基于變系數(shù)KdV-type理論模型的南海北部內(nèi)孤立波傳播演變過程研究
發(fā)布時間：2018-07-26 10:45
【摘要】：海洋內(nèi)孤立波的研究在軍事和海洋工程中具有重要的實際應用價值。近二十年來，由于海洋石油開采設施頻繁遭受內(nèi)孤立波破壞等事件的報導，研究人員開始將海洋內(nèi)孤立波的研究重點集中到了南中國海。大量的遙感觀測和現(xiàn)場調(diào)查表明南海北部是世界上海洋內(nèi)孤立波活動最為活躍的海區(qū)之一。近十年來，關于南海北部內(nèi)孤立波的生成、傳播和演化過程的研究一直是熱點問題。 密度層化流體中，基于弱非線性假設的Korteweg-de Vries（KdV）理論模型是描述海洋內(nèi)孤立波傳播和演化的一個簡化模型。該模型表征了海洋內(nèi)孤立波的非線性效應和頻散效應之間的動力平衡。本文首次系統(tǒng)地將以往僅在理論意義上研究的變系數(shù)KdV類型（KdV-type）理論模型應用于南海北部實際海洋底地形、連續(xù)層結和存在背景流的情形，并且討論了高階非線性和地轉等多種機制對內(nèi)孤立波傳播和演變過程的不同作用。同時，利用現(xiàn)場觀測的溫度振蕩和流速資料，驗證了理論模型在海洋內(nèi)孤立波傳播研究中的可行性。內(nèi)孤立波環(huán)境參數(shù)的變化一定程度上反映了該海域可能存在的內(nèi)孤立波的基本特征，以往關于這方面的研究相當稀少。本文利用氣候態(tài)逐月平均的溫鹽資料和環(huán)流模式輸出的流速數(shù)據(jù)作為背景場，研究了南海北部內(nèi)孤立波長內(nèi)波相速度c、非線性系數(shù)、高階非線性系數(shù)1和頻散系數(shù)等內(nèi)波環(huán)境參數(shù)的空間分布和季節(jié)變化，探討了背景流對內(nèi)波模態(tài)結構以及內(nèi)孤立波環(huán)境參數(shù)的影響。 研究表明，南海北部內(nèi)波環(huán)境參數(shù)的空間分布和季節(jié)變化特征主要取決于水深大小以及層結和背景流場等因素的強弱變化：（1）c和的大小主要取決于水深，且隨著水深的變淺，，兩者均逐漸減小。深水區(qū)層結的季節(jié)變化較小，c和的變化也很小。而在淺水區(qū)，層結的季節(jié)變化較為明顯，c和變化較顯著，且夏季的量值均明顯大于冬季的量值。（2）深水區(qū)，基本上為負值，到淺水區(qū)轉換為正值，負值向正值轉換分界線具有明顯的季節(jié)變化，其生成和消衰與層結的強弱變化有密切的關系。秋冬季層結較弱，該分界線明顯，且與200m等深線基本一致。春季，隨著層結的增強，該分界線開始逐漸消失，到夏季則基本不復存在。深水區(qū)，1多為正值，存在明顯的正值向負值的轉換分界線，該分界線常年存在。該分界線較的零值分界線所在位置更深，且伴隨季節(jié)變化產(chǎn)生移動，夏季位于較淺海域，冬季位于較深海域。（3）背景流對高模態(tài)內(nèi)波的模態(tài)結構影響較大，在流速較大的陸架海域這種影響尤為顯著。漲落潮流主要影響1的大小。在流速較大的海域，1在漲潮或落潮時，量值可相差一個量級。 對KdV-type理論模型進行的數(shù)值模擬研究發(fā)現(xiàn)：（1）非線性和頻散的變化是控制內(nèi)孤立波傳播和演變的主要機制。非線性增強時，波動振幅增大，頻散作用則使波動振幅減小。根據(jù)非線性和頻散作用之間的強弱，可將內(nèi)孤立波的傳播區(qū)域分為兩者相互平衡的平衡區(qū)和非線性作用占主導的變陡區(qū)。這種分區(qū)方法可用來解釋合成孔徑雷達（SAR）觀測到的南海東北部內(nèi)孤立波的分布特征。（2）高階非線性的作用主要影響大振幅內(nèi)孤立波的變形和非線性裂變。理論模型中考慮高階非線性項時，非線性效應的增強打破了KdV模型中非線性和頻散的平衡，從而造成內(nèi)孤立波振幅的增大，波形變窄。相應地，內(nèi)孤立波波致流速顯著增大。相比之下，高階非線性對于振幅較小的內(nèi)潮的傳播和裂變過程的影響是非常微弱的。（3）KdV-type理論模型能夠模擬地轉影響下內(nèi)孤立波長距離傳播時，波形的衰減和重現(xiàn)過程，這一發(fā)現(xiàn)與Helfrich（2007）在完全非線性理論框架下得到的結論一致。同時，高階非線性的作用將使內(nèi)孤立波的衰減過程將變慢。（4）地轉對單個內(nèi)孤立波沿著模擬斷面?zhèn)鞑r的影響不大，但明顯抑制了內(nèi)潮的非線性裂變。這種區(qū)別主要取決于Ostrovsky數(shù)的大小。對于單個內(nèi)孤立波，Ostrovsky數(shù)遠超過O(1)，非線性作用占主導地位。而對于內(nèi)潮，模擬區(qū)域的Ostrovsky數(shù)較小，因而地轉的影響較為顯著。 變系數(shù)KdV-type理論模型的模擬波形和計算流速與現(xiàn)場觀測的比較結果表明，理論模型能夠解釋弱非線性的內(nèi)孤立波以及某些非線性較強的內(nèi)孤立波，但在解釋振幅更大，非線性更強的內(nèi)孤立波時具有一定的局限性。
[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.
【學位授予單位】：中國海洋大學
【學位級別】：博士
【學位授予年份】：2014
【分類號】：P731.2
本文編號：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.
【學位授予單位】：中國海洋大學
【學位級別】：博士
【學位授予年份】：2014
【分類號】：P731.2
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