船舶随浪运动隐性仿真计算

本文利用Ｌｉａｐｕｎｏｖ理论，研究了船舶在规划波良运动的稳性；利用摄动理论，求解出船舶运动响应；并讨论了船舶横摇与垂荡运动频率、最大横摇角和波浪要素对稳性曲线ＧＺ的影响，以及流体动压力对稳性曲线的修正，从而给计算船舶在随浪中的稳性提供了一种。方法。     

不规则波下船舶运动响应特征数值分析

针对不规则波浪作用下Wigley型船的运动响应问题进行了系统的研究,采用统计学方法深入探讨了船舶不规则运动幅值和响应周期的分布规律,并通过傅里叶变换对船舶运动响应进行了频谱特征分析。结果表明,船舶横摇方向与升沉和纵摇方向随机运动的响应特征有显著差异。在升沉与纵摇方向,波浪谱峰频率远离自振频率,前十分之一大振幅运动对应周期离散性较小,基本稳定在波浪谱峰周期附近,但小振幅运动周期分布离散性较大,频谱分析指出船舶升沉与纵摇运动响应频谱在波浪谱峰频率附近出现明显峰值。而在横摇方向,波浪谱峰频率与自振频率相耦合,不同振幅的横摇运动响应周期均稳定在自振周期附近,且周期离散性较小,频谱分析也表明横摇运动响应频谱主要集中于船舶运动自振频率附近。     

规则波中船舶复原力和参数横摇研究

为研究规则波中船舶复原力变化规律及其对参数横摇的影响,首先,基于切片理论求解出船舶无横倾时在波浪中时间序列垂荡和纵摇运动,确定出波面与船体的相对位置;其次,利用三个坐标系之间的转换关系进而确定规则波中船体各横剖面左右舷与波面瞬时交点,求得各浸水剖面面积;然后对波浪压力沿船长湿表面积分,得出规则波中船舶复原力的Froude-Krylov部分。同时,利用作用在横倾船舶上的辐射力和绕射力,求出规则波中船舶复原力辐射力和绕射力部分。在复原力计算的基础上,确定一个参数横摇模型,实现波浪中参数横摇计算。以一艘集装箱船为例,研究了规则波中复原力变化以及参数横摇规律,复原力变化幅度是影响参数横摇的一个重要因素。     

瘫船稳性第二层薄弱性衡准研究

基于IMO第二代完整稳性草案中瘫船稳性第二层薄弱性衡准的有关研究,分析草案提出的简化计算方法,采用一个单自由度船舶横摇运动微分方程,利用例船CEHIPAR2792数据,编译相应程序,求得不规则横风横浪作用下瘫船横摇运动相应特征,进而计算特定海况下的倾覆概率及特定海区的平均倾覆指数,并与草案值进行对比。分析不同拟合扶正力臂曲线方法和剩余稳性高对计算结果的影响,并对瘫船稳性第二层薄弱性衡准方法进行修改。     

涌浪作用下港内大型集装箱船运动特性数值研究

随着船舶大型化和港口建设深水化发展,外海不同周期波浪作用下大型系泊船泊稳问题与小型系泊船相比出现了新的特点。为此,利用数值模型方法研究了在不同入射角度和周期的涌浪作用下港内大型系泊船的水动力响应,针对系泊船的泊稳情况探讨了船舶的运动规律和运动特性。研究发现,在涌浪周期较大的情况下,限定波高的泊稳标准不足以用来确定系泊船的正常作业条件,港内泊船的水平运动（纵荡、横荡和艏摇）极易超出运动标准值并影响装卸作业效率,并且船舶的水平运动表现出主要由次重力波主导的低频运动特性,而垂直运动（垂荡、横摇和纵摇）表现出主要由短波主导的波频运动特性。     

不同波长下KCS船运动响应与波浪增阻数值研究

准确预报船舶在波浪中的运动和力可以为船舶性能评估提供参考。采用naoe-FOAM-SJTU求解器，数值模拟固定和放开垂荡、纵摇自由度的KCS船在不同波长的迎浪规则波中的运动。首先运用数值造波方法生成不同波浪周期的Stokes一阶深水规则波，与Stokes波的理论值对比确保造波的准确性；然后计算固定或放开垂荡和纵摇自由度的KCS船在0.65 ≤ λ/L（波长/船长）≤1.95的遭遇波中的运动和阻力，研究KCS船的波浪增阻中绕射和辐射成分，且采用傅里叶分析法研究了运动与阻力的线性和非线性成分分布。结果表明，波浪绕射增阻受波长的影响不大，当波长接近船长时，船舶的垂荡和纵摇幅值以及波浪增阻均达到峰值，这主要由船体剧烈运动引起的辐射增阻导致，应避免船舶在此工况下航行。     

