H. S. Sii

Review of Uncertainty Reasoning Approaches as Guidance for Maritime and Offshore Safety-Based Assessment

Abstract Many different formal techniques have been developed over the past two decades for dealing with uncertain information for decision making. In this paper we review some of the most important ones, i.e., Bayesian theory of probability, Dempster-Shafer theory of evidence, and fuzzy set theory, describe how they work and in what ways they differ from one another, and show their strength and weakness respectively as well as their connection. We also consider hybrid approaches which combine two or more approximate reasoning techniques within a single reasoning framework. These have been proposed to address limitations in the use of individual techniques. The study is intended to provide guidance in the process of developing frameworks for maritime and offshore safety-based decision analysis using different methods for reasoning under uncertainty.

Use of fuzzy logic approaches to safety assessment in maritime engineering applications

Safety assessment based on conventional methods such as probability risk assessment (PRA) may not be well suited for dealing with innovative systems having a high level of uncertainty, particularly in the feasibility and concept design stages of a maritime engineering system. By contrast, safety models using fuzzy logic approaches employing fuzzy IF-THEN rules can model the qualitative aspects of human knowledge and reasoning processes without employing precise quantitative analyses. Fuzzy-logic-based approaches may be more appropriately used to carry out risk analysis in the initial design stages of large maritime engineering systems. This provides a tool for working directly with the linguistic terms commonly used in carrying out safety assessment. This paper focuses on the development and representation of linguistic variables to model risk levels subjectively. These variables are then quantified using fuzzy set theory. In this paper, the development of two safety evaluation frameworks using fuzzy logic approaches for maritime engineering safety-based decision support in the concept design stage are presented. An example is used to illustrate and compare the proposed approaches. Future risk analysis in maritime engineering applications may take full advantages of fuzzy logic approaches to complement existing ones.

A Fuzzy-Logic-Based Approach to Subjective Safety Modelling for Maritime Products

ABSTRACT Safety assessment based on conventional tools (e.g., probability risk assessment (PRA)) may not be well suited for dealing with systems having a high level of uncertainty, particularly in the feasibility and concept design stages of a maritime or offshore system. By contrast, a safety model using fuzzy logic approach employing fuzzy IF-THEN rules can model the qualitative aspects of human knowledge and reasoning processes without employing precise quantitative analyses. A fuzzy-logic-based approach may be more appropriately used to carry out risk analysis in the initial design stages. This provides a tool for working directly with the linguistic terms commonly used in carrying out safety assessment. This paper focuses on the development and representation of linguistic variables to model risk levels subjectively. These variables are then quantified using fuzzy sets. In this paper, the development of a safety model using fuzzy logic approach for modelling various design variables for maritime and offshore safety based Decision making in the concept design stage is presented. An example is used to illustrate the proposed approach.

Marine and Offshore Safety Assessment

Abstract This brief communication serves to introduce a marine and offshore safety assessment research project, which has been carried out at both Staffordshire and Liverpool John Moores Universities.

A design-decision support framework for evaluation of design options/proposals using a fuzzy-logic-based composite structure methodology

With the high cost of construction, operation and maintenance, the offshore industry is seeking ways of reducing both the time and money spent to provide high-quality offshore structures needed to support the oil and gas extraction and production. The successful selection process for choosing a design/procurement proposal is based on a high degree of technical integrity, high safety levels and low costs in construction, maintenance and operation. However, the objectives of maximizing the degree of technical performance, maximizing the safety and minimizing the cost incurred are usually in conflict. The evaluation of the technical performance, safety and cost is always associated with uncertainty, especially for a novel system in the initial concept design stages. In this paper, a decision support framework using a composite structure methodology is suggested for design evaluation of offshore engineering products in the initial stages. It is a multiple criteria decision-making framework, which provides a juxtaposition of safety, cost and technical performance objectives of a system during the evaluation to assist decision-makers in selecting the winning design/procurement proposal that best satisfies the requirement in hand. An example is used to illustrate the proposed framework.

