有限元网格自动生成算法的研究进展

有限元网格生成技术对有限元法的发展和工程应用效果关系重大。该文在分析大量有限元网格自动生成算法文献的基础上，对几种典型的有限元网格自动生成算法进行了总结，并指出它们各自的优缺点，同时探讨了有限元网格自动生成算法的发展趋势。     

CAD／CAM三维有限元网格自动生成典型方法与发展方向

经过对大量三维有限元网格自动生成算法文献的分析，对典型的三维有限元网格自动生成算法进行了归纳总结，同时总结了目前常用的网格优化方法，最后简述了三维有限元网格自动生成算法的发展趋势。     

基于UG/NX的齿轮参数化建模技术研究与实现

齿轮作为一种通用的传动机构，有其特殊的设计和加工方法。介绍了齿轮渐开线的形成原理。在UG／NX中，建立了生成渐开线的变量表达式，通过样条曲线拟合的方法，生成齿轮的完整渐开线轮廓，采用特征操作技术生成了渐开线齿轮的三维模型。     

小型 CAD 系统中装配图描述部分的生成技术

本文叙述了小型ＣＡＤ系统中装配图描述部分的生成技术，文中首先讨论了针对两种不同的装配图视图消隐方案的引出点自动生成方法，然后给出了一个引出线绘制方法，该方法不仅可避免引出线的相交，同时也考虑到了几种特殊情况的处理，最后，对明细表的自动生成进行了简单的介绍。     

坯料网格边界延展及规则化算法

提出了一种毛坯边界非等距外延方法，即将毛坯边界节点非等距外延后，利用NURBS曲线拟合技术生成等距的新毛坯边界，再用NURBS曲面蒙皮算法生成平面，然后通过网格生成算法将生成平面离散成网格，最后用一种基于协方差矩阵特征值的坯料边界规则化算法来得到具有规则形状的坯料。     

产品的分层结构模型及其拆卸方法的研究

文中提出了机电产品的分层树状结构模型，对约束关系矩阵进行了定义，研究了产品的拆卸序列的生成，给出了生成拆卸序列的规则并得到了拆卸序列生成的方法，这种方法对零部件的约束和限制做了前处理，使萁更接近实际的拆卸情况，因此在拆卸的开始就限制了拆卸组合的数量。大大提高了工作效率，使问题得以简化。     

二e英及其生成机理探讨

综述了二e英的特性、二e英对人体健康的危害及其生成机理，并深入探讨了二e英生成的四个基本条件，以期在今后的工作中进一步研究对二e英生成的抑制。     

可重构制造系统中基于相似性理论的虚拟制造单元生成方法

为实现可重构制造系统的逻辑重构，应用相似性理论对多种工件的多工艺路线进行相似性分析，提出了基于工艺相似性理论的设备集合模式的概念。建立了基于设备集合模式、图论和集合论的虚拟制造单元生成的框架模型，以及生成的有关定义、规则及算法。生成的有关定义包括伪设备、例外设备、设备集合模式识别和工艺路线更新等；生成规则包括候选首末设备生成和侯选制造单元处理两类规则；生成算法包括初始输入数据处理、候选制造单元生成、工艺路线更新和例外设备处理4个子算法。用Visual C 实现了所给出的算法，并通过示例测试验证了算法的正确性。     

基于弧长参数空间的汽车车身表面网格生成

提出了基于弧长参数空间的表面网格生成方法，即引入原始的CAD数据模型，通过弧长参数化将其正映射至参数空间，按照计算要求优化网格品质，再逆映射回物理空间，在映射的同时保留表面几何特征，以达到不改变曲面特征形状的目的。将其应用于汽车车身表面网格的生成，并取得了很好的效果。该方法为具有复杂几何外形的物体表面网格的生成提供了一个便利的途径，也为进一步生成三维空间网格奠定了基础。     

基于四叉树法和波前法的曲面网格剖分算法

提出了一种基于四叉树法和波前法的有限元网格生成算法。该算法首先将裁剪曲线边界离散成多边形，然后使用四叉树法对待划分裁剪参数曲面按细分要求进行递归分解，最终生成规则的栅格点，最后利用波前法的原理生成三角形网格，通过合并处理生成三角形与四边形混合网格。     

