基于变系数KdV-type理论模型的南海北部内孤立波传播演变过程研究
发布时间：2018-07-26 10:45
【摘要】：海洋内孤立波的研究在军事和海洋工程中具有重要的实际应用价值。近二十年来，由于海洋石油开采设施频繁遭受内孤立波破坏等事件的报导，研究人员开始将海洋内孤立波的研究重点集中到了南中国海。大量的遥感观测和现场调查表明南海北部是世界上海洋内孤立波活动最为活跃的海区之一。近十年来，关于南海北部内孤立波的生成、传播和演化过程的研究一直是热点问题。 密度层化流体中，基于弱非线性假设的Korteweg-de Vries（KdV）理论模型是描述海洋内孤立波传播和演化的一个简化模型。该模型表征了海洋内孤立波的非线性效应和频散效应之间的动力平衡。本文首次系统地将以往仅在理论意义上研究的变系数KdV类型（KdV-type）理论模型应用于南海北部实际海洋底地形、连续层结和存在背景流的情形，并且讨论了高阶非线性和地转等多种机制对内孤立波传播和演变过程的不同作用。同时，利用现场观测的温度振荡和流速资料，验证了理论模型在海洋内孤立波传播研究中的可行性。内孤立波环境参数的变化一定程度上反映了该海域可能存在的内孤立波的基本特征，以往关于这方面的研究相当稀少。本文利用气候态逐月平均的温盐资料和环流模式输出的流速数据作为背景场，研究了南海北部内孤立波长内波相速度c、非线性系数、高阶非线性系数1和频散系数等内波环境参数的空间分布和季节变化，探讨了背景流对内波模态结构以及内孤立波环境参数的影响。 研究表明，南海北部内波环境参数的空间分布和季节变化特征主要取决于水深大小以及层结和背景流场等因素的强弱变化：（1）c和的大小主要取决于水深，且随着水深的变浅，，两者均逐渐减小。深水区层结的季节变化较小，c和的变化也很小。而在浅水区，层结的季节变化较为明显，c和变化较显著，且夏季的量值均明显大于冬季的量值。（2）深水区，基本上为负值，到浅水区转换为正值，负值向正值转换分界线具有明显的季节变化，其生成和消衰与层结的强弱变化有密切的关系。秋冬季层结较弱，该分界线明显，且与200m等深线基本一致。春季，随着层结的增强，该分界线开始逐渐消失，到夏季则基本不复存在。深水区，1多为正值，存在明显的正值向负值的转换分界线，该分界线常年存在。该分界线较的零值分界线所在位置更深，且伴随季节变化产生移动，夏季位于较浅海域，冬季位于较深海域。（3）背景流对高模态内波的模态结构影响较大，在流速较大的陆架海域这种影响尤为显著。涨落潮流主要影响1的大小。在流速较大的海域，1在涨潮或落潮时，量值可相差一个量级。 对KdV-type理论模型进行的数值模拟研究发现：（1）非线性和频散的变化是控制内孤立波传播和演变的主要机制。非线性增强时，波动振幅增大，频散作用则使波动振幅减小。根据非线性和频散作用之间的强弱，可将内孤立波的传播区域分为两者相互平衡的平衡区和非线性作用占主导的变陡区。这种分区方法可用来解释合成孔径雷达（SAR）观测到的南海东北部内孤立波的分布特征。（2）高阶非线性的作用主要影响大振幅内孤立波的变形和非线性裂变。理论模型中考虑高阶非线性项时，非线性效应的增强打破了KdV模型中非线性和频散的平衡，从而造成内孤立波振幅的增大，波形变窄。相应地，内孤立波波致流速显著增大。相比之下，高阶非线性对于振幅较小的内潮的传播和裂变过程的影响是非常微弱的。（3）KdV-type理论模型能够模拟地转影响下内孤立波长距离传播时，波形的衰减和重现过程，这一发现与Helfrich（2007）在完全非线性理论框架下得到的结论一致。同时，高阶非线性的作用将使内孤立波的衰减过程将变慢。（4）地转对单个内孤立波沿着模拟断面传播时的影响不大，但明显抑制了内潮的非线性裂变。这种区别主要取决于Ostrovsky数的大小。对于单个内孤立波，Ostrovsky数远超过O(1)，非线性作用占主导地位。而对于内潮，模拟区域的Ostrovsky数较小，因而地转的影响较为显著。 变系数KdV-type理论模型的模拟波形和计算流速与现场观测的比较结果表明，理论模型能够解释弱非线性的内孤立波以及某些非线性较强的内孤立波，但在解释振幅更大，非线性更强的内孤立波时具有一定的局限性。
[Abstract]:The study of the solitary waves in the ocean has an important practical value in military and marine engineering. In the past twenty years, the researchers began to focus the research on the solitary waves in the ocean due to the frequent damage of the offshore oil mining facilities to the internal solitary waves. A large number of remote sensing observations and field investigations have been focused on the ocean. The northern South China Sea is one of the most active oceanic regions in the Shanghai ocean in the world. In the past ten years, the study of the formation, propagation and evolution of the solitary waves in the north of the South China Sea has been a hot issue.
