Probability Of Failure-free Operation Research Articles

Choosing Methodology of How to Manage Distributed Information Systems under Conditions of High Dynamics of Network Infrastructure

Purpose of research. is to identify a distributed system control method that, based on known parameters, would reduce the resource consumption of computing devices. An information system resource is probability of failure-free operation (FFO), which decreases over time for each node, the faster the higher its load.Methods. Frequency of system reconfiguration becomes relatively high with high dynamics of edge layer of a network and the need for reconfiguration is unpredictable. Reducing the total time spent on reconfiguration allows to increase time spent on solving functional computing tasks of the system and thereby reducing nodes load. Reconfiguration time can be reduced both by reducing failure detection time in distributed system and by reducing searching time for new configuration. A method for reducing failure detection time is described. The applicability analysis of system management methods (centralized, distributed leader, decentralized) is carried out on the basis of obtained analytical evaluations of failure detection time by the system in control conditions through one or another method. A numerical experiment allows to distinguish areas of system parameters, where it is preferable to use the method with a distingods. Frequency of system reconfiguration becomes relatively high with high dynamics of edge layer of a network and the need for reconfiguration is unpredictable. Reducing the total time spent on reconfiguration allows to increase time spent on solving functional computing tasks of the system and thereby reducing nodes load. Reconfiguration time can be reduced both by reducing failure detection time in distributed system and by reducing searching time for new configuration. A method for reducing failure detection time is described. The applicability analysis of system management methods (centralized, distributed leader, decentralized) is carried out on the basis of obtained analytical evaluations of failure detection time by the system in control conditions through one or another method. A numerical experiment allows to distinguish areas of system parameters, where it is preferable to use the method with a distinuished leader.Results. The main result of this work is a method of choosing how to manage distributed information systems in conditions of high dynamics of network infrastructure, focused on reducing of resource consumption in computing devices.Conclusion. The system reconfiguration time could be reduced by selecting the most appropriate control method. In this case, the time for solving functional tasks of application is increased, the workload of computing nodes is reduced, and therefore FFO values are increased over the planning horizon.

Particular aspects of determining reliability indicators of thermoelectric generator modules using experimental data

Resource tests allowed finding that the relative degradation of output power and efficiency of thermoelectric generator modules is not subject to linear law. This means that the distribution law for the failure time of such modules does not «copy» the distribution of their initial parameters, i.e. is neither normal nor logarithmically normal. Therefore, the aim of this paper is to find or select from among the existing such a failure time distribution law, which would clearly take into account the scattering of the rates of relative degradation of the parameters of thermoelectric generator modules. The paper substantiates the need to use diffusion-nonmonotonic failure time distribution for processing the results of resource tests of thermoelectric generator modules in order to determine their standardized reliability indicators and relative errors of the obtained values. It is proposed to determine the point estimates of the parameters of the law, namely the average failure time and the parameter of variation of the rate of degradation processes not by formulas obtained by the method of maximum likelihood, but by smoothing the probability of failure-free operation obtained by tests. The least squares method and Newton's method are used. Estimates obtained by the method of maximum likelihood serve as an initial approximation for Newton's method. This allows achieving significantly less error in determining standardized reliability indicators than when using the method of maximum likelihood.

SPACECRAFT RELIABILITY CALCULATIONS USING STATISTICAL REGULARITIES IN OCCURRENCES OF FAILURES IN DEVICES, UNITS AND ASSEMBLIES DURING THEIR OPERATION

The paper addresses reliability analysis of manned spacecraft with the use of statistical regularities in in-flight failures of their devices, units and assemblies. It formulates validity criteria for using a device failure in reliability analysis, proposes a method for analyzing and classifying failures which enables factoring in different types of failures in reliability analyses. It considers a hypothesis of the absence of statistically significant differences in probabilities of individual valid failures and demonstrates the feasibility of its adoption with the use of dispersion analysis. A method is developed for evaluating product reliability using a functional relationship between reliability and the number of failures occurring in flight which makes it possible to significantly simplify reliability analysis for complex products, to establish the number of in-flight failures that is acceptable from the standpoint of the product reliability requirements, to study various product architectures from the standpoint of reliability criteria. It proposes a method for evaluating the lower boundary for the probability of manned spacecraft completing their missions based on the failure modes, effects and criticality analysis, and demonstrates the feasibility of optimizing the product redundancy scheme based on the fault tolerance requirements. Key words: manned spacecraft, flight, failure, fault tolerance, classification of failures, reliability, probability of failure-free operation, statistical analysis, dispersion analysis.

