Probability Of No-failure Operation Research Articles

Визначення оптимальних норм надійності космічного апарата з урахуванням економічних показників

The goal of this paper is to develop a method for determining the values of system failure rates optimal in terms of net profit maximization with account for spacecraft mass limitations. It is adopted that the spacecraft systems are independent in terms of reliability, each of them can be only in two states (a functioning state or a failure state), and each equipment type of the special complex makes an independent contribution to the overall effect. The paper considers the case where the spacecraft system failure time obeys the exponential law. Use is made of the Lagrange multiplier method and numerical optimization methods. The problem is solved using the mass ? failure rate and cost ? failure rate relationships of the spacecraft systems. For the supporting complex, the dimension of the mathematical simulation problem is reduced to two: a formula is derived to find the optimal failure rates of all the systems of the supporting complex using the optimal failure rates of two systems of it. The variables for the special complex and the supporting complex are separated. Due to the fact that each special complex system makes an independent contribution to the overall effect, the problem for the whole spacecraft is reduced to a system of two equations for the special complex and the supporting complex and ncn equations in one variable for the special complex with two coupling variables between the supporting complex and the special complex where ncn is the number of the special complex systems. The paper presents a numerical-and-analytical method for spacecraft system failure rate optimization where the initial guess is specified indirectly: by specifying the supporting complex mass and probability of no-failure operation. The method may be used in the development of a space hardware design methodology accounting for economic factors. From the optimal values of the spacecraft system failure rates found using the mass ? failure rate and cost ? failure rate relationships, one can find the masses and costs of the spacecraft systems to be used in optimizing the parameters and development cost of the systems. The method is expected to increase the profitability and competitiveness of spacecraft under development.

THERMAL MANAGEMENT OF A SET OF THERMOELECTRIC COOLERS CONNECTED IN PARALLEL IN AN UNEVEN TEMPERATURE FIELD

A method of increasing the efficiency of thermoelectric system for providing thermal modes of distributed heat-loaded elements of an on-board information system is considered. It is shown that thermoelectric coolers are most susceptible to thermal effects. In accordance with the reliability model, they are connected in series with heat loaded elements and to a great extent determine their operability. The inclusion of thermoelectric coolers in the feedback loop of a thermal management system places increased demands on the dynamic performance of the coolers. However, dynamics and reliability performance are at odds with each other, requiring compromise approaches to cooler design and control. Studies have been carried out for an uneven temperature field, a typical dissipation power range, and a fixed geometry of thermocouple branches. Analytical relations for determining the relative operating current depending on the relative temperature difference at a given supply voltage, geometry of thermocouple branches and heat load value have been obtained. The range of actual values of the relative operating current in the area of relative temperature differences is determined. An analysis of relation between relative operating current and refrigerating factor, amount of consumed energy, heat dissipation capacity of a radiator, time of reaching steady-state mode and probability of no-failure operation has been carried out. The dependence of the relative failure rate, energy input, heat dissipation capacity of the heat sink and the number of thermocouples on the supply voltage has been investigated. This made it possible to determine the controlling features and to reveal the efficiency of controlling actions when the coolers are connected in parallel in an uneven temperature field. The possibility of selecting the optimum supply voltage taking into account the limiting factors for mass-size, energy, dynamic and reliability characteristics of a set of thermoelectric coolers with parallel electric connection is shown. This makes it possible to create thermoelectric systems for providing thermal modes with increased reliability while minimizing mass and dimensional characteristics.

BAYESIAN NETWORKS FOR RELIABILITY ANALYSIS OF TECHNICAL SYSTEM

The works to provide reliability assurance and enhancement are most effective at the early stages of life cycle. The common requirement is fast and precise performance of reiterated reliability analysis, as far as the system design development and the complete data accumulation on system components reliability. Recently, Bayesian networks has been introduced in reliability engineering. Bayesian networks are a promising tool for reliability analysis. Today, Bayesian networks are actively used to fault diagnosis and reliability estimates. In this article, utilization of the Bayesian networks for reliability analysis at the early stages of life cycle is studied. The reliability can be calculated by converting block diagrams or fault trees into Bayesian networks. Fault trees can easily be converted into Bayesian networks. Therefore, in this article, a perspective approach to combine the Bayesian networks mechanism and Fault tree analysis method is studied for reliability assessment of a technical system. The system is an electronic fire sensor. As a result, the developed model of Bayesian networks provides the estimation of failure probability at the conditions of real-life scenarios of system behavior; the calculation of the probability of no-failure operation of the system under control and its sub-systems; the detection of the elements that contribute the most to the failure probability. The Bayesian networks model can be easily built from the circuit diagram analysis and the FMEA (Failure Modes and Effects Analysis). In general, this method has the best capability in this real instance compared to other methods.

