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  • 1.
    Soleimanmeigouni, Iman
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Operation, Maintenance and Acoustics.
    Ahmadi, Alireza
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Operation, Maintenance and Acoustics.
    Arasteh Khouy, Iman
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Operation, Maintenance and Acoustics.
    Letot, Christophe
    Machine Design and Production Engineering Lab, Research Institute for the Science and Management of Risks, University of Mons,.
    Evaluation of the effect of tamping on the track geometry condition: a case study2018In: Proceedings of the Institution of mechanical engineers. Part F, journal of rail and rapid transit, ISSN 0954-4097, E-ISSN 2041-3017, Vol. 232, no 2, p. 408-420Article in journal (Refereed)
    Abstract [en]

    Tamping is one of the major activities applied by railway maintenance managers to recover track geometry condition. Modelling the tamping effectiveness along with track geometry degradation is essential for long term prediction of track geometry behaviour. The aim of this study is to analyse theeffect of tamping on the different track geometry measures, i.e. longitudinal level, alignment and cant; on the basis of inspection car records from a part of Main Western Line in Sweden. To model recovery after tamping a probabilistic approach is applied. The track geometry condition before tamping was considered as the dominant factor for modelling the model parameters. Correlation analysis has performed to measure the linear relation between the recoveries of the different geometry measures. The results show a moderate correlation between the recovery of the longitudinal level and that of the cant, and a weak correlation between the recovery of the longitudinal level and that of the alignment. Linear regression and Wiener process are also applied to model track geometry degradation and to obtain degradation rates. Theeffect of tamping on degradation rate is analysed. It is observed that the degradation rate was increased after tamping intervention.  

  • 2.
    Soleimanmeigouni, Iman
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Operation, Maintenance and Acoustics.
    Xiao, Xun
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Operation, Maintenance and Acoustics.
    Ahmadi, Alireza
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Operation, Maintenance and Acoustics.
    Xie, Min
    Department of Systems Engineering and Engineering Management, City University of Hong Kong, Kowloon.
    Nissen, Arne
    Trafikverket, Luleå.
    Kumar, Uday
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Operation, Maintenance and Acoustics.
    Modelling the evolution of ballasted railway track geometry by a two-level piecewise model2018In: Structure and Infrastructure Engineering, ISSN 1573-2479, E-ISSN 1744-8980, Vol. 14, no 1, p. 33-45Article in journal (Refereed)
    Abstract [en]

    Accurate prediction and efficient simulation of the evolution of track geometry condition is a prerequisite for planning effective railway track maintenance. In this regard, the degradation and tamping effect should be equipped with proper and efficient probabilistic models. The possible correlation induced by the spatial structure also needs to be taken into account when modelling the track geometry degradation. To address these issues, a two-level piecewise linear model is proposed to model the degradation path. At the first level, the degradation characteristic of each track section is modelled by a piecewise linear model with known break points at the tamping times. At the second level, Autoregressive Moving Average models are used to capture the spatial dependences between the parameters of the regression lines indexed by their locations. To illustrate the model, a comprehensive case study is presented using data from the Main Western Line in Sweden

  • 3.
    Mahmood, Yasser Ahmed
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Operation, Maintenance and Acoustics.
    Garmabaki, Amir
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Operation, Maintenance and Acoustics.
    Ahmadi, Alireza
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Operation, Maintenance and Acoustics.
    Verma, Ajit Kumar
    Western Norway University of Applied Sciences.
    Reliability model for frequency converter in electrified railway2018In: International Journal of Electrical Power & Energy Systems, ISSN 0142-0615, E-ISSN 1879-3517, Vol. 94, p. 385-392Article in journal (Refereed)
    Abstract [en]

    Reliability analysis of frequency converters based on failures and outages reports constitute an important basis for asset performance and management. Two- and four-state reliability models that recognize the operating characteristics of base load units and peaking units are presented and compared in this study. In this study, a four-state model is modified to a three-state model by combining the ‘needed’ and ‘not-needed’ forced-out states. Moreover, the transitions in the three-state model for power frequency converter have been designed according to real operational data. An outage-reporting database modelled considering IEEE STD 762 is presented and compared with the existing failure-reporting database of the case considered here. Furthermore, a method to extract information missing in the failure-reporting database by electrical readings is proposed to meet the requirements of the outage-reporting database. The study found that the results of indexes based on the IEEE four-state model are not reasonable for the frequency converter given their differences with the gas-turbine results under operational conditions. The forced outage rates and availability factors of twelve actual traction frequency converters of Swedish railways network are presented to validate the modified model.

  • 4.
    Soleimanmeigouni, Iman
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Operation, Maintenance and Acoustics.
    Ahmadi, Alireza
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Operation, Maintenance and Acoustics.
    Kumar, Uday
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Operation, Maintenance and Acoustics.
    Track geometry degradation and maintenance modelling: A review2018In: Proceedings of the Institution of mechanical engineers. Part F, journal of rail and rapid transit, ISSN 0954-4097, E-ISSN 2041-3017, Vol. 232, no 1, p. 73-102Article in journal (Refereed)
    Abstract [en]

    Increased demand for railway transportation is creating a need for higher train speeds and axle loads. These, in turn,increase the likelihood of track degradation and failures. Modelling the degradation behaviour of track geometry anddevelopment of applicable and effective maintenance strategies has become a challenging concern for railway infrastructuremanagers. During the last three decades, a number of track geometry degradation and maintenance modellingapproaches have been developed to predict and improve the railway track geometry condition. In this paper, existingtrack geometry measures are identified and discussed. Available models for track geometry degradation are reviewedand classified. Tamping recovery models are also reviewed and discussed to identify the issues and challenges of differentavailable methodologies and models. Existing track geometry maintenance models are reviewed and critical observationson each contribution are provided. The most important track maintenance scheduling models are identified and discussed.Finally, the paper provides directions for further research.

  • 5.
    Pourgol-Mohammad, Mohammad
    et al.
    Department of Mechanical Engineering, Sahand University of Technology, Tabriz.
    Hejaz, Amirmohsen
    Department of Mechanical Engineering, Sahand University of Technology, Tabriz .
    Ghasemi, Pejman
    School of Engineering-Emerging Technologies, Tabriz University, Tabriz .
    Ahmadi, Alireza
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Operation, Maintenance and Acoustics.
    Jalali-Vahid, Davoud
    Department of Mechanical Engineering, Sahand University of Technology, Tabriz.
    Design for reliability of automotive systems: case study of dry friction clutch2017In: International Journal of Systems Assurance Engineering and Management, ISSN 0975-6809, E-ISSN 0976-4348, Vol. 8, no 3, p. 572-583Article in journal (Refereed)
    Abstract [en]

    Design and production of highly reliable and safer automotive systems with longer life has been a challenge. The pressure is outcome of high competitive market and recent safety issues of reputable car manufacturers. In this paper, an integrated methodology is proposed based on design for reliability of automotive systems and considering its reliability/safety critical sub-systems. In the proposed approach, the FMEA results are used in the process of failure mode/mechanism identification. The basic failure data, mostly obtained from generic databases, are adjusted by multiplicative corrective factors to account for the design and environment impacts on system failure characteristics. The system is modeled by reliability block diagram method, simulated by Monte Carlo technique. The results of FMEA and reliability evaluation are used for system improvement by reducing the components’ failure rates and potential change of system configuration. The components’ reliability is improved by increasing the quality of components by utilization of high quality materials and modern manufacturing techniques. Modification of system configuration, e.g., adding redundancy, is an alternative for system reliability improvement in some cases. The results show that the friction lining component is the most critical elements in terms of reliability importance. After completion of this phase, an assessment is done for system reliability by comparing the system reliability targets. As a case study, dry friction clutch is studied for assessment of the proposed method. In this study, the life test requirement is researched for each component using a reliability testing techniques. Finally, the uncertainties are computed associated with the failure data and final reliability estimations and the results were presented with a confidence interval.

