Transmission Loss Of Sandwich Panels Research Articles

New designs of sandwich panels to mitigate high-frequency noise inside space vehicles

Radiation of noise to the interior of a space vehicle during liftoff and transonic climb is a long-standing problem. To attenuate noise inside the crew compartment during launch and in-space operation, sandwich panels have been employed in the pressurized outer shell to passively reduce the exterior noise transmission. However, the layouts and the sound transmission loss of the implemented sandwich panels have not been made available for public release. Against this idiosyncratic practice, this study envisioned disseminating the know-how on the sound attenuation ability of dissimilar sandwich panels. To efficiently absorb and dampen the acoustic energy, the sandwich panels were specifically configured using a honeycomb core, felts and a closed cell aluminum-foam in the material lay-up. The face sheets of the sandwich panels consisted of either glass fiber-reinforced epoxy or carbon fiber-reinforced epoxy composites. The sandwich panels were tested as acoustic barriers to a diffuse sound field in a sound transmission suite. As found, an increase in the panel thickness brought a decrease in the anti-symmetric coincidence frequency of sandwich panels. A rubber damping layer in the material lay-up added limp mass to a sandwich panel and reduced the panel vibration at excitation frequencies beyond 500 Hz. Multiple felts reinforced the sound transmission loss of a sandwich panel by dissipating the acoustic energy into thermal energy at the felt interstices in the frequency regime beyond 315 Hz. In conclusion, this study proposed optimized sandwich configurations considering the constitutive materials, number of material layers, material layer thickness and stacking sequence. The optimized sandwich configurations could fairly deliver the demanded sound transmission loss in the high-frequency regime.

An experimental study on the sound transmission loss of dissimilar fuselage sandwich panels of turbojet aircraft

The analysis of acoustic performance of sandwich panels, designed explicitly for fuselage sidewalls of turbojet aircraft, has been revisited numerous times. However, the layouts and the sound transmission loss of the airborne fuselage sandwich panels have not been made available for public release. Against this idiosyncratic practice, this study envisioned disseminating the know-how on the sound attenuation ability of dissimilar sandwich panels implemented in the fuselage of turbojet aircraft. To efficiently absorb and dampen the acoustic energy, the sandwich panels were systematically configured using a honeycomb core, felts and a closed cell aluminum-foam in the material lay-up. The face sheets of the sandwich panels were composed of either glass fiber-reinforced epoxy or carbon fiber-reinforced epoxy composites. The sandwich panels were tested as acoustic barriers to a diffuse sound field in a sound transmission suite consisting of two adjacent sound reverberation rooms. As found, a rubber damping layer in the material lay-up of a sandwich panel reinforced the sound transmission loss at frequencies beyond 500 Hz. Multiple felts augmented the sound transmission loss in the frequency regime beyond 315 Hz. The panel edges needed to be sealed properly to reproduce the sound transmission loss of a sandwich panel in successive experiments. This study leveraged many-faceted insights into the configuration (constituent materials, number of material layers, thickness, and stacking sequence) of commercially feasible sandwich panels. Besides, this study proposed optimized sandwich configurations based on the sound transmission loss, which will help aircraft manufacturers to apply these sandwich panels without further modifications.

Investigations about periodic design for broadband increased sound transmission loss of sandwich panels using 3D-printed models

Abstract Two types of sandwich panels are designed by using the periodic structure theory. A double-wall panel with mechanical links and a sandwich panel with rectangular core are studied. An oriented optimization of the elastic bending waves’ propagation versus the acoustic wavenumbers is achieved by using shifted core walls and by keeping the mass and stiffness of the system constant. Standard and optimized configurations are 3D-printed and sound transmission measurements are carried out by using a facility with an uncoupled reverberant-anechoic configuration. The experimental evidences of enlarged bending band-gaps and deformation mechanisms are proved using a reverse approach based on the acoustic radiation of the panels.

Sound transmission loss of sandwich panel with closed octahedral core

In this paper, an ultralightweight sandwich panel with closed octahedral core is proposed, which demonstrates excellent acoustic property of sound transmission loss as well as great mechanical performance. Simulation models are established with considerations of acoustic-structure interactions. The validity of simulation calculations is checked against experimental measurements with the tested specimens provided by additive manufacturing. Numerical discussions are conducted to demonstrate the effects of incident angles, topological parameters, and so on which should be helpful for practical design. This novel class of sandwich structure with closed octahedral core constructions shows promising engineering applications.

Prediction of Sound Transmission Loss for Finite Sandwich Panels Based on a Test Procedure on Beam Elements

An approach on the prediction of sound transmission loss for a finite sandwich panel with honeycomb core is described in the paper. The sandwich panel is treated as orthotropic and the apparent bending stiffness in two principal directions is estimated by means of simple tests on beam elements cut from the sandwich panel. Utilizing orthotropic panel theory, together with the obtained bending stiffness in two directions, the sound transmission loss of simply-supported sandwich panel is predicted by the modal expansion method. Simulation results indicated that dimension, orthotropy, and loss factor may play important roles on sound transmission loss of sandwich panel. The predicted transmission loss is compared with measured data and the agreement is reasonable. This approach may provide an efficient tool to predict the sound transmission loss of finite sandwich panels.

