Dr. Eng. Ahmed Raza

National Aviation University (Ukraine), Department of Electronics, Robotics, Monitoring and IoT Technologies, Post-Doc

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Dr. Eng. Ahmed Raza (د.م أحمد رضا), is a prominent Pakistani / Seychellois a professional Engineer who is currently, working as Technical Advisor at Federal Govt Entity - Abu Dhabi -UAE. His work in the field of Maintenance Management (Predictive, CBM & SOPs Governance has resulted in more than 50 publications, and presentations at well known internationally recognized journals and magazines

A - Total Professional Experience:
Over 28+ years of cumulative professional experience in:
• Engineering, infrastructure planning, and project delivery
• Strategic advisory roles within government and semi-government entities
• Technical governance, procurement, and contract management
• Multi-country and cross-border development projects
Construction value of the completed projects (without Land cost), amounting to US $ +15 Billion

B - Academic & Technical Background:
• Doctorate-level engineering background with strong research orientation, (field of Engineering Sciences 2018 from National Aviation University, Kyiv – Ukraine).
• Advanced technical expertise in:
o Infrastructure systems engineering
o Predictive maintenance and reliability engineering
o Strategic planning and feasibility assessment
o Digitization & AI implementation in the field of Maintenance Management & SOPs Governance
• Multilingual professional working capability (English, Arabic, Russian, Urdu, Punjabi)

C - Fields of interest
• Academic Research: Predictive Maintenance, AI Integration Frame Works with Various type of Maintenance types, Mathematical modelling of Remaining Useful life based on Predictive Analysis
• Digitization, Innovation & Smart Governance
• Urban development, Infrastructure & Built Environment
• Strategic Planning & Feasibility Studies

Dr. Eng. Ahmed Raza’s experience, strategic mindset, and multidisciplinary expertise are directly aligned with Country's’ priorities in the Sustainable Economy, digitization, and infrastructure development, Implementation of AI in the field of Technical, Administrative Management & SOPs in Governance.
Phone: +971508117725

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Papers by Dr. Eng. Ahmed Raza

Modelling of Predictive Maintenance for a Periodically Inspected System

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.

format_quoteDevelops a new predictive maintenance model incorporating decision rules based on remaining time to failure, improving predictive check efficacy.format_quote

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Generalized cost functions of avionics breakdown maintenance strategy

2017 IEEE Aerospace conference, 4-11 March, 2017, Big Sky, Montana, USA. – Conference proceedings, 2017

In this study, the generalized cost functions are proposed for choosing the optimal option of bre... more In this study, the generalized cost functions are proposed for choosing the optimal option of breakdown maintenance strategy of avionics systems. A mathematical model of avionics line replaceable unit (LRU) is developed. The model considers the main characteristics of the preflight checks and continuous testing of the LRU using built-in test equipment (BITE) in-flight. The equation for the mean time between unscheduled removals (MTBUR) is derived for an arbitrary and exponential distribution of time to failure. The cost functions are determined as the total operating costs separately for the warranty and post warranty period of operation. Different options of single-level, two-level and three-level maintenance are mathematically modeled and numerically analyzed for the warranty and post-warranty period of operation. The proposed analytical expressions take into account the trustworthiness of BITE, periodicity of preflight testing, cost of different maintenance operations, permanent and intermittent failure rate of LRUs and some other parameters. Numerical examples are included to illustrate the main features of the proposed mathematical models

Determination of the optimal maintenance threshold and periodicity of condition monitoring

by Dr. Eng. Ahmed Raza and Vladimir Ulansky

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.

Modelling of predictive maintenance for a periodically inspected system

Procedia CIRP Volume 59, 2017, Pages 95-101, Mar 2, 2017

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Modelling of Condition Monitoring with Imperfect Inspections

Proceedings of the 19th World conf. on nondestructive testing 2016, WCNDT 2016, 13-17 June, 2016, Munich, Germany, Jun 16, 2016

