本文關(guān)鍵詞：Phase-Field和VOF耦合方法及其在極限波問題中的應(yīng)用　出處：《清華大學(xué)》2016年博士論文　論文類型：學(xué)位論文

  更多相關(guān)文章： 極限波 表面張力 數(shù)值方法 水波破碎

【摘要】：水波的破碎問題是近岸海域內(nèi)最為重要的水動(dòng)力學(xué)問題之一,也是理論分析、實(shí)驗(yàn)觀測(cè)和數(shù)值模擬的難點(diǎn)問題。本文旨在建立一個(gè)可用于分析極限波運(yùn)動(dòng)和變形的高精度的數(shù)值模型,研究水波的破碎機(jī)理,分析表面張力對(duì)極限波的影響。本文建立了耦合了Phase-Field和VOF方法的新界面追蹤方法,完善了配套的數(shù)值模型及網(wǎng)格系統(tǒng)。新的耦合方法綜合了傳統(tǒng)的間斷表面方法和新近引入流體力學(xué)計(jì)算領(lǐng)域的擴(kuò)散表面方法,結(jié)合了兩類方法的優(yōu)點(diǎn);提出了一種新的邊界條件處理技術(shù),保證了計(jì)算的精度。模型求解基于有限體積法和PISO算法,求解簡(jiǎn)便,穩(wěn)定性強(qiáng)。新的耦合模型經(jīng)驗(yàn)證,能夠高精度的計(jì)算復(fù)雜表面問題,并且相對(duì)于非耦合模型極大的提高了計(jì)算效率,節(jié)約計(jì)算時(shí)間。本文將耦合模型應(yīng)于極限波問題的研究。對(duì)于行進(jìn)波問題采用了周期性邊界條件及動(dòng)坐標(biāo)系,將計(jì)算域縮小到單個(gè)波長(zhǎng),并采用受迫壓強(qiáng)造波,控制極限波的初始能量。計(jì)算條件考慮了不同初始能量,研究了對(duì)應(yīng)狀態(tài)下的極限波形態(tài)。研究表明,在保證網(wǎng)格精度足夠并且排除了表面張力作用的情況下,極限波的波峰處均會(huì)形成水舌。較強(qiáng)的初始能量迫使水波更早的達(dá)到極限狀態(tài),水舌的尺度以及水波處于極限狀態(tài)的持續(xù)時(shí)間隨著極限波初始能量的減小而減小;水波的漂移速度同樣隨著極限波初始能量的減小而小減;波峰處水質(zhì)點(diǎn)的最大速度會(huì)超過線性波理論計(jì)算得出的波速,與經(jīng)典理論相符。對(duì)于駐波問題,采用了晃蕩造波法,研究了晃蕩問題中的極限駐波問題。通過改變晃蕩的方式和振幅、振蕩時(shí)間等參數(shù),模擬了兩類不同的極限駐波形態(tài),結(jié)果與實(shí)驗(yàn)觀測(cè)吻合良好。耦合模型還用于研究表面張力對(duì)極限波的影響。通過改變表面張力系數(shù)和極限波的初始能量,分析了表面張力作用和慣性作用的相對(duì)強(qiáng)弱對(duì)極限波形態(tài)的影響。研究表明,對(duì)于較強(qiáng)的卷破波,表面張力集中作用于水舌前端和頸部,讓水舌前端變圓,降低水舌的射出角度,減小水舌的射出距離,與前波面形成的空氣間隙也隨之變小;對(duì)于較弱的卷破波,表面張力集中作用于凸起水體前端和趾部,阻止水舌的形成,波峰處的凸起增大到一定程度后,在重力的作用下沿前波面下滑,傾向于形成崩破波。
[Abstract]:The breakup of water waves is one of the most important hydrodynamic problems in the coastal waters, and it is also a theoretical analysis. The purpose of this paper is to establish a high precision numerical model for analyzing the motion and deformation of limit waves and to study the mechanism of water wave fragmentation. The influence of surface tension on the limit wave is analyzed. A new interface tracing method coupled with Phase-Field and VOF method is established in this paper. The new coupling method combines the traditional discontinuous surface method and the diffusion surface method which is recently introduced in the field of hydrodynamics calculation, and combines the advantages of the two kinds of methods. A new boundary condition processing technique is proposed to ensure the accuracy of the calculation. The model solution is based on the finite volume method and PISO algorithm. The solution is simple and stable. The new coupling model is verified. It can calculate the complex surface problem with high precision and greatly improve the efficiency compared with the uncoupled model. In this paper, the coupling model should be applied to the study of the limit wave problem. For the traveling wave problem, the periodic boundary conditions and the moving coordinate system are adopted, the computational domain is reduced to a single wavelength, and the forced pressure is used to generate the wave. The initial energy of the limit wave is controlled. The calculation conditions consider the different initial energy and study the shape of the limit wave in the corresponding state. The results show that the mesh accuracy is sufficient and the surface tension is excluded. The water tongue will be formed at the peak of the limit wave, and the stronger initial energy will force the water wave to reach the limit state earlier. The scale of the water tongue and the duration of the water wave in the limit state decrease with the decrease of the initial energy of the limit wave. The drift velocity of the water wave also decreases with the decrease of the initial energy of the limit wave. The maximum velocity of water quality at the peak is higher than that calculated by linear wave theory, which is consistent with the classical theory. For standing wave problem, the sloshing method is adopted. In this paper, the limit standing wave problem in sloshing problem is studied. By changing the mode and amplitude of sloshing, oscillation time and other parameters, two different kinds of limited standing wave patterns are simulated. The results are in good agreement with the experimental observations. The coupling model is also used to study the influence of surface tension on the limit wave by changing the surface tension coefficient and the initial energy of the limit wave. The effect of the relative strength of surface tension and inertia on the shape of the limit wave is analyzed. The results show that the surface tension focuses on the front end and neck of the water tongue and makes the front end of the water tongue round. The air gap between the water tongue and the front wave surface becomes smaller when the angle of the water tongue is reduced and the distance between the water tongue and the front wave surface is reduced. For the weaker curling wave, the surface tension acts on the front end and toe of the raised water body to prevent the formation of the water tongue, and when the protuberance at the peak increases to a certain extent, it glides along the front wave surface under the action of gravity. Tend to form burst waves.
【學(xué)位授予單位】：清華大學(xué)
【學(xué)位級(jí)別】：博士
【學(xué)位授予年份】：2016
【分類號(hào)】：O352

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