Optimal acoustic design of sandwich panels
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An optimization study to investigate the feasibility of an optimal acoustic design process for sandwich panels is presented here. Using a pattern search procedure it is shown that the average transmission loss of a panel may be improved through optimization over a range of frequency, and that the optimization procedure results in a shift of the panel symmetric coincidence frequency beyond the range of interest. Subject Classification: 55.75.Keywords:
Transmission loss
Optimal design
Sandwich panel
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The second-order statistical properties of point processes (PPs) are described by the coincidence function which can be measured by a coincidence device, but such measurements are long and complicated. We propose another method of measurement, and we analyze its performances. The starting point is that the coincidence function can be deduced from the probability density functions of the life times (the distances between points) of the process. The idea is to transform the PP into a positive signal whose values are these distances. From an appropriate processing of this signal, we deduce the coincidence function. For the validation of the method, we use PPs for which the coincidence function is known. The agreement between theory and experiment is, in general, excellent. Finally, the method is applied to measure the coincidence functions of some PPs for which no theoretical result is available.
Coincidence Counting
SIGNAL (programming language)
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Sound transmission class
Honeycomb
Sandwich panel
Statistical energy analysis
Transmission loss
Honeycomb structure
Critical frequency
Soundproofing
Reverberation room
Loss factor
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Citations (28)
Coincidence point
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Citations (2)
Honeycomb
Sound transmission class
Sandwich panel
Transmission loss
Statistical energy analysis
Honeycomb structure
Critical frequency
Loss factor
Soundproofing
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Sandwich panel which has a design involving acoustic comfort is always denser and larger in size than the design involving mechanical strength. The respective short come can be solved by exploring the impact of core geometry on sound transmission characteristics of sandwich panels. In this aspect, the present work focuses on the study of influence of core geometry on sound transmission characteristics of sandwich panels which are commonly used as aircraft structures. Numerical investigation has been carried out based on a 2D model with equivalent elastic properties. The present study has found that, for a honeycomb core sandwich panel in due consideration to space constraint, better sound transmission characteristics can be achieved with lower core height. It is observed that, for a honeycomb core sandwich panel, one can select cell size as the parameter to reduce the weight with out affecting the sound transmission loss. Triangular core sandwich panel can be used for low frequency application due to its increased transmission loss. In foam core sandwich panel, it is noticed that the effect of face sheet material on sound transmission loss is significant and this can be controlled by varying the density of foam.
Sound transmission class
Sandwich panel
Honeycomb structure
Honeycomb
Transmission loss
Soundproofing
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Citations (53)
To improve the optimal efficiency of mufflers,based on the mufflers' numerical modeling considering the effect of flow rate on their transmission loss,their parameters were analyzed with Latin hypercube design in the design of experiment( DOE).Combining with the improved simulated annealing algorithm,the single-objective and multi-objective optimization models for the dtransmission loss at peak frequencies of exhaust noise were established,respectively.The optimal design of mufflers was conducted.The result showed that the DOE method can effectively identify the contributions of mufflers' parmeters to their transmission loss and simplify the optimization model of mufflers;the average velocity of gas in mufflers has a great impact on the optimal results;the transmission loss of mufflers at the corresponding peak frequencies for the single objective optimization can reach the maximum value,while the multi-objective optimization can make the whole optimization results within the full frequency range better,the maximum reduction of exhaust noise is 31.73 d B,it is better than that of the single objective optimization.This study provided a new idea for the optimization design of mufflers.
Muffler
Latin Hypercube Sampling
Transmission loss
Optimal design
Design of experiments
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Activity measurements of 3H, 241Am and 60Co solutions were performed to compare digital coincidence modules used at PTB and POLATOM for TDCR and 4πβ(LS)-γ coincidence counting. The activities determined with various coincidence modules connected in parallel to the same counter at PTB were found to be consistent. Observed discrepancies caused by differences in the coincidence resolving time did not exceed 0.14%. Accidental coincidences simulated by a frequency generator were registered, and the coincidence resolving time was determined.
Coincidence Counting
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The higher stiffness-to-mass ratio of a honeycomb panel compared to a homogeneous panel results in a lower acoustic critical frequency. Above the critical frequency the panel flexural wave speed is acoustically fast and the structure becomes a more efficient radiator with associated lower sound transmission loss. Finite element models of honeycomb sandwich structures are presented featuring areas where the core is removed from the radiating face sheet disrupting the supersonic flexural and shear wave speeds that exist in the baseline honeycomb panel. These modified honeycomb panel structures exhibit improved transmission loss for a pre-defined diffuse field sound excitation. The models were validated by the sound transmission loss of honeycomb panels measured in the Structural Acoustic Loads and Transmission (SALT) facility at the NASA Langley Research Center. A honeycomb core panel configuration is presented exhibiting a transmission loss improvement of 3-11 dB compared to a honeycomb baseline panel over a frequency range from 170 Hz to 1000 Hz. The improved transmission loss panel configuration had a 5.1% increase in mass over the baseline honeycomb panel, and approximately twice the deflection when excited by a static force.
Sandwich panel
Transmission loss
Honeycomb
Honeycomb structure
Sound transmission class
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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.
Sound transmission class
Orthotropic material
Transmission loss
Sandwich panel
Loss factor
Honeycomb
Honeycomb structure
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Citations (17)