A high-pressure cell for kinetic studies on gas hydrates by powder x-ray diffraction

A new high-pressure-low-temperature cell was developed for in situ observations of gas hydrates by powder x-ray diffraction. The experimental setup allows investigating hydrate formation and dissociation as well as transformation processes between different hydrate crystal structures as a function of pressure, temperature, and feed gas composition. Due to a continuous gas flow, the composition of the gas phase is kept constant during the whole experiment. This is crucial for the formation of mixed hydrates formed from feed gas mixtures that contain one or more components in low concentrations. The pressure cell can be used in a pressure range between 0.1 and 4.0 MPa and a temperature range between 248 and 298 K. First results of time-resolved measurements of a mixed structure II CH(4) + iso-C(4)H(10) hydrate and a structure I CO(2) hydrate are presented.     

Study on gas hydrates for the solid transportation of natural gas

Natural gas hydrate typically contains 85 wt.% water and 15 wt.% natural gas, and commonly belongs to cubic structure I and II. When referred to standard conditions, 1 m³ solid hydrate contains up to 200 m³ of natural gas depending on pressure and temperature. Such the large volume of natural gas hydrate can be utilized to store and transport a large quantity of natural gas in a stable condition. In the present investigation, experiments were carried out for the formation of natural gas hydrate governed by pressure, temperature, gas compositions, etc. The results show that the equilibrium pressure of structure II is approximately 65% lower and the solubility is approximately 3 times higher than structure I. It is also found that for the sub-cooling of structure I and II of more than 9 and 11 K respectively, the hydrates are rapidly being formed. It is noted that utilizing nozzles for spraying water in the form of droplets into the natural gas dramatically reduces the hydrate formation time and increases its solubility at the same time.     

以制冷剂为工作介质的止推气体轴承静态特性分析*

针对离心式压缩机润滑问题,提出以R134a为润滑工质的动压气浮轴承,基于流体润滑的雷诺方程,从制冷剂与空气的流动对比出发,通过理论假设实现气体轴承的建模与分析,采用数值分析对气膜流场进行三维设计计算分析,得到动压止推轴承的气膜厚度分布、气膜压力分布、承载力、功率损耗等特性。结果表明:在相同的情况下以R134a为工质的气体轴承的承载力是空气的50%左右,两者的承载力都随着扇形瓦张角、转速的增大而增大,随倾斜面高度和节距比的增大而先增大后减小,随最小初始气膜厚度的增大而减小;在相同的情况下以R134a为工质的系统的功率损耗是空气的60%左右,两者系统的功率损耗受最小初始气膜厚度和速度的影响最大,转速越高、最小初始气膜厚度越小,两者的功率损耗越大。     

Development of a high pressure automated lag time apparatus for experimental studies and statistical analyses of nucleation and growth of gas hydrates

Nucleation in a supercooled or a supersaturated medium is a stochastic event, and hence statistical analyses are required for the understanding and prediction of such events. The development of reliable statistical methods for quantifying nucleation probability is highly desirable for applications where control of nucleation is required. The nucleation of gas hydrates in supercooled conditions is one such application. We describe the design and development of a high pressure automated lag time apparatus (HP-ALTA) for the statistical study of gas hydrate nucleation and growth at elevated gas pressures. The apparatus allows a small volume (≈150 μl) of water to be cooled at a controlled rate in a pressurized gas atmosphere, and the temperature of gas hydrate nucleation, T(f), to be detected. The instrument then raises the sample temperature under controlled conditions to facilitate dissociation of the gas hydrate before repeating the cooling-nucleation cycle again. This process of forming and dissociating gas hydrates can be automatically repeated for a statistically significant (>100) number of nucleation events. The HP-ALTA can be operated in two modes, one for the detection of hydrate in the bulk of the sample, under a stirring action, and the other for the detection of the formation of hydrate films across the water-gas interface of a quiescent sample. The technique can be applied to the study of several parameters, such as gas pressure, cooling rate and gas composition, on the gas hydrate nucleation probability distribution for supercooled water samples.     

