HAL is a multi-disciplinary open access archive for the deposit and dissemination of scientific r... more HAL is a multi-disciplinary open access archive for the deposit and dissemination of scientific research documents, whether they are published or not. The documents may come from teaching and research institutions in France or abroad, or from public or private research centers. L'archive ouverte pluridisciplinaire HAL, est destinée au dépôt et à la diffusion de documents scientifiques de niveau recherche, publiés ou non, émanant des établissements d'enseignement et de recherche français ou étrangers, des laboratoires publics ou privés.
In the challenge of reducing the weight of the vehicle structures, a particular focus has to be d... more 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 [0-200Hz]. 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.
Vibro-acoustic simulation in the mid-frequency range is of interest for automotive and truck cons... more Vibro-acoustic simulation in the mid-frequency range is of interest for automotive and truck constructors. The dissipative treatments used for noise and vibration control such as viscoelastic patches and acoustic absorbing materials must be taken into account in the problem. The Statistical modal Energy distribution Analysis (SmEdA) model consists in extending Statistical Energy Analysis (SEA) to the mid-frequency range by establishing power balance equations between the modes of the different subsystems. The modal basis of uncoupled-subsystems that can be estimated by the finite element method in the midfrequency range is used as input data. SmEdA was originally developed by considering constant modal damping factors for each subsystem. However, this means that it cannot describe the local distribution of dissipative materials. To overcome this issue, a methodology is proposed here to take into account the effect of these materials. This methodology is based on the finite element models of the subsystems that include well-known homogenized material models of dissipative treatments. The Galerkin method with subsystem normal modes is used to estimate the modal damping loss factors. Cross-modal coupling terms which appear in the formulation due to the dissipative materials are assumed to be negligible. An approximation of the energy sharing between the subsystems damped by
The introduction of a thermo-Viscous Fluid (TVF) between two skins, produces a sandwich with high... more The introduction of a thermo-Viscous Fluid (TVF) between two skins, produces a sandwich with high dissipation. This was studied by Hussain and Guyader 1 leading to equivalent material properties depending on skins and fluid core properties. An important result is that contrary to standard sandwich panels with polymers cores, the damping loss factor of such TVF sandwich is constant with frequency. When applying damping treatment on structures, bonded patches are generally used. In this paper the use of TVF sandwich patches on a panel is described through a model of heterogeneous plate, the predicted vibration response of the structure shows an increase of damping due to the patch. Estimation of modal damping loss factors for the plate with TVF sandwich patches are given depending on the patch size and TVF thickness.
Statistical modal Energy distribution Analysis (SmEdA) can be used to model a fluid-structure pro... more Statistical modal Energy distribution Analysis (SmEdA) can be used to model a fluid-structure problem based on modal information of the uncoupled-subsystems. Recently, the method has been extended to include the effect of a dissipative treatment (i.e. damping or absorbing material). In this paper, SmEdA is tested on a steel plate with/without damping treatment coupled to an acoustic cavity: the numerical result of the energy ratio is compared to experimental one. The data are analyzed for a mid-to-high frequency domain (up to 10 kHz in 1/3 octave band). Both subsystem loss factors are experimentally obtained by a high-resolution modal analysis method based on the ESPRIT algorithm applied to impulse responses of the plate and the cavity. Predicting the energy level requires an accurate estimation of subsystem damping levels. The uncertainty on measured loss factors leads to an uncertainty in the energy ratio depending on min/max damping levels of individual modes in a given frequency band. Once min/max damping levels of subsystems are determined, SmEdA is used to compute the upper and lower limits of the subsystem energy ratio. A comparison with experimental results shows that the measurement data fits in between the SmEdA bounds. In this paper, two types of dissipative treatments are studied: i) a viscoelastic patch on the plate (modeled as an equivalent single layer plate) and ii) a porous material inside the cavity (modeled as an equivalent fluid).
An additive damping treatment is an effective tool to control the dynamic response of builtup str... more An additive damping treatment is an effective tool to control the dynamic response of builtup structures, and it is widely utilized through industrial applications. By applying a viscoelastic layer on a given structure, the vibratory energy is dissipated through shear and in-plane motions at the layer interface. Modeling the effect of such a treatment in a complex mechanical system for the mid frequency domain is of interest. Statistical modal Energy distribution Analysis (SmEdA) has been developed as an alternative approach to Statistical Energy Analysis (SEA) for describing subsystems with low modal overlap. This technique is developed from the knowledge of the uncoupled subsystem modes. In this paper, one proposes to extend SmEdA by including the effect of a damping treatment. A damped subsystem consisting of a composite layer is modeled with the equivalent modulus of a single layer, which gives the same transverse displacement as a multi-layered system. The modal loss factor of a partially damped structure is estimated by the Modal Strain Energy method (MSE), and the results are well agreed with the Complex Eigenvalue Method (CEM). Finally, energy transmission between the damped structure and a coupled cavity can be deduced from SmEdA modeling, knowing the modeshapes and modal loss factors of the equivalent single layer and of the cavity. This method is applied for modeling a rectangular plate partially damped with an unconstrained viscoleastic layer coupled to a small acoustic cavity.
