Dimitrios Chronopoulos

Damping Enhancement of Composite Panels by Inclusion of Shunted Piezoelectric Patches: A Wave-Based Modelling Approach

The waves propagating within complex smart structures are hereby computed by employing a wave and finite element method. The structures can be of arbitrary layering and of complex geometric characteristics as long as they exhibit two-dimensional periodicity. The piezoelectric coupling phenomena are considered within the finite element formulation. The mass, stiffness and piezoelectric stiffness matrices of the modelled segment can be extracted using a conventional finite element code. The post-processing of these matrices involves the formulation of an eigenproblem whose solutions provide the phase velocities for each wave propagating within the structure and for any chosen direction of propagation. The model is then modified in order to account for a shunted piezoelectric patch connected to the composite structure. The impact of the energy dissipation induced by the shunted circuit on the total damping loss factor of the composite panel is then computed. The influence of the additional mass and stiffness provided by the attached piezoelectric devices on the wave propagation characteristics of the structure is also investigated.

Wave steering effects in anisotropic composite structures: Direct calculation of the energy skew angle through a finite element scheme

HIGHLIGHTSA systematic expression quantifying the wave energy skewing phenomenon is derived.A generic expression of the wavenumber angular sensitivity is derived.Structures can be of arbitrary anisotropy, layering and geometric complexity.The approach is efficient and not prone to finite differentiation numerical errors.Acoustic caustic behaviour of the group velocity curves can also be visualized. ABSTRACT A systematic expression quantifying the wave energy skewing phenomenon as a function of the mechanical characteristics of a non‐isotropic structure is derived in this study. A structure of arbitrary anisotropy, layering and geometric complexity is modelled through Finite Elements (FEs) coupled to a periodic structure wave scheme. A generic approach for efficiently computing the angular sensitivity of the wave slowness for each wave type, direction and frequency is presented. The approach does not involve any finite differentiation scheme and is therefore computationally efficient and not prone to the associated numerical errors.

On the Variability of the Sound Transmission Loss of Composite Panels Through a Parametric Probabilistic Approach

A robust model for the prediction of the variability of the vibro-acoustic response is presented in this paper. The dynamic response of composite panels is treated using a Statistical Energy Analysis (SEA) approach. One of the basic input parameters is the propagating flexural wavenumber of the modeled panel. The Wave Finite Element Method (WFEM) is used to investigate the dispersion characteristics of the layered panel. It is based on the evaluation of the mass and the stiffness matrices of a periodic segment of the structure. A polynomial eigenvalue problem is then formed for calculating the wavenumbers and the wave mode shapes. The main novelty in this paper consists in evaluating the influence of the variability of the mechanical parameters of the composite panel on its vibro-acoustic response, that is on its sound transmission loss (STL). This influence is quantified using the generalized polynomial chaos expansion. The efficiency of the approach is exhibited for isotropic and orthotropic panels.

The impact of temperature on wave interaction with damage in composite structures

The increased use of composite materials in modern aerospace and automotive structures, and the broad range of launch vehicles’ operating temperature imply a great temperature range for which the structures has to be frequently and thoroughly inspected. A thermal mechanical analysis is used to experimentally measure the temperature-dependent mechanical properties of a composite layered panel in the range of −100 ℃ to 150 ℃. A hybrid wave finite element/finite element computational scheme is developed to calculate the temperature-dependent wave propagation and interaction properties of a system of two structural waveguides connected through a coupling joint. Calculations are made using the measured thermomechanical properties. Temperature-dependent wave propagation constants of each structural waveguide are obtained by the wave finite element approach and then coupled to the fully finite element described coupling joint, on which damage is modelled, in order to calculate the scattering magnitudes of the waves interaction with damage across the coupling joint. The significance of the panel’s glass transition range on the measured and calculated properties is emphasised. Numerical results are presented as illustration of the work.

Wave sensitivity analysis for periodic and arbitrarily complex composite structures

Purpose This paper aims to present the development of a numerical continuum-discrete approach for computing the sensitivity of the waves propagating in periodic composite structures. The work can be directly used for evaluating the sensitivity of the structural dynamic performance with respect to geometric and layering structural modifications. Design/methodology/approach A structure of arbitrary layering and geometric complexity is modelled using solid finite element (FE). A generic expression for computing the variation of the mass and the stiffness matrices of the structure with respect to the material and geometric characteristics is hereby given. The sensitivity of the structural wave properties can thus be numerically determined by computing the variability of the corresponding eigenvalues for the resulting eigenproblem. The exhibited approach is validated against the finite difference method as well as analytical results. Findings An intense wavenumber dependence is observed for the sensitivity results of a sandwich structure. This exhibits the importance and potential of the presented tool with regard to the optimization of layered structures for specific applications. The model can also be used for computing the effect of the inclusion of smart layers such as auxetics and piezoelectrics. Originality/value The paper presents the first continuum-discrete approach specifically developed for accurately and efficiently computing the sensitivity of the wave propagation data for periodic composite structures irrespective of their size. The considered structure can be of arbitrary layering and material characteristics as FE modelling is used.

