Search results for "Reliability engineering"
showing 10 items of 224 documents
Reconfiguration: a key to handle exceptions and performance deteriorations in manufacturing operations
2005
During a manufacturing operation, exceptions may occur dynamically and unpredictably. Their occurrence may lead to the degradation of system performance or, in the worst case scenario may interrupt the production process by causing errors in the schedule plan. This paper classifies three families of exceptions: (1) out-of-order events such as machine breakdowns, (2) operational out-of-ordinary events such as rush orders and (3) deteriorations of manufacturing resource performance such as reductions of machines' utilization. In all cases, in order to maintain an adequate level of system performance, it is necessary to detect exceptions, to diagnose them quickly and to recover them by taking …
A Knowledge-Based System for the Automatic Generation of Plant Shutdown and Startup Schedules
1988
Abstract When the shutdown of a plant, or part of it, has been decided as consequence of a major fault, the generation of a safe shutdown schedule may be, for large and complex plants, a very difficult and delicate task. The same problem may be found when the plant must be restarted after the fault has been repaired, for the generation of a start-up schedule. The use of a knowledge-based system appears to be a suitable answer to this problem, allowing a high level of safety and a very fast generation process. The paper examines the process knowledge that needs to be included in such a knowledge-based system and proposes some knowledge representation forms that appear suitable for the task t…
Handling stakeholder uncertain judgments in strategic transport service analyses
2013
Abstract The quality level of services has to be constantly controlled, especially under conditions of competition increasing and limited resources. However, considering that service performance analyses are based on stakeholders' judgments, they can be characterized by possible uncertainties related to incompleteness for partial ignorance, imprecision for subjectivity and even vagueness. Therefore, under these conditions, unreliable results can be obtained by widely used service analysis methodologies. In the present paper, a methodology based on a recent extension of the SERVQUAL model, and that uses in combined manner the fuzzy set theory and the analytic hierarchy process method is prop…
Stochastic Fatigue Models for Efficient Planning Inspections in Service of Aircraft Structures
2008
For important fatigue-sensitive structures of aircraft whose breakdowns cause serious accidents, it is required to keep their reliability extremely high. In this paper, we discuss inspection strategies for such important structures against fatigue failure. The focus is on the case when there are fatiguecracks unexpectedly detected in a fleet of aircraft within a warranty period (prior to the first inspection). The paper examines this case and proposes stochastic models for prediction of fatigue-crack growth to determine appropriate inspections intervals. We also do not assume known parameters of the underlying distributions, and the estimation of that is incorporated into the analysis and d…
Inspection Policies in Service of Fatigued Aircraft Structures
2011
Fatigue is one of the most important problems of aircraft arising from their nature as multiple-component structures, subjected to random dynamic loads. For guaranteeing safety, the structural life ceiling limits of the fleet aircraft are defined from three distinct approaches: Safe-Life, Fail-Safe, and Damage Tolerance approaches. The common objectives to define fleet aircraft lives by the three approaches are to ensure safety while at the same time reducing total ownership costs. In this paper, the damage tolerance approach is considered and the focus is on the inspection scheme with decreasing intervals between inspections. The paper proposes an analysis methodology to determine appropri…
ADC based measurements: Identification of the parameters for the uncertainty evaluation
2009
In the last years, many Authors have dealt with the uncertainty evaluation of the measurement performed by using an analog-to-digital converter, proposing different approach to analyze the uncertainty propagation. In all these studies, it is clearly pointed out that starting from the manufacturer specifications is the least expensive, the least time consuming and, often, the most accurate way to assess the uncertainties. However, the Authors, which have proposed methodologies for the uncertainty assessment, use different parameters as starting point. One of the main reasons which has caused this situation is the coexistent of various Standards concerning the characterization of the analog-t…
Monitoring and energy performance assessment of an advanced DEC HVAC system in Morocco
2017
This work addresses the energy performance of a solar Desiccant and Evaporative Cooling (DEC) system working with the freescoo technology. Freescoo is an innovative solar air conditioning concept for ventilation, cooling, dehumidification and heating of buildings in residential and tertiary sectors. The monitoring of the system started in November 2016 and will continue until the end of 2017. Energy performances are evaluated according to the monitoring procedure for solar cooling systems developed by the Task 38 and 48 of the International Energy Agency experts. The analysis based on monitoring data shows that, for typical operating conditions in cooling mode, the electricity saving in com…
Reliability and Fabrication of Molds for Nanoimprinting
2010
During the last decade there has been a growing attention to nanoscaled materials and to the related technologies to produce them. The problems to overcome in the manufacturing of these kinds of items increase dramatically on decreasing the dimension of the devices. In this sense, the scientific research has been strongly stimulated to try to improve and optimize all the critical issues. One of the most attractive fields in nanomanufacturing is related to nanoimprinting, i.e. to the possibility to transfer a nanoscaled pattern from a mold to another substrate. In this technology, among the others, there are two main critical steps: the preparation of a good mold and the use of a correct rel…
A Technical Approach to the Energy Blockchain in Microgrids
2018
The present paper considers some technical issues related to the “energy blockchain” paradigm applied to microgrids. In particular, what appears from the study is that the superposition of energy transactions in a microgrid creates a variation of the power losses in all the branches of the microgrid. Traditional power losses allocation in distribution systems takes into account only generators while, in this paper, a real-time attribution of power losses to each transaction involving one generator and one load node is done by defining some suitable indices. Besides, the presence of P–V nodes increases the level of reactive flows and provides a more complex technical perspective. For this re…
Radiation Hardness Assurance Through System-Level Testing: Risk Acceptance, Facility Requirements, Test Methodology, and Data Exploitation
2021
International audience; Functional verification schemes at a level different from component-level testing are emerging as a cost-effective tool for those space systems for which the risk associated with a lower level of assurance can be accepted. Despite the promising potential, system-level radiation testing can be applied to the functional verification of systems under restricted intrinsic boundaries. Most of them are related to the use of hadrons as opposed to heavy ions. Hadrons are preferred for the irradiation of any bulky system, in general, because of their deeper penetration capabilities. General guidelines about the test preparation and procedure for a high-level radiation test ar…