二维甲板上浪问题数值模拟研究的新方法

甲板上浪问题一直是强非线性问题研究领域的热点,它是造成海洋浮式结构物损坏的重要因素.该文完整的阐述了用于研究甲板上浪问题的数值模拟解决方案,并对二维浮动物体的运动响应、甲板上浪进行了考察.模拟在二维数值波浪水池中完成,入射波由冲箱运动生成,水池远端采用海绵层吸收反射波浪,自由液面采用VOF方法捕捉,物体的运动为与波浪的耦合运动.最后将模拟得到的运动响应与试验进行了对比,同时对上浪载荷也进行了分析.     

基于数值波浪水池的波浪中船舶水动力计算

此文基于CFD方法建立了数值波浪水池,模拟了波浪的生成和传播,并对规则波浪中航行船舶的水动力进行了计算研究.文中讨论了适合船舶在波浪中航行的数值模拟的波浪环境表达,验证了参考坐标系下数值波浪水池中波浪生成和传播及消波等,模拟计算了多个航速项浪与斜浪航行的约束Wigley-Ⅲ船模的水动力以及项浪中航行船舶的波浪增阻.计算结果与DUT(Delft University of Technology)的试验数据及势流理论的结果吻合良好.对比和研究表明,本文的方法能细致描述船舶周围的流场,且比实验更易实现和控制,在船舶的水动力性能分析和运动预报等方面具有广阔的应用前景.     

舰船在波浪中补给的运动性能研究

本文介绍舰船在波浪中补给时的运动响应理论计算方法，运用三维势流理论计算两船的水动力相互作用和波浪扰动力。根据两船的相对运动进行两船补给时的相碰概率预报。预报结果与水池船模试验进行了初步验证，吻合较好。     

基于神经网络的船体剖面水动力机器学习与验证

该文以船体剖面水动力为研究对象,梳理了二维剖面几何特征和频率等与水动力关联关系。基于FFD方法生成系列船体剖面,并通过格林函数法计算出水动力系数形成相应的数据库。建立两种不同参数描述的几何剖面和水动力学习模型,采用神经网络建模训练获得了两种剖面水动力预报模型,对船体剖面横荡、垂荡、横摇和横荡-横摇四个模态的附加质量与阻尼系数进行预报,并将模型预测值与真实值、以及通过切片理论获得的全船垂荡水动力系数进行比较验证。研究表明,该模型能高效预报船体水动力,精度较高泛化能力强,为不同参数模型预报船舶水动力,为船舶设计的不同阶段提供了手段。     

规则波中弧形返浪墙的非线性水动力载荷数值模拟

运用基于FLUENT软件平台的二维数值波浪水槽,采用流体体积(VOF)方法处理波浪自由面,应用"解析松弛"方法实现了数值造波-消波。模拟规则波下不同返浪墙断面形式情况下的流场和水动力。应用直墙驻波理论解和物理模型试验结果验证了数值波浪水槽的可行性。比较波浪力的数值模拟与物理模型试验结果可以发现,水动力冲量的均方差小于水动力最大值的均方差,且水动力冲量的误差也小于水动力最大值,说明以冲量作为特征量能更好地描述水动力载荷的变化。在给定堤顶超高的条件下,不同堤脚超高和弧形返浪墙高度的组合对越浪量有明显影响:低弧趾超高和大半径弧面组合有利于降低越浪量,但水动力载荷也较大;高弧趾超高和小半径弧面组合越浪量较大。     

强迫运动柱体附加质量与阻尼系数的CFD计算

基于CFD的RANS方法,计入粘性和自由面的影响,模拟船舶剖面柱体的单自由度强迫摇荡运动,得到横荡、升沉、横摇及横荡对横摇的附加质量与阻尼系数,并与试验进行了比较,符合良好。两种不同网格进行试算比较表明:整体域移动网格的稳定性和计算效率要优于局部重划的非结构网格。最后,针对加装了舭龙骨的柱体进行强迫横摇运动模拟,求解大幅度横摇下的横摇阻尼,分析了舭龙骨尺度对横摇阻尼的影响。各种计算表明:无论是线性还是大幅度非线性运动,粘性CFD方法能有效地预报耐波性中各种运动模态的的水动力系数。     