A wave and finite element approach for computing the optimal damping layer characteristics for composite structures

The optimal mechanical and geometric characteristics for layered composite structures having damping layer inclusions and subject to vibroacoustic excitations are derived. A finite element description coupled to periodic structure theory is employed for the considered layered damped panel. Structures of arbitrary anisotropy as well as geometric complexity can be modeled by the exhibited approach. A numerical continuum-discrete approach for computing the sensitivity of the acoustic wave characteristics propagating within the modeled periodic composite structure is exhibited. The sensitivity of the acoustic transmission coefficient expressed within a statistical energy analysis context is subsequently derived as a function of the computed acoustic wave characteristics. The optimal mechanical and geometric characteristics satisfying the considered mass, stiffness and vibroacoustic performance criteria are sought by employing Newtons optimization method.

Vibroacoustics Under Aerodynamic Excitations

This paper gives a number of energy considerations related to the flow induced vibration and noise predictions. In this context, reduced modeling of structural-acoustic issues are the main red line of the work. The present paper deals thus with equivalent “rain on the roof” (ROF) excitations, which allow the modeling of spatially correlated broadband sources by statistically independent point forces. ROF excitation largely simplifies the expressions of the joint acceptance functions and can be easily modeled using finite element method (FEM). Two approaches are presented here and an equivalent model of excitation is developed and validated on acoustic and aerodynamic excitations, such as diffuse field or turbulent boundary layer (TBL) excitations. The first idea, considers the equivalence over the extended physical domain. It allows equivalent ROF excitation only for frequencies over the acoustic coincidence effect. The second method is based on the wavenumber space equivalence. Validation of this approach has been carried out for different acoustic and aerodynamic excitations, and for different structural boundary conditions. Numerical experiments show that this approach gives acceptable results for a wide frequency range specifically for TBL excitations. Then, the problem of the structural–acoustic response under aerodynamic sources is considered further. The structure is a composite structure of arbitrary thickness and anisotropy. The fully coupled system is modeled using a Statistical Energy Analysis like (SEA-like) approach, and the energetic characteristics for each subsystem are computed and compared to the direct FEM solution. The error of the reduced model calculations for each frequency band is presented and the limits of the reliability of the reduction are explored. Different strategies concerning the reduction process parameters are investigated in order to optimize the accuracy with respect to time efficiency. The loading applied to the model comprises typical random distributed excitations, such as a ‘rain-on-the-roof’ excitation, a diffused sound field and a Turbulent Boundary Layer (TBL) excitation.

Thermoacoustic effects on layered structures for the evaluation of structural parameters

The temperature dependent material characteristics of a layered panel are experimentally measured using a Thermal Mechanical Analysis (TMA) configuration. The temperature dependent wave dispersion characteristics of the panel are subsequently computed using a Wave Finite Element Method (WFEM). The WFEM predictions are eventually used within a wave context SEA approach in order to calculate the temperature dependent Sound Transmission Loss (STL) of the layered panel. Results on the STL for temperatures varying between -100 °C to 160 °C are computed for a structure operating at sea level. The importance of the glass transition region on the panel’s vibroacoustic response is exhibited and discussed.

EFFICIENT CALCULATION OF THE RESPONSE OF A STRUCTURAL ACOUSTIC SYSTEM UNDER AERODYNAMIC EXCITATIONS

Abstract. The problem of the dynamic response of a structural-acoustic system in the midfrequency range is hereby considered. The system is initially modelled using finite elements, and is subsequently reduced using the Second Order Arnoldi Reduction method (SOAR) resulting in radical reduction of calculation times. The fully coupled system is modelled using a Statistical Energy Analysis like (SEA-like) approach, and the energetic characteristics for each subsystem are computed and compared to the direct FEM solution. The error with respect to the full FE solution is presented and the limits of the reliability of the reduction are explored. The loading applied to the model comprises typical random aeroacoustic excitations, such as a diffused sound field and a Turbulent Boundary Layer (TBL) excitation.