Gnedenko e-Forum Information

THE COMPUTER ANALYSIS OF FAULTLESSNESS TRANSFORMERS OF POWER SUPPLY SYSTEMS

Algorithms of methods of an estimation of faultlessness transformers resulted at the set version of distinctive attributes and classification park transformers on groups with statistically various parameters of faultlessness. Algorithms serve one of distinctive features of the automated information control system developed by authors as reliability of transformers a power supply system.

NUMERICAL EXPERIMENT FOR RUIN PROBABILITY IN RISK MODEL

WITH DEPENDENT FINANCIAL AND INSURANCE RISKS

For discrete time risk model with dependent financial and insurance risks numerical experiment with recurrent procedure of ruin probability calculation is made. It shows that suggested recurrent procedure is much faster than application of usual Monte-Carlo method.

A NEW APPROACH FOR VERIFICATION OF SAFETY INTEGRITY LEVELS

The IEC standards 61508/61511 require that reliability targets for safety instrumented functions are defined and verified. The reliability targets are given as one out of a possible four safety integrity levels. For each safety integrity level there are many design requirements, including requirements for the probability of failure on demand. Verification of the requirements for the probability of failure on demand is usually based on a quantitative analysis. In this paper we argue that such an approach is better replaced by a semi-quantitative approach. The approach acknowledges that the probability of failure on demand requirement cannot be adequately verified only by reference to an assigned probability number. There is a need for seeing beyond the probability number. The key aspect to include is related to uncertainty.

ON HOW TO CONCEPTUALISE AND DESCRIBE RISK

A number of definitions and interpretations of the risk concept exist. Many of these are probability-based. In this paper we present and discuss a structure for characterising the definitions, which is founded on a clear distinction between (a) risk as a concept based on events, consequences and uncertainties; (b) risk as a modelled, quantitative concept; and (c) risk descriptions. The discussion leads to recommended perspective  for conceptualising and assessing risk, which is based on risk defined by (a), and the probability-based definitions of risk can be viewed as related model parameters and/or risk descriptions. Two ways of detailing the framework are outlined: the relative frequency-based approach and the Bayesian approach.

RISK AsSESSMENT oF Aircraft crash onto a nuclear power plant

External hazards can provide safety significant contributions to the risk in case of nuclear power plant operation because such hazards have the potential to reduce simultaneously the level of redundancy by damaging redundant systems and lines or their supporting systems. Therefore, risk assessment of all potential external hazards to the plant under consideration is part of the overall safety assessment. In this paper, the procedure for assessing the external hazard aircraft crash is described in more detail. The first step is an appropriate screening procedure in order to determine scope and content of the assessment, taking into account plant- and site-specific conditions. The second step is to determine the methodical approach for those cases where a full scope analysis has to be performed and the inclusion into the used overall risk model. The considerations regarding this hazard do not cover an intended aircraft crash.

ReLIABILITY OF MAIN TransformerS 

Key equipment for the electric power transmission is the transformer. Because of the high failure frequency and the resultant reliability and safety implications in particular of main transformers, an in-depth assessment is necessary. Main transformers are considered as a critical equipment because of the large quantity of oil in contact with high voltage elements. Experience has shown an increasing number of transformer explosions and fires in all types of power plants worldwide. Therefore, these phenomena have been investigated in more detail and are discussed with regard to potential root causes for these events such as potential influence of the age of the transformers. Moreover, possible diagnostic measures to avoid such events and enhance the reliability are shortly described. For investigating the current status of the reliability of transformers different types of databases have been evaluated.

BAYESIAN UNCERTAINTY DECISION ANALYSIS

Bayesian statistical decision theory would be questionable when applied directly to non-random uncertainty circumstances. In this paper, we investigate the basic elements of decision analysis oriented to observational data arising from a general uncertainty environment, so that a framework for Bayesian uncertainty decision doctrine is established. Further, we propose a copula-linked uncertainty marginals mechanism for constructing the uncertainty multivariate distributions to represent both observational data and an uncertainty parameter vector. This mechanism paves the way towards the establishment of an uncertainty posterior distribution of the parameter vector given the observational data, based on uncertain measure Axiom 5. Finally, we present an illustrative example of the development of a posterior uncertainty distribution for a parameter given a single observation, step by step. The significance of this paper is to establish for the first time a Bayesian uncertainty data inference and decision framework, which constitutes a critical step towards the establishment of uncertainty statistics and a Bayesian uncertainty decision theory.

