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.     

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。     

三体船在斜浪规则波中运动响应预报方法研究

对于三体船在波浪中的水动力预报,航速效应和主体与片体间水动力干扰效应是水动力载荷合理预报的关键之处,需合理考虑.二维半势流理论可较为准确反映上述效应,已在三体船顶浪中垂向运动响应理论预报上获得了较为满意的结果.在此基础上,该文探讨了该方法在三体船斜浪中运动特别是横摇预报上的应用.为较准确获得三体船横摇运动时粘性阻尼贡献,采用三体船模静水中自由横摇衰减试验获得了自由横摇运动衰减曲线,并经能量法处理获得了船舶横摇阻尼系数.然后,结合二维半理论,获得了三体船运动数值解.数值解与斜浪规则波中运动响应模型试验结果符合较好,反映本文所采用的数值方法可较好地预测三体船斜浪中水动力载荷和运动,可用于三体船在波浪中耐波性评估.     

船体各种剖面的横摇阻尼与旋涡的形状

本文运用求解N－S方程的手法研究船体的横摇阻尼问题。利用作者原先提出的计算方法，数值模拟船体各种二维横剖面在横摇时的粘性流场。计算结果表明涡的位置与实验结果相当吻合，同时给出了横摇时各种横剖面的剪切应力与压力分布，比较各种不同剖面的旋涡形状可以发现，对于船舯附近的剖面，船体周围有两个涡，而对于船首或船尾附近的剖面，船体周围只有一个涡。利用这一数值模拟结果计算了包括粘性影响的横摇阻尼，计算结果表明横摇阻尼中压力成分比剪切应力成分要大。     

A study of hybrid prediction method for ship parametric rolling

The parametric rolling(PR) in the head or following waves has been considered as one of the main stability failure modes in the development of the 2nd generation Intact Stability criterion by the International Maritime Organization(IMO).According to previous studies,the estimation methods of the roll damping affect the prediction of the PR significantly,and most of them are based on experiment data or Ikeda’s empirical formula.The accuracy of the estimation method for the roll damping could be a key aspect for the validity of its prediction for the full scale ship.In this research,a hybrid prediction method is developed for the numerical prediction of the parametric rolling when experiment data are not available for the roll damping.Comparison study is also carried out between the hybrid method and a nonlinear dynamics method,where the roll damping is estimated by the simplified Ikeda’s method and the direct CFD prediction method in a direct non-linear simulation based on the 3-D CFD approach in the model scale.It is shown that the results of the hybrid method are in satisfactory agreements with the model experiment results,and the method can be used for analysis especially at the early design stage where experiment data are often not available.     

三体船横摇运动性能三维数值研究

该文运用商业软件HydroStar对在横向规则波中航行的三体船的附体位置对其横摇性能的影响进行了数值计算研究.通过计算,本文得到了十二种不同的附体配置方案在三个航速下横摇频率响应函数曲线.计算结果表明:三体船的横摇性能主要受其附体的横向位置影响,附体纵向位置对横摇性能的影响要远小于横向位置的影响,在考察的范围内,航速对三体船的横摇性能影响微弱.     

Stability of a tumblehome hull under the dead ship condition

Some methods for direct stability assessment under the dead ship condition were currently developed by the international maritime organization(IMO)under the Second Generation Intact Stability Criteria.Model tests and simulations are carried out to validate the numerical methods used in assessing the stability under the dead ship condition.This is done in three stages.Firstly,the uncoupled roll mathematical model(1 DOF)is adopted to calculate the roll motion based on the irregular beam waves and the steady wind.Secondly,a drift free experiment is conducted to measure the roll motion under irregular beam waves with zero speed,and then two restrained experiments with counter weights and four springs are performed under the same condition.Finally,the effects of the drift and sway motions on stability under the dead ship condition are then verified by experimental results,and the results of the numerical methods are compared to the results of the model experiments.It is concluded that more accurate numerical methods could be developed for assessing the direct stability under the dead ship condition.     

Numerical simulations of viscous flows around surface ship by level set method

Numerical simulations of viscous flows around surface ships by coupling the 3D incompressible RANS equations with level set method are presented in this paper. The finite difference method is used to discretize the RANS equations with turbulent model SST k − ω. The fully nonlinear boundary condition at the free surface is satisfied at each time step and the evolution of the free surface is achieved by using the level set method. The coupled solver is applied to a benchmark case of viscous flows around an advancing Wigley ship with various Froude numbers. The computational results are in excellent agreement with experimental data. The simulations reveal clearly the generation and evolution of bow and stern waves.

