2,294 research outputs found
Production of identified and unidentified charged hadrons in Pb--Pb collisions at \sqrt{s_{\rm NN}}~5.02~TeV
In late 2015, the ALICE collaboration recorded data from Pb--Pb collisions at
the unprecedented energy of \sqrt{s_{\rm NN}}~5.02~TeV. The transverse-momentum
() spectra of pions, kaons and protons are presented. The evolution
of the particle ratios as a function of collision energy and centrality is
discussed. The ratio between -integrated particle yields are
measured and compared to different collision energies as well as smaller
collision systems. For the study of energy loss mechanisms in the QCD medium at
high transverse momenta, the nuclear modification factors () are
computed and compared with results obtained at lower energy
Advanced Diagnostics of Position Sensors for the Actuation Systems of High-Speed Tilting Trains
Trains tilting permits a train to travel at a high speed while maintaining an acceptable passenger ride quality with respect to the lateral acceleration, and the consequent lateral force, received by the passengers when the train travels on a curved track at a speed in excess of the balance speed built into the curve geometry. The tilting of a train carbody is performed by a control and actuation system which operates as a closed servoloop accepting the commands from the train control system, generating the torque necessary to tilt the carbody with respect to the bogie and measuring the tilt angle to close the control loop. Measurement of the tilt angle of each train vehicle is performed by two sensors located in the front and rear part of the vehicle. Since a correct tilt angle measurement is vital for the system operation and for ensuring a safe ride, in case of discrepancy between the signals of the two tilt angle sensors of any vehicle, the tilting operation is disabled and the train speed is reduced. An innovative tilt angle sensors health management system is herein presented that makes intelligent use of all available information to allow detection of malfunctioning of an individual tilt angle sensor, thereby enabling a continued operation of the tilting system and a high speed travel after a sensor failure occurs
PID performance of the ALICE-TOF detector in Run 2
In these proceedings we report on the status of the ALICE Time-Of-Flight
(TOF) detector. The running performance of the Run 1 (2009-2013) and Run 2
(2015-present) data taking campaigns are compared. The Particle IDentification
(PID) capabilities of the detector are presented and discussed in the light of
the improved detector calibration that allowed to reach a timing resolution of
56 ps
Prognostic and Health Management System for Fly-by-wire Electro-hydraulic Servo Actuators for Detection and Tracking of Actuator Faults ☆
Abstract Maintenance of flight control actuation systems is currently performed on a scheduled basis, however air fleet operators and component manufacturers are willing to move from scheduled maintenance to Condition Based Maintenance (CBM) in order to reduce maintenance costs and improve aircraft dispatchability. Prognostics and Health Management (PHM) systems are a critical part of CBM and are perceived as a breakthrough technology to effectively respond to an urgent and critical need to improve the readiness, availability, reliability, safety and maintainability of aerospace vehicles. This paper presents the results of an ongoing research activity focused on the development of a PHM system for fly-by-wire Electro-Hydraulic Servo Actuators (EHSA) without adding new sensors. The PHM system is being developed with the objective of detecting the most common faults, according to a failure mode effects and criticality analysis (FMECA). The paper describes in particular the tools used for detection and tracking of internal leakage faults of the hydraulic actuator, which is one of the most common faults of hydraulic servo-actuators in service, and for predicting its remaining useful life (RUL). The research work has been supported by the development of a nonlinear model for a reference EHSA, that has been implemented using physical equations and system parameters, taking into account environmental condition and disturbances. The model was validated through tests runs on a flight control actuator of a civil aircraft. Simulations are performed in nominal conditions and with progressive injection of degradation to verify the PHM algorithm. The performances of the PHM algorithms are evaluated by means of proper metrics
A powerful tool for automatic validation of a Modelica library for electromechanical actuation systems for primary flight controls
Validation process aims at verifying requirements, specifications and behaviour of the final product. The procedure, outlined in this paper, has been defined to assess the library developed during ACTUATION2015 research project whose components are focused on the simulation of electromechanical actuation systems applied to aeronautic field. Therefore the validation procedure is presented with references to the experience and knowledge acquired during that project. A Modelica based validation tool has been developed to automate the process and manage the components testing independently from their physical domain (e.g. Electrical, Mechanical, etc). The functions composing the validation library are discussed in the paper and significant examples are presented
A powerful tool for automatic validation of a Modelica library for electromechanical actuation systems for primary flight controls
Validation process aims at verifying requirements, specifications and behaviour of the final product. The procedure, outlined in this paper, has been defined to assess the library developed during ACTUATION2015 research project whose components are focused on the simulation of electromechanical actuation systems applied to aeronautic field. Therefore the validation procedure is presented with references to the experience and knowledge acquired during that project. A Modelica based validation tool has been developed to automate the process and manage the components testing independently from their physical domain (e.g. Electrical, Mechanical, etc). The functions composing the validation library are discussed in the paper and significant examples are presented
