An Irregular Wave Generating Approach Based on naoe-FOAM-SJTU Solver

In this paper,a wave generating approach for long-crest irregular waves in a numerical tank by our in-house solver naoe-FOAM-SJTU is presented.The naoe-FOAM-SJTU solver is developed using an open source tool kit,Open FOAM.Reynolds-averaged Navier？Stokes（RANS） equations are chosen as governing equations and the volume of fluid（VOF） is employed to capture the two phases interface.Incoming wave group is generated by imposing the boundary conditions of the tank inlet.A spectrum based correction procedure is developed to make the measured spectrum approaching to the target spectrum.This procedure can automatically adjust the wave generation signal based on the measured wave elevation by wave height probe in numerical wave tank.After 3 to 4 iterations,the measured spectrum agrees well with the target one.In order to validate this method,several wave spectra are chosen and validated in the numerical wave tank,with comparison between the final measured and target spectra.In order to investigate a practical situation,a modified Wigley hull is placed in the wave tank with incoming irregular waves.The wave-induced heave and pitch motions are treated by Fourier analysis to obtain motion responses,showing good agreements with the measurements.

CFD Investigations of Ship Maneuvering in Waves Using naoe-FOAM-SJTU Solver

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.

基于naoe-FOAM-SJTU求解器构建三维数值波浪水池

利用自主开发的naoe-FOAM-SJTU求解器构建三维数值波浪水池.naoe-FOAM-SJTU求解器是基于开源程序库OpenFOAM开发的两相流求解器.它以Navier-Stokes方程为控制方程,采用VOF方法捕捉自由面.所构建的数值水池具有完整的造波系统、消波系统以及波高探测系统,可以实现不同类型波浪的模拟.对所构建的三维数值波浪水池的原理和过程进行介绍,对小幅线性波、Stokes二阶波、斜向波以及不规则波进行了数值模拟,并将数值结果与理论解进行了比较,结果吻合的很好,说明基于naoe-FOAM-SJTU求解器构建的三维数值波浪水池具有较好的精度,可以为海洋工程流体问题的数值模拟提供有效的波浪条件.

Development of naoe-FOAM-SJTU solver based on OpenFOAM for marine hydrodynamics

A CFD solver naoe-FOAM-SJTU (The abbreviation naoe stands for naval architecture and ocean engineering) is developed based on the open source platform OpenFOAM with the purpose of simulating various marine hydrodynamic problems.In the present paper,self-developed modules,i.e.,wave generation and absorption,6 degrees of freedom motion,mooring system,dynamic overset grid,fluid-structure interaction,unsteady actuator line model,implemented on the open source platform OpenFOAM are introduced to illustrate the development of the marine hydrodynamics CFD solver.Furthermore,extensive simulations of marine hydrodynamic problems using the developed modules are conducted and validated by available experimental data.It has been proved that the CFD solver naoe-FOAM-SJTU is suitable and reliable in predicting the complex viscous flow around ship and offshore structures.Efficiency and accuracy need to be focused in the future development of the present CFD solver.

CFD数值模拟船舶在波浪中的回转操纵运动

[目的]船舶回转操纵运动能够反映出船舶的回转特性,与船舶的航行安全密切相关。[方法]为此,采用基于重叠网格技术的CFD求解器naoe-FOAM-SJTU,对标准船模ONRT在波浪中自由回转操纵运动进行直接数值模拟。运用动态重叠网格技术求解船、桨、舵系统复杂运动,计算中,螺旋桨转速对应于静水中的船模自航点进行35°转舵,实现自由回转船舶操纵运动。通过全粘性流场的整体求解,给出波浪中自由回转操纵运动中船舶六自由度运动、螺旋桨和舵的水动力载荷变化,以及波浪中船舶的回转圈特征参数,并与同试验结果进行对比。通过数值计算得到精细的流场信息,分析波浪对船舶自由回转操纵运动的影响。[结果]数值预报得到的船舶运动轨迹、回转圈参数与试验值吻合较好,证明naoe-FOAM-SJTU求解器对于波浪中船—桨—舵相互作用下的船舶自由回转操纵运动数值预报的适用性和可靠性。[结论]船舶回转操纵运动的数值模拟,可为回转性能的评估提供有效的前期评估手段。

