SSARS 2007 VOL 1

Berg Heinz-Peter, Görtz Rudolf, Kesten Jürgen
Methods for the treatment of common cause failures in redundant systems
Dependent failures are extremely important in reliability analysis and must be given adequate treatment so as to minimize gross underestimation of reliability. German regulatory guidance documents for PSA stipulate that model parameters used for calculating frequencies should be derived from operating experience in a transparent manner. Progress has been made with the process oriented simulation (POS) model for common cause failure (CCF) quantification. A number of applications are presented for which results obtained from established CCF models are available, focusing on cases with high degree of redundancy and small numbers of observed events.[full text]
Berg Heinz-Peter, Fröhmel Thomas, Winter Christian
Analysis of the impact of external flooding to nuclear installations
The German regulatory body has issued probabilistic safety assessment guidelines, elaborated for a comprehensive integrated safety review of all NPP in operation and containing a newly developed graded approach for the probabilistic assessment of external flooding. Main aspects are explained such as the underlying probabilistic considerations and the mathematical procedures for the calculation of exceedance frequencies. Exemplarily it has been investigated if extreme events such as tsunami waves could be a hazard for NPP at coastal sites in Germany.[full text]
Blokus-Roszkowska Agnieszka
Analysis of component failures dependency influence on system lifetime
In the paper the results of the reliability investigation of multi-state homogeneous parallel-series systems with independent and dependent components are presented. The multi-state reliability functions of such systems and other reliability characteristics in both cases are determined under the assumption that their components have exponential reliability function. Moreover the asymptotic approach to the reliability evaluation of these systems is also presented and the classes of limit reliability functions for the considered systems in both cases are fixed. Finally, the presented theoretical results are applied to the reliability evaluation of the shipyard rope transportation system. The comparison of the multi-state exact and limit reliability functions of the considered transportation system under the assumption that its components are independent and under the assumption that its components have failure dependency is performed and illustrated graphically.[full text]
Briš Radim

Stochastic ageing models – extensions of the classic renewal theory

Exact knowledge of the reliability characteristics as the time dependent unavailability coefficient for example, under influence of different ageing processes as well as under different failure types is very useful to the practitioners who have to find the optimal maintenance policy for their equipment. In this paper found models and their solutions have potential to face the optimisation task under the conflicting issues of safety and economics. Most of the solved models take into account ageing processes. An increasing tendency lately exists to include aging effects into the risk assessment models to evaluate its contribution. We developed different renewal models taking into account different ageing distributions of failures (Weibull, Erlang, log-normal): models with negligible renewal time, models with periodical preventive maintenance, alternating renewal process with lognormal distribution of failure time, and with two types of failures. [full text]
Budny Tymoteusz

Two various approaches to VTS Zatoka radar system reliability analysis

In the paper we propose two ways of reliability calculation of radar system in Vessel Traffic Services Zatoka. Reliability and availability of the system were calculated on the base of reliability of the system components. In the first approach there was assumed that system is series, in the second approach system is treated as a series-“m out of n”. We obtain different results. Conclusion is that choosing proper method of approach to system reliability and availability analysis is decisive in appropriate evaluation of those properties. [full text]
Cadini Francesco, Zio Enrico, Pedroni Nicola

Recurrent neural networks for dynamic reliability analysis

A dynamic approach to the reliability analysis of realistic systems is likely to increase the computational burden, due to the need of integrating the dynamics with the system stochastic evolution. Hence, fast-running models of process evolution are sought. In this respect, empirical modelling is becoming a popular approach to system dynamics simulation since it allows identifying the underlying dynamic model by fitting system operational data through a procedure often referred to as ‘learning’. In this paper, a Locally Recurrent Neural Network (LRNN) trained according to a Recursive Back-Propagation (RBP) algorithm is investigated as an efficient tool for fast dynamic simulation. An application is performed with respect to the simulation of the non-linear dynamics of a nuclear reactor, as described by a simplified model of literature.[full text]
Cha Ji Hwan, Mi Jie

A study on the performance measures of a system operated in random environment

Most devices (systems) are operated under different environmental conditions. The failure process of a system not only depends on the intrinsic characteristic of the system itself but also on the external environmental conditions under which the system is being operated. In this article we study a stochastic failure model in random environment and investigate the effect of the environmental factors on the failure process of the system. Some stochastic orderings will also be briefly discussed. [full text]
Dourmas N. Georgios, Nikitakos V. Nikitas, Lambrou A. Maria

A methodology for rating and ranking hazards in maritime formal safety assessment using fuzzy logic

Formal safety assessment of ships has attracted great attention over the last few years. This paper, following a brief review of the current status of marine safety assessment is focused on the hazards identification (HAZID) and prioritisation process. A multicriteria decision making framework, which is based on experts’ estimation, is then proposed for hazards evaluation. Additionally in this paper many aspects of the evaluation framework are presented including the synthesis of evaluation teams, the assessment of the importance of criteria, the evaluation of the consequences of the alternative hazards and the final ranking of the hazards. The proposed methodology has the innovative feature of embodying techniques of fuzzy logic theory into the classical multicriteria decision analysis. The paper concludes by exploring the potentiality of the above methodology in providing a robust and flexible evaluation framework suitable to the characteristics of a hazard evaluation problem.[full text]
Duarte José Caldeira, Soares Carlos Guedes

