沿岸流不稳定运动传播特性及其能量变化的研究

发布时间：2018-07-28 14:40

【摘要】：近年来,由于沿海地区的经济发展,沿岸建设和沿岸环境保护问题逐渐受到人们的重视,沿岸流问题也随之成为热点研究对象。本文以已有的平直斜坡上的沿岸流实验为基础,研究了沿岸流不稳定运动的传播特性和垂直岸线方向的能量变化特性,为今后更深入的研究沿岸流不稳定运动以及近岸低频运动建立一定的基础,因为,这对于更加深入探究近岸复杂水动力学特性具有比较重要的意义。本文研究结果对于近岸污染物、沉积物和泥沙的输移也有一定的参考价值。本文围绕上述内容主要作了以下几方面工作:1.首先基于相关性分析原理,分析沿岸流不稳定运动的传播特性。对所有实验波况(地形分为1:100坡和1:40坡;入射波分为规则波和不规则波)采集到的流速时间历程进行相关性分析,具体而言,对两不同列的流速仪的流速时间历程进行两两相关性分析,得到最大相关系数和对应的延迟时间,再通过确定相关系数相对最大,延迟时间相对较小的两流速仪,由三角形法则得出沿岸流不稳定运动的偏向角,即沿岸流不稳定运动的传播方向,并分析不同地形、波况下产生偏移的原因。结果表明在入射波为不规则波情况下,沿岸流不稳定运动向离岸方向的偏向角在15°到30°左右,且随入射波波高、周期的增大而增大,同时坡度也对结果有一定影响,陡坡时的偏向角明显大于缓坡;沿岸流不稳定运动在入射波为规则波情况下,沿岸流不稳定运动向离岸方向的偏向角在15°左右,入射波的波高和周期对偏向角大小有一定影响,但对于坡度的影响,缓坡时的偏向角明显大于陡坡。之所以沿岸流不稳定运动的方向有一定偏移而非平行于沿岸,在实际情况下,由于垂向环流系统的影响,造成向海方向偏移,并且床底部受海底回流的作用更加强烈,而质量输移流则对其表面附近的作用稍强。2.利用最大熵谱分析沿岸流不稳定运动在垂直岸方向的能量的变化特性,还分析了入射波波况对其能量的变化的影响。对所有实验波况采集到的流速时间历程,进行最大熵谱分析。对某一个波况而言,得到垂直岸线方向每一个流速仪位置处流速时间历程的最大熵谱,进而确定出三个最佳频率,并利用三角函数回归法求出这三个频率对应的幅值。这三个频率中,其中一个为沿岸流不稳定运动,根据波能与振幅的关系,通过幅值的变化来分析沿岸流不稳定运动的能量变化。另外,本文还研究了另外两个最佳频率的特性,并对它们是否为边缘波的猜想进行了判定。结果表明,在距离岸线位置很近时,由于水深较浅,还没有沿岸流不稳定运动的存在,所以此时另外两个低频运动的能量会大于沿岸流不稳定运动;随着沿岸距离的增加,此时沿岸流不稳定运动存在,另外两个低频运动与沿岸流不稳定运动的能量比值呈增大趋势,在平均沿岸流达到最大时达到峰值,之后呈减小趋势。这种变化趋势与沿岸流不稳定运动的变化趋势相同。另外,入射波波高和周期的变化对这两个低频波运动的能量有一定影响,但没有明显的随之增大或减小的趋势;对其他低频成分进行边缘波判定,结果表明在三个最佳频率中只有规则波情况下的0.03(0.04)Hz的低频运动为边缘波波动。3.利用小波互谱研究了沿岸流不稳定运动传播的时间-频率特性。利用小波互谱分析了所有波况下沿岸流不稳定运动传播的时间-频率特性,文中将所有实验波况分为规则波和不规则波入射两类进行分析。基于所获得的小波互相关等值线图,分析入射波高、周期、地形对其传播时-频特性的影响。结果表明,三个主要频率的相关程度都按自身的波动周期沿时滞横轴周期性变化,且相关程度都较高,其中沿岸流不稳定运动的相关系数绝对值峰值达0.8的相关度,在整个时域都有周期变化的时滞和固定的相位差,波动稳定,说明在破波点附近存在着强度较大并且稳定波动的沿岸流不稳定运动。坡度对相关程度具有一定的影响,陡坡情况下的互相关等值线图具有更加明显的周期性和更加集中的峰值,而入射波高、周期对相关程度的影响不大,从整体上来说,由于规则波和不规则波的破波带宽度不同,导致了不规则波的相关程度的峰值绝对值要大于规则波。
[Abstract]:In recent years, due to the economic development of coastal areas, the coastal construction and coastal environmental protection have gradually been paid attention to, and the problem of coastal flow has become a hot topic. Based on the existing coastal flow experiments on the straight slope, the energy of the propagation and vertical shore direction of the unsteady motion of the coastal flow is studied. The change characteristics will establish a certain foundation for the further study of coastal flow instability movement and near shore low frequency movement, because it is of great significance for further exploring the complex hydrodynamic characteristics of the near shore. The results of this study also have some reference value for the transportation of near shore pollutants, sediment and sediment. The main work of this paper is as follows: 1. first, based on the principle of correlation analysis, the propagation characteristics of the unsteady motion of the coastal flow are analyzed, and the correlation analysis is made for all experimental wave conditions (the terrain is divided into 1:100 slope and 1:40 slope, the incident wave is divided into regular and irregular waves). The 22 correlation analysis is carried out on the velocity time history of the two different column flow meters. The maximum correlation coefficient and the corresponding delay time are obtained. By determining the relative maximum coefficient of the correlation coefficient and the less delay time, the deviation angle of the unstable movement of the coastal flow is obtained by the triangle rule, that is, the propagation of the unsteady motion of the coastal current. The results show that the deviation angle of the unstable movement of the coastal current to the offshore direction is about 15 to 30 degrees, and increases with the increase of the incident wave, and the slope also has a certain influence on the result, and the steep slope deviates to Jiao Mingxian. In the case of regular waves, the instability movement of the coastal flow is about 15 degrees to the deviation angle of the offshore direction. The wave height and the period of the incident wave have a certain influence on the deflection angle, but the slope angle is obviously larger than the steep slope. The direction has a certain deviation, not parallel to the coast, in fact, due to