基于重叠网格的豪华邮轮多工况耐波性数值分析

[目的]在豪华邮轮的设计阶段,为了节约成本,需采用流体动力学(CFD)方法对设计中的邮轮进行耐波性能预报。[方法]以一艘大型豪华邮轮为研究对象,使用自主开发的船舶水动力学CFD求解器naoeFOAM-SJTU对模型尺度下的豪华邮轮进行耐波性数值模拟。耐波性的模拟在造波方式上采用速度入口输入式造波,对不同波高和不同浪向下的邮轮运动进行预报和总结。[结果]评估发现,目前设计得到的邮轮船模在最大航速、波高为0.0625,0.1和0.15 m工况下基本符合船舶舒适性要求;在设计航速下、波高为0.225 m、迎浪工况下符合船舶安全性要求。[结论]在完成计算的工况下,邮轮的船型设计符合船舶耐波性评估标准中的安全标准和舒适性标准。

岛礁附近浮式平台运动响应特性数值分析

利用基于开源平台Open FOAM自主开发的船舶与海洋工程水动力性能求解器naoe-FOAM-SJTU,数值模拟了近岛礁环境下规则波的演化特性以及带有系泊系统的浮式平台在相应波浪作用下的水动力性能。对于平台的水动力性能的研究发现,仿真结果与试验结果在平台自由衰减运动固有周期及RAO(response amplitude operator)方面吻合良好。对于波浪在近岛礁地形下的演化现象的研究,分析了波浪演化不对称性特性的成因,并分别给出了不同参数下波浪在地形上爬升时演化的具体特性,对于波高变化及波浪演化的频率成分进行量化的探究。研究发现,波浪周期越大,波高变化越明显,演化的非线性现象越明显,且波浪随着传播距离的增大演化出的阶数也在增大。

基于重叠网格的船模停船操纵CFD数值模拟

[目的]随着国际航运业的迅速发展,港口和航道变得日益拥堵,研究大型船舶的停船性能对于航行安全至关重要。[方法]使用基于开源CFD软件OpenFOAM自主开发的naoe-FOAM-SJTU求解器,以及船舶六自由度运动和带桨多级物体运动求解模块,采用重叠网格技术,对带桨KVLCC2船模进行紧急停船操纵数值模拟。首先,控制螺旋桨转速,使船模达到稳定自航状态;然后,在某时刻控制螺旋桨倒转,以达到紧急停船操纵的目的。通过对全粘性流场的整体求解,给出船模自航以及停船操纵过程中的运动状态和细致流场信息,分析倒车效应产生的原因,并将数值预报结果与相关试验数据进行对比验证。[结果]结果显示,数值预报结果与相关试验数据间误差在5%以内,证明采用naoe-FOAM-SJTU求解器对船舶倒车停船操纵问题进行数值预报是可靠的。[结论]所采用的方法可针对停船问题为船舶前期设计和操纵方式的选择提供参考。

豪华邮轮多航速兴波阻力的船型优化

[目的]豪华邮轮的型线优化设计,除了要考虑美学视角因素,更重要的是还要考虑在整个航行阶段都能满足绿色节能、安全舒适等方面的要求,其中针对多航速船舶阻力性能优化进行豪华邮轮的船型设计尤为重要。[方法]首先,基于自主开发的船型优化设计软件OPTShip-SJTU,以某豪华邮轮为原始船型,通过自由变形方法,对船艏、水线、船艉等位置进行局部变形;然后,通过基于Neumann-Michell(NM)势流理论的兴波阻力求解器NMShip-SJTU进行阻力评估,并结合优化算法得到不同航速下兴波阻力系数最优的船型;最后,采用经过广泛验证的高精度黏流求解器naoe-FOAM-SJTU对优化船型做进一步验证。[结果]结果显示,基于NM势流理论的兴波阻力优化可以得到多航速下总阻力性能更优的船型,相比基于黏流CFD评估进行优化,更高效,且得到的优化船型在2个航速下总阻力分别降低了0.65%和0.98%。[结论]研究表明,基于数值模拟的船型优化设计流程可以应用于豪华邮轮的阻力性能优化。

基于CFD的带附体KCS船在波浪中的阻力及纵摇优化

[目的]为了降低船体在波浪中的阻力并改善其耐波性,将给船体添加合适的附体,如减摇鳍和压浪板。[方法]首先,对仅在船艏添加减摇鳍和在船艉添加压浪板,以及在船艏、船艉均添加附体的3艘船采用黏流求解器naoe-FOAM-SJTU进行数值计算,并将这3艘船各自的阻力及纵摇与未添加附体的KCS船体进行对比;然后,通过改变减摇鳍宽度与压浪板长度得到30艘样本船,且对各样本船进行特定工况下的水动力性能评估;最后,根据各变形船的数值计算结果建立Kriging模型,依据该模型,利用遗传算法达到关于船体总阻力及纵摇幅值的Pareto前沿,再从中选取3艘典型的优化变形船进一步予以验证分析。[结果]结果显示,优化后的KCS船体在一个遭遇周期内纵摇幅值和平均阻力最大降幅分别达12.7%和12.5%。[结论]研究表明,在迎浪工况下,通过为KCS船体添加压浪板和减摇鳍,以及针对附体主尺度的优化,可以有效降低其在波浪中的总阻力,优化纵摇幅值。

