NUMERICAL PREDICTION OF SUBMARINE HYDRODYNAMIC COEFFICIENTS USING CFD SIMULATION

The submarine Hydrodynamic coefficients are predicted by numerical simulations.Steady and unsteady Reynolds Averaged Navier-Stokes(RANS) simulations are carried out to numerically simulate the oblique towing experiment and the Planar Motion Mechanism(PMM) experiment performed on the SUBOFF submarine model.The dynamic mesh method is adopted to simulate the maneuvering motions of pure heaving,pure swaying,pure pitching and pure yawing.The hydrodynamic forces and moments acting on the maneuvering submarine are obtained.Consequently,by analyzing these results,the hydrodynamic coefficients of the submarine maneuvering motions can be determined.The computational results are verified by comparison with experimental data,which show that this method can be used to estimate the hydrodynamic derivatives of a fully appended submarine.     

Numerical estimation of bank-propeller-hull interaction effect on ship manoeuvring using CFD method

This paper presents a numerical investigation of ship manoeuvring under the combined effect of bank and propeller. The incompressible turbulent flow with free surface around the self-propelled hull form is simulated using a commercial CFD software(ANSYS-FLUENT). In order to estimate the influence of the bank-propeller effect on the hydrodynamic forces acting on the ship, volume forces representing the propeller are added to Navier-Stokes equations. The numerical simulations are carried out using the equivalent of experiment conditions. The validation of the CFD model is performed by comparing the numerical results to the available experimental data. For this investigation, the impact of Ship-Bank distance and ship speed on the bank effect are tested with and without propeller. An additional parameter concerning the advance ratio of the propeller is also tested.     

基于重叠网格技术数值模拟船舶纯摇首运动

该文采用基于非定常RANS方程的黏性数值模拟方法,对标准船模DTMB5512裸船体在平面运动机构(PMM)控制作用下的纯摇首运动进行了数值模拟。文中数值计算采用基于开源CFD工具包Open FOAM和重叠网格技术开发的多功能水动力学求解器naoe-FOAM-SJTU。根据SIMMAN2014提供的标准算例,对同一运动频率下,在Fn=0.28工况下的3种不同运动幅值的纯摇首运动进行了数值计算,得出了船舶不同工况下的阻力、侧向力和转首力矩的历时曲线。并且根据操纵性数学模型(MMG)推导出相应的水动力导数值,所有计算结果同模型试验数据吻合较好,验证了采用当前处理方法数值求解纯摇首运动的可靠性。     

高速船甲板上浪的水体流动与冲击

针对高速船舶的甲板上浪,综合考虑船体外飘、船艏波面升高、波浪传播与船体运动等相关因素的影响,采用势流理论计算和CFD技术相结合的方法,建立了计入整船运动的船艏上浪计算模型,计算模拟并分析了甲板上水体流动形态及其对甲板结构的冲击作用。计算中船体运动通过势流理论给定,势流理论计算通过用户自定义函数嵌入Fluent软件,并通过二次开发实现了上浪现象的模拟。文中就迎浪状态下高速行驶的S175船甲板上浪进行了三维数值模拟研究,结果表明甲板上水体的流动及其对结构物的冲击载荷与试验吻合良好,该方法能够对上浪机理给出较为清晰的描述,能够分析预报甲板上浪对浮体结构物的破坏作用,为工程应用提供了良好的方法和途径。     

基于CFD方法的船/桨/舵干扰数值模拟

船/桨/舵相互干扰研究在传统船型优化设计和新船型的开发中具有重要意义。应用计算流体力学(CFD)方法对带桨的KCS集装箱船及带桨和舵的KVLCC2油船非稳态粘流场进行了数值模拟,其中船桨舵干扰计算分别采用动量源法、MRF法和滑移网格法,分析研究了各方法及其结果的异同。研究表明不同模拟计算方法均能合理预报出船/桨/舵相互干扰相互作用下速度场和压力场分布等详细流场信息,可用于计算船体阻力、表面压力和桨盘面伴流等。通过这种详细的数值模拟研究,可以更好地理解复杂流动干扰现象。     

