1,721,066 research outputs found
Rolling Bearing Diagnostics by means of EMD-Based Independent Component Analysis on Vibration and Acoustic Data
No full textA new laser vibrometry-based 2D selective intensity method for source identification in reverberant fields: part II. Application to an aircraft cabin
No full textThe selective intensity technique is a powerful tool for the localization of acoustic sources and
for the identification of the structural contribution to the acoustic emission. In practice, the
selective intensity method is based on simultaneous measurements of acoustic intensity, by
means of a couple of matched microphones, and structural vibration of the emitting object. In
this paper high spatial density multi-point vibration data, acquired by using a scanning laser
Doppler vibrometer, have been used for the first time. Therefore, by applying the selective
intensity algorithm, the contribution of a large number of structural sources to the acoustic
field radiated by the vibrating object can be estimated. The selective intensity represents the
distribution of the acoustic monopole sources on the emitting surface, as if each monopole
acted separately from the others. This innovative selective intensity approach can be very
helpful when the measurement is performed on large panels in highly reverberating
environments, such as aircraft cabins. In this case the separation of the direct acoustic field
(radiated by the vibrating panels of the fuselage) and the reverberant one is difficult by
traditional techniques. The work shown in this paper is the application of part of the results of
the European project CREDO (Cabin Noise Reduction by Experimental and Numerical
Design Optimization) carried out within the framework of the EU. Therefore the aim of this
paper is to illustrate a real application of the method to the interior acoustic characterization of
an Alenia Aeronautica ATR42 ground test facility, Alenia Aeronautica being a partner of the
CREDO project
A new laser vibrometry-based 2D selective intensity method for source identification in reverberant fields: part I. Development of the technique and preliminary validation
No full textThe selective intensity technique is a powerful tool for the localization of acoustic sources and
for the identification of the structural contribution to the acoustic emission. In practice, the
selective intensity method is based on simultaneous measurements of acoustic intensity, by
means of a couple of matched microphones, and structural vibration of the emitting object. In
this paper high spatial density multi-point vibration data, acquired by using a scanning laser
Doppler vibrometer, have been used for the first time. Therefore, by applying the selective
intensity algorithm, the contribution of a large number of structural sources to the acoustic
field radiated by the vibrating object can be estimated. The selective intensity represents the
distribution of the acoustic monopole sources on the emitting surface, as if each monopole
acted separately from the others. This innovative selective intensity approach can be very
helpful when the measurement is performed on large panels in highly reverberating
environments, such as aircraft cabins. In this case the separation of the direct acoustic field
(radiated by the vibrating panels of the fuselage) and the reverberant one is difficult by
traditional techniques. The first aim of this work is to develop and validate the technique in
reverberating environments where the location and the quantification of each source are
difficult by traditional techniques. The reverberant field is clearly challenging also for the
proposed technique, affecting the achievable accuracy, mainly due to the fact that coherence
between radiated and reverberated fields is often unknown and may be relevant. Secondly, the
applicability of the method to real cases is demonstrated. A laboratory test case has been
developed using a large wooden panel. The measurement is performed both in anechoic
environment and under simulated reverberating conditions, for testing the ability of the
selective intensity method to remove the reverberation
On the use of Lagrange Multiplier State-Space Substructuring in dynamic substructuring analysis
Full text linkIn this article, the formulation of Lagrange Multiplier State-Space Substructuring (LM-SSS) is presented and extended to directly compute coupled displacement and velocity state-space models. The LM-SSS method is applied to couple and decouple state-space models established in the modal domain. Moreover, it is used together with tailored post-processing procedures to eliminate the redundant states originated from the coupling and decoupling operations. This specific formulation of the LM-SSS approach made it possible to develop a tailored coupling form, named Unconstrained Coupling Form (UCF). UCF just requires the computation of a nullspace and does not rely on the selection of a subspace from a nullspace. An explanation of all the steps in order to compute state-space models without redundant states originated from the coupling and decoupling procedures is also given. By exploiting a numerical example, LM-SSS was compared with the Lagrange Multiplier Frequency Based Substructuring (LM-FBS) approach, which is currently widely recognized as a reference approach. This was done both in terms of: a) coupled FRFs derived by coupling the state-space models of two substructures and b) decoupled FRFs derived by decoupling the state-space model of a component from the coupled model. As for the first validation, LM-SSS showed to be suitable to compute minimal order coupled models and UCF turned out to have similar performance as other coupling forms already presented to the scientific community. As for the decoupling task, the FRFs derived from the LM-SSS approach turned out to perfectly match those obtained by LM-FBS. Moreover, it was also demonstrated that the elimination of the redundant states originated from the decoupling operation was correctly performed. As final validation, the approaches discussed were exploited on an experimental substructuring application. LM-SSS resulted to be a reliable SSS technique to perform coupling and decoupling operations with state-space models estimated from measured FRFs as well as to provide accurate minimal-order models