  • 6.
    Ahmadi, Alireza
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Operation, Maintenance and Acoustics.
    Soleimanmeigouni, Iman
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Operation, Maintenance and Acoustics.
    Letot, Christopher
    Machine Design and Production Engineering Unit, Research Institute for the Science and Manage ment of Risks, University of Mons.
    Block, Jan
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Operation, Maintenance and Acoustics.
    Inspection Optimization under imperfect maintenance performance2017In: 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 (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.

  • 7.
    Lopes, Julio C.O.
    et al.
    Division of Mechanical Engineering, Technological Institute of Aeronautics, São José dos Campo.
    Scarpel, Rodrigo
    Division of Mechanical Engineering, Technological Institute of Aeronautics, São José dos Campo.
    Abrahão, Fernando T.M.
    Laboratory of Logistics Engineering, Technological Institute of Aeronautics, São José dos Campo.
    Galar, Diego
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Operation, Maintenance and Acoustics.
    Ahmadi, Alireza
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Operation, Maintenance and Acoustics.
    Optmization In Performance-Based Logistics Contracts2017In: 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. 133-138Conference paper (Refereed)
    Abstract [en]

    Performance-based    Logistics    (PBL)    contracts    require  metrics  and  methodologies  set  in  a  systemic  way  to  provide  readiness  for  the  warfighter  at  reasonable  costs.  There  must be a clever and verifiable connection of metrics in order to access  and  analyze  data and  to  deliver  sound  and  consistent  inputs  for  the  entire  support  system  to  accomplish  its  goals.    A  system   of   incentives   and   penalties   usually   takes   place   and   suggests  functions  to  be  maximized  and/or  minimized  in  a  multi-criterion  and  highly  integrated  environment.  This  study  deals  with  the  optimization  of  the  entire  setup  of  Performance-Based Logistics  contracts  and  is  limited  to  a  preliminary  study  in  a  simple  scenario  that  has  showed  a  promises  results.    A  mixed  method, using both the Ɛ-Constraint  and    Goal  Programming  is  proposed to model the case. Results indicate that metrics used for reliability,    maintainability,    availability    and    supportability    (RAMS)  and  costs  can  be  optimized  simultaneously  for  clever  contracts.

  • 8.
    Ghodrati, Behzad
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Operation, Maintenance and Acoustics.
    Ahmadi, Alireza
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Operation, Maintenance and Acoustics.
    Galar, Diego
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Operation, Maintenance and Acoustics.
    Reliability Analysis of Switches and Crossings: A Case Study in Swedish Railway2017In: International Journal of Railway Research, ISSN 2361-5376, Vol. 4, no 1, p. 1-12Article in journal (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.

  • 9.
    Pourgol-Mohammad, Mohammad
    et al.
    Department of Mechanical Engineering, Sahand University of Technology, Tabriz, Iran.
    Makarachi, Peymaan
    School of Engineering- Emerging Technologies, Tabriz University, Tabriz, Iran.
    Soleimani, Morteza
    School of Engineering- Emerging Technologies, Tabriz University, Tabriz, Iran.
    Ahmadi, Alireza
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Operation, Maintenance and Acoustics.
    Reliability Enhancement of Centrifugal Pumps by Multi-Objective Genetic Algorithm Optimization2017In: International Journal of COMADEM, ISSN 1363-7681, Vol. 20, no 2, p. 23-30Article in journal (Refereed)
    Abstract [en]

    In this research, a methodology is presented to optimize the life performance of mechanical systems using multiple objective evolutionary algorithm. Conflicting objectives are encountered (e.g. low costs and longer service life) here along with significant number of constraints (e.g. technological limitations, weight and volume). To solve the design optimization problems, the objective function is weighted with a combination of the targets. The evolutionary algorithm (i.e. GA) is applied for minimization of the system failure rates, reliability allocation optimization. The failure rates are optimally estimated for the system?s critical components. Reliability allocation technique is utilized to determine the optimum reliability of the constituent components with higher failure rates. The reliability targets are determined for the components through the minimized failure rates. The methodology is demonstrated through a case study, on a centrifugal pump. The pump design requires consideration of several targets and requirements with different weight factors for satisfaction (e.g., availability, capability, efficiency and weight) along the pump life. Analytical Hierarchy Process (AHP) is utilized to determine the weights of the objectives. As a result of this research, the equipment design is improved, costly over-designs options are prevented and development tests are optimized.

  • 10.
    Pourgol-Mohammad, Mohammad
    et al.
    Sahand University of Technology, Tabriz.
    Ahmadi, Alireza
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Operation, Maintenance and Acoustics.
    Special issue of IREC2016 conference selected papers2017In: International Journal of Systems Assurance Engineering and Management, ISSN 0975-6809, E-ISSN 0976-4348, Vol. 8, no 3, p. 529-531Article in journal (Other academic)
  • 11.
    Modiri, Bahman
    et al.
    Mechanical Engineering Department, Sahand University of Technology, Tabriz, Iran.
    Pourgol-Mohammad, Mohammad
    Mechanical Engineering Department, Sahand University of Technology, Tabriz, Iran.
    Yazdani, Mojtaba
    Mechanical Engineering Department, Sahand University of Technology, Tabriz, Iran.
    Salimi, Hossein
    Mechanical Engineering Department, Sahand University of Technology, Tabriz, Iran.
    Salehpour-Oskouei, Farzin
    Mechanical Engineering Department, Sahand University of Technology, Tabriz, Iran.
    Ahmadi, Alireza
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Operation, Maintenance and Acoustics.
    Stochastic lifetime estimation of pressurized gas pipeline: Case study of the urban gas pipeline2017In: International Journal of COMADEM, ISSN 1363-7681, Vol. 20, no 2, p. 31-37Article in journal (Refereed)
    Abstract [en]

    Corrosion is a major contributor in gas pipeline degradation and failure. Due to significant sources of uncertainties in corrosion progression modelling, nondeterministicapproaches are more promising in recent researches. Several researches were conducted about probabilistic assessment of corrosion and itseffects in practical models. However, in these studies, either internal or external corrosion individually were separately evaluated, without taking intoaccount their correlated effects. In this study, a reliability analysis method is proposed for pressurized bare gas pipeline buried in soil by taking into accountboth corrosion effects from inside and the outside of the pipe. Environment effects are also studied on pipe’s corrosion by considering different soil types. Itwas observed that soil grain size has significant impact in corrosion occurrence. Consequently, sandy clay loam has the highest reliability index while clayand clay loam have the lowest values among these soil types.

