温度变化影响下基于神经网络的悬索桥损伤预警方法

提出了考虑温度变化影响的悬索桥结构损伤预警方法.首先,采用神经网络技术建立桥梁实测模态频率与温度的相关性模型,用以消除温度变化对模态频率的影响.然后,将不同温度下的实测模态频率进行＂温度归一化＂,在此基础上利用神经网络新奇检测技术建立自联想神经网络进一步识别模态频率的异常变化.通过润扬大桥悬索桥236d的实测数据分析验证了该方法的可行性.分析结果表明,不同季节下模态频率的相对变化平均约为2.0%,采用所提方法可以识别出悬索桥模态频率0.1%的异常变化,适用于悬索桥结构的在线整体状态监测.     

高应力比下路用水泥混凝土疲劳可靠度量化分析(英文)

为获得路用水泥混凝土在高应力比作用下其疲劳可靠度的变化规律,首先推导了包括混凝土疲劳寿命在内的单调随机变量的概率密度,然后推导了 Miner 与 Chaboche-Zhao 疲劳损伤模型的概率密度. 借助室内疲劳试验结果,获得这 2 种模型的疲劳损伤概率密度函数. 最后,将荷载作用次数代入上述函数,从而获得水泥混凝土疲劳可靠度随荷载作用次数的变化规律. 结果表明: 随着荷载作用次数的增加,相同应力比下,疲劳可靠度从 100%逐渐衰减为 0%; 无论何种应力比,在荷载作用初期,疲劳可靠度均有一个较为稳定的阶段; 随着应力比的增加,该稳定阶段逐渐缩短,且可靠度为 0%时对应的荷载作用次数也减小; 在可靠度衰减阶段,对于相同荷载作用次数,应力比越高,则混凝土可靠度越低; 此外,Miner 疲劳损伤模型比Chaboche-Zhao 疲劳损伤模型偏安全.     

独柱塔空间缆索自锚式悬索桥主鞍座空间受力分析

以南京江心洲大桥为工程背景,对空间缆索自锚式悬索桥主鞍座的相关问题进行研究.以大型通用有限元程序为平台,采用二次开发技术,建立精细化有限元模型,在此基础上采用合理的加载模式对其进行空间受力分析,并阐述与空间主鞍座相匹配的主缆切点简化修正方法.结果表明:空间主缆在成桥状态对主鞍座横向力的作用会造成鞍槽外侧壁应力大于内侧壁的应力;主缆横向体积力会对主鞍座压紧装置和鞍体产生梯度分布的竖向挤压力;自锚式悬索桥体系转换过程中缆索的几何非线性效应显著,体现在空缆到成桥状态主缆与主鞍座空间切点位置会有较大的变化.     

车辆荷载作用下脱空连续配筋混凝土路面的临界荷位（英文）

为了研究车辆荷载作用下脱空连续配筋混凝土路面的临界荷位,运用等效原理将椭圆形车辆荷载转化为等效的方形荷载,分析了车辆荷载作用下连续配筋混凝土路面板板底易脱空的位置,及脱空尺寸对连续配筋混凝土路面板应力与竖向位移的影响.研究结果表明:车辆荷载作用下连续配筋混凝土路面板板底脱空不可避免,脱空一般位于纵缝边缘与板角位置.脱空尺寸对板的横向最大拉应力和最大竖向位移影响显著,板角为车辆荷载作用下脱空连续配筋混凝土路面的临界荷位.分析结果为脱空的连续配筋混凝土路面的结构设计提供了理论基础.     

车辆集中荷载作用下脱空CRCP板的挠度与应力

基于挠度与应力等效原则,将作用于连续配筋混凝土路面(CRCP)中央的车辆集中荷载通过傅里叶级数展开为等效的半波正弦荷载.在荷载转换和小挠度弹性薄板理论的基础上,提出了车辆集中荷载作用下脱空地基上CRCP的挠度和应力计算公式,分析了参数的敏感性.结果表明:板的最大挠度与车辆集中荷载、板的宽度成正比,与板的横向弯曲刚度、板...     

独柱塔空间缆索自锚式悬索桥结构设计

南京江心洲大桥为主跨248 m的独柱塔空间缆索自锚式悬索桥.该桥造型新颖,设计独特.介绍该桥主要结构设计,为同类桥型提供参考.     