二维半理论的船舶运动及波浪增阻计算适用性研究

波浪增阻是计算船舶能效指标中气象因子w_f的关键。该文基于二维半理论(又称高速细长体理论)实现了船舶运动响应预报并采用辐射能量法开发了波阻增加计算程序。通过对不同航速下Wigley III和S175船的水动力、运动和波浪增阻的细致计算与分析,并与切片理论和三维航速修正法求解的结果及试验值进行了比较,验证该方法的可靠性和适用性。研究表明二维半理论适用于船舶运动与波浪增阻的计算,相较于工程上常用的切片理论和航速修正方法,计算结果准确性适用性更高,为船舶波阻增加预报提供了快速有效的手段。     

浅水FPSO舷侧波浪数值模拟

单点系泊FPSO具有风标效应,因此船首迎浪时的甲板上浪问题广受关注,然而在非共线海况下斜向迎浪时,会存在舷侧甲板上浪现象.基于FLUENT软件,建立三维数值波浪水池,对浅水中的FPSO在首迎浪、首斜浪时舷侧附近的波浪变形和波浪爬升现象进行数值模拟,对舷侧甲板上浪特性进行研究分析.结果表明,首迎浪时舷侧波浪爬升和甲板上浪不明显,首斜浪时波浪爬升主要集中在船舯附近,舷侧波浪受到反射波叠加的影响,波浪水体形成堆积和爬升,导致舷侧比船首更容易发生甲板上浪.     

时域格林函数法求解有航速船舶运动问题

准确预报波浪诱导运动和载荷响应在船舶设计中起着重要作用。该文基于三维时域Green函数法,应用改进的精细积分算法实现Green函数的精确数值计算,在此基础上,自主开发了船舶以定常航速在规则波中运动的三维时域数值模拟程序。为了验证理论方法及算法程序的可靠性,对Wigley型船在迎浪规则波中航行时的波浪力和运动响应进行了数值模拟,通过与试验值及频域计算结果的对比发现,三维时域数值模拟程序是稳定且可靠的,可用于解决有航速船舶在波浪中的微幅摇荡运动问题。     

深海采矿船减摇水舱减摇效果评估

船舶在海上航行或作业时最容易发生横摇,在各种航速下减摇水舱都能减小船舶横摇运动,因此越来越多的船舶使用减摇水舱减小横摇.在此背景下,针对一艘深海采矿船,开展减摇水舱减摇效果评估计算.首先在规则波中进行频域分析,基于受力平衡原理,得到船舶-减摇水舱耦合运动方程.在频域内求解耦合运动方程,得到不同激励下的船舶横摇响应.定性...     

A TIME-DOMAIN METHOD TO PREDICT SHIP MOTIONS IN OBLIQUE SEAS AT FORWARD SPEEDS

Time-domain analysis is used to predict wave loading and motion responses for a ship travelling at a constant speed in regular oblique waves.The combined diffraction and radiation perturbations,caused by the steady forward speed of the ship and her motions,are considered as a distribution of normal velocities on the wetted hull surface.The ship-hull boundary condition is exactly fulfilled by expressing the fluid normal velocities as a finite series in terms of the body geometry and the incident wave potential.As far as the authors are aware,no similar work is published todate. The new theory is applied to predict forces and motions at forward speed for a Wigley ship-hull in head waves and a catamaran-ferry in oblique waves.Predictions are compared with published theoretical and experimental results for the Wigley ship-hull,and the comparison is good.For the catamaran,a self-propelled model is built and tested in the large towing tank and seakeeping basin of the China Ship Scientific Research Centre,Wuxi     

NUMERICAL SIMULATIONS OF WAVE-INDUCED SHIP MOTIONS IN TIME DOMAIN BY A RANKINE PANEL METHOD

A time domain prediction of wave-induced ship motions by a Rankine panel method is investigated. Linear boundary conditions on free surface and mean wetted body surface are adopted, while the numerical damping method is used for the radiation conditions. The motions of two ships in regular head waves are computed by the present method. The related numerical results are compared with the experiment data and those from linear strip theory. The comparison shows satisfactory agreements for pitch and heave transfer functions.     