In the density stratified fluid, the Korteweg-de Vries (KdV) model based on the weakly nonlinear hypothesis is a simplified model describing the propagation and evolution of the solitary waves in the ocean. This model represents the dynamic equilibrium between the nonlinear effects of the solitary waves in the ocean and the dispersion effect of the ocean. This paper first systematically studies the previous study in a theoretical sense. The variable coefficient KdV type (KdV-type) theory model is applied to the actual ocean bottom topography, continuous layer and background flow in the north of the South China Sea, and the different functions of the high order nonlinear and geostrophic mechanisms on the propagation and evolution of the internal solitary waves are discussed. The feasibility of the model in the study of the solitary wave propagation in the ocean. The changes of the internal solitary wave environmental parameters reflect the basic characteristics of the possible internal solitary waves in the sea area to a certain extent. The previous studies on this area are rather rare. For the background field, the spatial distribution and seasonal variation of internal wave environment parameters such as the internal wave velocity C, the nonlinear coefficient, the high order nonlinear coefficient 1 and the frequency dispersion coefficient in the north of the South China Sea are studied, and the influence of the background flow on the internal wave modal structure and the internal solitary wave environment parameters is discussed.
The study shows that the spatial distribution and seasonal variation of the internal wave environmental parameters in the north of the South China Sea mainly depend on the strong and weak changes in the depth of water, the layer and the background flow field. (1) the size of C and its size mainly depend on the depth of water, and with the shallow water depth, both of them gradually decrease. The changes in the stratification of the deep water region are smaller, and the changes of the C and the water depth are also changed. In the shallow water area, the seasonal variation of the stratification is more obvious, the C and the change are more obvious, and the amount of the summer is obviously greater than that in the winter. (2) the deep water area is basically negative, and it is converted into positive value in the shallow water area, and the boundary of negative value to positive value has obvious seasonal variation, and its formation and attenuation and the strong and weak changes in the stratification are closely related. The stratification is weak in autumn and winter, and the boundary line is obvious and is basically consistent with the 200m contour line. In spring, with the enhancement of the stratification, the dividing line begins to disappear gradually, and it basically does not exist in the summer. The deep water area is more than 1 positive value, and there is a clear positive value to negative conversion boundary line. The line is in a deeper position and moves with seasonal variations, in the shallow waters in summer and in the deep waters in winter. (3) the background flow has great influence on the modal structure of high modal internal waves, especially in the sea shelf waters with higher velocity. The fluctuation trend mainly affects the size of 1. In the sea area with larger flow velocity, 1 is in the tide or ebb tide. At the time, the value can vary by one order of magnitude.
The numerical simulation of the KdV-type theoretical model shows that: (1) the variation of nonlinear and frequency dispersion is the main mechanism to control the propagation and evolution of the internal solitary waves. When the nonlinear enhancement, the amplitude of the wave increases and the frequency dispersion reduces the amplitude of the wave. This method can be used to explain the distribution characteristics of the solitary waves in the northeast of the South China Sea (SAR). (2) the effect of high order nonlinearity mainly affects the deformation and nonlinear fission of the large amplitude internal solitary waves. The theoretical model considers the high order In the nonlinear term, the enhancement of nonlinear effect breaks the equilibrium of nonlinear and dispersion in the KdV model, thus causing the amplitude of the internal solitary wave to increase and the waveform narrowed. Accordingly, the velocity of the internal solitary wave increases significantly. In contrast, the high order nonlinearity has a very weak effect on the propagation and fission process of the small amplitude of the internal tide. (3) The KdV-type theoretical model can simulate the decay and recurrence of the waveform when the internal isolated wavelength is transmitted, which is consistent with the conclusion obtained by Helfrich (2007) in the complete nonlinear theoretical framework. At the same time, the effect of high order nonlinearity will slow the decay process of the internal solitary waves. (4) a single internal solitary wave is transferred. There is little influence on the propagation of the simulated section, but it obviously inhibits the nonlinear fission of the internal tide. This difference depends mainly on the size of the Ostrovsky number. For a single internal solitary wave, the number of Ostrovsky is far more than O (1), and the nonlinear action is dominant. For the internal tide, the number of Ostrovsky in the simulated region is smaller, so the influence of the geostrophy is more obvious. It is.
The simulation waveforms of the variable coefficient KdV-type theory model and the comparison between the calculated velocity and the field observation show that the theoretical model can explain the weakly nonlinear internal solitary waves and some nonlinear strong internal solitary waves, but it has some limitations in the explanation of the larger amplitude and the stronger nonlinear internal solitary waves.
【学位授予单位】：中国海洋大学
【学位级别】：博士
【学位授予年份】：2014
【分类号】：P731.2
本文编号：2145754
[Abstract]:The study of the solitary waves in the ocean has an important practical value in military and marine engineering. In the past twenty years, the researchers began to focus the research on the solitary waves in the ocean due to the frequent damage of the offshore oil mining facilities to the internal solitary waves. A large number of remote sensing observations and field investigations have been focused on the ocean. The northern South China Sea is one of the most active oceanic regions in the Shanghai ocean in the world. In the past ten years, the study of the formation, propagation and evolution of the solitary waves in the north of the South China Sea has been a hot issue.
