Probability Of Failure-free Operation Research Articles

Mechanisms of ensuring the accuracy and reliability of data transmission over a radio channel using relay technology and their implementation on transceivers with LoRa modulation

The article is devoted to a detailed description of the algorithms of the operation of the relay-race data transmission system over a radio channel, which ensure high reliability of transporting the results of monitoring the operation of extended objects to the central control panel. The feature of the system is operation at a low power level of transmitters, energy efficiency, which ensures a long-term operation without maintenance, the ability to replace failed elements quickly without stopping the entire system, mobility — quick installation and start-up of the system. Energy efficiency and operation of the radio channel with a low transmitter power level is ensured by the use of SX 1276 (LoRa) transceivers. The accuracy and reliability of data transmission is ensured by original algorithms, which are described in the paper. In the relay data transmission system, it is possible to use up to 255 relay nodes with their installation at a distance of up to 4 km from each other. Two options of building a system with relay-race transmission have been developed: a system with a simple handover, a system with transmission «Through one». The second option provides more reliable data transfer and higher probability of uptime. With the number of relay nodes equal to 50, the probability of failure-free operation of a simple system is 0.268, and for the system with «Through one» transmission is 0.985.

Разработка математической модели функционирования электротехнических комплексов релейной защиты цифровых подстанций

The issues of introduction of electrical digital substations in the Russian Federation are considered. An existing criteria analysis for assessing the modern relay protection devices efficiency is carried out and an assessment of their sufficiency is made. A mathematical model development of the digital substations relay protection complexes operation has been developed using the queuing theory, the graphs theory and Markov chains. The failure-free operation probability calculated value of the relay protection complexes corresponds to the long-term analysis data. This indicates that the mathematical model is correct. The proposed mathematical model makes it possible to take into account the impact of the maintenance quality on the digital substation relay protection complexes efficiency.

Control of complex thermoelectric cooling units with mixed electrical connection in a uniform temperature field

The possibility of optimal thermal management of a number of temperature-dependent and heat-loaded elements of radio electronic equipment with calculated power dissipation is considered. Studies have been carried out in a uniform temperature field using a set of thermoelectric cooling devices and defined geometry of thermocouple branches. The correlation for determining the relative operating current depending on the relative temperature drop for a given supply voltage, thermal load and geometry of thermoelements branches has been obtained; the range of valid values of the relative operating current has been determined. Acomparative analysis of the basic parameters, reliability indices and dynamic characteristics of a group of thermoelectric devices included in the complex for different supply voltages and heat loads has been made. The possibility of selecting supply voltages of thermoelectric devices complex with regard to limiting factors for mass-size, power, dynamic and reliability characteristics to ensure the optimum thermal mode of a number of thermo-dependent elements of radio electronic equipment has been shown. With increasing supply voltage of thermoelectric devices complex with mixed electrical connection in uniform temperature field at given thermal load and geometry of thermoelements branches the following results are achieved. Steady-state time increases, the number of thermoelements increases, the cooling coefficient decreases, the amount of consumed energy increases, the heat dissipation capacity of the heat sink increases, and the functional dependence of the probability of failure-free operation on the total supply voltage has a maximum.

OPTIMAL FAULT DETECTION OF RIVER SHIP HULLS

The issue of determining the reliability of the hulls of inland and river-sea-going vessels after a known number of years of operation under given condition is considered. It is accepted that fault detection of a ship’s hull is a survey, measurement and evaluation of defects in each element of the ship’s hull in order to establish the methods and scope of repairs that ensure its reliable operation until the next regular survey under specified operating conditions. It is shown that the volume of residual thicknesses can be significantly reduced using the statistical data on wear rates presented in the Rules of the Russian River Register. At the same time, the reduction in the scope of measuring the parameters of defects retains the probability of detecting all defects of the hull elements to the level of 0.95, and the probability of failure-free operation of the hull until the next survey, after the elimination of the identified defects will be at least 0.95. A form of table for processing the values of the residual thicknesses of all elements in the inspection report and instructions for filling it out are given. Explanations for using the results of measurements and calculations at determining the technical condition of certain elements in the group and the ship’s hull as a whole are given. The last column of the table indicates the method of eliminating the defect of an element and groups of elements, and in the conclusion of the inspection report, the method of repair and its scope for the entire hull of the ship providing a suitable assessment of the condition after repair are indicated. The main advantage of this paper, in difference from the previous studies of the authors in this area, is that user-friendly (the designer of the defect report tables) nomograms, which allow you to reduce the number of measurements of the residual thicknesses of hull structure elements in the online mode, have been created. The performed study, allowing you to reduce the number of measurements while guaranteeing the reliable operation of the ship’s hull, will let the shipowner to reduce the cost of repair work by reducing the number of days of ship standing on the slipway (in the dock). In addition, the ship repair company will be able to free up its production facilities for the purpose of their subsequent loading with other ship repair or shipbuilding orders, which will increase the efficiency of their activities.

