曲线梁桥在车辆载荷下的动力响应研究

近年来随着我国公路交通的快速发展,曲线梁桥被大量工程采用.车辆过桥时的曲线桥振动涉及车辆三向载荷和桥梁弯扭耦合振动,有必要对其进行精确建模并深入研究.本文以某五跨连续曲线箱梁桥为背景,采用ABAQUS有限元软件建立该桥梁的模型,并利用Adams建立了三轴重型汽车整车模型,计算得到了不同工况下的轮胎力.通过编写基于Fortran语言的DLOAD和UTRACLOAD荷载子程序,将六个轮胎载荷作用于曲线桥上,分别进行了不同曲率半径、车速、载重和路面不平顺等条件下的曲线梁桥振动响应计算.研究表明:随着曲率半径的增加,桥梁跨中位移呈现略微下降的趋势;车辆行驶速度对跨中的横向位移及支座的支反力有较大影响;路面不平度等级越高,桥梁竖向挠度及弯矩的冲击效应越大.     

地热电采暖房间升温过程有限元仿真

研究优化控制地热采暖系统问题,为科学有效地确定地热电采暖系统中的电缆芯线参数和铺设路径,应用有限元仿真中的流固耦合仿真方法对室内地而及空气的温升过程进行了仿真计算,得到了加热后不同时间的室内温度场、压力场云图以及空气流动矢量图.从仿真结果分析得知,在不同的时间,温度场的总体分布一直呈现底部中间最高,沿纵向和横向逐渐降低的趋势.室内空气的流动在初始阶段内中心部分的上升速度较大,而到后期,四周空气的流动速度逐渐升高.随着加热时间的延长,房间内的温度渐趋于均匀,空气流动速度下降.仿真结果数据对地热电采暖系统的设计和施工具有重要的参考价值.     

预应力渡槽有限元分析

针对预应力混凝土能极大提高混凝土结构抗拉抗裂强度的特点,结合等效载荷自平衡原理,以南水北调工程中大型预应力混凝土渡槽为模型,采用三维有限元技术分析其受力性能,揭示预应力渡槽在施工、校核等不同工况下的应力和应变等特性.计算结果表明,整个渡槽结构应力、变形满足设计要求,可为施工设计提供参考.     

基于索-梁结构的斜拉桥非线性振动仿真研究

本文建立了索-梁结构的有限元模型,对斜拉桥线性和非线性振动问题进行研究.首先对结构进行模态分析,发现结构振动表现出全局模态,局部模态以及混合模态,且索梁两者之间固有频率相互影响,对低阶频率影响较大,对高阶频率影响较小.其次,应用有限元软件对索-梁结构的自由振动和强迫振动进行仿真研究.结果表明：整个自由振动过程中频率有先增大后减小的趋势,且最终小于真实频率;在强迫振动中,观察到了丰富的非线性振动现象,包括索的亚谐波共振和内共振,与以往的实验和理论研究结果定性上得到验证;为斜拉桥全桥非线性动力学分析提供参考.     

2自由度振荡水翼推进性能分析及实验研究

为了研究仿生水翼推进性能,设计了一种2自由度振荡水翼推进装置.实现了基于升力/阻力模式的2种振荡水翼推进方式.研制了振荡水翼推进性能实验平台,在循环水池环境下完成了不同参数耦合情况下振荡水翼推进性能实验.利用6轴力传感器测量水翼振荡时产生的推力/升力,并将实验结果与数值模拟结果对比,分析不同参数对推进性能的影响.实验结果表明,在升力推进模式下,增加拍旋运动幅值和振荡频率可以提高平均推力;随着位旋运动幅值的增加,平均推力呈现先增大后减小的趋势;随着来流速度的增大,平均推力逐渐减小.在阻力推进模式下,增加拍旋运动幅值和振荡频率均可提高平均推力.     

长期不同施肥对土壤无机硫组分的影响

通过棕壤长期定位施肥试验研究了玉米-玉米-大豆轮作方式下不同施肥处理对土壤无机硫各组分含量的影响,结果表明,长期施用有机肥或有机肥与化肥配合施用,可以显著提高土壤水溶性硫的含最;单施有机肥土壤中吸附态硫含量呈现先升高后降低的趋势,但总体为上升趋势;有机肥与化肥配合施用土壤中吸附态硫的含量在1991年前增长速率较快,此后基本保持平衡,而对照处理土壤中吸附态硫含量基本保持不变;各处理中除不施肥处理呈现缓慢下降趋势外,其他土壤盐酸可溶性硫的含量均持续增加.     

