Predicting parametric rolling in irregular head seas with added resistance taken into account

Parametric rolling in irregular head seas is investigated using numerical simulation in the time domain in this paper. The effect of the change in speed due to added resistance on parametric rolling is taken into account. Three methods of calculating the added resistance in irregular head seas are applied to this problem, and then Pinkster’s method, which considers the time-varying added resistance in irregular head seas, is extended for further investigations in this paper. Furthermore, the Froude–Krylov component of restoring variation is estimated with coupling from heave and pitch motions, and the hydrodynamic effects are extrapolated nonlinearly with regards to roll angle. Finally, the “practical non-ergodicity” of parametric roll is investigated with a model experiment at zero forward speed and using the simulation, and the effect of added resistance is investigated with the simulation.     

Parametric rolling prediction in irregular seas using combination of deterministic ship dynamics and probabilistic wave theory

In recent years there have been reports of serious accidents of parametric rolling for modern container ships and car carriers. For avoiding such accidents, a prediction method of parametric rolling in irregular seas is required. Since parametric rolling is practically non-ergodic, repetitions of numerical simulations or experiments could be not feasible to ascertain the behaviour. Therefore, in this paper, a method combining a stochastic approach with a deterministic approach in order to estimate the probabilistic index without such simple repetitions is developed. The ship's response in regular seas is estimated by solving an averaged system of the original 1-DoF roll model, and random waves necessary for occurrence of parametric rolling is achieved by using Longuet-Higgins’s or Kimura’s wave group theory. As a result, a fast and robust computation method of the probabilistic index is established. Finally, it is concluded that the proposed method is considered to be one of the useful tools for discussing the new IMO Intact Stability Code.     

规则迎浪中船舶参数横摇的三维时域预报方法研究

参数横摇是船舶因复原特性改变而引起的典型非线性现象。文章采用三维时域方法预报规则迎浪中船舶的参数横摇运动。该方法引入匹配面将流域分为内域和外域,内域中采用Rankine源来满足物面条件和线性自由面条件,而外域中应用时域格林函数来满足线性自由面条件和远场辐射条件。数值方法中,Froude-Krylov力和恢复力是通过对船舶瞬时湿表面积积分获得,同时考虑了横摇、垂荡和纵摇三自由度之间的耦合作用,以及非线性横摇阻尼的影响。数值结果与试验结果吻合很好,说明该方法可以有效地预报参数横摇。     

大型汽车滚装船参数横摇研究

对于航行在纵向波浪中的船舶,参数横摇是横稳性中典型的不利情形。文章对参数横摇作了介绍,并对某大型汽车滚装船进行了实例分析。首先,对船舶在纵向波浪中的稳性变化进行了计算;然后,根据衡准进行验证;最后,采用数值仿真方法,研究了稳性变化、横摇阻尼、航速、航向等参数对参数横摇的影响。     

纵向规则波中参数横摇的数值模拟

基于ITTC推荐的参数横摇运动方程,采用估算方法确定方程中的阻尼系数和复原力矩系数,数值模拟出船舶在规则波中的参数横摇情况,将上述方法具体应用于一艘滚装船船模的参数横摇预报,并与试验数据进行对比,验证了所采用方法的有效性。     

大型集装箱船参数横摇模型试验和数值模拟研究

以4000TEU集装箱船为研究对象,通过系列自航模型试验,确定其在迎浪规则波中发生参数横摇的限界。试验结果显示：在迎浪规则波中,参数横摇通常发生在波浪遭遇周期为横摇固有周期一半的附近;对应不同遭遇频率时参数横摇的发生,存在一个临界波高;航速的增加和舭龙骨的安装将使参数横摇发生的临界波高增加;当有初始干扰时,参数横摇发生的临界波高较小。而且,数值模拟结果与模型试验结果比较吻合。     

On the Parametric Resonance of Tumblehome Hullforms in a Longitudinal Seaway

This work presents a numerical study of the influence of topside shape on parametric roll in longitudinal seas. The ONR 3 Topsides hulls are used to compare the single degree-of-freedom rolling response of a destroyer-sized vessel with flared (model 5613), tumblehome (model 5613-1), and wallsided (model 5613-2) shapes above the waterline. Through this relative comparison, the key aspects of parametric resonance of a tumblehome hullform are highlighted, namely the reduction in head seas forward speed required to encounter parametric roll. A variant on the Mathieu equation is used to simulate roll motions.     

