LMT > Manifestations > *Séminaires du LMT*

Recherche - Valorisation

le 29 novembre 2012

Intervention de Sergio DE ROSA, Professeur à l'Université d'Ingéniérie aérospatiale de Naples, Frédéric II

Extrait de l'intervention

A summary of two approaches as developed and recently defined at pasta-lab will be presented and discussed. Both are related to the possibility to reduce the computational cost of given vibro-acoustic simulations and/or refine the quality of the investigations.

The first approach is related to the possibility of defining similitudes and/or predictive models among structural and structural-acoustic systems. The resulting procedure is named SAMSARA: Similitude and Asymptotic Models for Structural-Acoustic Research and Applications; it is the outcome of general modelling activities initially based on numerical and experimental investigations, but later formally defined by invoking the Energy Distribution Approach (EDA). A background overview of the procedure is here given and some more advances are presented by looking to a cylindrical thin shell. Some few rules are discussed in order to have an equivalent model able to represent under some hypotheses, the dynamic behaviour of the original one. Basically, it is shown how the linear dimension can be modified to produce a complete or distorted similitude and further the role of the damping for increasing excitation frequencies to recover the original response. Despite the extreme simplicity of the proposed models, the results are really encouraging. The final aim is to define equivalent (exact and approximated) models to be used in numerical and/or laboratory experiments.

On the other hand it is well known that the computational costs associated with the analysis of a stochastic response of a linear system can become unacceptable high, even using a full modal representation. A crude approach has been already tested some years ago and only recently it has been formally defined as a pseudo equivalent deterministic excitation (PEDE). This is based on the representation of a given spectral load by using roughly each column is used in a deterministic approach. The method allows a good representation without evaluating the eigenvalues and eigenvectors of the load matrix as done in the pseudo excitation method, (PEM). The PEM can be considered as an exact representation being based on the modal decomposition of the spectral excitation and PEDE is a low-frequency approximation. The approaches are compared with a full stochastic response for two simple systems: a chain of oscillators (mass and stiffness) and a plate. Both the systems are considered as excited by a spectral load representing the classical Corcos form for the wall pressure distribution due to a turbulent boundary layer. A dimensionless representation of the frequency axis is used to show the feasibility of the simulation response obtained by using PEDE.

The first approach is related to the possibility of defining similitudes and/or predictive models among structural and structural-acoustic systems. The resulting procedure is named SAMSARA: Similitude and Asymptotic Models for Structural-Acoustic Research and Applications; it is the outcome of general modelling activities initially based on numerical and experimental investigations, but later formally defined by invoking the Energy Distribution Approach (EDA). A background overview of the procedure is here given and some more advances are presented by looking to a cylindrical thin shell. Some few rules are discussed in order to have an equivalent model able to represent under some hypotheses, the dynamic behaviour of the original one. Basically, it is shown how the linear dimension can be modified to produce a complete or distorted similitude and further the role of the damping for increasing excitation frequencies to recover the original response. Despite the extreme simplicity of the proposed models, the results are really encouraging. The final aim is to define equivalent (exact and approximated) models to be used in numerical and/or laboratory experiments.

On the other hand it is well known that the computational costs associated with the analysis of a stochastic response of a linear system can become unacceptable high, even using a full modal representation. A crude approach has been already tested some years ago and only recently it has been formally defined as a pseudo equivalent deterministic excitation (PEDE). This is based on the representation of a given spectral load by using roughly each column is used in a deterministic approach. The method allows a good representation without evaluating the eigenvalues and eigenvectors of the load matrix as done in the pseudo excitation method, (PEM). The PEM can be considered as an exact representation being based on the modal decomposition of the spectral excitation and PEDE is a low-frequency approximation. The approaches are compared with a full stochastic response for two simple systems: a chain of oscillators (mass and stiffness) and a plate. Both the systems are considered as excited by a spectral load representing the classical Corcos form for the wall pressure distribution due to a turbulent boundary layer. A dimensionless representation of the frequency axis is used to show the feasibility of the simulation response obtained by using PEDE.

- Type :
- Séminaires - conférences
- Lieu(x) :
- Campus de Cachan