Numerical simulation and comparison of potential flow and viscous fluid models in near trapping of narrow gaps

Numerical simulation results of fluid oscillation in narrow gaps subjected to incident water waves are presented in this paper. Both viscous fluid model and potential flow model with artificial viscous damping are employed to investigate wave motions in a single narrow gap separated by twin bodies and double narrow gaps formed by three identical bodies. Variation of wave heights in the narrow gaps with incident wave frequency is compared with experimental data available in literatures. The numerical results demonstrate that both the viscous fluid model and the potential flow model are able to predict the resonant frequency reasonably well. However the conventional potential flow model (without introducing the artificial viscous damping) significantly over-predicts the wave height in narrow gaps around the resonant frequency. The potential flow model with artificial damping predicts resonant wave heights well with a properly tuned (or calibrated) damping coefficient. The horizontal wave force on the individual body is also examined in this work. It is found that a properly calibrated damping coefficient is also very important for estimating the horizontal wave forces on the structures. A damping coefficient of 0.4 in the potential flow model is found to result in satisfactory predictions of wave heights in the narrow gaps and the horizontal hydrodynamic force for the cases considered in this work.

     

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.     

Numerical study of roll motion of a 2-D floating structure in viscous flow

In the present study,an open source CFD tool,Open FOAM has been extended and applied to investigate roll motion of a 2-D rectangular barge induced by nonlinear regular waves in viscous flow.Comparisons of the present Open FOAM results with published potential-flow solutions and experimental data have indicated that the newly extended Open FOAM model is very capable of accurate modelling of wave interaction with freely rolling structures.The wave-induced roll motions,hydrodynamic forces on the barge,velocities and vorticity fields in the vicinity of the structure in the presence of waves have been investigated to reveal the real physics involved in the wave induced roll motion of a 2-D floating structure.Parametric analysis has been carried out to examine the effect of structure dimension and body draft on the roll motion.     

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.     

船舶在波浪中大幅度运动的工程算法

本文基于切片理论，计入船体运动时湿表面及其对船体流体动力性能的影响，提出了一种船舶在波浪中大幅度运动的工程估算方法，并通过对一系列６０船型计算，考虑了船舶在迎流中大幅度运动昱的运动特性、与波面的相对运动和船体瞬时受力。这一方法简单实用，对船舶方案设计有积极的意义。     

THE SECOND-ORDER HYDROELASTIC ANALYSIS OF A SWATH SHIP MOVING IN LARGE-AMPLITUDE WAVES

1. INTRODUCTION During the last two decades, the linear three-dimensional hydroelasticity theory[1,2] has been extensively applied to a wide range of fluid-structure interaction problems in the field of naval architecture and marine engineering[3-5]. Thes…     

船舶在长峰和短峰不规则波中运动的三维时域数值模拟

船舶在真实海况中的航行性能越来越受到重视。此文在规则波中航行船舶运动的时域预报方法的基础上,发展了长峰和短峰不规则波的数值模拟技术,建立了航行船舶在长峰和短峰不规则波中运动的三维时域数值模拟方法,并应用该方法对一条10万吨油轮进行了数值模拟研究,计算了该油轮在长峰不规则波中的运动响应。试验和计算结果表明此文方法有一定的精度。最后还对该油轮进行了短峰不规则波中运动的数值模拟。长峰和短峰不规则波中的计算结果比较表明短峰不规则波对该油轮运动可产生较大影响。