Performance Evaluation of a Prognostic Framework for Electro-Hydraulic Actuators for Stability Control Augmentation Systems with Different Sensors Suites
Stability Control Augmentation Systems (SCAS) are widely adopted to enhance the flight stability of rotary-wing aircraft operating in difficult aerodynamic conditions, such as low altitude missions, stationary flight nearby vertical walls or in presence of heavy gusts. Such systems are based upon small electro-hydraulic servosystems controlled in position through a dedicated servovalve. The SCAS operates with limited authority over the main control linkage translating the pilot input in the movement of the main flight control actuator. Being critical for the operability of the helicopter, the definition of a Prognostics and Health Management (PHM) framework for the SCAS systems would provide significant advantages, such as better risk mitigation, improved availability, and a reduction in the occurrences of unpredicted failures which still represent one of the most known downsides of helicopters due to their very severe operational environment. Since SCAS actuators are usually equipped with a low number of sensors, it is at the present time unclear whether a fully realized PHM system can be prepared without resorting to the introduction of additional sensors. This paper deals with this subject evaluating the performances of a fault diagnosis tool operating considering different sensors suite (traditional and with additional sensors), and different PHM strategies, using in-flight data or their combination with dedicated pre-flight checks to cover the most common failure modes. The analysis is then completed with an evaluation of the prognostic capabilities of the proposed strategies, highlighting benefits and limitations of the proposed solutions
Design of a PHM system for electro-mechanical flight controls: a roadmap from preliminary analyses to iron-bird validation
Literature on PHM is focused on research dedicated to the definition of new algorithms to achieve better failures prognosis or earlier and more accurate fault diagnosis, but lacks of examples on the design of novel PHM frameworks and the practical issues related with their implementation. This paper describes a roadmap for the design of a novel Prognostics and Health Management system while making reference to a real-case scenario applied to electro-mechanical actuators for flight control systems
Preliminary study towards the definition of a PHM framework for the hydraulic system of a fly-by-wire helicopter
On-board hydraulic systems are tasked to provide a number
of critical functions to ensure the in-flight operability of
rotary-wings vehicles; the hydraulic system is needed to
supply power to the flight control actuators and a number of
other utilities, as well as to condition the hydraulic fluid,
under a wide range of possible in-service conditions. Being
a flight-critical system, the definition of a Prognostics and
Health Management framework would provide significant
advantages to the users, such as better risk mitigation and
improved availability. Moreover, a significant reduction in
the occurrences of unpredicted failures, one of the more
known downsides of helicopters, is expected. A preliminary
analysis on the effects of the inception and progression of
several degradation types is the first step assess the
feasibility of a PHM system for new platforms, and which
failure modes are more likely to be observed. Further, since
several key components are frequently provided by different
suppliers to the airframer, this preliminary analysis would
allow to better assess if an Integrated Vehicle Health
Management approach, integrating signals coming from
different components, could be beneficial. To pursue this
study, a complete model of the hydraulic system for a flyby-wire helicopter has been prepared. Then, an in-depth
simulation campaign was pursued with the aim of studying
the interactions between different failure modes, the effects
that the propagating degradations have on the system
performances and which signals can be used to define a
robust set of features. The paper introduces the case-study
under analysis, a general configuration for fly-by-wire
helicopters, presenting the most prominent peculiarities of
the system and the effect of such peculiarities on the
definition of health monitoring schemes. The model is then
used to describe the behavior of the system under nominal
and degraded conditions is introduced. Between the possible
failure modes, the interaction between wear in several
mechanical components and the clogging of the hydraulic
lines filters was chosen as the subject of this study;
motivations are provided and the degradation model
described in detail. Hence, results of a wide-ranging
simulation campaign are presented, where the time-domain
response of the system is used to guide in the definition of a
proper set of features able to characterize the selected fault
cases. Selected features are presented, chosen according to
significant metrics such as correlation with the simulated
degradations, signal-to-noise ratio and accuracy. Two
different approaches with a varying degree of integration
between system signals are proposed and compared.
Prognostics is then pursued through well-known particle
filter algorithms. The analysis provides promising results on
the capability of successfully detecting, isolating and
identifying the selected fault mode; laying the foundations
for further and more comprehensive studies on the subject
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