The analytical modelling of a condition monitoring for a system which is subject to degradation o... more The analytical modelling of a condition monitoring for a system which is subject to degradation over time is considered. The system condition can be observed at discrete times by means of imperfect inspections. In addition to the critical threshold, for each time point of inspection a replacement threshold is introduced. The decision rule when checking system suitability for use in the upcoming time interval is analysed. The analytical equations for the probabilities of correct and incorrect decisions when checking system suitability are derived. The system operation process is analysed in an infinite time interval. Expressions are derived for determining a posteriori operational reliability indicators. A specific deterioration process is used to illustrate the proposed general expressions for the probabilities of correct and incorrect decisions and a posteriori operational reliability. Numerical examples illustrate the efficiency of the proposed approach.

format_quoteThis paper generalizes condition monitoring for systems with imperfect inspections, incorporating measurement errors into decision-making.format_quote

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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)

Modelling of operational reliability and maintenance cost for avionics systems with permanent and intermittent failures

Proc. of the 9thIMA International Conference on Modelling in Industrial Maintenance and Reliability - ISBN: 978-0-905091-31-0 , 2016

Current aviation data suggest that there are more than 400,000 no fault found (NFF) cases per yea... more Current aviation data suggest that there are more than 400,000 no fault found (NFF) cases per year. The existence of the NFF phenomenon has a negative impact upon avionics systems safety, availability and life cycle cost. Intermittent failures are the leading causes of NFF events in avionics systems. In this study, we examine the process of operation and maintenance of the line replaceable unit (LRU) in the presence of permanent and intermittent failures with an arbitrary distribution of time to failure. It is assumed that the LRU is continuously tested and both types of failures are automatically detected by the built-in test equipment (BITE). A mathematical model is developed to calculate the LRU operational reliability, the probability of the LRU recovery and the cost of maintenance. Different types of avionics systems redundancy are considered. A numerical example illustrates the evaluation of operational reliability and maintenance costs for a modern avionics system.

A Probabilistic model of periodic condition monitoring with imperfect inspections/

by Dr. Eng. Ahmed Raza and Vladimir Ulansky

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

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Optimal Thresholds for Stochastically Deteriorating Systems

engineering and computer science: Proceedings of the World congress on engineering and computer science 2015, WCECS 2015, 21-23 October, 2015, San Francisco, USA., 2015

We consider the analytical modeling of a condition-based monitoring for a system which is subject... more We consider the analytical modeling of a condition-based monitoring for a system which is subject to degradation over time. The system condition is described by a monotonically increasing stochastic process that can be observed at discrete times by means of imperfect inspections. In addition to the critical threshold, for each time point of inspection a replacement threshold is introduced. The decision rule when checking system suitability for use in the upcoming time interval is considered. The expressions for the probabilities of correct and incorrect decisions when checking system suitability are derived with considering the results of previous inspections. A specific deterioration process is used to illustrate the proposed general expressions for the probabilities of correct and incorrect decisions. To determine the optimal threshold at each time of inspection, it is proposed to use criteria such as the maximum a posteriori probability criterion, minimum Bayes risk criterion and minimum total error probability criterion. A numerical example illustrates the efficiency of the proposed approach.

format_quoteA novel model incorporates previous inspection results to optimize the maintenance threshold, enhancing economic efficiency.format_quote

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Modeling of discrete condition monitoring for radar equipment

2014 IEEE Microwaves, Radar and Remote Sensing Symposium, MRRS 2014 - Proceedings 13 November 2014, Article number 6956672, Pages 88-91, 2014

In this paper, the analytical modeling is curried out for condition-based imperfect inspections o... more In this paper, the analytical modeling is curried out for condition-based imperfect inspections of a stochastically and continuously deteriorating single-unit radar system. The system condition is described by a stochastic process with monotonically decreasing realizations. The decision rule used for checking the system suitability in the upcoming time interval is considered. The analytical expressions for the probabilities of correct and incorrect decisions when checking the suitability of a single-unit radar system are derived. A sufficiently general model of a random process with monotonically decreasing realizations is used to illustrate the proposed general expressions of the probabilities of correct and incorrect decisions.

Modelling condition monitoring inspection intervals

CRC Press, Taylor & Francis Group, 2015., 2015

This paper reports on the modelling of condition monitoring intervals. The proposed model is base... more This paper reports on the modelling of condition monitoring intervals. The proposed model is based on a regenerative stochastic process involving change in states of a single-unit system with imperfect inspections and perfect repair.An inspection consists of checking the system state parameters against the critical threshold levels. The decision rule used for inspecting the system condition is considered, and the probabilities of the correct and incorrect decisions are derived. The system operation process is analyzed in a finite time interval as a sequence of varying states. Expressions are derived for determining the mean times the system stays in various states during operation. The proposed model can be used for both sequential and periodic inspection policies, which allows maximization of system availability or minimization of the expected average cost per unit time.

