Stability Analysis of Bohai Oil-Drilling Ship No. 6 Under Static and Cyclic Loads

This paper presents a procedure to calculate the safety factor against sliding of a marine gravity structure subjected to a combination of static and cyclic loads. This procedure claculates the stress at the sliding surface by the finite element method (FEM) and takes the dynamic properties of clay into account. With this procedure, the stability of a Bohai oil-drilling ship is analyzed. The calculated safety factor is much smaller than 1, indicating that this oil-drilling ship would fail just as what had happened to it.

Roll stability catastrophe mechanism of a flooded ship on regular sea waves

Based on a typical one-free-degree ship roll motion equation, the cusp catastrophe model is built including the bifurca- tion set equation, splitting factor ＇u＇ and regular factor ＇v＇, where both ＇u＇ and ＇v＇ are further expressed with typical flooded ship parameters. Then, the roll catastrophe mechanism is analyzed mainly by means of ＇u＇, under the given parameters of a typical trawler boat. The aim of this research is to reveal the mutagenic mechanism of the roll stability and provide a reference for improving ship roll stability.

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.

A Multidisciplinary Method for Evaluating Ship Stability

The aim of this paper is to present the main results arisen from the joint efforts of the public-private partnership in being between CCII （Centro Cultura Innovativa d＇Impresa） of University of Salento and Apphia s.r.l.. This paper will focus on the results of the core of the OBSS （on board stability system） module that, starting from the exact 3D geometry of a ship hull, described by a discrete model in a standard format, the distribution of all weights onboard and the data acquired by the system, calculates ship floating conditions （in draught, heel and trim）. The proposed approach is based on geometry meshes represented by an universally accepted file format （named OBJ） first developed by Wavefront Technologies. Demonstration of the validity of the results is done by the authors using as hull model a simple rectangular box.

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.

The Application of a Smartphone in Ship Stability Experiment

The inclining experiment is the only regulatory tool to assess ship stability. This experiment is a time consuming process for both real-life tests and ship model experiments. The difficulty is mainly due to a bias in the measurement of heel angle. Nowadays, digital inclinometers are available, but they are expensive. In this study, the use of a smartphone application is presented for ship inclination and rolling-period tests. The idea consists of using accelerometer and gyroscope sensors built into the current smartphones for the measurements. Therefore, some experiments are carried out on an example trawler model to exhibit the uses and advantages of this method. The obtained results are in good agreement with those provided from the pendulum method and natural roll-period test. This application is new, easy, and more accurately assesses metacentric height during the inclining and rolling-period tests.

Design and Stability Analysis of Fuzzy Switched PID Controller for Ship Track-Keeping

The fuzzy switched PID controller which combines fuzzy PD and conventional PI controller is proposed for ship track-keeping autopilot In this paper. By using rudder angle, the whole voyage is divided into two operating regimes which named transient operating regime and steady operating regime respectively. The fuzzy PD controller is employed in transient operating regime for increasing response, reducing overshoot and shorting transition time. And conventional PI controller is used to improve the stable accuracy in steady operating regime. The global controller is achieved by fuzzy blending of all local controllers. Routh stability criterion is utilized to obtain the stability condition of closed-loop system. The simulation results show the effectiveness of proposed method.

The Applicability of Hydrofoils as a Ship Control Device

Centrifugal forces are commonly created when ships turn, which may cause a ship to capsize in a critical situation. A mathematical model has been developed to optimize the stability coefficients for ship, with the aim to prevent capsizing and to increase ship maneuverability in high-speed water craft. This model can be used to develop algorithms for control system improvement. The mathematical model presented in this paper optimized the use of multipurpose hydrofoils to reduce heeling and the trimming moment, maintaining an upright ship’s position and lessening the resistance via transverse force. Conventionally, the trimming and heeling of a ship are controlled using ballast water;however, under variable sea conditions it is sometimes difficult to control a ship’s motion using ballast water. In this case, a hydrofoil would be more stable and maneuverable than a ballast tank controlled vessel. A movable hydrofoil could theoretically be adapted from moveable aerofoil technology. This study proves the merit of further investigation into this possibility.

