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International audience; The City Lightweight and Innovative Cab (CLIC) project was a scientific collaboration gathering public and private organizations. The aim was to propose an innovative lighten truck cab, where a high strength steel was used. As long as it could affect directly the acoustic environment of the cab, it was necessary to be able to simulate the vibroacoustic behavior of the truck cab in the mid frequency range. The dissipative treatments used for noise and vibration control such as viscoelastic patches and acoustic absorbing materials must then be taken into account in the problem. A process based on the SmEdA (Statistical modal Energy distribution Analysis) method was developed and is presented in this paper. SmEdA allows us substructuring the global problem, to study the interaction between the floor and the interior cavity. The process consists in building finite element models (FEM) of each subsystem (floor, internal cavity), including the dissipative material (damping layer, poroelastic material). Standard modal FEM calculations are then performed for each uncoupled subsystem. From the spatial mode shapes, and the modal strain -kinetic energies, the modal loss factors of both subsystems are estimated. Finally, the pressure levels inside the cavity are deduced from the resolution of the SmEdA equations. To validate this process, a truck cabin has been excited mechanically on a rail of the floor and the pressure levels at different positions inside the cabin were measured for different configurations of dissipative treatment. Comparisons between SmEdA and experimental results allows us to assess the accuracy of the proposed method.

International audience; In the challenge of reducing the weight of the vehicle structures, a particular focus has to be done on the interior noise. Indeed, the weight reduction of the structure often implies an increase of the noise in the cabin.To maintain a constant acoustic performance, acoustic packages often have to be added, the challenge being that the weight of the acoustic materials added remains lower than the weight saved in the structure.In today’s engineering world, numerical simulation is the primary tool to assess the vibro-acoustic behavior of the vehicle during the design phase. To tackle the challenge of weight reduction, it is necessary to simulate accurately the vibro-acoustic response of the structure including the acoustic treatments.This paper presents the validation of a simulation method for the vibro-acoustic response of a truck cabin, taking into account the effect of acoustic treatments, in the frequency range [0-200 Hz].The method combined a modal scheme for the structure and the cavity with a physical scheme for the acoustic treatment (porous materials).The model consists in a truck cabin with its cavity and five acoustic treatments (three floormats, the headliner and the rear trim panel). A measurement campaign is performed to get reference NTFs, VTFs and local inertances. The model without any treatments is first correlated. The noise reduction given by each treatment alone as well as grouped together is simulated. The comparisons between the simulated and measured results show good agreement both in term of spectrum and amplitude. Although some discrepancies in the low frequency range remain unexplained, the method is considered as validated

International audience; The separation of combustion and mechanical contributions in diesel engine signals can be achieved by using Wiener filtering. The idea is to estimate in operation the transfer functions between cylinder pressure and response signals, accelerometers or microphones. This operation is particularly tricky because of the necessity to observe the response signals on very short time windows (a fraction of cycle) to isolate the contributions of each cylinder. Moreover, several mechanical excitations are occurring at the same time than the combustions, which cannot be removed by using windowing. These mechanical excitations are partly coherent with the combustion, generating a bias on estimated transfer functions. It has been shown in preceding works that a way of lowering significantly this bias is to work on the random parts of signals. The aim and the originality of this contribution is to show that the differences between transfer functions obtained from raw signals and from their random parts can be used for diagnosis purpose. This difference has indeed a physical interpretation, and can be used to improve our understanding concerning the source contributions and their transfer paths. These developments are illustrated by experimental data obtained on several diesel engines.

The experimental estimation of frequency response functions characterizing SISO linear systems is a well established topic. Several estimators are defined in the literature, each estimator being optimal depending upon the assumptions with respect to the balance of noise between the input and output of the system. H1 and H2 have to be used in case of presence of noise on output and input, respectively. The HV or Hs estimator is chosen if input and output are assumed to have equivalent SNR. These estimators are also established for MIMO linear systems, with additional difficulties due to the necessity of inversing cross spectral matrices. A transmissibility function is generally defined as a linear relationship between two outputs of a linear system. For MIMO systems, transmissibilities are not defined by the system only, it also depends on the input quantities. It is however possible to define a transmissibility matrix between two sets of outputs that is, under some assumptions, uniquely defined. This approach is especially the base of Operational Transfer Path analysis, an engineering method benefiting of a strong research effort in the last few years. This paper deals with the use of the application of MIMO system estimators to the experimental assessment of transmissibility matrices. Transmissibility matrices are generally estimated using a H1 like approach in the literature. The possibility of using H2 and Hs is presented in this work, from the theoretical point of view and with numerical and practical illustrations. ispartof: Mechanical Systems and Signal Processing vol:43 issue:1 pages:237-245 status: published

