ANN tool for impact detection on composite panel for aerospace application

Fleet maintenance and safety aspects represent a strategic aspect in the managing of the modern aircraft fleets. The demand for efficient techniques of system and structure’s monitoring represent so a key aspect in the design of new generation aircraft. This is even more significant for composite structures that can be highly susceptible to delamination of the ply, which is often very difficult to detect externally and can lead to a dramatic reduction of design strength and service life, as a consequence of impact damage. The purpose of the work is the presentation of an innovative application within the Non Destructive Testing field based upon vibration measurements. The aim of the research has been the development of a Non Destructive Test (NDT) which meets most of the mandatory requirements for effective health monitoring systems while, at the same time, reducing as much as possible the complexity of the data analysis algorithm and the experimental acquisition instrumentation

Experimental and Numerical Validation of an Automotive Subsystem through the Employment of FEM/BEM Approaches

Abstract In this paper a deep numerical analysis on an internal combustion engine cover is carried out. A hybrid numerical model has been used to evaluate the acoustic performance of engine cover. The Hybrid model is composed of two numerical models: FE (Finite Element) and BEM (Boundary Element Method) models. The FE model patterns structural system, whilst BEM model patterns fluid environment. The main aim of the present work is to characterize, through the employment of numerical simulation, the acoustic performance of the engine cover by using the NR (Noise Reduction) parameter. The numerical frequency response analysis has been implemented using acoustic impedance experimental data, measured for four different thicknesses of sound proof material forming the cover system. The spectrum of acoustic impedance has been evaluated in near field with a sophisticated probe, pressure-velocity probe (p-v probe). The analysis of the obtained results have highlighted the weaknesses as regards sound attenuation of the cover system and possible further improvements of cover system acoustic performance

An Hybrid FE/SEA Approach for Engine Cover Noise Assessment

In this paper a deep numerical analysis on an internal combustion engine’s cover is carried out. An Hybrid numerical model approach to evaluate the acoustic performance of engine's cover, has been used. The Hybrid model is composed of two numerical models: FE and SEA models. The model FE patterns the structural system, whilst model SEA patterns the acoustic environment. As main excitation an experimental data has been used for two considered engine conditions. The comparison in terms of sound pressure levels between the experimental and FEM/SEA analysis results shows a very good agreement, in the whole investigated frequency range. The obtained results encourage to use the numerical model for further investigations aimed at the improvement of its acoustic performances. The implemented numerical procedure can be applied successfully not only in automotive field but also in all problems where material acoustic performances, is due

Vibro-acoustic response of a turboprop cabin with innovative sidewall viscoelastic treatment

In recent years, it's considerably grown the market demand for increasingly performing and comfortable aircrafts as a new mandatory design target. Among the determining factors for the internal comfort, are included the noise and vibrations, the source of which is detected mainly in the propulsion unit especially in the case of turboprop category: the most significant component of the noise perceived inside a cabin is undoubtedly the blade-passage load exerted by the propeller. Recently were therefore tested techniques, both active and passive, of vibration emission reduction and sound absorption, however the goal remains to find solutions by extremely low-weight and easy to apply on the real mock-up. As known, a damping treatment is typically used to reduce noise coming from fuselage structure vibration under acoustic loading excitation. In such research context, the vibro-acoustic performance of the viscoelastic material for replacing the conventional interior blanket of the fuselage sidewall have been investigated for the well-known higher dissipation capacity and energy storage. Starting from experimental tests by means of different measurement techniques carried out on an innovative foam sample, the dynamic parameters were estimated according to identify suitably the material performance database for further finite element analysis on a turboprop fuselage model. The outcomes achieved have emphasized a significant role of the viscoelastic foam than the standard blanket with respect to the internal sound pressure levels abatement as well as the thermal insulation. The developed foam prototype is also easily integrable with an outer layer ensuring a fully removable embedded solution for the maintenance inspections

Experimental Acoustic Measurements in Far Field and Near Field Conditions: Characterization of a Beauty Engine Cover

Present work focuses on experimental acoustic characterization of an engine beauty cover in far field and near field conditions. Specifically, a comparison between results coming from the two different experimental measurement techniques is presented. Experimental campaign has been carried out on a car engine compartment at different operating conditions, by using on one hand a typical pressure microphone for far field measurements accordingly the related prescribed standards, and on the other hand the more innovative Microflown p-u intensity probe (pressure – particle velocity sensor) for near field measurements. In the latter case, experimental tests have been conducted adopting the Scan & Paint method, based on the acquisition of sound pressure and particle velocity by manually moving the probe across the sound field whilst filming the event with a camera. Differently obtained results have been then analyzed highlighting the peculiarities of each of the two techniques. Finally, evaluating noise emissions with and without cover presence, it has been possible to verify the acoustic performances of the component, identifying a less performing acoustic behavior of the material at some specific frequencies. Hence, future developments could regard the possibility to implement an optimization process through the analysis of different materials and configurations, in order to improve cover acoustic insulation properties at the frequencies of interests

