耦合VOF的非线性k-ε模型三维溃坝数值模拟

溃坝是一种伴随有巨大破坏力的灾害性的水流现象。三维溃坝的数值模拟能够为溃坝水流的研究分析提供科学的依据。针对瞬间全溃模型水流的复杂性,考虑水库下游障碍物的滞水及阻水作用,利用开源程序OpenFOAM建立了耦合VOF对流方程的三维非线性(NL)k-ε紊流数学模型求解雷诺时均纳维斯托克斯方程。采用有限体积法进行离散,利用PISO算法进行数值求解。通过模拟下游为三角形障碍物、矩形障碍物以及90°弯道的溃坝实验,并将模拟结果与实验结果进行对比分析,初步证明了该模型的准确性和鲁棒性。     

带自由面船体周围粘性流场数值模拟

利用FLUENT流体软件,通过求解三维粘性不可压RANS方程和使用标准k-ε湍流模型对带自由液面船体进行了周围粘性流场的数值模拟。自由液面采用VOF方法处理,得出了不同弗劳德数下船体的粘性阻力系数,并与ITTC1957给出的平板摩擦阻力系数计算公式以及巴普米尔粘压阻力系数公式两者所求的粘性阻力系数相比较,验证了本文方法的可行性,为船舶阻力预报提供了更为精确的流体分析方案。同时,利用VOF方法可以很好的捕捉自由液面波形,反应了船体的兴波现象,为船体优化设计提供重要的参考。     

浮式风机气动-水动耦合特性数值模拟（英文）

The exploration for renewable and clean energies has become crucial due to environmental issues such as global warming and the energy crisis. In recent years,floating offshore wind turbines(FOWTs) have attracted a considerable amount of attention as a means to exploit steady and strong wind sources available in deep-sea areas. In this study, the coupled aero-hydrodynamic characteristics of a spar-type 5-MW wind turbine are analyzed. An unsteady actuator line model(UALM) coupled with a twophase computational fluid dynamics solver naoe-FOAM-SJTU is applied to solve three-dimensional Reynolds-averaged NavierStokes equations. Simulations with different complexities are performed. First, the wind turbine is parked. Second, the impact of the wind turbine is simplified into equivalent forces and moments. Third, fully coupled dynamic analysis with wind and wave excitation is conducted by utilizing the UALM. From the simulation, aerodynamic forces, including the unsteady aerodynamic power and thrust, can be obtained, and hydrodynamic responses such as the six-degrees-of-freedom motions of the floating platform and the mooring tensions are also available. The coupled responses of the FOWT for cases of different complexities are analyzed based on the simulation results. Findings indicate that the coupling effects between the aerodynamics of the wind turbine and the hydrodynamics of the floating platform are obvious. The aerodynamic loads have a significant effect on the dynamic responses of the floating platform, and the aerodynamic performance of the wind turbine has highly unsteady characteristics due to the motions of the floating platform. A spar-type FOWT consisting of NREL-5-MW baseline wind turbine and OC3-Hywind platform system is investigated. The aerodynamic forces can be obtained by the UALM. The 6 DoF motions and mooring tensions are predicted by the naoe-FOAM-SJTU. To research the coupling effects between the aerodynamics of the wind turbine and the hydrodynamics of the floating platform, simulations with different complexities are performed. Fully coupled aero-hydrodynamic characteristics of FOWTs, including aerodynamic loads, wake vortex, motion responses, and mooring tensions, are compared and analyzed.     

绕船体自由表面流的数值模拟

本文采用RANS方程和VOF算法数值模拟了系列60粘性自由面流动，比较了幂指数律，二阶迎风，QUICK格式对计算结果的影响，详细给出了波形，阻力，伴流等的计算结果，与试验及其它计算结果比较显示本文的计算方法具有较好的计算精度，可用于船型性能分析和优化。     

海岸桩结构布置对波浪参数影响的数值模拟研究（英文）

In this study, the passage of waves through pile groups with different arrangements is investigated using a three-dimensional(3D)numerical model. For the simulations, waves of three different heights of 36, 58, and 81 mm, a fixed period of 0.88s, and a fixed wave length of 1.128 m were used. To simulate the waves and flow pattern through the piles, Reynolds-averaged Navier–Stokes(RANS) equations of fluid motion were solved based on the finite volume method(FVM). Piles were defined as obstacles in the rectangular domain using the fractional area/volume obstacle representation(FAVOR) method. The volume-of-fluid(VOF) and re-normalization group(RNG) methods were used to simulate the free surface and turbulence phenomenon, respectively. By performing different numerical simulations, the effect of coastal pile arrangements on wave pattern was studied and was compared with existing experimental data, and an acceptable agreement was achieved.     

