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Experimental bedforms by saline density currents

机译：盐水密度流的实验床形

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Bedforms are sedimentary features that can be generated on the seafloor by the interaction between density currents and mobile beds. Developing knowledge about the hydraulic and sedimentary processes involved during these events is in the interest of research groups and oil companies. Because of the magnitude of the density currents in its natural environment and the challenge in collecting data, studies in laboratory are of great value. We present results of 29 experiments focusing in the bedform development generated by saline currents, testing two different sediment types and three grain sizes: melamine (245 μm-plastic) and sands (206 and 485 μm). We analyzed the current velocity and fractional density profiles as well as pictures taken during and after each run. Results have showed classical velocity and concentration profiles, for 8 subcritical and 21 supercritical currents, with densimetric Froude numbers (Fr d ) between 0.5 and 2.2. Some correlations were identified, such as the decrease of the velocity peak height and increase in the mean velocity (with consequent reduction of the current thickness), due to an increase of the concentration and/or flume slope. The occurrence of bedforms was more likely for high discharge and concentration rates of current density, which directly influence the Fr d . Bedforms were classified according to the shear stresses values applied by the current to the bed, resulting in the generation of lower plane bed, ripples and dunes. Dunes and ripples were observed in supercritical flow conditions, which is a hydraulic scenario of bedforms generation not predicted by fluvial models. Thus, this study demonstrated the existence of differences in generation and, consequently, the classification approach for density current bedforms, compared to those generated by river flows. To this fact is attributed the hydrodynamic (velocity and concentration profiles) and sediment transport differences between fluvial flows and density currents. Further studies may be carried out in order to constructing new concepts of bedforms generation by density currents.
机译：床形是沉积特征，可以通过密度流和移动床之间的相互作用在海底生成。研究小组和石油公司的利益是要发展有关这些事件中涉及的水力和沉积过程的知识。由于自然环境中密度电流的大小以及收集数据的挑战，因此在实验室中进行研究非常有价值。我们介绍了29个实验的结果，这些实验的重点是盐水流产生的床形发育，测试了两种不同的沉积物类型和三种粒度：三聚氰胺（塑料245μm）和沙子（206和485μm）。我们分析了当前速度和分数密度分布以及每次运行期间和之后所拍摄的照片。结果表明，对于8个亚临界电流和21个超临界电流，经典的速度和浓度分布图，密度弗劳德数（Fr d）在0.5至2.2之间。由于浓度和/或水槽斜率的增加，确定了一些相关性，例如速度峰值高度的降低和平均速度的提高（因此，当前厚度减小）。高放电率和电流密度集中率更容易产生床形，这直接影响Fr d。根据电流施加到床的切应力值对床形进行分类，从而产生较低平面的床，波纹和沙丘。在超临界流动条件下观察到了沙丘和涟漪，这是河流模型无法预测的水力情景。因此，这项研究证明了与河流产生的密度相比，存在着差异的产生，因此，存在密度流床形的分类方法。归因于这一事实，是水流和密度流之间的水动力（速度和浓度分布）和沉积物传输差异。为了构建通过密度电流产生床形的新概念，可以进行进一步的研究。

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