A parametric study of wave loads on trimaran ships traveling in waves

In this paper, we present a spectral analysis based on wave loads to select suitable side-hull arrangements for a trimaran ship traveling in waves. Neglecting the steady flow effect, the three-dimensional source-distribution method, using a pulsating source potential incorporating the panel method, is adopted to solve the corresponding hydrodynamic coefficients. The significant values for wave loads, including shear forces, bending moments, and torsion moments at different locations on the main hull and connected deck with respect to different staggers and clearances, are derived by the spectral analysis. Several ship speeds and wave headings are also considered for comparison. This study offers more information for selecting the side-hull arrangement from the viewpoint of wave loads on trimaran ships, which may be regarded as helpful references for seakeeping design of these types of ships.     

A review of intact ship stability research and criteria

An investigation on capsizing of a vessel in a seaway is of paramount importance from the point of view of safety of life at sea. The present paper analyzes the major research efforts made throughout the world regarding intact stability and the establishment of stability criteria. Attempts have been made by the authors to draw conclusions from this analysis and to provide guidelines for future research efforts in the field of intact stability of ships.     

Experimental investigation of single blade and propeller loads by free running model test. Straight ahead sailing

The understanding and the accurate assessment of propeller loads in realistic operative scenario, both design and off-design conditions, is of paramount importance to design low emission and comfortable ships, fulfilling the requirements of structural integrity of the propulsion system, safety and continuity of operations at sea. To this purpose, a deeper characterization of the propeller functioning, in terms of averaged and fluctuating loads, can be attained by means of the quantification of the single blade loads. In this work, a novel set up that allows to monitor the loads developed by a single blade was implemented on a free running, self propelled maneuvering model with the aim to investigate in details the hydrodynamic interactions between the spatially non-homogeneous and time-variant wake of the hull and the propeller and a complete characterization of its performance. This preliminary work introduces the experimental setup and provides a preliminary overview of the results relative to straight ahead motion.     

Experimental investigation of blade and propeller loads: Steady turning motion

This paper is the continuation of the work described in [14], dedicated to the presentation of the results of propeller performance in behind-hull during straight ahead motion obtained by a novel experimental set-up for the measurements of single blade loads. In the present case, the study shows and discusses the single blade and propeller loads developed during steady turning conditions, that were simulated by means of free running, self propelled maneuvering tests for a twin screw configuration. Maneuvering conditions are critical for the ship propulsion system, because the performance of the propeller and the side effects related to its functioning (propeller–hull induced pressure and vibrations, noise) are completely different with respect to the design condition in straight ahead motion. Thrust and torque and generation of in-plane loads (force and moments), developed by the blade during the period, evolve differently for the two propellers, due to different propeller–wake interactions. The understanding and the accurate quantification of propeller loads, in these realistic operative scenarios, are pivotal to design low emission and comfortable ships, fulfilling the requirements of safety and continuity of operations at sea. The analysis is carried out revisiting the investigation in [14] for three different speeds (F_N = 0.26, 0.34 and 0.40) and a large set of rudder angles that span moderate and tight maneuvers.     

Full scale CFD seakeeping simulations for case study ship redesigned from V-shaped bulbous bow to X-bow hull form

Increasing propulsion efficiency, safety, comfort and operability are of the great importance, especially for small ships operating on windy sites like the North Sea and the Baltic Sea. Seakeeping performance of ships and offshore structures can be analysed by different methods and the one that is becoming increasingly important is CFD RANS. The recent development of simulation techniques together with rising HPC accessibility enables performance of advanced seakeeping simulations for ships in a full scale. The paper presents CFD seakeeping analysis for a case study vessel in two variants: V-shaped bulbous bow hull form (as built) and innovative hull form (X-bow type). The study presents the influence of redesigning the ship on selected seakeeping aspects. The advanced CFD model, with the application of overset mesh technique, was described in detail. Selected numerical results were validated on the basis of experimental testing in a towing tank and showed good agreement. The approach demonstrated here of performing the CFD seakeeping simulations for the analysis of ship performance in a full scale and close to real loading conditions has direct application to the design process as well as in determination of optimal operational parameters of any ship.     