波流作用下海上固定式风机基础的水动力性能数值模拟

海上风机基础长期受到海流、波浪等环境荷载的交互作用,作业难度较大,研究风机基础的水动力特性可为其设计及应用提供重要参考.文中基于自主研发的船舶与海洋工程CFD求解器naoe-FOAM-SJTU,对一座固定式高桩承台风机基础在波流作用下的水动力参数进行数值模拟,研究了波浪与海流联合作用时,该风机基础在不同水深、不同波高条件下的受力、表面压力以及波面爬升现象,并与上海交通大学海洋工程国家重点实验室的模型试验结果进行比较,计算结果显示naoe-FOAM-SJTU求解器可以很好地模拟波流联合作用下风机基础的水动力特性.

振荡流中二维圆柱的涡激振动数值模拟

[目的]在实际油气采集过程中,风、浪和海流的联合作用会使得平台做周期性的振荡运动,并在与平台相连的立管和海水间产生振荡流。圆柱在振荡流中的泄涡特性与在均匀流中的泄涡特性存在明显区别。[方方法]采用基于OpenFOAM开源平台自主开发的具有重叠网格功能的CFD求解器naoe-FOAM-SJTU,对在静水中做周期性振荡运动的二维刚性圆柱涡激振动进行数值模拟。首先,进行KC=3时的网格收敛性验证;随后,对KC=12时的振荡流中二维圆柱开展数值模拟。[结果]通过数值模拟结果对比,发现圆柱的横向振动加剧了升力系数的变化,使得泄涡方向和圆柱表面漩涡分离点的位置发生了明显变化。[结论]所得研究成果可作为基于切片法的振荡流中细长柔性立管涡激振动数值研究的基础。

毂帽鳍水动力性能数值研究

[目的]随着绿色船舶理念的兴起,船舶水动力节能技术逐渐成为研究的热点。为降低船舶航行中的能耗,[方法]采用上海交通大学万德成教授课题组自主开发的naoe-FOAM-SJTU求解器,对毂帽鳍的水动力特性进行预报;为了更好地考察毂帽鳍与螺旋桨之间的相互影响,计算时分别考察毂帽鳍对桨叶、桨毂以及毂帽的影响。[结果]结果显示,桨毂和毂帽受毂帽鳍的影响较小,毂帽鳍可明显降低螺旋桨扭矩,但对推力的影响较小;进一步研究发现,雷诺数对毂帽鳍的节能特性具有较大影响且存在着一个临界值,当低于临界值时,随着雷诺数的增加,其节能效果会有较大的提升,而在达到临界值后,其节能效果基本保持不变,从侧面说明了在达到临界雷诺数的实尺度时,毂帽鳍会有更好的节能特性。[结论]研究充分证明采用naoe-FOAM-SJTU求解器研究毂帽鳍的节能特性可靠,可为更多种类的节能装置研究提供参考。

波流夹角对浅水导管架平台载荷影响的计算分析

应用船舶与海洋工程CFD求解器—naoe-FOAM-SJTU,对一浅海风机基础的导管架平台在复杂波流环境中所受的波流载荷进行了仿真分析.计算了极限海况下该导管架平台的总体受力,并对一些结构上较为危险点的抨击压力进行了监测,将仿真结果与课题组在上海交通大学海洋工程国家重点实验室开展的模型试验结果进行对比验证.改变流场中波浪与海流的传播方向夹角,分析不同的波流夹角情况对导管架平台的整体载荷、危险点的抨击压力以及波流场演化的影响.计算过程中可以给出波浪爬高、流场形态以及平台周边的涡脱落现象等详细信息,从而为平台局部强度、桩基冲蚀等问题提供指导.