The Model Research on the Flooding Time of the Warship Damaged Compartment

Research on damage stability and unsinkability is a valuable source of knowledge of behaving a ship while flooding its compartments. The time when compartment is flooded （ty） and stability parameters are key elements which have influence on a rescue action. The knowledge of the time mentioned is very important for a commanding officer to make decisions while fighting for survival of the ship. Therefore, the purpose of research was to develop a method to accurately and quickly calculate the flooding time of selected ship compartment. To provide the information about the time ty, a new method was designed. This method was based on an accurate determination of the amount of water entering to the compartment. For this purpose, the permeability depends on the water level in the compartment. Next, the computer program was built for both the time tfcalculation and showing the flooding process. This method was tested experimentally and the results of the tests are presented in the paper. In the next part of research, which was carried out on the laboratory stand bed, the flooding time of damaged compartment of warship model was measured. The results of calculation are compared to the experiments and discussed.

A Direct Compensative Robust Optimal Control (DCROC) Law for Ship Straight-line Track-keeping

A linear quadratic optimal direct track-keeping control law was proposed based on first-order Nomoto nominal model. Furthermore, based on Lyapunov stabilized theory, considering parametric uncertainty from variations of ship speed and disturbances uncertain from wind, wave and sea current, a direct compensative robust optimal control (DCROC) law was developed. It can guarantee closed-loop system globally and uniformly converge to a remained set. High accuracy and robustness were achieved. By introducing some nonlinear blocks, closed-loop system achieves global and uniform asymptotical stableness. Numerical simulations on a Mariner Class ship are presented to validate the control law.

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.

Energy Optimization of the Fin/Rudder Roll Stabilization System Based on the Multi-objective Genetic Algorithm （MOGA）

Energy optimization is one of the key problems for ship roll reduction systems in the last decade. According to the nonlinear characteristics of ship motion, the four degrees of freedom nonlinear model of Fin/Rudder roll stabilization can be established. This paper analyzes energy consumption caused by overcoming the resistance and the yaw, which is added to the fin/rudder roll stabilization system as new performance index. In order to achieve the purpose of the roll reduction, ship course keeping and energy optimization, the self-tuning PID controller based on the multi-objective genetic algorithm （MOGA） method is used to optimize performance index. In addition, random weight coefficient is adopted to build a multi-objective genetic algorithm optimization model. The objective function is improved so that the objective function can be normalized to a constant level. Simulation results showed that the control method based on MOGA, compared with the traditional control method, not only improves the efficiency of roll stabilization and yaw control precision, but also optimizes the energy of the system. The proposed methodology can get a better performance at different sea states.

不同装载条件下小型渔船参数横摇的非定常RANS CFD仿真

Fishing boats have unique features that make them prone to changing loading conditions.When the boat leaves the port,the empty fish tank gradually fills up during fishing operations which may result in parametric roll(PR).This dangerous phenomenon that can lead to capsizing.The present study aims to understand better the behaviour of parametric roll in fishing boats and its relation to changing loading conditions.The study considers the effects of displacement and the GM/KM ratio on parametric roll,as well as the longitudinal flare distribution at the waterline.Two assessments to detect the parametric roll occurrence in early stage were carried out by using the level 1 assessment of parametric roll based on the Second Generation of Intact Stability criteria(SGIS)from International maritime Organisation(IMO)and the Susceptibility criteria of Parametric roll from the American Bureau of Shipping(ABS).Then,the CFD method is used to predict the amplitude of the parametric roll phenomenon.The results provide important insights to fishing vessel operators on how to manage loading conditions to maintain stability and avoid hazardous situations.By following the guidelines outlined in this study,fishing boats can operate more safely and efficiently,reducing the risk of accidents and improving the overall sustainability of the fishing industry.

