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SSARS 2009 Voulme 1

Abrahamsen Eirik Bjorheim, Aven Terje, Iversen Rune Sæbøe An integrated framework for safety management and uncertainty management in petroleum operations |

In petroleum operations, the safety management and the uncertainty management have traditionally been completely separated functions. The two disciplines are to large extent based on different scientific pillars and it has been difficult to obtain an integrated approach. However, the recent introduction of risk perspectives highlighting the uncertainty component of risk has provided an improved basis for development of such an approach. By seeing risk as the two-dimensional concept covering events and consequences on the one hand side and uncertainties on the other, the content and boundaries of risk assessments are changed. The gap between the two disciplines can to large extent be bridged. The purpose of the present paper is to present and discuss an integrated framework for these disciplines and traditions, based on this risk perspective. An example is included to show the practical implications of the framework. [full text] |

Abrahamsen Eirik Bjorheim, Aven Terje, Røed Willy A new visualizing tool for communicating cost-effectiveness of safety measures |

A cost-effectiveness analysis (CEA) is often used as basis for comparisons between competing safety measures. In a CEA indices such as the expected cost per expected number of lives saved are calculated. These indices are presented to the decision-makers, and seen in relation to reference values, they form the basis for assessment of the effectiveness of the safety measures. The appropriateness of using cost-effectiveness indices based on expected values have been thoroughly discussed in the literature. It is argued that uncertainty is not properly taken into account by the CEA, and extended frameworks for CEA are required. This paper represents a contribution to this end, by presenting a diagram that visualizes uncertainty in addition to the expected values as in the traditional CEA. The diagram is meant to be a presentation tool for semi-quantitative cost-effectiveness analyses used as a part of a screening process to identify safety measures to be assessed in a more detailed analysis. In the paper we discuss the use of the diagram in communication between analysts and other stakeholders, in particular the decision-makers. An example is presented to illustrate the applicability of the tool. [full text] |

Albeanu Grigore, Averian Alexandru, Duda Iordan Towards web applications reliability engineering |

There is an increasing request for web-based software systems, some of them to be used very intensive. The customers ask not only for fast design and implementation, but also for a high quality product. Considering reliability as an important quality attribute, this paper describes the current state of the art in designing, implementing, and testing web-based applications. An important attention is given to web-based software vulnerabilities and how to deliver secure software. Then, reliability modeling in the case of secure web-based software is discussed.[full text] |

Berg Heinz-Peter Corrosion mechanisms and their consequences for nuclear power plants |

It is well known that operational conditions in light water reactors strongly influence the corrosion processes. This paper gives an overview which types of corrosion are identified in operating practice based on the evaluation of events which are reported to the authorities in line with the German reporting criteria. It has been found that the main contributor is the stress corrosion cracking. Several examples of different corrosion mechanisms and their consequences are provided for PWR although a high standard of quality of structures, systems and components has been achieved. Recommendations have been given to check the plant specifications concerning the use of auxiliary materials or fluids during maintenance as well as to examine visually the outer surfaces of austenitic piping with regard to residua of adhesive or adhesive tapes within the framework of in-service inspections. However, events in the last two years shows that such problems cannot be totally avoided. [full text] |

Berg Heinz-Peter, Gersinska Rainer, Sievers Jürgen Proposal for estimating leak and break frequencies of piping systems in probabilistic safety assessment |

The estimation of leak and break frequencies in piping systems is part of the probabilistic safety assessment of technical plants. In this paper, the statistical method based on the evaluation of the German operational experience for piping systems with different diameters is described because an earlier estimation has been updated and extended introducing new methodical aspects and data. Major point is the inclusion of structure reliability models based on fracture mechanics calculation procedures. As an example of application the statistical estimation method for leak and break frequencies of piping systems with a nominal diameter of 50 mm (the volume control system of a German pressurized water reactor) was updated. Moreover, the evaluation of the operational experience was extended to 341 years with respect to cracks, leaks and breaks in the volume control system of German pressurized water reactors (PWR). Using the actual data base, new calculations of leak and break frequencies have been performed and the results have been compared with the previous values. [full text] |