MATHEMATICAL MODEL OF COMPUTER SYSTEM RELIABILITY IN RESIDUAL CLASSES

The subject of the article is the construction of a mathematical model of the reliability of a computer system (CS) that operates in a system of residual classes (RNS). This mathematical model is based on the use of structural sliding reservation. The purpose of the article is to increase the reliability of the CS, which operates in the system of residual classes, as well as to calculate and compare the reliability, in terms of the probability of failure-free operation, of the CS in the RNS and the ternary computing system, which operates in the positional binary number system (PBNS). Tasks: to analyze the influence of the number system used on the reliability of the CS; to investigate the properties of the RNS and determine their influence on the structure of the CS in the RNS; build a mathematical model of reliability and, on its basis, perform the calculation and comparative analysis of the reliability of the CS in the RNS and the tripled CS in the PBNS. Research methods: methods of analysis and synthesis of computer systems, number theory, coding theory in RNS, reliability theory. The following results are obtained. The paper shows that the provision of a given level of reliability in the design of the CS using the RNS is due to the presence of various types of redundancy at the same time: structural, informational, temporal, functional and load. In RNS, these types of redundancy can be effectively used to improve the reliability of the CS. The CS in the RNS represents a computational structure that is identical in structure and principle of operation to the sliding structural redundancy model in the PBNS in the case of a loaded (hot) mode of operation of the redundant elements. Proceeding from this, the paper presents a mathematical model of the reliability of the CS in the RNS. In this paper, the calculation and comparative analysis of the reliability of a tripled computing structure in a PBNS with an ideal majority element and a CS in an RNS with an ideal reliability automaton are carried out. Conclusions. As shown by the results of calculations and comparative analysis in some time intervals of operation, the probability of non-failure operation of the CS in the RNS is higher than the probability of non-failure operation of the aircraft in the PBNS with a tripled majority structure. This implies the effective use of the RNS to improve the reliability of the CS.

RELIABILITY ANALYSIS OF PRECISION GEARS WITH MODIFIED INITIAL TOOTH CONTOUR

The article presents the results of a theoretical study that was conducted as part of the search for solutions to the problems of calculating the operational reliability of gears of a new generation that have a significant deviation in the geometry of the profile of the teeth and the entire engagement from the standard initial contour. A method of plotting the wear of the working surfaces of gear teeth has been developed. The essence of the method is that the equation of the worn surface can be obtained by calculating the full variational derivative of the functional of the energy action of wear. Since wear reduces accuracy, the method is used to calculate the probability of failure-free operation of precision gears by the express method. The proposed article is one of the first works on the calculation of the operational reliability of precision gears with teeth profiled by the involute epitrochoid.

Probabilistic indicators of imperfect inspections used in modeling condition-based and predictive maintenance

This study proposes mathematical models for assessing the probabilistic indicators of imperfect inspections conducted when performing condition-based and predictive maintenance. The inspections used in mentioned types of maintenance differ in decision rules regarding system operability at the time of checkup. Contrary to the previous studies, we present the decision rule for each type of inspection on the time axis, which allows the formulation of the set of mutually exclusive events at discrete times. The correct and incorrect decisions correspond to true-positive, false-positive, true-negative, and false-negative events. We propose general expressions for computing the probabilities of possible decisions for both types of inspection. The paper introduces the effectiveness indicators of condition-based and predictive maintenance such as average operating costs, total error probability, and a posteriori probability of failure-free operation. We illustrate the developed approach by calculating the probabilities of correct and incorrect decisions using a specific stochastic deterioration process. The results of the calculations verify that probabilities of correct and incorrect decisions for both types of inspection are very substantially time-dependent despite the large number of published studies where these probabilities are independent of time.