高速滑行船体的气水界面效应模拟（英文）

High-speed planing crafts have successfully evolved through developments in the last several decades. Classical approaches such as inviscid potential flow–based methods and the empirically based Savitsky method provide general understanding for practical design. However, sometimes such analyses suffer inaccuracies since the air–water interface effects, especially in the transition phase, are not fully accounted for. Hence, understanding the behaviour at the transition speed is of fundamental importance for the designer. The fluid forces in planing hulls are dominated by phenomena such as flow separation at various discontinuities viz.,knuckles, chines and transom, with resultant spray generation. In such cases, the application of potential theory at high speeds introduces limitations. This paper investigates the simulation of modelling of the pre-planing behaviour with a view to capturing the air–water interface effects, with validations through experiments to compare the drag, dynamic trim and wetted surface area.The paper also brings out the merits of gridding strategies to obtain reliable results especially with regard to spray generation due to the air–water interface effects. The verification and validation studies serve to authenticate the use of the multi-gridding strategies on the basis of comparisons with simulations using model tests. It emerges from the study that overset/chimera grids give better results compared with single unstructured hexahedral grids. Two overset methods are investigated to obtain reliable estimation of the dynamic trim and drag, and their ability to capture the spray resulting from the air–water interaction. The results demonstrate very close simulation of the actual flow kinematics at steady-speed conditions in terms of spray at the air–water interface, drag at the pre-planing and full planing range and dynamic trim angles.     

在墩柱群周围波浪变形的数值模拟

我们曾经将基于Boussinesq方程的波浪数学模型用于研究海岸带非线性波浪的传播变形以及与建筑物的相互作用，数学模型采用有限差分法解出，为进一步验证模型的正确性和使用价值，又将模型用于解决浅水区域的墩柱群周围的波浪变形，结果得出较为精确的波浪分布，并表明保持适当间距的墩柱群可以有效阻挡波浪的传播，削减波浪强度，起到良好的防波效果，可望成为重力式防波堤的1种有效替代方案。     

层流状态下旋转圆柱绕流数值模拟研究（英文）

基于CFD方法对层流状态不同雷诺数下的旋转圆柱绕流进行数值模拟,分析在不同转速比α(0≤α≤8)下尾流涡流、升力系数、阻力系数和斯特劳哈尔数的特性。随着转速比的增大,发现五种尾流结构形态（漩涡脱落、稳定尾流、反向稳定尾流、单边涡和附着涡）。随着转速比的增大,平均升力系数先抛物线形式增大,然后线性增大,平均阻力系数减小,然后增大;斯特劳哈尔数随旋转比的增大而减小,且第二不稳定阶段的斯特劳哈尔数比第一不稳定阶段要小很多。随着雷诺数的增大,第一不稳定阶段的末尾向后移动,第二不稳定阶段的生成范围向前移动。     

绕船体自由面周围三维粘性流场的数值模拟

本文采用有限体积法通过求解不可压缩的雷诺平均(RANS)方程数值模拟了包括兴波的三维船体周围的粘性流场,湍流模式使用了子网格尺度模式(SGS)和Baldwin-Lomax模式相结合的混合模式.对于自由表面的处理,采用了任意拉格朗日-欧拉方法,网格为不仅与物体表面贴体,而且与自由表面贴体的动网格,即随着自由表面的变化要不断地重新划分网格.虽然此方法需要很长的计算时间,但能较好地描述船体的兴波情况.本文计算了系列60船模在Fn=0.316,Re=1.9×106时带自由面的粘性流场,计算结果与试验结果吻合较好.，An finite - volume method solving of incompressible RANS Equations is developed for the numeri-cal simulation of three - dimensional viscous flow with free - surface about a ship. A hybrid turbulence mod-el by combining the sub - grid scale (SGS) model and the Baldwin- Lomax model is used in this pa-per. The arbitrary - Lagrange - Euler formulation is devised for the treatment of free surface boundary condi-tion. The boundary - fitted coordinate system is fitted not only to the ship hull surface but also to the freesurface, so the computational grid is regenerated to follow the free surface deformation. Although this methodneeds spend much longer computational time, but it can fairly display wave pattern made by a ship. The nu-merical simulation has been carried out for viscous flow with free surface past Series 60 ship hull at Fn =0. 316, Re = 1.9 × 106. The computed results are in reasonable agreement with experimental measure-ments.     

