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SSARS 2008 Volume 1

Abrahamsen Eirik Bjorheim, Aven Terje Safety oriented bubble diagrams in project risk management |

In project risk management many firms use bubble diagrams to get a graphical presentation of a project’s most uncertain attributes. The bubble diagrams and procedures used to put attributes into these diagrams are seen to provide a rational framework for managing risks. In this paper we review and discuss the use of these diagrams and procedures. Special attention is given to the way safety is treated. We show that the standard use of bubble diagrams is not adequate for identification and follow up critical activities that affect safety. The main problem is that the present structure means that the uncertainty is not properly taken into account. In this paper a reformulated bubble diagram is suggested that better reflects safety related uncertainties. The offshore oil and gas industry is the starting point, but the discussion is to large extent general. [full text] |

Aldemir Tunc Dynamic methodologies for reliability and probabilistic risk assessment (PRA) |

Dynamic methodologies in reliability and PRA are those that explicitly account for the time element in probabilistic system evolution. Dynamic methodologies are usually needed when the system has more than one failure mode, control loops, and/or hardware/process/ software/human interaction. An overview of the dynamic methodologies proposed to date is given, including those that use dynamic event tree generation, continuous time-state space representation, the cell-to-cell mapping technique and graphical schemes. The use of dynamic methodologies for state/parameter estimation in on-line applications is also discussed. Potential on-line use of dynamic methodologies as operator assistance tools for risk informed accident management or normal operation is described and illustrated.[full text] |

Aven Terje Risk analysis and risk management. Basic concepts and principles |

This paper reviews and discusses some key concept and principles of risk analysis and risk management, based on a set of statements, formulated as myths about risk. Examples of such myths are: risk is equal to the expected value, risk equals uncertainty, risk can be expressed by probabilities, risk is equal to an event, risk acceptance criteria contribute to obtaining a high safety standard, and ALARP can be verified by cost-benefit analyses. It is concluded that risk needs to address both the consequences and the uncertainties about the consequences, and that it is necessary to see beyond expected values and probabilities[full text] |

Babiarz Bożena Operational reliability of heat supply systems |

The paper contains an analysis of the operational process of heat supply system with taking into consideration its reliability. The specific character of the operation of heat-supply systems has been considered in this work. In the process of the exploitation of heat-supply systems there have been distinguished five operational states, assuming as a criterion of the level of indoor temperature decrease in residential rooms. The method of modelling the operational reliability of heat-supply systems is worked out. The methodology of determining the overall index of heat-supply system reliability has been presented. The measure of heat-supply system reliability has been assumed as the scale/quantity of inadequate supply of heat power at a given state. Calculations have been carried out regarding the changeability of exterior conditions for one of the groups of customers – residential users. On the basis of the operational data for the heat supply system with two heat sources shortage quantities of heat power and the probability of their occurrence have been calculated as an application of this methodology.[full text] |

Baraldi Piero, Zio Enrico, Compare Michele Importance measures in presence of uncertainties |

This paper presents a work on the study of importance measures in presence of uncertainties originating from the lack of knowledge and information on the system (epistemic uncertainties). A criterion is proposed for ranking the risk contributors in presence of uncertainties described by probability density functions.[full text] |

Bérenguer Christophe On the mathematical condition-based maintenance modelling for continuously deteriorating systems |

This paper presents a modelling framework of condition-based maintenance policies for continuously deteriorating systems, based on semi-regenerative stochastic techniques.[full text] |

Berg Heinz-Peter Quantitative safety goals as a basis for decision making |

Internationally, probabilistic safety analyses represent the state of the art in the licensing process for new industrial facilities, but increasingly also for evaluating the safety level of older industrial plants, e. g. as part of periodic safety reviews of nuclear power plants. Quantitative safety goals have not yet reached the same level of acceptance. However, this depends on the type of industry. Most of the countries consider those criteria as safety targets rather than as sharply defined boundary values. The Netherlands and the United Kingdom are exceptions, they require demonstration of compliance with legally binding safety goals in the licensing procedure.[full text] |

Berg Heinz-Peter Risk and safety management – procedures, methods, experiences |

Risk management is an activity which integrates recognition of risk, risk assessment, developing strategies to manage it, and mitigation of risk using managerial resources. Some traditional risk managements are focused on risks stemming from physical or legal causes (e.g. natural disasters or fires, accidents, death). Financial risk management, on the other hand, focuses on risks that can be managed using traded financial instruments. Objective of risk management is to reduce different risks related to a pre-selected domain to an acceptable. It may refer to numerous types of threats caused by environment, technology, humans, organizations and politics. The paper describes the different steps in the risk management process which methods are used in the different steps, and provides some examples for risk and safety management.[full text] |

