河渠冰水力学、冰情观测与预报研究进展

冰情预报是进行防凌指挥、调度、决策的重要科学依据,也是一项复杂的系统工程,涉及冰水力学、热力学、气象及人工智能等学科。本文回顾了近几十年来冰水力学基础理论、模型实验和原型观测、冰情预报等方面的研究进展,包括:冰盖下流动的糙率计算,冰盖、冰塞、冰坝形成发展的理论研究及数值模拟,模型实验、原型观测典型成果,探地雷达、超声波技术、摄影、摄像、遥感、无人机航拍等现代冰情观测技术的发展与应用等。在此基础上,总结和归纳出研究现状及存在的一些急需解决的科学问题。     

湖冰侧、底部融化现场观测与热力学分析

为深入了解湖冰在弱水动力条件下消融的热力学过程,在融冰期对乌梁素海湖开敞水域处冰层开展侧、底部消融的原位测量,并观测了太阳辐射、气/冰/水/泥温和风等气象及水文要素。观测结果表明冰层侧壁随深度增加逐渐向内侧倾斜融化,冰层厚度逐渐减薄;开敞水域处水温和冰温均呈分层变化,上层水温和冰温日变化幅度较大。通过分析冰层侧、底部融化速率与气象及水文要素之间的变化关系,建立了用净太阳辐照度和水温来表达融化速率的参数化模型。冰底热通量是一项重要的热力学参数,基于冰底薄层的能量平衡,利用观测数据确定了开敞水域处冰层的平均冰底热通量,为11.47~135.61W·m~(-2),表明冰下水体不断向冰层传递热量。     

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.     

Modeling of thermodynamics of ice and water in seasonal ice-covered reservoir

A width-averaged 2-D numerical model for simulating vertical distributions of flow and water temperature in reservoirs with an ice cover is developed. In this model, the 2-D flow and water temperature distributions are solved by the finite volume method with the k-? turbulent model. The heat conduction in the ice cover is modeled by the vertical heat transfer and the heat exchanges through the air-ice and ice-water interfaces. The model is applied to a 153 km long reservoir in Songhua River and the simulated results are in a good agreement with the field data of both the vertical water temperature and the ice thickness. The simulated results show that the ice cover thickness in the reservoir is not uniform, the maximum thickness appears in the middle reach, the outflow temperature has an obvious variation as compared with the natural temperature, and a buoyant flow occurs in the reservoir surface at the freeze-up and break-up periods. The model can effectively simulate the water temperature and the ice conditions of large reservoirs in cold regions.     

弯道丁坝防冰结构布置形式试验研究

弯曲河流的凹岸易受到冰排的撞击而发生磨蚀、崩岸,该处的护岸工程也会在冰排撞击作用下发生破坏,丧失防护功能。研究冰排的运动规律,进而保护河岸意义重大。丁坝作为治河建筑物会明显改变水流条件,而冰排随水流而动,丁坝的存在必然会对冰排的运动产生影响。通过室内试验的方法研究了在河流凹岸布置丁坝后冰排的运动特性,比较了5种不同丁坝布置形式对冰排运动的影响。试验研究表明:从防冰效果看,双丁坝的布置方案要优于单丁坝布置方案;单丁坝布置方案中,弯道60°布置位置最佳;弯道首、尾部的双丁坝布置形式中,长丁坝的布置形式较短丁坝布置形式效果更好;在弯道后加置1~2个短丁坝可以使双丁坝布置形式的防护效果达到最佳。     

冰水堆积体开挖施工成本测算方法研究

在近几年的水电工程地质勘探中,发现了冰水堆积体这一特殊地质结构物,因其特殊的结构及物理特性,导致开挖施工成本测算难度较大,而且现行的预算定额中没有相应的子目作为参考,给工程投标报价、施工成本控制等带来了不便。以金沙江中游某电站大坝左岸趾板冰水堆积体开挖施工为例,介绍了一种比例换算法,即先统计冰积体开挖所发生的实际钻孔机械及爆破器材耗用量,然后将其与《水电建设工程耗算定额》中X级岩石开挖的预算定额数据对比,得出两者之间的比例关系,并以此作为冰积体开挖施工钻爆的测算依据。可为类似工程建设管理活动提供借鉴。     

