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Publications (8 of 8) Show all publications
Ahmadi, A., Soleimanmeigouni, I., Letot, C. & Block, J. (2017). Inspection Optimization under imperfect maintenance performance. In: Diego Galar, Dammika Seneviratne (Ed.), Proceedings of MPMM 2016: 6th International Conference on Maintenance Performance Measurement and Management, 28 November 2016, Luleå, Sweden. Paper presented at Maintenance Performance and Measurement and Management 2016(MPMM 2016). November 28, Luleå, Sweden (pp. 139). Luleå: Luleå tekniska universitet
Open this publication in new window or tab >>Inspection Optimization under imperfect maintenance performance
2017 (English)In: Proceedings of MPMM 2016: 6th International Conference on Maintenance Performance Measurement and Management, 28 November 2016, Luleå, Sweden / [ed] Diego Galar, Dammika Seneviratne, Luleå: Luleå tekniska universitet , 2017, p. 139-Conference paper, Oral presentation with published abstract (Refereed)
Abstract [en]

Scheduled maintenance and inspection development is one of the main requirements for emergency equipment and safety devices. These types of devices have hidden functions which are used intermittently or infrequently, so their failure will not be evident to the operating crew. The analytical model presented in this paper deals with the periodically tested units with overhauls (preventive maintenance) after certain number of inspections and a renewal after a series of overhauls. The cost based optimization method presented in this paper identifies the optimum interval and frequency of Failure Finding Inspection (FFI) and restoration. In the proposed model, repair due to failures found by inspection makes the unit As Bad As Old, and restoration/overhaul action rejuvenates the unit to any condition between As Good As New and As Bad As Old. As Good As New effectiveness also is considered for renewal action. It considers inspection and repair times, and takes into account the costs associated with inspection, repair, restoration, and also the cost of accidents due to the occurrence of multiple failure. The results show that when the unit is not under aging process, the optimal alternative for each inspection interval is the one with highest possible number of inspection without restoration. Finally, it is observed that when the cost of accident is quite high it is needed to perform inspections at smaller intervals to control the risk of accident.

Place, publisher, year, edition, pages
Luleå: Luleå tekniska universitet, 2017
Series
Trafikverkets forskningsportföljer
National Category
Other Civil Engineering
Research subject
FOI-portföljer, Vidmakthålla
Identifiers
urn:nbn:se:trafikverket:diva-6074 (URN)978-91-7583-841-0 (ISBN)
Conference
Maintenance Performance and Measurement and Management 2016(MPMM 2016). November 28, Luleå, Sweden
Projects
Simulering av spårgeometri
Funder
Swedish Transport Administration, TRV 2016/61672
Available from: 2023-03-17 Created: 2023-03-17 Last updated: 2023-03-17Bibliographically approved
Soleimanmeigouni, I. & Ahmadi, A. (2016). A Survey on Track Geometry Degradation Modelling. In: Uday Kumar; Alireza Ahmadi; Ajit Kumar Verma; Prabhakar Varde (Ed.), Current Trends in Reliability, Availability, Maintainability and Safety: An Industry Perspective. Paper presented at International Conference ICRESH-ARMS 2015 : 01/06/2015 - 04/06/2015 (pp. 3-12). Encyclopedia of Global Archaeology/Springer Verlag
Open this publication in new window or tab >>A Survey on Track Geometry Degradation Modelling
2016 (English)In: Current Trends in Reliability, Availability, Maintainability and Safety: An Industry Perspective / [ed] Uday Kumar; Alireza Ahmadi; Ajit Kumar Verma; Prabhakar Varde, Encyclopedia of Global Archaeology/Springer Verlag , 2016, p. 3-12Conference paper, Published paper (Refereed)
Abstract [en]

Railway transportation is exposed to a higher demand that necessitates the use of trains with higher speed and heavier axle loads. These increase the track geometry degradation rate, which needs a more effective control on geometry degradation. Keeping the track geometry in acceptable levels requires proper inspection and maintenance planning that inevitably entails in-depth knowledge of track geometry degradation. In addition, it is needed to identify the most effective approach for degradation modelling. To do so, it is vital to synthesis published results into a summary of what is known and validated and what is not as a major step. To this end, this paper reviews track degradation models, discusses various degradation measures, and proposes directions for future researches. It is found that combining the mechanistic and statistical approaches can leads to a more accurate prediction of track geometry degradation behaviour.