the influence of the vertical circulation system, it causes the direction of the sea direction, and the bottom of the bed is more strongly affected by the undersea backflow, while the mass transfer flow is slightly stronger by.2. using the maximum entropy spectrum to analyze the unsteady movement of the coastal flow in the vertical direction. The effect of the energy change is also analyzed. The maximum entropy spectrum analysis is carried out for the velocity time history collected by all experimental wave states. For a certain wave state, the maximum entropy spectrum of the velocity time calendar is obtained at the position of each velocity meter in the direction of the vertical shore line, and then three optimal frequencies are determined. Rate, and using the trigonometric function regression method to find the corresponding amplitude of the three frequencies. In these three frequencies, one of them is the unstable motion of the coastal flow. According to the relation between the wave energy and the amplitude, the variation of the amplitude is used to analyze the energy change of the unstable motion of the coastal flow. In addition, the characteristics of the other two other optimal frequencies are also studied and the results are also studied. The results show that the boundary wave's conjecture has been determined. The results show that there is no unstable movement of the coastal flow because of the shallow depth of the shore line, so the energy of the other two other low-frequency motions will be larger than the unstable movement of the coastal flow, and along with the increase of the coastal distance, the unsteady movement of the coastal flow exists, and the other is the existence of the unsteady movement of the coastal flow. The energy ratio of the two low frequency and coastal unsteady movement increases, and reaches the peak when the average coastal flow reaches the maximum and then decreases. This trend is the same as the trend of the unstable movement of the coastal flow. In addition, the variation of the incident wave height and the period of the wave is certain for the energy of the two low frequency waves. There is no obvious tendency to increase or decrease with it, and the edge wave of other low-frequency components is determined. The results show that the low frequency motion of 0.03 (0.04) Hz under the condition of the regular wave at the three best frequency is the edge wave motion.3. using the wavelet cross spectrum to study the time and frequency characteristics of the unsteady motion of the coastal current. The wave cross spectrum is used to analyze the time and frequency characteristics of the unsteady motion of the coastal flow under all wave conditions. All the experimental waves are divided into two categories: regular waves and irregular waves. Based on the obtained wavelet cross-correlation contour map, the influence of incident wave height, period and terrain on the time frequency characteristics of the wave is analyzed. The results show that three The correlation degree of the main frequency varies periodically along the time lag axis, and the correlation degree is high. The correlation coefficient of the correlation coefficient of the unsteady motion of the coastal flow is up to 0.8, and the time delay and the fixed phase difference are stable in the whole time domain, which indicates the existence of the fluctuation near the broken wave point. The slope has a certain influence on the correlation degree, and the cross correlation contour map in the case of steep slope has more obvious periodicity and more concentrated peak, but the influence of the period on the correlation degree is not great, from the rule wave and the irregularity from the whole. The width of wave breaking band is different, leading to the absolute absolute value of the degree of correlation of irregular waves is greater than regular waves.
【学位授予单位】：太原理工大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TV139.2

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