相对公平关切下考虑产品设计的再制造合作模式与供应链协调

将相对公平关切和产品可再制造性设计同时纳入由一个制造商和一个再制造商构成的供应链中,构建外包和授权两种再制造合作模式下供应链的决策模型,研究制造商的再制造合作模式选择问题,分析最优再制造合作模式下再制造商相对公平关切和产品可再制造性设计对供应链生产定价决策及利润的影响,并设计相应的协调策略.研究结果表明:外包再制造是制造商的最优再制造合作模式;在外包再制造供应链中,再制造商的相对公平关切虽会降低制造商利润,但能提高供应链系统利润;产品可再制造性设计对再制造商总是有利的;外包价格契约能够实现外包再制造供应链的协调.     

Savonius风力机横纵向重叠比对功率因数的影响

为研究叶片重叠比对Savonius风力机功率性能的影响,提出横向重叠比与纵向重叠比2个结构参数。建立二维有限元分析模型,应用FLUENT进行非定常数值模拟,基于RNG k ε湍流模型,采用滑移网格模拟风力机转动,得到不同横向重叠比和纵向重叠比时的平均功率因数。结果表明：随着横向重叠比和纵向重叠比的增加,风力机的平均功率因数均先增大后减小;横向重叠比的最优值为0.10,纵向重叠比的最优值为－0.05,对应的平均功率因数为0.251 5。     

桥梁裂缝的成因和控制研究现状及发展综述

本文探讨了桥梁混凝土的裂缝的成因和施工控制方法,并从设计、施工等力一面提出一些相应的预防及处理措施。通过不同整治方法处理后,延长了桥梁的使用寿命,提高了桥梁的承载力。     

基于APDL桥梁参数化有限元分析方法研究

针对以往桥梁建模方法比较复杂与花费时间较长的缺点,以及有限元分析过程与建模过程脱节的技术问题,以混凝土斜拉桥A字型桥塔为例,提出一种基于桥塔点云模型边界特征约束的参数化建模方法,再运用参数化设计语言APDL编写程序,使得参数化在有限元分析过程中得以继承。此方法最大的特点是在点云模型特征边界约束参数关系基础上建立桥塔的有限元模型,然后根据桥塔实际受力荷载情况进行加载,最后计算模型并提取实验结果。实验结果表明,该方法能快速建立桥塔的参数化模型和提高有限元分析的有效性,进而可以得出桥塔结构的稳定性分析,为桥梁健康保护提供相应的依据。     

Ultimate load carrying capacity of the Lu Pu steel arch bridge under static wind loads

This paper investigates the ultimate load carrying capacity of the Lu Pu Bridge under static wind loads through the spatial finite element model. Both geometric and material nonlinearities are involved in the analysis. The Lu Pu Bridge is a long-span half-through-type steel arch bridge with a 550 m-long central span under construction in Shanghai, China. This will be the longest central span of any arch bridge in the world. Three load combinations are used in the ultimate load capacity analysis of the bridge. Combination I: combined dead and live loads over the entire bridge. Combination II: combined dead and wind loads. Combination III: combined dead load, wind load and live load over the entire bridge. Ultimate load capacity of the bridge is first investigated under load combinations I and II. Attention is paid mainly to investigate the load capacity of the bridge under load combination III. In the case of load combination III, the influences of several parameters (i.e., loading sequence, three components of wind loads and wind loads of individual bridge element) on the ultimate load capacity of the bridge are discussed. It is concluded that wind loads result in significant reduction in the ultimate load capacity when applied wind loads become large.     

一种基于桥梁横向裂缝的病害识别方法

桥梁安全是交通安全中最重要的部分之一,桥梁定检是对桥梁安全最有效的评价方法,而在桥梁定检中对病害的识别尤其重要.据相关统计,我国混凝土桥梁的病害中有80％以上是由裂缝造成的,因此对桥梁的健康检测主要是对桥梁表观裂缝的检测与测量.为了提高检测的准确性和效率,统计桥梁裂缝病害图片的识别精度与收敛性,本文结合卷积神经网络(C...     

基于无线传感器网络的桥梁结构健康监测系统研究

随着通信技术、传感器技术的发展,新型的桥梁健康监测技术不断涌现。基于无线传感器网络的桥梁结构健康监测是将无线传感器网络技术与结构健康监测相结合,应用频率法通过加速度传感器测得一段时间内的桥梁拉索张力,经过无线传感器网络将数据传输到监测平台,从而达到对桥梁健康状况的监测。     

Sensitivity analysis of bridge flutter with respect to mechanical parameters of the deck

A methodology for carrying out an analytical sensitivity analysis of the flutter phenomenon in long-span bridges is developed. Decks of bridges are generally bluff bodies and therefore the aeroelastic forces under wind action have to be experimentally evaluated in wind tunnels. Such forces depend on the response frequency of the bridge, which is not known until the problem is solved. Consequently, the calculus of the critical wind speed that initiates the flutter instability comprises a complex nonlinear eigenvalue problem. During the design phase, the sensitivity analysis gives very interesting information about the gradient of the flutter speed with respect to the key chosen design variables, moments of inertia of the bridge deck. The presented method is applied to the Great Belt and Vasco da Gama Bridges, as well as to the old Tacoma Bridge.     

