Vibro-acoustic behavior of a multilayered viscoelastic sandwich plate under a thermal environment:

Sound radiation and transmission loss characteristics of a honeycomb sandwich panel with composite facings: Effect of inherent material damping

Abstract: This paper presents the results of numerical studies carried out on vibro-acoustic and sound transmission loss behaviour of aluminium honeycomb core sandwich panel with fibre reinforced plastic (FRP) facings. Layered structural shell element with equivalent orthotropic elastic properties of core and orthotropic properties of FRP facing layer is used to predict the free and forced vibration characteristics. Followed by this, acoustic response and transmission loss characteristics are obtained using Rayleigh integral. Vibration and acoustic characteristics of FRP sandwich panels are compared with aluminium sandwich panels. The result reveals that FRP panel has better vibro-acoustic and transmission loss characteristics due to high stiffness and inherent material damping associated with them. Resonant amplitudes of the response are fully controlled by modal damping factors calculated based on modal strain energy. It is also demonstrated that FRP panel can be used to replace the aluminium panel without losing acoustic comfort with nearly 40 percent weight reduction.

Buckling and vibro-acoustic response of the clamped composite laminated plate in thermal environment

Abstract: Composite structures are extensively applied in aircraft and marine industries because of their high stiffness-to-weight ratios and other advantages The composite structures in the hypersonic aircraft are usually exposed to the thermal and noise environment The paper is focused on the buckling and vibro-acoustic response of the clamped composite laminated plate excited by a concentrated harmonic force in the thermal environment The analytical solution of vibration and acoustic response for fully clamped boundary condition is derived in the paper Meanwhile, the natural frequencies and buckling temperatures of the plate in uniform temperature environment are also derived by applying the classical laminate theory (CLT) and first order shear deformation theory (FOSDT) The vibration response is obtained by applying the mode superposition method, while the sound pressure and radiation efficiency are calculated by Rayleigh integral in sequence The accuracy of the presented method is verified by the numerical simulations The structural and acoustic response affected by the thermal load is demonstrated through a numerical example

Vibro-acoustic response and sound transmission loss characteristics of truss core sandwich panel filled with foam

Abstract: This paper presents the studies carried out for improving the acoustic behavior of truss core sandwich panel, which is mostly used in aerospace structural applications. The empty space of the truss core is filled with polyurethane foam (PUF) to achieve better vibro-acoustic and sound transmission loss characteristics. Initially equivalent elastic properties of the foam filled truss core sandwich panel are calculated. Then, the vibration response of the panel under a harmonic excitation is obtained based on the equivalent 2D finite element model. Finally, the vibration response is given as an input to the Rayleigh integral code built in-house to obtain the acoustic and sound transmission loss characteristics. The results revealed that PUF filling of the empty space of the truss core, significantly reduces resonant amplitudes of both vibration and acoustic responses. It is also observed that foam filling reduces the overall sound power level significantly. Similarly, sound transmission loss studies revealed that, sudden dips at resonance frequencies are significantly reduced. Also an experiment is conducted on forced vibration response of honeycomb core sandwich panel to show that equivalent 2D model can be used for predicting sound power level and transmission loss behavior.

Bending and free vibration analysis of foam-filled truss core sandwich panel:

Abstract: This paper presents the studies carried out on bending and free vibration behavior of truss core sandwich panel filled with foam typically used in aerospace applications. Equivalent stiffness prope...

Piecewise shear deformation theory and finite element formulation for vibration analysis of laminated composite and sandwich plates in thermal environments

Abstract: In this paper, a piecewise shear deformation theory for laminated composite and sandwich plates is presented by integrating the advantages of the layerwise theory and equivalent single layer theory. A C0 continuous four-noded quadrilateral isoparametric plate element based on this theory is developed for free and forced vibration analysis of laminated composite and sandwich plates in thermal environments. The accuracy and effectiveness of piecewise shear deformation theory and finite element formulation are validated by comparing the numerical results obtained by the present finite element formulation with the analytical and exact results available in literatures as well as the numerical results computed by MSC.Nastran software. It is demonstrated that the piecewise shear deformation theory and finite element formulation are suitable for the vibration analysis of thin and thick laminated composite and sandwich plates. As compared with the layerwise theory, high-order zigzag theory and high-order equivalent single layer theory, the piecewise shear deformation theory is able to produce a sufficiently accurate result at a very low computational cost. The work reported in this paper provides an efficient modeling approach for thermal vibration analysis of laminated composite and sandwich plates in practical engineering.

Fourier Acoustics: Sound Radiation and Nearfield Acoustical Holography

Abstract: Preface. Fourier Transforms & Special Functions. Plane Waves. The Inverse Problem: Planar NAH. Cylindrical Waves. The Inverse Problem: Cylindrical NAH. Spherical Waves. Spherical NAH. Green Functions & the Helmholtz Integral. Index.

Finite Element Prediction of Damping in Structures with Constrained Viscoelastic Layers

Abstract: An efficient method is described for finite element modelling of three-layer laminates containing a viscoelastic layer. Modal damping ratios are estimated from undamped normal mode results by means of the modal strain energy method. Comparisons are given between results obtained by the MSE method implemented in NASTRAN, by various exact solutions for approximate governing differential equations, and by experiment. Results are in terms of frequencies, modal damping ratios, and mechanical admittances for simple beams, plates, and rings. Application of the finite element -- MSE method in design of integrally damped structures is discussed.

The Finite Element Method in Heat Transfer Analysis

Abstract: Conduction Heat Transfer and Formulation. Linear Steady State Problems. Time Stepping Methods for Heat Transfer. Non--Linear Heat Conduction Analysis. Phase Change Problems----Solidification and Melting. Convective Heat Transfer. Nomenclature. Index.

Loss Factors of Viscoelastic Systems in Terms of Energy Concepts

Abstract: The definition of loss factor in terms of energy quantities is re‐examined, particularly as it applies to composite viscoelastic systems. A restatement of this definition in terms of a corresponding viscoelastic spring is used to show that this definition is extremely useful for massless (ideal viscoelastic spring) systems, but may be applied unambiguously to spring systems with a single attached mass only at resonance. Simple relations are presented which express the loss factors of series‐parallel arrays of massless viscoelastic springs in terms of properties of the individual components. Implications of these relations in damping of composite structures are discussed. (This work was supported in part by the Aeronautical Systems Division, U. S. Air Force.)