液压工程机械在高原环境的维护防控要求

<正>高原地区气候特点为:海拔高、气压低、空气密度及含氧量低、低温期长、年平均气温低,昼夜温差大、气候干燥、沙尘大、光照时间长和紫外线强等。这些条件严重影响工程机械的工作性能和使用效率。高原环境下工程机械使用维护要求及防控措施可归纳为以下几点。     

增强筑路机械高原适应性的措施

筑路机械在工程施工时经常需要在高原山区进行野外作业。高原山区的施工特点是地势高,空气密度低,温度变化大,坡道多。这些特殊的自然条件将使筑路机械的工作能力明显下降。为了适应高原山区的自然条件,有利于筑路机械的正常使用,必须要采取相应的技术改进措施。     

非理想状态气体密度的Matlab计算程序设计

本文针对范德瓦尔方程式的求解过程进行了理论推导,并在理论公式推导结果的基础上,利用Matlab语言编写了用于非理想气体单点状态的密度计算和非理想气体密度-压力-温度曲线绘制程序.该程序能对氮气、氲气和氧气等11种满足范德瓦尔方程的常见气体的密度、压力和温度3者之间的关系进行准确表达,且该程序操作全过程有中文提示,使用前不需要阅读说明书便可操作.     

XGL50高原装载机的高原环境适应性研究

结合 XGL50高原装载机的开发,提出了轮式装载机为适应高原环境所必须采取的应对措施,并针对不同海拔高度进行了匹配研究.分析和高原试验表明:整机匹配是合理的,应对措施是可行的.     

装甲车辆柴油机冷却系统在高原环境下控制方案优化研究

针对装甲车辆柴油机在高原地区关键部件不能得到有效冷却导致柴油机故障频发,影响着装甲车辆的可靠性和作战效能发挥的问题,研究高原环境下柴油机冷却系统控制方案优化方法,提出了基于柴油机工况开环控制和基于柴油机出水口温度PID闭环反馈相结合的控制方法。最后以海拔5000m时为例编制了开环控制MAP图,对控制方案进行了模型仿真,结果表明优化后的控制系统能够有效提高冷却系统散热能力。     

柴油机高原环境工作特性分析研究

中国西部大开发为汽车工业与配套动力带来巨大发展机遇,高原环境特点对发动机产生很大的影响,研究高原柴油机增压技术非常必要。研究介绍高原环境气候特点,分析高原环境对柴油机增压技术工作性能的影响,提出改善柴油机性能的技术措施。以某4缸柴油机为研究机型,对比单级增压对柴油机变海拔条件下工作特性的影响,在4km海拔下分析叶片开度对柴油机性能的影响。表明选配二级增压可提高柴油机对海拔变化适应性。低转速工况可变二级增压柴油机叶片开度在40%～70%转矩最大,有效燃油消耗率最低。增大叶片开度可降低排气背压,提高增压器效率,有效降低油耗率;中高转速时热传损失随叶片开度增大降低。     

高原环境对汽车发动机性能影响分析

在总结西藏汽车保有量增长情况和西藏高原环境高海拔所带来的空气稀薄,气压低,含氧量少的基础上,分析了高原地区对汽车使用性能的影响,提出了相应的措施,对于减少汽车在高原地区使用过程中发动机的过热及异常磨损,提高汽车的燃油经济性,减少环境污染具有非常重要的意义。     

CFM56系列发动机高高原环境下点火故障分析

经过几十年的发展,CFM56系列发动机展现了优秀的可靠性和经济性,但在面对高高原机场海拔高、空气稀薄,常导致高高原运行的飞机出现点火悬挂、点火失败的故障.为了更好地改善高高原运营航班的点火成功率,本文对影响点火故障的因素展开研究,结合高原环境对雾化效果产生的影响以及索特尔平均直径SMD(Sauter Mean Diameter)的经验公式,量化分析喷射压力和燃烧室背压对雾化效果的综合性影响.最后结合影响点火成功的因素,提出了通过推迟供油点火时机、增加启动燃油供应等方法提高点火成功率的建议,为高高原机场运行的航空发动机提供参考.     

