same result for the palladium (111) face. The mode is there favored by a decrease of the four electrons repulsions caused either by a smaller number of metal neighbours for the surface atom (Pt(110)) or by a reduced radial expansion of the metal orbitals (Pd(111)). This coordination is associated with a smaller hybridization of the ethylene molecule. The results are extended to the adsorption of butadiene and this allows a qualitative explanation of the better selectivity for butadiene partial hydrogenation on palladium compared with platinum.     

Crystal structures and melting points of unsaturated triacylglycerols in theβ phase

Theβ-phase crystal structures of unsaturated triacyl-glycerols (TAGs) have been analyzed. Long spacings and melting points of monounsaturated TAGs such as16· O· 16 and16· O ·18 indicate aβ-3C packing mode with a methyl terrace that differs from that of the saturatedβ- 3 TAGs. In addition to the hydrocarbon chain subcell packing and the methyl terrace structure, the conformation of the oleoyl chain also has to be considered. This conformation is analyzed in connection with the symmetry relation between the two half-layers on either side of the plane through the double bonds. Geometric analysis shows four possibilities, which have been explored further by means of energy minimization computations. In these calculations the structure of the oleoyl chain, in its crystalline environment, has been optimized while taking all relevant intramolecular and intermolecular forces into account. Though the calculations reveal relatively small energy differences between the four possibilities, the most likely structure can still be identified. On the basis of the results obtained for the monounsaturated TAGs, proposals for the crystal structures of diunsaturated (e.g., O · 18 · O) and triunsaturatede.g., O· O · O TAGs are briefly outlined.     

板坯加热的三维数值模型开发与验证

建立了板坯加热的三维数学模型,采用内节点法对板坯进行了网格划分,采用全隐式有限差分法对数学模型进行了离散,最后采用无条件稳定的Douglas ADI方法对离散方程进行求解。运用Visual Basic编程工具编制了仿真计算软件,实施了“黑匣子”测试并根据测试结果对软件计算模块进行了修正。修正后软件的计算结果与测试结果对比最大相对误差1．99％,验证了软件的准确可靠性。该软件的开发成功,为连续式加热炉的设计和优化生产提供了方便可靠的计算工具。     

计及电气化铁路两相交流供电系统不对称性的输电网实用故障计算方法比较研究

随着我国电网的发展和铁路建设的需要，电气化铁路采用了两相交流供电系统直接并入电力输电网的牵引模式。数量众多的这种不对称结构供电系统的接入，给采用对称分量法作为故障分析方法的现有输电网故障计算及继电保护整定计算软件带来了新的问题。本文根据两相交流供电系统的结构特点，提出了基于相量模型以及等效三相模型的实用故障计算方法，并将其与现有计算方法进行比较研究。算例验证了三种算法的有效性和实用性，现有输电网故障计算程序添加部分模块即可利用本文所述的故障计算方法实现功能扩展。利用本文所述基于等效三相模型的计算方法实现的程序包已应用于实际工程。     

特高压线路铁塔施工关键技术研究

特高压线路的铁塔重量大、铁塔高、横担长、结构复杂。介绍根据不同的塔型、地形和交通状况,选择合适的组塔方案,配备合适的组塔抱杆。并介绍内抱杆组立铁塔施工技术、施工工艺、受力计算和工器具选择。