Reliability in mechanical systems projects

Sufficient safety of the parts, which determines the safety of the system specified by the technical assignment, is the necessary quality of the project, the subject of the design engineer’s attention and the customer’s requirement. An extensive task is the collection of data for iterative refinement of the resource for project details in a probabilistic aspect. It can be significantly reduced when using approximate methods for estimating the resource at intermediate stages of refining the project to the required resource with a calculated probability of failure-free operation. Thus, by the analysis of dimensionless relations of parameters of models of fatigue damage development, it is possible to obtain tools of numerical estimation of technological and constructive techniques of increase of a resource of details and their rational combination. The paper deals with the numerical measures of various directions of upgrading the fatigue life of the parts, derived from the dimensionless relations of the parameters of fatigue damage development models.

Computational and Experimental Study of the Stress State of the Opposed Compressor Connecting Rod to Assess the Probability of Failure-Free Operation

Computational and Experimental Study of the Stress State of the Opposed Compressor Connecting Rod to Assess the Probability of Failure-Free Operation

ДОСЛІДЖЕННЯ ТОЧНОСТІ УНІФІКОВАНОГО ПІДХОДУ МЕТОДУ ФУНКЦІЙ ПРАЦЕЗДАТНОСТІ ДЛЯ ФУНКЦІЇ КОЕФІЦІЄНТУ ЗАПАСУ

The article dwells on the accuracy of the unified approach of the survival function method (SFM), which is used to determine the probability of failure-free operation (PFFO) of the launch vehicles mechanical systems at the design stage. For the survival function in the form of a safety factor, which is universal, depending on the order of its expansion in the Taylor series, as well as the order of used numerical characteristics of the input parameters (factors determine the main errors of the unified approach), the accuracy of obtaining the numerical characteristics of the state variable and, ultimately, PFFO is analyzed. The case of normal distribution of bearing capacity and stress was considered, as well as the case when the indicated random variables followed the Gram-Charlier distributions. An expression is proposed for the density of the safety factor distribution in the case when the bearing capacity and stress are described by the Gram-Charlier distributions.
 The calculations have confirmed that the linearization method (first-order approximation) for nonlinear survival functions and non-normal distributions of its arguments can lead to a significant deviation of the reliability factor from the exact value. The orders of expansion of the survival function in the Taylor series and the numerical characteristics of its arguments are determined, which are recommended for practical use for PFFO determination in case of non-linear survival functions, as well as the case when the input parameters have non-normal distributions. Separately, the case of limiting the order of the used numerical characteristics of the survival functions arguments is considered, and recommendations are made to improve the accuracy of the SFM unified approach. For non-normal distributions of bearing capacity and stress, a very slow convergence of the numerical characteristics of the third and fourth orders to exact values was obtained with increasing orders of expansion of the survival functions in the Taylor series and used numerical characteristics of the input parameters. The Gram-Charlier distribution, used to describe the state variable in nonlinear models, allows obtaining a PFFO value closer to the exact one than the normal distribution.

Spectral analysis of gas dynamic processes in the inlet system of a piston engine with turbocharger

THE PURPOSE. To carry out a comparative analysis of the spectra of gas-dynamic characteristics of flows in the intake systems of piston engines with and without turbocharging, to assess the degree of influence of the turbocharger on the flow structure in such systems, and also to propose a method for the gas-dynamic improvement of processes in the system under consideration. METHODS. Due to the complexity of the object of research, an experimental approach was taken as a basis. The experiments were carried out on a single-cylinder piston engine model, which could be equipped with a turbocharger. A system for collecting and processing experimental data based on an analog-to-digital converter was used in the study. Data on changes in local values of velocity and static pressure of pulsating flows in the intake system during the engine's operating cycle were obtained using a constant temperature hot-wire anemometer and a fast-acting pressure sensor. Spectral analysis of functions of flow velocity and pressure versus time was carried out on the basis of the fast Fourier transform algorithm.RESULTS. The article presents a comparative analysis of the spectra of the amplitudes of the velocity and pressure pulsations in the intake system of an engine with and without turbocharging. Also proposed is a method for stabilizing the pulsating flow in the intake system by installing a leveling grid in the outlet channel of the turbocharger compressor. CONCLUSION. It is shown that the installation of a turbocharger leads to a significant change in the structure of gas flows in the intake system of the engine. It has been established that the presence of a leveling grid in the intake system of a turbocharged piston engine leads to a decrease in the low-frequency amplitudes of the flow velocity and pressure pulsations up to 30%. It is shown that the probability of failure-free operation of an automobile engine (cylinder diameter – 82 mm, piston stroke – 71 mm) increases by almost 1% when a leveling grille is used in the intake system.