Relationships between safety culture aspects – A work process to enable interpretation

Knowledge about the existing safety culture in a maritime organization such as in shipping companies or on board ships can enable the formulation of effective interventions to maintain and improve safety culture and safety in the organization. When assessing the safety culture, questionnaires developed for this purpose are often used. This paper proposes a work process that facilitates the analysis and interpretation of the relationships between safety culture aspects using questionnaire data. The work process includes the use of variable cluster analysis where the cluster solutions are presented in dendrograms. These were found to be an excellent way to visualize complex relationships in the quantitative data and to facilitate the understanding of the safety culture concept. Results are presented from applying the statistical process to safety culture data from six Swedish ships in international traffic. The visualized safety culture results can enable group discussions about safety on different organizational levels and can constitute an important input to the continuous improvement processes for safety and safety culture.     

螺旋桨对海冰切削作用的DEM-FEM耦合分析

当船舶在冰区航行时,螺旋桨会与海冰相互碰撞并导致桨叶的变形和损坏,进而影响船舶的航行安全。为研究海冰与螺旋桨的相互作用过程,采用离散元(DEM)—有限元(FEM)耦合方法构建海冰—螺旋桨切削模型。海冰和螺旋桨模型分别采用具有黏结—破碎特性的球体离散单元和8节点六面体有限单元构造。基于该DEM-FEM耦合模型讨论了不同切削深度下,螺旋桨所承受冰载荷的特点和规律;最后,研究了螺旋桨切削海冰过程中进速系数、推力系数、扭矩系数之间的对应关系,并讨论了海冰—螺旋桨相互作用过程中冰压力、Mises应力和变形的分布特点。以上研究可为寒区船舶安全航行和螺旋桨设计提供有益的参考。     

液舱晃荡载荷计算与强度校核系统研究

随着薄膜型LNG运输船的需求量不断增加,晃荡载荷已成为船舶安全性研究的重要内容之一。本文结合中国船级社规范所推荐的公式,对薄膜型LNG船晃荡水平的载荷进行研究,提出载荷计算方法和流程,在MSC.patran的基础上结合二次开发语言PCL,设计了一套晃荡载荷计算与校核系统。该系统对有限元模型进行前后处理,设计了舱室识别算法来搜索晃荡载荷的作用域,实现薄膜型LNG船晃荡载荷的自动计算与施加,完成屈服强度评估。通过算例测试证明本系统自动计算结果的有效性和准确性,可以为工程设计人员大大节约工作量,大幅度提高工作效率。     

Numerical prediction of green water incidents

Green water loads on moored or sailing ships occur when an incoming wave significantly exceeds the freeboard and water runs onto the deck. In this paper, a Navier–Stokes solver with a free surface capturing scheme (i.e. the VOF model; [Hirt and Nichols, 1981]) is used to numerically model green water loads on a moored FPSO exposed to head sea waves. Two cases are investigated: first, green water on a fixed vessel has been analysed, where resulting waterheight on deck, and impact pressure on a deck mounted structure have been computed. These results have been compared to experimental data obtained by [Greco, 2001] and show very favourable agreement. Second, a full green water incident, including vessel motions has been modelled. In these computations, the vertical motion has been modelled by the use of transfer functions for heave and pitch, but the rotational contribution from the pitch motion has been neglected. The computed water height on deck has been compared to the experimental data obtained by [Buchner, 1995a] and it also shows very good agreement. The modelling in the second case was performed in both 2-D and 3-D with very similar results, which indicates that 3-D effects are not dominant.     

Investigation on Effects of Vertical Degree of Freedom on Gap Resonance Between Two Side-by-Side Boxes Under Wave Actions

China Ocean Engineering - The possible wave resonance in the narrow gap formed by the parallel arrangement of ships will lead to the sharp increase of wave loads and the rapid growth of motion...     