Some Novel Risk-modelling and Decision-making Approaches

Abstract The safety culture in the marine and offshore industries has changed significantly over the last decade. The importance of employing a risk-based regime has been widely recognised. This allows safety engineers to use novel risk modelling and decision making approaches to deal with problems that cannot be treated in a rational manner using conventional methods. In this paper, following the review of the current status of risk assessment in both the marine and offshore areas, a general discussion on risk modelling and decision making is described. Four novel risk modelling and decision making approaches are then described with illustrative examples. Finally, brief recommendations on further development in risk modelling and decision making are suggested.

A safety-cost based design-decision support framework using fuzzy evidential reasoning approach

This paper illustrates a subjective safety-cost based design-decision support framework using fuzzy logic and evidential reasoning approaches. The framework is divided into three parts. The first one is for safety estimate and synthesis including fuzzy rule-based safety estimate using fuzzy rule-based evidential reasoning (FRB-ER) approach, as well as the safety synthesis using evidential reasoning approach. Considering the cost incurred for the safety improvement in a design option, the second part focuses on synthesising the safety and cost estimates using evidential reasoning approach to obtain the overall evaluation of the whole system for each design option. The third part is to apply the overall evaluation for the design selection. An illustrative example is used to demonstrate the application of the proposed framework.

The Evidential Reasoning approach for Inference in rule-based systems

In this paper a generic Rule-base Inference Methodology using the Evidential Reasoning approach (RIMER) is proposed. A new knowledge representation scheme in a rule-base is proposed using a belief structure and fuzzy set theory. In this scheme, a rule-base is designed on the basis of the belief structure with belief degrees embedded in all possible consequents to capture vagueness, incompleteness and nonlinear causal relationships, whilst traditional IF-THEN rules can be represented as a special case. In an established rule-base, an input to an antecedent attribute is transformed into a belief distribution. Subsequently, inference in such a rule-base is implemented using the evidential reasoning approach. The scheme is further extended to inference in hierarchical rule bases. A numerical study is provided to illustrate the potential applications of the proposed methodology.

The Application of Approximate Reasoning Methodologies to Offshore Engineering Design Based on Risk Assessment

In dealing with complex and ill-defined systems of an offshore application, modelling of human reasoning for the purpose of risk assessment requires the effectiveness of a systematic logic-based approach. Floating production, storage and offloading (FPSO) installations, for example, combine traditional process technology with marine technology, and thus are quite dependent on technical design and operational safety control. Such safety-critical dependencies require novel approaches to properly analyse the risk involved. Hence, a proposed framework utilising approximate reasoning and evidential reasoning approaches is provided for modelling the assessment task. As based on fuzzy set theory, the model enables uncertainties to be described mathematically and further processed in the analysis of the structures. The forms of membership functions that could be used in representing fuzzy linguistic variables to quantify risk levels are presented. A case study of collision risk between FPSO and shuttle tanker due to technical failure during tandem offloading operation is used in this paper to illustrate the application of the proposed model. Furthermore, the obtained results from the case study provide confirmation that at various stages of offshore engineering systems design process the framework of incorporated approximate reasoning is a suited and convenient tool for attaining reliable risk analysis.© 2004 ASME

Design for Safety of Large Marine Engineering Products

As maritime engineering products become more and more complex and the public concern regarding their safety increases, design for safety has attracted more and more attention in the marine and offshore industries. This paper reviews the current practices in risk assessment employed in the marine and offshore industries. The issues in risk assessment of large maritime engineering products are highlighted. A design for safety methodology is described together with the typical supporting risk assessment techniques. Several novel safety modelling and decision making techniques are outlined. Examples are used to demonstrate two novel risk modelling and decision making tools described with an aim of providing safety engineers with an opportunity to appreciate the novel approaches.Copyright