Papers by Vladimir Ulansky
Determination of the optimal maintenance threshold and periodicity of condition monitoring
This study focuses on modelling the condition-based maintenance (CBM) for the safety-critical sys... more This study focuses on modelling the condition-based maintenance (CBM) for the safety-critical systems. For such systems, the criterion of the maintenance effectiveness is to ensure the specified level of the operational reliability at the minimal maintenance costs. A mathematical model of operational reliability and average maintenance costs for the system under imperfect inspections is developed. The system operation and maintenance are modelled on a finite time interval. For the first time, the problem of the joint optimization of the replacement thresholds and intervals between condition monitoring is mathematically formulated for the safety-critical systems. The proposed CBM model can be used for both sequential and periodic inspection policies. Numerical examples illustrate the features of the proposed approach to mathematical modelling of CBM.
Aerospace, Jan 17, 2024
This article is an open access article distributed under the terms and conditions of the Creative... more This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY
Aerospace
Maintenance is an essential part of long-term overall equipment effectiveness. Therefore, it is e... more Maintenance is an essential part of long-term overall equipment effectiveness. Therefore, it is essential to evaluate maintenance policies’ effectiveness in addition to planning them. This study provides a classification of technical systems for selecting maintenance effectiveness indicators and a classification of maintenance models for calculating these indicators. We classified the systems according to signs, such as system maintainability, failure consequences, economic assessment of the failure consequences, and temporary mode of system use. The classification of systems makes it possible to identify 13 subgroups of systems with different indicators of maintenance effectiveness, such as achieved availability, inherent availability, and average maintenance costs per unit of time. When classifying maintenance models, we used signs such as the system structure in terms of reliability, type of inspection, degree of unit restoration, and external manifestations of failure. We identi...
Aerospace
The operable state of a system is maintained during operation, which requires knowledge of the sy... more The operable state of a system is maintained during operation, which requires knowledge of the system’s state. Technical diagnostics, as a process of accurately obtaining information about the system state, becomes a crucial stage in the life cycle of any system. The study deals with the relevant problem of uncertainty quantification of imperfect diagnostics. We considered the most general case when the object of diagnostics, the diagnostic tool, and the human operator can each be in one of the many states. The concept of a diagnostic error is introduced, in which the object of diagnostics is in one of many states but is erroneously identified as being in any other state. We derived the generalized formulas for the probability of a diagnostic error, the probability of correct diagnosis, and the total probability of a diagnostic error. The proposed generalized formulas make it possible to determine the probabilistic indicators of diagnosis uncertainty for any structures of diagnostic...
Applied Sciences, 2021
Negative differential resistance (NDR) is inherent in many electronic devices, in which, over a s... more Negative differential resistance (NDR) is inherent in many electronic devices, in which, over a specific voltage range, the current decreases with increasing voltage. Semiconductor structures with NDR have several unique properties that stimulate the search for technological and circuitry solutions in developing new semiconductor devices and circuits experiencing NDR features. This study considers two-terminal NDR electronic circuits based on multiple-output current mirrors, such as cascode, Wilson, and improved Wilson, combined with a field-effect transistor. The undoubted advantages of the proposed electronic circuits are the linearity of the current-voltage characteristics in the NDR region and the ability to regulate the value of negative resistance by changing the number of mirrored current sources. We derive equations for each proposed circuit to calculate the NDR region’s total current and differential resistance. We consider applications of NDR circuits for designing microwa...
Generalization of minimax and maximin criteria in a game against nature for the case of a partial a priori uncertainty
Heliyon, 2021
This study proposes a new criterion for choosing the optimal decision in a game against nature un... more This study proposes a new criterion for choosing the optimal decision in a game against nature under a partial a priori uncertainty. The paper's main novelty consists in examining the situation when a part of the a priori probabilities of states of nature is known, and the other part is unknown. We prove the theorems for choosing the optimal decision as for the payoff and risk matrix, as well as for the profit matrix in the situation of a partial a priori uncertainty. The proposed approach also generalizes the Bayes, Wald, Savage, Hurwicz, and Laplace criteria since the minimum average payoff (or risk) for each of these criteria we can quickly obtain from the article's derived formulas. A practical example of a game against nature under a partial a priori uncertainty illustrates the proposed approach and shows its effectiveness compared to well-known criteria. We show that the introduced criterion provides the choice of a decision that is also optimal in conditions of risk, which indicates the effective use of the vector of known a priori probabilities.