  • 12.
    Garmabaki, Amir
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Operation, Maintenance and Acoustics.
    Ahmadi, Alireza
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Operation, Maintenance and Acoustics.
    Block, Jan
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Operation, Maintenance and Acoustics.
    Pham, Hoang
    Department of Industrial & Systems Engineering, Rutgers University, Piscataway, NJ.
    Kumar, Uday
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Operation, Maintenance and Acoustics.
    A Reliability Decision Framework for Multiple Repairable Units2016In: Reliability Engineering & System Safety, ISSN 0951-8320, E-ISSN 1879-0836, Vol. 150, p. 78-88Article in journal (Refereed)
    Abstract [en]

    In practice, the analyst is often dealing with multiple repairable units, installed in different positions or functioning under different operating conditions, and maintained by different disciplines. This paper presents a decision framework to identify an appropriate reliability model for massive multiple repairable units. It splits non-homogeneous failure data into homogeneous groups and classifies them based on their failure trends using statistical tests. The framework discusses different scenarios for analysing multiple repairable units, according to trend, intensity, and dependency of the units’ failure data. The proposed framework has been verified in a fleet of aircraft and in two simulated data sets. The results show a reliability model of multiple repairable units may contain a mixture of different stochastic models. Considering single reliability models for such populations may cause erroneous calculation of the time to failure of a particular unit, which can, in turn, lead to faulty conclusions and decisions. When dealing with massive and non-homogeneous multiple repairable units, the application of the proposed framework can facilitate the selection of an appropriate reliability model.

  • 13.
    Soleimanmeigouni, Iman
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Operation, Maintenance and Acoustics.
    Ahmadi, Alireza
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Operation, Maintenance and Acoustics.
    A Survey on Track Geometry Degradation Modelling2016In: 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 (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.

  • 14.
    Letot, Christophe
    et al.
    Machine Design and Production Engineering Unit, Research Institute for the Science and Management of Risks, University of Mons.
    Soleimanmeigouni, Iman
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Operation, Maintenance and Acoustics.
    Ahmadi, Alireza
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Operation, Maintenance and Acoustics.
    Dehombreux, Pierre
    Machine Design and Production Engineering Unit, Research Institute for the Science and Management of Risks, University of Mons.
    An adaptive opportunistic maintenance model based on railway track condition prediction2016In: IFAC-PapersOnLine, ISSN 2405-8963, Vol. 49, no 28, p. 120-125Article in journal (Refereed)
    Abstract [en]

    Maintaining a track line in a good condition is a continuous challenge since it has to deal with various track line heterogeneities that contribute to accelerate its degradation. As a result, railway tracks should be inspected regularly to detect geometry faults and to plan maintenance actions in consequence. A maintenance plan that minimizes track maintenance cost is highly desirable by infrastructure managers. This paper presents an adaptive maintenance scheduling based on track condition prediction. The degradation indicator is the standard deviation of the longitudinal (SDL) level that is sampled on every 200m-long track section. Standards define some thresholds on this indicator that correspond to different levels of severity and related penalty costs. From collected data, a degradation model that uses a random coefficient Wiener degradation-based process is built. A probabilistic model to simulate the recovery effect after the maintenance action (tamping) is also used. Based on this degradation and recovery models, a cost model is built to find the optimal time for tamping on a single track section. After that we use a Monte Carlo approach to assess the performance of the cost model for the whole track line, considering both calendar based and adaptive opportunistic tamping actions. The results show that the adaptive opportunistic maintenance strategy has a lower cost per unit of time than the systematic preventive maintenance.

  • 15.
    Soleimanmeigouni, Iman
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Operation, Maintenance and Acoustics.
    Ahmadi, Alireza
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Operation, Maintenance and Acoustics.
    Letot, Christophe
    Machine Design and Production Engineering Lab, Research Institute for the Science and Management of Risks, University of Mons.
    Nissen, Arne
    Trafikverket.
    Kumar, Uday
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Operation, Maintenance and Acoustics.
    Cost-Based Optimization of Track Geometry Inspection2016Conference paper (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.

  • 16.
    Kumar, Uday
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Operation, Maintenance and Acoustics.
    Ahmadi, AlirezaLuleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Operation, Maintenance and Acoustics.Verma, Ajit KumarDepartment of Electrical Engineering, Indian Institute of Technology, Bombay, International Institute of Information Technology, P-14, Pune Infotech Park, Phase-1, Hinjawadi.Varde, PrabhakarBhabha Atomic Research Centre, Trombay, Mumbai.
    Current Trends in Reliability, Availability, Maintainability and Safety: An Industry Perspective2016Collection (editor) (Refereed)
  • 17.
    Garmabaki, Amir
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Operation, Maintenance and Acoustics.
    Ahmadi, Alireza
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Operation, Maintenance and Acoustics.
    Ahmadi, Mahdieh
    Department of Industrial Engineering, Mazandaran University of Science and Technology, Babol.
    Maintenance Optimization Using Multi-Attribute Utility Theory2016In: 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. 13-25Conference paper (Refereed)
    Abstract [en]

    Several factors such as reliability, availability, and cost may consider in the maintenance modeling. In order to develop an optimal inspection program, it is necessary to consider the simultaneous effect of above factor in the model structure. In addition, for finding the optimal maintenance interval it is necessary to make trade-offs between several factors, which may conflicting each other as well. The study comprises of mathematical formulating an optimal interval problem based on Multi-Attribute Utility Theory (MAUT). The aim of the proposed research is to develop a methodology with supporting tools for determination of optimal inspection in a maintenance planning to assure and preserve a desired level of performance measure such as reliability, availability, risk, etc. For verification and validation purposes, the proposed methodology (analysis approach) and tools (models) will be applied in a real case which given by the literature.

  • 18.
    Karim, M.R.
    et al.
    Department of Statistics, University of Rajshahi.
    Ahmadi, Alireza
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Operation, Maintenance and Acoustics.
    Murthy, D.N.P
    School of Mechanical and Mining Engineering, The University of Queensland, St Lucia.
    Modelling of Maintenance Data2016In: 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. 409-424Conference paper (Refereed)
    Abstract [en]

    The modelling of maintenance data starts with the black-box approach (where the model selection is based solely on the maintenance data) and then through the grey-box approach for proper analysis (where one can gain insights to build better models). These models allow for more effective maintenance of the object. This paper deals with the grey-box approach to modelling. It discusses the process of modelling and illustrates this through a real case study

  • 19.
    Ahmadi, Alireza
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Operation, Maintenance and Acoustics.
    Soleimanmeigouni, Iman
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Operation, Maintenance and Acoustics.
    Block, Jan
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Operation, Maintenance and Acoustics.
    Letot, Christophe
    University of Mons.
    Optimum failure management strategy for periodically inspected units with imperfect maintenance2016In: IFAC PAPERSONLINE, ISSN 2405-8963, Vol. 49, no 12, p. 799-804Article in journal (Refereed)
    Abstract [en]

    The aim of this paper is to develop a reliability-based cost model for periodically inspected units subject to hidden functions, with imperfect restoration (overhaul) action after a certain number of inspections. In the model, effectiveness of the consecutive restoration actions is considered, and possible alternative maintenance strategies are identified and compared. The method is based on the Total Cost and identifies the optimum interval and frequency of inspections, as well as restoration that minimize the total life cycle cost. In the proposed model, repair due to failures found by inspection is considered as minimal repair, and restoration/overhaul action is considered as normal repair. The result also shows that for a specific value of restoration effectiveness (θ0), when θ> θ0, the behavior of alternatives tends to as-bad-as-old and for θ< θ0 tends to an as-good-as-new. It is also observed that when the cost of accident is high it is needed to perform inspections at smaller intervals.