DEVELOPMENT OF METHODS OF RELIABILITY ASSESSMENT FOR TURRET BALL BEARING RING OF A BMP-2 INFANTRY FIGHTING VEHICLE

A large part of BMP-2 Infantry Fighting Vehicles needs to replace turret ball bearing rings. Under realization of replacement of spare parts and components made in Russia with domestic ones, KNVO "Fort" MVO Ministry of Internal Affairs of Ukraine made an experimental batch of balls for turret ball bearing rings of infantry fighting vehicles BMP type. As a result of modernization of a turret ball bearing ring, steel balls were replaced with balls made of composite material.
 A turret ball bearing is a large radial thrust bearing, cages of which are turret races. A stabile lower race is fixed by means of screws to a top of the vehicle‟s hull. Above the fixed race there is a movable upper race to which the turret is bolted.
 A method for assessing the reliability of turret ball bearing rings of military armored vehicles was developed. The results of tests of turret ball bearing rings of BMP-2 infantry fighting vehicle tower are given. The reliability of turret ball bearing rings of armored vehicles was assessed taking into account the damage to the balls. The main types of damage to the balls: non-compliance of balls average diameter and non-compliance of the spherical shape of the ball to the requirements of operating documentation. The impact of the probability of no-failure operation of the balls on the durability of the ball bearing is determined.
 It is necessary to take into account the presence of damage to the balls when determining the durability of the ball bearing. To validate the adequacy of the method, it is necessary to increase the test time of the ball bearing by conducting tests during its operation.

Theoretical principles of redundancy and patterns of transport and technological complexes’ adaptation to the operating conditions

The paper addresses the issues of improving the performance of the handling and transport complex at a mining enterprise. It presents statistical estimates for the general standard reliability of the transport system, which should correspond to similar indicators of subsystems of equipment, machinery, etc. We studied the operation of a rock mass transportation system used in open-pit mines. The handling and transport complex includes dump trucks of various capacities and a single-bucket elevator. The process of rock mass excavation and transportation depends on weather and climatic conditions. Among the factors that affect the transport system performance, the following can be distinguished: air temperature, snowdrifts, gas accumulation in the pits, and, as a result, reduction of the visibility range, leading to a decrease in the average speed of vehicles. The mathematical models of transportation are based on the well-known methods of forming excavator and truck fleets. To calculate the reliability of the transport system in the pit, it is necessary to have data on the probability of no-failure operation and the mean time between failures for each vehicle. Information about the state of the vehicles was obtained based on the results of statistical analysis. During optimization calculations, the following restrictions and assumptions were accepted: the limit state of a vehicle was determined by the mileage of 250,000 km; the distribution of the fleet vehicles’ mileage was subject to the Weibull law with the variation factor approximately equal to 1. In this case, the distribution of the mean time between failures can be considered exponential. Analysis of statistical data on the operational reliability of vehicles showed that random failures prevail. When simulating the operation of handling and transport complexes, it is necessary to take into account the parametric and technological connection between individual machines operating within these systems. The developed methodology for justification of the level of equipment adaptation to the operating conditions is aimed at improving the reliability of handling and transport complexes involved in mining production.

Optimization of Systems Repair Plans and Assessment of the Useful Life of Nuclear Power Plant Equipment

This paper presents a computer-aided method of planning the volumes of repairs of systems of nuclear power units and a method for calculating their gamma-percentile life. This planning is carried out on the basis of predicting the reliability indicator, the probability of no-failure operation for a certain time period, with the gamma-percentile life of the equipment being determined by solving the corresponding equations. The tasks considered are related to an important energy problem of extending the operation of nuclear power units. Its importance is determined mainly by economic feasibility: it is cheaper to assess the useful life of a nuclear power unit and, on this research basis, extend its operation, than create a new unit. It is also shown that the calculation of the probability of a radiation accident at a nuclear power unit is associated with the results of planning the repairs of its systems, with assessment of its useful life. An optimization problem is formulated: it is required to find such a plan for the volumes of repair of a system that, with limited repair costs, its reliability indicator for a given duration deviates least from the maximum permissible value. The solution to the problem is based on calculating the structural reliability of the system. A graphological image of the system is built in the form of a composition of graphological images of typical structures. After the reliability indicator of typical structures has been calculated, the structures are replaced with individual structural elements, which makes it possible to simplify the initial graphological image of the system in a computational scenario and calculate its reliability indicator. The determination of the repair volume is carried out by applying a version of the coordinate-wise optimization method. To assess the gamma-percentile life, a model is adopted, in which the recoverable equipment components have an unlimited life, although, of course, they "age", and the non-recoverable components spend their life up to the level when their replacement becomes conditioned by the violation of the requirement for the maximum permissible value of the system reliability indicator. Estimates of the gamma-percentile life of the equipment are calculated by planning system repairs on a sequence of intervals of annual energy production by a nuclear power unit.