烯效唑处理下绿豆农艺性状稳定性及性状间相互关系分析

为加强绿豆育种性状选择,以绿丰2号、绿丰5号和JLPX02绿豆为试验材料,选用3个浓度的烯效唑进行浸种,采用大田试验,测定供试绿豆的14个农艺性状,应用方差分析、相关性分析和主成分分析方法进行性状的综合评价,研究烯效唑处理下绿豆农艺性状表现的稳定性及各农艺性状间的相互关系。结果表明,分枝数、根重、根瘤数、单株荚数、单株鲜重和单株粒重6个性状在3个品种(系)中均发生大幅度变异,稳定性弱;主茎节数、株高、荚长、单荚粒数、百粒重5个农艺性状的变异系数均较小,稳定性强;百粒重与荚长呈极显著相关,相关系数最大为0.906;产量与分枝、单荚粒数、单株粒重呈显著相关。主成分分析中,第1主成分中,百粒重、荚长、单株荚数为主要反映荚因子指标;第2主成分中,单株鲜重、单株粒重、分枝为主要反映植株因子指标;第3主成分中,根重、侧根数、根瘤数为主要反映根系因子指标;第4主成分中,单荚粒数、产量为主要反映产量因子指标。综上说明,绿豆的分枝、单株荚数、单株粒重、产量、单株鲜重可作为高产材料选择的主要参考性状,百粒重、荚长、主茎节数、单荚粒数可作为高稳定性性状为材料选择提供参考。

双桨双舵内倾船型的横甩失稳运动预报研究

目前国际海事组织(IMO)已经发布了第二代完整稳性衡准骑浪/横甩直接稳性评估方法的最终指南,如何准确高效地数值预报骑浪/横甩运动是目前骑浪/横甩直接稳性评估方法中亟待解决的关键问题。本文构建一个纵荡-横荡-垂荡-横摇-纵摇-首摇六自由度运动耦合的数学模型,该数学模型首先在纵荡-横荡-横摇-首摇四自由度操纵性数学模型基础上考虑垂荡和纵摇运动的影响,采用基于加强积分的切片法求解垂荡和纵摇运动的幅值和相位,可以有效解决尾浪中高航速船舶直接耐波性时域计算容易发散的问题;其次,船舶在波浪中的Froude-Krylov力和绕射力是通过对船体平均湿表面进行压力积分获得的。同时,在数学模型中还考虑非线性水动力导数、静水横倾产生的水动力和非线性横摇阻尼等因素。在螺旋桨推力和舵力模型中考虑由于波浪粒子速度和船舶速度共存产生的水动升力的影响,舵力模型中还加入了垂荡、纵摇运动对波浪中双舵实时出入水导致的舵力动态变化。最后,以双桨双舵的ONR内倾船型为研究对象,开展尾斜浪中骑浪/横甩数值预报,分析船-波的初始相对位置对船舶骑浪/横甩运动的影响。计算结果表明,文中建立的六自由度骑浪/横甩数学模型具有足够的计算精度,可以用于骑浪/横甩的直接稳性评估。

港口与船公司新型合谋策略的演化与均衡分析

为在新型轴辐合谋背景下探讨港航系统实施轴辐合谋模式的可能性,构建一个港口和两家船公司之间的轴辐合谋模型,分析具有产能约束的港口和船公司在轴辐合谋下的均衡策略。研究发现:轴辐合谋前,船公司之间默契合谋会对港口利润造成损失;轴辐合谋后,港口和船公司分别降低其服务价格和运价,在保证船公司利润不变的情况下港口利润得到改善,港航系统总利润实现增加;从长期角度看轴辐合谋将成为港口和船公司的最优策略。港口与船公司轴辐合谋的稳定性大于船公司默契合谋的稳定性。该研究结果可为预防和规制航运业新的合谋模式提供决策参考。