International audience

Operational transfer path analysis (OTPA) is a diagnosis method aiming to identify and rank noise transmission paths in dynamic systems. The particularity of the method is to require no preliminary acquisition of a transfer matrix between excitation and response dofs, as it is the case for classical TPA approaches. OTPA is based on the identification of a transmissibility matrix between some input and output responses measured for various operating conditions. The first difficulty of the method concerns the definition of this transmissibility matrix, from either a theoretical or experimental point of view. The second difficulty is the use of this matrix for diagnosis purposes, requiring some assumptions leading to potential misunderstandings. Theoretical aspects of the method are firstly discussed in this work. Secondly, an experimental validation is carried out on an academic test setup, and OTPA results are compared to the classical TPA approach. ispartof: pages:1-1 ispartof: pages:1-1 ispartof: Acoustics 2012 location:Nantes, France date:23 Apr - 27 Apr 2012 status: published

The experimental estimation of frequency response functions characterizing SISO linear systems is a well established topic. Several estimators are defined in the literature, each estimator being optimal depending upon the assumptions with respect to the balance of noise between the input and output of the system. H1 and H2 have to be used in case of presence of noise on output and input, respectively. The HV or Hs estimator is chosen if input and output are assumed to have equivalent SNR. These estimators are also established for MIMO linear systems, with additional difficulties due to the necessity of inversing cross spectral matrices. A transmissibility function is generally defined as a linear relationship between two outputs of a linear system. For SIMO systems, transmissibility functions are uniquely defined. The Hs estimator is thus advised if both outputs are of equivalent SNR. In the case of MIMO systems, transmissibility functions are no more defined by the system only, it also depends on the input quantities. It is however possible to define a transmissibility matrix between two sets of outputs that is, under some assumptions, uniquely defined. This approach is especially the base of Operational Transfer Path analysis, an engineering method benefiting of a strong research effort in the last few years. This paper deals with the use of the application of MIMO system estimators to the experimental assessment of transmissibility matrices. Transmissibility matrices are generally estimated using a H1 like approach in the literature. The possibility of using H2 and Hs is presented in this work, from the theoretical point of view and with a numerical illustration. ispartof: pages:3563-3569 ispartof: PROCEEDINGS OF INTERNATIONAL CONFERENCE ON NOISE AND VIBRATION ENGINEERING (ISMA2012) / INTERNATIONAL CONFERENCE ON UNCERTAINTY IN STRUCTURAL DYNAMICS (USD2012) vol:5 pages:3563-3569 ispartof: ISMA2012 location:Leuven date:17 Sep - 19 Sep 2012 status: published

Operational Transfer Path Analysis (OTPA) is very attractive from a practical point of view, as it not requires an expensive measurement campaign in which transfer functions are measured, as is the case in the traditional Transfer Path Analysis (TPA). Instead, transmissibilities are measured from operational data, making the method relatively cheap in terms of measurement efforts. In practice, however, a lot of difficulties have to be overcome in order to obtain reliable path estimates. In this paper the Operational Transfer Path Analysis (OTPA) technique is applied to a small gearbox. Laboratory experiments are presented, discussing the use of singular value decomposition to determine the number of physical transmission paths involved, the development of verification checks, and finally the application of OTPA to estimate the strengths of the transmission paths. A comparison with the classical Transfer Path Analysis (TPA) will be included as well. Shortcomings of both the OTPA and TPA method are discussed and conclusions are drawn from the experiments. ispartof: pages:1-1 ispartof: pages:1-1 ispartof: Acoustics 2012 location:Nantes, France date:23 Apr - 27 Apr 2012 status: published

Colloque avec actes et comité de lecture. Internationale.; International audience; L'objet de cette communication est d'illustrer l'applicabilité de certaines méthodes dites ‘de cohérences' au diagnostic vibro-acoustique d‘un moteur d'automobile. Après un rappel des outils d'analyse specrale existant dans la bibliographie, nous présenterons une méthodologie originale permettant d'optimiser le diagnostic lorsque l'objet étudié a un comportement vibro-acoustique complexe d'un point de vue statistique. Le potentiel et l'efficacité de cette approche seront ensuite illustrés par deux applications expérimentales : l'analyse vibro-acoustique d'un moteur essence à l'arrêt sollicité par une source maîtrisée puis l'analyse du même moteur en fonctionnement.