风机基础TLP平台在波浪中运动性能的CFD数值分析

随着海上风能的开发向深水发展,支撑风机的载体平台越来越受到关注。在经济性与安全性、稳定性的多重要求下,张力腿平台(TLP)在海洋风能资源的开发中体现出了重要地位。采用基于开源平台OpenFOAM开发的计算流体动力学(CFD)水动力学求解器naoe-FOAM-SJTU对一座处于中等水深下的风机基础水下TLP(STLP)的运动响应进行了数值模拟与研究。文中使用弹簧锚链模型模拟STLP的垂向系泊锁链系统,模拟该平台在不同波浪环境下的运动响应情况。首先将STLP单自由度自由衰减CFD模拟结果与已有全耦合时域分析结果进行对比,验证了naoe-FOAM-SJTU求解器及使用弹簧模型模拟STLP系泊系统的准确性与可靠性。随后在考虑非线性波浪载荷的情况下研究极端海况下与一般作业海况下STLP的运动响应情况,计算工况中的风机基础所受弯矩及锚链受力情况,并详细展示流场、速度场信息,分析高阶波浪成分、不同海况等条件对于STLP运动性能的影响。研究结果表明,TLP在中等水深中具有良好的运动性能,naoe-FOAM-SJTU求解器可以有效模拟水中生产平台在波浪环境下的水动力问题,并可以对整个流场进行可视化展示与分析。

基于重叠网格方法浮筒涡激运动特性数值分析

浮筒被广泛应用在海洋工程中,研究浮筒的涡激运动对于减少其对海洋平台构件的疲劳损坏具有指导意义。传统的动网格方法在处理浮筒转动运动时会因网格变形过大导致计算不收敛,采用了重叠网格方法以解决这一问题。数值试验采用了基于开源工具包OpenFOAM自主开发的naoe-FOAM-SJTU求解器。分别进行了自由衰减数值试验和涡激运动数值试验。研究表明,随着折合速度的增加,浮筒的顺流向、横流向、垂荡和艏摇运动频率增加,且顺流向与垂荡频率相近,横流向与艏摇频率相近;其次,根据涡量场分布,表明浮筒前一时刻的泻涡会影响到浮筒之后时刻的周向涡量分布;最后,研究发现自由端对于浮筒尾流场泻涡有着显著影响,为将来探究减少浮筒涡激运动的方法提供指导。

全附体ONRT船模在波浪中自航的数值模拟（英文）

采用基于重叠网格技术的CFD方法数值研究了全附体ONRT船模在迎浪工况中自航的水动力特性.文中数值计算采用自主开发的面向船舶与海洋工程的CFD求解器naoe-FOAM-SJTU.自航计算中船体运动及螺旋桨转动等通过重叠网格技术完成,波浪环境则采用求解器中的三维数值造波和消波模块实现.计算中自航船模的螺旋桨转速通过静水自航数值计算得出,波浪工况计算采用东京2015 CFD会议中标准算例进行设置.数值计算结果,如船体运动、实时航速变化等,与试验数据进行了对比分析.此外,给出了数值预报的推力和扭矩系数,并且通过详细的流场信息来分析和解释了船模在波浪中自航过程中的水动力变化情况.数值预报结果同试验值吻合较好,说明采用当前结合重叠网格技术和CFD的数值方法可以很好地预报波浪中自航问题.

单点系泊FPSO在波浪中响应的数值计算分析

为了研究单点系泊FPSO在波浪中的响应,论文使用了万德成教授课题组基于开源CFD计算软件 OpenFOAM开发的船舶海洋工程求解器naoe-FOAM-SJTU.论文首先使用了wave2foam进行空场造波,对于 参考文献的规则波进行了模拟.随后对单点系泊的FPSO进行了自由衰减的计算,与试验势流结果进行对比, 验证了方法的可行性.然后论文计算了单点系泊的FPSO在迎浪条件下时域运动情况,并分析了 FPSO锚链 受力情况.此后,论文改变了锚链布置位置,并就两种锚链布置的锚链受力和船体运动情况进行了对比. 最后,论文验证了naoe-FOAM-SJTU求解器对于单点系泊的FPSO能够模拟其波浪响应情况,其结果达到了 较高精度.

Numerical Analysis of a Floating Offshore Wind Turbine by Coupled Aero-Hydrodynamic Simulation

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.

Numerical Prediction of Added Resistance and Vertical Ship Motions in Regular Head Waves

The numerical prediction of added resistance and vertical ship motions of one ITTC （Intemational Towing Tank Conference） S-175 containership in regular head waves by our own in-house unsteady RANS solver naoe-FOAM-SJTU is presented in this paper. The development of the solver naoe-FOAM-SJTU is based on the open source CFD tool, OpenFOAM. Numerical analysis is focused on the added resistance and vertical ship motions （heave and pitch motions） with four very different wavelengths （ 0.8Lpp 〈 2 〈 1.5L ） in regular head waves. Once the wavelength is near the length of the ship model, the responses of the resistance and ship motions become strongly influenced by nonlinear factors, as a result difficulties within simulations occur. In the paper, a comparison of the experimental results and the nonlinear strip theory was reviewed and based on the findings, the RANS simulations by the solver naoe-FOAM-SJTU were considered competent with the prediction of added resistance and vertical ship motions in a wide range of wave lengths.