Electronics, 2020
This paper proposes a novel operational amplifier (OPA) voltage-controlled oscillator (VCO) circu... more This paper proposes a novel operational amplifier (OPA) voltage-controlled oscillator (VCO) circuits on the basis of impedance converters. The VCO can operate over a frequency range exceeding unity-gain bandwidth due to the location of the tank circuit, not at the output of the OPA, but at the noninverting input. The paper presents the mathematical modeling of oscillated amplitude and start-up conditions. The simulation results confirm the theoretical achievements. The designed and simulated VCO uses an ultra-low noise wideband OPA LMH6629MF, covers a frequency band between 0.830 GHz and 1.429 GHz, and exhibits a maximum in-band total harmonic distortion (THD) of 1.7%. It has a maximum in-band phase noise of −139.3 dBc/Hz at 100 kHz offset frequency and has an outstanding value of a standard figure of merit (FoM) of −198.6 dBc/Hz. The zero-peak amplitude of output voltage is from 3.2 V to 4 V for all generated frequencies at a supply voltage of ±5 V. The fabricated prototype-oscilla...
Entropy, 2019
Condition-based maintenance (CBM) is a promising technique for a wide variety of deteriorating sy... more Condition-based maintenance (CBM) is a promising technique for a wide variety of deteriorating systems. Condition-based maintenance’s effectiveness largely depends on the quality of condition monitoring. The majority of CBM mathematical models consider perfect inspections, in which the system condition is assumed to be determined error-free. This article presents a mathematical model of CBM with imperfect condition monitoring conducted at discrete times. Mathematical expressions were derived for evaluating the probabilities of correct and incorrect decisions when monitoring the system condition at a scheduled time. Further, these probabilities were incorporated into the equation of the Shannon entropy. The problem of determining the optimal preventive maintenance threshold at each inspection time by the criterion of the minimum of Shannon entropy was formulated. For the first time, the article showed that Shannon’s entropy is a convex function of the preventive maintenance threshold...
Energies, 2019
Among the different maintenance techniques applied to wind turbine (WT) components, online condit... more Among the different maintenance techniques applied to wind turbine (WT) components, online condition monitoring is probably the most promising technique. The maintenance models based on online condition monitoring have been examined in many studies. However, no study has considered preventive maintenance models with incorporated probabilities of correct and incorrect decisions made during continuous condition monitoring. This article presents a mathematical model of preventive maintenance, with imperfect continuous condition monitoring of the WT components. For the first time, the article introduces generalized expressions for calculating the interval probabilities of false positive, true positive, false negative, and true negative when continuously monitoring the condition of a WT component. Mathematical equations that allow for calculating the expected cost of maintenance per unit of time and the average lifetime maintenance cost are derived for an arbitrary distribution of time t...
Electronics, 2019
Electronic devices and circuits with negative differential resistance (NDR) are widely used in os... more Electronic devices and circuits with negative differential resistance (NDR) are widely used in oscillators, memory devices, frequency multipliers, mixers, etc. Such devices and circuits usually have an N-, S-, or Λ-type current-voltage characteristics. In the known NDR devices and circuits, it is practically impossible to increase the negative resistance without changing the type or the dimensions of transistors. Moreover, some of them have three terminals assuming two power supplies. In this paper, a new NDR circuit that comprises a combination of a field effect transistor (FET) and a simple bipolar junction transistor (BJT) current mirror (CM) with multiple outputs is proposed. A distinctive feature of the proposed circuit is the ability to change the magnitude of the NDR by increasing the number of outputs in the CM. Mathematical expressions are derived to calculate the threshold currents and voltages of the N-type current-voltage characteristics for various types of FET. The cal...
Procedia Manufacturing, 2018
Under the concept of "Industry 4.0", production processes will be pushed to be increasingly inter... more Under the concept of "Industry 4.0", production processes will be pushed to be increasingly interconnected, information based on a real time basis and, necessarily, much more efficient. In this context, capacity optimization goes beyond the traditional aim of capacity maximization, contributing also for organization's profitability and value. Indeed, lean management and continuous improvement approaches suggest capacity optimization instead of maximization. The study of capacity optimization and costing models is an important research topic that deserves contributions from both the practical and theoretical perspectives. This paper presents and discusses a mathematical model for capacity management based on different costing models (ABC and TDABC). A generic model has been developed and it was used to analyze idle capacity and to design strategies towards the maximization of organization's value. The trade-off capacity maximization vs operational efficiency is highlighted and it is shown that capacity optimization might hide operational inefficiency.