HYBRID RELIABILITY MODELLING WITH IMPRECISE PARAMETER

The real world phenomena are often facing the co-existence reality of different formality of uncertainty and thus the probabilistic reliability modeling practices are very doubtful. Under complicated uncertainty environments, hybrid variable modeling is important in reliability and risk analysis, which includes Bayesian distributional theory, random fuzzy distributional theory, as well as fuzzy random distributional theory as special distribution families. In this paper, we define a new hybrid lifetime which is specified by a random lifetime distribution with imprecise parameter with an uncertainty distribution. We furthermore define the average chance distribution as a quality index for quantifying the hybrid lifetime and accordingly the average chance reliability is derived.

SAFETY OPTIMIZATION OF A FERRY TECHNICAL SYSTEM IN VARIABLE OPERATION CONDITIONS

The general model of the safety of complex technical systems in variable operation conditions linking a semi-Markov modeling of the system operation process with a multi-state approach to system safety analysis and linear programming are applied in maritime transport to safety and risk optimization of a ferry technical system.

RBF NETWORKS FOR IMAGING POINTS

The paper demonstrates new approach of rendering the graph point series called gantts. The gantts are placed in the two dimensional graph which contains the information about available production sources in the real manufacturing process. To have the interaction with a user, gantts are accompanied with the description text giving detailed information about each gantt. All gantt descriptions must be displayed without overlapping with each other. To optimize this task, the modified version of the RBF neural network with biases is applied. With respect to the similarity to the RBF structure, the new type of neural network is named RBF 2. We also give the picture of positive and negative attributes of the solution based on the neural network architecture.

AN EXTENDED METHODOLOGY FOR RISK BASED INSPECTION PLANNING

Inspection planning is an important activity in process industries, and one of the key tools used for such planning is the risk based inspection (RBI) methodology. The RBI is commonly used in planning of inspections for static mechanical equipment, in particular piping networks. The inspections are prioritized based on risk, expressed as expected values, integrating the likelihood and consequences of failures. In this paper we suggest an extension of the RBI methodology which reflects risk and uncertainties beyond expected values. We argue that such an extension is essential for adequately supporting the inspection planning. A pipeline example from the Norwegian oil and gas industry is presented to illustrate and discuss the suggested approach.

COLREGS COMPLIANCE IN EVOLUTIONARY SETS OF COOPERATING SHIP TRAJECTORIES

In general, Evolutionary Sets of Cooperating Ship Trajectories combine some of the assumptions of game theory with evolutionary programming and aim to find optimal set of cooperating trajectories of all ships involved in an encounter situation. In a two-ship encounter situation the method enables the operator of an on-board collision-avoidance system to predict the most probable behaviour of a target and to plan the own manoeuvres in advance. In a multi-ship encounter the method may be used to help an operator of a VTS system to coordinate the manoeuvres of all ships. The improvement presented here is a new way of modelling some of the COLREGS rules. Due to this change, the method is now able to find solutions, which are more compliant with COLREGS, more intuitive and consequently – safer from the navigator’s point of view. The paper contains a detailed description of collision-avoidance operators used by the evolutionary method and simulation examples of the method’s results for digital maps.

FUZZY FAILURE RISK ANALYSIS IN DRINKING WATER TECHNICAL SYSTEM

Drinking water technical system is an essential element of urban infrastructure. The operation of this system is inseparably connected with a risk of failure. The main problem in the risk of failure analysis of water pipe network is the uncertainty of the information collected on the description of failure. In order to consider the uncertainty of information, the theory of fuzzy sets was used. The fuzzification of frequency, severity and the consequences of the incident scenario is basic input for fuzzy risk analysis. The presented model is part of a complex model of risk management of failures in drinking water technical system manly in water pipe network and can be used in practice in system operator’s decision-making process. An adaptation of the fuzzy set theory to analyse risk of failure of water mains is not a standard approach for water works. An effect of the analysis of different sources of risk can be used for the design of a more reliable safety system assurance.