超细长三体船耐波性试验研究

通过三体船模型耐波性试验,包括横摇试验,规则波中的迎浪试验,研究了侧体布置位置和舭龙骨对三体船横摇运动的影响以及在波浪中的纵摇和垂荡运动特点。     

涌浪环境中铺管船横摇机理及模型试验研究

"海洋石油201"号等多艘铺管船在东海海域进行铺管施工时受低频涌浪环境影响横摇运动强烈,严重影响了正常铺管作业。为了分析铺管船横摇过大的原因,从理论上分析了铺管船可能发生较大横摇的波浪条件,并对"海洋石油201"号铺管船在遭遇波浪周期等于横摇固有周期1/2倍和1倍,不同波高的规则波中航向角分别为0°、30°、60°和90°时的运动特性进行了模型试验。试验结果表明铺管船遭遇周期为其横摇固有周期一半的涌浪时未发生参数横摇,而遭遇与其横摇固有周期接近的涌浪时发生谐摇是导致其横摇运动过大的原因。研究成果与相应的气象资料结合,可为铺管船施工气候窗口的选择提供依据。     

半潜式平台垂向运动低频响应特性

对半潜式平台垂向运动性能(包括垂荡、横摇和纵摇)进行数值计算分析。与模型试验结果的比较表明,对于半潜式平台这类由柱体组成的结构物进行水动力数值预报,忽略粘性力作用会使得低频运动响应计算结果产生偏差,需要应用三维势流理论和Morison公式相结合的方法。横摇和纵摇运动固有频率均低于波浪频率,在波浪慢漂力作用下会出现显著低频运动响应。垂荡运动是否出现低频响应则与所处海况联系紧密。     

波浪作用下缆船拖带系统非线性运动数值模拟

基于船舶操纵性运动方程和拖缆的三维动力学运动方程,提出了被拖点位置匹配的方法,建立了拖船—拖缆—被拖船系统整体非线性拖带动力学模型。为了考察被拖船航向稳定性与横向稳性的关系以及波浪载荷作用的影响,被拖船采用水平面四自由度运动方程,并引入了波浪的作用力和力矩。拖船采用PD控制方法较真实地模拟了拖船航向改变的运动过程。对一个拖船—拖缆—被拖船系统(5 000 t的拖船和3 000 t的被拖船)在时域内进行了规则波浪作用下拖带运动的模拟,计算结果表明被拖带船舶在波浪中运动呈现运动稳定、不稳定和临界状态3种可能的特性。根据模拟计算结果,认为波浪中拖带航向稳定是被拖带船舶保持稳性的必要条件。     

Capsizing Probability of Dead Ship Stability in Beam Wind and Wave for Damaged Ship

The International Maritime Organization has developed the second-generation intact stability criteria. Thus, damage stability criteria can be established in the future. In order to identity the capsizing probability of damaged ship under dead ship condition, this paper investigates two methods that can be used to research the capsizing probability in time domain, which mainly focus on the nonlinear righting lever GZ curve solution. One method subjects the influence of damaged tanks on the hull shape down to the wind and wave, and the other method is consistent with the real-time calculation of the GZ curve. On the basis of one degree of freedom rolling equation, the solution is Monte Carlo method, and a damaged fishery bureau vessel is taken as a sample ship. In addition, the results of the time-domain capsizing probability under different loading conditions are compared and analyzed. The relation of GM and heeling angle with the capsizing probability is investigated, and its possible reason is analyzed. On the basis of combining the time-domain flooding process with the capsizing probability calculation, this research aims to lay the foundation for the study of capsizing probability in time domain under dead ship condition, as well as provide technical support for capsizing mechanism of dead ship stability and damage stability criteria establishment in waves.     

Parametric roll due to hull instantaneous volumetric changes and speed variations

Parametric roll of a containership in head sea condition has been studied in the paper. A time domain routine for GZ righting arm calculation based on exact underwater hull geometry has been implemented into a two-degree-of-freedom procedure for roll response calculation. The speed variation due to e.g. added resistance has been accounted for in the model by the surge velocity. The ship roll motion due to a regular wave critical for parametric roll occurrence has been simulated, as well as the ship roll response in a severe stochastic sea. The present method has been compared with other existing methods for parametric roll prediction.     

