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1.
通过自由落体的入水方式,分别在静水和规则波中开展了两种不同横剖面的曲面楔形体入水砰击问题试验研究。使用高速摄像系统记录楔形体入水过程流场演变和运动特性,采用加速度传感器和压力传感器进行数据的动态采集。试验结果表明,在静水中入水时,外凸剖面楔形体入水砰击后模型两侧的射流飞溅比反曲剖面更剧烈,而在楔形体前端的水面以下部分形成的气腔更小;在规则波中入水时,对于相同模型,在波峰和上跨零点相位下模型入水砰击后两侧的射流飞溅比在波谷相位更剧烈。相同工况时,反曲剖面模型所受砰击的加速度峰值和压力峰值更小;在相同的入水速度下,对于相同模型,波浪载荷和砰击载荷的共同作用会使模型所受砰击压力显著增大。  相似文献   

2.
基于神经网络的平底结构砰击压力预报   总被引:1,自引:0,他引:1  
陈震  肖熙 《海洋工程》2005,23(2):26-31,41
对利用神经网络预报平底结构入水砰击压力的方法进行了探讨。首先利用仿真软件计算各种情况下平底结构入水所产生的砰击压力,以此形成训练神经网络的数据集。其次利用数据集对三层反馈式网络进行了训练,讨论了不同隐含层节点数对该非线性系统的拟合能力,并且对梯度下降法、动量修正法和基于优化的LM算法的有效性和精度进行了比较,最后得出了适合平底结构入水砰击系统的网络结构。  相似文献   

3.
基于三维边界元方法研究了三维轴对称体入水砰击载荷的数值算法。算法从三维力学模型出发,继承了Wagner自由液面抬升理论,引入浸深因子Cw以确定自由液面抬升高度,并且将自由液面线性化处理,同时考虑网格运动,在自由液面附近对网格进行截断重构,以确保水下湿面积的精准。算法中使用考虑加权运动项的非线性伯努利方程计算得到入水结构的表面压力,进一步积分可得入水结构的总体受力。此外,文中分别通过Nisewanger的圆球入水试验与Alaoui的圆锥入水试验对算法的正确性及适用性进行了验证。  相似文献   

4.
楔形体在波浪中自由入水的数值模拟   总被引:1,自引:0,他引:1  
物体入水时波浪的影响不可忽略,基于流体力学模型采用VOF法,并利用自定义函数,模拟了楔形体的自由入水过程;同时结合推波板原理及海绵层消波理论实现了数值水槽的造消波,完成了波浪中楔形体自由入水的模拟,计算了楔形体入水时所受的水作用力、自由液面变化及物面压强分布等,研究了不同波高、周期以及在波浪不同位置入水时对楔形体的影响。结果表明:本文建立的数值模型可很好地模拟楔形体入水造成的射流及空泡的形成发展过程,波浪对楔形体入水的影响主要由波浪内部流场变化及表面波形决定,在波浪不同位置处入水对楔形体受力及入水形态均有较大影响。  相似文献   

5.
导管推进器是一种普遍应用于无人遥控潜水器(ROV)等潜器中的特种推进器。在桨叶与导管之间的梢隙中存在非常复杂的流动,本研究基于大涡模拟(LES)对导管推进器的梢隙流动进行了数值模拟分析。通过对时间步长的收敛性研究,建立两套基于不同网格类型的计算模型。将计算与试验结果进行对比,比较两种不同类型网格模拟结果的差异,发现切割体网格能够更好地捕捉到泄涡的细节,并结合梢隙流场的原理分析了泄涡发展的过程,梢隙涡的驱动力是吸力面、压力面之间的压差。此外,随着进速系数增大,梢隙周向的涡管轴向分布范围减小,主泄涡发生位置延后,泄出涡的长度和数量都有所减少。  相似文献   

