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- Unmanned aerial vehicle safety assessment modelling through petri NetsPublication . Gonçalves, P.; Sobral, José; Ferreira, L. A.Currently we are facing an increasing trend of use of Unmanned Aerial Vehicles (UAV) in various activities both civilian and military. Although there is no legal framework for the operation of these systems, regulatory authorities require the demonstration of a safety level equivalent to manned aircraft. It is known the high vulnerability of the UAV not only to unexpected failures of their systems but also to the environment. The purpose of this paper is to present a safety assessment process modelling of a UAV by Petri Nets, that can be accepted by certifying bodies, considering the recommendations of STANAG 4671 UAV Airworthiness Requirements Specification (USAR) for analysis of fault conditions that lead to the most feared events. It is intended to show through the use of Petri Nets the frequency that the UAV enters the identified states described as most feared events; the ability of the UAV to react after being in a fault situation to the inputs of the operating crew in order to enhance trust and to facilitate the operation authorization process in UAV operations. The results obtained allowed to identify and to define critical areas and corrective actions that will lead to an acceptable level of risk for the regulatory authority.
- Maintenance of technical installations in buildings based on asset life cycle analysisPublication . Sobral, José; Gaspar, D.; Almeida, N.This paper shows the importance of maintenance in buildings regarding the availability, reliability, maintainability, safety, and costs (RAMS+C) of the physical assets that make part of technical installations, taking into consideration all their life cycle. Some important standards related to asset management and maintenance are referred and some methodologies are described helping to understand the potential application to buildings of such tools that are often used in the industrial field. As fire is one of the major concerns when analyzing all potential risks in buildings and as it is common to install fire protection systems in a way to prevent fire occurrence or to protect buildings against such events, the paper also presents an illustrative example related to a fire extinguishing system showing the applicability of the referred concepts and methodologies and the importance of its maintenance. Some studies state that when facing a fire about one-third of the safety systems do not work properly just because of the lack of inspection, test, or maintenance of such systems.
- Development of a tool for selection and acquisition of medical devices based on the analytic hierarchy processPublication . Oliveira, V.; Sobral, José; Ribeiro, M. MargaridaThe existence of a tool to select and acquire Medical Devices is fundamental to manage the Life Cycle (LC) of Medical Devices (MD). The objective of this work is to create a structured, organized and optimized application to use on the selection and acquisition stage of a tender process, in order to help those responsible for the decision make. In addition it will turn the process exempt and transparent. The methodology is based on a defined hierarchical multi criteria decision making approach, the Analytic Hierarchy Process (AHP) optimizing and validating all the requirements stated in a tender process and ensuring, free from human manipulation, that the best option will be chosen. The demonstrative study is applied to Computed Tomography (CT), with the aim of applying the methodology in the selection and acquisition of the best choice between four alternatives. The developed tool includes some weights that are assigned to the established criteria and sub-criteria according to the present and future needs of each healthcare provider. It has been proven that the price is not the only criteria, and perhaps not the most important. All technical and operational requirements as maintenance costs, availability, image quality, safety, and client satisfaction must also be included in the decision making process.
- Establishment of optimal physical assets inspection frequency based on risk principlesPublication . Sobral, José; Ferreira, LuísRisk Based Inspection (RBI) is a risk methodology used as the basis for prioritizing and managing the efforts for an inspection program allowing the allocation of resources to provide a higher level of coverage on physical assets with higher risk. The main goal of RBI is to increase equipment availability while improving or maintaining the accepted level of risk. This paper presents the concept of risk, risk analysis and RBI methodology and shows an approach to determine the optimal inspection frequency for physical assets based on the potential risk and mainly on the quantification of the probability of failure. It makes use of some assumptions in a structured decision making process. The proposed methodology allows an optimization of inspection intervals deciding when the first inspection must be performed as well as the subsequent intervals of inspection. A demonstrative example is also presented to illustrate the application of the proposed methodology.
- Fire safety barrier availability analysisPublication . Sobral, José; Carlos Guedes SoaresThis paper shows several ways to analyse the performance of a safety barrier, depending on the objective to be achieved and present a method to analyse binary components usually present on sensor systems of safety barriers. An application example of a water-based fire system is presented and the Probability of Failure on Demand (PFD) of the sensor system is determined based on the analysis of pressure switches installed in this safety barrier. The knowledge of such information will allow the determination of safety barrier’s availability.