Planning of a Group of Dynamic Systems Operation Program Based on the Failure Time Prediction

The article is devoted to the justification of group of dynamic systems (DS) operation program based on the failure time prediction. The following assumptions are made: the group includes DS operating under the same conditions, but having different service life; the composition of the DS includes a number of potentially faulty elements with similar values of reliability indicators; for each element a number of parameters are measured and the failure of the DS occurs when at least one of the controlled parameters leaves the tolerance range. The use of a piecewise linear regression model of parameter drift corresponding to the life cycle of DS is justified. The rule of correction of the linear model is formed based on the results of last measurements of the controlled parameters. A unified algorithm for calculating the reliability characteristics in a group of DS based on the drift of controlled parameters is proposed. At the first step, the probability of failure-free operation for a given time and a gamma-percent resource is calculated for one controlled parameter. At the second step, the time moment of a DS failure (which is assumed to happen when at least one controlled parameter leaves the tolerance range) is calculated. At the third step, the reliability characteristics of a group of DS are predicted using a mixture of distributions. The realization of a random variable corresponding to a random mixture is modeled as follows: first, DS is selected at random, then a random variable is modeled in accordance with its distribution function. The mixture distribution function is expressed as a weighted sum of the component distribution functions. Model examples allowing to rank the considered DS according to the predicted failure time with subsequent adjustment of the operation program are considered.

Predictive model of risks in railroad transport when diagnosing axle boxes of freight wagons

The research is aimed at developing a predictive model of the risks in railroad transport when using diagnostics of the axle boxes of freight wagons, which will allow assessing traffic safety during the operation of freight wagons. To develop a predictive model of the risks in railroad transport, the approaches of the probability theory were used. The constructed predictive model of the risks makes it possible to assess traffic safety during freight transportations; to determine further measures to reduce them; to evaluate the diagnostic method. The authors developed a predictive model of the risks in railroad transport when using the diagnostic methods of freight wagons’ axle boxes during maintenance and repair of axle box. This model includes the probability of failure-free operation of the axle boxes of freight wagons, the probability of identifying of the technical condition of the axle boxes of freight wagons, the significance of the diagnostic parameter and its relative assessment after appropriate maintenance, repair or technical control.

Development of a prediction model for the probability of failure-free operation of elements and components of the main equipment of hydroelectric power plant

A structural diagram of calculation of reliability of hydraulic turbines is proposed taking into account control of arameters of state of system elements, based on data of the map of setpoints of automation and process protection of hydroturbine of HPP. Failure-free operation of hydraulic unit systems and assemblies was analyzed for reliability indicators. The main elements of the system are identified. The safety of HPP operation largely depends on the reliability of the main generating equipment. Hydroturbine equipment of a hydroelectric power plant is designed for specific operating conditions characteristic for each type of hydroelectric power plant. This allows for each type of turbine to efficiently obtain the greatest amount of hydraulic power if they operate under proper conditions. Therefore, when evaluating reliability indicators, it is proposed to take into account weighting factors reflecting the degree of influence of a particular parameter on the reliability of the system. The obtained results were compared according to the proposed model and according to the regulatory methodology for assessing the probability of system failure-free operation in a generalized form. Based on the results, a model is proposed that takes into account the failures of the hydraulic unit elements to predict the probability of trouble-free operation in order to ensure the reliability of equipment operation beyond the design service life and reduce operating costs.