航海通告自动获取系统的设计与实现

目前,从互联网获取航海通告数据是提高海图产品现势性、保障舰船航行安全的主要途径之一。基于对国内外网站特点、网页结构及网络爬虫技术、数据库技术的研究,提出了自动获取航海通告网页数据的总体方案;通过研发应用系统,实现了通告爬取、数据整理、数据库管理等主要功能。测试结果表明:较之传统工作方式,利用该系统获取的航海通告数据具有准确性、完整性、实时性和高效性,将为海图一体化生产体系提供更高质量的基础数据源支持。     

The Panama Ship Registry: 1917–2017

The Panama Ship Registry has its origins in the year 1917. Nowadays, Panama has the largest vessel registry in the world. The second placed registry in the world ranking is Liberia, which does not have even half the number of Panamanian ships. In this Centennial, the aim of this paper is to analyse the evolution of the Panamanian Registry, the structure of the Panamanian-flagged fleet and the level of compliance with international standards in relation to maritime safety and working conditions. To undertake the analysis, two different qualitative and quantitative approaches are compared and integrated for the evaluation of the Panama Ship Registry: the degree of ratification and enforcement of the Conventions and Recommendations of the International Maritime Organization and International Labour Organization, and the results of Panamanian flagged vessels in inspections carried out within the major Port State Control Memoranda of Understanding. This paper fills a research gap by discussing an approach to the concept of flag of convenience and flag State, Panama is more an international registry, whose role is becoming less important from the points of view of safety or working conditions. The fleet performance evolution has been very positive as evidenced by the data presented in this article regarding Port State Control.     

IMO框架下智能船舶适航的法律规制研究

随人工智能技术发展,智能船舶因其无人化、智能化的特点而与传统国际法律制度产生碰撞。当前,国际海事组织将制定“海上自主水面船舶规则”工作提上日程,航行安全问题作为其中的高度优先事项,受到各国广泛关注。船舶适航作为承运人的主要义务之一,是保障航行安全的先决条件。但智能船舶是否需要符合适航标准,如果适用会产生哪些法律障碍并如何解决等诸多问题亟待研究。对此,应修订《国际海上避碰规则》并明确智能船舶适船技术标准,明确岸基操作人员的法律地位并制定其资格取得、培训、值班标准,明确安全配员标准及需船员在船承担的职责的履行方式。     

The diminishing age gap between polar cruisers and their ships: A new reason to codify the IMO Guidelines for ships operating in polar waters and make them mandatory?

Ice, harsh weather, severe cold, and remoteness increase the risks of navigating the Arctic. Robust ships and shipboard systems to support routine operations and effectively respond to accidents and emergency situations are necessary. In spite of these challenges, the cruise ship industry is reportedly preparing to expand its passenger capacity, destinations, and operating season in the Arctic. An examination of the Arctic cruise ship fleet shows that the most capable ships are approaching the end of their service lives and may be replaced during the next decade. A window of opportunity is open for the international community to act on concerns about the safety of cruise ships in Polar Regions by codifying and making mandatory the International Maritime Organization's Guidelines for ships operating in Polar waters. A mandatory code would provide regulatory guidance to ship-builders at a critical point in the process of procuring new Arctic cruise ships and ensure that suitably constructed and outfitted ships would serve Arctic cruisers.     

Automatic collision avoidance of multiple ships based on deep Q-learning

As the number of ships for marine transportation increases with the globalisation of the world economy, waterways are becoming more congested than before. This situation will raise the risk of collision of the ships; hence, an automatic collision avoidance system needs to be developed. In this paper, a novel approach based on deep reinforcement learning (DRL) is proposed for automatic collision avoidance of multiple ships particularly in restricted waters. A training method and algorithms for collision avoidance of ships, incorporating ship manoeuvrability, human experience and navigation rules, are presented in detail. The proposed approach is investigated not only by numerical simulations but also by model experiments using three self-propelled ships. Through the systematic numerical and experimental validation, it is demonstrated the developed approach based on the DRL has great possibility for realising automatic collision avoidance of ships in highly complicated navigational situations.     

Wave-in-deck loads on exposed jetties

This paper presents results from research on the hydraulic loadings of exposed (unsheltered) jetties (open pile piers with decks and beams). The work presented here focuses on results from physical model tests on wave-induced loads on deck and beam elements of exposed jetties and similar structures. These tests investigated the physics of the loading process, and provided new guidance on wave-in-deck loads to be used in design. Wave forces and pressures were measured on a 1:25 scale model of a jetty head with projecting elements. Structure geometry and wave conditions tested were selected after an extensive literature review (summarised in the paper) and consultation with the project steering group. Different configurations were tested to separate 2-d and 3-d effects, and to identify the effects of inundation and of down-standing beams.     

