Research of Sound Transmission Loss of Aircraft Sidewall with the Resonators

2012 ◽  
Vol 214 ◽  
pp. 194-199
Author(s):  
Li Ming Shi
Keyword(s):  
Transmission Loss ◽  
Sound Transmission ◽  
Side Wall ◽  
General Aviation ◽  
Sound Transmission Loss ◽  
Low Frequencies ◽  
Theory And Experiment ◽  
General Aviation Aircraft

This paper suggesting a method that improving T.L. at low frequencies of general aviation aircraft side wall configuration by installing resonators between double panel.In this paper, through the theory and experiment results, explains the proposed view is correct.

scholarly journals SOUND TRANSMISSION LOSS OF A DOUBLE-LEAF SOLID-MICROPERFORATED PARTITION UNDER NORMAL INCIDENCE OF ACOUSTIC LOADING

2011 ◽  
Vol 12 (3) ◽  
Author(s):  
Ahmad Yusuf Ismail
Keyword(s):  
Transmission Loss ◽  
Noise Source ◽  
Sound Transmission ◽  
Normal Incidence ◽  
Acoustic Excitation ◽  
Sound Transmission Loss ◽  
Low Frequencies ◽  
Vehicle Cabin ◽  
Preliminary Study ◽  
The Mathematical Model

The micro-perforated panel (MPP) is recently well-known as an alternative ‘green‘ sound absorber replacing the conventional porous materials. Constructed from a solid panel which provides a non-abrassive structure and also an optically attractive surface, there gives a feasibility to implement such a panel inside a vehicle cabin. This paper is the preliminary study to investigate the sound transmission loss (TL) of a solid panel coupled with a micro-perforated panel to form a doube-leaf partition which is already known as a lightweigth stucture for noise insulation in vehicles and buildings. The mathematical model for the TL subjected to normal incidence of acoustic excitation is derived. The results show that its performance substantially improves at the troublesome frequency of mass-air-mass resonance which occurs in the conventional double-leaf solid partition. This is important particularly for the noise source predominant at low frequencies. This can also be controlled by tuning the hole size and number as well as the air gap between the panels.  ABSTRAK: Panel bertebuk mikro (micro-perforated panel (MPP)) kebelakangan ini dikenali sebagai alternatif penyerap bunyi yang mesra alam menggantikan bahan berliang lazim. Dibina daripada satu panel padu yang memberikan satu struktur tak lelas dan juga satu permukaan yang menarik, ia memberikan kemungkinan penggunaan panel tersebut di dalam kabin kenderaan. Tesis ini merupakan kajian permulaan dalam mengkaji hilang pancaran bunyi (sound transmission loss (TL)) oleh satu panel padu yang digandingkan dengan satu panel bertebuk mikro. Kaedah ini menghasilkan satu sekatan lembar kembar yang sememangnya dikenali sebagai struktur ringan penebat bunyi di dalam kenderaan dan bangunan. Model matematik diterbitkan untuk TL tersebut dengan menjalankan pengujaan akustik yang tuju normal. Keputusan menunjukkan bahawa prestasi meningkat dengan ketara pada frekuensi yang susah semasa resonans jisim-udara-jisim berlaku di dalam sekatan padu lembar kembar  lazim. Ini penting terutamanya untuk sumber bunyi yang pradominan pada frekuensi rendah. Ia juga boleh dikawal dengan menalakan saiz dan jumlah lubang serta luang udara di antara panel-panel  tersebut.

scholarly journals On the Frequency Up-Conversion Mechanism in Metamaterials-Inspired Vibro-Impact Structures

Acoustics ◽  
2019 ◽  
Vol 1 (1) ◽  
pp. 156-173 ◽  
Author(s):  
Anuj Rekhy ◽  
Robert Snyder ◽  
James Manimala
Keyword(s):  
Transmission Loss ◽  
Sound Transmission ◽  
Normal Incidence ◽  
Large Mass ◽  
Dominant Frequency ◽  
Energy Transfer Mechanism ◽  
Sound Transmission Loss ◽  
Low Frequencies ◽  
Limited Effectiveness ◽  
The Impact

Conventional acoustic absorbers like foams, fiberglass or liners are used commonly in structures for industrial, infrastructural, automotive and aerospace applications to mitigate noise. However, these have limited effectiveness for low-frequencies (LF, <~500 Hz) due to impractically large mass or volume requirements. LF content being less evanescent is a major contributor to environmental noise pollution and induces undesirable structural responses causing diminished efficiency, comfort, payload integrity and mission capabilities. There is, therefore a need to develop lightweight, compact, structurally-integrated solutions to mitigate LF noise in several applications. Inspired by metamaterials, tuned mass-loaded membranes as vibro-impact attachments on a baseline structure are considered to investigate their performance as an LF acoustic barrier. LF incident waves are up-converted via impact to higher modes in the baseline structure which may then be effectively mitigated using conventional means. Such Metamaterials-Inspired Vibro-Impact Structures (MIVIS) could be tuned to match the dominant frequency content of LF acoustic sources. Prototype MIVIS unit cells were designed and tested to study energy transfer mechanism via impact-induced frequency up-conversion and sound transmission loss. Structural acoustic simulations were done to predict responses using models based on normal incidence transmission loss tests. Simulations were validated using experiments and utilized to optimize the energy up-conversion mechanism using parametric studies. Up to 36 dB of sound transmission loss increase is observed at the anti-resonance frequency (326 Hz) within a tunable LF bandwidth of about 300 Hz for the MIVS under white noise excitation. Whereas, it is found that under monotonic excitations, the impact-induced up-conversion redistributes the incident LF monotone to the back plate’s first mode in the transmitted spectrum. This up-conversion could enable further broadband transmission loss via subsequent dissipation in conventional absorbers. Moreover, this approach while minimizing parasitic mass addition retains or could conceivably augment primary functionalities of the baseline structure. Successful transition to applications could enable new mission capabilities for aerospace and military vehicles and help create quieter built environments.