MARKOV MODEL OF WIRELESS SENSOR NETWORK AVAILABILITY

The use of wireless sensor networks (WSN) in industry and for forest fire detection has recently become increasingly popular. Assessment of the availability of such networks is an important task, since they perform essential functions in critical situations. Sensor networks can be used to prevent and detect forest fires, and they must meet high availability requirements. Various options for organizing the WSN system are considered - with and without recovery. For such systems, the paper evaluates the probability of no-failure operation, as well as the readiness function, taking into account the network coverage ratio. In the paper the Markov WSN model for evaluating its availability function is developed taking into account the network coverage area. The obtained graphical dependencies allow us to evaluate how a change in the failure rate of sensors or system equipment affects the availability function value. The goal of this paper is to obtain metrics to assess the availability of system for monitoring forest by WSN and the availability function of a network using the Markov models. A special metric, so-called coverage availability factor is suggested in this paper taking into account different combinations of sensor failures which influence on completeness of monitoring forest fires.

ОЦЕНКА НАДЕЖНОСТИ ЭНЕРГЕТИЧЕСКОГО ОБОРУДОВАНИЯ НА РАННИХ СТАДИЯХ ПРОЕКТИРОВАНИЯ

The minimization of the manufacturing and further maintenance cost of power equipment dictated by economic requirements leads to decreasing in metal consumption, growing in the stress of its assemblies, increasing in the design lifetime and overhaul periods, and decreasing in the amount of metal condition monitoring. At the same time, the design requirements for the reliability parameters are constantly advance due to the growing required level of industrial safety. The issue of ensuring the reliability parameters is acute already at the early stages of design when the final decisions about construction, material performance, operating modes, manufacturing, and repair technologies have not yet been made. The proposed calculation approach takes into account the individual characteristics of the developed power equipment and makes it possible to assess its reliability already in the early stages of design. It uses the correlation between the probability of no-failure operation and safety factors. So, it allows us to significantly reduces design time and cost.

PROBABILITY OF NO-FAILURE OPERATION OF THE SURFACE PART OF OIL-CONTAINING REINFORCED CONCRETE MARINE STATIONARY PLATFORMS OF GRAVITATIONAL TYPE

The development of offshore hydrocarbon deposits in Russia contributes to the introduction of new types of stationary offshore gravity-type platforms. The construction of these facilities should be technically and economically feasible, while ensuring the required reliability and durability. One of the reliability criteria is a guaranteed forecast of the life cycle of the platforms, which may cause the platform to stop working prematurely for repair and restoration work. Therefore, the search for optimal methods of life cycle assessing is an urgent task. An assessment of the impact of operating environments on reinforced concrete platforms showed that chloride ions and carbon dioxide in the zone of variable moistening of the trunk part of the caisson have the greatest impact. The article provides an analysis of foreign regulatory and technical documents in the field of ensuring the durability of concrete and reinforced concrete in comparison with the domestic standard. The latter showed significant lags in requirements for primary protection measures, namely in ensuring the density of concrete, cement consumption, etc. The results of the analysis of the life cycle of reinforced concrete when exposed to carbon dioxide taking into account the «Duracrete» model for the surface part of the «Berkut», «Astokhskaya-B» and «Pelytun-Lunskaya-A». The parameters of the life cycle of the platform were determined, i.e. the reliability index and the risk probability, which showed that with a protective layer thickness of 50 mm, a complete loss of reliability will occur in 100 years, the intersection of the reliability index curves and the probability of risk will occur in the period of 30 - 40 years. In order to clarify the beginning of the first repair work, the authors proposed an additional definition of the «probability of no-failure operation» of the offshore platform. Calculations have shown that this period may occur 25 years after the start of operation.

Predicting the No-Failure Microcontroller Operation Probability in a Geostationary Orbit

The results of radiation tests of microcontrollers of the ATmega-128 type in a wide range of dose rates and temperatures have been used to estimate the probability of no-failure operation of microcontrollers in real operating conditions. The Eyring function has been used to take into account the temperature effect.