  • 20.
    Mahmood, Yasser Ahmed
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Operation, Maintenance and Acoustics.
    Abrahamsson, Lars
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science. Kungliga tekniska högskolan, KTH.
    Ahmadi, Alireza
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Operation, Maintenance and Acoustics.
    Verma, Ajint K.
    Stord/Haugesund University College.
    Reliability Evaluation of Traction Power Capacity in Converter-fed Railway Systems2016In: IET Generation, Transmission & Distribution, ISSN 1751-8687, E-ISSN 1751-8695Article in journal (Refereed)
    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

  • 21.
    Garmabaki, Amir
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Operation, Maintenance and Acoustics.
    Ahmadi, Alireza
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Operation, Maintenance and Acoustics.
    Mahmood, Yasser Ahmed
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Operation, Maintenance and Acoustics.
    Barabadi, Abbas
    Tromsø University.
    Reliability Modelling of Multiple Repairable Units2016In: Quality and Reliability Engineering International, ISSN 0748-8017, E-ISSN 1099-1638, Vol. 32, no 7, p. 2329-2343Article in journal (Refereed)
    Abstract [en]

    This paper proposes a model selection framework for analysing the failure data of multiple repairable units when they are working in different operational and environmental conditions. The paper provides an approach for splitting the non-homogeneous failure data set into homogeneous groups, based on their failure patterns and statistical trend tests. In addition, when the population includes units with an inadequate amount of failure data, the analysts tend to exclude those units from the analysis. A procedure is presented for modelling the reliability of a multiple repairable units under the influence of such a group to prevent parameter estimation error. We illustrate the implementation of the proposed model by applying it on 12 frequency converters in the Swedish railway system. The results of the case study show that the reliability model of multiple repairable units within a large fleet may consist of a mixture of different stochastic models, i.e. the HPP/RP, TRP, NHPP and BPP. Therefore, relying only on a single model to represent the behaviour of the whole fleet may not be valid and may lead to wrong parameter estimation.

  • 22.
    Minbashi, Niloofar
    et al.
    School of Railway Engineering, Iran University of Science and Technology, Tehran.
    bagheri, Morteza
    School of Railway Engineering, Iran University of Science and Technology, Tehran.
    Golroo, Amir
    Department of Civil and Environmental Engineering, Amirkabir University of Technology, Tehran.
    Arasteh Khouy, Iman
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Operation, Maintenance and Acoustics.
    Ahmadi, Alireza
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Operation, Maintenance and Acoustics.
    Turnout Degradation Modelling Using New Inspection Technologies: A Literature Review2016In: 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. 49-63Conference paper (Refereed)
    Abstract [en]

    Turnouts are of the most critical components of railway track which are prone to high static and dynamic forces leading to more intense degradation. They require more inspection than other parts of a railway track as they are potential safety hazards. As a result, turnout degradation processes are crucial to be understood by infrastructure manager to plan for their maintenance and renewal in advance. Two approaches have been introduced in the literature to achieve a thorough understanding of degradation processes in turnouts. The first one acts to develop degradation models based on influential parameters and historical data and then to predict degradation processes in the future; while the second one tries to improve inspection through using new concepts and technologies leading turnout condition data to be better captured over time. The purpose of this paper is to review all available resources regarding these two approaches and provide a guide for further research into turnout studies

  • 23.
    Hamodi, Hussan
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Operation, Maintenance and Acoustics.
    Lundberg, Jan
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Operation, Maintenance and Acoustics.
    Jonsson, Adam
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mathematical Science.
    Ahmadi, Alireza
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Operation, Maintenance and Acoustics.
    Case Study: Model for economic lifetime of drilling machines in the Swedish mining industry2015In: The Engineering Economist, ISSN 0013-791X, E-ISSN 1547-2701, Vol. 60, no 2, p. 138-154Article in journal (Refereed)
    Abstract [en]

    The purpose of this paper is to develop a practical economic replacement decision model to identify the economic lifetime of a mining drilling machine. A data driven optimisation model was developed for operating and maintenance costs, purchase price and machine resale value. Equivalent present value of these costs by using discount rate was considered. The proposed model shows that the absolute optimal replacement time (ORT) of a drilling machine used in one underground mine in Sweden is 115 months. Sensitivity and regression analysis show that the maintenance cost has the largest impact on the ORT of this machine. The proposed decision making model is applicable and useful and can be implemented within the mining industry.

  • 24.
    Murthy, D.N.P
    et al.
    School of Mechanical and Mining Engineering, The University of Queensland, St Lucia.
    Karim, M.R.
    Department of Statistics, University of Rajshahi.
    Ahmadi, Alireza
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Operation, Maintenance and Acoustics.
    Data management in maintenance outsourcing2015In: Reliability Engineering & System Safety, ISSN 0951-8320, E-ISSN 1879-0836, Vol. 142, p. 100-110Article in journal (Refereed)
    Abstract [en]

    Most businesses view maintenance as tasks carried out by technicians and the data collected is mostly cost related. There is a growing trend towards outsourcing of maintenance and the data collection issues are not addressed properly in most maintenance service contracts. Effective maintenance management requires proper data management - data collection and analysis for decision-making. This requires a proper framework and when maintenance is outsourced it raises several issues and challenges. The paper develops a framework for data management when maintenance is outsourced and looks at a real case study that highlights the need for proper data management.

  • 25.
    Garmabaki, Amir Soleimani
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Operation, Maintenance and Acoustics.
    Ahmadi, Alireza
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Operation, Maintenance and Acoustics.
    Block, Jan
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Operation, Maintenance and Acoustics.
    Fleet-level reliability estimation of repairable units2015In: Safety and Reliability: Methodology and Applications / [ed] Tomasz Nowakowski; Marek Mlynczak; Anna Jodejko-Pietruczuk; Sylwia Werbinska-Wojciechowska, London: CRC Press, 2015, p. 1977-1982Conference paper (Refereed)
    Abstract [en]

    This paper investigates reliability analysis of a repairable unit at fleet level. In fleet, multiple similar systems are running in different operating environments. In fact, due to the highly censored data as well as high variations in failure rate within the fleet, merging the datasets becomes a challenge. The non-parametric analysis is used to capture the failure trend of repairable units at fleet level. Consequently, fleet data have been aggregated and the actual number of failure has been compared with the expected total number of failures. In addition, parametric models are used to model the reliability trend obtained through a non-parametric approach to identify the reliability parameters at fleet level. Real data are used to demonstrate the applicability and validity of the proposed method. Results shows the accuracy of log-linear process is reasonably acceptable.

  • 26.
    Hamodi, Hussan
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Operation, Maintenance and Acoustics.
    Lundberg, Jan
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Operation, Maintenance and Acoustics.
    Al-Gburi, Majid
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    Ahmadi, Alireza
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Operation, Maintenance and Acoustics.
    Ghodrati, Behzad
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Operation, Maintenance and Acoustics.
    Model for economic replacement time of mining production rigs including redundant rig costs2015In: Journal of Quality in Maintenance Engineering, ISSN 1355-2511, E-ISSN 1758-7832, Vol. 21, no 2, p. 207-226Article in journal (Refereed)
    Abstract [en]

