706 research outputs found
Optimizing a Multi-State Cold-Standby System with Multiple Vacations in the Repair and Loss of Units
A complex multi-state redundant system with preventive maintenance subject to multiple
events is considered. The online unit can undergo several types of failure: both internal and those
provoked by external shocks. Multiple degradation levels are assumed as both internal and external.
Degradation levels are observed by random inspections and, if they are major, the unit goes to a
repair facility where preventive maintenance is carried out. This repair facility is composed of a single
repairperson governed by a multiple vacation policy. This policy is set up according to the operational
number of units. Two types of task can be performed by the repairperson, corrective repair and
preventive maintenance. The times embedded in the system are phase type distributed and the
model is built by using Markovian Arrival Processes with marked arrivals. Multiple performance
measures besides the transient and stationary distribution are worked out through matrix-analytic
methods. This methodology enables us to express the main results and the global development in
a matrix-algorithmic form. To optimize the model, costs and rewards are included. A numerical
example shows the versatility of the model
Stochastic Analysis of Two Non-identical Unit Parallel System Incorporating Waiting Time and Preventive Maintenance
The reliability of two non-identical unit’s parallel system with two kinds of failures common cause failure and partial failures is inspected. Moreover, the preventive maintenance and waiting time to repair, a significant aspect of reliability analysis, has also been incorporated. The proposed system is assumed to a function properly if at least one of the unit is in operate mode. The system goes for preventive maintenance at random apaches. Supplementary variable technique and Laplace transform have used for solution. Our results are compared with the previous results to observe the effect of preventive maintenance and failure rates on system performance
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A review of asset management literature on multi-asset systems
This article gives an overview of the literature on asset management for multi-unit systems with an emphasis on two multi-asset categories: fleet (a system of homogeneous assets) and portfolio (a system of heterogeneous assets). As asset systems become more complicated, researchers have employed different terms to refer to their specific problems. With an
objective to facilitate readers in searching conducive studies to their interests, this paper establishes a novel classification scheme for multi-unit systems in accordance with essential features such as diversity of assets and intervention options. Moreover, discerning differences in characteristics between cross-component and cross-asset interactions, we select three types of potential multi-component dependencies (performance, stochastic, and resource) and extend their notions to be applicable to multi-asset systems. The investigation into these dependencies enables the identification of problems that could exist in real industrial settings
but are yet to be determined in academia. Ultimately, we delve into modelling approaches adopted by previous researchers. This comprehensive information allows us to offer the insights into the current trends in multi-asset maintenance. We expect that the output of this review paper will not only stress research gaps on multi-asset systems, but more importantly
help systematise future studies on this aspect
Optimal maintenance of multi-component systems: a review
In this article we give an overview of the literature on multi-component maintenance optimization. We focus on work appearing since the 1991 survey "A survey of maintenance models for multi-unit systems" by Cho and Parlar. This paper builds forth on the review article by Dekker et al. (1996), which focusses on economic dependence, and the survey of maintenance policies by Wang (2002), in which some group maintenance and some opportunistic maintenance policies are considered. Our classification scheme is primarily based on the dependence between components (stochastic, structural or economic). Next, we also classify the papers on the basis of the planning aspect (short-term vs long-term), the grouping of maintenance activities (either grouping preventive or corrective maintenance, or opportunistic grouping) and the optimization approach used (heuristic, policy classes or exact algorithms). Finally, we pay attention to the applications of the models.literature review;economic dependence;failure interaction;maintenance policies;grouping maintenance;multi-component systems;opportunistic maintenance;maintencance optimization;structural dependence
Profitability, reliability and condition based monitoring of LNG floating platforms: a review
The efficiency and profitability of Floating, Production, Storage and Offloading platform (FPSO) terminals depends on various factors such as LNG liquefaction process type, system reliability and maintenance approach. This review is organized along the following research questions: (i) what are the economic benefit of FPSO and how does the liquefaction process type affect its profitability profile?, (ii) how to improve the reliability of the liquefaction system as key section? and finally (iii) what are the major CBM techniques applied on FPSO. The paper concluded the literature and identified the research shortcomings in order to improve profitability, efficiency and availability of FPSOs
PERFORMANCE EVALUATION MODELING OF PRE-TREATMENT UNIT IN GAS PROCESSING PLANT
This paper presents a report for Final Year Project (FYP). The title of the research project is Performance Evaluation Modeling of Pre-Treatment Unit (PTU) in Gas Processing Plant which under manufacturing from mechanical field. The project is conducted at one of Gas Processing Plant which is Pre-treatment Unit (PTU). The project started with identification of critical component for PTU, construction of reliability block diagram (RBD) and reliability analysis based on RBD model. During the completion of the project, the researcher has been assisted by reliability engineer from PETRONAS Gas Berhad in verifying the RBD model. The outcome of this project is a model of reliability that could be used by plant management to evaluate the current reliability of the PTU. Besides, this research can analyze whether that equipment has achieved target plant reliability and identify the sub-component that reduces the overall reliability of the system. This paper includes introduction, literature review, methodology, result and discussion and conclusion. The report will include introduction, literature review and theory, methodology, result and discussion, conclusion and recommendation and reference
Improving the profitability, availability and condition monitoring of FPSO terminals
The main focus of this study is to improve the profitability, availability and condition monitoring of Liquefied Natural Gas (LNG) Floating Production Storage and Offloading platforms (FPSOs). Propane pre-cooled, mixed refrigerant (C3MR) liquefaction is the key process in the production of LNG on FPSOs. LNG liquefaction system equipment has the highest failure rates among the other FPSO equipment, and thus the highest maintenance cost. Improvements in the profitability, availability and condition monitoring were made in two ways: firstly, by making recommendations for the use of redundancy in order to improve system reliability (and hence availability); and secondly, by developing an effective condition-monitoring algorithm that can be used as part of a condition-based maintenance system.
