环件辗扩过程仿真中的自适应单元重划分

在环件辗扩过程动力显式有限元分析中发现,大变形造成单元的畸变。研究了单元自适应重划分算法。在分析工件单元变形的度量基础上,提出了基于空间域离散误差的单元重划分触发准则。基于传统的栅格法思想,针对环件辗扩的特殊性建立了标准栅格,通过边界拟合和节点平滑完成了重划单元的生成。通过平滑物理量、新单元节点在旧单元中包含测试以及新旧单元间物理量的映射完成了物理量的继承和传递。最后,通过算例验证了单元自适应重划分算法的有效性。     

采用多目标进化模型的无监督故障特征选择算法

高维故障特征数据易影响诊断的处理速度和识别率,而传统单目标特征选择算法易融入主观偏好,从而影响特征选择的质量。为此,提出一种无监督的多目标进化特征选择算法。采用熵度量作为相关度目标,采用相关系数的概念设计了冗余度目标,算法同时将这两个目标作为优化对象;利用样本在各个特征上的分布信息,设计了导向性的种群初始化过程和变异算子,以提高算法的优化能力;还利用集成的方法得到了所有特征的重要度序列。对5组UCI数据和3组往复式压缩机故障数据的测试结果表明,该算法比已有的几种特征选择算法更具优势。     

汽车油冷器典型失效分析

目的分析汽车机油冷却器的典型缺陷,寻找其产生的根本原因,制定相应的措施,从而避免此类问题的再次发生。方法通过对失效车辆的分布进行统计分析,锁定失效车辆的范围。使用扫描电子显微镜对失效部位的微观结构进行观察,通过能谱仪对腐蚀部位周围的腐蚀产物进行分析,发现其主要成分为Al_2O_3,并且发现了Cl~-。结合前人的腐蚀理论,并对比分析,确定腐蚀主要是由于Cl~-的穿透作用导致的孔蚀。通过对防冻液进行统计分析,并对当时防冻液样品中Cl~-的含量进行检测,确定腐蚀元素的来源为防冻液。通过分析防冻液的混合工艺,现场检查油库的应急操作,并且进行模拟实验,可以确定由于油库人员的操作不当导致消毒液中的Cl~-被大量引入储水罐的混合用水中,最终使加注的防冻液带有强烈的腐蚀性。结果防冻液的混合用水中Cl~-的含量远高于正常水平。结论防冻液的混合用水中Cl~-含量过高,导致铝合金表面钝化膜被穿透,最终形成了典型的铝合金孔蚀失效。     

Effects of Se substitution on the thermoelectric performance of n-type Co4Sb11.3Te0.7−xSex skutterudites

A series of double-substituted Co₄Sb_11.3Te_0.7?xSe_x skutterudites have been fabricated by combining the solid state reaction and the spark plasma sintering method, and the effects of Se substitution on the thermoelectric properties are characterized by measurements of the electrical conductivity, the Seebeck coefficient and the thermal conductivity in the temperature range of 300–800 K. Doping Se into the Co₄Sb_11.3Te_0.7?xSe_x matrix suppresses the carrier concentration, and the electrical conductivity actually decreases with the Se content. However, moderate Se doping is effective in enhancing the thermoelectric performance of the n-type Co₄Sb_11.3Te_0.7?xSe_x, because of the resulted dramatically decreased thermal conductivity. Analyses indicate that the heightened point-defect scattering induced by Se doping together with the electron–phonon scattering induced by Te doping is responsible for the reduction of lattice thermal conductivity of these compounds.     

On the mechanism of formation of zinc pack coatings

The mechanism of the formation of zinc (Zn) pack coatings is studied with scanning electron microscopy (SEM), X-ray diffraction (XRD) and differential scanning calorimetry (DSC). DSC showed that the coatings formation takes place in three steps. The initial step (at 193.9 °C) is endothermic and involves the transformation of α-NH₄Cl to β-NH₄Cl and the NH₄Cl decomposition to NH₃ and HCl. During the second step (at 248.6 °C), which is exothermic, Zn²⁺ salts are formed and especially ZnCl₂. Finally at 264.1 °C Zn is deposited by an endothermic reaction on the ferrous substrate through the decomposition of ZnCl₂. The as-cast Zn diffuses into the iron lattice forming the gamma (Γ-Fe₁₁Zn₄₀) and delta (δ-FeZn₁₀) phases. Al₂O₃ is not involved in the above-mentioned mechanism and acts only as filler.     

