旋风铣多齿机夹式刀具的设计

为了实现大螺距T型螺纹(工件外径大于200毫米,螺距大于16毫米)的旋风铣削,保证产品加工精度,提高刀具的寿命及生产效率,设计一种机夹式刀具,用于旋风铣加工大批量大螺距T型螺纹产品。设计两套机夹刀具,分别用于产品的粗加工和精加工;机夹式刀具的设计结构采用可多次使用的刀体部件及可快速更换的刀片;铣削时采用错齿的左右刀片;刀片材料采用硬质合金;通过变更刀片的相应参数,改善刀片在加工时的受力情况及铣削产品的质量,提高刀具使用寿命。     

AR(P)模型的P取值试验

AR(P)模型的p值求解,严格而言应通过计算解决,但无论哪一种计算方法,都要求一定的,甚至足够大的样本量,而土木工程施工监控的相关规范规定,监控落实的最晚期限,也不能超过3d～5d,显然仅依据3个～5个(组)样本,算不出正确的p值来,因此在具体工作中,p值往往人为设置.不同p值的AR(P)模型各自具有不同的特点.笔者分别应用p=2、p=3的AR(P)模型,进行隧道边墙收敛变形分析,认为,若需要尽早落实监控工作,预测精度要求又不是太高,模型的p宜取2;如果项目工期较长,预报精度期望较高的情况下,p取3更合适.     

房屋建筑节能施工技术的探讨

随着经济的发展、时代的进步,城市建设规模不断扩大。建筑耗能十分严重,为国家和社会带来了能源、资源负担,同时,也影响了企业的经济效益。减少建筑能耗,提高资源、能源的利用效率,为国家和社会节省更多的能源资源,已经成为建筑企业所面临的一大挑战。     

吹填软土地基改性真空预压法漫谈

在我国一些沿海地区,经常采用大面积的围海造陆。但是,在围好的地区经常是一些淤泥场。这些软土地基的承载力比较小,需要进行处理后才能够使用。本文将针对吹填软土地基的改性真空预压法进行研究,进一步提高软土地基的承载能力。     

基于整体刀盘的摆线齿端齿盘切齿加工

为了实现在国产数控锥齿轮铣齿机上加工摆线齿端齿盘,对摆线齿端齿盘的切齿加工原理和加工方法进行了研究.基于摆线齿端齿盘的结构特点,提出了采用整体刀盘加工摆线齿端齿盘的加工方法,并通过改变刀盘半径和刀刃圆弧半径对轮齿齿长曲率和齿高曲率进行了修正.基于摆线齿端齿盘的切齿加工原理,提出了加工摆线齿端齿盘的刀盘参数以及机床调整参数的计算方法,对摆线齿端齿盘进行了刀盘干涉检查.通过实际的切齿加工、齿形误差检测以及接触区着色检验,验证了在国产数控锥齿轮铣齿机上采用整体刀盘加工摆线齿端齿盘的加工原理和加工方法的正确性和可行性.     

长大距离下的洗车机无人值守技术改造

广州地铁二十一号线各场段配置的洗车机洗车作业仍采用有人值守的方式,人员工时利用率低.针对广州地铁二十一号线各场段的实际情况,对长大距离下洗车机无人值守功能改造进行了研究,提出了通过光纤通讯进行远程监控的方案,对二十一号线各场段配置的洗车机进行安装改造,实现无人值守洗车,有效提升了工作效率,降低了人力成本.     

大型船用低速柴油机的工作过程和故障模拟

为减少船舶主机实时故障诊断的响应时间和故障的实验成本,对柴油机“平均值法”模型进行改进,并分别对空气滤清器脏堵、机舱温度升高、扫气口脏堵、排气阀漏气、排气烟囱脏堵、冷却系统故障、中冷器水侧污垢、涡轮转子机械故障、涡轮喷嘴脏堵这9种故障进行模拟,利用相对偏差进行参数分析,为后续故障诊断提供可靠的数据样本.     

Numerical modeling and optimization of laser soldering for Micro‐USB electric connector

The laser soldering process was introduced in Micro‐USB electronic packaging in this paper. Numerical modeling and analysis was used for laser process parameter design, because experimental measurements of peak temperature and soldering stress are expensive and often intractable. Accurate knowledge of the residual stress and distortion is a prerequisite for the reliability of the electric connector. The present work proposes a three‐dimensional transient heat transfer model of Micro‐USB package laser soldering process. The calculated thermal cycles and distribution are subsequently used to calculate the distortion and thermal stresses. Meanwhile, the effect of process parameters on residual stress and pin distortion was discussed, and the tensile strength, microstructure, and residual stresses of laser soldering were tested. It can be concluded that the proper laser soldering parameters and power can improve the mechanical property of solder joints on Micro‐USB connector. Copyright © 2014 John Wiley & Sons, Ltd.     

Contact duration aware evaluation for content dissemination delay in mobile social network

Groups of people with mobile phones using short‐range connections such as WiFi and Bluetooth to propagate messages can be modeled as, with regard to regular absence of end‐to‐end connection, mobile social networks (MSNs), which can be exploited to offload a significant amount of mobile content from the overloaded infrastructure networks such as 3G. The study of content transmission delay for the applications of mobile content dissemination in MSNs is an important problem, because to enhance the network capacity, the traffic is offloaded at the cost of inducing longer delay. In contrast to existing works, which ignore the factors of contact duration limits and large content size, we present a contact duration aware framework to model the content dissemination process in MSNs, give an explicit expression for the average content dissemination delay, and reveals its relationship with various system parameters of content size, users’ selfishness, number of involved subscribers, infecting ratio, and so on. We apply our proposed model to real‐life traces to assess its reliability by comparing the theoretical results with measured statistics and present extensive upshots to evaluate the influence of various parameters on system performance. The results demonstrate the accuracy of our proposed framework and reveal that system parameters of content size, system infecting ratio and intragroup transmission are the most important factors to influence the content dissemination delay. Copyright © 2013 John Wiley & Sons, Ltd.     

Dead‐time elimination SVPWM of six‐leg inverter

We present a six‐leg voltage source inverter (VSI) with a single DC link to feed a three‐phase inductive load. The space vector pulse width modulation (SVPWM) of the six‐leg inverter is studied in detail. The novel switching strategy in one sampling period for H bridge is proposed to avoid the 180° phase shift of the PWM signals for upper and lower side switches. Based on the novel switching strategy, a dead‐time elimination SVPWM is proposed, which can be easily implemented on a digital signal processor. Experimental results are presented to demonstrate the validity and features of the proposed novel SVPWM. © 2015 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.