水库异重流的三维数值模拟及影响因素分析

不同水沙条件下异重流的潜入位置以及潜入后流速和含沙量的垂向分布规律是研究异重流运动规律的关键要素,对优化水库异重流的排沙调度、提高水库运用效益等至关重要。本文利用SCHISM三维水沙数学模型对水库异重流水槽试验进行了数值模拟,结果表明模型能够得到符合实际情况的垂线流速和含沙量分布,且异重流潜入后的平均厚度、平均流速和平均含沙量均与实测值吻合较好。对异重流模拟结果的分析发现,入口流量和含沙量的增加造成异重流运动速度越快,而入口含沙量的减小和流量的增加会造成异重流厚度增加。异重流垂向流速和含沙量的无量纲化分布受到入口水沙条件的影响,表现在其与断面Froude数的相关性,Froude数越大,则最大流速点与河床的距离越小,最大流速越大;含沙量致密层的厚度越小,对应的含沙量也越大。此外,潜入点位置也受入口水沙条件的影响,表现在潜入水深与入口水深之比随入口Froude数增加而增加的定量关系,由此可以利用入口水沙条件预报异重流潜入的位置。研究结果不仅验证了SCHISM模型用于模拟水库异重流运动的优势,而且丰富和完善了关于异重流潜入点位置及流速和含沙量垂向分布受入口水沙条件影响的变化规律。     

民用运输机场飞行区消防给水管道选用要点分析

当前飞行区消防给水管道选材无相应的标准,影响飞行区消防给水管道选用因素较多,管道渗漏所造成的损失(尚不包括机场运营第三方损失)远远大于材料本身。结合相关机场工程实例,通过对飞行区常用消防管道的基本材料性能、公称压力、埋深、管道连接与补偿及管道单位造价的对比分析,提出管道的安全性(结构强度与低渗漏性)是设计人员应该考虑的第一要素,单位管长管道接口数是衡量管道安全性的重要指标。选择成熟稳定质量的管道(并提出原料性能限制)及连接方式,降低单位管长管道接口数,并做好管道补偿设计,对于飞行区消防给水管道防渗漏及耐压力波动、耐不均匀沉降、耐管道轴向位移等方面具有重要的意义。     

基于专利技术关联度的中间人角色划分方法研究

基于专利数据构建的发明人合作网络有助于分析发明人中间人角色,揭示发明人创新合作规律,对于企业研发人才管理和知识管理具有重要指导意义。群体划分是中间人角色划分的一个关键步骤,以往文献大多基于网络结构或者给定网络边界进行群体划分,忽视了专利发明人的知识交流环境和特征。鉴于此,基于专利技术关联度,利用专利著录项中的IPC分类号信息判断企业发明人所属技术知识领域,再以技术知识领域为边界设计一套算法,将发明人归入互斥子群,最终对中间人角色进行高效划分,寒武纪公司数据验证了中间人角色划分算法具有较高的准确性和有效性。     

Effects of runoff voting rules on number of parties and candidates' political experience: Evidence from a law change in Peru

We study the effect of a change in electoral rules on political competition, measured by the number of candidates and their political experience. We explore the effects of a change in legislation, introduced a year before the gubernatorial elections in Peru on the number of parties that participated in these elections. We also investigate how the legislative change affected the political experience of the candidates. Given that the legislative change did not apply to elections for provincial mayors, we use those elections as a control group, in a difference-in-differences design. Our estimates show the number of parties registered increased by a margin of around 2.2 after the legislative change. The change also increased the candidates' years of accumulated political experience, particularly in the subsequent gubernatorial elections.     

二维水力模拟在河流生态需水湿周法中的应用

湿周法是河流生态需水量计算中使用较为常见的一种水力学方法,通常采用一维的水力分析结果作为计算依据。二维水力模拟能提供更为细致全面的河道水力参数分布,通过对某水电站坝下13.3 km河道进行平面二维水力模拟,对其在湿周法中的应用进行了探讨。采用弗汝德数(Fr)作为浅滩生境划分标准,把浅滩生境较为集中的河段作为湿周法分析的浅滩河段。随后根据平面二维水力模拟结果,给出了浅滩断面相对湿周-流量关系曲线,采用斜率为1的斜率法计算得到了各浅滩断面的生态需水量。结果表明,采用二维水力模拟结果给出的曲线更为合理。     

