无谐波异步电动机软启动器的设计

文章介绍了一种以AT89C51单片机为主控核心器件,运用双向可控硅过零触发的PWM技术,实现异步电动机电源的调压控制的软起动器,它既可达到软起动器控制电动机起动电流的目的,又克服了一般软起动器易产生谐波污染的缺陷,有一定的实用推广价值。     

干船坞气控卧倒门的仿真模型

深入了解干船坞气控卧倒门系统的动态特性,以便缩短坞门的设计周期,节约试验费用;运用机械系统动力学自动分析软件ADAMS,建立了干船坞气控卧倒门系统的动力学仿真模型。通过对仿真模型的运行表明:用所述的仿真模型研究干船坞气控卧倒坞门系统的动态特性是完全可行的。     

外加电流阴极保护技术在天津港滚装码头预制梁中的应用

外加电流阴极防护是钢筋混凝土结构防腐蚀的主要技术手段之一。文章结合外加电流阴极保护技术在天津港滚装码头预制梁工程中的实际应用,介绍了外加电流阴极保护的原理和保护效果,是国内工程中的首次应用,将为我国今后外加电流阴极防护技术的发展和进步提供重要的参考和借鉴。     

一种新型双燃料喷射器设计与数值模拟

在现有共轨喷油器的基础上,提出一种适用于液态天然气(LNG)液喷的新型双燃料喷射器结构,并运用AMESim软件建立柴油和天然气喷射过程的计算模型,研究柴油压力、LNG压力、柱塞直径和控制腔进油孔孔径对针阀运动和喷油速率的影响规律,验证了设计方案的可行性,也为适用于 LNG液喷的引燃柴油/天然气新型双燃料喷射器的设计提供理论依据.     

船舶电网谐波分析

本文介绍了电力推进船舶谐波,阐明了谐波产生的原因和谐波的危害,分析总结了抑制船舶谐波的方法和措施。     

Back-Calculation of Ground Stress Field and Rockburst Analysis for Wunvfeng Tunnel北大核心CSCD

Studying the in-situ stress distribution at a tunnel site is very important to determine surrounding rock characteristics, the engineering design and the construction scheme. By using the multiple linear regression method based on the least square algorithm, the initial geostress field is analyzed and the corresponding regression coefficients are obtained. The ground stress obtained from the proposed back analysis is reasonable and can meet the demands of the engineering applications. From the rockburst risk level distribution diagram, it is speculated that the Wunvfeng tunnel is in the high filed stress area. Field monitoring should be strengthened and emergency plans should be made to cope with the rockburst risks during the construction process. © 2018, Editorial Office of "Modern Tunnelling Technology". All right reserved.     

Enhanced traffic information dissemination to facilitate toll road utilization: a nested logit model of a stated preference survey in Texas

This paper investigates the effects of the provision of traffic information on toll road usage based on a stated preference survey conducted in central Texas. Although many researchers have studied congestion pricing and traffic information dissemination extensively, most of them focused on the effects that these instruments individually produce on transportation system performance. Few studies have been conducted to elaborate on the impacts of traffic information dissemination on toll road utilization. In this study, 716 individuals completed a survey to measure representative public opinions and preferences for toll road usage in support of various traffic information dissemination classified by different modes, contents, and timeliness categories. A nested logit model was developed and estimated to identify the significant attributes of traffic information dissemination, traveler commuting patterns, routing behavior, and demographic characteristics, and analyze their impacts on toll road utilization. The results revealed that the travelers using dynamic message sign systems as their primary mode of receiving traffic information are more likely to choose toll roads. The potential toll road users also indicated their desire to obtain traffic information via internet. Information regarding accident locations, road hazard warnings, and congested roads is frequently sought by travelers. Furthermore, high-quality congested road information dissemination can significantly enhance travelers’ preferences of toll road usage. Specifically the study found that travelers anticipated an average travel time saving of about 11.3 min from better information; this is about 30 % of travelers’ average one-way commuting time. The mean value of the time savings was found to be about $11.82 per hour, close to ½ of the average Austin wage rate. The model specifications and result analyses provide in-depth insights in interpreting travelers’ behavioral tendencies of toll road utilization in support of traffic information. The results are also helpful to shape and develop future transportation toll system and transportation policy.     

厦门港建设绿色港口途径探讨

发展绿色港口作为港口行业转变发展方式的重要措施,已成为现代港口发展的重要标志。本文根据绿色港口的内涵及厦门港的实际情况,从码头企业和厦门港口管理局两个层面分别提出了厦门港建设绿色港口的相关措施,以有效指导厦门港开展绿色港口的建设工作。     

桥梁工程事故回顾分析与对策探讨

本文通过回顾从19世纪初以来世界上主要发生的桥梁事故情况,选取其中三个较为典型的桥梁事故,分析其倒塌的原因,并结合作者收集的信息,统计出桥梁事故发生的规律,从而对避免桥梁工程事故的发生提出一些建议和对策。     

扩底抗拔桩极限承载力半经验半理论计算方法与试验验证

文章考虑了土体力学特性,以及桩身材料性质、桩长与桩径(含扩底直径)、桩顶埋深、桩顶卸载与加载、群桩效应等诸多因素的影响,结合工程经验给出了计算扩底抗拔桩极限承载力的半经验半理论方法;根据扩底抗拔桩破坏面位置不同,将扩底抗拔桩破坏模式分为三类(即破坏面延伸至地表的整体剪切破坏、破坏面介于地表与扩孔段之间的局部剪切破坏与破坏面位于扩孔段附近的冲剪破坏),推导出了整体剪切破坏模式的极限平衡状态方程;并依据扩底抗拔桩轴对称条件与土体抗拉强度小的力学特征,给出了求解整体破坏面的微分筒数值解法;利用经验法估算了局部剪切破坏、冲剪破坏模式下的端阻力,进而给出了任意土层中扩底抗拔桩承载力计算步骤与方法;最后,结合一足尺试验的计算分析与承载力测试比较,验证了计算方法的可靠性与精确度。