波浪中远洋船舶耦合运动的数值模拟

利用基于FLAC3D和基于UDEC的2种传统方法对船舶耦合运动进行数值模拟,结果准确性较低。针对上述问题,提出一种新的基于CFD的远洋船舶耦合运动数值模拟研究方法。首先给出船舶耦合运动的假定条件,然后建立反映问题本质的数学模型,接着利用有限体积法对该方程进行离散,最后利用有限差分法对离散后的方程进行求解,完成船舶耦合运动数值模拟。结果表明:与基于FLAC3D和基于UDEC的2种传统方法相比,利用本研究方法对船舶耦合运动进行数值模拟,模拟结果准确性提高6.3%和14.5%,达到了研究目的。     

三维船体横摇运动数值模拟及舭龙骨阻尼特性研究（英文）

为研究舭龙骨阻尼特性及尺寸航速等因素的影响,本文基于计算流体动力学方法分别对有、无舭龙骨三维船体的自由横摇衰减运动以及强迫横摇运动进行数值模拟研究,有无舭龙骨的三维船体的横摇阻尼之差即为舭龙骨阻尼。对F_r=0.138、初始横摇角10°带舭龙骨船体的自由横摇衰减数值模拟算例作了验证与确认分析,自由横摇衰减时历曲线与实验结果吻合较好,固有周期和横摇阻尼精度较高。进一步分析研究了不同几何尺寸、初始横摇角、航速以及频率等参数对舭龙骨阻尼的影响。自由横摇衰减模拟研究中舭龙骨阻尼随着舭龙骨宽度、初始横摇角度的增大而增大;当航速为0时,舭龙骨阻尼在总阻尼占比最大,航速对舭龙骨阻尼绝对值影响较小。强迫横摇模拟研究表明:当横摇角一定,舭龙骨阻尼随着频率的增大而非线性增大,在固有频率附近,粘性效应不可忽略。     

基于BEM与VOF耦合模型的潜堤附近波浪变形研究*

BEM和VOF方法是目前模拟近岸波浪变形的2种有效方法。以这2种模型为基础构建了一个前域应用BEM、后域应用VOF方法的波浪数值计算耦合模型（BEM+VOF模型）,并应用该模型对波浪越过水下潜堤的波面变形过程进行研究。结果表明,计算值与实验值吻合良好,说明本文建立的波浪耦合模型可以很好地模拟波浪和结构物的相互作用。     

基于MPS-FEM耦合方法研究波浪与结构的相互作用（英文）

Nowadays, an increasing number of ships and marine structures are manufactured and inevitably operated in rough sea. As a result, some phenomena related to the violent fluid-elastic structure interactions(e.g., hydrodynamic slamming on marine vessels, tsunami impact on onshore structures, and sloshing in liquid containers) have aroused huge challenges to ocean engineering fields. In this paper, the moving particle semi-implicit(MPS) method and finite element method(FEM) coupled method is proposed for use in numerical investigations of the interaction between a regular wave and a horizontal suspended structure. The fluid domain calculated by the MPS method is dispersed into fluid particles, and the structure domain solved by the FEM method is dispersed into beam elements. The generation of the 2D regular wave is firstly conducted, and convergence verification is performed to determine appropriate particle spacing for the simulation. Next, the regular wave interacting with a rigid structure is initially performed and verified through the comparison with the laboratory experiments. By verification, the MPS-FEM coupled method can be applied to fluid-structure interaction(FSI) problems with waves. On this basis, taking the flexibility of structure into consideration, the elastic dynamic response of the structure subjected to the wave slamming is investigated, including the evolutions of the free surface, the variation of the wave impact pressures, the velocity distribution,and the structural deformation response. By comparison with the rigid case, the effects of the structural flexibility on wave-elastic structure interaction can be obtained.     

用naoe-FOAM-SJTU求解器数值模拟船舶在波浪上的操纵运动问题（英文）

Ship maneuvering in waves includes the performance of ship resistance, seakeeping, propulsion, and maneuverability. It is a complex hydrodynamic problem with the interaction of many factors. With the purpose of directly predicting the behavior of ship maneuvering in waves, a CFD solver named naoe-FOAM-SJTU is developed by the Computational Marine Hydrodynamics Lab(CMHL) in Shanghai Jiao Tong University. The solver is based on open source platform OpenFOAM and has introduced dynamic overset grid technology to handle complex ship hull-propeller-rudder motion system. Maneuvering control module based on feedback control mechanism is also developed to accurately simulate corresponding motion behavior of free running ship maneuver. Inlet boundary wavemaker and relaxation zone technique is used to generate desired waves. Based on the developed modules, unsteady Reynolds-averaged Navier-Stokes(RANS) computations are carried out for several validation cases of free running ship maneuver in waves including zigzag, turning circle, and course keeping maneuvers. The simulation results are compared with available benchmark data. Ship motions, trajectories, and other maneuvering parameters are consistent with available experimental data, which indicate that the present solver can be suitable and reliable in predicting the performance of ship maneuvering in waves. Flow visualizations, such as free surface elevation, wake flow, vortical structures, are presented to explain the hydrodynamic performance of ship maneuvering in waves. Large flow separation can be observed around propellers and rudders. It is concluded that RANS approach is not accurate enough for predicting ship maneuvering in waves with large flow separations and detached eddy simulation(DES) or large eddy simulation(LES) computations are required to improve the prediction accuracy.     

