Sensitivity analysis of the probabilistic damage stability regulations for RoPax vessels

In the light of the newly developed harmonised probabilistic damage stability regulations, set to come into force in 2009, this article presents a systematic and thorough analysis of the sensitivity of the Attained Subdivision Index with reference to a wide range of related design parameters. The sensitivity of the probabilistic regulations was investigated for a typical large RoPax vessel, with variation of parameters, such as the number, positioning and local optimisation of transverse bulkheads; the presence and position of longitudinal bulkheads below the main vehicle deck; the presence of side casings; and the height of the main deck and double bottom. The effects of water on deck and of operational parameters (draught, centre of gravity and trim) were also investigated. The results of the study, presented in graphical form, can provide valuable assistance to the designer when determining subdivision characteristics at the very early stage of the design process, resulting in optimal, efficient and safe ships.     

Parametrical studies of a new numerical model for controlled ship motions in extreme astern seas

Parametrical studies based on numerical simulations were carried out for very steep regular waves to assess possible improvements in the state-of-the art numerical modelling of the control and capsizing behaviour of ships in following and quartering seas. A nonlinear 6-DOF numerical model has been developed with the inclusion of frequency-dependent terms, the so called memory effects, and a flexible axis system that allows straightforward combination of seakeeping and manoeuvring models while accounting for extreme motions. The previously undertaken validation analyses using extensive model test data provided qualitatively good agreement, whereas the comparison with numerical models without coupling of the vertical motions and frequency-dependent hydrodynamic terms embodied in radiation forces identified improvements in the accuracy. However, to broaden the assessment of the numerical model, further parametrical numerical analyses were carried out using two ships, which had previously been tested in the validation analyses, for various operational and environmental conditions. These parameters were changed in accordance with the recommendations from international organisations and experience from model tests to realise and avoid dangerous conditions that often result in capsizing, such as broaching associated with surf riding and low-cycle resonance. As a result of the parametric analysis, we discuss the sensitivity of the improvements in the numerical model for various critical operational and design parameters and its possible use to provide a link between the ship's behavior and these parameters.     

Risk analysis for RoPax vessels

The paper presents the results of a recent risk analysis study for RoPax vessels, carried out as part of the activities of the SAFEDOR Integrated Project. The objective of this study was to investigate the causes of hazards during RoPax operation and quantify, to the extent possible, their frequencies and consequences. Potential scenarios initially identified and prioritised during a Hazard Identification (HAZID) session were used in the process.     

A RANS-based technique for simulation of the flow near a rolling cylinder at the free surface

Accurate prediction of roll motion is very important in ship dynamics, particularly when the safety of the ship is in question. In this paper "COMET," a Reynolds averaged Navier–Stokes (RANS) solver, is used to simulate the flow in the vicinity of a rectangular cylinder rolling at the free surface and to demonstrate the potential of RANS-based techniques in complex flows with free surfaces. The method adopted is based on an unstructured collocated finite-volume technique, which uses a variation of the SIMPLE scheme for pressure correction. An advanced interface capturing technique known as high resolution interface capturing (HRIC) is used for tracking the free surface with reduced numerical diffusion. The results derived are compared with available numerical and experimental results, showing good agreement on added moment of inertia and damping coefficients, whilst accurately predicting other main features of the flow. However, further validation for other geometries and extension to 3-D hull forms are essential before applications to practical problems are realised. Received: January 26, 2000 / Accepted: October 2, 2000     

Development of Bayesian network models for risk-based ship design

In the past fifteen years, the attention of ship safety treatment as an objective rather than a constraint has started to sweep through the whole maritime industry. The risk-based ship design (RBD) methodology, advocating systematic integration of risk assessment within the conventional design process has started to takeoff. Despite this wide recognition and increasing popularity, important factors that could potentially undermine the quality of the results come from both quantitative and qualitative aspects during the risk assessment process. This paper details a promising solution by developing a formalized methodology for risk assessment through effective storing and processing of historical data combined with data generated through first-principle approaches. This method should help to generate appropriate risk models in the selected platform (Bayesian networks) which can be employed for decision making at design stage.     

绕Wigley船自由表面粘性流场计算

本文采用商用粘性流场求解软件COMET计算带自由液面绕Wigley船的粘性流动，网格数约为216000。计算中使用标准k-ε湍流模式和壁函数。用HRIC算法确定自由面。同时域步进法得到稳态解，计算的在傅氏数为0.30时的阻力结果与模型试验测量值吻合良好。预报的船体周围的波型及船体表面的波面形状也较合理。     

A risk-based first-principles approach to assessing green seas loading on the hatch covers of bulk carriers in extreme weather conditions

This paper aims to present and explain the work undertaken at the SSRC on the Safety of Bulk Carriers in extreme weather conditions over the past 3 years, to draw conclusions deriving there from, concerning key influencing design, operational and environmental parameters and to offer recommendations regarding the rule development process and on the way forward considering research, development and implementation to ship design and operation with the view to improving the safety of these ships cost-effectively. In severe storms, hatch covers of low freeboard vessels such as bulk carriers are the first-line of protection against flooding. Present methods of hatch covers design are still empirical because impact loads due to green seas and structural behaviour due to this type of loads have not been examined, hence not known accurately. The loading due to green seas is implicitly non-linear and, as model test results demonstrated, bulk carriers in extreme conditions are exposed to significant loads, which in some cases exceed current design standards. Since the consequences of hatch cover failure are potentially catastrophic, the risk of this happening should be quantified in probabilistic terms as required by modern safety standards. To this end, the paper aims to propose and implement a methodology for estimating probabilities of deck wetness and impact loads due to green seas as a function of key design and operational parameters.     

一种计算SES船尾波(Wash wave)的数值方法

本文提出了一种无限深水中表面效应船(Surface Effect Ship,SES)尾波(Wash wave)数值方法.SES的尾波被表达成分布在气垫上的压力在静水中航行产生的兴波波浪场.在线性势流假设下,该尾波可解析地表示为积分形式,而其被积函数带有奇性并高频振荡.文中提出了一个变换,使变换后对不同的航速,SES船形(气垫形状)和所要计算的波浪场位置尾波计算中的被积函数是单调变化,因而易于数值计算.积分中的奇性也予以去除.数值计算结果表明本文提出的数值方法具有较高的计算效率而且结果与已发表的结果吻合良好.文中给出了一些SES船尾波(Wash wave)的计算结果,并进一步分析了SES尾波(Wash wave)中的局部和非局部波浪场成分.文中还尝试使用本文方法预报常规高速双体船的尾波(Wash wave),结果发现预报与水池测量结果相当吻合.     

带舭龙骨柱体的横摇阻尼的粘性流计算

文章用RANSE求解器计算在自由面上带舭龙骨二维柱体的横摇水动力系数(附加惯量和阻尼).采用有限体积法(VOF)和两相流技术在时间域内求解柱体横摇强迫振荡所扰动的带自由面粘性流场.由柱体所受到的横摇水动力矩的时间历程导出横摇水动力系数.文中所给算例与已公开发表的试验结果吻合令人满意.     

Robust analysis of cost-effectiveness in formal safety assessment

The paper probes the robustness of the present method for evaluating the cost-effectiveness (CE) of risk control options, which are identified through the International Maritime Organisation Guidelines on Formal Safety Assessment (FSA). We highlight the deficiencies of the current CE method, undermining its lucidity and consistency in application. The proposed approach outlines a mathematical formulation that neatly integrates all aspects of CE measures along with its application based on the Pareto dominance concept. We benchmark our method against CE results found in the FSAs for cargo and passenger ships, demonstrating the ease of application and clarity of interpretation.