     

计及定常流的三维物体的辐射问题

本文对在波浪中以定常速度般行的物体建立了拟线性理论，在此基础上采用基本源法，利用高边元划分网格，计算了有定常航速物体的附加质量和阻尼系系数，从与实验值及其它计算方法的计算值的比较可看出，本文提供的计算方法是成功的。     

基于CFD的船-舵水动力干扰数值研究

该文采用基于RANS方程求解的CFD方法,对匀速直航的船-舵系统的黏性绕流场进行数值模拟,计算了不同船速和不同舵角下的船-舵水动力干扰系数,计算中忽略了自由面兴波及螺旋桨的影响。文中以KVLCC1船、舵模型为研究对象,首先将数值计算的船舶水动力及船-舵水动力干扰系数结果与模型试验数据进行比较,验证了所采用数值方法的有效性;随后,对船-舵系统、裸船体和敞水舵分别进行计算,通过水动力计算结果的比较以及流场分析,对船-舵水动力相互作用进行了数值研究。     

CRITERION OF STOCHASTIC LAYER NEAR A PLANAR HOMOCLINIC ORBIT OF NONLINEAR DYNAMICAL SYSTEM

ＣＲＩＴＥＲＩＯＮＯＦＳＴＯＣＨＡＳＴＩＣＬＡＹＥＲＮＥＡＲＡＰＬＡＮＡＲＨＯＭＯＣＬＩＮＩＣＯＲＢＩＴＯＦＮＯＮＬＩＮＥＡＲＤＹＮＡＭＩＣＡＬＳＹＳＴＥＭＡｌｂｅｒｔＣ．Ｊ．Ｌｕｏ（ＤｅｐａｒｔｍｅｎｔｏｆＭｅｃｈａｎｉｃａｌ＆Ｉｎｄｕｓｔｒｉａｌ...     

超谐共振横摇下液舱晃荡特性数值研究

该文从船舶非线性横摇运动方程出发,采用多尺度法,获得其在正横规则波中的超谐共振稳态解,并将其作为液舱运动的外部激励。在此基础上,基于Open FOAM开源代码,采用基于VOF的两相流模型模拟液舱内气液运动,研究了船舶在超谐共振横摇条件下的液舱晃荡动特性问题。结果表明,在超谐共振横摇条件下,自由液面易出现翻卷、破碎等强非线性现象,舱壁压力时历表现出多峰型特征,其峰值要远大与简谐激励的情况,而且舱内液体晃荡在两个谐波成分的差频附近发生共振响应。     

SLOW DRIFT DAMPING FORCE ACTING ON A CYLINDER IN WAVES

ＳＬＯＷＤＲＩＦＴＤＡＭＰＩＮＧＦＯＲＣＥＡＣＴＩＮＧＯＮＡＣＹＬＩＮＤＥＲＩＮＷＡＶＥＳ￥ＨｕＣｈａｎｇ－ｈｏｎｇ（ＫｙｕｓｈｕＵｎｉｖｅｒｓｉｔｙ，ｋａｓｕｇａ，Ｊａｐａｎ）ＬｉｕＹｉｎ－ｚｈｏｎｇ（ＳｈａｎｇｈａｉＪｉａｏＴｏｎｇＵｎｉｖｅｒｓ...     

TIME-DOMAIN ANALYSIS OF WAVE FORCES ON SHIPS WITH FORWARD SPEED

Analyses of wave forces on Wigley and Series 60 ships at forward speedare presented in time domain which is based on a free surface transient Green functionwith linearized condition. The main effort focus on the investigation of the numerical sta-bility of time stepping calculation and the waterline intergal contribution to the excitingforces. Numerical study shows that the stable results can be obtained when a wall-sided as-sumption is used at the stern only and the effect of waterline can be neglected. Compar-isons have been made between the present time domain calculations and other works. Nu-merical results for the added resistance on a C_B=0.8 ship in short waves are presentedbased on the assumption that the steady disturbance of ship hull can be neglected.     

