| 1. |
- Hosseini Yazdi, Morteza, et al.
(författare)
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Experimental Study of Rolling Element Bearing Failure Pattern Based on Vibration Growth Process
- 2019
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Ingår i: Proceedings of the 29th European Safety and Reliability Conference (ESREL). - Singapore : Research Publishing Services. ; , s. 1179-1186
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Konferensbidrag (refereegranskat)abstract
- Rolling-element bearing (REB) Failure is one of the most common failure in rotary machines in industry. Therefore, this concern draws attention to the concept of diagnostic and the prediction of REB failure. The efficacy of vibration analysis in this area has led many researchers to focus on this topic in recent decades. Defective bearings such as fatigue, surface roughness, and corrosion can lead to disastrous accidents. Therefore, providing an algorithm for the detection and classification of bearing defects is valuable and useful. The prediction of the bearing's lifetime is important to ensure the planned production in an industrial unit. In this paper, different models for performance degradation of mechanical parts and signal processing techniques are presented for fault detection in ball bearings. Then, the failure modes of bearings and their relations to the final fault using the vibration signals are discussed. Thereafter, by examining the experimental data of the PRONOSTIA test and using the root mean square of signals, the degradation performance of the bearings and the corresponding failure patterns are obtained. In addition, using the results of frequency analysis via Envelope method, the initiated/existed defects on the bearings of each test are detected. In the application of this method, selection of appropriate frequency band for filtering the vibration signal is important. By analyzing the results, it can be concluded that any ball bearing failure pattern does not necessarily refer to a specific defect. Also, the proper area for filtering a signal in envelope analysis is not necessarily a resonance region, but it should also check several areas to select the best area.
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| 2. |
- Hosseini Yazdi, Morteza, et al.
(författare)
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Prognostic of rolling element bearings based on early-stage developing faults
- 2020
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Ingår i: International Journal of COMADEM. - England : COMADEM International. - 1363-7681. ; 23:1, s. 55-60
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Tidskriftsartikel (refereegranskat)abstract
- Rolling-element bearing (REB) failure is one of the general damages in rotating machinery. In this manner, the correct prediction of remaining useful life (RUL) of REB is a crucial challenge to move forward the unwavering quality of the machines. One of the main difficulties in implementing data-driven methods for RUL prediction is to choose proper features that represent real damage progression. In this article, by using the outcomes of frequency analysis through the Envelope method, the initiated/existed defects on the ball bearings are identified. Also, new features based on developing faults of ball bearings is recommended to estimate RUL. Early-stage faults in ball bearings usually include inner race, outer race, ball and cage failing. These features represent the sharing of each failure mode in failure. By calculating the severity of any failure mode, the contribution of each mode can be considered as the input to an artificial neural network. Also, the wavelet transform is used to choose an appropriate frequency band for filtering the vibration signal. The laboratory data of the ball bearing accelerated life (PROGNOSTIA) are used to confirm the method. To random changes reduction in recorded vibration data, which is primary in real-life experiments, a pre-processing calculation is connected to the raw data. The results obtained by using new features shows a more accurate estimation of the bearings' RUL and enhanced prediction capability of the proposed method. Also, results indicate that if the contribution of each failure mode is considered as the input of the neural network, then RUL is predicted more precisely.
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| 3. |
- Ahmadi, Alireza, et al.
(författare)
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Estimation of economic consequences of aircraft system failures
- 2012
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Ingår i: Communications in Dependability and Quality Management. - 1450-7196. ; 15:1, s. 39-49
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 4. |
- Ahmadi, Alireza, et al.
(författare)
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Optimum Failure Finding Inspection During Extended Operation Life
- 2013
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Konferensbidrag (refereegranskat)abstract
- 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
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| 5. |
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| 6. |
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| 7. |
- Ahmadi, Alireza, et al.