Place, publisher, year, edition, pages
Encyclopedia of Global Archaeology/Springer Verlag, 2016
Series
Trafikverkets forskningsportföljer
Series
Lecture Notes in Mechanical Engineering, ISSN 2195-4356
National Category
Other Civil Engineering
Research subject
FOI-portföljer, Vidmakthålla
Identifiers
urn:nbn:se:trafikverket:diva-6073 (URN)10.1007/978-3-319-23597-4_1 (DOI)2-s2.0-85006361529 (Scopus ID)0d35d95c-b94f-41cf-923e-ede84f670870 (Local ID)978-3-319-23596-7 (ISBN)978-3-319-23597-4 (ISBN)0d35d95c-b94f-41cf-923e-ede84f670870 (Archive number)0d35d95c-b94f-41cf-923e-ede84f670870 (OAI)
Conference
International Conference ICRESH-ARMS 2015 : 01/06/2015 - 04/06/2015
Projects
Simulering av spårgeometri
Funder
Swedish Transport Administration, TRV 2017/123291
Note

Godkänd; 2016; Bibliografisk uppgift: Containing selected papers from the ICRESH-ARMS 2015 conference in Lulea, Sweden, collected by editors with years of experiences in Reliability and maintenance modeling, risk assessment, and asset management, this work maximizes reader insights into the current trends in Reliability, Availability, Maintainability and Safety (RAMS) and Risk Management. Featuring a comprehensive analysis of the significance of the role of RAMS and Risk Management in the decision making process during the various phases of design, operation, maintenance, asset management and productivity in Industrial domains, these proceedings discuss key issues and challenges in the operation, maintenance and risk management of complex engineering systems and will serve as a valuable resource for those in the field. ; 20151222 (andbra)

Available from: 2016-09-30 Created: 2023-03-17Bibliographically approved
Soleimanmeigouni, I., Ahmadi, A., Letot, C., Nissen, A. & Kumar, U. (2016). Cost-Based Optimization of Track Geometry Inspection. In: : . Paper presented at World Congress of Railway Research : 29/05/2016 - 02/06/2016.
Open this publication in new window or tab >>Cost-Based Optimization of Track Geometry Inspection
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2016 (English)Conference paper, Oral presentation only (Refereed)
Abstract [en]

Track geometry bear huge static and dynamic forces that accelerate degradation process. As a result, railway track should be inspected regularly to detect geometry faults and to plan maintenance actions in advanced. An inspection plan that minimizes track maintenance cost is highly desirable by infrastructure managers. This paper proposes constructing an integrated model to identify the optimum track geometry inspection interval. To this end, it develops a long term prediction model combining degradation, shock event, and tamping recovery models. It applies the Wiener process to model track geometry degradation, simulates shock event times using an exponential distribution, and uses a probabilistic model to model recovery after tamping. With the proposed integrated model and simulation, it is possible to identify the optimum track geometry inspection frequencies that minimize total track maintenance costs.

Series
Trafikverkets forskningsportföljer
National Category
Other Civil Engineering
Research subject
FOI-portföljer, Vidmakthålla
Identifiers
urn:nbn:se:trafikverket:diva-6072 (URN)c55ed309-0501-42a8-805f-d86f7f125a90 (Local ID)c55ed309-0501-42a8-805f-d86f7f125a90 (Archive number)c55ed309-0501-42a8-805f-d86f7f125a90 (OAI)
Conference
World Congress of Railway Research : 29/05/2016 - 02/06/2016
Projects
Simulering av spårgeometri
Funder
Swedish Transport Administration, TRV 2017/123291
Note

Godkänd; 2016; 20160826 (solmei)