6.
为了研究波浪与抛石潜堤相互作用过程中大自由表面变形和堤内渗流等强非线性紊流运动问题,利用改进的MPS法,建立了模拟波浪与抛石潜堤相互作用的MPS法数值计算模型。模型将抛石潜堤假定为均质多孔介质,采用Drew的二相流运动方程描述多孔介质内外的流体运动;通过在动量方程中增加非线性阻力项,并引入亚粒子尺度紊流模型,模拟波浪与可渗结构物相互作用过程中的紊流运动。选取“U”型管中多孔介质内渗流过程和孤立波与可渗潜堤相互作用两个典型的渗流问题,通过将数值计算结果与理论解和实测值的对比分析,对所提出的MPS法紊流渗流模型的模拟精度进行验证。结果表明:基于改进的MPS法构建的垂向二维紊流渗流模型可以很好地再现“U”型管中多孔介质内渗流以及波浪作用下可渗潜堤内外的复杂流场,显著缓解流-固界面处的压力震荡与粒子分布不均匀问题,实现了较高的模拟精度。  相似文献   

7.
MPS方法数值模拟液舱晃荡问题   总被引:1,自引:0,他引:1  
基于无网格粒子法MPS方法(moving particle semi-implicit method)研究了液舱晃荡问题。针对二维矩形液舱晃荡问题进行了数值验证,结果表明MPS方法能够很好地计算晃荡产生的拍击压力。同时将MPS方法应用到带隔板的液舱晃荡问题计算中,分析了二维和三维带隔板液舱晃荡问题。计算结果表明:隔板的存在很大程度地限制了流体的水平运动,隔板附近出现了自由面的翻卷、破碎和融合现象,MPS方法能够很好地模拟这些流动现象。计算得到的波高与实验测得的波高吻合较好,表明MPS方法模拟带隔板的晃荡问题具有一定的可靠性。  相似文献   

8.
大涡模拟及其在海洋湍流数值模拟中的应用   总被引:4,自引:1,他引:3  
本文概述了大涡模拟的定义及特征,介绍了大涡模拟的几种常用方法以及它在海洋湍流场数值模拟中的应用,并指出了一些尚待改进的问题。  相似文献   

9.
尝试建立1种基于无单元法的涡激振动数值模拟算法,并给出适用于涡激振动分析的前处理自动布点方法.基于无单元法理论,使用动最小二乘法构造形函数,利用无单元伽辽金法,采用速度和压力分离模式,及手工布点和自动布点2种方法所得出的节点布置形式,对流场控制方程进行空间离散,模拟二维涡激振动的流场形态,并对VIV相关参数进行分析,计算不同节点布置情况下的升力系数(Cl)、曳力系数(Cd)及斯特罗哈数(St),并与物理模型实验结果进行对比.计算结果表明,无单元伽辽金法应用于立管VIV分析是可行的,且文中采用2种布点方法均能较好的模拟流场中泻涡脱落的形态,计算结果与传统方法和物理模型实验结果吻合良好.证明文中2种布点方法都能用于固定圆柱的二维VIV分析,但自动布点法能够更好地适用于复杂问题的计算及圆柱体在流场中的VIV动力响应分析.  相似文献   

10.
从三维边界元方法出发,基于Wagner的自由液面抬升理论,采用数值仿真的方法研究了圆球入水的问题。通过数值模拟与轴对称体入水试验结果的正确性及适用性进行验证的基础上,并分析了不同半径的球体在不同速度下的入水总体受力和表面压力的变化规律。计算结果表明随着球体半径和入水速度的增加,峰值压力迅速增加,受力峰值与球体半径的平方和入水速度平方成正比关系;球体表面压力系数的分布计算结果表明,在测试点与水开始接触时压力系数最大,然后迅速减小;压力系数和入水速度无关,但和入水深度相关。  相似文献   