Optimisation of the preventive maintenance plan of a series components system with Weibull hazard function

In this paper we propose an algorithm to calculate the optimum frequency to perform preventive maintenance in equipment that exhibits Weibull hazard function and constant repair rate in order to ensure its availability. Based on this algorithm we have developed another one to solve the problem of maintenance management of a series system based on preventive maintenance over the different system components. We assume that all components of the system still exhibit Weibull hazard function and constant repair rate and that preventive maintenance would bring the system to the as good as new condition. The algorithm calculates the interval of time between preventive maintenance actions for each component, minimizing the costs, and in such a way that the total downtime, in a certain period of time, does not exceed a predetermined value. [full text]
Duffey Romney B., Saull John W.

Risk prediction for modern technological systems

We have already examined the worldwide trends for outcomes (measured as accidents, errors and events) using data available for large complex technological systems with human involvement. That analysis was a dissection of the basic available, published data on real and measured risks, for trends and inter-comparisons of outcome rates. We found and showed how all the data agreed with the learning theory when the accumulated experience is accounted for. Here, learning includes both positive and negative feedback, directly or indirectly, as a result of prior outcomes or experience gained, in both the organizational and individual contexts. Our purpose here and now is to try to introduce some predictability and insight into the risk or occurrence of these apparently random events. In seeking such a general risk prediction we adopt a fundamental theoretical approach that is and must be testable against the world’s existing data. Comparisons with outcome error data from the world’s commercial airlines, the two shuttle failures, and from nuclear plant operator transient control behaviour, show a reasonable level of accord. The results demonstrate that the risk is dynamic, and that it may be predicted using the MERE learning hypothesis and the minimum failure rate, and can be utilized for predictive risk analysis purposes. [full text]
Dziula Przemysław, Jurdziński Mirosław, Kołowrocki Krzysztof, Soszyńska Joanna

On multi-state safety analysis in shipping

A multi-state approach to defining basic notions of the system safety analysis is proposed. A system safety function and a system risk function are defined. A basic safety structure of a multi-state series system of components with degrading safety states is defined. For this system the multi-state safety function is determined. The proposed approach is applied to the evaluation of a safety function, a risk function and other safety characteristics of a ship system composed of a number of subsystems having an essential influence on the ship safety. Further, a semi-markov process for the considered system operation modelling is applied. The paper also offers a general approach to the solution of a practically important problem of linking the multi-state system safety model and its operation process model. Finally, the proposed general approach is applied to the preliminary evaluation of a safety function, a risk function and other safety characteristics of a ship system with varying in time its structure and safety characteristics of the subsystems it is composed of. [full text]
Eid Mohamed

Time-dependant modelling of systems: some open questions

Time dependent modelling of complex system is one of the important topics in system reliability engineering. Although system complexity is increasing, the existing models are numerically satisfactory. However, some formal development is still lacking in reliability theory. A full system time-dependency modelling and analysis is not possible without some formal answers on critical transitions and related issues. This is still one of the open questions in system reliability theory. Some promising development relative to critical states is given in this paper with an application case. [full text]
Elleuch Mounir, Ben Bacha Habib, Masmoudi Faouzi

Improvement of manufacturing cells with unreliable machines

The performance of cellular manufacturing (CM) is conditioned by disruptive events, such as failure of machines, which randomly occur and penalize the performance of the cells and disturb seriously the smooth working of the factory. To overcome the problems caused by the breakdowns, we develop a solution, based on the principle of virtual cell (VC) and the notion of intercellular transfer that can improve performances of the system. In this context, we use an analytical method based on Markov chains to model the availability of the cell. The found results are validated using simulation. The proposed solution in this paper confirmed that it is possible to reduce the severity of breakdowns in the CM system and improve the performances of the cells through an intercellular transfer. Simulation allowed a validation of the analytical model and showed the contribution of the suggested solution. [full text]
Galor Wiesław

The ships impact in ground of port water area

The existing ports are expected to handle ships bigger than those for which they were designed. The main restriction in serving these ships is the depth of port waters, which directly affects the safety of a manoeuvring ship. The under keel-clearance of a ship in the port water area should be such that a ship moves safely. In some specific conditions it happen the ship strike the sea bottom. The undesired impact against the ground can damage the ship hull. The paper presents the algorithm of ships movement parameters during contact with the ground. [full text]
Van Gelder, P.H.A.J.M.