    Purpose - This paper presents a practical model to determine the economic replacement time (ERT) of production machines. The objective is to minimise the total cost of capital equipment, where total cost includes acquisition, operating, maintenance costs and costs related to the machine’s downtime. The costs related to the machine’s downtime are represented by the costs of using a redundant machine. Design/methodology/approach - Four years of cost data are collected. Data is analysed, practical optimisation model is developed and regression analysis is done to estimate the drilling rigs ERT. The artificial neural network (ANN) technique is used to identify the effect of factors influencing the ERT of the drilling rigs.Findings - The results show that the redundant rig cost has the largest impact on ERT, followed by acquisition, maintenance and operating costs. The study also finds that increasing redundant costs per hour have a negative effect on ERT, while decreases in other costs have a positive effect. Regression analysis shows a linear relationship between the cost factors and ERT. Practical implications - The proposed approach can be used by the decision maker in determining the economic replacement time of production machines which used in mining industry.Originality/value - The research proposed in this paper provides and develops an optimisation model for economic replacement time of mining machines. This research also identifies and explains the factors that have the largest impact on the production machine’s ERT. This model for estimating the ERT has never been studied on mining drilling rigs.Keywords Decision support model, Life cycle cost, Optimisation, Replacement timePaper type Research paper

  • 27.
    Ahmadi, Alireza
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Operation, Maintenance and Acoustics.
    Garmabaki, Amir
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Operation, Maintenance and Acoustics.
    Ghodrati, Behzad
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Operation, Maintenance and Acoustics.
    Kumar, Uday
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Operation, Maintenance and Acoustics.
    Optimum inspection interval for hidden functions during extended life2015In: International Journal of COMADEM, ISSN 1363-7681, Vol. 18, no 3, p. 45-49Article in journal (Refereed)
  • 28.
    Garmabaki, Amir
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Operation, Maintenance and Acoustics.
    Ahmadi, Alireza
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Operation, Maintenance and Acoustics.
    Mahdavi, Iraj
    Mazandaran University of Science and Technology, Babol.
    Ahmadi, Mahdieh
    Mazandaran University of Science and Technology, Babol.
    Reliability modeling of open source software based on adoption behavior under stochastic environment2015In: Safety and reliability of complex engineered systems: proceedings of the 25th European Safety and Reliability Conference, ESREL 2015, Zürich, Switzerland, 7-10 September 2015 / [ed] Luca Podofilini; Bruno Sudret; Božidar Stojadinović; Enrico Zio; Wolfgang Kröger, Boca Raton: CRC Press, 2015, p. 3995-3999Conference paper (Refereed)
    Abstract [en]

    In the current digitalized world, Open Source Software (OSS) methodology provides greater value to users and leads to increased revenue for the OSS companies. This paper investigates reliability modeling for OSS. Most of software reliability models proposed in literature for OSS projects are based on closed-form methodology and do not consider the properties of OSS in the model structure. This paper models the rate of adoption of volunteers to OSS using diffusion theory and considered as fault detection rate. However, the fault detection rate may vary in such a testing environment; a modified SRGM based on Itô type Stochastic Differential Equation (SDE) is proposed to describe realistic situations. The proposed model have been verified on real data sets from open source projects, as the Apache project, which has been released in the market with new features. Results show the proposed model can describe the failure process for open source software accurately.

  • 29.
    Mahmood, Yasser Ahmed
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Operation, Maintenance and Acoustics.
    Ahmadi, Alireza
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Operation, Maintenance and Acoustics.
    Verma, Ajit Kumar
    Department of Electrical Engineering, Indian Institute of Technology, Bombay, International Institute of Information Technology, P-14, Pune Infotech Park, Phase-1, Hinjawadi.
    Evaluation and Selection for Availability Improvement of Frequency Converters in Electrified Railway2014In: International Journal of Power and Energy Systems, ISSN 1078-3466, E-ISSN 1710-2243, Vol. 34, no 4, p. 162-172Article in journal (Refereed)
    Abstract [en]

    Railway traction power supply systems (TPSSs) that work at low frequencies contain frequency converters (FCs) that convert the adequate power from a public grid to a traction grid. Availability and system importance analysis is a key aspect of overall system performance. It identifies the weakest areas of a system and indicates where resources must be invested to achieve maximum improvement. Availability analysis of FC types is crucial to reduce outages of traction power that lead to traffic delays and cancellations due to unavailability of FCs. The aim of this study is to rank FC types on the basis of priority of needs for reliability and maintainability improvement so that the availability can be enhanced. The proposed approach involves collection of outage data by calculating performance measures, and then these measures are compared via a comparative chart. Thereafter, opinions of experts are collected and aggregated through linguistic variables, and the FC types are then identified using analytic hierarchy process. Reliability, availability and maintainability (RAM) have been used as the criteria to identify the FC types. In addition to power sharing, capacity and service factors are considered to be productivity measures. Probabilistic performance indexes are used to measure availability, maintainability and productivity, whereas the mean number of outages is used as a reliability index.

  • 30.
    Block, Jan
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Operation, Maintenance and Acoustics.
    Ahmadi, Alireza
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Operation, Maintenance and Acoustics.
    Tyrberg, Tommy
    Saab Aerotech.
    Kumar, Uday
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Operation, Maintenance and Acoustics.
    Fleet-level Reliability of Multiple Repairable Units: a Parametric Approach using the Power Law Process2014In: International Journal of Pedagogy, Innovation and New Technologies, ISSN 0973-1318, E-ISSN 2392-0092, Vol. 10, no 3, p. 239-250Article in journal (Refereed)
    Abstract [en]

    The application of parametric reliability analysis methods for repairable units, such as Power law process, is quite clear and straightforward for a single repairable unit. However, in practice, the analyst needs to know the reliability characteristics of units at a fleet level. The application of parametric reliability analysis methods at the fleet level, even if it is limited in scope, is quite complex. The aim of this paper is to describe the use of the power law process for multiple repairable units with differing reliability characteristics, to predict the expected number of failures at fleet level. The empirical data used in the paper are based on field data gathered during the operational life of two types of multi repairable units used in the Swedish military aircraft system FPL 37 Viggen from 1977 to 2006. The paper performs the trend test using TTT-based MIL-HDBK-189 and Laplace tests, and assesses the equality of shape-parameters for the intensity function of the power law process for multiple units. Estimation of the scale- and shape-parameters using maximum likelihood estimation is also performed. The parametric approach using power law process was found to yield relatively accurate estimations of number of failures, compared to empirical data

  • 31.
    Ahmadi, Alireza
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Operation, Maintenance and Acoustics.
    Ghodrati, Behzad
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Operation, Maintenance and Acoustics.
    Garmabaki, Amir Soleimani
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Operation, Maintenance and Acoustics.
    Kumar, Uday
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Operation, Maintenance and Acoustics.
    Optimum inspection interval for hidden functions during extended life2014Conference paper (Refereed)
  • 32.
    Block, Jan
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Operation, Maintenance and Acoustics.
    Ahmadi, Alireza
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Operation, Maintenance and Acoustics.
    Tyrberg, Tommy
    Logistics Analysis and Fleet Monitoring, Saab Support and Services, Linköping.
    Söderholm, Peter
    Luleå University of Technology, Department of Business Administration, Technology and Social Sciences, Business Administration and Industrial Engineering.
    Part-out-based spares provisioning management: A military aviation maintenance case study2014In: Journal of Quality in Maintenance Engineering, ISSN 1355-2511, E-ISSN 1758-7832, Vol. 20, no 1, p. 76-95Article in journal (Refereed)
    Abstract [en]

    Purpose – The purpose of this paper is to present the prerequisites for a part-out-based spares provisioning (PBSP) programme during the phase-out of an aircraft fleet. Furthermore, associated key decision criteria are identified and a framework for the phase-out management process is presented. Design/methodology/approach – Once a decision has been taken to phase-out an aircraft fleet, a number of routines for operations, maintenance and storage are affected and new tasks and functions must be introduced before initiating the actual parting-out process. A decision-making system and a management framework is needed to manage spares planning during the end-of-life phase to ensure availability at minimum cost and to ensure a manageable risk of backorders. Findings – For PBSP programme during the phase-out of an aircraft fleet to succeed and be cost-effective, a number of linked processes, tasks and decisions are required, e.g., those included in the framework proposed in this paper (see Figure 3). A successful implementation of PBSP also requires that these processes and tasks are carried out in a timely manner and that the communications between the concerned parties are prompt, clear and direct. One experience from the studied case is that close and trustful contacts and cooperation between the operator and maintenance provider(s) will greatly facilitate the process. Originality/value – Although the PBSP method is fairly commonly applied within both the military and the civilian sector, somewhat surprisingly very literature has been published on the subject. Indeed, remarkably little has been published on any aspects of maintenance during the end-of-life period.

