基于小波和考虑底摩擦不稳定理论对沿岸流不稳定时空变化及模式研究

发布时间：2018-05-16 06:52

本文选题：小波变换 + 沿岸流　；参考：《太原理工大学》2015年硕士论文

【摘要】：近海岸区域及海岸带是受环境影响较为严重的地区，这是因为波浪的演化及破碎会导致沿岸流不稳定运动规律十分的复杂，会影响到沿岸上污染物复杂的扩散规律。自从人们发现沿岸流不稳定运动以来，许多国内外学者对沿岸流不稳定运动及其现象进行了广泛的研究，发现沿岸流不稳定运动对近海岸区域污染物及沉积物输移的研究有着重要的意义，深入了解沿岸流不稳定运动的理论可以使我们更好的处理近海岸区域的复杂问题。为了更加直接、清晰、全面的认识沿岸流不稳定运动的特性，本文主要利用小波分析方法和考虑底摩擦的沿岸流不稳定模型来研究其时空变化特性和沿岸流不稳定模式变化。首先，采用小波方法对不规则波致沿岸流不稳定运动时空变化进行研究。利用小波方法得到流速时间历程的小波谱，通过对小波谱的分析研究沿岸流不稳定运动的时空变化，详细分析了平直斜坡上、两种坡度下沿岸及垂直岸方向的沿岸流不稳定运动时空变化特征及其和边缘波的相互联系和影响。其次，通过建立考虑底摩擦的不稳定模型，根据所给出的沿岸流单峰速度剖面（n3和n6）和地形数值计算出在平直斜坡上、坡度为1:100条件下，不同底摩擦系数对应的沿岸流不稳定运动的增长率、传播速度随波数的变化情况和扰动速度随岸线距离的分布。最后，在给定了沙坝地形坡度为1:40和1:100条件下，模拟出了双峰速度剖面，利用沿岸流线性不稳定模型计算得出这两种坡度情况下沿岸流不稳定增长率、传播速度随波数的变化情况和沿岸流扰动速度随岸线距离的分布。通过小波分析对沿岸流不稳定运动时空变化特性进行研究，发现沿岸流不稳定运动产生后会出现连续性现象，并且不会与低频波以及其他形式的低频波有能量上的交换；沿岸流不稳定运动产生的波动在沿岸方向相比垂直岸方向的波动能量显得更强烈；沿岸流不稳定运动随岸线距离的增加会提前产生能量；坡度的增大会使沿岸流不稳定运动在沿岸和垂直岸方向上的作用变得更强；边缘波可以和沿岸流不稳定运动同时在垂直岸线方向和沿岸方向存在；相同条件下沿岸流不稳定运动具有一定的可重现性。在平直斜坡上、两种速度剖面并考虑底摩擦的沿岸流不稳定增长率的研究结果表明，底摩擦会影响沿岸流不稳定运动，，底摩擦系数越大沿岸流不稳定增长率越小；在两种速度剖面下，不同底摩擦系数下的增长率极值对应的波数是固定不变的；对沿岸流不稳定模型数值计算出的扰动速度进行了分析，发现有无底摩擦情况下两种速度剖面所对应的沿岸流扰动速度都呈现出周期性波动。通过对文中六种双峰速度剖面、沙坝地形坡度1:40和1:100条件下沿岸流不稳定运动增长率变化情况的研究，表明有无底摩擦情况下的沿岸流不稳定运动几乎都会出现两种增长模式，两种模式都是由沿岸流的前剪切及后剪切所引起的；通过沿岸流不稳定模型计算出的扰动速度场发现，两种坡度下的扰动速度场都呈现出周期性波动；坡度影响沿岸流不稳定运动增长率和破波点发生的位置，坡度增大会使沿岸流不稳定运动增长率变大，而且沿岸流不稳定运动破波点发生的位置越靠近海岸。
[Abstract]:The coastal zone and coastal zone are more seriously affected by the environment. This is because the evolution and fragmentation of the waves will lead to the complexity of the irregular motion of the coastal flow, which will affect the complex diffusion of pollutants along the coast. Since the unstable movement of the coastal flow has been found, many domestic and foreign scholars have been unstable to the coastal flow. The constant motion and its phenomenon have been widely studied. It is found that the unsteady motion of the coastal flow is of great significance to the study of the transport of pollutants and sediments near the coastal region. The theory of the unsteady movement of the coastal currents can make us better deal with the complex problems of the coastal areas.
In order to make a more direct, clear and comprehensive understanding of the characteristics of the coastal flow instability, this paper mainly uses the wavelet analysis method and the unsteady model of the coastal flow considering the bottom friction to study the temporal and spatial variation characteristics and the variation of the coastal flow instability model.
Firstly, the wavelet method is used to study the spatio-temporal variation of the unsteady wave induced unsteady motion of the coastal currents. The wavelet method is used to obtain the small wave spectrum of the time history of the flow. By the analysis of the small wave spectrum, the temporal and spatial variation of the unsteady motion of the coastal current is studied, and the coastal and vertical bank directions on the flat slope and the two slopes are analyzed in detail. The temporal and spatial variation characteristics of flow instability and its relationship with edge waves.
Secondly, by setting up an unstable model considering the bottom friction, the growth rate of the unsteady motion of the coastal flow is calculated on the flat slope based on the single peak velocity profile (N3 and N6) and the terrain value given on the flat slope. The gradient of the slope is 1:100, and the propagation velocity varies with the wave number and the velocity of the disturbance along the shore. The distribution of the line distance.