State- and output-feedback robust path-following controllers for underactuated ships using Serret–Frenet frame

This paper develops state- and output-feedback controllers that force an underactuated surface ship to follow a predefined path at a constant forward speed controlled by the main thruster system under the presence of environmental disturbances induced by wave, wind and ocean-current. The proposed controllers are designed using Lyapunov’s direct method and the popular backstepping. The unmeasured sway and yaw velocities are estimated by introducing a new nonlinear passive observer. A stability result for nonlinear cascade systems with nonvanishing uncertainties is introduced to analyze closed-loop stability. Numerical simulations using the real data of a monohull ship are provided to illustrate the effectiveness of the proposed methodology for path following of underactuated ships.     

Subharmonic oscillations in nonlinear rolling

In this paper the rolling motion of a ship is examined with particular regard to the possibility of obtaining oscillations which are subharmonic to the excitation frequency. Three different mechanisms are found to be responsible for this phenomenon, the importance of which has already been recognized in the context of ship stability. The first is related to a strong symmetric or non-symmetric nonlinearity in the righting arm. The second is linked to the harmonic composition of sea waves and the third to the well known parametric excitation caused by coupling between different ship motions in a following sea.The onset of subharmonics is related to a threshold value for the excitation strongly depending on damping. The more appropriate analytical methods for a theoretical study of each mechanism are suggested.     

Using wavelet transforms to analyze nonlinear ship rolling and heave-roll coupling

The use of wavelet transforms is explored to investigate the nonlinear dynamical characteristics of ship roll and coupled heave-roll motion. The harmonic character, double period character and chaotic character are observed via a time–frequency window of the wavelet transform. Typical wave parameters in different stability regions are considered. Features such as restoring rolling, divergence rolling, steady state and chaotic responses of ship roll are obtained as well. The investigation in this paper not only highlights the feasibility of using wavelet transforms in the analysis of nonlinear dynamic characteristics of ship rolling in waves, but also shows how it could enhance the analysis abilities.     

Numerical simulation of PMM tests for a ship in close proximity to sidewall and maneuvering stability analysis

As the maneuverability of a ship navigating close to a bank is influenced by the sidewall, the assessment of ship maneuvering stability is important. The hydrodynamic derivatives measured by the planar motion mechanism (PMM) test provide a way to predict the change of ship maneuverability. This paper presents a numerical simulation of PMM model tests with variant distances to a vertical bank by using unsteady RANS equations. A hybrid dynamic mesh technique is developed to realize the mesh configuration and remeshing of dynamic PMM tests when the ship is close to the bank. The proposed method is validated by comparing numerical results with results of PMM tests in a circulating water channel. The first-order hydrodynamic derivatives of the ship are analyzed from the time history of lateral force and yaw moment according to the multiple-run simulating procedure and the variations of hydrodynamic derivatives with the ship-sidewall distance are given. The straight line stability and directional stability are also discussed and stable or unstable zone of proportional-derivative (PD) controller parameters for directional stability is shown, which can be a reference for course keeping operation when sailing near a bank.     

The development of ship registration policy in China: Response to flags of convenience

In order to expand registered fleet tonnage and strengthen ship management, China began to introduce a special tax-free ship registration (STFSR) policy in July 2007. However, more than eight years following its implementation, the policy ended in complete failure at the end of 2015. This paper comprehensively evaluates the main content and implementation process of the Chinese STFSR policy, analyzes the effects of the policy, and summarizes the concrete reasons for the policy's failure and lessons to be learnt. A new governance framework is being designed and future directions are being developed to explore how the government can implement a successful ship registry policy. This research is intended to provide new ideas and information to the Chinese shipping industry's policymakers and stakeholders in order to handle the “flagging out” problem, thereby mitigating the current adverse situation of ship flagging overseas while strengthening the management of ship operation.     

On the parametric resonance of container ships

This work deals with parametric resonance which poses a great danger especially for container ships sailing in following or head seas. Important parameters that are effective in roll resonance are pointed out. For this purpose, a containership is taken as an example to analyze its stability in longitudinal waves based on the method worked out by American Bureau of Shipping (ABS). Unfavorable sailing conditions such as heading and speed, which directly depend on the environmental conditions, have been determined for this particular ship. These conditions may be reported to the master to guide him to keep his ship out of parametric resonance zones. Numerical details of the procedure have been worked out and provided as well.     

船体尾流场测试试验的若干关键技术研究

根据带不同尾部特征的水滴形船体模型水下伴流场的测量试验情况，对测试系统的几个关键技术进行了较详细的探讨。通过分析研究表明：水下测量试验系统的稳定性好，功能齐全且自动化程度高，在试验研究中有必要对测试技术方面的若干关键环节加以注意，以保证测试的准确性和精度。