Technical equipment justification methodology for the cultivation of grain crops

The article presents a methodology for evaluating tillage and seeding aggregates, taking into account soil and climatic conditions of farms. We offer a comprehensive assessment index of the performance of sowing machines and complexes for sowing crops, which takes into account productivity, fuel efficiency, sowing quality and reliability of the technological process to a certain point in time. Unit serviceability is measured by the ratio of the unit's capacity during the main time to the capacity during the shift time. Fuel consumption indicator for machines is the ratio of tillage depth, for seeders it is the sowing depth to specific fuel consumption. Soil cultivation quality is assessed by indicators of ridging and crumbling of the soil, the quality of sowing by the ratio of the actual seeding rate and the depth of seeding to the given technical specifications. The integral functions of the distribution of probabilities of failure-free operation in the form of an exponential law of distribution are used as an indicator of reliability assessment. For calculations, the results of agrotechnical and economic evaluation, taken from the protocols of machine tests at machine test stations, are used. Based on the research, effective sets of machines for the cultivation of crops, which are characterized by low costs, high quality of work and reliability, were proposed. In first place were taken by the grain seeders S-6PM2, SZP-3,6B, SZP-5,4, AMAZONE D9-60 Super; seeding complexes KSKP2,1D × 5 OMICH, Kuzbass PK-8,5, John Deere "730". The second place was taken by John Deere 455, ASTRA SZT-5,4, SKP-2,1D × 5, Pronto 12NT Horsch, DMC Primera 9000; seeding complexes Irtysh-10, AGRATOR-combidisk-9000, Kuzbass PK-9,7A.

Thermal control of parallelly connected thermoelectric coolers in a uniform temperature field

The possibility of using a set of thermoelectric devices to control the thermal regime of a number of thermo-dependent and heat-loaded elements of radio-electronic equipment, which are subject to increased requirements for reliability indicators and dynamic characteristics, is considered. A mathematical model of a thermoelectric device has been developed for a uniform temperature field, a typical range of power dissipation of the products used, a range of standard values of the supply voltage, and a fixedgeometry of thermoelement legs. A relation is obtained for determining the relative operating current depending on the relative temperature difference at a given supply voltage, the geometry of the thermoelement branches, and the magnitude of the thermal load. The region of real values of the relative operating current in the zone of relative temperature differences is determined for a given geometry of branches and thermal load. An analysis is made of the relationship between the relative operating current of a single-stage thermoelectric cooler and the coefficient of performance, the amount of energy expended, the heat-removing capacity of the radiator, the time to reach a stationary mode, and the probability of failure-free operation. The dependence ofthe relative failure rate and the probability of failure-free operation, the amount of energy expended, the heat-removing capacity of the radiator, and the number of thermoelements on the supply voltage of the thermoelectric cooler has been studied. This made it possible to evaluate the control features and identify the effectiveness of the control actions when the coolers are connected in parallel in a uniform temperature field. The possibility of choosing the optimal supply voltage is shown, taking into account a number of restrictive factors in terms of weight, size, energy, dynamic and reliability characteristics of a complex of thermoelectric coolers as part of systems for ensuring thermal regimes of heat-loaded radio-electronic equipment.

Вероятностная оценка эффективности функционирования социальных систем в условиях негативных факторов

An approach to the quantitative assessment of the open social system efficiency of a non-technical nature is con-sidered. The task is formulated from the standpoint of assessing complex indicators that take into consideration the conditions of external influences on an open non-technical system. Formalizing the formulated problem is carried out within the framework of the reliability theory methods. A two-parameter generalized analytical expression is obtained for calculating a probabilistic assessment of the open system efficiency, taking into consideration the nature of destructive impacts. An approach to calculating the probability of failure-free operation of such systems is substantiated, considering the frequency of failures caused by negative consequences from destructive impacts. The results of analytical modelling are presented in assessing the probabilistic indicators of open non-technical systems, in which the degradation of ongoing processes can be described on the basis of an exponential law. The processes of a non-technical nature corresponding to the specified distribution are given, which include the aging of information, the level of residual knowledge, the number of divorces by the number of years lived, motivational stability, etc., characteristic of such areas as pedagogy and psychology. The author considers an example of applying a reasonable approach in relation to the “burnout syndrome” based on analysing control points and time intervals, which allows predicting the future state of the diagnosed person according to the current assessments. Conclusions are made and directions for further research are determined.