Analysis of sound transmission through sandwich panels.

Due to their advantages over the conventional metal structure, sandwich structures have become used increasingly in transportation vehicles in recent years. However, they have some less favorable properties. In this paper, sound transmission through foam-filled honeycomb sandwich panels was studied using the statistical energy analysis (SEA). Modal density, critical frequency, and the radiation efficiency of sandwich panels were analyzed. The sound transmission loss and radiation efficiency of sandwich panels were predicted theoretically and measured experimentally. The measured results agree with the theoretical predictions quite well. An important observation is that, for foam-filled honeycomb sandwich panels, the radiation efficiency does not decrease to a plateau value at frequencies beyond the critical frequency. Although the high damping helps to improve the sound transmission loss in the critical frequency range, the overall transmission loss of sandwich panels is lower than their heavy metal counterparts. Therefore, the foam-filled honeycomb design must be modified to obtain good noise isolation capability, and a trade-off between the overall stiffness and the sound transmission properties should be considered in the design stage.

Predicting the Sound Transmission Loss of Sandwich Panels by Statistical Energy Analysis Approach

AbstractA statistical energy analysis (SEA) approach is used to predict the sound transmission loss (STL) of sandwich panels numerically. Unlike conventional SEA studies of the STL of sandwich panels, which consider only the antisymmetric (bending) motion of the sandwich panel, the present approach accounts for both antisymmetric and symmetric (dilatational) motions. Using the consistent higher-order sandwich plate theory, the wave numbers of the waves propagating in the sandwich panel were calculated. Using these wave numbers, the wave speed of the propagating waves, the modal density, and the radiation efficiency of the sandwich panels were determined. Finally, the sound transmission losses of two sandwich panels were calculated and compared with the experimentally measured values, as well as with conventional SEA predictions. The comparisons with the experimental data showed good agreement, and the superiority of the present approach relative to other approaches is discussed and analyzed.

Transmission loss assessments of sandwich structures by using a combination of finite element and boundary element methods

In this work, formulation of a 2D fully‐coupled finite element method (FEM)/boundary element method (BEM) to simulate the measurements of sound transmission loss of sandwich panels is presented. Specifically, the structural behavior of the sandwich panels, based on a consistent higher‐order theory, is implemented using finite element method (FEM), and the reverberant/anechoic chambers are accessed by boundary element method (BEM). The coupling between the structure and the acoustic medium is achieved by assuming the continuity of the normal velocities at the interface. The absorption of the receiving anechoic chamber is calibrated by comparing the numerically‐predicted sound pressure level difference between the two chambers with the Sewell’s expression for the forced transmission. The obtained correction factors are then used without any modification to predict transmission loss of other sandwich panels with different dimensions and material properties. Numerical examples are presented to validate the numerical procedure. Compared with traditional finite element approach, the proposed hybrid method provides more computation efficiency, and, hence, can be used to study acoustic behavior of sandwich panels at higher frequencies.

Further studies of transmission loss of sandwich panels

Further studies are presented of the effects of various structural and material parameters on the transmission loss through acoustic panels. The work was based on models previously used to study the transmission loss of sandwich panels made up of soft elastic cores whose basic properties were isotropic, the core being sandwiched between two relatively stiff skins which are also isotropic [C. L. Dym and M. A. Lang, J. Acoust. Soc. Am. 56, 1523–1532 (1974); and Dym et al., J. Acoust. Soc. Am. 59, 364–367 (1976)]. In the present instance the core is taken to be orthotropic and the two skins, each of which is itself isotropic, are no longer assumed to have the same material properties and geometry. Calculations of transmission loss are presented and the effects of the orthotropy of the core and the asymmetry of the skin structures are examined. The implications of this analysis for future optimization studies are pointed out. [Work supported by NSF.]

Transmission of sound through sandwich panels: A reconsideration

A reconsideration of a previous study of the transmission loss of sandwich panels is presented. An erroneous calculation of the transmission loss is corrected, and new results are presented. Also, some interesting implications for the design of walls of high transmission loss are pointed out. Subject Classification: [43]55.75.

The Coincidence Wall: A New Design for High Transmission Loss or High Structural Damping

A recent paper by this author presented a theory of the transmission loss of sandwich panels. This paper presents a design concept for a high transmission-loss barrier operating above its critical frequency following this theory. Calculations indicate that this panel can exceed mass-law performance over an extended frequency range when certain parametric requirements are exceeded. This concept may be applied to damping of very stiff structures to achieve high composite-loss factors. Experimental verification of these results is presented and discussed.