THE ASSESSMENT OF THE RELIABILITY OF ELECTRONIC COMPONENTS OF FOREIGN PRODUCTION ON THE RESULTS OF TESTS OF SMALL SAMPLES

Within the framework of this article the question of reliability evaluation of electronic component base of foreign production, used as a part of electronic equipment of spacecrafts is considered. The reliability of electronic equipment of spacecrafts directly depends on the reliability of the electronic component base used as a component of it. This electronic component base should provide strict requirements for the active shelf life of the spacecrafts. To date, the requirements for gamma-percentile time to failure of electronic components used as a part of electronic equipment of spacecrafts, reaching 150,000 hours under standard value of у = 95%. Confirmation of such requirements is possible only in case of testing large samples for a long time, which entails considerable economic costs. This inevitably leads to the need to use and develop new ideas and methods of the theory of reliability. In this article, to confirm the reliability requirements for the electronic component base, it is proposed to generalize the estimated score and the data obtained from the results of accelerated tests for reliability, on the basis of the Bayesian theorem. In the result of the investigation was determined by the values of the failure rate of electronic components, as well as the possibility of increasing the value of probability of no failure operation у to a value of 99%, while maintaining the requirements of the gamma-percentile time to failure of electronic components base used as a part of electronic equipment of spacecrafts.

Mathema' cal model of varia' on of output opera' onal characteris' cs of steam turbines of thermal power plants

In this article we have studied the statistic materials for failures and malfunctions that aff ect the performance of heat power installations. This is a qualitative analysis and quantitative assessment of indicators of reliability of different turbine types. In the paper, there is presented a mathematical model of variation for output characteristics of a turbine depending on the number of failures observed in the course of operation. The mathematical model is based on methods of mathematical statistics, the probability theory and methods of matrix calculus. The novelty of this model lies in the fact that it allows predicting variation of control parameters and the output characteristic in an explicit form. The parameters that can be assumed as such characteristics are: average load, heat generation and electric power generation, running time, amount of time spent on emergency repair, number of staff participating in repair, cost of repair, income from sales of thermal and electric energy, availability quotient, probability of no-failure operation, etc. Based on the statistical data obtained at operation of steam turbines, quality and quantitative assessments of reliability indicators has been presented. Specific measures are suggested for elimination of causes of failures of components of turbines and turbine equipment. These are the failures of turbine blades caused by exhaustion of service life and extreme fatigue of metal that are accounted for the largest number of cases of damage and failure of turbines. Statistics of failures of bearings are affected by both internal and external factors of technical and operational nature. Damage of bearings and parts of rotors most often leads to unscheduled shutdown and repair of the turbine. The most common failures are those of the main oil pump and oil pipelines. According to statistical data, it is possible to develop appropriate measures for improvement of output characteristics. This is a so-called a model of management of output characteristic. For the purpose of management of the output characteristic, a probabilistic model taking into account the operating influences in an explicit form has been offered. A specific example of variation of turbines' output characteristics over a long-term period of operation has been given.

ESTIMATION OF QUALITY PARAMETERS IN THE RADIO FLIGHT SUPPORT OPERATIONAL SYSTEM

The paper considers the structure of the operational system of radio equipment, determines the procedures related to the estimation of the quality parameters in the radio flight support operational system, using the ready-to-operate factor and the probability of no failure operation in a finite time interval, and shows the analytical ratios for the probability density function (PDF).

Reliability of the Steering Gear of Truck Vehicles

Findings concerning wear process of steering gear joints of the truck vehicles are provided. Characteristics of probability of no-failure operation as a function of wear rate of steering joints and pivot connections are determined.

Evaluation of member reliability in chemical and petroleum machinery based on failure mechanics

Currently a large number of items are manufactured by welding sheets or casting iron, other metals, and alloys. This inevitably leads to crack defects of rather large size [ I ]. Tolerable sizes, numbers, and locations for defects are noted in standardized technical manuals. Let us determine a member's probability of no-failure operation; this is a basic reliability factor. Let us examine the case of failure under static loading in the presence of crack defects. It is recommended that a critical loading-intensity coefficient (fracture toughness) determined experimentally [2] be adopted as an indicator of material resistance to quasibrittle failure under a one-time loading. The probability of no-failure operation is P = P (A'~-K l ~ 0) , where KIc is the fracture toughness and K i is the loading-intensity coefficient. For known distribution densities of fracture toughness, fl(Kic), and loading-intensity coefficient, f2(Kl)