俄乌冲突背景下“一带一路”沿线原油海运网络结构特征及变化分析

国际地缘政治对运输网络格局的影响是经济地理和交通地理的重要议题之一,探究俄乌冲突背景下“一带一路”沿线原油海运网络结构特征变化,可为该领域研究提供新的论据。文章采用AIS船舶轨迹大数据和复杂网络分析法,分析了2019—2022年“一带一路”沿线原油海运网络整体特征、节点重要性与核心边缘和组团耦合结构的变化特征,并探究了海运网络结构变化对中国原油进口稳定性的影响。结果表明:1)海运格局发生了结构性演变。港口间的联系密度、强度和网络通达性均呈现先增后减趋势;网络无标度特性不断增强,原油海运向部分主要联系集聚,出口端更加明显;俄乌冲突后中国与中东原油海运联系取代了部分中俄原油海运联系。2)海运港口重要性格局与核心边缘结构处于动态变化中。出口港综合重要性先略有降低,俄乌冲突后大幅增加;网络结构经历了单核―多核―单核的转变,俄乌冲突后国际原油市场供需格局改变,较大规模的出口港对原油海运网络中广大进口港和其他中小规模出口港的控制力明显加强。3)海运网络核心边缘与组团耦合结构前期变化稳定,后期变化突出。俄乌冲突后核心边缘与组团耦合结构在核心港、地理分布和组团规模方面发生明显变革。4)海运网络变化对中国原油进口稳定性的影响显著且具有异质性。中国原油进口网络的稳定性先增后减,俄乌冲突后的降幅远大于冲突发生前的增幅;相比环渤海湾和长三角港口,东南沿海、珠三角和西南沿海港口的原油进口稳定性受俄乌冲突影响更大。

船舶多时间尺度能源管理系统研究

近年来随着能源日益短缺,船舶动力系统正向新能源化升级转型,但新能源出力的不确定性也为系统的经济、安全运行带来了新的挑战。因此传统船舶能源管理已不再适用,亟需适用于现代船舶的综合能源管理系统。针对以上情况,提出了一种上层采用能源优化调度、底层协调控制以及与智能算法相结合的综合能源管理策略,构建了新能源船舶微电网系统模型,并在相应的仿真平台上模拟了船舶处于加速航行、正常航行、减速航行以及停泊等四种不同运行工况。最后,在Matlab/Simulink平台上搭建了系统各部分的仿真模型,通过仿真结果,验证了所提出的策略能够在维持直流侧母线电压和系统稳定的前提下,实现供需双侧功率的高效平衡。

基于扩张状态观测器的滑模预测串级舵减摇控制

针对在定权重模型预测舵减摇控制下的欠驱动船舶转向响应较慢的问题,提出一种基于模糊扩张状态观测器(FESO)的滑模预测串级舵减摇控制方法。建立线性三自由度欠驱动船舶运动模型,设计FESO来估计船舶状态和外部扰动,设计离散自适应滑模控制(DASMC)作为串级外环航向控制,以外环控制作为预期控制律,设计模型预测控制(MPC)作为串级内环减摇控制。通过分析船舶的航向误差和航行情况,设计模糊规则在不同航行情况下改变MPC目标函数的状态权重和控制输入权重,理论证明了所设计观测器的收敛性和控制方法的闭环稳定性。通过对一艘多用途海军舰艇进行数值仿真分析,在航向改变的情况下,所设计的控制器减摇率在保证减摇效果的同时,相比固定权重线性MPC在30°的转向的响应时间更少,证明了所提方法能有效提升欠驱动船舶减摇时对转向的响应。

河道非法采砂对堤防防洪安全影响分析及研究

河道非法采砂社会影响恶劣,是各部门重点打击的对象,监管中传统手段是对开采出的河砂价值进行鉴定,实际往往难以界定,立案困难。针对非法采砂实例利用侧扫声呐对水下地貌特征进行探测,用无人测量船对水下地形进行测量,给出采砂区的平面范围、深度和体积等,对堤防稳定性进行计算,分析研究发现河道采砂区深泓点左右摆动严重,堤防抗滑稳定安全系数不足,严重影响河势稳定,危害防洪安全。文章采用的方法可对非法采砂进行定性定量判定,成本低、适应性强、效率高,为识别非法采砂、进行司法处理提供有效技术支撑,也可适用于中小河流非法采砂的监管。