11.
Moving particle semi-implicit (MPS) method is a fully Lagrangian particle method which can easily solve problems with violent free surface. Although it has demonstrated its advantage in ocean engineering applications, it still has some defects to be improved. In this paper, MPS method is extended to the large eddy simulation (LES) by coupling with a sub-particle-scale (SPS) turbulence model. The SPS turbulence model turns into the Reynolds stress terms in the filtered momentum equation, and the Smagorinsky model is introduced to describe the Reynolds stress terms. Although MPS method has the advantage in the simulation of the free surface flow, a lot of non-free surface particles are treated as free surface particles in the original MPS model. In this paper, we use a new free surface tracing method and the key point is "neighbor particle". In this new method, the zone around each particle is divided into eight parts, and the particle will be treated as a free surface particle as long as there are no "neighbor particles" in any two parts of the zone. As the number density parameter judging method has a high efficiency for the free surface particles tracing, we combine it with the neighbor detected method. First, we select out the particles which may be mistreated with high probabilities by using the number density parameter judging method. And then we deal with these particles with the neighbor detected method. By doing this, the new mixed free surface tracing method can reduce the mistreatment problem efficiently. The serious pressure fluctuation is an obvious defect in MPS method, and therefore an area-time average technique is used in this paper to remove the pressure fluctuation with a quite good result. With these improvements, the modified MPS-LES method is applied to simulate liquid sloshing problems with large deforming free surface. Results show that the modified MPS-LES method can simulate the large deforming free surface easily. It can not only capture the large impact pressure accurately on rolling tank wall but also can generate all physical phenomena successfully. The good agreement between numerical and experimental results proves that the modified MPS-LES method is a good CFD methodology in free surface flow simulations.  相似文献   

12.
Experiments and numerical methods are developed to investigate the water entry of a freefall wedge with a focus on the evolution of the pressure on the impact sides (the side contacting water) and the top side (the dry side on the top of the wedge), evolution of the global hydrodynamic loads, evolution of the air–water interface, and wedge motion. It is found that a typical water entry of a freefall wedge can be divided into slamming, transition, collapse and post-closure stages. A single-fluid numerical model is presented to simulate the first three stages. The results are compared to experiments and good agreements are obtained. A two-fluid BEM is proposed to investigate the influence of the air flow before the closure of the cavity created on the top of the wedge. It is found that for the closure of the 2D cavity, the air flow starts to play an important role just before closure but due to the short duration, the influence of air flow on the body velocity and configuration of the air–water interface is limited.  相似文献   

13.
Impact problems associated with water entry have important applications in various aspects of naval architecture and ocean engineering. Estimation of hydrodynamic impact forces especially during the first instances after the impact is very important and is of interest. Since the estimation of hydrodynamic impact load plays an important role in safe design and also in evaluation of structural weight and costs, it is better to use a reliable and accurate prediction method instead of a simple estimation resulted by analyzing methods. In landing of flying boats, some phenomena such as weather conditions and strong winds can cause asymmetric instead of symmetric descent. In this paper, a numerical simulation of the asymmetric impact of a wedge, as the step of a flying boat, considering dynamic equations in two-phase flow is taken into account. The dynamic motion of the wedge in two-phase flow is solved based on finite volume method with volume of fluid (VOF) scheme considering dynamic equations. Then the effects of different angles of impact and water depth on the velocity change and slamming forces in an asymmetric impact are investigated. The comparison between the simulation results and experimental data verifies the accuracy of the method applied in the present study.  相似文献   

14.
柱体绕流问题是流体力学领域一个非常经典的问题。当流体流经柱体时,由于黏性的存在,会发生许多复杂的流动现象,如流动分离、涡旋周期性生成与脱落等,经常被作为标准验证算例。同时,柱体绕流广泛存在于实际工程中,并在一定工况下可能对工程产生巨大危害,因此对柱体绕流进行深入研究具有重要意义。研究中,拟将一种无网格类方法——半隐式移动粒子方法(moving particle semi-implicit method,简称MPS)引入到柱体绕流问题的数值研究中,并对不同雷诺数下二维方柱绕流问题进行数值模拟。首先,使用基于MPS方法自主开发的MLParticle-SJTU求解器,结合入口边界条件和出口边界条件,模拟了雷诺数Re分别为40、200和1 000时均匀来流条件下的方柱绕流。随后,将模拟的绕流结果与文献中试验和数值计算结果进行了对比,结果吻合较好,并且在雷诺数为200和1 000时,可以清晰地捕捉到方柱尾流中的卡门涡街现象,验证了MPS方法在柱体绕流问题模拟上的有效性和适用性。  相似文献   

