Probability Of Failure-free Operation Research Articles

Mathematical Modeling and Examination of the Effects of Structural Redundancy in а Class of Computer-Based Fault Tolerant Systems

Abstract The present article models and examines k˅n systems, in particular Triple modular redundancy (2˅3) and 3˅5. The aim of the study is to derive mathematical models, which are used for determining the impact of structural redundancy (the number of channels n and the threshold of the quorum function k) on the reliability of the system. The probability of failure-free operation p and the Mean Time Between Failures (MTBF) are used as reliability indicators.

Information technology for determining the structural fault tolerance index of technical objects

It is proposed the information technology for evaluating the structural reliability of technical objects, the structure of which corresponds to one of the known types of neural networks. Structure of the information technology contains morphological model that allows for the formation and change in the structure of the object model being studied by the rules, based on the determination of the probability of failure-free operation in reliability theory

Модель взаимосвязи геометрии ветвей термоэлементов и показателей надежности однокаскадных охладителей в режиме Q0max

The authors consider the influence of the geometry of thermoelectric branches on the performance reliability of single-stage thermoelectric devices (TED) operating at maximum cooling capacity at 2.0 W thermal load for any values of temperature difference (from 10 to 60 K). A model of correlation of these parameters is presented. It is shown that when the ratio of height of a thermoelectric branch to its cross-section area decreases, failure rate of a single-stage TED reduces, and therefore failure-free operation probability increases.

Study of a Computer-Based Control System with Fault-Tolerant and Fail-Safe Behavior

Abstract The software and hardware of Safety Critical Systems - SCS, which control special critical technology process or operation, are subject of enhanced requirements for reliability and inadmissibility of any incorrect controlling influences (safety) after failures. This paper suggests and investigates a hybrid computerbased fail-safe/fault-tolerance FST-structure with single reservation, which has the qualities to meet these requirements. The base system 2 ∨ 2, based on which it is built, is studied in the previous edition of Information Technjlogies and Control. For derivation of probabilistic models through which to establish the efficiency of the strutucral redundancy in a fault-tolerant structure, in this paper are used the published results. Formulas are derived for the probability of failure-free operation (availability coefficient), for safe failure and for unidentified (dangerous) failure. Models are found for calculation of the enhancement of reliability and the variation of safety relative to the base system 2 ∨ 2. Subject of analysis are type software and hardware modifications of the proposed general scheme used in the practice of different companies, which manufacture and operate SCSs. It is proven that at the expense of acceptable hardware redundancy and insignificant increase of dangerous failures the probability of interruption of the operation of the FST- system and its down-time due to failure may decrease by tenths of thousands of times.

Performance Factors of a Wireless Sensor Network of Rectangular Mesh Configuration

A wireless sensor network of rectangular mesh configuration and between 20 and 260 clusters of smart sensors is studied. The probability of failure-free operation and the duration of the polling cycle are estimated.

Determination of failure-free operation probability in adhesive joints at high temperatures

This paper studies the processes of change in the strength of adhesive joints at prolonged exposure to elevated temperatures. It is proposed to divide the temperature range in which the adhesive material is used into two ranges: the first one is characterized by processes of gradual reduction of heat resistance, and the second by processes of thermal degradation. Models that describe the behavior of the adhesive material and make it possible to consider the fundamentally different pattern of changes in their heat and thermal stability are proposed. Using the example of determining the thermal and heat resistance performance of the polyurethane adhesive, it is shown how to determine the probability of its failure-free operation.

Selection of parameters combination of thermoelectric materials for development of high-reliability coolers

The possibilities of constructing two-stage high-reliability thermoelectric devices using the same combinations of parameters of raw materials in stages with equal efficiency at the series electrical connection of the stages were considered. The calculation data of the basic reliability parameters and indicators of the two-stage thermoelectric device using different combinations of parameters in stages for temperature changes from 60K to 90K and operation modes: maximum cooling capacity, maximum cooling capacity at a given current, maximum coefficient of performance, minimum failure rate were given. It was proved that the approach to the thermocouple material selection by average efficiency, electrical conductivity and thermal conductivity indicators, adopted in the industrial production of thermoelectric modules is not optimized in terms of reliability of thermoelectric modules. As a result of the analysis of reliability indicators of thermoelectric cooler for different combinations of parameters of raw materials, the possibility of increasing the probability of failure-free operation by more than 10% for all operation modes was revealed. It was shown that an increase in thermoelectric cooling capacity in stages increases the cooling capacity or decreases the number of thermocouples, which together with the use of raw materials with high electrical conductivity allows to reduce the total failure rate and increase the probability of failure-free operation of two-stage devices.