多级可分离式AUV系统设计与仿真分析

多级可分离式自主水下航行器(MS-AUV)可搭载多种不同功能的载荷舱,并在目标海域完成载荷舱布放。其在海洋探测,海防等领域具有较高的应用价值。对MS-AUV进行了主体结构和分离机构的设计和研究,其中功能载荷舱与航行器本体采用真空连接方式,实现多级连接,降低了机构的复杂性,提高了载荷舱分离运动的稳定性和安全性。为了研究载荷舱与航行器分离的安全性,采用CFD和六自由度(6-DOF)刚体运动学的耦合方法来模拟其在水下的分离运动。在仿真过程中,采用弹簧光顺和局部重构混合网格生成方法的非结构化动态网格可以很好地适应大距离多体分离运动。仿真结果表明,在一定工况条件下,提高MS-AUV初始航行速度V0和分离机构弹簧刚度K有利于载荷与航行器本体分离。通过上述研究工作,验证了载荷分离方法的可行性,缩短研制周期,降低设计成本,对多级可分离式AUV样机的设计制造具有重要的参考价值。     

Numerical Simulation on the Resistance Performance of Ice-Going Container Ship Under Brash Ice Conditions

Ice resistance prediction is a critical issue in the preliminary design of ships navigating brash ice conditions, which is closely related to the safety of a ship to navigate encounter brash ice, and has significant effects on the kinds of propellers and motor power needed. In research on this topic, model tests and full-scale tests on ships have thus far been the primary approaches. In recent years, the application of the finite element method (FEM) has also attracted interest. Some researchers have conducted numerical simulations on ship–ice interactions using the fluid–structure interaction (FSI) method. This study used this method to predict and analyze the resistance of an ice-going ship, and compared the results with those of model ship tests conducted in a towing tank with synthetic ice to discuss the feasibility of the FEM. A numerical simulation and experimental methods were used to predict the brash ice resistance of an ice-going container ship model in a condition with three concentrations of brash ice (60%, 80%, and 90%). A comparison of the results yielded satisfactory agreement between the numerical simulation and the experiments in terms of both observed phenomena and resistance values, indicating that the proposed numerical simulation has significant potential for use in related studies in the future.     

Methods for ultimate limit state assessment of ships and ship-shaped offshore structures: Part II stiffened panels

The present paper is Part II of a series of three papers on methods useful for the ultimate limit state assessment of ships and ship-shaped offshore structures. In contrast to Part I [Paik et al., 2007a. Methods for ultimate limit state assessment of ships and ship-shaped offshore structures: Part I unstiffened plates, Ocean Engineering, doi:10.1016/j.oceaneng.2007.08.004] that deals with unstiffened plates, the present paper (Part II) is focused on methods for the ultimate limit state assessment of stiffened plate structures under combined biaxial compression and lateral pressure actions. The object structure is the bottom part of an AFRAMAX-class hypothetical double-hull oil tanker structure designed by IACS common structural rules (CSR) method, that is the same ship studied in Part I. Three candidate methods, namely ANSYS nonlinear finite element method, DNV PULS method, and ALPS/ULSAP method, are employed for the present study. The results and insights developed from the present study are summarized in terms of ultimate strength characteristics of bottom-stiffened plate structures.     

宽带波浪载荷下海洋结构物内应力范围及疲劳损伤分析

研究短期海况中海洋结构物在宽带波浪载荷作用下交变应力过程中的应力范围的概率分布及结构疲劳损伤问题.首先从应力的功率谱密度出发,利用小波变换作为工具,对应力过程进行模拟.然后用雨流计数法识别出应力过程中对结构造成疲劳损伤的应力范围,并用Weibull分布对应力范围的分布进行了拟合;最后给出了应力范围服从Weibull分布时结构疲劳损伤的计算方法.