15.
As a gridless particle method, the MPS (Moving Particle Semi-implicit) method has proven useful in a wide variety of engineering applications including free-surface hydrodynamic flows. Despite its wide range of applicability, the MPS method suffers from some shortcomings such as non-conservation of momentum and spurious pressure fluctuation. By introducing new formulations for the pressure gradient and a new formulation of the source term of the Poisson Pressure Equation (PPE), and by allowing a slight compressibility, we have proposed modified MPS methods for the prediction of wave impact pressure on a coastal structure. The improved performance of the modified methods is shown through the simulation of numerous wave impact problems (including the impacts by a dam break flow, a flip-through and two cases of slightly-breaking waves) in comparison with the experimental data.  相似文献   

16.
Wedge entry into initially calm water   总被引:2,自引:0,他引:2  
This paper presents results of calculations based on the Cauchy's theorem method of Vinje and Brevig1 for the two-dimensional entry of wedges of various angles into initially calm water. The problem has a long history which is briefly reviewed in the introduction, and significant progress has been made with both linear theories (valid for low entry speed) and with theories which treat the free surface conditions exactly but with the assumptions of zero gravity and constant speed of entry. This simplifies the problem to one which is self-similar in dimensionless space variables ξ = x/vt and η = y/vt and this has a number of consequences. For wedges with half-angles up to about 45° and with high entry speeds, the numerical approach, which includes gravity, validates these assumptions and the agreement between both free surface displacements and pressure distributions on the wetted wedge surface is excellent except in the region of the jet of fluid which rises up the side of the wedge. Because the potential flow initial value problem is singular at the intersection of the free surface and wedge surface, exact numerical resolution of the jet is not possible. Nevertheless, the rest of the fluid motion is insensitive to the treatment of the jet, which itself may be calculated quite realistically. Of particular interest (but little practical relevance) is the pressure on the upper part of the wedge surface (in the jet region) which according to self-similar theories is very small but positive, but which is calculated to be small but negative by the numerical scheme. This effect, which is enhanced when gravity is included, is insensitive to the numerical resolution of the jet and suggests that the jet may separate from the wedge surface, the new intersection point being where the pressure vanishes on the wedge surface. A modified numerical scheme allows this to happen and the results are in qualitative agreement with the experiments by Greenhow and Lin.2

The numerical method presented here is extremely versatile and a number of other effects may be explored. Examples of transient motion, non-constant speed of entry, oblique entry and complete penetration of the surface so that a cavity is formed behind the wedge are presented.  相似文献   


17.
A numerical model has been developed to study sloshing of turbulent flow in a tank with elastic baffles. The Moving-Particle Semi-implicit method(MPS) is a kind of meshless Lagrangian calculation method. The large eddy simulation(LES) approach is employed to model the turbulence by using the Smagorinsky Sub-Particle Scale(SPS)closure model. This paper uses MPS-FSI method with LES to simulate the interaction between free surface flow and a thin elastic baffle in sloshing. Then, the numerical model is validated, and the numerical solution has good agreement with experimental data for sloshing in a tank with elastic baffles. Furthermore, under external excitations,the MPS is applied to viscous laminar flow and turbulent flow, with both the deformation of elastic baffles and the wave height of the free surface are compared with each other. Besides, the impact pressure with/without baffles and wave height of free surface are investigated and discussed in detail. Finally, preliminary simulations are carried out in the damage problem of elastic baffles, taking the advantage of the MPS-FSI method in computations of the fluid–structure interaction with large deformation.  相似文献   

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