A Technique of the Distributed Information Systems Control Method Choice under the High Network Dynamics Conditions

Purpose of research. The purpose of this study is to select a method for managing a distributed system, which, based on known parameters, would reduce the consumption of resources of computing devices. The resource of an information system is understood as the probability of failure-free operation (reliability function), which degrades over time for each node, the faster, the higher its workload.Methods. Considering that with high dynamics of the edge layer of the network, the frequency of system reconfigurations becomes relatively high, and the need for reconfigurations is unpredictable, reducing the total time spent on reconfigurations makes it possible to increase the time spent on solving functional computational problems of the system and thereby reduce the load of nodes. The reconfiguration time can be reduced both by reducing the time for detecting a failure in a distributed system, and by reducing the new configuration forming time. In this paper, a method for reducing the time of the failure detection is considered. The analysis of the applicability of system control methods (centralized, with a distributed leader, decentralized) is based on the obtained analytical estimates of the time the system detects a failure under control conditions using one method or another. A numerical experiment makes it possible to identify areas of system parameters, where it is preferable to use the method with a distributed leader.Results. The main result of this work is a methodology for choosing a method for managing distributed information systems in conditions of high dynamics of the network infrastructure, focused on reducing the consumption of resources of computing devices.Conclusion. System reconfiguration time can be shortened by choosing the most appropriate control method. Thus, the time allotted for solving the functional tasks of the application increases, the workload of the computational nodes decreases, and, therefore, the FBG values increase over the planning horizon.

Diagnostics and reliability of current receivers

The most vulnerable element of modern electric buses, which are dynamically charged, are pantographs. The article describes the main reasons for the wear and tear of pantographs. The calculation of the probability of failure-free operation of the pantograph systems is made.

Calculating the probability of the failure-free operation of spur gear transmissions

The article presents an improved method for calculating the probability of failure-free operation of case-hardened spur gear transmissions. The existing methods for calculating the probability of failure-free operation of gear transmissions are analyzed. The failure tree for a case-hardened spur gear transmission is presented. The probability of failure-free operation of case-hardened cylindrical gear transmissions is presented as the product of the probabilities of failure-free operation of the gear and the wheel according to the following criteria (failure types): contact endurance (pitting), bending endurance (tooth breakage), and tooth interior fatigue fracture (deep contact chipping). An algorithm has been developed for calculating the probability of failure-free operation of case-hardened spur gear transmissions. To restore the torque distribution density function in the proposed method, nonparametric statistics methods are implemented. In the calculation of contact stresses, the skew angle is taken into account, which is the sum of two angles: the skew angle due to deformations of the transmission elements and the housing; the total angle of technological misalignment of wheel tooth surfaces, caused by errors in the manufacture of the teeth and mounting errors during the assembly of the transmission. An example of a test calculation of the probability of failure-free operation of a case-hardened spur gear transmission according to the presented method is given. Based on the work performed, conclusions are formulated.

ASSESSMENT OF THE RESIDUAL LIFE-TIME OF THE ELEMENTS OF THE CENTRIFUGAL PUMP OF THE ENERGY INSTALLATION ON THE BASIS OF STATISTICAL ASSESSMENT OF FATIGUE WITH PREDICTED WEAR DUE TO CORROSION

In this article, the residual resource of a centrifugal pump was anticipated, which operates an overestimated resource in the pumping line of a nuclear power plant. The results of theoretical and numerical modeling of its stress-strain state with a change in the geometry of the hull parts are presented. Three-dimensional FE models have been developed that take into account the actual geometry of pump parts, as well as a forecast of their possible changes during further operation. The change in the geometry of the structure is taken into account on the basis of extrapolation of data on the thickness of the hull walls obtained over a long service life. Calculations to determine the static strength are made for the main operating mode of the pump (under normal operating conditions). In places of welds, the cyclic strength was checked separately, while taking into account the decrease in their strength due to an increase in equivalent stress amplitudes by dividing them by the coefficient of reduction in the strength of the weld. The process of thinning of the wall of the pump housing under the action of erosive-corrosive wear is modeled. This process is random, so it was modeled taking into account the equations of wear growth kinetics. As a result of the research, the damage parameter and the probability of failure-free operation of the structure were obtained. These parameters are determined taking into account the predicted values of the percentage thinning of the pump housing wall and the obtained characteristics of the statistical deformation state of the structure.