Optimal policies of condition-based maintenance under multiple imperfect inspections

Transactions on engineering technologies: collective monograph. – Springer, 2016., Jun 24, 2016

This study provides analytical modeling of condition-based maintenance with periodic imperfect in... more This study provides analytical modeling of condition-based maintenance with periodic imperfect inspections for a stochastically deteriorating system. In addition to the critical threshold, for each time point of inspection a replacement threshold is introduced. An inspection consists of checking the system state parameter against the replacement threshold 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 with considering the results of previous inspections. For the first time it is shown that even in case of perfect inspections the probabilities of incorrect decisions are nonzero when checking system suitability. To determine the optimal replacement threshold at each time of inspection, different criteria are proposed to use such as maximum net income, minimum Bayes risk, and minimum total error probability. The proposed approach is illustrated by deriving the probabilities of correct and incorrect decisions for a linear stochastic deterioration process model. A numerical example is given

Cost Model for Assessing Losses to Avionics Suppliers During Warranty Period

Advances in through-life engineering services. Decision Engineering: collective monograph. – Springer, 2017., 2017

Reduction of warranty maintenance costs is a critical issue to the manufacturers of avionic produ... more Reduction of warranty maintenance costs is a critical issue to the manufacturers of avionic products. A method to reduce expected warranty costs is the determination of all components of financial losses to avionic product suppliers during the warranty period with further minimisation of these losses. This study interlinks the warranty, reliability and maintenance indicators of avionic products. Mathematical models are proposed for analysing and assessing financial costs to avionic system suppliers during the warranty period. The developed mathematical models consider the warranty period, reliability indicators with respect to permanent and intermittent failures, redundancy, number of spare parts, cost of restoration and transportation and penalties for exceeding the duration of warranty repair or replacement. Numerical examples illustrating the proposed models are provided.

A mathematical model for digital avionics systems maintenance taking into account intermittent failures - МАТЕМАТИЧЕСКАЯ МОДЕЛЬ ОБСЛУЖИВАНИЯ ЦИФРОВЫХ СИСТЕМ АВИОНИКИ С УЧЕТОМ ПЕРЕМЕЖАЮЩИХСЯ ОТКАЗОВ

ISSN 1028-9763. Математичні машини і системи, 2018, № 1 , 2018

Анотація. У даний час вартість технічного обслуговування авіоніки становить близько 30% від загал... more Анотація. У даний час вартість технічного обслуговування авіоніки становить близько 30% від загальної вартості обслуговування повітряних суден. Великий вплив на вартість обслуговування авіоніки справляє високий рівень переміжних відмов. У статті розроблено математичну модель для розрахунку коефіцієнта готовності і вартості обслуговування безперервно-контрольованих легкознімних блоків систем авіоніки, схильних до постійних і переміжних відмов. Отримано ма-тематичні вирази для коефіцієнта готовності резервованих систем авіоніки, що враховують кі-лькість запасних легкознімних блоків в обмінному фонді авіакомпанії. Досліджено залежність ко-ефіцієнта готовності від інтенсивності постійних і переміжних відмов.
Ключові слова: легкознімний блок, постійна відмова, переміжна відмова, коефіцієнт готовності, коефіцієнт простою, інтенсивність відмов, резервована система.

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Mathematical Model of Corrective Maintenance Based on Operability Checks for Safety Critical Systems

American Journal of Applied Mathematics, 2018

Maintenance based on equipment operability checks is widely used for technical systems of various... more Maintenance based on equipment operability checks is widely used for technical systems of various physical nature. For commercial and military aircraft such checks are carried-out after a certain amount of time according to specific maintenance programs. Therefore, great attention in the research literature is paid to the mathematical modeling of maintenance on the basis of equipment operability checks. In this study, a mathematical model of corrective maintenance with operability checks at discrete times for the safety critical systems is considered. The criterion of the corrective maintenance effectiveness is proposed to provide a given level of operational reliability with minimum maintenance costs. A finite time interval is considered for modeling the moments of the system operability checks. The graph of decision making is analyzed for imperfect operability checks and the probabilities of possible decisions are determined. Analytical equations for the operational reliability and expected maintenance costs are derived for an arbitrary distribution of time to failure. The criteria of determining optimal policies of sequential checks are formulated. Numerical examples illustrate the developed theory. For the first time it has been shown that conditional probabilities of correct and incorrect decisions when checking system operability are dependent on the time of failure and parameters of the degradation model. Numerical calculations have shown that in the case of mixing deteriorating systems with different initial time points of operation, the interval between operability checks converges to a constant periodicity.