VOF与LevelSet耦合的界面计算方法及其对波浪破碎过程的模拟

破碎波浪传播过程的数值模拟是研究波浪破碎特性的重要手段。文章提出了一种用于计算界面的VOF和Level Set耦合算法,从而利用VOF方法质量守恒、Level Set方法能够更准确计算法向量的优点。体积分数采用一种较新的VOF几何方法——isoAdvector方法计算,并在此基础上建立了基于等值面的界面重构算法,Level Set函数通过几何迭代方法进行计算并用于计算法向量。通过溃坝问题的求解,验证了该方法的有效性,并将其应用于波浪在地形上传播破碎问题的求解,与实验结果进行对比,说明该方法可以很好地模拟复杂地形上的波浪传播破碎问题。     

基于γ界面捕捉模型的近场水下爆炸数值模拟（英文）

随着对水下爆炸现象研究的逐步深入,近场水下爆炸的数值模拟研究越来越受到重视。近场水下爆炸数值模拟当中的主要难点在于多相流运动以及界面捕捉方法的研究。文章提出一种较为稳定的近场水下爆炸数值模拟方法,其包含了五阶WENO重构以及HLLC近似黎曼求解器的格式,对于多相流界面的捕捉方法基于γ模型。文中的求解格式通过了一维激波管问题以及二维轴对称问题的验证,计算结果与理论解和实验结果吻合较好。在此基础上将该方法推广到近场水下爆炸过程中冲击波传播以及近水面爆炸现象的模拟,模拟结果较为满意。该文的研究方法能够为后续的近场水下爆炸过程中的空泡以及水射流的研究提供指导。     

基于CFD软件的三维船体粘性流的数值模拟

利用商业CFD计算软件FLUENT,在不考虑自由液面情况下,对某低速肥大型船进行粘性流数值模拟,得到在不同傅氏数下的船体摩擦阻力系数及船体周围流场信息,通过把数值模拟计算的摩擦阻力系数和经验公式相比较,验证了FLUENT用于预报三维船体摩擦阻力的有效性,所得到的船体周围的流场信息可以为线型的优化提供一定的参考数据。     

循环载荷下考虑累积塑性影响的船体板CTOD理论及数值模拟研究（英文）

裂纹尖端张开位移(CTOD)是研究大范围屈服的低周疲劳破坏的重要参数之一,其值可反映结构材料抵抗低周疲劳裂纹形成和扩展的能力,是评估结构材料韧性的重要参量以及分析低周疲劳破坏引起裂纹扩展的主要控制参量。文章基于弹塑性断裂力学理论,从循环J积分着手,以裂纹尖端累积塑性应变为重要参量,建立循环载荷下船体板CTOD理论模型,并在有限元模拟中分析了应力比、应力幅等相关因素影响。将本模型结果与有限元计算结果进行了比较,发现结果吻合良好。结果表明:在考虑累积塑性影响下,该模型能较好地反映在循环载荷下船体板CTOD的变化规律,同时也为正确评估循环载荷下船体板低周疲劳破坏与累积塑性破坏两种破坏模式耦合作用的总体断裂破坏提供了途径。     

不规则波浪的数值模拟

优良的波浪环境条件是研究非线性波浪和浮式结构物相互作用问题的基础.文章在数值波浪水池中对不规则波浪进行了数值模拟,造波通过摇板的运动实现,消波通过在水池后段设置消波区实现,自由液面由VOF方法捕捉.对计算所得的波浪时历进行谱分析并将所得谱与理论谱进行了比较,吻合良好.     

波浪中航行两船模池壁干扰效应的数值研究（英文）

对规则波中顶浪并行航行的两船模,基于频域移动脉动源格林函数建立了有效表达池壁效应的三维数学模型,该模型采用分布源积分方法求解近距航行两船模的波浪作用力和运动响应,并利用镜像原理将水池格林函数表示为开阔水域的格林函数和由镜像点源组成的无穷级数。分析移动脉动源格林函数的远场传播模态及其特性可知,当τ0.272(τ为斯特劳哈尔数)时各传播波模态均不在点源的上游出现,故此时点源波系的影响范围可由环形—扇形波的半楔角确定,在此基础上计及船模辐射—绕射波的池壁反射作用对自身和另一船模的干扰,依据船型要素、水池宽度和两船相对位置,采用六个几何临界半楔角表征船体的辐射—绕射波,提出了并行航行两船模的池壁效应判别方法。数值研究表明:不同镜像次数下水池格林函数的数值差异主要体现在距船艏较远处,在兼顾计算精度与效率的原则下可选取有限项级数的水池格林函数作为积分内核,而池壁效应对近距航行两船运动响应的影响主要体现在长波区。