Blokus-Roszkowska Agnieszka, Kołowrocki Krzysztof Reliability and availability of a ground ship-rope transporter in variable operation conditions |

In the paper the environment and infrastructure influence of the ground ship-rope transporter operating in Naval Shipyard in Gdynia on its operation processes is considered. The results are presented on the basis of a general model of technical systems operation processes related to their environment and infrastructure. The transporter operation process is described and its statistical identification is given. Next, the reliability, risk and availability evaluation of the transporter in variable operation conditions is presented. In addition, the reliability and availability basic characteristics of the system assuming its components’ failure dependence are determined. Finally, the obtained results for the ground ship-rope transporter under the assumption that its components are dependent and independent are compared. [full text] |

Blokus-Roszkowska Agnieszka, Kołowrocki Krzysztof Reliability and availability of a shipyard ship-rope elevator in variable operation conditions |

In the paper the environment and infrastructure influence of the ship-rope elevator operating in Naval Shipyard in Gdynia on its operation processes is considered. The results are presented on the basis of a general model of technical systems operation processes related to their environment and infrastructure. The elevator operation process is described and its statistical identification is given. Next, the elevator is considered in varying in time operation conditions with different its components’ reliability functions in different operation states. Finally, the reliability, risk and availability evaluation of the elevator in variable operation conditions is presented.[full text] |

Briš Radim Direct unavailability calculations of highly reliable systems |

The paper presents a new analytical algorithm which is able to carry out direct and exact reliability quantification of highly reliable systems with maintenance (both preventive and corrective). A directed acyclic graph is used as a system representation. The algorithm allows take into account highly reliable and maintained input components. All considered models are implemented into the new algorithm. The algorithm is based on a special new procedure which permits only summarization between two or more non-negative numbers that can be very different. If the summarization of very small positive numbers transformed into the machine code is performed effectively no error is committed at the operation. Reliability quantification is demonstrated on a real system from practice and on its highly reliable modifications. The selected system is frequently used system - high pressure injection system occurring in many late references. [full text] |

Cadini Francesco, Avram Diana, Zio Enrico Particle filtering for the estimation of system mode of operation |

Efficient diagnosis and prognosis of system faults depend on the ability to estimate the system state on the basis of noisy measurements of the system dynamic variables and parameters. The system dynamics is typically characterized by transitions among discrete modes of operation, each one giving rise to a specific continuous dynamics of evolution. The estimation of the state of these hybrid dynamic systems is a particularly challenging task because it requires keeping track of the transitions among the multiple modes of system dynamics corresponding to the different modes of operation. In this paper a Monte Carlo estimation method is illustrated with an application to a case study of literature which consists of a tank filled with liquid, whose level is autonomously maintained between two thresholds. The system behavior is controlled by discrete mode actuators, whose states are estimated by a Monte Carlo-based particle filter on the basis of noisy level and temperature measurements. [full text] |

Cadini Francesco, Zio Enrico, Golea Lucia R., Petrescu Cristina A. Multi-objective genetic algorithms for the reliability analysis and optimization of electrical transmission networks |

The results of two applications of multi-objective genetic algorithms to the analysis and optimization of electrical transmission networks are reported to show the potential of these combinational optimization schemes in the treatment of highly interconnected, complex systems. In a first case study, an analysis of the topological structure of an electrical power transmission system of literature is carried out to identify the most important groups of elements of different sizes in the network. The importance is quantified in terms of group closeness centrality. In the second case study, an optimization method is developed for identifying strategies of expansion of an electrical transmission network by addition of new lines of connection. The objective is that of improving the transmission reliability, while maintaining the investment cost limited. [full text] |