基于活动的日活动计划模型

根据基于活动的出行需求预测思想和建模方法建立了日活动计划模型。应用长春市居民出行调查数据进行了参数标定和模型验证,并用"模拟-比较-评价"方法将已建模型应用于交通需求管理政策的制定和评价。结果表明,建立基于活动的日活动计划模型,可全面有效地模拟预测和分析居民活动安排情况,对交通需求管理策略进行初步的评价研究。     

Electronic transport properties of Fe-doped CoSb3 prepared by encapsulated induction melting

Fe-doped CoSb₃ skutterudites were prepared by encapsulated induction melting and their thermoelectric and electronic transport properties were investigated. The positive signs of Seebeck and Hall coefficients for all Fe-doped specimens revealed that Fe atoms successfully acted as p-type dopants by substituting Co atoms. Carrier concentration increased with increasing Fe doping content and the Fe dopants could affect the electronic structure of CoSb₃ and generate excess holes. However, carrier mobility decreased with increasing doping content, which indicates that the hole mean free path was reduced by the impurity scattering. Seebeck coefficient and electrical resistivity were almost independent of carrier concentration between 5.8 × 10¹⁹ and 2.0 × 10²⁰ cm^− 3 because the increase in carrier concentration by doping was competitive with the decrease in carrier mobility by the impurity scattering. Seebeck coefficient showed a positive value at all temperatures examined and it increased as the temperature increased. Temperature dependence of electrical resistivity suggested that Co_1 − xFe_xSb₃ is a highly degenerate semiconducting material. Thermal conductivity was considerably reduced by Fe doping and the lattice contribution was dominant in the Fe-doped CoSb₃ skutterudites.     

Study of thermal stability of CoSb3 skutterudite by Knudsen effusion mass spectrometry

Thermoelectric materials play an important role in the field of renewable energy for their ability of thermal energy conversion into electricity (thermoelectric generator) and reversibly electric energy conversion into thermal energy (thermoelectric heat pump or Peltier cooling). Doped CoSb₃ based skutterudites represent one of the very promising categories for the development of highly efficient thermoelectric materials for the conversion of waste heat to electricity. The thermoelectric efficiency, however, is closely related to thermal and phase stability as the current materials contain volatile elements (Sb, Sr, Yb, etc.), which can evaporate at operation conditions and thus cause structure changes and damage the thermoelectric properties. For a better understanding of the thermal behaviour of complex multicomponent CoSb₃ based skutterudite systems, a study of the thermal stability of primary CoSb₃ skutterudite is necessary.In this work, the thermal and phase stability of primary CoSb₃ skutterudite prepared by ball milling and hot pressing was investigated using thermal analysis and Knudsen effusion mass spectrometry performed on a Netzsch STA 409 CD/3/403/5/G apparatus, a specially-adapted type of the commercial STA 409 CD - QMS 403/5 Skimmer Coupling Instrument. Results, including data on phase transformations and those from vapour pressure measurements of antimony, supported by measurements of diffusion profiles and microstructure observations are summarized and used for evaluation of the long term thermal stability of the material.     

某轿车气动特性的CFD分析及优化

以一轿车模型为研究对象,采用CFD仿真的方法,对其车身表面压力分布和车身周围气流状况进行了深入地分析和研究,阐明了轿车气动阻力产生的原因.为了实现对气动阻力的优化,结合全局优化方法和局部优化方法的优点,将迭代的思想引入局部优化方法中,通过迭代式的局部改型,保证了优化过程中气动阻力是一直降低的.结果表明,气动阻力系数由0.338降至0.317,降幅6.21%,取得了很好的效果.