- Reliability database for unmanned aerial vehicles based on morphological analysisPublication . Gonçalves, Paula; Sobral, José; Ferreira, Luis António AndradeThe certification process plays an important role in aircraft safety and operation, assuring a high degree of confidence in accomplishing their objectives. Unfortunately, in the field of Unmanned Aerial Vehicles (UAV), there is not enough information to enable an acceptable decision-making process regarding compliance with certification requirements. To overcome this limitation, a methodology was developed based on morphological analysis principle, taking advantage of the knowledge and behaviour of similar items and affecting them with the necessary corrective factor in accordance to the differences in design, operation and environment. The objective is to establish an initial maintenance program as an important requirement to operate any kind of aircraft. This paper presents the methodology and the obtained results for a UAV under development concerning the establishment of a maintenance program regarding its certification process.
- Preventive maintenance of critical assets based on degradation mechanisms and failure forecastPublication . Sobral, José; Guedes Soares, CarlosWhen dealing with critical physical assets it is very important to monitor some parameters just to observe and predict the potential time to failure and thus establish a preventive maintenance activity avoiding the unwanted failure occurrence and its consequences. According to periodic (or continuous) data gathered along the time concerning selected parameters it is possible to observe tendencies and determine time to failure, assuming a pre-defined value as the critical one, corresponding to asset failure. The present paper deals with this type of condition monitoring outlining the importance of predicting time to failure and illustrating it with an example where the evolution of a degradation parameter on time for several similar assets is observed and, based on that, the time to failure is determined, allowing to establish the right moment for maintenance for these type of assets operating in these conditions.
- Assessment of the adequacy of safety barriers to hazardsPublication . Sobral, José; Guedes Soares, CarlosThe assessment of safety barriers performance is often achieved through tests or inspections in order to determine their availability or probability of failure on demand (PFD). The ultimate objective of these activities is to observe if the safety barrier is operational and to detect possible hidden failures. However, sometimes due to error in design or changes performed on the installation, the referred safety barrier is not adequate or no longer suitable to face the current level of risk. In the present paper is made a description of safety barriers as important means concerning risky situations and a methodology to evaluate the adequacy of a safety barrier is proposed. This methodology links the safety integrity level of an assessed safety barrier to the probability of occurrence of the hazardous event that it should protect. There is a pre-selection of the classified dangerous undetected safety function failures that will be used to determine the probability of failure on demand (PFD) and the safety barrier adequacy to a specific risk. It will be also possible to estimate the probability of occurrence of a hazardous situation corresponding to the simultaneity of the initiating hazardous event and the safety barrier fault (when a demand occurs).
- Increasing availability through maintainability growth using partial Multi Criteria Decision Making (pMCDM)Publication . Sobral, José; Ferreira, L. A.In the last decades considerations about equipments' availability became an important issue, as well as its dependence on components characteristics such as reliability and maintainability. This is particularly of outstanding importance if one is dealing with high risk industrial equipments, where these factors play an important and fundamental role in risk management when safety or huge economic values are in discussion. As availability is a function of reliability, maintainability, and maintenance support activities, the main goal is to improve one or more of these factors. This paper intends to show how maintainability can influence availability and present a methodology to select the most important attributes for maintainability using a partial Multi Criteria Decision Making (pMCDM). Improvements in maintainability can be analyzed assuming it as a probability related with a restore probability density function [g(t)].
- Review of condition-based maintenance strategies for offshore wind energyPublication . Kang, Jichuan; Sobral, José; Guedes Soares, CarlosThe existing maintenance strategies of offshore wind energy are reviewed including the specific aspects of condition-based maintenance, focusing on three primary phases, namely, condition monitoring, fault diagnosis and prognosis, and maintenance optimization. Relevant academic research and industrial applications are identified and summarized. The state of art, capabilities, and constraints of condition-based maintenance are analyzed. The presented research demonstrates that the intelligent-based approach has become a promising solution for condition recognition, and an integrated data platform for offshore wind farms is significant to optimize the maintenance activities.