$Figure 3. 3D image of the conditional PDF of the random error in the evaluation of the operating time to failure A (6\n) as a function of the arguments 6 and o, for n = 300 h. The probabilities of the correct and incorrect decisions (9)-(12) are very much dependent on the time of failure 1. In Figure 3, the 3D image of the conditional PDF of the error in the evaluation of the operating time to failure as a function of the arguments 6 and o, for n = 300 h is shown. As can be seen from Figure 3, with an increase in the standard deviation of the measurement error of the system state parameter ©,, the conditional PDF A (6|n) is also flattened, which indicates an increase in the variance of the random error in evaluating the operating time to failure, A.$

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Maintenance Model of Digital Avionics

MDPI, 2018

The cost of avionics maintenance is extremely high for modern aircraft. It can be as high as 30% ... more The cost of avionics maintenance is extremely high for modern aircraft. It can be as high as 30% of the aircraft maintenance cost. A great impact on the cost of avionics maintenance is provided by a high level of No Fault Found events (NFF). Intermittent faults are the leading cause of the NFF appearance in avionics. The NFF rate for avionics systems is between 20% and 50%. The practice of avionics operation and maintenance confirms the relevance of assessing the impact of intermittent faults on the maintenance cost and the choice of such option of the maintenance management, in which the negative impact of the intermittent faults is minimized. In this paper, a new mathematical model of digital avionics maintenance is developed. Key maintenance effectiveness indicators are selected. General mathematical expressions are obtained for the average availability, mean time between unscheduled removals (MTBUR), and expected maintenance cost of single unit and redundant avionics systems, which are subject to permanent failures and intermittent faults. The dependence of the maintenance effectiveness indicators on the rate of permanent failures and intermittent faults is investigated for the case of exponential distribution of time to failures and faults. The dependence of average availability on the number of spare units in the airline's warehouse is also analyzed. On the base of the proposed maintenance model, different options of avionics maintenance management are considered. Numerical examples illustrate how to reduce the expected maintenance cost of avionics systems.

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Electronic Circuit with Controllable Negative Differential Resistance and its Applications

MDPI, 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 calculated current and voltage thresholds are compared with the simulation results. The possible applications of the proposed NDR circuit for designing single-frequency oscillators and voltage-controlled oscillators (VCO) are considered. The designed NDR VCO has a very low level of phase noise and has one of the best values of a standard figure of merit (FOM) among recently published VCOs. The effectiveness of the proposed oscillators is confirmed by the simulation results and the implemented prototype.

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Sinusoidal Oscillators Operating at Frequencies Exceeding Unity-Gain Bandwidth of Operational Amplifiers

MDPI, 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-oscillator based on OPA LMH6624 operates at a frequency of 583.1 MHz with a power level of 0 dBm.

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Optimal Preventive Maintenance of Wind Turbine Components with Imperfect Continuous Condition Monitoring

MDPI, 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 to degradation failure. A numerical example of WT blades maintenance illustrates that preventive maintenance with online condition monitoring reduces the average lifetime maintenance cost by 11.8 times, as compared to corrective maintenance, and by at least 4.2 and 2.6 times, compared with predetermined preventive maintenance for low and high crack initiation rates, respectively.

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Optimization of Condition Monitoring Decision Making by the Criterion of Minimum Entropy

MDPI, 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 for each moment of condition monitoring. It was also shown that the probabilities of correct and incorrect decisions depend on the time and parameters of the degradation model. Numerical calculations show that the proposed approach to determining the optimal preventive maintenance threshold can significantly reduce uncertainty when deciding on the condition of the monitoring object.

format_quoteCondition monitoring of a radar transmitter shows that exceeding 25 kV necessitates corrective maintenance, highlighting practical application of CBM model.format_quote