Blokus-Roszkowska Agnieszka, Kołowrocki Krzysztof Modelling environment and infrastructure of shipyard transportation systems and processes |

In the paper an analytical model of port transportation systems environment and infrastructure influence on their operation processes is constructed and presented in an example of shipyard rope transportation systems in Naval Shipyard in Gdynia. A general semi-markov model of a system operation process is proposed and the methods of its parameters statistical identification are presented. Further, the shipyard rope transportation system and the ship rope elevator operation processes are analyzed and their operation states are defined. A preliminary collection of statistical data necessary to the ship transportation systems’ operation processes identification is included.[full text] |

Bouvard Keomany, Artus Samuel, Bérenguer Christophe, Cocquempot Vincent Maintenance cost study for deteriorating systems: age-replacement policy vs. condition-based maintenance policy |

This paper deals with the maintenance cost of deteriorating systems. Two maintenance strategies are studied: age-replacement and condition-based maintenance. To compare these two policies, degradation models are used: these models characterize the degradation level but also the system time-to-failure. In order to compute the optimal condition-based maintenance cost, we suppose that the main influencing sources are the preventive threshold, the inspection frequency and the inspection cost. Numerical examples illustrate the maintenance cost computation and compare the optimal costs of both policies. [full text] |

Carpignano Andrea, Ganci Francesco Uncertainties on risk analysis: the consequence assessment in an hydrogen refuelling station |

The paper concerns the problem of uncertainty associated to risk analysis of complex technological systems; this problem is not easy to resolve and manage. This is because such uncertainty has never been simple to quantify and, despite several innovative techniques able to properly manage uncertainties are available, none of these methodologies is integrated on the risk analysis in order to evaluate the error propagation. Also the itself risk analysis is not a precisely defined procedure but rather a complicated process of several parts and, moreover, each part is characterized by its own uncertainty. Several studies highlighted as the phases which mainly contribute to the overall uncertainty of a risk analysis are consequence and vulnerability studies. In order to provide a signifying approach to the problem, the working team has decided to focus their attention on a very important target for population safety: the hydrogen refuelling station for automotive.[full text] |

Cha Ji Hwan Burn-in procedures in accelerated environment and system maintenance policies |

Burn-in is a widely used engineering method which is adopted to eliminate defective items before they are shipped to customers or put into field operation. In order to shorten the burn-in process, burn-in is most often accomplished in an accelerated environment. However, there have been few probabilistic or stochastic models for the burn-in procedures in accelerated environment. In this paper, under a new stochastic model for accelerated burn-in procedure, the problems of determining both optimal accelerated burn-in time and optimal replacement policy are considered. Components are burned-in under an accelerated environment, then those surviving the burn-in procedure are put into field operation and they are maintained under a replacement policy. The properties of the optimal accelerated burn-in time and optimal replacement policy are obtained and a numerical example which illustrates the usage of obtained results will be presented.[full text] |

Flage Roger, Aven Terje Expressing and communicating uncertainty in relation to quantitative risk analysis (QRA) |

A quantitative risk analysis (QRA) should provide a comprehensive, informative and balanced picture of risk, in order to support decisions. To achieve this, a proper treatment of uncertainty is a prerequisite. Most approaches to treatment of uncertainty in QRA seem to be based on the thinking that uncertainty relates to the calculated probabilities and expected values. This causes difficulties when it comes to communicating what the analysis results mean, and could easily lead to weakened conclusions if large uncertainties are involved. An alternative approach is to hold uncertainty as a main component of risk, and regard probabilities as epistemic-based expressions of uncertainty. In the paper the latter view is taken, and we describe what should be the main pillars of a risk description following this approach. We also indicate how this approach should relate to decision-making. An important issue addressed is how to communicate the shortcomings and limitations of probabilities and expected values. Sensitivity analysis plays a key role in this regard. An example is included to illustrate ideas and findings.[full text] |

Grabski Franciszek, Załęska-Fornal Agata Applications of bootstrap and resampling methods in empirical Bayes estimation of reliability parameters |

Bootstrap and resampling methods are the computer methods used in applied statistics. It is a type of Monte Carlo method based on observed data. Bradley Efron described it in 1979 and he has written a lot about the method and its generalizations since then. Here we apply these methods in an empirical Bayes estimation using bootstrap or resampling copies of the data to obtain an empirical prior distribution. [full text] |