(författare)
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Risk based maintenance decision for periodically tested repairable components subject to hidden failure
- 2011
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Ingår i: Proceedings of 2nd International Conference on Reliability, Safety and Hazard - ICRESH 2010. - Piscataway, NJ : IEEE Communications Society. - 9781424483440 - 9781424483433 ; , s. 197-204
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Konferensbidrag (refereegranskat)abstract
- This paper aims to develop a graphical method to facilitate the identification of risk and cost of postponement of restoration for repairable components which are periodically tested and whose failures are hidden, i.e, are detectable by inspection or upon demand. The paper focuses on the items which are under aging, however, the methodology is flexible to implement for any aging pattern. The paper considers Failure Finding Inspection (FFI) with restoration actions (FFI+Res), for the “safety effect” categories of hidden failures. As-bad-as-old (ABAO) inspection effectiveness and as-good-as-new (AGAN) restoration effectiveness are considered. In case of repair due to findings by inspection, as-bad-as-old repair effectiveness is considered. The graphical methodology proposed in this paper considers inspection and repair times, as well as the costs associated with accident, inspection, repair, and restoration, and takes into account the opportunity losses due to the maintenance downtime. The analytical approach is based on the Mean Fractional Dead Time. In the case of an operational limit, when it is not possible to remove the unit for restoration, or one needs to use the unit longer than the expected operating time, the paper introduces an approach to analyzing the possibility of and conditions for providing an extension to the restoration interval that satisfies the risk constraints and the business requirements at the same time.
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| 8. |
- Ahmadzadeh, Farzaneh, et al.
(författare)
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Mean Residual Life Estimation Considering Operating Environment
- 2012
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Konferensbidrag (refereegranskat)abstract
- The cost of maintenance of mechanized and automated mining systems is too high necessitating efforts to enhance the effectiveness of maintenance systems and organization. For effective maintenance planning, it is important to have a good understanding of the reliability and availability characteristics of the systems. This is essential for determining the Mean Residual Life (MRL) of systems so that maintenance tasks could be planned effectively. In this paper we used the statistical approach to estimate MRL. A Weibull proportional hazard model (PHM) with time-independent covariates was considered for modelling of the hazard function so that operating environment could be integrated in the reliability analysis. Methods are presented for calculating the conditional reliability function and computing the MRL as a function of the current conditions to guarantee the desired output. The model is verified and validated using data from the Hydraulic system of an LHD fleet from a Swedish mine. The results obtained from the analysis is useful to estimate the remaining useful life of such system which can be subsequently used for effective maintenance planning and help controlling unplanned stoppages of highly mechanized and automated systems.
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| 9. |
- Al-Chalabi, Hussan S., et al.
(författare)
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Downtime analysis of drilling machines and suggestions for improvements
- 2014
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Ingår i: Journal of Quality in Maintenance Engineering. - 1355-2511 .- 1758-7832. ; 20:4, s. 306-332
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Tidskriftsartikel (refereegranskat)abstract
- Purpose– The purpose of this paper is to analyse and compare the downtime of four drilling machines used in two underground mines in Sweden. The downtime of these machines was compared to show what problems affect downtime and which strategies should be applied to reduce it.Design/methodology/approach– The study collects failure data from a two-year period for four drilling machines and performs reliability analysis. It also performs downtime analysis utilising a log-log diagram with a confidence interval.Findings– There are notable differences in the downtime of most of the studied components for all machines. The hoses and feeder have relatively high downtime. Depending on their downtime, the significant components can be ranked in three groups. The downtime of the studied components is due to reliability problems. The study suggests the need to improve the reliability of critical components to reduce the downtime of drilling machines.Originality/value– The method of analysing the downtime, identifying dominant factors and the interval estimation for the downtime, has never been studied on drilling machines. The research proposed in this paper provides a general method to link downtime analysis with potential component improvement. To increase the statistical accuracy; four case studies was performed in two different mines with completely different working environment and ore properties. Using the above method showed which components need to be improved and suggestions for improvement was proposed and will be implemented accordingly.
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| 10. |
- Allahkarami, Zeynab, et al.
(författare)
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Identifying the mixed effects of unobserved and observed risk factors on the reliability of mining hauling system
- 2021
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Ingår i: International Journal of Systems Assurance Engineering and Management. - : Springer. - 0975-6809 .- 0976-4348. ; 12:2, s. 281-289
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Tidskriftsartikel (refereegranskat)abstract
- Reliability is widely used as a performance indicator of mining equipment to achieve a cost-effective maintenance plan. Reliability is a function of time as well as environmental and operational factors. Applying an adequate model by taking into account the mentioned factors is vital to ensure an accurate estimation of reliability characteristics. The aim of this study is to investigate the application of mixed frailty model to describe both observed and unobserved heterogeneity in reliability analysis of mining equipment. The capability of the model is assessed using field data from a fleet of dump trucks in an open-pit mine. The results indicate that the proposed model is superior to the traditional Cox model when data are heterogeneous. The results also show that the operator's skill and road conditions have a significant effect on the reliability of dump trucks.
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