An investigation of different methods for the prevention of parametric rolling

The parametric rolling of modern containerships is emerging as a serious problem, to the extent that its effects warrant a study into its prevention. In light of this, two methods for reduction of parametric rolling are proposed and examined by physical model experiments. The first is a sponson attached to the side of a ship, the purpose being to decrease the rate of change of the rollrestoring moment. The second is an antirolling tank to increase roll damping. By conducting free-running model experiments for a 6600-TEU post-Panamax container ship with sponsons under typical parametric rolling conditions, it was found that the sponsons could decrease the magnitude of parametric rolling. The antirolling tank could prevent parametric rolling completely in certain conditions, even in severe head seas. Using the damping coefficients from experimentally derived data of a model ship with an antiroll tank, a numerical simulation was established. The numerical model was then compared with the free-running model experiments. The results indicated that the numerical model could qualitatively verify the experimental results. Finally, an attempt to optimise the size of an antirolling tank for preventing parametric rolling for the subject post-Panamax container ship in the North Pacific Ocean is presented.     

横向规则波作用下的船舶倾覆

运用安全池理论研究了某近海干货船在横向规则波作用下的船舶倾覆问题.用阿当姆斯预估-校正法数值求解时域内单自由度非线性横摇方程.采用三维格林积分方程法计算水动力系数的频域特性.分析了非线性横摇方程中势流阻尼、非线性阻尼以及在横向规则波作用下波高和频率对安全池的影响.     

粘性流中船舶横摇阻尼计算

船舶横摇阻尼的确定是准确预报船舶在波浪中运动的关键之一.本文以粘性流理论为基础,以连续性方程和N-S方程为控制方程.对Series 60船型的二维横剖面绕流进行了数值模拟,计算分析了不同工况下船体剖面的横摇阻尼系数,并与相关实验结果进行了比较.对比和研究表明,本文的方法能给出船舶横摇运动诱导的涡,船体的横摇阻尼等,可进一步拓展应用于船舶在波浪中运动的分析预报和优化设计等方面.     

基于统一模型的船舶迎浪参数横摇数值预报及其舵减摇研究

国际海事组织（IMO）正致力于第二代完整稳性规范的制定,而参数横摇一直是船舶动态完整稳性研究的热点。文章采用考虑船舶操纵性和耐波性运动耦合的统一模型对迎浪规则波下的船舶参数横摇运动进行了时域数值模拟。在时域模型中,六自由度耐波性运动辐射绕射力采用切片理论计算,并由脉冲响应函数法转化到时域。非线性回复力和入射波力采用瞬时湿表面压力积分方法计算。操纵性运动基于MMG模型,依据统一理论将操纵性与耐波性运动进行耦合计算。文中先应用简化三自由度模型对三艘集装箱船进行了参数横摇样船计算,并进行了初步的模型实验验证,依据结果对比分析了横摇惯性矩、初稳性高和方形系数对参数横摇的影响。基于统一模型分析了操纵性运动对参数横摇的影响,并进行了参数横摇舵减摇研究。     

Nonlinear analysis of parametric rolling in longitudinal and quartering seas with realistic modeling of roll-restoring moment

Parametric rolling of a containership in longitudinal and quartering seas is examined by applying nonlinear dynamics to a 1DOF mathematical model with realistic modeling of the wave effect on roll-restoring moment. In our previous work, we confirmed that a mathematical model with a roll-restoring moment in waves calculated with the Froude–Krylov assumption could considerably overestimate the danger of capsizing associated with parametric rolling. Therefore, in the present work, all numerical calculations based on nonlinear analysis were carried out with the direct aid of a measured roll-restoring moment in waves. For this purpose, captive model experiments were conducted for various sets of wavelengths in longitudinal seas. This experiment demonstrates that the Froude–Krylov prediction could not explain the wavelength effect on restoring moment as the wave-steepness effect. Using the numerical model with the aid of this measured roll-restoring moment, the Poincaré mapping technique was applied to identify bifurcation structures of roll motions not only in longitudinal seas, but also in quartering seas. As a result, it was confirmed that capsizing associated with parametric rolling is more likely to occur in following seas than in quartering seas. However, period-doubling and chaos appeared in quartering seas. Finally, an averaging method assuming a period-2 orbit was applied to the same model with the same conditions as the Poincaré map. Reasonably good agreement was obtained between the numerical results with a Poincaré map and those with the averaging method in longitudinal seas, but the averaging method has limited capability in quartering seas.     

参数横摇薄弱性衡准研究

鉴于国际海事组织（IMO）第二代完整稳性衡准工作组正在制定参数横摇薄弱性衡准。文章首先编制了参数横摇第一层和第二层薄弱性衡准的计算程序,其中采用解析稳态解法求解横摇响应,并给出了衡准中关键参数即波浪中稳性高变化的计算方法;其次以国际标模 C11集装箱为例详细分析了参数横摇衡准的计算过程,同时分析了横摇阻尼对计算结果的影响;最后通过与试验结果的比较,验证了衡准方法的一致性及程序的可靠性。     