Software Reliability Modeling using Soft Computing Techniques: Critical Review

To obtained solutions to problems quickly, accurately and acceptably, a large number of soft computing techniques have been developed, but it is very difficult to find out which one is the most suitable and can be used globally. In this paper, we have provided an overview of existing soft computing techniques, and then critically analyzed the work done by the various researchers in the field of software reliability. The probability of failure-free operation of a software system for a specified time in a specifies environment. Further to this, we have also compared soft computing techniques in terms of software reliability modeling capabilities.

НАДІЙНІСТНО-ОРІЄНТОВАНЕ ПРОЕКТУВАННЯ ДВОКАСКАДНОГО ТЕРМОЕЛЕКТРИЧНОГО ПРИСТРОЮ В САПР КРИТИЧНИХ СИСТЕМ

The paper deals with the design of thermally loaded vehicles with two-stage thermoelectric cooling devices in CAD critical systems. In the design of thermoelectric cooling devices thermally loaded elements that are part of the critical information systems , an integral characteristic is reliability. The fundamental approach to ensure the reliability is the parametric method , because the failure rate of the components are naturally included in the resulting intensity of a system failure. The importance of the parametric approach for the design of reliable information systems and its constituent components predetermines considerable attention to the development of computer-aided design in this direction. Research is aimed at solving problems of increasing the reliability of thermal loaded funds with cascade thermoelectric cooling devices that occur in CAD of critical information systems in a wide range of thermal loads, are relevant. Application of cascade thermoelectric cooling devices provides the highest reliability in comparison with other types of coolers. Quantitative estimation of reliability indices is crucial in the early stages of design and development tools of thermal- critical systems. The implementation of a subsystem CAD parametric models of the relationship of reliability and the basic parameters of a two-stage thermoelectric cooling device based on the selected mode of operation are proposed. Using this model allows to carry out reliability - oriented design of a two-stage thermoelectric cooling device in CAD critical systems. CAD subsystem provides quantitative estimation of the failure rate and probability of failure of the two-stage thermoelectric cooling devices at the design stage in accordance with the specifications. When designing the thermal-funds, proposed by CAD, calculated parameters of two-stage thermoelectric cooling devices provide the minimum failure rate, which is the determining criterion. Comparative analysis of calculated data for the basic parameters of a two-stage thermoelectric device of specified design shows a choice of current modes of functioning, capable of predicting and significantly improve the performance of the failure rate and the probability of failure-free operation.

ПІДВИЩЕННЯ НАДІЙНОСТІ ОДНОКАСКАДНИХ ТЕРМОЕЛЕКТРИЧНИХ ОХОЛОДЖУЮЧИХ ПРИСТРОЇВ ЗА РАХУНОК ВИКОРИСТАННЯ РІЗНИХ ВАРІАНТІВ СПОЛУЧЕНЬ ПАРАМЕТРІВ ПЕРВИННИХ МАТЕРІАЛІВ ОДНАКОВОЇ ЕФЕКТИВНОСТІ

The article represents possibilities of improving the reliability of single-stage thermoelectric cooling device by using different combinations of the original materials averaged parameters of the same efficiency, namely, thermoelectric power factor, electrical conductivity and the thermal conductivity for various changes in temperature and operating modes for a given height to the cross-sectional area branches of the thermocouple.There were obtained simple analytical expressions that provide the interconnection of reliability, namely, failure rate, the number of thermocouples of thermoelectric cooling capacity single-stage thermoelectric cooling device for different combinations of parameters of the source material. The calculations of single-stage thermoelectric devices basic parameters for different operating modes on the mode of maximum cooling capacity to minimum failure rates for different ranges of temperature changes from 0 to 60 K, and various combinations of options thermoelectric materials with differing efficiency parameters, electrical conductivity, thermoelectric power factors, the geometric parameters of thermocouples are presented. It is shown the possibility of failure rate reducing and increasing of cooler failure-free operation probability through the use of original materials with the same efficiency for greater conductivity.