  • 33.
    Ghodrati, Behzad
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Operation, Maintenance and Acoustics.
    Ahmadi, Alireza
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Operation, Maintenance and Acoustics.
    Product Support Logistics Based on System Reliability Characteristics and Operating Environment2014In: IEEE International Conference on Industrial Engineering and Engineering Management: IEEM 2013, Bangkok, Thailand; 10 - 13 December 2013, Piscataway, NJ: IEEE Communications Society, 2014, p. 457-461, article id 6962453Conference paper (Refereed)
    Abstract [en]

    The environmental conditions in which the equipment is to be operated, such as temperature, humidity, dust, operators’ skill, etc, often have considerable influence directly on the product reliability and indirectly on the product supportability characteristics. This paper, after discussing the factors influencing product reliability, describes a method to estimate spare part requirements based on estimation of the actual reliability of a product under the influence of the product-operating environment using a proportional hazard model. In this research only non-repairable components/parts in repairable systems are studied. Results express a considerable difference between considering and ignoring the operating environmental factor on system performance. So, this factor should be seriously considered while dimensioning product support and service delivery performance strategies, since it will have an impact on operation, maintenance and service quality.

  • 34.
    Ahmadi, Alireza
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Operation, Maintenance and Acoustics.
    Block, Jan
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Operation, Maintenance and Acoustics.
    Garmabaki, Amir
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Operation, Maintenance and Acoustics.
    Project: Efficient Performance Based Air Vehicle Maintenance, Supported by VINNOVA (NFFP-6), Luleå University of Technology, Saab Support and Services, SAAB Aeronautics2014Other (Other (popular science, discussion, etc.))
  • 35.
    Ahmadi, Alireza
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Operation, Maintenance and Acoustics.
    Block, Jan
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Operation, Maintenance and Acoustics.
    Garmabaki, Amir
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Operation, Maintenance and Acoustics.
    Project: Enhanced Life Cycle Assessment for Performance-Based Logistics, Supported by Vinnova (NFFP-5), Saab Support Service and Luleå University of Technology2014Other (Other (popular science, discussion, etc.))
  • 36.
    Block, Jan
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Operation, Maintenance and Acoustics.
    Ahmadi, Alireza
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Operation, Maintenance and Acoustics.
    Tyrberg, Tommy
    Saab Support and Services.
    Using Monte Carlo simulation as support for decision making while negotiating a PBL contract2014In: IEEE Aerospace Conference. Proceedings, ISSN 1095-323X, article id 6836495Article in journal (Refereed)
    Abstract [en]

    In connection with performance-based logistics (PBL) contracts for aircraft fleets it is very important to carefully analyse both operations and maintenance before and during the contract negotiation phase. Monte Carlo Simulation is a valuable methodology in this context since it allows delimiting and exploring a complex parameter space in a transparent and relatively easily visualized manner. With timely analyses it is possible to identify both technical and economic risks and minimize the possible consequences, a process that benefits both parties in the negotiation process. This paper describes a part of this process in connection with the negotiation of a PBL contract for the Swedish Air Force SAAB 105 (SK 60) trainer fleet between Saab AB and the Swedish Defence Materiel Administration (FMV). The information used in the simulations was largely empirical data derived from previous operations of the aircraft system. The main factors that were simulated were operational requirements, fleet size, spares inventories, turn-around times, failure rates and influence of extraneous factors (e. g. weather). The simulations resulted in considerable savings due to reduction of the active fleet size, and increased reclamation of surplus spares and units from retired aircraft.

  • 37.
    Gupta, Suprakash
    et al.
    Department of Mining Engineering, Indian Institute of Technology.
    Rahber, Anjum
    Department of Mining Engineering, Indian Institute of Technology.
    Ahmadi, Alireza
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Operation, Maintenance and Acoustics.
    Kumar, Uday
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Operation, Maintenance and Acoustics.
    A vector-dissimilarity-based approach for multi-criteria decision making2013In: International Journal of Systems Assurance Engineering and Management, ISSN 0975-6809, E-ISSN 0976-4348, Vol. 4, no 3, p. 249-261Article in journal (Refereed)
    Abstract [en]

    Decision making in complex environments is influenced by a large number of conflicting and incommensurable factors. It is multidimensional and the influencing factors affect the decision process to varying degrees. The performance measurement of decision alternatives in multi-criteria decision making (MCDM) may be represented as a multidimensional vector in real space. The technique for order preference by similarity to ideal solution (TOPSIS) is a popular MCDM tool. However, sometimes this technique shows its inability to differentiate between decision alternatives. In this paper the limitations of TOPSIS are examined, and an improvement is suggested. The proposed new method uses the vector dissimilarity approach to remove the boundary restrictions and achieve greater sovereignty. The improved method has been demonstrated through a case study of maintenance design for dump trucks deployed in a large surface mine.

  • 38.
    Mahmood, Yasser Ahmed
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Operation, Maintenance and Acoustics.
    Ahmadi, Alireza
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Operation, Maintenance and Acoustics.
    Verma, Ajit
    Karim, Ramin
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Operation, Maintenance and Acoustics.
    Kumar, Uday
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Operation, Maintenance and Acoustics.
    Availability and reliability performance analysis of traction frequency converters: a case study2013In: International Review of Electrical Engineering, ISSN 1827-6660, Vol. 8, no 4, p. 1231-1242Article in journal (Refereed)
    Abstract [en]

    The frequency converter is one of the main parts of the traction power supply system (TPSS) and converts adequate traction power from the power company to the electric vehicle. In the Swedish railway network, this system comprises around 133 frequency converters with a total capacity reach of 1,295 MVA and covers around 9,543 km of electrified railway. The aim of this article is to evaluate and compare the reliability, availability and maintainability (RAM) performances of the ten models of converters used in the Swedish railway system. The key performance indicators introduced by the IEEE Std 762 methodology have been used to measure and compare the RAM performance of the converters. Moreover, the mean cumulative function (MCF) has also been used for the monitoring and comparison of the field reliability of converters versus the operating time, capacity factor and converted power. The study shows that, in general, both the static and the rotary types have a high level of availability ranging from 97%-99%. The results also show that the TGTO model (a static type) has the lowest RAM performance among all the models. In addition, it has been found that using IEEE Std 762 or the MCF alone does not always provide a complete answer. Therefore, the study suggests using both the IEEE Std 762 and the MCF methodology to arrive at a more realistic result. The study has shown that the MCF based on the capacity factor gives a good result compared with the results obtained using the MCF based on the operating time and on the converted power as a measure of the usage intensity.