浅窄航道船舶线性位置导数估算

本文采用简化的一元流分析方法，引入非均匀流的概念对浅水中的细长体理论作了修正，计算了船舶在浅窄航道中斜航时的线性位置导数，计算中对粘性影响作了适当修正。计算结果与试验值吻合较好，且本法简便，便于在船舶设计初始阶段对浅窄航道船舶线性位置导数的估算。     

URANS simulations of ship motion responses in long-crest irregular waves

In this paper, numerical prediction of ship motion responses in long-crest irregular waves by the URANS-VOF method is presented. A white noise spectrum is applied to generate the incoming waves to evaluate the motion responses. The procedure can replace a decade of simulations in regular wave with one single run to obtain a complete curve of linear motion response, considerably reducing computation time. A correction procedure is employed to adjust the wave generation signal based on the wave spectrum and achieves fairly better results in the wave tank. Three ship models with five wave conditions are introduced to validate the method. The computations in this paper are completed by using the solver naoe-FOAM-SJTU, a solver developed for ship and ocean engineering based on the open source code OpenFOAM. The computational motion responses by the irregular wave procedure are compared with the results by regular wave, experiments and strip theory. Transfer functions by irregular wave closely agree with the data obtained in the regular waves, showing negligible difference. The comparison between computational results and experiments also show good agreements. The results better predicted by CFD method than strip theories indicate that this method can compensate for the inaccuracy of the strip theories. The results confirm that the irregular wave procedure is a promising method for the accurate prediction of motion responses with less accuracy loss and higher efficiency compared with the regular wave procedure.     

Direct calculation method of roll damping based on three-dimensional CFD approach

The effect of roll damping on the prediction of a ship's motion is significant. A method based on the 3-D CFD approach for calculating the roll damping of a ship is proposed in this paper. The free decay experiments of 4 different types of ships at zero velocity are carried out. The roll damping coefficients are calculated and compared with the experiment results, with a good agreement. It is shown that the method adopted in this paper could be used to simulate the free rolling of a ship in the calm water at zero velocity very well and with good, stable accuracy for the prediction of the roll damping, and also with good applicability. This method may be further developed for the prediction of a full scale ship in the future.     

SIMULATION OF TANK SLOSHING BASED ON OPENFOAM AND COUPLING WITH SHIP MOTIONS IN TIME DOMAIN

Tank sloshing in ship cargo is excited by ship motions, which induces impact load on tank wall and then affects the ship motion. Wave forces acting on ship hull and the retardation function are solved by using three-dimensional frequency domain theory and an impulse response function method based on the potential flow theory, and global ship motion is examined coupling with nonlinear tank sloshing which is simulated by viscous flow theory. Based on the open source Computational Fluid Dynamics (CFD) development platform Open Field Operation and Manipulation (OpenFOAM), numerical calculation of ship motion coupled with tank sloshing is achieved and the corresponding numerical simulation and validation are carried out. With this method, the interactions of wave, ship body and tank sloshing are completely taken into consideration. This method has quite high efficiency for it takes advantage of potential flow theory for outer flow field and viscous flow theory for inside tank sloshing respectively. The numerical and experimental results of the ship motion agree well with each other.     

喷水推进系统在浅水高速工况下适应性问题的数值分析

针对单级喷水推进系统在浅水高速工况下适应性差的问题,提出了双级对转泵喷水推进方式。采用高质量结构化网格对数值模拟系统的各部件进行区域离散,利用不可压缩RANS方程模拟出喷水推进装置内复杂的流动情况。设计条件下的计算结果与理论推导结果的吻合性证实了数值方法的合理性。比较设计工况下的流量、喷水泵叶片的空化范围,得出了在输入功率相同的情况下,相比较单级喷水推进系统,双级喷水推进方式可以提高浅水作业能力的结论,并进一步探索最小航行深度。     

Study of a Compressed Air Vessel for Controlling the Pressure Surge in Water Networks: CFD and Experimental Analysis

