196,102 research outputs found
The role of gut hormones in controlling the food intake: what is their role in emerging diseases?
No full textStructural vibration and sound power radiation modelling for a light train wheel
No full textThe noise generating characteristics of a light train wheel has been studied theoretically. Nowadays different approaches using several software tools, present on the market, can be used. This paper shows the different results using two different approaches. One is based on the use of the FEM and BEM methods. The second is based on the well known procedure using the commercial software: TWINS. Both procedures use a FEM model of the wheel. The wheel analysed is a "resilient wheel" in which a visco-elastics layer is located between the type and the web. Particular attention is dedicated to the modelling of the interface between a visco-elastics layer and the two steel parts. The finite elements model is used to calculate the mode shape and the modal masses. The modal damping is predicted by a complex numerical modal analysis of the finite element model in which a material specific damping parameter is used. Experimental modal analysis tests are also executed in order to better identify and confirms the damping values. The FEM modal parameters are used as input in the TWINS software, whose results in terms of global sound power have next been used within a ray tracing noise of the whole vehicle. Comparison of predicted and experimentally measured nose field have been at the end of the activity performed and herein reported
Acoustic characterisation and noise limitation strategies for a modern electrical train
No full textThis paper concerns with the noise characterisation and limitation on a new electrical train that showed, during preliminary operational noise test, an excessive noise emission especially related to the electrical motor operation.
In order to better understand the genesis of such a noise and to subsequently plan effective solutions to reduce the generated overall noise and vibration level it was firstly necessary to understand the vibro-acoustical behaviour of the motor itself, both in terms of eigenmodes and of forced response.
In this paper the experimental modal analysis and the running modes analysis results of the electrical motor are presented and discussed with the aim to design adequate solutions to the problem. A modification of the motor has been proposed in terms of design changes whose experimental results will be discussed in the last part of the paper
Interior active noise control in turbofan aircraft: optimal actuators positioning using dedicated genetic algorithms
No full textInterior active noise control in turbofan aircraft: Optimal actuators positioning using dedicated genetic algorithm
No full textThis paper presents the activities developed by the authors within the first year of the research project named M.E.S.E.M.A. (Magnetoelastic Energy Systems for Even More Electric Aircraft) funded by the European Commission within the 6th Framework Program and coordinated by the "Dipartimento di Ingegneria Aerospaziale" of the University of Naples "Federico II" (DPA). One of the main targets for the MESEMA Consortium consists in reducing the level of disturbance noise in turbofan aircraft; a noise & vibration control system using magnetostrictive actuators has been designed and produced, with the goal of controlling noise & vibrations in a wide band frequency range between 150 - 500 Hz. The environmental noise & vibration excitations was representative of a small/medium turbofan aircraft case. Final results of the task will be represented by a system made up of 30 actuation/sensing devices connected to a system performing control of external disturbances as well as of the devices' intrinsic non linearity. As experimental test article a fuselage mockup of the ATR42/72 aircrafts family has been chosen available at the acoustic laboratory in the Alenia plant; due to its geometry and overall dimensions it well represents a fuselage section of an hypothetic regional jet. Within this paper the authors present most of the numerical activities developed in the project in order to design the actuation system as well as to optimize the location of the control devices. The numerical (finite element) model of the mock-up has been developed, correlated with experimental modal analysis results and updated in order to match the best way possible the experimental reality. This model has then been employed to carry out a deep simulation activity aimed at the evaluation of the required control actuators performances in terms of force spectra as far as their optimal placements for control purposes. In order to select among the many possible set of control actuator configurations an optimisation activity was required. The used optimisation method is based on "genetic" algorithms. For this analysis 126 actuators potential locations were selected on frames or stiffeners of the two middle bays of the mock-up. The authors developed the genetic algorithm code in MATLAB framework. The paper presents in the end the experimental characterization of the control actuators demonstrating how a good correlation between numerical and experimental activities has been achieved. © 2007 by the American Institute of Aeronautics and Astronautics, Inc. All rights reserved
AN OPTIMIZATION PROCESS EXPERIENCE FOR HVACNOISE EMISSION AND FLOWS DISTRIBUTION INSIDE APASSENGER’S TRAIN WAGON
No full textNoise emission from train HVAC systems has become an important factor for passenger
comfort. Consequently, efforts are made during the design phase to minimize noise generation, and
to improve sound quality.
Predictive tools for the fluid dynamics and acoustic behavior of components, subsystems and
whole systems early on in the design phase are therefore desirable. In this paper a combined
Computational Fluid Dynamics (CFD) and Acoustic BEM approach for the prediction of sound
generation and propagation has been used to evaluate and optimize the system performances, with
reference to a new train platform.
As a first step of the activity, preliminary models have been assessed on the basis of design
inputs; results of the simulation process have been demonstrated some lack of performances with
reference the technical specification documents.
A system design modification has so been implemented in the direction of requirement
fulfillment in the respect of design constraints.