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。     

土塞效应对PCC桩振动特性影响的数值模拟

采用ABAQUS建立土塞效应作用下PCC桩的三维有限元模型,对土塞效应下PCC桩的低应变瞬态动测响应进行模拟,得出不同土塞率、不同土塞与桩壁摩擦系数下的桩顶速度时域和频域响应。结果表明:(1)随着土塞率的增大,速度时域曲线中的第一阶反射波峰的幅值减小,且幅值减小依然受三维效应的影响。(2)随着摩擦系数的增大,速度时域曲线中的第一阶反射波峰与第二阶反射波峰的幅值逐渐减小,且第一阶反射波峰幅值的减小程度较为微弱、呈线性变化,第二阶反射波峰幅值的减小程度更为显著、呈非线性变化,波形在第二个反射波峰之前才开始出现分离现象。(3)土塞效应导致波动在土塞段传播的速度减小,土塞效应越强,削减作用越强。(4)土塞效应削弱了纵向振动,横向振动与弯曲振动的耦合,从而导致PCC桩导纳曲线共振峰幅值下降。     

Flow over embankment gabion weirs in free flow conditions

In this study, a series of laboratory tests were performed to investigate the effects of side ramp slope, crest length, and porous media properties on the flow regimes, water-surface profiles, discharge coefficients, and energy dissipation in embankment gabion weirs with upstream and downstream slopes. 24 physical models of solid and gabion weirs with three different upstream/downstream slopes (90°, 45° and 26.5°) were created. To investigate the complexity of flow over the porous-fluid interface and through the porous material, three-dimensional (3D) numerical simulations were developed. In numerical simulation, the standard k-ε turbulence model was utilized. A structured mesh domain was used to simulate the physical model. Water surface profiles above the porous weirs were used for comparison between the numerical simulations and measured data. These comparisons helped determine variables in the numerical simulations. Numerical simulation enables visualization of streamlines around and through the gabion weirs. In addition, mean stream wise velocity profiles above and within the porous structures were obtained. Numerical simulations showed that a reduction in the slope of the upstream face leads to an increased curvature of streamlines and the velocity distribution exhibits a non-uniform wavy shape due to the geometrical properties of the weirs. As the velocity profiles move downstream, the velocity distribution within the porous structures were more affected by the presence of the pores. The experimental results show that decreasing upstream slopes, from 90° to 26.5°, leads to decreased discharge coefficients. However, in all cases, gabion weirs lead to greater discharge coefficients than those of similar solid weirs. For milder side slopes, discharge ratios (flow passing through all faces of the gabion weirs over the inlet discharge) decreased nonlinearly. Moreover, with increasing the inlet discharge, relative energy dissipation was reduced up to 45% in gabion weirs.     

Retard function and ship motions with forward speed in time-domain

The time-domain calculations of retard function and ship motions in waves by the direct time-domain method （DTM） and the frequency to time-domain transformation method （FTTM） are compared and analyzed. A Wigley-hull-form ship and an $60 ship moving in waves are examined, and the corresponding retard functions are in good agreement with those given by DTM and FTTM. The comparison of retard functions in different forward speeds by the two methods is observed, and the results of ship motions in forward speed are also compared with the experimental data. On this basis, the advantage and disadvantage of them are discussed.     

波浪周期对系泊船舶运动影响试验研究

系泊船舶泊稳是港口设计和营运过程中的重要问题,系泊船舶泊稳标准从实质上讲就是限制系泊船舶的运动量。较长周期波浪作用下的系泊船舶泊稳问题愈来愈受到各方的关注,选取了一艘10万吨级散货船进行横向不规则波作用下的系泊模型试验,在同一波高下变化入射波浪周期,通过系列试验,分析波浪周期对系泊船舶横移、横摇和升沉运动的影响。研究结果表明,系泊船舶横移运动量总体上均随着波浪周期的增大而增大,横移运动对波浪周期的响应敏感程度是变化的;系泊船舶横摇和升沉运动量均随着波浪谱峰周期的增大先增大然后减小,当波谱谱峰周期与相应的船舶固有周期接近时,横摇和升沉运动量均出现了一次峰值。     

随浪中船舶复原力计算和试验研究

目前国际海事组织第二代完整稳性衡准正在制定中,纯稳性丧失被列入五种稳性失效模式之一,随浪中复原力变化是纯稳性丧失薄弱性衡准和稳性直接评估的关键因素。该文以C11集装箱船为对象,对随浪不同波浪条件下的横摇复原力进行了试验测量,得到了不同横摇角度时的复原力变化,分析了不同波浪条件下复原力的变化规律;并开发波浪中复原力计算方法和程序,对随浪中船舶横摇复原力进行了计算分析,最后和试验结果进行了对比,有效验证了计算方法的准确性和有效性,为纯稳性丧失直接评估方法的实现奠定了基础,为船舶第二代完整稳性衡准的建立提供了技术支撑。