Влияние эффективности исходных материалов на показатели надежности термоэлектрических охлаждающих устройств. Часть 2: Двухкаскадные ТЭУ

Extended operation temperature range of elements and electronic equipment components using thermoelectric devices necessitates the use of cascade thermoelectric cooling devices. One of the best ways to improve the reliability of thermoelectric coolers is to improve the efficiency of thermoelectric materials. The article presents the research results on the influence of thermoelectric efficiency of initial materials on the failure rate and probability of failure of the two-stage thermoelectric cooler within temperature range of 60 to 90 K for maximum cooling operation modes and low failure rate. The results have shown that with the increase in the thermoelectric efficiency of the material thermocouples the maximum temperature difference in cascades increases, the working current and the ratio of the elements number in the adjoining cascades decreases (depending on the current mode in cascades of thermoelectric device from the mode of the maximum cooling capacity up to the minimum failure rate), the cooling coefficient increases, the failure rate reduces and the probability of failure-free operation of two-stage thermoelectric cooler increases. Thus, it is shown that the increase in the thermoelectric efficiency of initial materials can significantly reduce the failure rate and increase the probability of failure-free operation of the two-stage thermoelectric devices depending on temperature difference and the current mode of operation.

Software Reliability Modeling using Soft Computing Techniques: Critical Review

To obtained solutions to problems quickly, accurately and acceptably, a large number of soft computing techniques have been developed, but it is very difficult to find out which one is the most suitable and can be used globally. In this paper, we have provided an overview of existing soft computing techniques, and then critically analyzed the work done by the various researchers in the field of software reliability. The probability of failure-free operation of a software system for a specified time in a specifies environment. Further to this, we have also compared soft computing techniques in terms of software reliability modeling capabilities.

Fatigue Life Prediction of Engineering Structures under Multivariable Random Loading Using Structural Model

The article describes the case of multivariable random loading, which occurs when the caterpillar suspension component acts as a set of loads of independent random processes. In the danger zone details of the changes in the components of the stress tensor are independent random processes. As an example of parts operating at such a loading the author discusses tracked vehicle road arm.Presently, there are no standard techniques for the estimation of fatigue life under random multivariable loading currently available. The article describes the method of estimating the fatigue life for this type of load, based on the calculation of microplastic deformation. It uses a structural model of the material, based on the description of the deformation diagram of dependence by Ramberg-Osgood. To identify the model of accumulation of damage conventional mechanical and fatigue characteristics of the material were used. Accounting for natural dispersion of fatigue characteristics allowed to get the result as a function of the probability of failure-free operation. The validity of the approach is confirmed by comparing the calculation results with the experimental data. The practical application of the technique is illustrated by the example of predicting the durability and reliability of heavily loaded parts of the high-speed caterpillar vehicle.

Modeling of Operation Processes and Reliability Assurance of Engineering Machines under the Multivariable Time-varying Random Loading

The article describes the case of multivariable random loading, which occurs when the caterpillar suspension component acts as a set of loads of independent random processes. In the danger zone details of the changes in the components of the stress tensor are independent random processes. As an example of parts operating at such a loading the author discusses tracked vehicle road arm. Presently, there are no standard techniques for the estimatation of fatigue life under random multivariable loading currently available. The article describes the method of estimating the fatigue life for this type of load, based on the calculation of microplastic deformation. It uses a structural model of the material, based on the description of the deformation diagram of dependence by Ramberg-Osgood. To identify the model of accumulation of damage conventional mechanical and fatigue characteristics of the material were used. Accounting for natural dispersion of fatigue characteristics allowed to get the result as a function of the probability of failure-free operation. The validity of the approach is confirmed by comparing the calculation results with the experimental data. The practical application of the technique is illustrated by the example of predicting the durability and reliability of heavily loaded parts of the high-speed caterpillar vehicle.

Predicting the endurance of adhesive joints

The paper studies the causes of loss of efficiency of designs with adhesive joints and models for determining their endurance and probability of failure-free operation upon gradual and sudden failure. For the model of gradual failure, we propose a technique for assessing the maximum allowable value of the output parameter, for which the shear strength is most often used, and the rate of degradation processes of adhesive materials. Examples of calculating the endurance are given.