一种新型单象限变频器预充电电路设计

针对传统的单象限变频器预充电电路存在结构和控制复杂,接触器、充电电阻等主要器件成本高、体积大的问题,设计了一种新型单象限变频器预充电电路。该电路采用三相半控整流桥替换传统的单象限变频器预充电电路中的二极管整流桥,并去掉了接触器和充电电阻;当变频器启动时,通过同步电路和单片机控制电路,三相半控整流桥的触发角从120°有规律地减小到0°,从而可使电容的充电电流在允许范围之内。试验结果表明,该电路结构简单、性能可靠、控制灵活。     

Dynamic response of bridges to moving trains: A study on effects of random track irregularities and bridge skewness

This paper describes research undertaken to consider the dynamic responses of an existing railway bridge subjected to moving trains. The study investigated dynamic effects produced by different service trains, as well as the influence of random track irregularities and bridge skewness. This research was carried out using the dynamic bridge–train interaction (DBTI) model developed and previously verified by the authors. Generally, dynamic amplification of displacements was found to be moderate and compared favourably with recommendations of current design codes. The use of complex numerical models for bridge–train dynamics produced detailed dynamic responses; such results may be quite beneficial to bridge owners in the assessment of existing bridges which exhibit excessive dynamic responses. Random track irregularities were found to have minor effects on the dynamic amplification factors and bridge accelerations; however, lateral responses of the bridge were considerably affected by irregularities. Effects of irregularities were more pronounced in train responses; generally, the train responses increased with decreasing track profile quality. Bridge skewness was found to increase fundamental natural frequency of the bridge; this leads to a shift in the dynamic amplification factor towards higher speeds and alterations of its magnitude. Three-dimensional models were found necessary for accurate predicting of this response.     

Virtual wind tunnel: An alternative approach for the analysis of bridge behaviour under wind effects

The study of bridge responses under wind-induced loads is based upon full aeroelastic model testing or hybrid methods which use section model tests and subsequent computer analysis. Both methodologies present several strong points and some shortcomings, specially related with the visualization of the bridge dynamic behaviour. Nowadays, advances and improvements in computational power and computer aided design technologies make possible a new way towards the feasible design of long span bridges considering its aerodynamic and aeroelastic behaviour. The virtual wind tunnel (VWT) technique developed by the authors joins together accurate section model testing with computer aided design in order to obtain a detailed computer visualization of the complete bridge behaviour under wind flow. The results obtained for the Tacoma Narrows Bridge and the Messina Strait Bridge are presented.     

风干扰下的四旋翼无人机ADRC控制律设计

针对小型四旋翼无人机飞行过程中姿态控制容易受侧向风干扰的问题,研究了一种自抗扰控制(ADRC)律.首先分析了侧向风对旋翼的推力,然后建立了风速的组合模型,利用自抗扰控制方法对风的干扰进行估计和补偿,最后在Matlab平台上对所提出的ADRC控制律进行仿真验证.从仿真结果看ADRC控制能够较好地对侧向风的干扰进行估计补偿,从而保证姿态控制具有较好的稳定性.     

基于光纤光栅振动传感器的桥梁索力实时监测

将研制成功的光纤光栅振动传感器以及桥梁索力实时监测系统应用于武汉长江二桥进行索力长期远程实时监测.光纤光栅振动传感器输出的信号可在光纤中进行远程传输,能在任何气候条件下长期稳定工作,适合于桥梁拉索索力的长期远程实时监测;开发的桥梁索力实时监测系统软件,具有拉索特征频率自动识别能力,可以实时进行索力计算.通过对武汉长江二桥拉索索力的实时监测,得到了桥梁索力的分布及其运行状况,为桥梁安全评估提供了可靠的依据.该系统可推广应用于其他大型斜拉索桥.     

基于IaaS云平台的无线传感网实时监测系统

本文基于中科大IaaS云平台设计并实现了一种无线传感网实时监测系统.利用6LoWPAN建立可自组网的无线传感器网络,系统中各个传感器节点将传感器采集的数据发送至汇聚节点,汇聚节点通过网络将数据传送至中科大云平台服务器中进行记录和分析.本文采用Nginx作为Web服务器,uWSGI应用服务器和Tornado应用服务器分别处理用户的非实时数据和实时数据请求.采用WebSocket技术实现实时数据的传输,提高了系统实时性.测试结果表明本文对构建可靠且可灵活部署的实时监测系统具有指导意义.