【作者】 孙学尧；

【导师】 张怀新；

【作者基本信息】 上海交通大学 ， 船舶与海洋结构物设计制造， 2011， 硕士

【摘要】 在计算流体力学领域中,对于大变形自由表面的问题研究一直在不断的进展。计算流体力学领域中的数值模拟方法主要分为无网格法和网格法两种,其中无网格法在解决表面问题具有得天独厚的优势。移动粒子半隐式法(Moving-Particle Semi-Implicit Method, MPS)是一种新的基于拉格朗日(Lagrange)粒子的无网格方法,MPS法着眼于跟踪粒子的运动学和动力学性质变化过程。因此MPS法不需要建立网格,尤其在模拟大变形自由表面的问题可以简化网格布置的过程,得到比较理想的模拟效果。?MPS法虽然在模拟自由液体自由表面有一定的优势,但是自身的压力振荡性问题严重限制了此方法在工程上的应用。在MPS法的研究过程中许多人做了相关缓解压力的研究,但效果都不是特别好。本文从MPS压力产生的原因着手,在MPS法的压力泊松方程中加入了在计算流体力学领域中常用的保证流体不可压缩性的散度为0的条件共同控制压力方程,减少压力的振荡性。利用缓解压力振荡的改进MPS法和原方法进行了溃坝模型和液舱晃荡模型进行模拟验证。通过这两个算例的对比验证了缓解压力振荡的改进MPS法在数值模拟过程中成功的缓解了压力振荡现象。波浪是船舶与海洋工程类和港口航道与近海工程中最重要的动力因素之一。数值波浪水池是研究波浪的主要数值手段之一,既避免了建立物理模型的费时费力,同时数值波浪水池在空间尺度、可控制性方面具有更大的扩展性。本文根据上海交通大学的船模拖曳水池的模型进行等比例缩小,成功地利用MPS法的初始模拟完成了数值水池的建立。在数值模拟领域中,大涡模拟是一种最新的解决湍流这种最常见的流动模式的研究方法,效果比较不错。本文将MPS法大涡模拟成功的应用在新建立的数值水池上,并进行造波模拟。针对MPS法大涡模拟造成的水池波浪振荡过大的问题,利用新开发的缓解压力振荡的改进MPS法大涡模拟进行造波模拟,成功的控制了数值水池造波压力过大的问题,得到不错的造波效果。同时在MPS法大涡模拟的造波过程中针对不动核函数进行造波模拟的比较,得出KF1核函数适用于改进MPS法大涡模拟的造波模拟。最后利用KF1核函数的数值造波模拟研究了改进方法中的松弛因子对于数值造波的影响。更多还原

【Abstract】 In the Computational Fluid Dynamics, the flows including large deforming free surface have been studied for a long time. The main numerical simulation methods in CFD are grid method and meshless method and meshless method have an advantage on resolving flow problem with free surface. Moving-Particle Semi-Implicit Method (MPS) is a new meshless numerical method which bases on Lagrange particle, which trace the changing feature of dynamic and kinematic. Due to the advantage in free surface simulation, the MPS method plays more and more important role in numerical research.?Although MPS have a good result in simulation with free surface, the pressure fluctuation restricts the application in engineering. People had some study on reduce the pressure fluctuation, but they did not get some good results. This paper focuses on the reason on the pressure oscillation, therefore combine the pressure Poisson equation with divergence-free condition which is usually used to ensure the incompressibility of flows. There are two kinds of cases being numerical simulated which are water collapse and ship roll sloshing. Comparing to the original MPS method, the result from the new method is real, so that the new method has good practicability and reliability.Wave is one of the most important dynamic factors in the Naval architecture and Ocean Engineering and Coastal Engineering. It is used to establish model to solve such problem. Numerical wave tank had become a main way to study waves. It can not only save huge amout of time than physical model, but also have more expansibility on scale and controllability. A numerical wave tank has been build successfully based on ship model test towing tank in SJTU.Large Eddy Simulation(LES) is a new method proposed to solve turbulent flows which is common in the world and it has good effect. LES is used in the new numerical wave tank to generate wave numerically. The constract has been made based on different kernel function and KF1 is suitable for numerical wave generation. This paper combines LES with new modified MPS to generate wave numerically to reduce the pressure oscillation successfully. At last, the influence of relaxation factor to the numerical wave has been studied based on KF1 kernel function.更多还原