  • 39.
    Block, Jan
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Operation, Maintenance and Acoustics.
    Ahmadi, Alireza
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Operation, Maintenance and Acoustics.
    Tyrberg, Tommy
    Saab Support and Services.
    Kumar, Uday
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Operation, Maintenance and Acoustics.
    Fleet-level reliability analysis of repairable units: a non-parametric approach using the mean cumulative function2013In: International Journal of Pedagogy, Innovation and New Technologies, ISSN 0973-1318, E-ISSN 2392-0092, Vol. 9, no 3, p. 333-344Article in journal (Refereed)
    Abstract [en]

    Complex technical systems are normally repaired rather than replaced when they fail. It is often desirable to analyze the reliability characteristics of these systems based on data generated in a customer use environment, in order to assess the reliability, frequency of failure or other parameters which may be influenced by the systems’ age and usage. Despite the advantages of continuously analyzing reliability data to be able to improve the maintenance programme continuously, methods such as parametric and non-parametric analysis are often ignored due to a belief that the mean time between failures (MTBF) is sufficient to describe the reliability pattern of repairable units. This paper describes the use of the mean cumulative function (MCF) and linear estimates based on the recurrence rate to predict the expected number of failures in the future. Reliability data from two repairable units are used to verify the procedure and comparison. The empirical data used in the paper is based on field data gathered during the operational life of the Swedish military aircraft system FPL 37 Viggen from 1977 to 2006, which essentially is the whole life cycle of the system.

  • 40.
    Mahmood, Yasser Ahmed
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Operation, Maintenance and Acoustics.
    Ahmadi, Alireza
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Operation, Maintenance and Acoustics.
    Verma, Ajint
    Stord/Haugesund University College.
    Kumar, Uday
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Operation, Maintenance and Acoustics.
    Fuzzy fault tree analysis: a review of concept and application2013In: International Journal of Systems Assurance Engineering and Management, ISSN 0975-6809, E-ISSN 0976-4348, Vol. 4, no 1, p. 19-32Article in journal (Refereed)
    Abstract [en]

    Fault tree analysis (FTA) is a widely used method for analyzing a system’s failure logic and calculating overall reliability. However, application of conventional FTA has some shortcomings, e.g. in handling the uncertainties, allowing the use of linguistic variables, and integrating human error in failure logic model. Hence, Fuzzy set theory has been proposed to overcome the limitation of conventional FTA. Fuzzy logic provides a framework whereby basic notions such as similarity, uncertainty and preference can be modeled effectively.The aim of this paper is to present a review of the concept of fuzzy theory with fault tree analysis and their applications since 1981, to reflect the current status of Fuzzy Fault Tree Analysis (FFTA) methodologies, their strengths, weaknesses, and their applications. This paper explains the fundamentals of fuzzy theory and describes application of fuzzy importance for using FFTA. The concept of the failure possibility and uncertainty analysis by using FFTA is discussed, and concludes with discussion on the application of FFTA in different fields. The review reveals the effectiveness of the FFTA in comparison with conventional FTA, when there is inadequate amount of accurate reliability oriented information.

  • 41.
    Mahmood, Yasser Ahmed
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Operation, Maintenance and Acoustics.
    Ahmadi, Alireza
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Operation, Maintenance and Acoustics.
    Verma, Ajint K.
    Stord/Haugesund University College.
    Identification of Frequency Converter Models For Availability Improvement2013In: International Journal of Electrical Engineering, ISSN 1812-3031, Vol. 20, no 4Article in journal (Refereed)
  • 42.
    Mahmood, Yasser Ahmed
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Operation, Maintenance and Acoustics.
    Ahmadi, Alireza
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Operation, Maintenance and Acoustics.
    Verma, Ajit
    University of Haugesund.
    Identifying the critical of frequency converter models2013In: 10th International Conference on Condition Monitoring and Machinery Failure Prevention Technologies 2013, CM 2013 and MFPT 2013, 2013, p. 784-792Conference paper (Refereed)
    Abstract [en]

    The Swedish traction power supply system (TPSS) has approximately 134 frequency converters; there are two main types, static and rotary, with ten different models. Previous work performed a Reliability, Availability, and Maintainability (RAM) analysis of the converters to estimate their performance. The aim of this article is to use these RAM components to rank the converter models and identify the models that need more attention to improve overall operational availability. The study finds that the performance factor aggregated from IEEE Std 762 indexes can rank the converters. Furthermore, the paper has been found that the rotary models Q48 and TGTO have a low performance from RAM point of view.

  • 43.
    Ahmadi, Alireza
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Operation, Maintenance and Acoustics.
    Ghodrati, Behzad
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Operation, Maintenance and Acoustics.
    Rantatalo, Matti
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Operation, Maintenance and Acoustics.
    Optimum Failure Finding Inspection During Extended Operation Life2013Conference paper (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

  • 44.
    Garmabaki, Amir Soleimani
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Operation, Maintenance and Acoustics.
    Ahmadi, Alireza
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Operation, Maintenance and Acoustics.
    Kapur, P.K
    Amity University.
    Kumar, Uday
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Operation, Maintenance and Acoustics.
    Predicting software reliability in a fuzzy field environment2013In: International Journal of Reliability, Quality and Safety Engineering (IJRQSE), ISSN 0218-5393, Vol. 20, no 3Article in journal (Refereed)
    Abstract [en]

    The testing-development phase has been carried out in a given control environment. However, the product will be used in different operating environment by different end-users, which is unknown to the developer. The operating environment may range from a very clean one up to a harsh environment. These uncertain operating environments will impact to the reliability and performance of the software which may differ from the testing phase reliability. We consider that the effect of environment on reliability has a fuzzy nature. The fuzzy effects of the field environments can be captured by a unit-free environmental factor. To overcome this problem, the fuzzy probabilistic theory may be used in the processing of stochastic parameters, taking into account their fuzzy nature. The proposed model is based on Weibull distribution. The aim of this paper is to introduce a fuzzy field environment (FFE) reliability model that covers both the testing and operating phases in the development cycle. Illustration examples of the proposed model have been validated on data collected from two industries. © 2013 World Scientific Publishing Company.

  • 45.
    Ghodrati, Behzad
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Operation, Maintenance and Acoustics.
    Ahmadi, Alireza
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Operation, Maintenance and Acoustics.
    Galar, Diego
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Operation, Maintenance and Acoustics.
    Reliability analysis of switches and crossings: a case study in Swedish railway2013Conference paper (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.

  • 46.
    Hoseinie, Hadi
    et al.
    Hamedan University of Technology.
    Ahmadi, Alireza
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Operation, Maintenance and Acoustics.
    Ghodrati, Behzad
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Operation, Maintenance and Acoustics.
    Kumar, Uday
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Operation, Maintenance and Acoustics.
    Reliability-centered maintenance for spray jets of coal shearer machine2013In: International Journal of Reliability, Quality and Safety Engineering (IJRQSE), ISSN 0218-5393, Vol. 20, no 3Article in journal (Refereed)
    Abstract [en]

    Spray jets constitute one of the most important parts of each type of rock cutting machine, especially the drum shearer. This system cools the cutting picks and controls the dust emission. The blockage of spray jets causes the coal shearer machine to stop automatically. Therefore, the reliable performance of this system assists the achievement of a smooth coal cutting operation. Field's data shows that the maintenance of this system is time-consuming and causes major downtimes in the production process. Therefore, it is essential to find an optimum preventive maintenance task and intervals, to reduce the downtime and minimize the associated costs of the machine. The aim of this paper is to identify an applicable and effective maintenance task, with its associated interval, for management of the failure modes of the spray jets of coal shearers. A case study has been conducted on spray jets of double-drum shearer machine in Tabas Coal Mine in Iran. In the study, the RCM approach is used to select an applicable and effective maintenance task. The failure data were analyzed using a parametric approach to evaluate the reliability of the spray jets, and to estimate the reliability parameters. A reliability-based cost modeling has been implemented to identify the optimum maintenance interval and frequencies of restoration for the spray jets. In the study, a cost rate function (CRF) has been introduced in which an as-good-as-new (AGAN) effectiveness for restoration actions is considered. The CRF also considers restoration and repair times, and takes into account the costs associated with repair and restoration, and the opportunity cost of the equipment's lost production due to maintenance downtime, to arrive at the most cost-effective maintenance intervals. The results of the analysis have shown that the minimum cost per unit of time, $46.5/h, will be achieved within a range of intervals i.e., T = 210 h to T = 260 h.