ЩОДО ОЦІНЮВАННЯ ВІДПОВІДНОСТІ МАТЕМАТИЧНОЇ МОДЕЛІ БЕЗВІДМОВНОСТІ БОЙОВИХ ЗАСОБІВ ЗЕНІТНИХ РАКЕТНИХ ВІЙСЬК ВИМОГАМ ДО МАТЕМАТИЧНИХ МОДЕЛЕЙ

The article presents a variant of the procedure for assessing the compliance of the mathematical model of the reliability of anti-aircraft missile warfare equipment with the requirements for mathematical models using the example of the Buk self-propelled fire launcher. Parameters affecting change of serviceability of self-propelled fire plant operation in conditions of combat situation are determined. The use of the Weibull distribution allows, by varying the parameter values, to increase the guarantee of the implemented self-propelled fire plant reliability indicators, stated in technical conditions, during its operation in the troops. If necessary, this model can also take into account factors that arise suddenly, for example, taking into account the staffing of the self-propelled fire plant of the anti-aircraft missile regiment to assess the possible (predicted) value of average daily losses, taking into account various measures to reduce the values of the predicted average daily losses. Values calculated using this model react markedly to changes in model parameters, are set within the specified restrictions. In addition, it is possible to determine the time between failures. The accuracy of the results of calculating certain quantities using the mathematical model was estimated by absolute and relative errors. The calculations indicate the relative simplicity of the mathematical model, because it uses simple mathematical methods. The ability to vary the parameters of scale and shape parameters (taking into account aging), the mathematical model of IED failure makes it possible to obtain individual (partial) results obtained using previously used similar models, which emphasizes the evolution of this model. The improved method of mathematical modeling quite adequately reflects the trouble-free operation of the anti-aircraft missile system "Buk" taking into account the conditions of hostilities and meets the requirements for mathematical models. Keywords: probability of failure-free operation, parameters of mathematical model, combat situation, absolute error, time between failures, average daily combat losses.

Improving the efficiency of autonomous electrical complexes of oil and gas enterprises

In accordance with the Energy Strategy until 2035, the possibility of increasing the efficiency of energy use of secondary energy resources in the form of associated oil and waste gases has been substantiated by increasing the energy efficiency of the primary energy carrier to 90-95 % by means of cogeneration plants with a binary cycle of electricity generation and trigeneration systems with using the energy of the waste gas to cool the air flow at the inlet of gas turbine plants. The conditions for maintaining the rated power of the main generator with variations in the ambient temperature are shown. An effective topology of electrical complexes in a multi-connected power supply system of oil and gas enterprises according to the reliability condition is presented, which allows increasing the availability factor by 0.6 %, mean time between failures by 33 %, the probability of failure-free operation by 15 % and reducing the mean time of system recovery by 40 %. The article considers the use of parallel active filters to improve the quality of electricity and reduce voltage drops to 0.1 s when used in autonomous electrical complexes of oil and gas enterprises. The possibility of providing uninterrupted power supply when using thyristor systems for automatic reserve input has been proven. A comparative analysis was carried out to assess the effect of parallel active filters and thyristor systems of automatic transfer of reserve on the main indicators of the reliability of power supply systems of oil and gas enterprises.

