Phase-Field和VOF耦合方法及其在极限波问题中的应用

发布时间：2018-01-11 10:27

本文关键词：Phase-Field和VOF耦合方法及其在极限波问题中的应用　出处：《清华大学》2016年博士论文　论文类型：学位论文

【摘要】：水波的破碎问题是近岸海域内最为重要的水动力学问题之一,也是理论分析、实验观测和数值模拟的难点问题。本文旨在建立一个可用于分析极限波运动和变形的高精度的数值模型,研究水波的破碎机理,分析表面张力对极限波的影响。本文建立了耦合了Phase-Field和VOF方法的新界面追踪方法,完善了配套的数值模型及网格系统。新的耦合方法综合了传统的间断表面方法和新近引入流体力学计算领域的扩散表面方法,结合了两类方法的优点;提出了一种新的边界条件处理技术,保证了计算的精度。模型求解基于有限体积法和PISO算法,求解简便,稳定性强。新的耦合模型经验证,能够高精度的计算复杂表面问题,并且相对于非耦合模型极大的提高了计算效率,节约计算时间。本文将耦合模型应于极限波问题的研究。对于行进波问题采用了周期性边界条件及动坐标系,将计算域缩小到单个波长,并采用受迫压强造波,控制极限波的初始能量。计算条件考虑了不同初始能量,研究了对应状态下的极限波形态。研究表明,在保证网格精度足够并且排除了表面张力作用的情况下,极限波的波峰处均会形成水舌。较强的初始能量迫使水波更早的达到极限状态,水舌的尺度以及水波处于极限状态的持续时间随着极限波初始能量的减小而减小;水波的漂移速度同样随着极限波初始能量的减小而小减;波峰处水质点的最大速度会超过线性波理论计算得出的波速,与经典理论相符。对于驻波问题,采用了晃荡造波法,研究了晃荡问题中的极限驻波问题。通过改变晃荡的方式和振幅、振荡时间等参数,模拟了两类不同的极限驻波形态,结果与实验观测吻合良好。耦合模型还用于研究表面张力对极限波的影响。通过改变表面张力系数和极限波的初始能量,分析了表面张力作用和惯性作用的相对强弱对极限波形态的影响。研究表明,对于较强的卷破波,表面张力集中作用于水舌前端和颈部,让水舌前端变圆,降低水舌的射出角度,减小水舌的射出距离,与前波面形成的空气间隙也随之变小;对于较弱的卷破波,表面张力集中作用于凸起水体前端和趾部,阻止水舌的形成,波峰处的凸起增大到一定程度后,在重力的作用下沿前波面下滑,倾向于形成崩破波。
[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.
【学位授予单位】：清华大学
【学位级别】：博士
【学位授予年份】：2016
【分类号】：O352

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