钢轨表面缺陷图像自适应分割算法

针对钢轨表面缺陷提取时的灰度分布不均与杂散光干扰问题,在背景差分法的基础上提出了一种钢轨表面缺陷图像自适应分割算法.首先,通过统计钢轨图像中各行像素灰度特征,结合其均值与标准差分布曲线快速提取钢轨表面区域;然后,进行区域与边缘特征的均值窗口自适应选取;最后,根据均值模糊原理建立背景图像模型并进行图像差分,实现了钢轨表面缺陷分割.实验结果表明:提出的轨面提取算法快速、有效;钢轨表面缺陷自适应分割算法在凸显图像中缺陷部分的同时,有效减少了光照变化和反射不均的影响.该方法对测试图像的召回率和准确率分别达到了95.4%和81.3%.     

山区河流浅水条件下漂石对河床响应与泥沙补给影响的试验研究

受暴雨洪水与滑坡、泥石流灾害的影响,山区河流床沙多为宽级配卵砾石泥沙,甚至出现较多的漂石,从而影响近底水流结构与推移质输移特性。基于野外漂石河流的调查,通过概化试验,探讨了漂石颗粒对河床冲淤的影响;对比分析了不同水沙条件下漂石对推移质输沙率过程的影响;根据床面粗化程度与漂石状态相异的两种类型对比试验,探讨了漂石对不同水沙条件下推移质输沙率的影响程度。初步表明：随着漂石颗粒相对暴露度（D/h,漂石等效粒径与平均水深之比）的减少,漂石对其尾部区域水流的混掺越加突出,从而对河床的冲刷能力变大;根据本试验采用的水沙参数,漂石对推移质输沙率的扩大效应为几倍至十几倍。     

In‐stream construction‐induced suspended sediment in riverine ecosystems

Construction activities within the wetted‐perimeter of rivers, referred to as in‐stream construction, are prevalent economically and environmentally motivated activities having direct interactions with sensitive lotic environments. Currently, there is a paucity of research related to in‐stream construction activities and their effects on aquatic ecosystems. In‐stream construction‐induced suspended sediment may result in harmful effects to aquatic flora and fauna. Regulatory frameworks worldwide focus primarily on concentration, with limited consideration for duration and no consideration for spatial extents of suspended sediment exposures. This research develops theoretical concentration, duration, and spatial extent exposure risk relationships for riverine ecosystems to demonstrate the influence of each mechanism during typical in‐stream construction activities. To reduce exposure risk, concentration and duration may be considered pragmatically, based on anticipated activity characteristics and site conditions. Spatial exposure characteristics are important to consider, as illustrated by our finding that activities located near the channel centerline may result in greater exposure risk than similar activities conducted near the streambank. Current regulatory frameworks worldwide do not sufficiently consider all exposure risk mechanisms present during in‐stream construction‐induced suspended sediment releases, possibly inhibiting efforts to reduce adverse environmental effects. This research improves our understanding of suspended sediment in lotic environments and may help environmental managers better evaluate and manage in‐stream construction activities.     

Sediment flux from Lesser Zab River in Dokan Reservoir: Implications for the sustainability of long‐term water resources in Iraq

Prudent management of Iraqi water resources under climate change conditions requires plans to be based on actual figures of the storage capacity of existing reservoirs. With the absence of sediment flushing measures, the actual storage capacity of Dokan Reservoir (operated since 1959) has been affected by the amount of sediment delivered during its operational life leading to an undetermined reduction in its storage capacity. In consequence, there has not been an update on the dam's operational storage capacity curves. In this research, new operational curves were established for the reservoir based on a recent bathymetric survey undertaken in 2014. The reduction in reservoir capacity during the period between 1959 and 2014 was calculated by the mean of the difference between the designed storage capacity and the storage capacity which was concluded from the 2014 bathymetric survey. Moreover, the rate of sediment transported to the reservoir was calculated based on the overall quantities of accumulated sediment and the water discharge of the Lesser Zab River into the reservoir. The results indicate that the dam capacity is reduced by 25% due to sedimentation of an estimated volume of 367 million cubic metres at water level 480 m.a.s.l. The annual sedimentation rate was about 6.6 million cubic metres, and the sediment yield was estimated to be 701.2 t?km^?3?year.     