Оценка надeжности стохастически неоднородной толстостенной трубы по критерию длительной прочности

We have developed a method of probabilistic reliability evaluation of microheterogeneous thick-walled pipe, based on the already received solution of the stochastic creep boundary value problem. The rheological properties of the material were described using random function of one variable (radius $r$). Damage parameter $0< \omega(t) <1$ was introduced here to study the process of degradation of the material during creep stage. Also the power law of the rate of $\omega(t)$ change on the equivalent stress σe , determined by Sdobyrev criterion, is assigned. The reliability evaluation is made by the mean integral value of the equivalent stress. We have found a random time before destruction and its distribution function, which was approximated by lognormal law. The problem of the probability of failure-free operation was calculated for a thick-walled microheterogeneous pipe with the specified parameters. The obtained results allow to evaluate reliability of stochastically inhomogeneous axisymmetric structural elements if necessary statistical data are obtained from the experiment.

Backup Alternatives for 110 kV Lines

The paper describes backup alternatives for 110 kV lines. Line backup is one of input parameters used to optimise the renovation of 110 kV lines. The optimisation is based on the principle of reliability centred maintenance (RCM) which depends on the technical condition and importance of a particular element. The paper starts with illustrating the method of reliability schemes. This method enables the evaluation of failure-free operation probability. The probability of a failure-free operation can be estimated for all backup types of 110 kV lines existing in the distribution network. To compare different backup alternatives, type lines were selected and calculated with. The results of the method helped estimate the effects of a line failure for a particular distribution district.

Reduction of reliability testings of data-measuring system due to its functional redundancy

The article considers one of the ways of improvement of efficiency of testings of reliability of data-measuring system in the form of reduction of the total procedure due to its functional redundancy. The research is required because the bulk of the total expenditure falls on tests, and this significantly affects the amount of funding when creating complex engineering systems. To solve this problem we have calculated the ratio of functional redundancy of the system and the probability of failure-free operation for different values of influencing factors. It is shown that a quantitative measure of performance of a certain condition for the reliability of the system is the possibility of its implementation. We presented the criterion of its performance from the perspective of systematic review. We considered the questions of the risk to reduce the reliability testing procedures. We highlighted the limit requirements for the operation of data-measuring system, which is checked in conditions of reduction of testings of its reliability due to functional redundancy.

ОСОБЕННОСТЬ КОРРЕКЦИИ МЕТОДОВ РАСЧЕТА НА УСТОЙЧИВОСТЬ ПОДКРЕПЛЕННЫХ ЦИЛИНДРИЧЕСКИХ ОБОЛОЧЕК ПРИ ОСЕВОМ СЖАТИИ С ИСПОЛЬЗОВАНИЕМ ОПЫТНЫХ ДАННЫХ

The paper is focused on empirical dependences of coefficients of stability from the normalized axial force parameter to adapt more efficiently methods of analysis to experimental data and reduce the coefficient of variation of a random variable. The accuracy of the methods of analysis is further improved with correcting functions, where parameters of design are given as corresponding exponents. The efficiency of design of a stiffened shell is estimated to meet the criterium of minimum mass for the design loading with several methods of analysis for a specific directive safety factor and also in case it is described with a dependence from corresponding coefficients of variation of the random variable for the frozen probability of failure-free operation of the shell structure. Keywords: stiffened cylindrical shells, axial compression, buckling, increase in accuracy of the method of analysis, design dependences for coefficients of stability, correcting functions, analysis of efficiency.

Software Reliability Prediction using Neural Networks

Predicting the Software reliability is a pertinent issue and it is a major concern of software developers and engineers in changing environment considerations. Software reliability models are developed to estimate the probability of failure free operation of the software for a long time. Many Software Reliability Growth Models (SRGM) were developed to give the latent number of faults in the software product. However none of these models performing to the expectations of the developers of the software. In this paper, A research is made using artificial neural network models to monitor the performance of the software that leads to predict the software reliability. The MLP model outperforms SVR model, and based on the results, these models can be considered to be a reasonable alternative for software quality prediction.