大型桥梁模态参数识别的一种方法

提出一种综合运用经验模态分解(EMD)与随机减量技术(RDT)来识别大型桥梁模态参数的方法。首先利用EMD将桥梁在环境激励下的非平稳响应分解成一系列准平稳的本征模函数(IMF)分量,然后用RDT从中提取自由衰减响应,最后将该自由响应表达为一般解析形式,综合运用参数识别理论、最优估计理论识别出桥梁结构的多阶模态参数。利用南京长江大桥实测动力响应识别该桥的模态参数,并将识别结果与有限元分析结果及有关实测值进行比较,表明该方法具有很好的识别精度,适用于大型桥梁的模态参数识别。     

多类混凝土和各向同性岩石损伤比强度准则

针对已有损伤比变量下的损伤比强度理论仅适用于混凝土且偏平面略有内凹等不足,基于多轴应力下混凝土损伤比强度理论的一般形式,根据已有试验资料关于普通混凝土、再生骨料混凝土、轻骨料混凝土和各向同性岩石破坏包络面的特征,建议考虑Lode角和静水压力对受压损伤比影响以及考虑材料类型对受拉损伤比影响的六参数损伤比变量表达式,且损伤...     

硫酸钠对水泥砂浆的物理侵蚀作用

采用150 g/L的硫酸钠溶液半浸泡的试验方法,以砂浆抗蚀系数为指标,研究了相对湿度和温度变化条件下,硫酸钠溶液的不同结晶产物Na2SO4(无水芒硝)与Na2SO4·10H2O(芒硝)对砂浆试件的物理侵蚀作用和不同条件下硫酸钠溶液的物理侵蚀特性及相关机理.结果表明:与环境温度变化条件相比,硫酸钠溶液在相对湿度变化条件下对砂浆试件造成物理侵蚀作用更为严重,这主要是在相对湿度变化条件下,硫酸钠溶液的结晶产物Na2SO4与Na2SO4·10H2O发生相互转化造成的.硫酸钠溶液形成Na2SO4结晶产物时,其对砂浆造成的物理侵蚀破坏作用较形成的Na2SO4·10H2O结晶产物更为显著.     

Computer-aided robot modeling,programming and simulation

The use of interactive computer graphics for simulation and off line programming provides a powerful tool in implementing robots. This capability essentially became available with the CAD/CAM system.This paper will present the theory of robot modeling and simulation techniques. An overview of CAD/CAM system in robotic application, such as robot off-line programming, simulation and workcell layout will also be represented.     

Networks without user observability

In present-day communication networks, the network operator or an intruder could easily observe when, how much and with whom the users communicate (traffic analysis), even if the users employ end-to-end encryption. With the increasing use of ISDNs, this becomes a severe threat. Therefore, we summarize basic concepts to keep the recipient and sender or at least their relationship unobservable, consider some possible implementations and necessary hierarchical extensions, and propose some suitable performance and reliability enhancements.     

Bearing capacity of surface circular footings on granular material under low gravity fields

Low gravity fields have been simulated through magnetic acceleration to conduct experimental study on bearing capacity of circular footings on a type of crushable planetary regolith simulant,which has comparable density and particle size distribution of lunar soil.The load-settlement responses of surface spread footings are obtained by investigating the relative density,footing size and gravity effects.Applying the hyperbolic asymptote method,normalised foundation stiffness and ultimate bearing capacity are obtained by curve fitting and predicted by power functions using multivariate nonlinear regression.The results show that the nonlinear gravity effect is not negligible,related to stress condition,soil dilatancy and mobilised friction angle.A cone penetration test(CPT)-based method for prediction of bearing capacity is proposed with correlations between ultimate bearing capacity of footings and shallow penetration stiffness of CPTs,avoiding the uncertainties of soil property estimations.Analyses of allowable bearing capacity and footing influence zone in consideration of footing size and gravity effects could therefore improve the design of shallow foundations on the Moon and Mars,and provide new understandings and potential implications to the bearing capacity of shallow foundations on crushable granular material in both terrestrial and extraterrestrial geotechnical engineering.     

隧道内火灾烟气流动对疏散救援的影响研究

利用商业CFD软件PHOENICS 3.5对雪峰山特长隧道进行了火灾的数值模拟,研究了在不同纵向通风风速的条件下,隧道内火灾的烟雾浓度场、温度场等的纵向、横向分布规律和烟气的回流情况,并研究了火灾烟气的动态发展规律,同时分析其对疏散救援的影响,最后提出了控制烟雾、满足火灾救援和人员疏散的有效措施,其结论可为研究隧道内的烟气的流动情况和制定疏散救援方案提供重要参考依据.     

公路隧道火灾时人员疏散的模拟预测

隧道的疏散设计以保护人员的生命安全为首要目标.为此开发了隧道火灾时人员疏散的模拟预测模型TUNEV (tunnel evacuation) ,该模型包含了简单的火灾时人员行为数据库和隧道防火结构参数,通过定性和定量的分析计算,其结果能发现疏散设计中的不足,为人员疏散方案提供参考依据.此外,该模型还可作为辅助的消防演习工具.文章阐述了模型的有关概念,并对雪峰山隧道工程实例进行了疏散模拟,最后简述了TUNEV预测模型的验证和应用.     

预应力混凝土连续箱梁桥施工控制

论述了预应力混凝土连续箱梁桥施工控制的理论体系、方法、内容、原则及实施过程,分析了影响施工控制的主要因素和关键技术。通过监测给出了施工控制参数,有效地调整了桥梁的内力和线形,为提高桥梁施工精度和安全提供了保证。     

基于多目标的未来桥梁工程师培养与课程体系建设

课程体系是大学人才培养和实现既定培养目标的主要载体。在总结美国、德国、苏联的工科人才培养模式以及我国工程教育发展历程的基础上,结合我国的教育国情以及目前的交通行业发展需求,提出了未来桥梁工程师纵向三级人才培养和横向不同桥梁专业人才培养的“多目标”培养思路,并分析了其与我国高等学校土木工程专业本科教育培养目标、国际CDIO工程教育理念、行业人才培养需求的一致性;最后,建立了基于中南大学“通识教育+学科教育+专业教育+个性培养”这个纵向链条的桥梁工程本科教学课程体系,并制定了桥梁工程专业横向课程群,完整构建了三级人才和不同桥梁专业人才的培养模式,从而实现基于多目标的未来桥梁工程师培养。