Cha Ji Hwan, Yun Won Young On a general standby system and its optimization |

Redundancy or standby is a technique that has been widely applied to improving system reliability and availability in the stage of system design. In this paper, we consider a standby system with two units in which the first unit (unit 1) starts its operation under active state and the other unit (unit 2) is under cold standby state at the starting point. After a specified time s (switching time), the state of unit 2 is changed to warm standby state and, as soon as the operating unit 1 fails, the state of unit 2 is changed to active state. If unit 1 fails before time s, the system fails. Units can fail at both active and warm standby states. A general method for modeling the standby system is adopted and, based on it, system performance measures (system reliability and mean life) are derived. We consider the problem of determining optimal switching time which maximizes the expected system life. Some numerical examples are studied. [full text] |

Duffey Romney Managing and predicting risk, safety and stability in a challenging world |

It should be obvious that we must learn from our mistakes, so all of society, and ourselves, should have progressively safer, less risky systems and behaviors as we learn. Accidents are seemingly random in their occurrence, but in fact, this very apparent randomness is also containing information. The information we have researched and analysed covers nearly 200 years of knowledge from literally millions of multitudinous observations. The failure rate provides the expression for the probability of any outcomes, and the resulting curve is called the Human Bathtub. By quantifying the randomness, the uncertainty and the disorder, we have provided a new objective measure of “safety culture”, “organizational learning” and “engineering resilience”. We have linked individual learning and skill acquisition to the systematic risk reduction observed for entire systems with increasing experience. The results will be of interest to those interested and engaged in risk management, and in the social sciences where risk perception is important. [full text] |

Grabski Franciszek, Załęska-Fornal Agata Bootstrap methods for the censored data in empirical Bayes estimation of the 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 censored data to obtain an empirical prior distribution. [full text] |

Guo Renkuan, Nyirenda Juwa, Guo Danni Random fuzzy Poisson processes |

Poisson processes, particularly the time-dependent extension, play important roles in reliability and risk analysis. It should be fully aware that the Poisson modeling in the current reliability engineering and risk analysis literature is merely an ideology under which the random uncertainty governs the phenomena. In other words, current Poisson Models generate meaningful results if randomness assumptions hold. However, the real world phenomena are often facing the co-existence reality and thus the probabilistic Poisson modeling practices may be very doubtful. In this paper, we define the random fuzzy Poisson process, explore the related average chance distributions, and propose a scheme for the parameter estimation and a simulation scheme as well. It is expecting that a foundational work can be established for Poisson random fuzzy reliability and risk analysis. [full text] |

Guo Renkuan, Nyirenda Juwa, Dunne Tim, Guo Danni Random fuzzy continuous-time Markov chains |

Continuous-time Markov chains is an important subclass in stochastic processes, which have facilitated many applications in business decisions, investment risk analysis, insurance policy making and reliability modeling. It should be fully aware that the existing continuous-time Markov chains theory is merely an ideology under which the random uncertainty governs the phenomena. However, the real world phenomena are often revealing the randomness and vagueness co-existence reality and thus the probabilistic continuous-time Markov chains modeling practices may be not adequate. In this paper, we define the random fuzzy continuous-time Markov chains, explore the related average chance distributions, and propose a scheme for the parameter estimation and a simulation scheme as well. It is expecting that a foundational work can be established for reliability modeling and risk analysis, particularly, repairable system modeling. [full text] |

Guze Sambor, Kwiatuszewska-Sarnecka Bożena, Soszyńska Joanna The computer program to verify the hypothesizes and to predict the parameters for operational process |

The theoretical background and technical information for the program are presented. Further, the components of the program are described and user manual is given. [full text] |

Guze Sambor, Smolarek Leszek Modelling the ship safety on waterway according to navigational signs reliability |

An approach to safety analysis connected with consecutive “m out of n” systems is presented. Further, the consecutive “m out of n: G” system is defined and the recurrent formula for its reliability function evaluation are proposed. Next the IALA buoys and leading lights system are introduced. Moreover, the safety states model for ship navigation are defined. Further, analysis of safety during manoeuvre in restricted area with curved draws is illustrated. [full text] |