In the density stratified fluid, the Korteweg-de Vries (KdV) model based on the weakly nonlinear hypothesis is a simplified model describing the propagation and evolution of the solitary waves in the ocean. This model represents the dynamic equilibrium between the nonlinear effects of the solitary waves in the ocean and the dispersion effect of the ocean. This paper first systematically studies the previous study in a theoretical sense. The variable coefficient KdV type (KdV-type) theory model is applied to the actual ocean bottom topography, continuous layer and background flow in the north of the South China Sea, and the different functions of the high order nonlinear and geostrophic mechanisms on the propagation and evolution of the internal solitary waves are discussed. The feasibility of the model in the study of the solitary wave propagation in the ocean. The changes of the internal solitary wave environmental parameters reflect the basic characteristics of the possible internal solitary waves in the sea area to a certain extent. The previous studies on this area are rather rare. For the background field, the spatial distribution and seasonal variation of internal wave environment parameters such as the internal wave velocity C, the nonlinear coefficient, the high order nonlinear coefficient 1 and the frequency dispersion coefficient in the north of the South China Sea are studied, and the influence of the background flow on the internal wave modal structure and the internal solitary wave environment parameters is discussed.
The study shows that the spatial distribution and seasonal variation of the internal wave environmental parameters in the north of the South China Sea mainly depend on the strong and weak changes in the depth of water, the layer and the background flow field. (1) the size of C and its size mainly depend on the depth of water, and with the shallow water depth, both of them gradually decrease. The changes in the stratification of the deep water region are smaller, and the changes of the C and the water depth are also changed. In the shallow water area, the seasonal variation of the stratification is more obvious, the C and the change are more obvious, and the amount of the summer is obviously greater than that in the winter. (2) the deep water area is basically negative, and it is converted into positive value in the shallow water area, and the boundary of negative value to positive value has obvious seasonal variation, and its formation and attenuation and the strong and weak changes in the stratification are closely related. The stratification is weak in autumn and winter, and the boundary line is obvious and is basically consistent with the 200m contour line. In spring, with the enhancement of the stratification, the dividing line begins to disappear gradually, and it basically does not exist in the summer. The deep water area is more than 1 positive value, and there is a clear positive value to negative conversion boundary line. The line is in a deeper position and moves with seasonal variations, in the shallow waters in summer and in the deep waters in winter. (3) the background flow has great influence on the modal structure of high modal internal waves, especially in the sea shelf waters with higher velocity. The fluctuation trend mainly affects the size of 1. In the sea area with larger flow velocity, 1 is in the tide or ebb tide. At the time, the value can vary by one order of magnitude.
The numerical simulation of the KdV-type theoretical model shows that: (1) the variation of nonlinear and frequency dispersion is the main mechanism to control the propagation and evolution of the internal solitary waves. When the nonlinear enhancement, the amplitude of the wave increases and the frequency dispersion reduces the amplitude of the wave. This method can be used to explain the distribution characteristics of the solitary waves in the northeast of the South China Sea (SAR). (2) the effect of high order nonlinearity mainly affects the deformation and nonlinear fission of the large amplitude internal solitary waves. The theoretical model considers the high order In the nonlinear term, the enhancement of nonlinear effect breaks the equilibrium of nonlinear and dispersion in the KdV model, thus causing the amplitude of the internal solitary wave to increase and the waveform narrowed. Accordingly, the velocity of the internal solitary wave increases significantly. In contrast, the high order nonlinearity has a very weak effect on the propagation and fission process of the small amplitude of the internal tide. (3) The KdV-type theoretical model can simulate the decay and recurrence of the waveform when the internal isolated wavelength is transmitted, which is consistent with the conclusion obtained by Helfrich (2007) in the complete nonlinear theoretical framework. At the same time, the effect of high order nonlinearity will slow the decay process of the internal solitary waves. (4) a single internal solitary wave is transferred. There is little influence on the propagation of the simulated section, but it obviously inhibits the nonlinear fission of the internal tide. This difference depends mainly on the size of the Ostrovsky number. For a single internal solitary wave, the number of Ostrovsky is far more than O (1), and the nonlinear action is dominant. For the internal tide, the number of Ostrovsky in the simulated region is smaller, so the influence of the geostrophy is more obvious. It is.
The simulation waveforms of the variable coefficient KdV-type theory model and the comparison between the calculated velocity and the field observation show that the theoretical model can explain the weakly nonlinear internal solitary waves and some nonlinear strong internal solitary waves, but it has some limitations in the explanation of the larger amplitude and the stronger nonlinear internal solitary waves.
【学位授予单位】：中国海洋大学
【学位级别】：博士
【学位授予年份】：2014
【分类号】：P731.2
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