基于响应面法的钢拱桥可靠度分析

大型复杂桥梁结构的极限状态函数都是隐式的非线性函数,采用传统的可靠性分析方法可能无法实现,但利用响应面有限元法可以很好地解决这类问题。利用响应面法对一下承式钢拱桥拱肋、主梁在正常使用极限状态下的轴向应力、竖向位移的可靠度进行了分析,并根据拟合出的各极限状态函数显式表达式得出了相应的可靠度指标,说明响应面有限元法是计算下承式钢拱桥构件可靠度的有效方法。     

机械零部件的可靠性设计分析

可靠性设计已广泛应用于机械零件设计.分析了机械零部件传统设计方法与可靠性设计方法在设计思想、设计原理上的区别,介绍了机械零件强度设计的应力-强度干涉理论,讨论了机械零件强度可靠度计算的一般表达式,并给出了机械零件可靠度设计的工程实例分析.通过实例设计结果的分析比较,说明可靠性设计的可行性与实用性.     

基于ANSYS排水泵注塑模型腔疲劳可靠性分析

以洗衣机排水泵注塑模具型腔为研究对象,利用有限元分析软件ANSYS对其静力和型腔疲劳寿命进行分析,找到损伤最严重的节点位置,对其进行疲劳优化设计,并运用可靠性设计理论中的应力-强度干涉模型方法计算出模具型腔可靠度.结果表明：随着注塑模具型腔压力值的增加,型腔的最大应力和变形量也随之增加,最大应力发生在型腔底部,型腔寿命的最小位置均出现在型腔内侧底面与侧面的圆环处,与其各自应力集中点位置刚好吻合,注塑模具型腔可靠度为0.888 8,型腔工作可靠.     

随机有限元的直接法

提出了一种不修改通用有限元程序建立的随机有限元方法，即计算机随机产生多组零件尺寸，用通用有限元软件对每组数据进行计算，求出零件危险截面应力等。对应力数据进行检验，若应力服从正态分布、指教分布、威布尔分布、对教正态分布中任一种，强度可靠度可通过公式或数值积分得到。若应力分布不确定，则可靠度用Monte Carlo法求出。变形的可靠度用同样方法解决。用该方法编写的计算机程序，使形状复杂零件的可靠度计算成为可能。     

车辆与路面相互作用下的5轴重型卡车非线性动态分析

基于车辆悬挂系统和轮胎的几何非线性特性分析,建立了一重型卡车三维非线性动态模型,采用动态车轮载荷的影响因子即动载荷应力因子、最大和最小垂直动载系数,对路面随机不平度与重型车辆之间的动态相互作用进行了评价.采用Matlab/Simulink软件对建立的非线性动态系统模型及影响因子进行仿真计算.分析了不同路面条件对车辆行驶...     

大跨径钢桥面铺装动响应分析

为了研究车辆随机荷载作用下的大跨径钢桥面铺装层动响应,首先根据目前钢桥面铺装的平整度现状,利用功率谱密度函数模拟桥面不平度;然后选取单轮车辆模型计算由桥面不平度引起的行驶车辆随机动荷载;最后采用瞬态动力分析方法计算了铺装层的竖向位移及最大横向拉应力等主要力学响应,并与以往的移动恒载作用下铺装层的动响应及静力计算结果做了比较、分析表明,针对铺装层而言,相邻的2块横隔板的跨中位置为最不利荷栽位置;考虑桥面不平度情况下铺装层的最大竖向位移和最大横向拉应力的峰值分别是只考虑冲击系数的移动恒载作用下的1.33倍和1.39倍、研究结果为铺装层的混合料和结构设计提供了理论依据,对桥面施工及维护提出了严格要求.     

Numerical Analysis of Influencing Factors on Temperature Field and Airflow Distribution of the Displacement Ventilation System

Indoor air quality and thermal comfort are important features of indoor environment, In this paper, a numerical simulation based on the k-ε model of CFD is used to analyze factors such as loading, exterior-protected construction, blowing-in rate that play an important role in the temperature field and airflow field of the displacement ventilation system. Exterior-protected construction has little influence on indoor temperature distribution of displacement ventilation systems and the influence is limited only in a small area near the external wall when the indoor heat source is the main cooling load. The height of a room has little influence on indoor temperature field, and the temperature gradient of active region is basically unchanged. In the system combined with a displacement ventilation system and a cooling system, the height also has little influence. When the cooling load is high,the indoor heat source creates a strong convective plume, which will make the average indoor air age lower, the ventilation efficiency higher and the elimination of pollutant easier. Air supply rate plays an important role in displacement ventilation systems. The increase of air supply rate that can be realized by increasing the air supply velocity and enlarging the area of air inlet will increase the mass capability of the system and diminish the vertical temperature gradient. From the comparison between simulations and experiments, it is concluded that this simulation are creditable.     