  • 47.
    Ghodrati, Behzad
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Operation, Maintenance and Acoustics.
    Ahmadi, Alireza
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Operation, Maintenance and Acoustics.
    Galar, Diego
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Operation, Maintenance and Acoustics.
    Spare parts estimation for machine availability improvement addressing its reliability and operating environment: case study2013In: International Journal of Reliability, Quality and Safety Engineering (IJRQSE), ISSN 0218-5393, Vol. 20, no 3Article in journal (Refereed)
    Abstract [en]

    Industrial operation cost analysis shows that, in general, maintenance represents a significant proportion of the overall operating costs. Therefore, the improvement of maintenance follows the final goal of any company, namely, to maximize profit. This paper studies spare parts availability, an issue of the maintenance process, which is an important way to improve production through increased availability of functional machinery and subsequent minimization of the total production cost. Spare parts estimation based on machine reliability characteristics and operating environment is performed. The study uses an improved statistical-reliability (S-R) approach which incorporates the system/machine operating environment information in systems reliability analysis. For this purpose, two methods of Poisson process and renewal process are introduced and discussed. The renewal process model uses a multiple regression type of analysis based on Cox’s proportional hazards modeling (PHM). The parametric approaches with baseline Weibull hazard functions and time independent covariates are considered, and the influence of operating environment factors on this model is analyzed. The outputs represent a significant difference in the required spare parts estimation when considering or ignoring the influence of the relevant system operating environment. The difference is significant in the sense of spare parts forecasting and inventory management which can enhance the parts and consequently machine availability, leading to economical operation and savings.

  • 48.
    Mahmood, Yasser Ahmed
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Operation, Maintenance and Acoustics.
    Ahmadi, Alireza
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Operation, Maintenance and Acoustics.
    Karim, Ramin
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Operation, Maintenance and Acoustics.
    Kumar, Uday
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Operation, Maintenance and Acoustics.
    Verma, Ajint
    Stord/Haugesund University College, Haugesund.
    Fransson, Niklas
    Trafikverket.
    Comparison of frequency converter outages: a case study on Swedish TPS system2012Conference paper (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.

  • 49.
    Ahmadi, Alireza
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Operation, Maintenance and Acoustics.
    Gupta, Suprakash
    Banaras Hindu University, Varanasi.
    Ghodrati, Behzad
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Operation, Maintenance and Acoustics.
    Galar, Diego
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Operation, Maintenance and Acoustics.
    Estimation of economic consequences of aircraft system failures2012In: Communications in Dependability and Quality Management, ISSN 1450-7196, Vol. 15, no 1, p. 39-49Article in journal (Refereed)
    Abstract [en]

    A large portion of the direct and indirect aircraft operational costs stems from the consequences of decisions made during the maintenance program development. Decision on maintenance task selection for non-safety category of failures, is based on the cost effectiveness, in which the cost of preventive maintenance should be less than the costs associated with the corrective action and failure consequence. Although the assessment of the direct cost for preventive and corrective maintenance is quiet straightforward, however quantification and estimation of the cost associated with the consequence of failure is a great challenge. This is due to a long list of contributory factors and lack of adequate data regarding the cost headings. This study attempts to estimate the economic consequences of aircraft system failures which lead to a technical delay. The paper considers financial losses, mostly due to the additional unexpected costs related to the flight crew, passengers, aircraft itself, ramp and airport, when one of the cost headings, e.g. the pre-fixed crew cost is known. The experience of the field experts has been used following a pairwise comparison technique to compare the cost headings, and to estimate the contribution of each one to the total cost of a delay. The study shows that the proposed model can be a tool to assess the cost of failure consequences in aircraft operation, when there is a limited data and information regarding the cost headings.

  • 50.
    Garmabaki, Amir Soleimani
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Operation, Maintenance and Acoustics.
    Ahmadi, Alireza
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Operation, Maintenance and Acoustics.
    Kapur, P.K
    Amity University.
    Kumar, Uday
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Operation, Maintenance and Acoustics.
    Predicting software reliability in a fuzzy-random field environment2012Conference paper (Refereed)
    Abstract [en]

    The development of a new complex software or industrial system produces a series of prototypes that may contain faults during the processes, including development, design, and production. Therefore, during the early stages of prototyping complex systems, reliability often faces a major challenge in meeting the desired requirements level. For these reasons, a typical reliability improvement process is carried out in order to achieve a specific software/system reliability level. Incorrect estimation of reliability could lead to an inappropriate system design and implementation of incorrect maintenance policies.Many software reliability models have been proposed to help software developers and managers to assess the level of the reliability and estimation of the development cost. Among these software reliability models, Non-Homogenous Poisson Process (NHPP) based models have been successfully applied to model the software failure processes, and predict the number of software failures. NHPP has been used also to determine “time to stop testing” and release the software.Usually, the testing-development phase has been carried out in a given control environment. However, the product will be used in different operating environment by different end-users, which is unknown to the developer. The operating environment may range from a very clean one up to a harsh environment. These uncertain operating environments will impact to the reliability and performance of the software which may differ from the testing phase reliability. Hence the effect of environmental factors on reliability should be considered for estimation of the operational phase reliability. In fact the effect of environment on reliability has a fuzzy nature and quiet random. On the other hand, it is well known that the probability distribution and its parameters cannot be univocally defined. To overcome this problem, the fuzzy probabilistic theory may be used in the processing of stochastic parameters, taking into account their fuzzy nature. In fact, the fuzzy random effects of the field environments can be captured by a unit-free environmental factor. Based on the fuzzy probability distribution and its properties, we can define a fuzzy reliability function. The aim of this paper is to introduce a Fuzzy random field environment (FRFE) reliability model that covers both the testing and operating phases in the development cycle. The proposed model is based on Weibull distribution. It should be noted that the testing costs is one the major concern in software/system development. Several researcher investigated software/System release policies to minimize development cost while satisfying a reliability objective. Although the length of testing phase directly relates to the number of errors removed, but leads to a significant financial loss by increasing testing cost and delay in delivery. Further, releasing software in the market before reaching its desired level of reliability (which is fixed by the manager) may increase the maintenance cost during operational phase as well as create risk to lose future market.For a critical software system, the penalty costs resulting from the software failures are much more significant than the software development costs themselves. Therefore, the total software/ system cost should consist of not only the development costs, but also the penalty costs resulting from the software failure in operational phase. For software developers and managers, the following questions need to be answered (1) How to allocate the resources to ensure the on-time delivery of a software product? (2) When to stop testing and release the software from current software testing activities? (3) Is the software product really reliable in field? To answer the above mentioned questions, the paper proposes a cost function using proposed FRFE reliability model, to determine the optimal release policies.

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