路堤块石自然对流机理的室内模拟试验研究

为研究路堤块石在边界温度周期波动条件下的自然对流发生机理及降温效应的表征参数,采用室内模拟方法对50×50×65cm3尺寸的不同块石试样进行了试验和理论分析,结果表明:平均RAYLEIGH数能描述块石层自然对流的发生情况,不同厚度的块石层将产生不同的对流模式,厚度大的块石层所产生的自然对流降温效应也较大,上层砂砾加下层块石的结构自然对流效应最弱。块石层降温效果取决于块石粒径、层厚及铺筑在路堤中的位置,这一结论对多年冻土地区路堤设计、施工,合理确定块石铺筑层厚、铺筑层位具有现实指导意义。     

钢管活性粉末混凝土轴压短柱受力性能试验研究

进行22根钢管活性粉末混凝土(钢管RPC)轴压短柱试验,分析其荷载-变形曲线、破坏特征和影响极限承载力的主要因素。试验研究表明:钢管RPC轴压短柱的荷载-纵向应变曲线弹性阶段约为极限荷载的90％~95％;套箍系数ξ较小时,在达到极限荷载后承载力急剧下降;ξ较大时,在达到极限荷载后承载力下降平缓并呈回升趋势。ξ较小的试件多呈剪切破坏形态;ξ较大的试件所有断面上均被墩粗,试件的上、下两端明显局部鼓曲。构件承载力随RPC强度fc的提高而提高,两者基本成线性关系;套箍系数ξ越大,构件承载力也越大,但钢管对RPC的约束效果比对普通混凝土的差。提出的钢管RPC轴压短柱极限承载力的实用计算公式计算出的结果与试验结果吻合良好。     

液压马达实验方法研究

介绍了液压试验分类方式,根据其独具的特点对在用液压马达性能试验加载方法进行分析,并分类对工程机械用各种液压马达在泵工况下进行试验的可行性进行了探讨.     

岩土锚固力的确定及应用

选定粤赣高速公路有代表性的6种岩层,对其全、强、弱风化层组成的路堑高边坡锚索加固工程进行了69次破坏性拉拔试验。试验中对每种不同风化程度的岩(土)层采用锚固长度为1m、2m、3m的现场拉拔试验,计算出锚索加固边坡的锚固力值,为验证高边坡工程设计提供了准确的力学参数,也为全线高边坡工程的施工工艺提供指导性意见。同时,节省了大量的试验费用和时间,获得了显著的经济效益。     

A design method of tensile triangles and low transformation temperature weld metal for reduction of stress concentration and residual stress of welded joints

Stress concentration and residual stress have a significant influence on fatigue life of welded joints. In order to reduce the stress concentration of welded joints, a mathematical design method of tensile triangles (MTT) based on bionics was applied to weld shape design. Accordingly, the stress concentration of various weld beads in the corner boxing welded joint and the fillet welded T-joint was dissected using our in-house FEM software JWRIAN. It was found that there existed a large stress concentration in the conventional welded joints, whereas those welded joints with elongated weld bead were accompanied by a lower stress concentration, especially for elongated weld bead with MTT design. Furthermore, among the weld shapes of the corner boxing fillet welded joint, the rectangle shape of weld bead had the minimum stress concentration factor (1.05). For the fillet welded T-joint with MTT design, the stress concentration of weld toe decreased dramatically with the increase of the index of designed shape, but there was a minor difference of stress concentration at weld root between the weld beads with MTT design. In addition, application of low transformation temperature (LTT) weld metal utilizing martensitic transformation to the fillet welded T-joints can produce compressive residual stress at weld toe.     

Electric vehicles and residential parking in an urban environment: Results from a stated preference experiment

This paper presents the results of a preference survey of 1545 respondents’ willingness to purchase electric vehicles (EVs) in Philadelphia. We pay particular attention to respondents’ willingness to pay for convenient charging systems and parking spaces. If the value of dedicated parking substantially outweighs the value of convenient charging systems, residential-based on-street charging systems are unlikely to ever be politically palatable. As expected, respondents are generally willing to pay for longer range, shorter charging times, lower operating costs, and shorter parking search times. For a typical respondent, a $100 per month parking charge decreases the odds of purchasing an EV by around 65%. Across mixed logit and latent class models, we find substantial variation in the willingness to pay for EV range, charge time, and ease of parking. Of note, we find two primary classes of respondents with substantially different EV preferences. The first class tends to live in multifamily housing units in central parts of the city and puts a high value on parking search time and the availability of on-street charging stations. The second class, whose members are likelier to be married, wealthy, conservative, and residing in single-family homes in more distant neighborhoods, are willing to pay more for EV range and charge time, but less for parking than the first group. They are also much likelier to consider purchasing EVs at all. We recommend that future research into EV adoption incorporate neighborhood-level features, like parking availability and average trip distances, which vary by neighborhood and almost certainly influence EV adoption.     

圆形隧道施工对不同深度地层沉降影响的模型试验研究

为了预测圆形隧道施工引起地表以下不同埋深地层沉降特征,首先,通过理论推导不同地层最大沉降位移与沉降槽宽度系数的函数关系;然后,建立包括试验台架、地层模型、圆形隧道开挖模型以及测量地层变形装置的平面应变模型试验系统。通过理论解析和模型试验可知:1)地表以下地层的最大沉降位移与沉降槽宽度系数成反比;2)不同深度地层的沉降位移随着地层埋深的增加而增大,且地表以下地层沉降槽曲线仍然符合正态分布;3)通过对模型试验数据进行回归分析,得到黏土地表以下不同深度地层沉降槽宽度系数的计算公式,从而为预测圆形隧道施工地表以下不同深度地层竖向位移提供了一种可靠的计算方法。     

城市地下道路分(合)流匝道通风阻力特性

为分析多点进出结构的城市地下道路空气流动特性,以长沙市营盘路湘江隧道为原型,通过现场实测、缩尺模型试验以及CFD软件数值模拟方法,对分(合)匝道通风阻力特性进行了研究,考察了雷诺数、风量比、分岔角度对分(合)流匝道阻力特性的影响规律。研究结果表明:1)主隧道与匝道风量比、主隧道与匝道夹角是影响分(合)流匝道局部阻力系数的关键因素;2)城市地下道路分(合)流匝道局部阻力变化特性,不宜简单套用通风管道的三通构件的参数;3)结合最小二乘法和Matlab软件对计算结果进行多因素回归分析,给出了基于长沙营盘路湘江隧道的分(合)流匝道主隧道和匝道的局部阻力系数关联式。研究结果可为复杂结构城市地下道路通风系统阻力特性分析及通风工程优化设计提供方法参考。     

油底壳有限元模态分析及实验验证

以EQ491型发动机油底壳为研究对象,通过有限元法得到了油底壳模型的固有频率和振型,运用模态实验技术,验证了有限元模型的合理性。在原始有限元模型的基础上,对油底壳模型进行约束模态分析,验证了油底壳结构的合理性,即油底壳固有频率远大于发动机机体激振频率。     

轴流式涡轮机动叶片的叶顶间隙对其气动性能影响

采用数值方法对不同叶顶间隙下某型号船用轴流式涡轮机的气动性能进行了对比分析.结果表明,叶顶间隙对喷嘴环前缘的压力分布和涡轮内的温度分布影响明显,过小和过大的叶顶间隙都会导致喷嘴环前缘高压力区的产生,并导致涡轮内局部高温度区域扩大;随着叶顶间隙的增大,喷嘴环后缘底部、吸力面及叶顶间隙内局部高熵区随之增大,燃气能量损失增大.