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首页> 外文学位 >Ice-cover influence on flow and bedload transport in dune-bed channels.
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Ice-cover influence on flow and bedload transport in dune-bed channels.

机译：冰沙对沙丘河床通道中水流和河床载荷的影响。

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The study describes the influences of floating level ice-covers on flow and bedload transport in dune-bed channels, and proposes a semi-empirical method for calculating flow resistance in such channels. Heretofore, cover influence was poorly understood, with the consequence that engineers lacked a satisfactory method for calculating resistance in ice-covered alluvial channels.; Two series of laboratory experiments were performed to determine the influence of floating covers. The experiments were designed and interpreted in accordance with a set of key parameters established by means of dimensional analysis of ice-covered alluvial flow variables. The parameters, supported by results from the experiments presented here and in prior studies, enabled development of the semi-empirical calculation procedure mentioned above. In one series, the bed was loose and could deform in relation to the flow. In the other, the bed was fixed to facilitate detailed measurements of the flow velocity field over dunes without and with a cover. The loose-bed experiments provide data on the ultimate influence of ice-cover on flow depth, bulk flow velocity, bed roughness, dune geometry, and bedload transport rate; the fixed-bed experiments reveal the initial flow response to ice-cover presence. The principal findings are that ice-cover increases flow depth, decreases bulk flow velocity, significantly decreases bedload transport rate and dune steepness, and increases dune length. These changes are accomplished not only through a reduction of bed shear stress, but also a reduction of Reynolds stress and turbulent kinetic energy over the dune-bed. Sediment transport relations developed from open-water data are applicable to ice-covered dune-bed flows, provided they are supplied with actual bed shear stress.; The measurements of velocity field over a dune showed that cover presence and increasing roughness redistribute the flow over a vertical section, diminishing flow speed near the cover, but, by deflecting more flow to the bed, maintain near-bed velocities during the initial stages of bed adjustment to ice-cover presence.
机译：这项研究描述了浮冰覆盖层对沙丘河床通道中的水流和基床输运的影响，并提出了一种半经验方法来计算此类通道的流阻。迄今为止，人们对覆盖层的影响了解甚少，其结果是工程师缺乏一种令人满意的方法来计算冰覆冲积层中的阻力。进行了两个系列的实验室实验，以确定浮动覆盖物的影响。根据通过冰覆盖的冲积流量变量的维分析建立的一组关键参数来设计和解释实验。这些参数得到此处和先前研究中的实验结果的支持，可以开发上述的半经验计算程序。在一个系列中，床是松散的并且相对于流量可能变形。另一方面，固定床是为了便于详细测量不带盖和带盖的沙丘上的流速场。松散床实验提供了关于冰盖对流深，整体流速，床面粗糙度，沙丘几何形状和床面负荷输送速率的最终影响的数据；固定床实验揭示了对冰盖存在的初始流动响应。主要发现是，冰盖增加了水流深度，降低了整体流速，显着降低了床荷运输速度和沙丘陡度，并增加了沙丘长度。这些变化不仅可以通过降低床层切应力来实现，而且可以通过降低沙丘床上的雷诺应力和湍动能来实现。从露天水域数据得出的泥沙输移关系适用于冰覆盖的沙丘床层流，但要为其提供实际的床层切应力。沙丘上速度场的测量结果表明，覆盖层的存在和粗糙度的增加会在垂直截面上重新分配流量，从而减小了覆盖层附近的流速，但是，通过将更多的流量偏转到床层，可以在初始阶段保持近床层速度。床调整到冰盖的存在。

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