Revisit submergence of ice blocks in front of ice cover–an experimental study

The present paper studies the stabilities of ice blocks in front of an ice cover based on experiments carried out in laboratory by using four types of ice blocks with different dimensions. The forces acting on the ice blocks in front of the ice cover are analyzed. The critical criteria for the entrainment of ice blocks in front of the ice cover are established by considering the drag force caused by the flowing water, the collision force, and the hydraulic pressure force. Formula for determining whether or not an ice block will be entrained under the ice cover is derived. All three dimensions of the ice block are considered in the proposed formula. The velocities calculated by using the developed formula are compared with those of calculated by other formulas proposed by other researchers, as well as the measured flow velocities for the entrainment of ice blocks in laboratory. The fitting values obtained by using the derived formula agree well with the experimental results.     

低弗劳德数梯形墩-悬栅消力池水力特性

针对大单宽流量、低弗劳德数消力池内消能问题,通过物理模型试验方法,对比分析消力池内加设梯形墩和悬栅消能工后水力特性和消能效果,优化梯形墩-悬栅消力池布置形式。结果表明：在低弗劳德数水流条件下,梯形墩-悬栅联合消能工断面水深分布均匀,消力池底板沿程压力分布梯度和时均压力分布系数波动幅度较小,整体稳定性较优;动能修正系数基本保持在1<α<2的范围内,可有效改善入池断面流速分布;消能率由传统消力池的52.25%、70.37%、75.89%分别提升至56.74%、75.95%、79.22%;梯形墩-悬栅消力池内悬栅单排等间距、高度与尾坎同高布置时,梯形墩呈双排交错形式布置在距池首0.35L左右处对于整体流态改善明显,消力池出口流速可降至0.4 m/s,消能率提高至59.63%、76.12%、79.37%,研究结果可为同类工程的底流消能问题提供一种新思路。     

Sediment Pulse Behaviour Following Dam Removal in Gravel‐Bed Rivers

As dams approach the end of their useful life, there is need to predict where and how accumulated sediment will move following dam removal to estimate and mitigate the impacts of this process on aquatic habitat and infrastructure. Flume studies suggest that sediment pulses disperse in place for most dams, but it is hypothesized that certain conditions (e.g., low Froude number, fine pulse grain size, small pulse sizes, and large peak discharge) may characterize pulses that translate downstream. However, quantitative analyses of sediment pulse behavior have not been widely conducted in field settings. We thus analyzed bathymetric data from four field sites in Oregon to investigate the reliability of flume‐derived hypotheses (1) whether dispersion or translation dominates across a range of dam removal physiographies using multiple methods of evaluation and (2) if Froude number, pulse material grain size, relative pulse size, and discharge can predict reservoir sediment movement mode. Results indicated that dispersion generally dominated pulse behavior in the field setting, with some limited evidence of translational movement in individual years. The Froude number appeared to be the most reliable for anticipating pulse behavior. Further work is needed to link generalized sediment pulse behavior to sediment mobilization and transport processes. Copyright © 2016 John Wiley & Sons, Ltd.     

急流弯道水流露底现象研究

为了解急流弯道水流聚集在凹岸的成因,以便在弯道设计和管理中避免水流露底现象发生,根据急流露底弯道水流速度比较快、在没遇到边壁之前沿直线运动的特点,利用动量方程,推导出急流弯道露底的界限。结果表明急流弯道露底与弯道半径、弯道宽度以及水流的Fr有十分密切的关系,当弯道转弯半径与弯道宽度比小于Fr减去0.5时,就会出现露底现象。结论与前人的试验研究结果大致吻合。     

A note on the “size” of determinacy and indeterminacy

Summary. It is shown in this note that in an incomplete markets economy with uncountably many states of the world there may be uncountably many isolated equilibria as well as uncountably many non-isolated equilibria. Moreover, both subsets can be simultaneously of second category. Therefore, none of the subsets can be considered negligible with respect to the other, neither from a cardinality point of view nor from a topological one. Unfortunately, this fact prevents from claiming that these economies may have “typically” determinate equilibria – even though uncountably many of them – as would have been desirable for comparative statics exercises. Received: May 19, 1995; revised version: March 24, 1997