Exploiting Continuous Scanning Laser Doppler Vibrometry in timing belt dynamic characterisation
No full textUnderwater image pre-processing for photogrammetric application
No full textThis work describes a new method for correcting underwater images acquired under natural illumination condition and targeted to photogrammetry for 3D object reconstruction. In particular, a comparison between the new approach and a previous one from literature is presented. The new approach demonstrated to be a feasible and robust solution to improve quality, colour and contrast in underwater imaging by means of a three-step procedure. The focus of the paper is on 3D reconstruction of small-sized corals in shallow water. The colour of pre-processed images, with a visible green-blue colour cast, are enhanced and the higher images quality eases the whole object reconstruction acquired in a poor visible scene. The higher performance of the proposed method is experimentally demonstrated
Envelope Cepstrum Based Method for Rolling Bearing Diagnostics
No full textThe task of identifying a faulty roller element bearing has been so far faced through the use of envelope analysis. As it is well known the main issue linked to such approach is related to the definition of the optimal band-pass filter which can enhance the defect characteristics when the vibration signal is affected by severe noise. The Kurtogram has overcome this limit by letting the optimal band-pass filter be selected in a semi-automatic way, that is by exploiting the potentials of the Spectral Kurtosis. This paper aims at presenting an alternative algorithm which is able to cope with faults characterised by an impulsive-periodic nature. It is well known that faults characterised by periodic-impulsive nature are identifiable by means of cepstral analysis while damages inducing modulation effects are usually assessed via envelope processing. The presented algorithm combine two instruments, since it is based on the Fourier spectrum of the cepstrum squared envelope. Such spectrum allows to isolate the modulation effect by centring the modulating frequency around the DC component. In this paper the algorithm is applied to both synthesized data reproducing typical damaged rolling bearing signals and experimental data. Results achieved by exploiting the proposed algorithm are compared to the ones obtained by applying conventional envelope analysis based on Spectral Kurtosis
Recovery of mode shapes from Continuous Scanning Laser Doppler Vibration Data: a Mode Matching Frequency Domain Approach
No full textExploiting Continuous Scanning Laser Doppler Vibrometry and Wavelet Processing for Damage Detection
No full textMode matching of Continuous Scanning Laser Doppler Vibration data in the frequency domain
No full textApplications as structural diagnostics, condition monitoring and fatigue testing are requiring the development of vibration tests characterized by reduced testing time, fine spatial resolution and high Signal to Noise Ratio (SNR). In this context, Continuous Scanning Laser Doppler Vibrometry (CSLDV) can have a great impact as a substitute of classic Discrete Scanning Laser Doppler Vibrometry (SLDV). In fact, CSLDV makes it possible to measure the target structural vibration much faster and with finer spatial resolution than SLDV, as well keeping an acceptable level of SNR. CSLDV joins together the spatial and time information, because the vibration datum obtained from the laser, which continuously scans (over time and space) the structure under test, is modulated by the Operational Deflection Shape (ODS) excited during the experiment. This results in a spectrum characterized by sideband patterns uniquely associated to the ODS excited. However, the current drawback in fully exploiting CSLDV in everyday testing is related to the necessity of being managed by an expert operator who knows how to extract meaningful information from data measured. This paper proposes a procedure which aims to automatize the information extraction process from CSLDV signals, in order to ease the utilization of CSLDV in vibration laboratories. The idea starts from a simple observation: if the mode shapes of the structure under test are known a priori, e.g. from a numerical model, an analytical formulation or previous measurements, as is the case for fatigue tests, it is possible to settle a procedure that searches for similarities between those known mode shapes (the candidate mode shapes) and ODSs that actually modulate the signal measured. This procedure can therefore be considered a pattern matching technique that is able to identify the resonance frequency related to each ODS and the mode shapes that better match with the ODSs excited. A detailed description of the algorithm is given in this paper. Moreover, the procedure is analyzed in order to discuss its sensitivity to noise, overlapping of resonance frequencies (close modes situation) and ODS complexity. The application of the approach to experimental data is also discussed
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