Gucma Lucjan Models and methods of ship-bridge collisions risk assessment |

The chapter presents methods and models used nowadays for risk assessment of ship-bridge collisions [full text] |

Gucma Lucjan, Schoeneich Marta Monte Carlo method of ship’s underkeel clearance evaluation for safety of ferry approaching to Ystad Port determination |

The paper is concerned with the analysis of simulation research results of newly design Piast ferry entering to modernized Ystad Port. The ship simulation model is described. After execution of real time simulations the Monte Carlo method of underkeel clearance evaluation is applied to asses the probability of ferry touching the bottom. The results could be used in risk assessment of ships entering to the ports.[full text] |

Gucma Maciej Risk based model of information optimization in maritime electronic chart application |

The paper is concerned on a statistical approach to the solution of practically very important problem, of risk based criteria’s, in field of testing and development of a sea electronic chart. Criteria estimation in human - computer systems is difficult, and not in every case might be satisfactory. In many cases wrong criteria estimation might occur in inapplicability of whole system. In paper author copes with universal model of information optimization for navigation chart system using example of pilot navigation system. [full text] |

Guo Renkuan, Guo Danni DEAR theory and applicability in system dynamics analysis |

In this paper, we introduce our newly created DEAR (an abbreviation of Differential Equation Associated Regression) theory, which merges differential equation theory, regression theory and random fuzzy variable theory into a new rigorous small sample based inferential theoretical foundation. We first explain the underlying idea of DEAR modelling, its classification, and then the M-estimation of DEAR model. Furthermore, we explore the applicability of DEAR theory in the analysis in system dynamics, for example, repairable system analysis, quality dynamics analysis, stock market analysis, and ecosystem analysis, etc. [full text] |

Guo Renkuan, Guo Danni Fuzzy regression – a scalar variable formation |

In reliability, quality control and risk analysis, fuzzy methodologies are more and more involved and inevitably introduced difficulties in seeking fuzzy functional relationship between factors. In this paper, we propose a scalar variable formation of fuzzy regression model based on the credibility measure theoretical foundation. It is expecting our scalar variable treatments on fuzzy regression models will greatly simplify the efforts to seeking fuzzy functional relationship between fuzzy factors. An M-estimator for the regression coefficients is obtained and accordingly the properties and the variance-covariance for the coefficient M-estimators are also investigated in terms of weighted least-squares arguments. Finally, we explore the asymptotic membership function for the coefficient M-estimators.[full text] |

Guze Sambor Reliability analysis of two-state series-consecutive “m out of k: F” systems |

A non-stationary approach to reliability analysis of two-state series and consecutive “m out of k: F” systems is presented. Further, the series-consecutive “m out of k: F” system is defined and the recurrent formulae for its reliability function evaluation are proposed. Moreover, the application of the proposed formulae to reliability evaluation of the radar system composed of two-state components is illustrated. [full text] |

Guze Sambor Reliability analysis of two-state consecutive “m out of l: F”-series systems |

A non-stationary approach to reliability analysis of two-state series and consecutive “m out of k: F” systems is presented. Further, the consecutive “m out of k: F”-series system is defined and the recurrent formulae for its reliability function evaluation are proposed. Moreover, the application of the proposed formulae to reliability evaluation of … composed of two-state components is illustrated.[full text] |

Guze Sambor, Kołowrocki Krzysztof, Soszyńska Joanna Modelling environment and infrastructure influence on reliability and operation processes of port oil transportation system |

In the paper a probabilistic model of industrial systems environment and infrastructure influence on their operation processes is proposed. Semi-markov processes are used to construct a general model of complex industrial systems’ operation processes. Main characteristics of this model are determined as well. In particular case, for a port oil transportation system, its operation states are defined, the relationships between them are fixed and particular model of its operation process is constructed and its main characteristics are determined. Further, the joint model of the system operation process and the system reliability is defined sand applied to the reliability evaluation of the port oil transportation system.[full text] |

Jodejko Anna Maintenance problems of technical systems composed of heterogeneous elements |

The paper gives a short insight into the complexity of maintenance problems of a system composed of heterogeneous elements. The article proposes a simple algorithm to define parameters of block maintenance policy of multi-unit systems composed of elements with economic dependency. The procedure may be used especially in the case when elements of a system are not identical in the sense of their probability characteristics and analytical solution is inaccessible. [full text] |