Available from: 2023-03-17 Created: 2023-03-17 Last updated: 2023-03-17Bibliographically approved
Mahmood, Y. A., Abrahamsson, L., Ahmadi, A. & Verma, A. K. (2016). Reliability Evaluation of Traction Power Capacity in Converter-fed Railway Systems. IET Generation, Transmission & Distribution
Open this publication in new window or tab >>Reliability Evaluation of Traction Power Capacity in Converter-fed Railway Systems
2016 (English)In: IET Generation, Transmission & Distribution, ISSN 1751-8687, E-ISSN 1751-8695Article in journal (Refereed) Submitted
Abstract [en]

A Traction Power Supply System (TPSS) supplies electricity for train propulsion on electrified railways. In many countries, electrified railways have single-phase low-frequency AC power systems fed by frequency converters (FCs). Outages of power will significantly weaken the TPSS, cause operational problems and ultimately lead to traffic disruption in the form of speed reduction, train delays, or cancellations. The aim of this study is to propose an approach to analyse the reliability of power conversion capacity to discover the reasons for ‘loss of load”. The paper assumes train delays are caused by converter outages, shortages of reserve power capacity for unexpected train loads, or a combination of the two. It considers the availability performance of the converter station and evaluates the reliability of the conversion power capacity. It proposes a power-traffic factor (PTF) to aggregate and quantify train power demands. The PTF can be related to the availability of traction power capacity and will identify areas with risks of power shortages. The study finds the shortage in power leading to train delays in some regions of the system is due to a shortage of reserve power capacity

National Category
Other Civil Engineering
Research subject
FOI-portföljer, Strategiska initiativ
Identifiers
urn:nbn:se:trafikverket:diva-5953 (URN)a295cadd-7a75-4579-b7ae-5c2050fd8743 (Local ID)a295cadd-7a75-4579-b7ae-5c2050fd8743 (Archive number)a295cadd-7a75-4579-b7ae-5c2050fd8743 (OAI)
Projects
JVTC
Funder
Swedish Transport Administration, TRV 2011/58769
Note

Upprättat; 2015; 20150224 (yasahm)

Available from: 2016-09-29 Created: 2023-03-02
Ahmadi, A., Ghodrati, B. & Rantatalo, M. (2013). Optimum Failure Finding Inspection During Extended Operation Life. In: : . Paper presented at International Conference on Recent Advances in Railway Engineering : 30/04/2013 - 01/05/2013.
Open this publication in new window or tab >>Optimum Failure Finding Inspection During Extended Operation Life
2013 (English)Conference paper, Oral presentation only (Refereed)
Abstract [en]

In a complex system such as railway and aviation equipment’s, it may be necessary to employ a combination of Failure Finding Inspection (FFI) and a scheduled discard task, as suggested by Reliability-Centered Maintenance (RCM). This strategy ensures an adequate level of availability of hidden functions, as well as the reduction of the risk of multiple failures to an acceptable level. However, in some situations, operators prefer to extend the discard life of components beyond their recommended life limit, due to the operational restrictions. This necessitates the definition of an optimal Failure Finding Inspection interval for the extended life period. This paper aims to provide a mathematical model for defining optimal FFI interval, during the extended period of the replacement life. A cost function (CF) is developed to identify the cost per unit of time associated with different FFI intervals, for the proposed extended period of life, i.e. postponement period. The proposed method concerns as-bad-as-old (ABAO) inspection and repairs (due to failures found by inspection). It considers inspection and repair times, and takes into account the costs associated with inspection and repair, the opportunity cost of lost production due to maintenance downtime created by inspection and repair actions, and also the cost of accidents due to the occurrence of multiple failure