International audience; The City Lightweight and Innovative Cab (CLIC) project is a scientific collaboration gathering public and private organizations. The aim is to propose an innovative lighten truck cab, where a high strength steel is used. As long as it could affect directly the acoustic environment of the cab, it is necessary to be able to simulate the vibroacoustic behavior of a truck cab in the mid frequency range. SmEdA (Statistical modal Energy distribution Analysis) method allows us substructuring the global problem, to study the interaction between the floor and the interior cavity. The process consists in building finite element models (FEM) of each subsystem (floor, internal cavity), including the dissipative material (damping layer, poroelastic material). Standard modal FEM calculations are then performed for each uncoupled subsystem. From the spatial mode shapes, and the modal strain and kinetic energies, the modal loss factors of both subsystems are estimated. Finally, the pressure levels inside the cavity are deduced from the resolution of the SmEdA equations. This process allows us taking into account the dissipative energy effects. To validate it, the cab is excited at the truck frame links, and the pressure levels on the driver’s ears are compared between numerical and experimental results.

International audience; In the context of aeronautics, automotive and construction applications the design of lightened multilayer plates with optimized vibroacoustical damping and isolation performances remains a major industrial challenge and a hot topic of research. This paper focuses on the vibrational behavior of three-layer composites plates in broad-band frequency range. Several aspects are studied through measurement techniques and analytical modeling of two sandwich systems: symmetrical steel/polymer/steel and nonsymmetrical steel/polymer/aluminum plates. Contactless measurements of the velocity field made using a scanning laser vibrometer allow estimating the equivalent single layer complex rigidity in the mid/high frequency ranges. Coupled with low/mid frequency estimations obtained with a high-resolution modal analysis method, the frequency dependent equivalent Young’s modulus and equivalent loss factors of the two composites plates are finally identified for the whole [0-5 kHz] band. The results are in very good agreement with an equivalent single layer analytical modeling based on wave propagation analysis. The comparison with this model allows identifying the frequency dependent complex modulus of the polymer core layer through inverse resolution. Dynamical mechanical analysis measurements are also performed on the polymer layer alone to compare with the values obtained through inverse method. Again, a good agreement between these two estimations over the broad-band frequency range demonstrates the validity of the approach.

L'objet de cette communication est d'illustrer l'applicabilité de certaines méthodes dites "de cohérences" au diagnostic vibro-acoustique d'un moteur d'automobile. Après un rappel des outils d'analyse specrale existant dans la bibliographie, nous présenterons une méthodologie originale permettant d'optimiser le diagnostic lorsque l'objet étudié a un comportement vibro-acoustique complexe d'un point de vue statistique. Le potentiel et l'efficacité de cette approche seront ensuite illustrés par deux applications expérimentales : l'analyse vibro-acoustique d'un moteur essence à l'arrêt sollicité par une source maîtrisée puis l'analyse du même moteur en fonctionnement.

International audience

National audience; L'objet de cette communication est d'illustrer l'applicabilité de certaines méthodes dites ‘de cohérences' au diagnostic vibro-acoustique d'un moteur d'automobile. Après un rappel des outils d'analyse specrale existant dans la bibliographie, nous présenterons une méthodologie originale permettant d'optimiser le diagnostic lorsque l'objet étudié a un comportement vibro-acoustique complexe d'un point de vue statistique. Le potentiel et l'efficacité de cette approche seront ensuite illustrés par deux applications expérimentales : l'analyse vibro-acoustique d'un moteur essence à l'arrêt sollicité par une source maîtrisée puis l'analyse du même moteur en fonctionnement. ResumeEN : The object of this communication is to illustrate the applicability of coherence methods to the vibroacoustic diagnosis of a gasoline engine. Methods of partial, multiple or virtual coherences are useful tools based on traditional approaches of signal processing and are known and applied since several decades. We will first of all present a methodology based on coherence approaches, using several original indicators and tools to optimize the diagnosis. The potential and the effectiveness of this approach will be then illustrated by an experimental application: the vibroacoustic analysis of a gasoline engine.