双层流体中冰脊拖曳系数的实验研究

发布时间：2019-04-23 11:48

【摘要】：全球气温升高在北极地区被放大,称为“北极放大”现象。北极海冰在过去几十年内发生了前所未有的快速变化,导致海冰范围和厚度的持续衰减,在本世纪中页就有可能出现夏季无冰的北冰洋。北极海冰的快速变化对北半球乃至我国的天气和气候造成了越来越显著的影响,而且使得北极航道的开通成为可能,而成为各国政府关注的焦点。作为目前海冰研究的重要手段,数值模拟对北极海冰的快速变化仍然模拟得不够准确,说明对海冰的关键物理过程仍缺乏深入理解。海冰拖曳系数是海冰动力学模型中的重要参数,对于研究冰.水动力作用过程至关重要。为了完善冰.水拖曳系数的参数化方案,同时考虑到现场观测中对冰.水界面的动力过程进行观测的困难程度,本文针对冰.水界面上的冰脊形拖曳力和拖曳系数开展了实验室物理模拟实验研究。首先,目前海冰拖曳系数参数化的研究多针对于均匀流体,没有考虑海洋分层的情况,而北极夏季海冰边缘区内的海水盐度跃层由于海冰融化的影响一般出现在较浅的位置,有可能对浮冰或者冰脊的运动造成影响。因此,为改进冰.水界面的海冰拖曳系数的参数化方案,在实验室原有水槽的基础上进行了设备改造,建立了分层流体模拟系统,包括盐水注入系统,拖曳力测量系统,运动平台系统,配重系统等。为分层流体实验的开展奠定了基础。其次,作为对比实验,开展了单层流体中的冰脊拖曳力测量,考虑了6种不同形状的冰脊模型在5种入水深度与12种水流流速下所受拖曳力的变化。分析说明单层流体中冰脊拖曳力随着冰脊底角、水流流速和冰脊入水深度的增大而增大,冰脊所受拖曳力与速度的平方存在良好的线性关系,这一结论验证了拖曳力理论公式。对拖曳系数的分析结果说明,单层流体中冰脊拖曳系数随着水流流速的增大基本保持不变,随着冰脊入水深度的增大而缓慢增大且增幅较小,随着冰脊底角的变大而显著变大。冰脊底角是影响单层流体中冰脊拖曳系数的主要因素。最后,与单层流体的实验组次一致进行了双层流体中的冰脊形拖曳力实验。结果显示,双层流体中的冰脊拖曳力与单层流体中的变化规律存在明显区别,当弗洛德数处于1-2区间时,双层流体中的冰脊拖曳力呈现先增加后减小的趋势；当弗洛德数大于2之后,双层流体中的冰脊拖曳力与单层流体中的对应值基本一致,这主要是由于界面内波的影响造成的。而拖曳系数变化过程也较单层流体的情况存在差别,除了冰脊倾角的影响外,弗洛德数对双层流体中拖曳系数的影响也很明显。在弗洛德数较小(0.7)时,拖曳系数随着弗洛德数增加迅速衰减,与冰脊角度无关；而在弗洛德数较大(0.7)时,拖曳系数随着冰脊角度的增大而增大,与弗洛德数无关。因此采用分段拟合的方式得到双层流体中冰脊拖曳系数的参数化关系。
[Abstract]:Global warming is magnified in the Arctic, known as the Arctic magnification. Arctic sea ice has undergone unprecedented rapid changes over the past few decades, leading to a continuous decline in the extent and thickness of sea ice, with the possibility of a summer ice-free Arctic Ocean on the middle page of this century. The rapid change of Arctic sea ice has caused more and more significant effects on the weather and climate in the northern hemisphere and even in China, and has made it possible to open the Arctic waterway, which has become the focus of attention of the governments all over the world. As an important means of sea ice research, numerical simulation is still not accurate enough to simulate the rapid change of Arctic sea ice, which shows that the key physical process of sea ice is still lack of in-depth understanding. The drag coefficient of sea ice is an important parameter in the dynamic model of sea ice. The hydrodynamic process is essential. To perfect the ice. Water drag coefficient parameterization scheme, taking into account in-situ observations of ice. This paper deals with the difficulty of observing the dynamic process of water interface. The drag force and drag coefficient of ice ridge on water interface are studied by physical simulation in laboratory. First of all, the current research on the parameterization of sea ice drag coefficient does not take account of ocean stratification for homogeneous fluids. However, the saliniferous leaps in the Arctic summer sea ice edge region generally appear in a shallow position due to the effect of sea ice melting. It may have an impact on the movement of ice floes or ice ridges. Therefore, in order to improve ice. The parameterization scheme of the sea ice drag coefficient of the water interface has been reformed on the basis of the original flume in the laboratory, and the layered fluid simulation system has been established, including the saline injection system, the towing force measurement system and the motion platform system. Weighing system, etc. It lays a foundation for the development of stratified fluid experiments. Secondly, as a comparative experiment, the drag forces of ice ridges in single-layer fluids are measured, and the variation of drag forces of six ice ridges with different shapes under 5 inlet depths and 12 flow velocities is taken into account. The analysis shows that the drag force of ice ridge in single layer fluid increases with the increase of the bottom angle of the ice ridge, the velocity of flow and the depth of water entering into the ice ridge. There is a good linear relationship between the drag force and the square of the velocity on the ice ridge. This conclusion verifies the theoretical formula of the drag force. The analysis results of the drag coefficient show that the drag coefficient of ice ridge in single layer fluid remains unchanged with the increase of flow velocity, increases slowly with the increase of water depth of the ice ridge, and increases significantly with the increase of the bottom angle of the ice ridge. The bottom angle of ice ridge is the main factor that affects the drag coefficient of ice ridge in single layer fluid. Finally, the ice ridge drag force experiment in the double layer fluid is carried out in accordance with the experimental group of the single layer fluid. The results show that the drag force of ice ridge in the double layer fluid is obviously different from that in the single layer fluid. When the Froude number is in the range of 1 ~ 2, the drag force of the ice ridge in the double layer fluid increases first and then decreases. When the Froude number is greater than 2, the drag force of the ice ridge in the double layer fluid is basically consistent with the corresponding value in the single layer fluid, which is mainly due to the influence of the internal wave at the interface. In addition to the dip angle of the ice ridge, the influence of Froude number on the drag coefficient in the double layer fluid is also obvious. When the Froude number is small (0.7), the drag coefficient decreases rapidly with the increase of the Froude number, independent of the angle of the ice ridge. When the Froude number is larger (0.7), the drag coefficient increases with the increase of the angle of the ice ridge, independent of the Froude number. Therefore, the parameterized relation of the drag coefficient of ice ridges in two-layer fluid is obtained by means of piecewise fitting.
【学位授予单位】：大连理工大学
【学位级别】：硕士
【学位授予年份】：2016
【分类号】：P731.15

【参考文献】