HAL is a multi-disciplinary open access archive for the deposit and dissemination of scientific r... more HAL is a multi-disciplinary open access archive for the deposit and dissemination of scientific research documents, whether they are published or not. The documents may come from teaching and research institutions in France or abroad, or from public or private research centers. L'archive ouverte pluridisciplinaire HAL, est destinée au dépôt et à la diffusion de documents scientifiques de niveau recherche, publiés ou non, émanant des établissements d'enseignement et de recherche français ou étrangers, des laboratoires publics ou privés.
In the challenge of reducing the weight of the vehicle structures, a particular focus has to be d... more 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 [0-200Hz]. 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.
Vibro-acoustic simulation in the mid-frequency range is of interest for automotive and truck cons... more Vibro-acoustic simulation in the mid-frequency range is of interest for automotive and truck constructors. The dissipative treatments used for noise and vibration control such as viscoelastic patches and acoustic absorbing materials must be taken into account in the problem. The Statistical modal Energy distribution Analysis (SmEdA) model consists in extending Statistical Energy Analysis (SEA) to the mid-frequency range by establishing power balance equations between the modes of the different subsystems. The modal basis of uncoupled-subsystems that can be estimated by the finite element method in the midfrequency range is used as input data. SmEdA was originally developed by considering constant modal damping factors for each subsystem. However, this means that it cannot describe the local distribution of dissipative materials. To overcome this issue, a methodology is proposed here to take into account the effect of these materials. This methodology is based on the finite element models of the subsystems that include well-known homogenized material models of dissipative treatments. The Galerkin method with subsystem normal modes is used to estimate the modal damping loss factors. Cross-modal coupling terms which appear in the formulation due to the dissipative materials are assumed to be negligible. An approximation of the energy sharing between the subsystems damped by
The introduction of a thermo-Viscous Fluid (TVF) between two skins, produces a sandwich with high... more The introduction of a thermo-Viscous Fluid (TVF) between two skins, produces a sandwich with high dissipation. This was studied by Hussain and Guyader 1 leading to equivalent material properties depending on skins and fluid core properties. An important result is that contrary to standard sandwich panels with polymers cores, the damping loss factor of such TVF sandwich is constant with frequency. When applying damping treatment on structures, bonded patches are generally used. In this paper the use of TVF sandwich patches on a panel is described through a model of heterogeneous plate, the predicted vibration response of the structure shows an increase of damping due to the patch. Estimation of modal damping loss factors for the plate with TVF sandwich patches are given depending on the patch size and TVF thickness.
Statistical modal Energy distribution Analysis (SmEdA) can be used to model a fluid-structure pro... more Statistical modal Energy distribution Analysis (SmEdA) can be used to model a fluid-structure problem based on modal information of the uncoupled-subsystems. Recently, the method has been extended to include the effect of a dissipative treatment (i.e. damping or absorbing material). In this paper, SmEdA is tested on a steel plate with/without damping treatment coupled to an acoustic cavity: the numerical result of the energy ratio is compared to experimental one. The data are analyzed for a mid-to-high frequency domain (up to 10 kHz in 1/3 octave band). Both subsystem loss factors are experimentally obtained by a high-resolution modal analysis method based on the ESPRIT algorithm applied to impulse responses of the plate and the cavity. Predicting the energy level requires an accurate estimation of subsystem damping levels. The uncertainty on measured loss factors leads to an uncertainty in the energy ratio depending on min/max damping levels of individual modes in a given frequency band. Once min/max damping levels of subsystems are determined, SmEdA is used to compute the upper and lower limits of the subsystem energy ratio. A comparison with experimental results shows that the measurement data fits in between the SmEdA bounds. In this paper, two types of dissipative treatments are studied: i) a viscoelastic patch on the plate (modeled as an equivalent single layer plate) and ii) a porous material inside the cavity (modeled as an equivalent fluid).
An additive damping treatment is an effective tool to control the dynamic response of builtup str... more An additive damping treatment is an effective tool to control the dynamic response of builtup structures, and it is widely utilized through industrial applications. By applying a viscoelastic layer on a given structure, the vibratory energy is dissipated through shear and in-plane motions at the layer interface. Modeling the effect of such a treatment in a complex mechanical system for the mid frequency domain is of interest. Statistical modal Energy distribution Analysis (SmEdA) has been developed as an alternative approach to Statistical Energy Analysis (SEA) for describing subsystems with low modal overlap. This technique is developed from the knowledge of the uncoupled subsystem modes. In this paper, one proposes to extend SmEdA by including the effect of a damping treatment. A damped subsystem consisting of a composite layer is modeled with the equivalent modulus of a single layer, which gives the same transverse displacement as a multi-layered system. The modal loss factor of a partially damped structure is estimated by the Modal Strain Energy method (MSE), and the results are well agreed with the Complex Eigenvalue Method (CEM). Finally, energy transmission between the damped structure and a coupled cavity can be deduced from SmEdA modeling, knowing the modeshapes and modal loss factors of the equivalent single layer and of the cavity. This method is applied for modeling a rectangular plate partially damped with an unconstrained viscoleastic layer coupled to a small acoustic cavity.
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Papers by Ha Dong Hwang