Polymer and Geocomposite Impervious Screen Reliability Assessment

The article examines the operational reliability and technical efficiency assessment of polymer (geomembranes) and geocomposite (bentonite mats) impervious channel coating developed designs. Criteria for impervious channel screen reliability and technical efficiency are proposed based on the domestic and foreign experience generalization in the composite materials use and conducted efficiency studies in terms of water permeability, strength, efficiency, and durability. Two options of developed highly efficient structures for polymer and geocomposite channel linings are presented. The graph of change in screen failure-free operation probability was obtained based on the impervious screen failure-free operation probability calculation results, depending on the survey areas and the failure amount.

Thermal and mechanical improvement of the air supply system of a turbocharged piston engine

A method of thermomechanical improvement of pulsating air flows in the intake system of a turbocharged piston engine is described. The main objective of this study is to develop a method for suppressing the rate of heat transfer to improve the reliability of a piston turbocharged engine. A brief review of the literature on improving the reliability of piston engines is given. Scientific and technical results were obtained on the basis of experimental studies on a full-scale model of a piston engine. The hot-wire anemometer method was used to obtain gas-dynamic and heatexchange characteristics of gas flows. Laboratory stands and instrumentation facilities are described in the article. The data on gas dynamics and heat exchange of stationary and pulsating air flows in gas-dynamic systems of various configurations as applied to the air supply system of a turbocharged piston engine are presented. A method of thermomechanical improvement of flows in the intake system of an engine based on a honeycomb is proposed in order to stabilize the pulsating flow and suppress the intensity of heat transfer. Data were obtained on the air flow rate and the local heat transfer coefficient both in the exhaust duct of the turbocharger compressor (i.e., without a piston engine) and in the intake system of a supercharged engine. A comparative analysis of the data has been carried out. It was found that the installation of a leveling grid in the exhaust channel of a turbocharger leads to an intensification of heat transfer by an average of 9%. It was found that the presence of a leveling grid in the intake system of a piston engine causes the suppression of heat transfer within 15% in comparison with the baseline values. It is shown that the use of a modernized intake system in a diesel engine increases its probability of failure-free operation by 0.8%. The data obtained can be extended to other types and designs of air supply systems for heat engines.

Methodological approaches to creating the electronic databases of building operation safety

One of the tasks of ensuring the safety of construction sites is to maintain or increase the design reliability of buildings and structures during their renovation and reconstruction. The reliability of the object is calculated at all stages of its life cycle and for kinds of work corresponding to these stages. An effective method of determining quality indicators is the registration method, which is based on observations of the actual condition of the building structure. The registration of the condition of the elements and the construction is carried out through complex characteristics allowing to estimate the rate of imperfections (defects and damages-DD) progression throughout time, and to define their criticality level. For building structures (facilities), the registered DD allows performing the analysis of types, consequences, and the criticality of possible failures (FMECA classification). The proposed strategy includes the process approach to resource management through developing a system of accounting and functional controlling, analysis, and regulation of safety. One of the alternate solutions of the problem may be the establishment of information systems based on registration methods, namely electronic databases (DB) of defects and damages of structures. Information databases in the conditions of an actual enterprise may become the first but still very important step on the way to generalizing and controlling the data about the actual state of building structures and facilities for further decision-making concerning their operation and maintenance. The database is to be implemented in the network form, with a clear hierarchical access framework and editing capabilities for the officials, the ability to generate reports and extracts. The obtained results in the framework of the reliability-assurance program should provide the ability to calculate the probability of failure-free operation, the residual resource with assigned level of risk.

Analysis of the reliability of the plates of complex shapes for the cams of automatic half-hose machines by the criterion of fatigue strength

The purpose of the work is to develop the algorithm for calculation of the probability of failure-free operation of flexible plates of complex shapes for the cams, using the criterion of fatigue strength, to make decisions on minimization of their sizes with the subsequent evaluation of the implemented measures. The studies are performed on the example of a plate for the cam, the configuration of which provides both beam and double console deformations at the same time. The comprehensive approach is presented, which includes dynamic analysis of the needle impact on the cam surface, computer simulation of geometric parameters of the plate by the finite element method (FEM) according to the condition of strength, and classical principles of mathematical statistics and Theory of Probability. The finite-element model with a volumetric 8-node element is used, which allows, with ease of calculations, to obtain the results with a high accuracy when determining the stress-deformed state of the study object. The computer simulation is performed using Code_Aster software with free access. Also, in the calculation of reliability, the random nature of the multifactorial influence on the value of the plate fatigue limit and the loading variations of the cam are considered. When determining the equivalent forces, taking into account the cyclical operation of the machine, the forces that affect the cams during the production of one product are taken as a loading. The numbers of cycles corresponding to these loadings are calculated by the formulas, which are made as a result of the analysis of trajectories of needles motion concerning the cams when knitting different sections of the product. When calculating equivalent stresses, only stresses that influence the accumulation of fatigue failures are used, that is, the values greater than the half of the detail fatigue limit.The proposed computational approach can be used to generate the cams with flexible work plates of different configurations, including under the equal stress condition.

