PWM逆变器高性能控制技术研究

本文分析了PWM逆变器控制的特点,采用了一种高性能的双环（瞬时输出电压外环和电容电流内环）控制方法,控制系统参数利用极点配置的方法计算,计算简单。在通过仿真分析了该控制方案的可行性之后进行了实验。实验结果表明该方案简单实用,能完美地达到逆变器输出波形的各项性能指标要求,很适于应用在工业领域。     

AHP＋模糊综合评判法在港口安全生产状态评价中的应用

如何判断港口生产是否存在安全问题,并找出存在安全问题的生产环节,以便及时采取应对措施显得尤为重要。基于上述背景条件,建立安全生产状态评价指标体系,采用AHP对各评价指标权重予以确定,最后用模糊综合评判法评价港口安全生产的状态。     

基于瞬时无功功率理论谐波和无功电流检测的仿真研究

随着电力系统发展,对无功功率和谐波进行快速、动态补偿的需求越来越大,进行无功补偿和谐波抑制,实时、准确的测量和分析是至关重要的。因此要能准确、快速地从畸变的负载电流和电压中检测无功和各次谐波,就得采取适当的快速检测无功的方法。基于瞬时无功功率理论检测方法的成功应用,能较好地解决谐波电流和无功电流检测问题。     

一种基于优先级的TDMA动态时隙分配算法

根据帧结构的不同对现有的时隙分配算法进行了分类,并结合各自的特点对其综合性能进行比较分析。参考美军Link-22的现有资料和动态时隙分配算法的特点,提出了一种适用于Link-22的动态时隙分配算法,并设计了帧结构与算法流程。     

三车道公路隧道射流风机设置位置研究

射流风机的升压效果不仅与风机本身的性能有关,还与风机位置等外部条件有关.运用大型通用CFD软件对三车道公路隧道中射流风机的射流场进行模拟,并根据计算结果确定公路隧道中射流风机的合理安装位置.结果表明,射流风机的纵向影响距离在200 m范围内,当风机纵向间距大于100 m时即可获得理想的升压效果.为了减小两股射流之间的干扰及隧道壁面的影响,一组中两台风机的净距应在2～5d(d为风机直径)之间,最佳净距在3～4 d之间.     

路基不同压实度下地震动力响应分析

为了了解填土路基在地震作用时的动力响应及路基提高压实度对抵抗地震破坏的效果,文章利用软件FLAC3D建立半路基模型,输入一段实测汶川地震波,模拟计算路基不同压实度在地震剪切波作用下的动力响应,以分析路肩处动力响应与路基趾部的比值随压实度增加的变化趋势,得到压实度对路基水平和竖直方向地震动力响应的影响方式。     

大型运输车荷载作用下的刚构拱桥加固方案分析

文章通过运用大型通用有限元软件ANSYS建立桥梁有限元模型,对刚构拱桥在大型运输车荷载作用下的受力特点进行分析,提出针对性的加固方案,并采用有限元模型分析了加固方案的可行性。     

一种铠装缆绞车控制系统设计与研究

针对现有铠装缆绞车缆绳拉力容易受外界因素干扰,导致控制精度不高,尤其在拉力临界值时,由于拉力的跳变导致张力保护模式和正常模式来回切换等问题。研究提出了铠装缆绞车控制系统工作流程的优化,对拉力信号进行四阶滤波处理。详细介绍了绞车控制系统的硬件设计、软件设计和关键技术处理。同时对绞车系统进行智能化故障监控,达到智能故障诊断的目的。     

Numerical Simulation of Shield Tunnelling Under a Historic Building Based on the Local Stiffness Correction Method (DMSM)北大核心CSCD

The district modified stiffness method (DMSM) considers the effect of joints and hand holes on the stiff-ness of the lining ring, assuming the stiffness around the joint and hand hole is to be reduced and the stiffness else-where is not changed. Considering the stiffness reduction of the lining ring caused by the segment’s circumferential joint, the internal force of the lining structure, the ground surface settlement and the displacement response of the surrounding soil body induced by shield driving are analyzed by an HS small strain constitutive model, and a 3D FEM model is established to analyze the interactions among the tunnel, soil body and building to apply to the dou-ble-line running tunnel of Shanghai Metro Line 11, which crosses under a historic building. In contrast, a 3D numeri-cal model based on the routine method (RMM) is set up and a comparison with the site measured data is conducted,with results indicating that they agree very well. The simulation results show that the existing building not only changes the surface settlement trough but also largely reduces horizontal displacement at the corresponding measuring points of the settlement trough; the distortion values of the existing building are related to the positions of the tunnel face and the location of the building; and the final distortion doesn’t decrease after completion of tunnel construction, but major residual distortion remains. This simulation method provides a reference for the control of disturbances during shield construction in soft rock. © 2018, Editorial Office of "Modern Tunnelling Technology". All right reserved.     

The interactions between online shopping and personal activity travel behavior: an analysis with a GPS-based activity travel diary

Accompanying the widespread use of the Internet, the popularity of e-commerce is growing in developing countries such as China. Online shopping has significant effects on in-store shopping and on other personal activity travel behavior such as leisure activities and trip chaining behavior. Using data collected from a GPS-based activity travel diary in the Shangdi area of Beijing, this paper investigates the relationships between online shopping, in-store shopping and other dimensions of activity travel behavior using a structural equation modelling framework. Our results show that online buying frequency has positive effects on the frequencies of both in-store shopping and online searching, and in-store shopping frequency positively affects the frequency of online searching. Frequent online purchasers tend to shop in stores on weekends rather than weekdays. We also found a negative effect of online buying on the frequency of leisure activities, indicating that online shopping may reduce out-of-home leisure trips.