At last, the Shuangfeng velocity profile is simulated under the condition of the slope of the sand dam at 1:40 and 1:100, and the unsteady growth rate of the coastal flow is calculated with the coastal streamline instability model. The variation of the propagation velocity with the wave number and the distribution of the coastal flow disturbance velocity along with the distance of the shore line.
The time and space characteristics of the unsteady motion of the coastal flow are studied by the wavelet analysis. It is found that the instability of the coastal flow will occur continuously after the unsteady movement of the coastal flow, and does not have the energy exchange with the low frequency waves and other forms of low frequency waves; the waves produced by the unsteady motion of the coastal flow are in the direction of the vertical bank in the direction of the coastal flow. The dynamic energy appears more intense; the unsteady motion of the coastal flow will generate energy in advance with the increase of the coastline distance; the increase of the slope will make the unsteady movement of the coastal flow stronger in the direction of the coastal and vertical banks, and the edge wave can exist in the vertical and coastal directions at the same time as the unsteady movement of the coastal flow; The unsteady motion of the coastal flow has a certain reproducibility. On the flat slope, the results of two velocity profiles and the unsteady growth rate of the coastal current considering the bottom friction show that the bottom friction will affect the unsteady movement of the coastal flow, the smaller the bottom friction coefficient is, the smaller the growth rate of the coastal flow instability is, and the difference is different under the two velocity profiles. The wave number corresponding to the extreme value of the growth rate under the bottom friction coefficient is fixed and constant, and the perturbation velocity calculated by the numerical calculation of the coastal flow instability model is analyzed. It is found that the coastal flow disturbance velocity corresponding to the two velocity profiles under the case of bottomless friction shows a periodic fluctuation. Six kinds of Shuangfeng velocity profiles in the paper, sand, sand, are found. The study on the variation of the growth rate of the unsteady movement of the coastal flow under the condition of the dam terrain at 1:40 and 1:100 shows that there are almost two growth modes in the unsteady movement of the coastal flow under the condition of bottom friction. The two models are all caused by the front and rear shear of the coastal flow, and the disturbance calculated by the coastal flow instability model. The dynamic velocity field shows that the disturbance velocity field under the two slopes has periodic fluctuation, and the slope affects the growth rate of unsteady movement and the location of the breaking point. The increase of the slope will increase the growth rate of the unstable movement of the coastal flow, and the location of the breaking point of the unstable coastal flow is closer to the coast.

【学位授予单位】：太原理工大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：P731.2

【参考文献】