压杆纵横弯曲的高阶应变理论解

将高阶应变弹性理论引入细长压杆的纵横弯曲问题中,考察了内禀长度对于纵横弯曲的行为,尤其是中点挠度、最大压力等的影响。结果表明:内禀长度对比外特征尺度不可忽略时,压杆纵横弯曲的最大压力降低;中点挠度也明显受到轴向力、横向力、材料刚度、压杆长度(即外特征尺度)以及内禀长度的影响。工作对于承受纵横弯曲作用的微尺度压杆的设计、制造及使用有一定的指导意义。     

Buckling response of offshore pipelines under combined tension, bending, and external pressure

The buckle and collapse of offshore pipeline subjected to combined actions of tension, bending, and external pressure during deepwater installation has drawn a great deal of attention. Extended from the model initially proposed by Kyriakides and his co-workers, a 2D theoretical model which can successfully account for the case of simultaneous tension, bending, and external pressure is further developed. To confirm the accuracy of this theoretical method, numerical simulations are conducted using a 3D finite element model within the framework of ABAQUS. Excellent agreement between the results validates the effectiveness of this theoretical method. The model is then used to study the effects of several important factors such as load path, material properties, and diameter-to-thickness ratio, etc., on buckling behaviors of the pipes. Based upon parametric studies, a few significant conclusions are drawn, which aims to provide the design guidelines for deepwater pipeline with solid theoretical basis.     

Simulation of the Response of Glass Window Under Blast Load

In the investigation of accidental explosion scene,the damage on the glass is one of the typical traces which can be used to decide the characteristic of the explosion source.To analyze the response of glass under the blast load,a numerical model was developed.In the model,the brittleness glass model was adopted.A 'node release' method,which had some special merits compared with the erosion method was used to simulate the rupture of the glass In the calculation,several problems which play major role in the response of the glass were discussed.The velocity and the displacement of the glass fragment were two major factors.The numerical results are very helpful for the design and hazard assessment.     

影响高中生英语学习因素调查研究

对高中生英语学习因素的调查分析结果表明:其影响因素是多方面的,有学校对英语学习的重视程度、家长对学生英语成绩的期许和评价、英语教师是否具有扎实的专业知识等外部因素;有英语学习者学习英语的兴趣程度、英语学习者学习英语的努力程度、英语学习者是否掌握适合自己的英语学习方法等内部因素。其中,外部因素主要涉及学校、家庭、英语教师等方面,内部因素主要涉及英语学习者个人,包括个体的情感、态度及认知差异等。     

关于位移共振的条件

对位移共振条件进行了讨论,认为发生位移共振不只是策动力的频率符合必要的条件,振动系统的参量也要满足一定的要求.     

Assessment of outcome-oriented learning: External or in-course?

Effective assessment is crucial to ourcome-based learning programs. One choice to be made in such programs is whether assessment of student learning should be carried out within course structures or external to them. Advantages to each approach are suggested, along with other factors affecting the decision. The overall recommendation is for external assessment, primarily because it can more effectively maintain reliability and validity.     

Seismic ductility of very-high-strength-concrete short columns subject to combined axial loading and cyclic lateral loading

The seismic ductility of reinforced very-high-strength-concrete (VHSC) short columns was studied by combinatively applying axial load and low cyclic lateral load on specimens to simulate seismic impact. Twelve specimens with concrete compressive strength ranging from 95.6 MPa to 118.6 MPa and a shear-span ratio of 2.0 were tested for shear failure pattern and fear force-displacement hysteretic responses. Combinative application of axial load and low cyclic lateral load to VHSC short columns incurs shear failure. The displacement ductility is much smaller when the axial load ratio is larger;whereas a larger stirrup ratio is accompanied with a better displacement ductility. The relationship of displacement ductility factor, μ?, with stirrup characteristic value, λv, and test axial load ratio, nt, is μ?=(1 8λv)/(0.33 nt). By this relationship and relevant codes for aseismatic design, the axial load ratio limits for aseismatic design of reinforced VHSC (C95 to C100) short columns for frame construction are respectively 0.5, 0.6, and 0.7 for seismic classes I, II, and Ⅲ;corresponding minimum characteristic values of stirrups are calculated according to the required characteristic values of at least 1.273 times of experimental results. These data are very useful to aseismatic engineering.