Acoustic optimization of a high-speed train composite sandwich panel based on analytical and experimental Transmission Loss evaluation integrated by FE/Test correlation analysis

Present work purpose is to optimize the acoustic attenuation properties of a composite sandwich panel used for a high-speed train structure, choosing the best panel configuration which allows to improve the performances. Firstly, Nilsson’s analytical formulation for Transmission Loss (TL) evaluation has been implemented and experimentally validated on a typical material used for high-speed railway applications, highlighting the opportunity to use a different material to satisfy the new required design specifications. Different materials and stratifications have been then considered and TL parameter of each configuration have been calculated using Nilsson’s formulation, characterizing acoustic behavior in the frequency domain. Once found the composition which ensures the best compromise between high acoustic insulation and low weight, the panel has been physically realized. Finally, an experimental and a numerical modal analysis have been performed on it. Starting from both FE simulation and impact testing outcomes, a correlation study through the computation of the Modal Assurance Criterion (MAC), has been carried out. A good agreement between numerical and experimental analyses has been found, obtaining a reliable FE model for future improvements

Acoustic Optimization of a High-speed Train Composite Sandwich Panel Based on Analytical and Experimental Transmission Loss Evaluation Integrated by FE/Test Correlation Analysis

Abstract Present work purpose is to optimize the acoustic attenuation properties of a composite sandwich panel used for a high-speed train structure, choosing the best panel configuration which allows to improve the performances. Firstly, Nilsson's analytical formulation for Transmission Loss (TL) evaluation has been implemented and experimentally validated on a typical material used for high-speed railway applications, highlighting the opportunity to use a different material to satisfy the new required design specifications. Different materials and stratifications have been then considered and TL parameter of each configuration have been calculated using Nilsson's formulation, characterizing acoustic behavior in the frequency domain. Once found the composition which ensures the best compromise between high acoustic insulation and low weight, the panel has been physically realized. Finally, an experimental and a numerical modal analysis have been performed on it. Starting from both FE simulation and impact testing outcomes, a correlation study through the computation of the Modal Assurance Criterion (MAC), has been carried out. A good agreement between numerical and experimental analyses has been found, obtaining a reliable FE model for future improvements

Automotive Materials: An Experimental Investigation of an Engine Bay Acoustic Performances

In this work an extensively experimental analysis aimed to verify the sound insulation properties of the engine bay of a commercial passenger car is carried out, evaluating the possibility to adopt different sound absorbing materials, to be applied under engine cover nylon skin, in the place of commonly used polyurethane foams. Experimental tests were performed on the vehicle at different stationary operating conditions, employing typical pressure microphones for far field measurements, according to the related prescribed standards. A limited number of materials has been initially selected through a preliminary analysis, and then employed for creating different engine cover configurations, which were subsequently tested in real engine operating conditions. For a good understanding of the obtained results, an experimental investigation through an innovative in situ impedance method aimed to assess acoustic properties of each considered material has been also performed. Among all the tested materials, only one able to ensure better acoustic performance at mid and high frequencies with respect to the already existing cover configuration, has been finally identified, after considering other selection criteria such as an adequate high temperature resistance and the most cost-effective solution. Future analyses will regard investigations on the use of additional materials, for solving problem in attenuating engine noise also at low frequencies

Experimental vibro-acoustic analysis of the gear rattle induced by multi-harmonic excitation

The paper reports a wide vibro-acoustic experimental investigation of the gear rattle phenomenon induced by multiharmonic excitation. The analysis is performed by using different measurement techniques which allow some of the significant parameters in this type of investigation to be acquired on a specific test rig: the angular rotations of the gears by using encoders; the accelerations obtained from a triaxial accelerometer; the sound pressure level determined by employing both acoustic microphones; the correct evaluation of the acoustic sources by utilizing a p–v sound intensity probe. Performance indices were adopted to compare the dynamic behaviours of the system with respect to some parameters, such as the speed of the pinion, the fluctuations in the speed of the pinion and the lubrication conditions. The results of the comparative analysis show very good agreement between the vibro-acoustic measurements and the results from the encoder-based method; this has helped us to interpret the physical behaviour of the gear pair with respect to the impacts occurring between the teeth during the different phases of the phenomenon. Moreover, the study indicates interesting aspects of the effects of multi-harmonic excitation on the rattle phenomenon, with particular attention to the influence of lubrication on the reduction in the rattle noise

CARATTERIZZAZIONE ACUSTICA DI NAVI IN PORTO

Le sorgenti acustiche portuali sono molte e variegate: tra queste, le navi occupano un posto di primo piano. La caratterizzazione della sorgente nave non è molto trattata in letteratura e presenta aspetti problematici legati alle dimensioni del mezzo ed alla sua complessità impiantistica. Il testo riporta i risultati di una campagna sperimentale condotta nel porto di Napoli su diversi tipi di imbarcazione in condizioni transitorie e stazionarie. L’attività è propedeutica alla formulazione di un modello di propagazione verso le zone abitate che circondano il porto