热仿真分析在前舱熔断丝盒上的应用及验证

通过模拟某轻客车的前舱熔断丝盒上加载实际负载时的温升分布,建立有限元分析的零部件模型,重点对继电器的热分析模块进行优化。基于有限体积法的FLOEFD热仿真分析软件对整个熔断丝盒的温升分布进行仿真,并和实物试验结果进行对比分析,验证仿真分析模型的可靠性,对后续产品热设计的优化具有指导作用。     

低温环境下的锚链性能和选用标准

随着极地航道和油气资源的开发,造船和海工行业开始更多地关注现有装备在极地低温条件下的使用性能。锚链是船舶和平台定位用的重要组件,在使用过程中不可避免会暴露在冰冷海水和极地寒冷的空气中,有时甚至会受到浮冰冲击。钢铁材料的性能会受到低温的影响,从而产生脆化并降低可靠性。文章研究了不同等级的锚链(包括系泊链)材料在低温下的拉伸和冲击性能,并结合现有船级社规范中关于低温环境使用的材料和锚链的要求,对此类条件下锚链的设计和选用提出了参考。     

The effect of railway local irregularities on ground vibration

The environmental effects of ground-borne vibrations generated due to localised railway defects is a growing concern in urban areas. Frequency domain modelling approaches are well suited for predicting vibration levels on standard railway lines due to track periodicity. However, when considering individual, non-periodic, localised defects (e.g. a rail joint), frequency domain modelling becomes challenging. Therefore in this study, a previously validated, time domain, three-dimensional ground vibration prediction model is modified to analyse such defects. A range of different local (discontinuous) rail and wheel irregularity are mathematically modelled, including: rail joints, switches, crossings and wheel flats. Each is investigated using a sensitivity analysis, where defect size and vehicle speed is varied. To quantify the effect on railroad ground-borne vibration levels, a variety of exposure–response relationships are analysed, including: peak particle velocity, maximum weighted time-averaged velocity and weighted decibel velocity. It is shown that local irregularities cause a significant increase in vibration in comparison to a smooth track, and that the vibrations can propagate to greater distances from the line. Furthermore, the results show that step-down joints generate the highest levels of vibration, whereas wheel flats generate much lower levels. It is also found that defect size influences vibration levels, and larger defects cause greater vibration. Lastly, it is shown that for different defect types, train speed effects are complex, and may cause either an increase or decrease in vibration levels.     

延崇高速公路金家庄特长螺旋隧道温度场分布规律及保温层研究

为揭示寒区螺旋隧道温度场时空分布规律，依托金家庄特长螺旋隧道，采用现场监测方法研究寒区螺旋隧道温度场变化规律。基于此，通过数值模拟建立三维模型探究进口风速风温对温度场的影响，并拟合结果数据获得保温层敷设长度计算公式。研究表明： 1）随着进洞深度的增加，进、出口洞壁处空气年平均温度上升，而年温度振幅减小； 出口年温度振幅变化幅度略小于进口。2）隧道贯通后，洞内温度受两侧洞外相对低温的共同作用，同一断面处年平均温度下降，年温度振幅增大。3）隧道在直线段温度场分布规律与同条件的直线隧道一致，从曲线段开始内外径温度曲线发生分叉，外径侧温度较直线隧道温度大；而内径侧温度反之。4）进口风速越大、风温越低，对隧道温度场越不利，通过拟合公式，金家庄特长螺旋隧道进口的保温层长度至少需要1 239 m。     

Measuring the car ownership impact of free-floating car-sharing – A case study in Basel,Switzerland

Free-floating car-sharing schemes operate without fixed car-sharing stations, ahead reservations or return-trip requirements. Providing fast and convenient motorization, they attract both public transport users and (former) car-owners. Thus, their impact on individual travel behavior depends on the user type. Estimating the travel behavior impact of these systems therefore requires quantitative data. Using a two-wave survey approach (shortly after launch of the scheme plus one year later) including travel diaries, this research indicates that (due to their membership) 6% of the free-floating car-sharing customers reduce their private vehicle ownership. Moreover, the results suggest that free-floating car-sharing both complements and competes with station-based car-sharing.     

框架结构钢筋混凝土面板裂缝分析与防治

对重庆果园港区码头现浇钢筋混凝土面板裂缝进行理论分析，找出产生裂缝的原因，并针对性地采取措施。这些措施包括：提高混凝土本身抗拉强度；采用混凝土后浇带方式在施工期间解除束缚面板混凝土的约束；通过对混凝土原材料、配合比的优化和采取施工措施来减少混凝土的自生收缩、塑性收缩、干缩及温度变化和内外温差引起的收缩，从而大大降低混凝土的收缩应力。     

现浇箱梁桥桥面板受力分析

为了研究现浇预应力混凝土城市桥梁桥面板的受力、 构造及配筋， 以天水市藉口镇藉河大桥工程的3～35 m现浇预应力混凝土梁为例， 采用Midas Civil程序进行桥面板结构计算， 在此基础上提出常规现浇箱梁桥面板的倒角尺寸。计算结果表明: 城市桥梁车辆荷载轴重较大， 且由于新桥涵通规基本组合对车辆荷载分项系数的提高， 以往的小尺寸倒角桥面板在腹板根部抗剪承载力已显不足， 需增大倒角尺寸以满足桥面板抗剪承载力要求。     

PEG/SiO2型控温相变沥青混合料的性能

为了解决沥青路面的高温病害,以相变材料等体积替代沥青混合料中的一部分细集料,希望通过相变材料自身的相变过程来调节路面温度。试验得出:掺入相变材料后,混合料的降温效果最大可达到6℃,持续时间约3 h。试验结果显示混合料的马歇尔稳定度下降,流值上升,低温性能及水稳定性均有一定下降,但是仍满足规范要求;进行的车辙试验效果不理想,高温稳定性下降较多。说明了掺入相变材料可以对沥青混合料进行温度调控,但是在一定程度上降低了混合料的性能。     

批量生产多循环闭式冷锻铝材成形误差机械热偶合有限元分析

在冷成形加工中因为工件和模具中的温度随时间变化而使工件的成形误差也随之变化，以前的成形误差分析仅涉及单个工件加工循环。同时考虑机械效应和热力效应对成形误差的影响，对批量生产多循环闭式冷锻铝材成形过程中工件的成形误差进行了有限元分析，给出了一个包含成形各个阶段所产生的成形误差的误差分析公式。该公式可用于诸如挤压成形等其他成形工艺。这一分析工作为高精密成形误差补偿方法的研究提供了指导。     

A bi-objective bi-level signal control policy for transport of hazardous materials in urban road networks

A bi-objective bi-level signal control optimization for hazardous material (hazmat) transport is considered to assess trade-offs between travel cost and environment impacts such as public risk exposure. A least maxi-sum risk model with explicit signal delay is presented to determine generalized travel cost for hazmat carriers. Since the bi-level signal control problem is generally a non-convex program, a bundle method using generalized gradients is proposed. A bounding strategy is developed to stabilize solutions of the bi-level program and reduce relative gaps between iterations. Numerical comparisons are made with other risk-averse models. The results indicate that the proposed bi-objective bi-level model becomes even amiable to signal control policy makers since provides flexible solutions whilst is acceptable to carriers since takes account of travel delay at signal-controlled junctions. Moreover, the trade-offs between public risk and generalized travel costs are empirically investigated among different risk models with a variety of weights. As a result, the proposed model consistently exhibits highly considerable advantage on mitigation of public risk whilst incurred less cost loss as compared to other alternatives.