Methods for risk analysis in disaster reduction

This paper discusses a proposal for a risk management tool for applications to risk reduction of natural hazards. [full text]
Grabski Franciszek

Applications of semi-Markov processes in reliability

The basic definitions and theorems from the semi-Markov processes theory are discussed in the paper. The semi-Markov processes theory allows us to construct the models of the reliability systems evolution within the time frame. Applications of semi-Markov processes in reliability are considered. Semi-Markov model of the cold standby system with repair, semi-Markov process as the reliability model of the operation with perturbations and semi-Markov process as a failure rate are presented in the paper. [full text]
Grabski Franciszek

The random failure rate

A failure rate of the object is assumed to be a stochastic process with nonnegative, right continuous trajectories. A reliability function is defined as an expectation of a function of a random failure rate process. The properties and examples of the reliability function with the random failure rate are presented in the paper. A semi-Markov process as the random failure rate is considered in this paper. [full text]
Grabski Franciszek, Załęska-Fornal Agata

The model of non-renewal reliability systems with dependent time lengths of components

The models of the non-renewal reliability systems with dependent times to failure of components are presented. The dependence arises from some common environmental stresses and shocks. It is assumed that the failure occurs only because of two independent sources common for two neighbour components. The reliability function of series and parallel systems with components depending on common sources are computed. The reliability functions of the systems with dependent and independent life lengths of components are compared. [full text]
Guo Renkuan

An univariate DEMR modelling on repair effects

Repairable system analysis is in nature an evaluation of repair effects. Recent tendency in reliability engineering literature was estimating system repair effects or linking repair to certain covariate to extract repair impacts by imposing repair regimes during system reliability analysis. In this paper, we develop a differential equation motivated regression (abbreviated as DEMR) model with a random fuzzy error term based on the axiomatic framework of self-dual fuzzy credibility measure theory proposed by Liu [5] and grey differential equation models. The fuzzy variable indexes the random fuzzy error term will be used to facilitate the evaluation of repair effects. We further propose a parameter estimation approach for the fuzzy variable (repair effect) under the maximum entropy principle. [full text]
Guze Sambor

Numerical approach to reliability evaluation of two-state consecutive “k out of n: F” systems

An approach to reliability analysis of two-state systems is introduced and basic reliability characteristics for such systems are defined. Further, a two-state consecutive “ out of : F” system composed of two-state components is defined and the recurrent formulae for its reliability function are proposed. The algorithm for numerical approach to reliability evaluation is given. Moreover, the application of the proposed reliability characteristics and formulae to reliability evaluation of the system of pump stations composed of two-state components is illustrated. [full text]
Guze Sambor, Kołowrocki Krzysztof

Reliability analysis of multi-state ageing consecutive „k out of n: F” systems

A multi-state approach to reliability analysis of systems composed of ageing components is introduced and basic reliability characteristics for such systems are defined. Further, a multi-state consecutive “ out of : F” system composed of ageing components is defined and the recurrent formulae for its reliability function are proposed. Moreover, the application of the proposed reliability characteristics and formulae to reliability evaluation of the steel cover composed of ageing sheets is illustrated. [full text]
Hryniewicz Olgierd

Statistical analysis of interval and imprecise data – applications in the analysis of reliability field data

The analysis of field lifetime data is much more complicated than the analysis of the results of reliability laboratory tests. In the paper we present an overview of the most important problems of the statistical analysis of field lifetime data, and present their solutions known from literature. When the input information is partial or imprecise, we propose to use interval arithmetics for the calculation of bounds on reliability characteristics of interest. When this information can be described in a more informative fuzzy form, we can generalize our interval-valued results to their fuzzy equivalents. [full text]
Jóźwiak Ireneusz J., Laskowski Wojciech

A short note on reliability of security systems

Telecommunication systems become a key component of critical infrastructure. One of the main elements of such systems is computer system. The organizations which can be involved in crisis management (e.g. government agencies, etc. ) need to know results of security drawbacks in their systems. Moreover, they should have a tool for analysing the results of decision made in security context. And often the following question is raised: why do security systems fail? To answer it in this paper the aspects of reliability are discussed. From this point of view the security systems are analysed. We hope that thanks to such approach we will be able to reach some characteristics of security incidents occurrence. Moreover, we hope to use our results to build security attributes metrics. In addition, we present thesis that predictions of occurrence of incidents is impossible, so we should focus on registration of incidents type. On such a foundation we can formulate conclusions about drawbacks in configurations or administration of information systems. In our research we have observed that in case of some class of information systems, the availability incidents are the most dangerous. And we conclude that only using technologies with good reliability characteristics can lead to solving this problem. [full text]
Karbasian Mahdi, Mahdavi Mojtaba

A new method for computing the reliability of composite systems

This paper tries to represent a new method for computing the reliability of a system, which is arranged in series or parallel model. In this method we estimate life distribution function of whole system using the asymptotic Extreme Value (EV) distribution of Type I, or Gumbel theory. We use EV distribution in minimal mode, for estimate the life distribution function of series system and maximal mode for parallel system. All parameters also are estimated by Moments method. Reliability function and failure (hazard) rate and p-th percentile point of each function are determined. Other important indexes such as Mean Time to Failure (MTTF), Mean Time to repair (MTTR), for non-repairable and renewal systems in both of series and parallel structures will be computed. [full text]