Numerical simulation first and experimental measurements later have been demonstrated the
good results of this approach, both in terms of better flows distribution and of noise emission inside
the wagon.
Within the paper, the numerical modeling methods, the numerical results and the
experimental evaluation comparison are presented and discussed
NUMERICAL/EXPERIMENTAL CHARACTERIZATION OF A PIEZOELECTRIC DRIVEN ELECTROMEDICAL DEVICE
No full textThe present work refers to the numerical/experimental characterisation of an electromedical
device, based on piezo actuator technologies, used for dermacosmetic applications.
Special focus was given to the fatigue related problems that have arisen during the operational
life of the device, and which are related to the high frequency dynamic loads to which the
device itself is subjected.
Preliminary studies have indicated a recursive crack faults that characterize, the slim
extremities of the devices (bar); previous test, also put in evidence, that the crack location
generally lies along an operational deflection mode nodal line.
To better understand the physical phenomena at the basis of this circumstance and to design
specific solutions to overcome this problem, a set of numerical and experimental activities
have been planned and performed.
The set of activities may be summarised as follow:
FEM modelling of the bar devices and extraction of eigen-frequencies and modes
FEM modelling of forced response to the piezoelectric excitation and the calculation
of fatigue parameters
Experimental vibrational analysis by the use of scanning laser technique; operational
mode shapes extraction.
It should be noted that the use of the laser technique has permitted the identification of the
high frequency modes and has avoided problems which could arise with accelerometers due
to their dimensions, mass loading effects and limited frequency response.
The results of this program have shown good agreement between the experimental and
numerical values and have identified also the significant influence of the boundary conditions
on the life on the bar.
The study has also identified some possible solutions including the modification of the
material, change of shape, or the use of a different soldering technology [1] [2]
Dimensioni e caratteristiche del lavoro sommerso/irregolare. Sintesi
No full textISFOL, Iadevaia V., Mainardi M., Dimensioni e caratteristiche del lavoro sommerso/irregolare. Sintesi, 2011. Isfol OA: Technical Report. Il documento presenta la sintesi dei risultati di una ricerca sulle caratteristiche distintive e sulle motivazioni del lavoro nero e irregolare nel settore dell’agricoltura. Si è proceduto, in primo luogo, ad una ricostruzione dell’occupazione nel settore dell’agricoltura, realizzata su dati della rilevazione continua sulle forze di lavoro dell’Istat (RCFL 2009). Si è proceduto poi a sviluppare un’analisi sui dati sull'irregolarità del lavoro utilizzando sia i dati Istat che quelli scaturenti dai controlli esercitati dai diversi organismi di vigilanza. L’analisi sui dati dell’irregolarità è stata arricchita di ulteriori elaborazioni statistiche a livello provinciale finalizzate a fornire una griglia di indicatori utili alla definizione dell’approfondimento sul campo e alla individuazione dei casi di studio territoriali. 2011technical report. il documento presenta la sintesi dei risultati di una ricerca sulle caratteristiche distintive e sulle motivazioni del lavoro nero e irregolare nel settore dell’agricoltura. si è proceduto, in primo luogo, ad una ricostruzione dell’occupazione nel settore dell’agricoltura, realizzata su dati della rilevazione continua sulle forze di lavoro dell’istat (rcfl 2009). si è proceduto poi a sviluppare un’analisi sui dati sull'irregolarità del lavoro utilizzando sia i dati istat che quelli scaturenti dai controlli esercitati dai diversi organismi di vigilanza. l’analisi sui dati dell’irregolarità è stata arricchita di ulteriori elaborazioni statistiche a livello provinciale finalizzate a fornire una griglia di indicatori utili alla definizione dell’approfondimento sul campo e alla individuazione dei casi di studio territoriali. 2011 dimensioni e caratteristiche del lavoro sommerso/irregolare. sintesi valeria iadevaia michela mainard
AN INNOVATIVE NUMERICAL APPROACH FOR TRAIN PASS-BY NOISE FORECASTING
No full textThis paper deals with an engineering method for the prediction of vehicle pass-by noise based on a FEM/ BEM exterior acoustic calculation in the frequency domain. The researchers simulate, in a virtual environment, the experimental outdoor pass-by noise measurement. The simulated pass-by noise campaign is synthesized from multiple acoustic transfer functions between a line of virtual microphones located 7.5m on the side of the vehicle and each noise source. A numerical FEM/BEM train bogie acoustic model has been created within the MSC ACTRAN commercial softwares. Wheel-rail rolling noise, engine and powertrain noise acoustic source have been implemented and posi-tioned inside the FEM and BEM model to demonstrate the validity of the proposed methods. The contribu-tion from noise sources, expressed both in terms of sound pressure level and overall value, to the pass-by noise were evaluated up to 5 kHz. The virtual pass-by-noise assessment has been then validated by experi-mental measurement of the complete four coach’s train with respect to different speed regimes
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