2 research outputs found
Mathematical maintenance models of vehicles’ equipment
Dissertation for obtaining a scientific degree of Doctor of Philosophy within the
specialty 05.22.20 «Maintenance and repair of vehicles». – National Aviation University,
Kyiv, 2018.The thesis addresses the critical scientific problem of creating the appropriate
maintenance models for digital avionics systems and degrading equipment of vehicles,
which increases the operational effectiveness of such systems significantly.
The thesis research includes the analysis of the current state and models of digital
avionics maintenance. The study describes the necessity for developing the mathematical
maintenance models for redundant digital avionics systems, considering the discontinuous
nature of their operation, continuous nature of in-flight testing, possibility of both permanent
and intermittent failures and organization of several maintenance levels using various
diagnostic tools for detecting both failure types.
Another focus of the thesis is the analysis of modern trends and mathematical models
of condition-based maintenance (CBM) of vehicles’ equipment. The necessity of developing
new CBM mathematical models for degrading equipment of vehicles, considering the
probabilities of correct and incorrect decisions when checking system suitability for use in
the upcoming operation interval, and the possibility of joint determination of the optimum
inspection schedule and replacement thresholds for systems that affect and do not affect
safety have been substantiated.
The scientific novelty of the primary results obtained in the course of the thesis
research is as follows:
1. For the first time, mathematical models to evaluate the operational reliability
indicators of continuously monitored line replaceable units/line replaceable modules
(LRUs/LRMs) and redundant avionics systems over both finite and infinite time interval,
which, unlike known models, consider the characteristics of both permanent and intermittent
2failures, have been developed. These models allow evaluating the impact of intermittent
failures on the availability and mean time between unscheduled removals (MTBUR) of
LRU/LRM.
2. For the first time, generalized expressions to calculate the average maintenance
costs of redundant avionics systems, considering the impact of permanent and intermittent
failures, have been developed for alternative maintenance options that differ by the number
of maintenance levels (one, two or three), which allows choosing the optimal maintenance
option during warranty and post-warranty periods.
3. For the first time, a mathematical model of CBM, based on condition monitoring
at scheduled times has been developed, which, unlike the known models, considers the
probabilities of correct and incorrect decisions made when checking system suitability. This
model allows formulating the criteria of determining the optimal replacement threshold for
each inspection time and substantially reduce the likelihood of system failure in the
forthcoming interval of operation.
4. For the first time, generalized mathematical expressions to calculate the
effectiveness indicators of CBM over a finite time interval, as well as the criteria of joint
optimization of the inspection schedule and replacement thresholds for systems that affect
or do not affect the safety, have been developed. These results allow significantly improve
the availability, reduce average maintenance costs and reduce the number of inspections.
The practical value of the results obtained in the thesis is as follows:
1. The techniques to calculate probabilistic and time-related indicators of
maintenance effectiveness for digital avionics LRUs/LRMs over finite and infinite operating
intervals have been developed. The proposed procedures allow to estimate the availability,
operational reliability function (ORF), and mean time between unscheduled removals
(MTBUR) of LRUs/LRMs during warranty and post-warranty maintenance periods for both
federated avionics (FA) and integrated modular avionics (IMA) architectures;
2. A technique for minimizing the warranty maintenance cost of the redundant digital
avionics systems has been developed, demonstrating (through the example of the ADIRS
system of the Airbus A380 aircraft) that in the case of the optimal option of warranty
maintenance, the average maintenance cost per aircraft decreases by 28 %;
33. A technique for minimizing the post-warranty maintenance cost of the redundant
digital avionics systems has been developed. It demonstrates (through the example of the
ADIRS system of the Airbus A380 aircraft) that a three-level maintenance option with an
intermittent fault detector (IFD) at I and D levels, is optimal as it reduces the total expected
maintenance costs by 11 times compared to a one-level option, and by over 8.5 times
compared to a two-level option without IFD;
4. A technique for determining the optimal replacement thresholds when monitoring
the condition of the degrading system at scheduled times has been developed, which allows
to significantly reduce the system failure probability in the forthcoming interval of
operation.
5. A technique for joint determination of the optimal replacement threshold and
periodicity of suitability checking when monitoring the system condition has been
developed, which allows to substantially increase the availability of systems while
significantly reducing the number of inspections.
The results of the thesis research may be used in the development and maintenance of
FA and IMA systems, as well as degrading equipment of vehicles
Safety and Reliability - Safe Societies in a Changing World
The contributions cover a wide range of methodologies and application areas for safety and reliability that contribute to safe societies in a changing world. These methodologies and applications include: - foundations of risk and reliability assessment and management
- mathematical methods in reliability and safety
- risk assessment
- risk management
- system reliability
- uncertainty analysis
- digitalization and big data
- prognostics and system health management
- occupational safety
- accident and incident modeling
- maintenance modeling and applications
- simulation for safety and reliability analysis
- dynamic risk and barrier management
- organizational factors and safety culture
- human factors and human reliability
- resilience engineering
- structural reliability
- natural hazards
- security
- economic analysis in risk managemen