缓坡沿岸流不稳定性特征研究

发布时间：2018-03-28 14:28

  本文选题：沿岸流　切入点：不稳定　出处：《大连理工大学》2015年博士论文

【摘要】：目前对沿岸流的实验研究主要针对现场实验和较陡坡实验情况,为了研究缓坡情况下的沿岸流是否存在不同于陡坡情况的特征,本文通过物理模型实验和数值模拟研究了缓坡情况下的平均沿岸流和沿岸流不稳定运动,得到了缓坡地形条件下不同于陡坡情况下的波高、波浪增减水和平均沿岸流速度分布特征以及其对应的沿岸流不稳定运动特征。本文针对1：100和1：40平坡海岸进行了不同波高和不同周期规则波和不规则波所产生的沿岸流的物理模型实验,讨论了所采用的被动式水流循环系统所引起的沿岸流的沿岸均匀性,给出了缓坡情况下波高、波浪增减水和平均沿岸流速度分布特征：缓坡情况下,波浪破碎后,波高呈下凹趋势,坡度越缓,波高下凹的趋势越明显；波浪增减水向岸增长趋势逐渐变缓,坡度越缓,波浪增减水向岸增长趋势越缓；1：100坡度平均沿岸流海岸一侧分布呈下凹趋势而相应的1：40坡度呈上凸的趋势。为了讨论这一速度分布特征所产生的机理,本研究采用平均沿岸流数值模型进行了平均沿岸流数值模拟,结果表明影响这些速度剖面特征的主要因素为破波带内波高分布和水底摩擦力表达式的选取,对后者更为敏感。1：100坡度海岸沿岸流速度剖面可由水流型水底摩擦力来计算出,而1：40坡度海岸沿岸流速度剖面可由波浪型水底摩擦力来计算出。为了显示沿岸流不稳定所引起的水流速度波动特征,模型实验中采用了在流场中注入连续输入的墨水来显示速度的波动,并通过CCD记录了显示的结果。通过图像处理,给出了对应不同波况的墨水输移特征以及它们所显示的沿岸流不稳定所引起的水流中涡运动的特征。沿岸流不稳定的特征周期通过最大熵谱估计分析确定,特征波长可由墨水的波动波长来显示。采用沿岸流线性不稳定分析给出了1：100和1：40坡度下不同的平均速度分布所导致的不同的不稳定增长模式。1：100坡度多数波况沿岸流不稳定存在前剪切和后剪切两个不稳定模式,而1：40坡度仅存在后剪切不稳定模式。不稳定分析所给出的不稳定波动周期和波长与实验结果进行了对比。通过数值求解水平二维近岸环方程,研究了实验中1：100和1：40.海岸坡度各波况所对应的沿岸流非线性不稳定演化的特征,给出了缓坡情况下坡度、波高和不规则波对沿岸流不稳定的影响以及不稳定作用下的墨水扩散,特别讨论了这些因素对由沿岸流不稳定所引起的涡运动的影响。通过逐次近似的方法给出了波浪场(Stokes质量输移流和一阶波浪水质点速度二者叠加)中离散系数的解析表达式,并首次提出了二阶离散系数。讨论了Stokes质量输移流和一阶波浪水质点速度对波浪场中离散系数的贡献,讨论了各部分离散系数的物理意义及量值大小。
[Abstract]:At present, the experimental research on coastal current is mainly aimed at the field experiment and the steep slope experiment. In order to study whether the coastal current under the gentle slope condition has the different characteristics from the steep slope situation, In this paper, through physical model experiment and numerical simulation, the mean coastal current and the unstable motion of coastal current in gentle slope are studied, and the wave height under gentle slope is obtained, which is different from that in steep slope. The characteristics of velocity distribution of wave increasing and decreasing water and average coastal current and their corresponding characteristics of unstable motion of coastal current are studied. In this paper, different wave heights, different periodic regular waves and irregular waves are carried out along the coast of flat slope at 1: 100 and 1:40. The physical Model experiment of Coastal current, The coastal uniformity of the coastal current caused by the passive flow circulatory system is discussed. The characteristics of wave height, wave increase and decrease and average coastal current velocity distribution in the case of gentle slope are given: in the case of gentle slope, when the wave is broken, the characteristics of the distribution of the wave height, the increase and decrease of the wave and the velocity of the average coastal current are given. The trend of wave height is concave, the lower the slope, the more obvious the concave trend of wave height, the slower the increasing trend of wave increasing and decreasing water, the slower the slope. The more slowly the trend of increasing and decreasing the water from wave to shore, the slower the trend of 1: 100 slope average along the coast is concave and the corresponding 1:40 slope is upward convex. In order to discuss the mechanism of this velocity distribution, In this study, the numerical model of average coastal current is used to simulate the average coastal current. The results show that the main factors affecting the characteristics of these velocity profiles are the distribution of wave height in the breaking zone and the selection of the expression of the bottom friction. More sensitive to the latter. 1: 100 slope, the coastal current velocity profile can be calculated from the flow type of bottom friction. At 1:40 slope, the coastal current velocity profile can be calculated by the wave bottom friction. In order to show the characteristics of the velocity fluctuation caused by the instability of the coastal current, In the model experiment, continuous inputted ink was injected into the flow field to show the fluctuation of velocity, and the result was recorded by CCD. The characteristics of ink transport corresponding to different wave conditions and the characteristics of vortex motion in the flow caused by the instability of the coastal current are given. The characteristic periods of the instability of the coastal current are determined by the maximum entropy spectrum estimation. The characteristic wavelengths can be shown by the wave wavelengths of ink. By using the linear instability analysis of coastal currents, different unstable growth modes. 1: 100 slopes with different average velocity distributions at 1: 100 and 1:40 slopes are given. There are two unstable modes of flow instability, pre-shear and post-shear. But at 1:40 slope, there is only a post-shear instability model. The unstable wave period and wavelength derived from the instability analysis are compared with the experimental results. The horizontal two-dimensional near-shore ring equation is solved numerically. In this paper, the characteristics of the nonlinear instability evolution of the coastal current corresponding to the wave conditions of the coastal slope are studied. The effects of slope, wave height and irregular waves on the instability of the coastal current and the ink diffusion under the unstable action are given. In particular, the influence of these factors on the vortex motion caused by the instability of the coastal current is discussed. The analytical expressions of the discrete coefficients in the wave field, Stokes mass transport and the first order wave water quality point velocity superposition are given by the successive approximation method. The contribution of the Stokes mass transport current and the point velocity of the first order wave water quality to the discrete coefficients in the wave field is discussed, and the physical meaning and the magnitude of the discrete coefficients of each part are discussed.
【学位授予单位】：大连理工大学
【学位级别】：博士
【学位授予年份】：2015
【分类号】：P731.2
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本文编号：1676720