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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.
- 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)].
- Development of unmanned aerial vehicles maintenance strategy under an asset management frameworkPublication . Gonçalves, P.; Sobral, José; Ferreira, L. A.Many organizations in a large number of countries all around the world are now awaking for a new reality concerning potential applications for the usage of unmanned aerial vehicles (UAV) or unmanned aerial systems (UAS). What was initially strictly applied for military purposes or pure private entertainment has now widespread for other purposes as for example for book or pizza delivery to customers. In manned commercial and military aircraft the MSG (Maintenance Steering Group) philosophy is usually followed and is the root of all inspection schedules in a process starting before an aircraft enters service. However, for the UAV (or UAS), as a system, there are not yet such procedures and each operator establishes the needed requirements on the development stage. The question is how to integrate this type of equipment in an asset management framework as presented in the PAS 55 or the recent ISO 55000. The objective of this paper is to show an exemple of the development of a UAV where these issues are discussed and some proposals to integrate them on an asset management framework regarding the design for effectiveness and design for safety are made on an early stage of an asset engineering process.
- Availability of fire pumping systems under periodic inspectionPublication . Sobral, José; Ferreira, L. A.Fire pumping systems are often used for firefighting in the majority of buildings, can they be residential, commercial, industrial or any other type. These systems are responsible for the needed water flow and pressure on manual or automatic devices installed for building protection purposes. Thus, it is very important to assure their availability when an undesirable fire event occurs. This paper focuses fire pumping systems' availability when they are submitted to regular periodic inspections or tests. These inspections or tests are performed to observe the system behavior and detect potential hidden failures of some component or subsystem. The methodology proposed in this paper is focused in the first stage on the analysis of the probability of failure on demand of critical equipment and analyzing the probability of success of this important stage. It is also shown the influence of inspection or tests frequency on the desired availability of the fire pumping system.