Air chambers show good ability in controlling the pressure surge from a water hammer (WH) phenomenon. To simulate an air chamber and study the behavior of air inside it, a compressed air vessel (CAV) is considered in a pressurized system. The current work consists of experimental tests and one-dimensional (1D) and two-dimensional (2D) computational fluid dynamics (CFD) simulations for an air pocket within a CAV in the case of rapid pressurization and the occurrence of WH in a pressurized system. The pressure variations create vorticity and turbulence with oscillating behaviors, but the available 1D models are unable to simulate those phenomena adequately. Therefore, by using the measured data, proper CFD analysis is conducted considering the effect of the wall, y ⁺ , mesh size, turbulence, and the wall treatment method to better understand the behavior of the system. Results of the CFD simulation show that realizable k-ε turbulence model, when coupled with the enhanced wall treatment (EWT) method, works adequately for modeling the pressure oscillation. The volume of fluid (VOF) model and the piecewise linear interface calculation (PLIC) method have presented good ability in the prediction of the air-water interface.     

An overview of simulation-based hydrodynamic design of ship hull forms

This review paper presents an overview of simulation-based hydrodynamic design optimization of ship hull forms. A computational tool that is aimed to accomplishing early-stage simulation-based design in terms of hydrodynamic performance is discussed in detail. The main components of this computational tool consist of a hydrodynamic module, a hull surface modeling module, and an optimization module. The hydrodynamic module includes both design-oriented simple CFD tools and high-fidelity CFD tools. These integrated CFD tools are used for evaluating hydrodynamic performances at different design stages. The hull surface modeling module includes various techniques for ship hull surface representation and modification. This module is used to automatically produce hull forms or modify existing hull forms in terms of hydrodynamic performance and design constraints. The optimization module includes various optimization algorithms and surrogate models, which are used to determine optimal designs in terms of given hydrodynamic performance. As an illustration of the computational tool, a Series 60 hull is optimized for reduced drag using three different modification strategies to outline the specific procedure for conducting simulation-based hydrodynamic design of ship hull forms using the present tool. Numerical results show that the present tool is well suited for the hull form design optimization at early design stage because it can produce effective optimal designs within a short period of time.     

基于IDDES方法的模型尺度和实尺度VLCC阻力预报与流场分析

随着CFD技术的发展和计算机运算能力的提高,CFD在船舶设计中发挥着越来越重要的作用。目前CFD对于船舶阻力的计算基本集中在模型尺度,一方面因为实尺度缺乏相关的实验数据,导致缺乏对实尺度高雷诺数下近壁面湍流模型和壁面函数的探索;另一方面也是因为在实尺度计算中,非定常特征更加明显,数值计算的复杂性会大大增加,传统的RANS方法处理起来较为困难。该文应用基于OpenFOAM开发的船舶与海洋工程水动力求解器naoe-FOAMSJTU,应用改进的DES模型—IDDES,采用CFD方法同时对模型尺度和实尺度的32万吨VLCC进行阻力预报,并分别与RANS的计算结果、实验结果/三因次换算结果进行比较分析。在实尺度计算中考虑到表面粗糙度的影响,采用带粗糙度补贴的壁面函数进行近壁面处理。该文探讨了采用IDDES方法在船模和实船阻力预报中的可行性,同时也对实尺度和模型尺度下的流场进行了讨论与对比分析。     

一种基于CFD的船舶总阻力预报方法

根据船体阻力成因和预报方法的讨论分析,提出了基于CFD理论计算进行实船阻力预报的一种新方法,基于黏性流理论对叠模求解以获得船体黏性阻力,基于理想流体理论直接求解Euler方程获得船体兴波阻力。通过对系列60船型与KCS船型在各航速下船体阻力计算和试验结果的比较表明,该方法计算速度快,经济性好,预报精度满足工程需要,有较强的工程实用性。     

Hydrodynamic interaction.among hull,rudder and bank for a ship sailing along a bank in restricted waters

By applying a CFD tool to solve the RANS equations, the viscous flow around a model of hull-rudder system towed along a bank in shallow water is numerically simulated. Hydrodynamic forces and moments acting on the ship are calculated for different ship-bank distances and rudder angles. A container ship, KCS, is taken as an example for the numerical study. Under the assumption of low ship speed, the influences of free surface elevation and ship squat are assumed to be negligible. Based on the calculation results, the hydrodynamic interaction among the hull, rudder and bank is analyzed.     