URANS prediction of roll damping for a ship hull section at shallow draft

It is analytically difficult to calculate roll damping of ships due to the effects of viscosity. Therefore, computational fluid dynamics (CFD) has become a powerful tool in predicting roll damping recently. The unsteady flow around a forced rolling hull section with bilge keels can be calculated using a commercial URANS code which includes the viscous effects. In this study, two-dimensional (2D) roll damping calculations for a S60 midsection with bilge keels including free surface effects are performed for shallow draft case. The first objective of the study is to show whether the URANS code can be used to predict roll damping coefficient correctly. The second one is to show why Ikeda’s estimation method is insufficient at shallow draft case. Sinusoidal forced roll motion calculation method of roll damping moment with the help of a sliding interface and a fixed roll axis is successfully applied to predict roll damping coefficient. The calculations are carried out for different roll motion periods and amplitudes to validate the accuracy of the URANS code for different cases. Numerical results are compared with experiments, which were carried out at the towing tank facility of Osaka Prefecture University (OPU), and Ikeda’s estimation method. The results show that the URANS code is capable of predicting roll damping coefficients in a good agreement with experimental results and can be used further to develop a better model for prediction of roll damping.     

Study of damaged ship motions taking into account floodwater dynamics

This paper presents an application of shallow water theory to describe the motion of floodwater inside a rolling ship in damage condition. The time domain theoretical approach to the coupled problems of ship and water inside compartment motions is briefly described, including the method used to solve for the water motion characteristics and forces exerted on the ship. This approach is applied to the study of the behaviour of a passenger Ro–Ro ship in regular beam seas and numerical results are given for the intact and damaged conditions. Comparison is made with experimental results. For the damaged condition, the characteristics of the floodwater motion are studied in the time domain for a number of different wave frequencies. The shape of the free-surface and phase of water motion in relation to the ship roll motion are shown for several wave frequencies. The dynamic floodwater roll moment is also shown and compared with the static roll moment (flat horizontal free surface), allowing the conclusion that the dynamic roll moment is much larger than the static roll moment, for high wave frequencies, and is in phase opposition in relation to the roll motion.     

油船强迫横摇试验及分析研究

采用自制的横摇试验设备和控制系统,进行油船船模在三种横摇幅值下的强迫横摇试验,横摇试验周期为0.8~20 s,全方位探究零航速不同横摇周期时强迫横摇力矩以及力矩和运动之间相位的变化规律。试验发现,随横摇周期的增大,横摇力矩先减小,试验周期到达横摇固有周期附近时横摇力矩最小,之后横摇力矩逐渐增大,当横摇周期很长,船舶横摇缓慢,此时横摇力矩基本保持不变;同一横摇周期和不同横摇幅值下,横摇力矩与横摇幅值成倍数关系。随着横摇周期的减小,附加惯量成线性增加,横摇阻尼非线性明显,并随横摇幅值的增加而增大。     

船舶参数激励非线性横摇运动方程

讨论了船舶在海浪上运动时参数激励产生的机理，建立了船舶参数激励和波浪激励非线性横摇运动方程。本文工作为研究倾覆机理奠定了基础。     

五体船波浪中运动与增阻的主片体协同优化研究

以波浪中的运动和增阻为目标,进行了五体船主体型线、片体主尺度和布置的协同优化。解决了型线自动变换、参数化自动建模及计算网格合并等关键技术,实现了五体船全船的自动建模。利用ISIGHT进行建模与水动力计算的集成,建立了主片体协同多目标优化系统。运用遗传算法进行多目标优化,结果表明优化后五体船运动和增阻都有所改善,并对非规则波中的情况进行了一定的探讨。     

船舶参数激励非线性随机横摇运动分析

研究了随机纵浪中船舶的参数激励横摇运动。将船舶初稳性高作为时变的随机参数激励,应用随机平均法和FPK方程,分析了船舶的参数激励横摇运动微分方程。考虑航速、船舶瞬时湿表面积及随机波浪,建立了船舶横摇幅值概率密度、概率分布函数及其均值的计算方法。以某渔政船为例,计算了不同航速时船舶随机横摇幅值的概率密度、概率分布函数及其均值。结果表明,参数激励谱峰频率为横摇固有频率的2倍时,发生主参数共振,船舶横摇严重,船舶倾覆发生的概率增加。     

深水起重铺管船横摇运动性能分析(英文)

For a large floating vessel in waves,radiation damping is not an accurate prediction of the degree of roll unlike other degrees of freedom motion.Therefore,to get the knowledge of roll motion performance of deepwater pipelay crane vessels and to keep the vessel working safety,the paper presents the relationship between a series of dimensionless roll damping coefficients and the roll response amplitude operator(RAO).By using two kinds of empirical data,the roll damping is estimated in the calculation flow.After getting the roll damping coefficient from the model test,a prediction of roll motion in regular waves is evaluated.According to the wave condition in the working region,short term statistics of roll motion are presented under different wave parameters.Moreover,the relationship between the maximal roll response level to peak spectral wave period and the roll damping coefficient is investigated.Results may provide some reference to design and improve this kind of vessel.