C3MR liquefaction system reliability modelling was undertaken using the time-dependent Markov approach. Four different system options were studied, with varying degrees of redundancy. The results of the reliability analysis indicated that the introduction of a standby liquefaction system could be the best option for liquefaction plants in terms of reliability, availability and profitability; this is because the annual profits of medium-sized FPSOs (3MTPA) were estimated to increase by approximately US1,190 million to US500/ton) in 2013 and 2014.
Typically, centrifugal turbines, compressors and blowers are the main items of equipment in LNG liquefaction plants. Because centrifugal equipment tops the FPSO equipment failure list, a Condition Monitoring (CM) system for such equipment was proposed and tested to reduce maintenance and shutdown costs, and also to reduce flaring. The proposed CM system was based on a novel FFT-based segmentation, feature selection and fault identification algorithm.
A 20 HP industrial air compressor system with a rotational speed of 15,650 RPM was utilised to experimentally emulate five different typical centrifugal equipment machine conditions in the laboratory; this involved training and testing the proposed algorithm with a total of 105 datasets. The fault diagnosis performance of the algorithm was compared with other methods, namely standard FFT classifiers and Neural Network. A sensitivity analysis was performed in order to determine the effect of the time length and position of the signals on the diagnostic performance of the proposed fault identification algorithm. The algorithm was also checked for its ability to identify machine degradation using datasets for which the algorithm was not trained. Moreover, a characterisation table that prioritises the different fault detection techniques and signal features for the diagnosis of centrifugal equipment faults, was introduced to determine the best fault identification technique and signal feature.
The results suggested that the proposed automated feature selection and fault identification algorithm is effective and competitive as it yielded a fault identification performance of 100% in 3.5 seconds only in comparison to 57.2 seconds for NN. The sensitivity analysis showed that the algorithm is robust as its fault identification performance was affected by neither the time length nor the position of signals. The characterisation study demonstrated the effectiveness of the AE spectral feature technique over the fault identification techniques and signal features tested in the course of diagnosing centrifugal equipment faults. Moreover, the algorithm performed well in the identification of machine degradation.
In summary, the results of this study indicate that the proposed two-pronged approach has the potential to yield a highly reliable LNG liquefaction system with significantly improved availability and profitability profiles
A coloured Petri net framework for modelling aircraft fleet maintenance
The aircraft fleet maintenance organisation is responsible for keeping aircraft in a safe, efficient operating condition. Through optimising the use of maintenance resources and the implementation of maintenance activities, fleet maintenance management aims to maximise fleet performance by, for example, ensuring there is minimal deviation from the planned operational schedule,that the number of unexpected failures is minimised or that maintenance cost is kept at a minimum. To obtain overall fleet performance, the performance of individual aircraft must first be known. The calculation of aircraft performance requires an accurate model of the fleet operation and maintenance processes. This paper aims to introduce a framework that can be used to build aircraft fleet maintenance models. A variety of CPN (coloured Petri nets) models are established to represent fleet maintenance activities and maintenance management, as well as the factors that have a significant impact on fleet maintenance including fleet operation, aircraft failure logic and component failure processes. Such CPN models provide an ideal structured framework for Monte Carlo simulation analysis, within which calculations can be performed in order to determine numerous fleet reliability and maintenance performance measures
Maintenance and marginal cost analysis of a two-unit cold standby system
Ankara : Department of Industrial Engineering and the Institute of Engineering and Sciences of Bilkent University, 1997.Thesis (Master's) -- Bilkent University, 1997.Includes bibliographical references leaves 97-102.The Marginal Cost Analysis (MCA) of maintenance policies is a concept
gaining interest in the recent years. This approach, due to Berg, has been
categorized as an Economics Oriented Approach, as different from the classical
probability centered approach. The MCA has been successfully applied to the
Age Replacement and the Block Replacement policies, and was shown to be
flexible enough to permit extensions and generalizations.
In this thesis, we apply the MCA approach to a more complex model. We
consider a two-unit cold standby system. Upon failure of the working unit in
the time interval [0,T) the unit is replaced by the standby unit if available.
If the standby unit is in repair, the system is down, and a downtime cost is
incurred. The item inspected at time T is in one of two states: “good” , or
“critical” . The good unit continues operation, whereas a unit in critical state
is sent to repair. The switchover is immediate. We derive and compare the
marginal cost function as well as the long-run cost per unit time function.Hamdaoui, ChokriM.S
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