Quantifying water quality and flow in multi-branched urban estuaries for a rainfall event with mass balance method

In this study, field observations were conducted after a heavy rainfall event in the Sumida and Shakujii rivers in Tokyo, Japan. The flow dynamics and fluxes of salt, suspended sediment (SS), and dissolved oxygen (DO) were investigated with the mass balance method. The fractions of fresh water and saltwater in seaward and landward flows were separated. The maximum salt flux in the Shakujii River was 53.8 kg/s during the flood tide, and those in the Sumida River were 680.3 kg/s at the upstream station and 703.7 kg/s at the downstream station. The trends of SS and DO fluxes were similar in both rivers. In the Shakujii River, the highest SS (3.1 kg/s) and DO (0.4 kg/s) fluxes appeared during the flood tide after rainfall. In the Sumida River, the maximum SS fluxes (6.1 and 6.3 kg/s at the upstream and downstream stations, respectively) and DO fluxes (1.15 and 1.21 kg/s at the upstream and downstream stations, respectively) appeared during the ebb tide. The mass balance method was used to estimate discharge, salinity, SS concentration, and DO concentration at a station with missing data. The results show that the estimated salinity and SS concentration had a significant correlation with the on-site observations, with correlation coefficients (R) of 0.950 and 0.835, respectively, but not for DO concentration (R = 0.638). The disparity between the computed and measured data may be explained by the differences in velocity, salinity, topography, sedimentation, and the presence of organic matter. The analysis based on the advective salt transport components found a lower salt flux per unit width in the Shakujii River (0.36 kg/(m·s)) in comparison with that in the Sumida River (2.88 kg/(m·s)). This indicates a higher probability for salt retention in the Shakujii River.     

基于轮轨表达式的轮轨接触坐标计算方法

为了能更真实地在车辆-轨道动力学的仿真计算模型中反映轮轨之间的接触状态,结合具有具体函数表达式的车轮踏面和钢轨轮廓曲线并利用迹线法原理,在考虑轮对的横向位移、垂向位移、摇头角及侧滚角的条件下,计算出轨顶区域与车轮之间的最小垂向距离,来判断轮轨的接触状态,并根据非线性赫兹接触理论求轮轨接触点处的轮轨法向力.     

闽江下游径流量和北港分流比变化及其对水龄的影响研究

利用闽江下游多年水文资料,分析了干流流量时空变化和北港分流比变化趋势,并借助EFDC模型研究水口水库下泄流量和北港分流比对闽江下游水体水龄的影响。分析表明:闽江干流径流量年际变化不均匀,北港分流比则经历了由小变大再变小的趋势。模拟的闽江水龄结果可知水龄与下泄流量成反比关系,北港分流比减小将增加北港水体交换时间,同时减少南港水体交换时间;水龄可以定量地描述污染物在北港河道的停留时间,为保障北港水源地水质安全,需要增大枯水期上游水口水库下泄流量和增大北港分流比。     

城际轨道深基坑支护优化及实测分析

为研究莞惠城际轨道基坑施工方案的可靠性,结合莞惠城际轨道工程深基坑开挖的具体实践,基于现场实测数据,对深基坑开挖过程中桩体水平位移、桩顶水平位移、地表沉降、支撑轴力、地下水位变化规律进行了全面深入的研究.结果表明:降水对地表沉降有较大影响,施工中应予以重视;钢支撑的预应力对基坑的变形特别是围护结构侧向位移控制有较大影响;钢支撑轴力远小于设计值,设计方案可以进一步优化;优化后的支护方案较好地限制了基坑变形.     

GAAS80焊机焊接U76CrRE钢轨工艺研究

分析了GAAS80/580焊接原理,结合GAAS80闪光焊机焊接工艺特点,制定了U76CrRE钢轨的焊接工艺。采用落锤试验检验焊头质量,并对断口形貌进行扫描,能谱分析表明,断口缺陷处低熔点共晶硫化物的形成是裂纹产生的主要原因。在此基础上优化焊接工艺参数,降低预热阶段的电压、减小烧化阶段的位移、提高烧化阶段的闪光速度。优化后的U76CrRE钢轨焊接工艺通过了落锤试验,各项力学性能符合铁道部钢轨焊接标准的相关要求。     

Mixed convective heat and mass transfer analysis for peristaltic transport in an asymmetric channel with Soret and Dufour effects

The present investigation addresses the simultaneous effects of heat and mass transfer in the mixed convection peristaltic flow of viscous fluid in an asymmetric channel. The channel walls exhibit the convective boundary conditions. In addition, the effects due to Soret and Dufour are taken into consideration. Resulting problems are solved for the series solutions. Numerical values of heat and mass transfer rates are displayed and studied. Results indicate that the concentration and temperature of the fluid increase whereas the mass transfer rate at the wall decreases with increase of the mass transfer Biot number. Furthermore, it is observed that the temperature decreases with the increase of the heat transfer Biot number.