CFM56系列发动机高高原环境下点火故障分析

经过几十年的发展,CFM56系列发动机展现了优秀的可靠性和经济性,但在面对高高原机场海拔高、空气稀薄,常导致高高原运行的飞机出现点火悬挂、点火失败的故障.为了更好地改善高高原运营航班的点火成功率,本文对影响点火故障的因素展开研究,结合高原环境对雾化效果产生的影响以及索特尔平均直径SMD(Sauter Mean Diameter)的经验公式,量化分析喷射压力和燃烧室背压对雾化效果的综合性影响.最后结合影响点火成功的因素,提出了通过推迟供油点火时机、增加启动燃油供应等方法提高点火成功率的建议,为高高原机场运行的航空发动机提供参考.     

考虑范德华力的微型活齿传动系统应力分析

提出了一种微型集成活齿传动系统,介绍了其工作原理,推导了微尺度下任一活齿在不同啮合位置的静力学方程,利用范德华势函数对活齿所受的范德华力进行求解,研究了考虑范德华力时啮合活齿所受波发生器、活齿架、中心轮三者作用力的变化规律;运用Hertz理论,对活齿与波发生器、活齿架、中心轮的接触应力进行了理论推导,并研究了微结构不同几何参数对活齿所受作用力及接触应力规律的影响。     

基于MEMS粘附问题中关键表面力的分析

粘附是MEMS器件在加工、操作过程中特有的现象,根据微机械中作用力的尺度效应与表面效应,分析表面张力、范得瓦耳斯力、静电力对粘附的影响机理,同时给出了抗粘附的常用的技术方法.     

SF_6气体密度控制器在极端环境中的应用

详细分析了SF6气体密度控制器在高海拔低气压地区以及低温地区的极端环境中应用的情况,通过根据实际的使用环境对密度继电器的设定值进行合理的修正及合理选择密度继电器在高压电器设备上的安装位置,提升密度继电器的准确性和可靠性,进而保证高压电气设备正常稳定安全运行。     

Modeling and simulation of AFM cantilever with two piezoelectric layers submerged in liquid over rough surfaces

In this paper, the vibration of an atomic force microscope (AFM) cantilever in tapping mode with two whole piezoelectric layers submerged in liquid medium is investigated. In the performed modeling, the sample surface has been considered as rough, and to show these surface asperities, two models of Rumpf and Rabinovich have been employed for analyzing the attractive Van der Waals force. This paper has been organized in two sections. The first section deals with the functioning of cantilever over rough surfaces, which accompanies the changes of the attractive Van der Waals force, and the second section involves the changes in the Van der Waals force which lead to a change in the liquid medium. The cantilever is totally submerged in the liquid. To show the effect of liquid on cantilever, first, only the cantilever tip is immersed in the liquid and it is dynamically analyzed. Then, the cantilever is totally submerged and then taken out of the liquid, so that the additional mass and damping of the cantilever could be calculated. In these two manners of cantilever immersion in liquid, the effects of the added mass and damping on the cantilever can be measured. When a cantilever vibrates totally in liquid, since the mass and damping of the liquid that is present on the cantilever cannot be determined, first, the cantilever's natural frequency in liquid is estimated in the laboratory and then by using this frequency and the cantilever stiffness (which is not medium-dependent and is always considered as constant), the additional mass and damping of the cantilever are determined.     

干气密封在裂解气压缩机上的应用

简述了101J裂解气压缩机上原机械密封存在的问题.根据该裂解气压缩机的特点,将原机械密封改造为新型的非接触式密封(即干气密封).详细阐述了带中间迷宫的串联式干气密封的工作原理、整个改造的实施情况以及密封的开车运行状况.结果证明,串联式干气密封在裂解气压缩机上的成功应用,从根本上解决了压缩机原密封的失效问题,保证了机组的安全、稳定、长期、满负荷运行.     