Harnpornchai Napat Genetic algorithms-aided reliability analysis |

A hybrid procedure of Genetic Algorithms (GAs) and reliability analysis is described, discussed, and summarized. The procedure is specifically referred to as a Genetic Algorithms-aided (GAs-aided) reliability analysis. Two classes of GAs, namely simple GAs and multimodal GAs, are introduced to solve a number of important problems in reliability analysis. The problems cover the determination of Point of Maximum Likelihood in failure domain (PML), the computation of failure probability using the GAs-determined PML, and the determination of multiple design points. The MCS-based method using the GAs-determined PML is specifically implemented in the so-called an Importance Sampling around PML (ISPML). The application of GAs to each respective problem is then demonstrated via numerical examples in order to clarify the procedures. With an aid from GAs, reliability analysis is possible even if there is no information about the geometry or landscape of limit state surfaces and the total number of crucial likelihood points. In addition, GAs significantly improve the computational efficiency and realize the analysis of rare events under constrained computational resources. The implementation of GAs to reliability analysis for building up the hybrid procedure is readily because of their algorithmic simplicity. [full text] |

Olgierd Hryniewicz Confidence bounds for the reliability of a system from subsystem data |

The paper is concerned with the construction of lower bounds for the reliability of a system when statistical data comes from independent tests of its elements. The overview of results known from literature and obtained under the assumption that elements in a system are independent is given. It has been demonstrated using a Monte Carlo experiment that in the case when these elements are dependent and when their dependence is described by Clayton and Gumbel copulas these confidence bounds are not satisfactory. New simple bounds have been proposed which in some practical cases have better properties than the classical ones. [full text] |

Jurdziński Mirosław, Guze Sambor, Kamiński Piotr Time differences in operation states of “Stena Baltica” ferry during the open water areas passages |

The paper deals with analysis of ships operation states in open water areas effected by environmental constraints influencing on ship sea keeping parameters in application to “Stena Baltica” ferry operated at the Baltic Sea between Gdynia and Karlskrona harbors. [full text] |

Kołowrocki Krzysztof, Kwiatuszewska-Sarnecka Bożena, Soszyńska Joanna Preliminary reliability, risk and availability analysis and evaluation of bulk cargo transportation system in variable operation conditions |

In the paper, definitions and theoretical results on system operations process, multi-state system reliability, risk and availability modelling are illustrated by the example of their application to a bulk cargo transportation system operating in Gdynia Port Bulk Cargo Terminal. The bulk cargo transportation system is considered in varying in time operation conditions. The system reliability structure and its components reliability functions are changing in variable operation conditions. The system reliability structures are fixed with a high accuracy. Whereas, the input reliability characteristics of the bulk cargo transportation system components and the system operation process characteristics are not sufficiently exact because of the lack of statistical data. Anyway, the obtained evaluation may be a very useful example in simple and quick systems reliability characteristics evaluation, especially during the design and improving the transportation systems operating in ports. [full text] |

Kołowrocki Krzysztof, Soszyńska Joanna Reliability, risk and availability based optimization of complex technical systems operation processes Part 1. Theoretical backgrounds |

A convenient new tool for solving the problem of reliability and availability evaluation and optimization of complex technical systems is presented. Linking a semi-markov modeling of the system operation processes with a multi-state approach to system reliability and availability analysis is proposed to construct the joint general model of reliability and availability of complex technical systems in variable operation conditions. This joint model and a linear programming is proposed to complex technical systems reliability and availability evaluation and optimization respectively. [full text] |

Kołowrocki Krzysztof, Soszyńska Joanna Reliability, risk and availability based optimization of complex technical systems operation processes Part 2 Application in port transportation |

The joint general model of reliability and availability of complex technical systems in variable operation conditions linking a semi-markov modeling of the system operation processes with a multi-state approach to system reliability and availability analysis and linear programming considered in the paper Part 1 are applied in maritime industry to reliability, risk and availability optimization of a port piping oil transportation system. [full text] |