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Technical management of vlcc/vlbc hull structures based on safety case principles

Lee, J A (2008) Technical management of vlcc/vlbc hull structures based on safety case principles. Doctoral thesis, Liverpool John Moores University.

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Abstract

Recent high profile accidents involving environmental damage caused by structural failures in ageing oil tankers and bulk carriers has highlighted the importance of structural integrity issues involving these types of ships. Between 1980 and 1996, there were 186 total losses of bulk and combination carriers and 1,278 lives lost. These events have led to concerns from the public, media and within the international maritime community, about deteriorating ship structural safety standards and the environmental impact. Evidence suggests that structural failure may account for more ship losses than hitherto believed. Industry critics have complained that the quality of designs for new tonnage and effectiveness of the present control mechanisms governing structural condition for vessels in service, are inadequate. Due to the relatively low safety margins inherent in modern commercial ship structural designs, a buyer beware policy prevails in ship procurement. A weakness in current ship design practice appears to be the difficulty of incorporating an owner's individual preferences. Recognising that to be effective, improvements in ship structural design must be implemented at the design stage, this study addresses the challenge of further improving the structural safety and performance of large bulk ships through exercising specific options related to the structural design of the ship within the remit of the buyer. A broad comprehensive literature survey was conducted to cast a wide net around the problem. The complex web of regulatory controls affecting the design and operation of bulk ship hull structures was analysed and problems involving design, construction and maintenance of these vessels were uncovered to build evidence to justify proposing an improved method. An analysis of recent high profile tanker and bulk carrier accidents involving structural failure was performed, to determine root causes. These findings formed the basis for a proposed novel risk-based "design for safety" framework The core of the method is the new evidential reasoning (ER) algorithm developed on the basis of a MCDA evaluation framework and the evidence combination rule of the Dempster-Shafer (D-S) Theory. A number of structural design options focused on the cargo tank mid body area of a typical double hull VLCC were evaluated. A set of quantitative and qualitative criteria were identified and articulated, leading to a structural evaluation framework for eliciting preferences for competing options. The MCDAlER model provides a risk-based, rational, transparent methodology for rapid techno-economic evaluation of alternative structural designs, putting buyers in a stronger position to balance risks and determine the expected structural safety outcomes of different designs. The ER modelling is performed using the Intelligent Decision System (IDS) software program developed by Yang and Xu. The method was tested with an example and validated through a sensitivity study. Finally, the evidence necessary for constructing and demonstrating the MCDAlER structural evaluation framework was used to build the arguments for a safety case approach to hull structures using the Australian Offshore safety case model. The safety case for hull structures is built upon a foundation of existing prescriptive statutory and classification society structural regulatory requirements. The advantages of the safety case applied to oil tankers were explained, including suggestions for a new regulatory approach. The application of new technology and tools was discussed.

Item Type: Thesis (Doctoral)
Subjects: H Social Sciences > HD Industries. Land use. Labor > HD61 Risk Management
V Naval Science > VM Naval architecture. Shipbuilding. Marine engineering
Divisions: Maritime and Mechanical Engineering
Date Deposited: 14 Mar 2017 10:37
Last Modified: 14 Mar 2017 10:37
URI: http://researchonline.ljmu.ac.uk/id/eprint/5919

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