Estimation of the residual resource of several buildings and structures as a single object

In this article, the author raises the problem of assessing the residual resource of an object, which consists of several buildings and structures. Four different approaches to solving this problem are presented. The advantages and disadvantages of these approaches are presented. The areas of their application are indicated. Within the framework of these approaches, one can use the direct enumeration method, the combinatorial method, the algebra of logic, the general logical-probabilistic method. The author has developed two possible options for calculating the residual resource of these objects using the general logical-probabilistic method. It is proposed to develop a Methodology for calculating the residual life of such objects before the survey. The author indicates the main points that must be prescribed in the developed Methodology. An example of calculating an object consisting of five buildings is given. The scheme of functional integrity is constructed according to the general logical-probabilistic method. In the program complex “Arbiter” the static and probabilistic-time calculation of the given scheme is performed. Then the calculation of the object as a whole was carried out according to the “2 of 5” system. As a result, the value of the probability of failure-free operation and the residual resource of the object as a whole is shown.

АВТОМАТИЗАЦІЯ ПРОТИАВАРІЙНОГО КЕРУВАННЯ ЕНЕРГОСИСТЕМОЮ НА ОСНОВІ ЛОГІКО-ІМОВІРНІСНОГО МОДЕЛЮВАННЯ НАДІЙНОСТІ ПРОДУКЦІЙНИМИ МЕРЕЖАМИ ПЕТРІ

The paper presents the results of research on methods for constructing knowledge bases of decision support systems for dispatch control of power supply systems in crisis situations. Models of products based on Petri nets are proposed for assessing the parameters of reliability of power supply systems. An algorithm for calculating the reliability parameters of the electrical network using analytical matrix equations of Petri nets has been implemented. The work is devoted to the topical problem of intellectualization of power supply systems and means of automation of control of large power systems. The relevance of research in the field of building intelligent power systems is grounded. The basic requirements for the reliability of modern power supply systems are formulated. The concept of intellectualization of power systems and management of their reliability is a stable trend in the development of large energy systems and automated dispatch control systems. The solution to the problem lies in the implementation of intelligent decision support systems. The main task of the work is to model the reliability of the power supply system in order to build an effective knowledge base about the parameters of the reliability of the power supply system. For this purpose, we use a probabilistic approach to assessing reliability. This approach is based on the concepts of the probability of failure-free operation and the probability of failure, which are expressed in terms of the failure rate. On the basis of the obtained models, the construction of intelligent software systems for dispatching can be carried out taking into account the reliability indicators of the components of power supply systems. As a mechanism for formalizing failure circuits in power supply circuits, the production approach of knowledge representation is applied, which implements conjunctive-disjunctive connections of statements associated with failures. The outlined approach is invariant in relation to subject areas, which makes it possible to build effective decision support systems in the field of operational emergency control of the energy system.

Methods for calculating the reliability of power supply systems

The aim was to determine the reliability indicators of a power supply system using an artificial neural network model. A model for calculating technical reliability was developed using the following methods: an algorithm for calculating reliability indicators of power supply systems, the method of failure rate of a power supply system and a forecasting model using artificial neural networks. It was established that a power supply system is formed by an open radial power supply circuit. The failure rate of the power supply subsystem was determined by calculating the failure rate of i-th element of the subsystem. As a result of calculating the probability of failure-free operation of the subsystem for various conditions (5 time intervals), it was found that with an increase in the operating time from 100 to 500 h, a linear increase in the rate of system failures occurs from 0.0051 to 0.0073 1/h. A comparison of the obtained mean-to-failure values of the main and the same backup subsystem in the unloaded mode with an absolutely reliable switch (269.62 h) with the main and the same backup subsystem in the loaded mode (202.21 h) was carried out. The results differ by 67.41 h, which indicates a higher degree of reliability of the first method. The software package Prognoz_INS_2020 was developed. An acceptable accuracy of no more than 2.17% was obtained by comparing the results of the conventional calculation of the failure rate of power supply systems and using the Prognoz_INS_2020 software package. This indicates the efficiency of the proposed software package in reliability calculations at operating energy enterprises. The proposed methods for assessing technical reliability both using the conventional model and a model based on an artificial neural network made it possible to assess the state of power supply systems, which helps to prevent dangerous emergencies.