压力式SF_6气体密度控制器生产及使用中应注意的几个问题

阐述了SF6气体的物理特性,定量分析了温度引起的表壳内压变化对仪表示值的影响,介绍了2种检漏方法的区别及漏率的计算,说明了仪表温度补偿机理、原则及使用环境条件对仪表正常工作的影响。     

Implementation of a piezoresistive MEMS cantilever for nanoscale force measurement in micro/nano robotic applications

The nanoscale sensing and manipulation have become a challenging issue in micro/nanorobotic applications. In particular, a feedback sensor-based manipulation is necessary for realizing an efficient and reliable handling of particles under uncertain environment in a micro/ nano scale. This paper presents a piezoresistive MEMS cantilever for nanoscale force measurement in microrobotics. A piezoresistive MEMS cantilever enables sensing of gripping and contact forces in nanonewton resolution by measuring changes in the stress-induced electrical resistances. The calibration of a piezoresistive MEMS cantilever is experimentally carried out. In addition, as part of the work on nanomanipulation with a piezoresistive MEMS cantilever, the analysis on the interaction forces between a tip and a material, and the associated manipulation strategies are investigated. Experiments and simulations show that a piezoresistive MEMS cantilever integrated into a microrobotic system can be effectively used in nanoscale force measurements and a sensor-based manipulation.     

Dynamic coupling correlation of gas film in dry gas seal with spiral groove

In working state, the dynamic performance of dry gas seal, generated by the rotating end face with spiral grooves, is determined by the open force of gas film and leakage flow rate. Generally, the open force and the leakage flow rate can be obtained by finite element method, computational fluid dynamics method and experimental measurement method. However, it will take much time to carry out the above measurements and calculations. In this paper, the approximate model of parallel grooves based on the narrow groove theory is used to establish the dynamic equations of the gas film for the purpose of obtaining the dynamic parameters of gas film. The nonlinear differential equations of gas film model are solved by Runge-Kutta method and shooting method. The numerical values of the pressure profiles, leakage flux and opening force on the seal surface are integrated, and then compared to experimental data for the reliability of the numerical simulation. The results show that the numerical simulation curves are in good agreement with experimental values. Furthermore, the opening force and the leakage flux are proved to be strongly correlated with the operating parameters. Then, the function-coupling method is introduced to analyze the numerical results to obtain the correlation formulae of the opening force and leakage flux respectively with the operating parameters, i.e., the inlet pressure and the rotating speed. This study intends to provide an effective way to predict the aerodynamic performance for designing and optimizing the groove styles in dry gas seal rapidly and accurately.     

加氢压缩机干气密封的失效与改进

分析了加氢密封的压缩机干气密封常见的损坏失效方式,通过实例分析了干气密封污染的原因,提出了干气密封的供气系统改进和结构改进,改进后压缩机运行良好.采取了重新加工轴承腔、建立逻辑控制系统及二级排放口开在密封腔上端等三种措施,解决了润滑油向干气密封的流动问题。提出了干气密封系统污染的预防措施。     

The effect of hydrogen gas environment on fretting fatigue strength of materials used for hydrogen utilization machines

The objective of this study is the characterization of the fretting fatigue strength in a hydrogen gas environment. The test materials were a low alloy steel SCM435H, super alloy A286 and two kinds of austenitic stainless steels, SUS304 and SUS316L. The test was performed in hydrogen gas at 0.12 MPa absolute pressure. The purity of the hydrogen gas was 99.9999%. The fretting fatigue limit was defined by the fretting fatigue strength at 30 million cycles. For all materials, the fretting fatigue strength in the hydrogen gas environment increased in the short-life region. However, the fretting fatigue strength in the hydrogen gas environment decreased in the long-life region when exceeding 10 million cycles except for SCM435H, while there was no reduction in the fretting fatigue strength in air between 10 and 30 million cycles. The reduction rate was 18% for A286, 24% for SUS304 and 7% for SUS316L. The tangential force coefficient in the hydrogen gas environment increased when compared to that in air. It can be estimated that this increase is one of the causes of the reduced fretting fatigue strength found in a hydrogen gas environment. In order to discuss the extension of the fretting fatigue life in hydrogen gas observed at the stress level above the fretting fatigue limit in air, continuous measurement of the fretting fatigue crack propagation was performed in a hydrogen gas environment using the direct current potential drop method. As a result, it was found that the extension of the fretting fatigue life was caused by the delay in the start of the stable crack propagation.