scholarly journals Tuning acoustic performance of multi-chamber hybrid mufflers

2021 ◽  
Author(s):  
Van-Hai Trinh
Keyword(s):  
Transmission Loss ◽  
Sound Transmission ◽  
Numerical Approach ◽  
Geometrical Parameters ◽  
Sound Transmission Loss ◽  
Expansion Chamber ◽  
Low Frequencies ◽  
Acoustic Performance ◽  
Chamber Length ◽  
Perforated Tube

In this paper, we investigate the functional acoustic performance of multi-chamber mufflers using a numerical approach. The wave propagation governing in expansion chamber domains is first introduced and solved by the finite element method. Our numerical results of selected muffler configurations are compared with the reference predictions model and experiments in order to validate the present procedure. Then, the influence of the geometry characteristics of typical and hybrid configurations of multi-chambered mufflers (number of sub-chambers, micro-perforated tube structure) on their sound transmission loss is studied. The obtained results indicate that the structure of the considered muffler has a strong effect on their acoustical performance, and the location and the high level of resonances of the sound transmission loss behavior are strongly related to the number of sub-chambers as well as micro-perforated tube characteristics. By tuning geometrical parameters (e.g., having a small perforation ratio), we enable to design mufflers having a higher sound transmission loss (up to 110 dB) at low frequencies (~ 195 Hz) but a constraint space (e.g., acoustic chamber length of 300 mm).

Sound Transmission Loss of Adaptive Sandwich Panels Treated With MR Fluid Core Layer

2016 ◽  
Author(s):  
Masoud Hemmatian ◽  
Ramin Sedaghati
Keyword(s):  
Magnetic Field ◽  
Applied Magnetic Field ◽  
Transmission Loss ◽  
Sandwich Panels ◽  
Sound Transmission ◽  
Core Layer ◽  
Sound Transmission Loss ◽  
Mr Fluid ◽  
Low Frequencies ◽  
Fluid Core

This study aims to investigate the sound transmission loss (STL) capability of sandwich panels treated with Magnetorheological (MR) fluids at low frequencies. An experimental setup has been designed to investigate the effect of the intensity of the applied magnetic field on the natural frequencies and STL of a clamped circular plate. A multilayered uniform circular panel comprising two elastic face sheets and MR fluid core layer is fabricated. It is shown that as the applied magnetic field increases, the fundamental natural frequency of the MR sandwich panel increases. Moreover, the STL of the panel at the resonance frequency considerably increases under applied magnetic field. Furthermore, an analytical model for the STL of the finite multilayered panels with MR core layer is developed and compared with the experimental measurements. The MR core layer is treated as a viscoelastic material with complex shear modulus. It is shown that good agreement exists between the analytical and experimental results. Parametric study has also been conducted to investigate the effect of face sheets and core layers’ thickness.

scholarly journals Analysis of the transmission loss of double-leaf panels with an equivalent spring–mass model for studs

2020 ◽  
Vol 37 ◽  
pp. 126-133
Author(s):  
Yuan-Wei Li ◽  
Chao-Nan Wang
Keyword(s):  
Distribution Curve ◽  
Transmission Loss ◽  
Sound Transmission ◽  
Experimental Results ◽  
Sound Insulation ◽  
Sound Transmission Loss ◽  
Mass Model ◽  
Steel Stud ◽  
Panel Thickness ◽  
Stiffness Distribution

Abstract The purpose of this study was to investigate the sound insulation of double-leaf panels. In practice, double-leaf panels require a stud between two surface panels. To simplify the analysis, a stud was modeled as a spring and mass. Studies have indicated that the stiffness of the equivalent spring is not a constant and varies with the frequency of sound. Therefore, a frequency-dependent stiffness curve was used to model the effect of the stud to analyze the sound insulation of a double-leaf panel. First, the sound transmission loss of a panel reported by Halliwell was used to fit the results of this study to determine the stiffness of the distribution curve. With this stiffness distribution of steel stud, some previous proposed panels are also analyzed and are compared to the experimental results in the literature. The agreement is good. Finally, the effects of parameters, such as the thickness and density of the panel, thickness of the stud and spacing of the stud, on the sound insulation of double-leaf panels were analyzed.

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