Fiber optic sensing technology for detecting gas hydrate formation and decomposition

A fiber optic-based distributed sensing system (DSS) has been integrated with a large volume (72 l) pressure vessel providing high spatial resolution, time-resolved, 3D measurement of hybrid temperature-strain (TS) values within experimental sediment-gas hydrate systems. Areas of gas hydrate formation (exothermic) and decomposition (endothermic) can be characterized through this proxy by time series analysis of discrete data points collected along the length of optical fibers placed within a sediment system. Data are visualized as an animation of TS values along the length of each fiber over time. Experiments conducted in the Seafloor Process Simulator at Oak Ridge National Laboratory clearly indicate hydrate formation and dissociation events at expected pressure-temperature conditions given the thermodynamics of the CH(4)-H(2)O system. The high spatial resolution achieved with fiber optic technology makes the DSS a useful tool for visualizing time-resolved formation and dissociation of gas hydrates in large-scale sediment experiments.     

小型CO_2制冷系统换热器的设计及应用

为了设计一套应用于展示柜的小型CO2制冷系统,利用整个系统的循环计算结果,得出系统换热器的负荷,以气体冷却器为例,进行了详细的理论计算。以理论计算的结果为依据,定制了一套气体冷却器、蒸发器及回热器,在相同的条件下,测试了本系统的性能,结果显示,系统能够满足要求,将本系统与R134a制冷系统进行对比,结果显示,本系统的性能更优,将本系统与国外同类产品进行对比,结果显示,本系统的性能稍差,测试结果表明了本系统的换热器理论设计完全可行。     

亚临界CO_2流体性质及沸腾相变特性分析

分析了亚临界CO2流体的性质,并与R22和R134a进行了比较。结果表明,CO2的蒸发压力较高,表面张力较低,饱和液相和气相密度比较低,饱和液相粘度较小,比热较高,导热系数较大。微量不凝性气体NC-1对CO2气相物性影响较小。气泡核化分析表明,当过热度和蒸发温度相同时,CO2气泡临界半径以及所含蒸气分子数量级均比R22和R134a小很多,更易于气泡产生。总之,CO2的热物理性更有助于沸腾传热。     

Tribological Characteristics and Tribochemical Reactions of Various Ceramics Lubricated with HFC-134a Gas

The role of tribochemical products in the friction and wear reduction of ceramics with different fractional ionic character in CF₃CH₂F (HFC-134a) gas was investigated using a ball-on-disk type tribometer. Without exposure to air, the wear tracks on the disks were characterized with the aid of a micro-spot X-ray Photoelectron Spectroscope (XPS) whose analytical chamber was connected to the friction chamber of the tribometer. Further, the adsorption and desorption behaviors of HFC-134a molecules on the nascent surfaces of the ceramics were studied using an adsorption test apparatus in high vacuum. It was found that the lubricating effect of HFC-134a gas was closely related to the fractional ionic or covalent characters of the ceramics. HFC-134a gas was more effective in lubricating ionic ceramics than the covalent ceramics. XPS analysis revealed that metal fluorides were mainly formed on the frictional surfaces of the ionic ceramics, whereas the composition of the tribochemical products on the frictional surfaces of the other ceramics was complicated. The adsorption tests proved that HFC-134a was decomposed to an olefin CF₂=CHF on the nascent surfaces of the ionic ceramic Al₂O₃ and the covalent ceramics. However, the formation of organic fluorine-containing compounds was not detected on the frictional surfaces of the ionic ceramics by XPS. This result implies that the mechanism of tribochemical reactions is strongly dependent on the bond type of ceramics. It is concluded that the low friction and wear of the ionic ceramics in HFC-134a gas result from the metal fluorides formed with high surface concentration on the sliding surfaces.     

DSC法测定甲烷水合物的临界温度

天然气水合物是在一定压力温度条件下，天然气中某些气体组分与水形成的一种复杂且不稳定的白色结晶固体。本文采用差示扫描量热法（DSC）测定天然气水合物的形成温度，使用十二烷基磺酸钠（SDS）作为促进剂。测试周期短，测得的甲烷水合物形成临界温度与理论值很接近。     

R134a工质用于高温空调器的理论及实验研究

从理论和实验两方面分析了工质R134a在高温空调器中应用的可行性，并与高温空调器目前常用工质R142b进行了比较，结果表明，R134a不但能适合高温空调器的特殊工作环境，而且可获得比R142b更大的制冷量，因而为高温空调中采用R134a替代R142b进行了有益的探索。