康明斯6BT柴油机窜气问题的研究

介绍了窜气对柴油机性能的不利影响,通过活塞环密封系统的动力学分析,阐述发动机窜气产生的内在机理,并给出了计算发动机窜气量的公式。     

公路砖石拱桥加固原理及实效分析

以砖石拱桥的加固实例为工程背景,对砖石拱桥原拱圈下增设拱圈、原拱上增设钢筋混凝土拱圈、钢杆件拉结、钢板箍与螺栓锚固等几种加固方法的施工工艺流程、适用范围、注意事项等进行描述和探讨.     

港口高压电缆卷筒滑环箱防凝露措施

凝露造成高压电缆卷筒滑环箱绝缘下降、箱体内元器件损坏,必须加以解决。分析凝露形成条件和造成高压电缆卷筒滑环箱故障的原因。提出温度控制法和湿度控制法两种措施。效果良好,可供参考。     

内压载荷下X80管道裂纹应力分布规律研究

为了研究内压作用下管道裂纹应力场分布规律,以含有表面裂纹的X80管道为研究对象,对不同形状、不同方向、不同内压、不同尺寸的含裂纹管道进行仿真分析和实验验证。结果表明:裂纹尖端处应力远大于裂纹中心应力。裂纹形状对应力影响作用较小,随着裂纹方向与管道轴向夹角增大,裂纹尖端应力先增大后减小,随着管道内压、裂纹深度、裂纹长度的增大,裂纹尖端处应力随之线性增大。其中,裂纹长度对裂纹尖端应力的影响小于管道内压和裂纹深度。     

格拉斯磁环匀强磁场分析

以毕奥-萨伐尔定律为基础,建立亥姆霍兹线圈以及格拉斯磁环中心磁场分布模型,并计算了它们内部的轴向磁感应强度分布,绘出了空间分布图,分析了轴向磁感应强度与x、y坐标的关系,分析结果得到了亥姆霍兹线圈和格拉斯磁环内部匀强磁场分布区域,通过比较得到格拉斯磁环内部的匀强磁场区域比亥姆霍兹线圈内部的匀强磁场分布区域更大的结论。     

Local joint flexibility of tubular X-joints stiffened with external ring or external plates

In the present paper, the Local Joint Flexibility (LJF) of the ring-stiffened X-joints and plate-stiffened X-joints under compressive load is investigated. In the first phase, a finite element (FE) model was generated and verified with the results of available experimental tests and equations. In the next phase, a set number of 234 FE models were created to evaluate the role of the external ring size (β_r and τ_r), the external plate size (β_p and τ_p), and the connection geometry (γ, τ, and β) on the LJF factor (f_LJF). In these FE models, the weld connecting the chord and brace members was generated. The results indicated that the f_LJF of a plate stiffened joint can be down to 76% of the f_LJF of the corresponding un-stiffened joint. Also, the effect of the ring size on the f_LJF was more than the effect of the plate size on the f_LJF, because of the stiffener position. Despite the notable effect of the ring and the plate on the f_LJF, there is not any study or formula on tubular connections stiffened with ring or plate. Therefore, the FE results were used to propose two parametric formulas for determining the f_LJF in X-joints with external ring or external plate under brace compressive load. Moreover, the derived formulas were checked based on the UK DoE acceptance criteria.     

基于GOOSE机制的城市轨道交通中压环网继电保护方案优化

针对目前城市轨道交通中压环网继电保护存在的问题,提出了基于GOOSE(面向通用对象的变电站事件)机制的中压环网的继电保护优化方案,有效地解决了传统过流保护级差配合困难的问题.该方案是以GOOSE光纤以太网为基础,以闭锁逻辑为核心的数字通信电流保护方案.将GOOSE信号进行分类,并对中压供电环网系统各种可能出现的故障进行动作行为分析.最后,通过RTDS(动态数字仿真系统)仿真试验,证明该方案在各种故障情况下,都能保证继电保护的选择性、速动性、灵敏性和可靠性.     

提高车用发动机活塞环摩擦学性能的试验研究

制备了直接离子渗氮环与超声滚压加工-离子渗氮环两类摩擦学试样。利用电子显微镜、硬度计、X射线衍射仪和能谱仪,对表面改性层进行了表征,分析了超声滚压预处理对316L不锈钢活塞环离子渗氮行为的影响;在润滑油条件下,使用往复式摩擦磨损试验机,对比考察了直接渗氮环和超声滚压-渗氮环的摩擦学性能。结果表明,超声滚压-渗氮环相对于直接渗氮环渗氮层的氮含量增加了2.9倍,显微硬度提高了1.1倍,摩擦因数降低了0.04,耐磨性提高了2.8倍。发动机台架试验表明,超声滚压-渗氮环与硼铸铁氮化气缸套的匹配性最好。     

Analysis and improvement of authenticatable ring signcryption scheme

We show that the Zhang-Yang-Zhu-Zhang identity-based authenticatable ring signcryption scheme is not secure against chosen plaintext attacks.Furthermore, we propose an improved scheme that remedies the weakness of the Zhang-Yang-Zhu-Zhang scheme.The improved scheme has shorter ciphertext size than the Zhang-Yang-Zhu-Zhang scheme.We then prove that the improved scheme satisfies confidentiality, unforgeability, anonymity and authenticatability.     

温度变化引起桥梁裂缝的分析与预防

温度裂缝是桥梁裂缝常见形式之一,通过对温度裂缝产生原因的分析,提出了可以借鉴和使用的预防方法,希望对桥梁施工有所帮助。