Procedia CIRP, 2017
Predictive maintenance includes condition monitoring and prognosis of future system condition whe... more Predictive maintenance includes condition monitoring and prognosis of future system condition where maintenance decision-making is based on the results of prediction. In this paper, the modelling of predictive maintenance is conducted. It is assumed that the system is periodically checked by using imperfect measuring equipment. The decision rule for the predictive checking is formulated and the probabilities of correct and incorrect decisions are derived. The effectiveness of the predictive maintenance is evaluated by the average availability and downtime cost per unit time. The mathematical models are proposed to calculate the maintenance indicators for an arbitrary distribution of time to failure. The proposed approach is illustrated by determining the optimal number of predictive checks for a specific stochastic deterioration process. Numerical example illustrates the advantage of the predictive maintenance compared to the corrective maintenance.
Assessing the impact of intermittent failures on the cost of digital avionics' maintenance
2016 IEEE Aerospace Conference, 2016
Modern aviation data suggest that there are more than 400,000 no fault found (NFF) cases per year... more Modern aviation data suggest that there are more than 400,000 no fault found (NFF) cases per year, where a false alarm is given and no fault is detected after investigation. The NFF cost was estimated to be over $2Bn per year in 2013. The existence of the NFF phenomenon has a negative impact upon avionics systems safety, availability and life cycle cost. Therefore, it is important to reduce the negative impact of NFF events. Intermittent failures are the leading causes of NFF events in avionics systems. In this study, we consider a line replaceable unit (LRU) subject to permanent and intermittent failures with an arbitrary law of failure time distribution. We assume that LRU is continuously tested and both types of failures are automatically detected by the built-in test equipment (BITE). When the LRU is rejected, the replacement is carried out. Dismantled LRUs are directed to repair facilities for re-testing, and if necessary, repairing. A mathematical model is developed to determine the LRU availability and the mean time between unscheduled removals (MTBUR). Different variants of avionics maintenance management are considered for warranty and post-warranty period. MTBUR, total expected cost (TEC), and availability of redundant systems are determined for each variant of warranty and post-warranty avionics maintenance management. Numerical examples demonstrate the efficiency of each variant of avionics maintenance management. It is shown that excellent economic efficiency has the variant of post-warranty maintenance with automatic test equipment (ATE) and intermittent fault detector (IFD).
Procedia CIRP, 2015
Continuous growth in modern avionics systems complexity allows the extension of the functionality... more Continuous growth in modern avionics systems complexity allows the extension of the functionality of flight control and navigation systems and leads to an increase in operating expenses. Currently, avionics maintenance costs approximately 30% of the total aircraft maintenance costs. Great impact on the avionics maintenance cost has high rate of intermittent failures, which has been estimated as approximately 50% in military avionics. Here, a mathematical reliability model of continuously tested LRU subject to permanent and intermittent failures is developed. Mathematical expressions for availability of redundant systems are derived considering the spare part system sufficiency. A detailed analysis of the three different variants of the breakdown maintenance strategy (BMS) of modern avionics systems is presented. A criterion of optimizing the number of spare parts is proposed. Some considerations for choosing the optimum variant of the BMS are outlined.
Applied Sciences
Modern avionics can account for around 30% of the total cost of the aircraft. Therefore, it is es... more Modern avionics can account for around 30% of the total cost of the aircraft. Therefore, it is essential to reduce the operational cost of avionics during a lifetime. This article addresses the critical scientific problem of creating the appropriate maintenance models for digital avionics systems that significantly increase their operational effectiveness. In this research, we propose the lifecycle cost equations to select the best option for the maintenance of digital avionics. The proposed cost equations consider permanent failures, intermittent faults, and false-positives occurred during the flight. The lifecycle cost equations are determined for the warranty and the post-warranty interval of aircraft operation. We model several maintenance options for each period of service. The cost equations consider the characteristics of the permanent failures and intermittent faults, conditional probabilities of in-flight false-positive and true-positive as well as the cost of different mai...
Proceedings of The World Congress on Engineering 2015, pp999-1004, 2015
This study provides analytical modeling of condition monitoring with periodic imperfect inspectio... more This study provides analytical modeling of condition monitoring with periodic imperfect inspections of a stochastically deteriorating system. An inspection consists of checking the system state parameter against the critical threshold level in the upcoming time intervals. A new decision rule is proposed for inspecting the system condition, which is based on the comparison of the time of inspection with the estimated remainder of the time to failure. Based on this decision rule, general expressions are derived for calculating the probabilities of correct and incorrect decisions. The proposed approach is illustrated by deriving the probabilities of correct and incorrect decisions for a linear stochastic deterioration process model. Based on the derived expressions, the Bayes risk and minimum total error probability criteria are specified to determine the optimal threshold. A numerical example is given to illustrate the proposed approach for determining the optimal threshold when checking system suitability. Index Terms-Decision rule, functional failure level, imperfect inspection, measurement error of time to failure, threshold
Uploads
Papers by Vladimir Ulansky