The Method of Assessing Traffic Safety in Railway Transport

To identify and predict risks in the work, a method for assessing traffic safety in railway transport is proposed. On the basis of statistics on the failure of freight cars during operation, the characteristic distribution laws for types of wear were determined. As a result, the dependences of the probability of failure-free operation of freight cars on the operating life were obtained and the centers of gravity of the areas that are used to characterize and assess the risk were determined. When designing a freight car, it is possible to establish risk values obtained on the basis of statistical data, which opens up the possibility of improving traffic safety in railway transport. In the developed method for assessing traffic safety in railway transport, the use of a graphical risk matrix is proposed. It is also proposed to combine the dependencies of the probability of failure-free operation of freight cars to calculate the total risk. This allows you to get a graphical risk matrix taking into account three types of wear of a freight car to assess traffic safety. The number of dependencies of the probability of failure-free operation of freight cars can be increased if failures are observed for other reasons.

Influence of tightening fitting accuracy for resource connection

A dependence have obtained for determining the design tolerance of fit, as one of the characteristics of the model of parametric failure of a joint with an interference fit, the calculation is carried out taking into account the wear rate and the parameters of its dispersion at a certain resource and a given probability of failure-free operation. On the example of calculating a connection with an interference fit, it have shown that the choice of a fit without a margin of accuracy cannot ensure the operational reliability of the connection, but only guarantees the absence of failures at the initial stage of work – during the warranty period. It have proven that with the right choice of fit accuracy, it is possible to achieve a significant increase in the resource of failure-free operation.

ФОРМУЛИРОВКА МЕТОДА ОЦЕНКИ ВЕРОЯТНОСТИ БЕЗОТКАЗНОЙ РАБОТЫ КОНСТРУКЦИЙ НА ОСНОВЕ СОЧЕТАНИЯ СТАТИСТИЧЕСКОГО МОДЕЛИРОВАНИЯ И ЧИСЛЕННЫХ МЕТОДОВ ОЦЕНКИ НАПРЯЖЕНИЙ

In this paper, methods for estimating the reliability of constructions are considered. The formulation of a method for estimating the reliability of the design based on a combination of statistical modeling and numerical methods for evaluating stresses is given. The method is based on a "load – bearing capacity" model, which takes into account both stochasticity of mechanical properties of construction materials, randomness of geometric characteristics, and loads of a probabilistic nature. This new method is a system of n nested cycles. The number of governing parameters n depends on the design. The load variation series is calculated in the body of the internal cycle. The load is calculated numerically in terms of stresses using the finite element method. Any commercial solver such as Nastran, Ansys, or Abaqus can be used for this purpose. The probability of failure-free operation (reliability) is calculated involving the variational series of loads and load-carrying ability. For this purpose, the formalized estimation method based on empirical distributions is used. Fundamentals of the latter are available in the monograph "Reliability in Engineering Design" written by Kapur K.C. and Lamberson L.R.. A primary function of the proposed method is to evaluate the probability of failure-free operation of constructions under stationary or quasi-stationary random loads.

Technique for ensuring safety of transportation vehicles through the analysis of their structural reliability

The article is devoted to the development of a technique for the assessment of the influence of the structural reliability of transportation vehicles on their safety. This technique includes: an analysis of the automotive vehicle as a complex technical system, its structural elements greatly influencing road safety (RS); calculation of mean-time-between-failures and time for recovery of subsystems, assemblies and parts, probability of failure-free operation. As a result of the technique application, recommendations as to intervals of the replacement of automotive vehicle’s elements depending on the required probability of failure-free operation are released.