Series
Trafikverkets forskningsportföljer
Keywords
Cost Function, Failure Finding Inspection, Hidden Failures, Reliability-Centered Maintenance (RCM), Optimal Inspection.
National Category
Other Civil Engineering
Research subject
FOI-portföljer, Äldre portföljer
Identifiers
urn:nbn:se:trafikverket:diva-12436 (URN)12240af1-a693-4437-a5c2-bfb199714c03 (Local ID)12240af1-a693-4437-a5c2-bfb199714c03 (Archive number)12240af1-a693-4437-a5c2-bfb199714c03 (OAI)
Conference
International Conference on Recent Advances in Railway Engineering : 30/04/2013 - 01/05/2013
Projects
JVTC
Funder
Swedish Transport Administration, TRV 2011/58769
Available from: 2023-12-21 Created: 2023-12-21 Last updated: 2023-12-21
Ghodrati, B., Ahmadi, A. & Galar, D. (2013). Reliability analysis of switches and crossings: a case study in Swedish railway. In: : . Paper presented at International Conference on Recent Advances in Railway Engineering : 30/04/2013 - 01/05/2013.
Open this publication in new window or tab >>Reliability analysis of switches and crossings: a case study in Swedish railway
2013 (English)Conference paper, Oral presentation only (Refereed)
Abstract [en]

It is reported that switches and crossings (S&C) are one of the subsystems that cause the most delays on Swedish Railways while accounting for at least 13% of maintenance costs [6]. It is the main reason why we chose to base our study on this subsystem.Intelligent data processing allows understanding the real reliability characteristics of the assets to be maintained. The first objective of this research is to determine the S&C reliability characteristics based on field data collection. Because field failure data are typically strongly censored, an especial statistics software package was developed to process field failure data, as commercial packages have not been found satisfactory in that respect. The resulting software, named RDAT® (Reliability Data Analysis Tool) has been relied upon for this study: it is especially adapted to statistical failure data analysis.In the next step the availability of studied switches and crossings is estimated based on the reliability characteristics founded in the first step.

Series
Trafikverkets forskningsportföljer
Keywords
Banbyggnad, Drift och underhåll, Informationsteknik, Intelligenta transportsystem, ITS, Spårtrafik
National Category
Other Civil Engineering
Research subject
FOI-portföljer, Äldre portföljer
Identifiers
urn:nbn:se:trafikverket:diva-12428 (URN)f1f6a193-608a-493d-94db-e261a346538a (Local ID)f1f6a193-608a-493d-94db-e261a346538a (Archive number)f1f6a193-608a-493d-94db-e261a346538a (OAI)
Conference
International Conference on Recent Advances in Railway Engineering : 30/04/2013 - 01/05/2013
Projects
JVTC
Funder
Swedish Transport Administration, TRV 2011/58769
Available from: 2023-12-21 Created: 2023-12-21 Last updated: 2023-12-21
Mahmood, Y. A., Ahmadi, A., Karim, R., Kumar, U., Verma, A. & Fransson, N. (2012). Comparison of frequency converter outages: a case study on Swedish TPS system. In: : . Paper presented at World Academy of Science, Engineering and Technology Conference : WASET 2012 28/11/2012 - 29/11/2012.
Open this publication in new window or tab >>Comparison of frequency converter outages: a case study on Swedish TPS system
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2012 (English)Conference paper, Oral presentation only (Refereed)
Abstract [en]

The purpose of this paper is to survey the unavailability of the two main types of converters used in the Swedish traction power supply (TPS) system, i.e. the rotary and the static converter. The number of outages and the outage rate has been used to analyze and compare the unavailability of rotary and static converters. The mean cumulative function (MCF) has been used to analyze the number of outages and the unavailability trends, while the forced outage rate (FOR) concept has been used to analyze the outage rates.

The study shows that the outages due to converter failure occur at a constant rate by calendar time at most of the converter stations, while very few stations have an increasing or a decreasing rate. It has also been found that the static converters have a higher number of outages and a higher outage rate by calendar time compared to the rotary converter types.

The results of the study show that combining the number of outages and the forced outage rate gives a better view of the converters’ performance, and provides support for the maintenance decision. In fact, using one of them alone does not reflect reality. Comparing these two indexes is also helpful in identifying the areas where extra resources are needed to improve maintenance planning and where improvements can reduce the outage in the TPS system.