A one-dimensional polynomial chaos method in CFD-Based uncertainty quantification for ship hydrodynamic performance＊

A one-dimensional non-intrusive Polynomial Chaos (PC) method is applied in Uncertainty Quantification (UQ) studies for CFD-based ship performances simulations. The uncertainty properties of Expected Va...     

Numerical simulation of rotating arm test for prediction of submarine rotary derivatives

The numerical method is used for predicting the rotary-based hydrodynamic coefficients of a submarine. Unsteady RANS simulations are carried out to numerically simulate the rotating arm test performed on the SUBOFF submarine model. The dynamic mesh method is adopted to simulate the rotary motions. From the hydrodynamic forces and moments acting on the submarine at different angular velocities, the rotary derivatives of the submarine can be derived. The computational results agree well with the experimental data. The interaction between the sail tip vortex and the cross flow in the hull boundary layer is discussed, and it is shown that the interaction leads to the "out-of-plane" loads acting on the submarine.     

浅水深对160kDWT FPSO水动力系数的影响

FPSO系泊于浅水中时,由于安全性问题,浅水深对其运动与载荷的影响正逐渐引起重视。本文利用三维线性势流理论和源汇分布法研究一艘160kDWTFPSO在浅水中的辐射问题,对不同水深下FPSO的水动力系数进行了数值计算。结果表明,浅水深时,一方面,3个垂向运动(垂荡、横摇和纵摇)附加质量有显著增加,特别是水深吃水比减小到1.3后,更是以几何倍数增长;另一方面,6自由度运动的阻尼系数均有明显增加,特别是横摇阻尼系数,随着水深吃水比的减小而成倍数增长。由于浅水中水动力系数的显著增加,FPSO垂向运动幅度也必将较大地趋于缓和,从而不易导致浅水FPSO碰底现象的发生。     

基于相空间重构技术的舰船摇荡极短期预报

舰船运动受各种非线性因素影响严重,且舰船自身6个自由度的运动间存在相互耦合,在很多情况下表现为混沌。本文提出了基于相空间重构技术的舰船摇荡极短期预报模型,包括加权一阶局域法多步预报模型和RBF神经网络局域法多步预报模型。仿真表明,两种模型均能有效预报舰船摇荡极短期运动。     

Modelling the Influence of Aquatic Vegetation on the Hydrodynamics of an Alternative Bank Protection Measure in a Navigable Waterway

Computational fluid dynamics (CFD) has become an effective tool for assessing hydrodynamics in complex environments. This paper reports on a CFD study of navigation‐induced flows in a shallow, wave‐protected, littoral habitat of the urban Spree River. It was constructed as a rehabilitation structure for aquatic organisms and subject to abundant growth of aquatic and riparian vegetation. This study aims to quantify the hydrodynamics induced by vessel movements and its consequences for water exchange and lateral connectivity between the habitat and the main channel with three representative, natural densities of aquatic plants. The simulations revealed both high efficiency of the rehabilitation structure in reducing hydrodynamic forces in the littoral and a superimposed reduction of hydrodynamic forces, and increase of flushing time with increased plant cover. Higher vegetation density resulted in lower wave propagation and lower connectivity of the rehabilitation structure with the fairway. Thus, natural succession of aquatic vegetation in the shallow habitats leads to increasing isolation and finally to terrestrialization. Maintaining the functionality of the rehabilitation structure as habitat for other aquatic organisms requires either plant removal or preferably adaptive modification, e.g. by successively increasing the openings to the main channel and letting the plants take over the protective function of the technical facilities. The developed CFD model helps to find hydrodynamically optimized solutions and to support decision‐making process for maintaining littoral refuges for plants and weak swimming organisms in navigable waterways. Copyright © 2016 John Wiley & Sons, Ltd.