基于布拉格光纤光栅的静冰压力传感研究

针对现有电传感器在高寒地区测量静冰压力存在的问题,提出了一种基于布拉格光纤光栅的静冰压力传感测量系统,可实现对静冰压力的定点在线测量。通过测得冰层内部静冰压力和温度同时变化过程中的光纤光栅布拉格波长,经过温度补偿消除了静冰压力测量过程中温度的影响,利用压力与布拉格光栅中心波长的关系得到静冰压力的测量值。同时,利用混沌光源良好的互相关性,通过相关峰的位置,实现了对静冰压力的定点测量。本实验对-10℃~-5℃温度范围内,实验室条件下的模拟静冰压力进行了测量,对系统进行了温度补偿,温度补偿曲线线性拟合度为99.56%,有效地消除了交叉敏感,可满足实际工程应用中静冰压力的测量要求。     

冰盖下桥墩局部冲刷随时间变化的试验研究

在寒冷地区,河道中冰盖的存在会改变河道流速分布。与明流条件相比,冰盖条件下水流最大流速点会向河床移动,加剧桥墩周围的局部冲刷。过度的局部冲刷会导致桥梁倒塌。基于水槽清水冲刷试验,对冰盖与明流条件下圆柱型桥墩局部冲刷随时间的变化进行了研究,试验结果表明：冰盖下桥墩局部冲刷速率大于明流。平衡冲刷深度比明流条件下的约大12%,且冲刷平衡所需时间比明流条件下的要约大10%。分析了水流强度与无量纲冲刷深度的关系以及冰盖与明流条件下冲刷深度变化速率的差异,给出了冰盖下局部冲刷深度随时间变化的经验方程,研究成果可供实际工程参考。     

黄河什四份子弯道河冰生消及冰塞形成过程分析

什四份子弯道因其特殊的河道形态及地理位置而成为黄河内蒙古段易发生冰塞断面。通过对2014—2015年冬季该段野外冰情监测及水文、气象资料分析,结合Landsat8遥感影像数据解译,研究了什四份子弯道河冰生消及冰塞形成过程。结果表明,野外观测结合遥感影像解译能够准确地反映河冰的时空特性。该河段弯道凹岸处冲积岸冰及凸岸静态岸冰的生长,极大地束窄了河面宽度,降低了水流的输冰能力,而使其成为初始卡冰位置;冰盖至此向上游发展,弯道下游因来冰量减少和上下游水力坡度增大而形成清沟;受弯道径向水流方向改变及弯道螺旋流的影响,导致冰花在冰盖下主槽与滩地的交界处堆积;稳封期受气温升降变化使得冰盖表面冻融交替,冲积冰反射率增大,后期解译的遥感影像中平滑岸冰面积较初始封河期增加。     

Consumer Willingness to Pay for Dairy Products With the 100% Canadian Milk Label: A Discrete Choice Experiment

ABSTRACT

A component of the supply management policy governing the Canadian dairy sector is a requirement that all milk and cream sold in Canada be sourced from Canadian producers. Cheese, yogurt, and ice cream, however, can be made using imported milk components. Recently, the Dairy Farmers of Canada launched a 100% Canadian Milk label for products that contain only milk and milk ingredients produced in Canada. Featuring a discrete choice experiment, a Canada-wide survey of dairy consumers is used to elicit their willingness-to-pay for milk and ice cream carrying the 100% Canadian Milk label. The results show that Canadian consumers are willing to pay more for milk and ice cream products that carry the label. Consumer knowledge of the dairy sector affects their willingness to pay for this labeling information. Implications for the use of the Canadian origin label and suggestions for further research are discussed.