Series
Trafikverkets forskningsportföljer
Keywords
Frequency Converter, Forced Outage Rate, Mean Cumulative Function, Traction Power Supply, Electrified Railway Systems
National Category
Other Civil Engineering
Research subject
FOI-portföljer, Äldre portföljer
Identifiers
urn:nbn:se:trafikverket:diva-12440 (URN)95bf611a-bc4c-4409-9393-1653ca8caa9b (Local ID)95bf611a-bc4c-4409-9393-1653ca8caa9b (Archive number)95bf611a-bc4c-4409-9393-1653ca8caa9b (OAI)
Conference
World Academy of Science, Engineering and Technology Conference : WASET 2012 28/11/2012 - 29/11/2012
Projects
JVTC
Funder
Swedish Transport Administration, TRV 2011/58769
Available from: 2023-12-21 Created: 2023-12-21 Last updated: 2023-12-21
Ahmadi, A., Kumar, U. & Ghodrati, B. (2011). Risk based maintenance decision for periodically tested repairable components subject to hidden failure. In: P V Varde (Ed.), Proceedings of 2nd International Conference on Reliability, Safety and Hazard - ICRESH 2010: Mumbai Dec 15-16, 2010. Paper presented at International Conference on Reliability, Safety and Hazards : 14/12/2010 - 16/12/2010 (pp. 197-204). Piscataway, NJ: IEEE Communications Society
Open this publication in new window or tab >>Risk based maintenance decision for periodically tested repairable components subject to hidden failure
2011 (English)In: Proceedings of 2nd International Conference on Reliability, Safety and Hazard - ICRESH 2010: Mumbai Dec 15-16, 2010 / [ed] P V Varde, Piscataway, NJ: IEEE Communications Society , 2011, p. 197-204Conference paper, Published paper (Refereed)
Abstract [en]

This paper aims to develop a graphical method to facilitate the identification of risk and cost of postponement of restoration for repairable components which are periodically tested and whose failures are hidden, i.e, are detectable by inspection or upon demand. The paper focuses on the items which are under aging, however, the methodology is flexible to implement for any aging pattern.

The paper considers Failure Finding Inspection (FFI) with restoration actions (FFI+Res), for the “safety effect” categories of hidden failures. As-bad-as-old (ABAO) inspection effectiveness and as-good-as-new (AGAN) restoration effectiveness are considered. In case of repair due to findings by inspection, as-bad-as-old repair effectiveness is considered.

The graphical methodology proposed in this paper considers inspection and repair times, as well as the costs associated with accident, inspection, repair, and restoration, and takes into account the opportunity losses due to the maintenance downtime.

The analytical approach is based on the Mean Fractional Dead Time. In the case of an operational limit, when it is not possible to remove the unit for restoration, or one needs to use the unit longer than the expected operating time, the paper introduces an approach to analyzing the possibility of and conditions for providing an extension to the restoration interval that satisfies the risk constraints and the business requirements at the same time.

Place, publisher, year, edition, pages
Piscataway, NJ: IEEE Communications Society, 2011
Series
Trafikverkets forskningsportföljer
Keywords
Constraint optimization, Cost function, Failure Finding Inspection, Hidden failures, Inspection interval, Mean Fractional Dead lime, Multiple failure, Postponement of maintenance, Risk, Safety
National Category
Other Civil Engineering
Research subject
FOI-portföljer, Äldre portföljer
Identifiers
urn:nbn:se:trafikverket:diva-12486 (URN)10.1109/ICRESH.2010.5779546 (DOI)2-s2.0-79959629259 (Scopus ID)964ab7a0-e8e8-11df-8b36-000ea68e967b (Local ID)978-1-4244-8344-0 (ISBN)978-1-4244-8343-3 (ISBN)964ab7a0-e8e8-11df-8b36-000ea68e967b (Archive number)964ab7a0-e8e8-11df-8b36-000ea68e967b (OAI)
Conference
International Conference on Reliability, Safety and Hazards : 14/12/2010 - 16/12/2010
Projects
JVTC
Funder
Swedish Transport Administration, TRV 2011/58769
Available from: 2016-09-30 Created: 2024-01-04
Organisations
Identifiers
ORCID iD: ORCID iD iconorcid.org/0000-0001-7083-4009

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