METHODICAL APPARATUS FOR ENSURING THE CORRECTION OF SINGLE ERRORS AND DETECTION OF DOUBLE ERRORS IN STORAGE DEVICES

The analysis of errors that occur during the operation of static storage devices (SD) is carried out. The conclusion is drawn that single and double errors are most likely to occur in memory devices (single errors appear with a probability of up to 80 %, double errors up to 20 – 25 %, and errors of other multiplicity account for up to 2 %). Methods for protecting storage devices from single and double errors are considered. It has been established that at present, for the correction of single errors and the detection of double errors, a modified Hamming code is widely used, which uses for this purpose an additional parity bit for all bits of the code set. The necessity of developing a code that corrects single errors and detects double errors while reducing information redundancy is substantiated. Regularities have been identified that make it possible to form rules for encoding information, and when decoding, to form three additional checks for an error sign to determine erroneous bits in the event of indistinguishable error syndromes. The corrective ability of the proposed method of information coding is investigated. It has been established that the proposed code allows correcting all single errors, detecting all double errors and, at the same time, correcting some of the double errors that simultaneously occur in information and check bits. A regular information coding procedure is described for correcting single and detecting double errors while reducing information redundancy by one check bit and, consequently, reducing hardware costs associated with storing the values of check bits in a memory device. A comparative evaluation of the detection ability and information redundancy of the proposed method with a modified Hamming code is carried out using the example of coding an 11-bit information word. It has been established that for the code (15,11), the implementation of the proposed method makes it possible to detect all single and double errors, correct 100 % of single errors and 27 % of double errors, and use four check digits for these purposes (one less check digit than modified Hamming code). The conclusion is made that the reduction of information redundancy makes it possible to increase the code speed and reduce hardware costs associated with storing the values of a given bit in a memory device and, therefore, increase the probability of failure-free operation and reliability of the memory device operation while reducing information and hardware redundancy.

МЕТОД АНАЛІТИЧНОГО МОДЕЛЮВАННЯ БЕЗВІДМОВНОСТІ БОЙОВИХ ЗАСОБІВ ЗЕНІТНИХ РАКЕТНИХ ВІЙСЬК

The article sets out a method for analytical modeling of the recoverability of anti-aircraft missile forces using the example of a self-propelled fire launcher (SOU) of the Buk anti-aircraft missile system. The main attention is paid to one of the properties of technical reliability, namely the reliability of weapons and military equipment. This is especially true of the IWT anti-aircraft missile forces, the failure to fulfill the tasks of which due to failures in operation can lead to serious consequences in operation or battle. The improved method of mathematical modeling of reliability allows taking into account the possibility of developing elements of aging and wear of MCS components in the process of expending the released resource at the operation stage, as well as taking into account the conditions of hostilities by using and developing a mathematical model in the form of a Weibull distribution in order to obtain more guaranteed indicators of reliability. It is advisable to select the final value of the mean hour of MTBF failure taking into account reaching the value of the ratio between the number of MTBF disabled due to only limited technical reliability and the amount of equipment that failed due to enemy fire action. This will increase the efficiency of the system for updating damaged MDS during hostilities, and improve the planning of production activities of repair bodies. It will also be possible to increase the overall combat effectiveness of the anti-aircraft missile regiment in the process of repelling a raid of air attack vehicles. When setting the specified ratio value, the required MTBF value can be calculated (before failure). The improved method of mathematical modeling adequately reflects the failure-free operation of the combat vehicles of the Buk anti-aircraft missile system, taking into account the conditions of hostilities. Keywords: probability of failure-free operation, failure-free simulation, continuous operation time, distribution parameters, time between failures, limited technical reliability.

Methods for determining the probability of failure-free operation of the engine of machines with an electronic control system

The method for determining the probability of failure-free operation of the electronic control system of the engine of machines, which allows not to release them on the line in a pre-failure state, is presented, and the main reasons for the occurrence of failures and malfunctions in its elements are presented. The given information can be applied in the course of forecasting the residual resource of the given system.