Low Frequency Acoustic Performance in Ducts Using Honeycomb Layer Systems

2008 ◽  
Vol 15 (1) ◽  
pp. 21-34
Author(s):  
Wing-Cheong Tang
Keyword(s):  
Noise Reduction ◽  
Transmission Loss ◽  
Minimum Weight ◽  
Low Frequency ◽  
Superior Performance ◽  
Composite Sandwich ◽  
System A ◽  
Composite Sandwich Structures ◽  
Mass Spring ◽  
Air Cavities

The use of composite materials, like honeycomb structures, in the building industry is growing rapidly, due to their superior performance (very high Sound Transmission Loss) and significant weight reduction over conventional materials. An experimental investigation into low-frequency duct noise reduction using honeycomb sandwich panels is presented. Composite sandwich structures with an air gap between panels provide low-frequency sound absorption. The waves in the duct are coupled with those in the porous layer and the air cavities. The energy is dissipated as a result of the resonant mass-spring behavior of the system. A significant impact on the noise reduction is obtained by using a comparatively stiff honeycomb panel, in combination with a thin metallic duct wall with minimum weight. A noise reduction up to 12dB, below 300 Hz, is demonstrated.

Active sensing of impact damage in composite sandwich panels by low frequency Lamb waves

2008 ◽  
Vol 112 (1131) ◽  
pp. 279-283 ◽  
Author(s):  
C. Soutis ◽  
K. Diamanti
Keyword(s):  
Lamb Waves ◽  
Impact Damage ◽  
Low Frequency ◽  
Practical Applications ◽  
Reinforced Plastics ◽  
Composite Sandwich ◽  
Composite Sandwich Structures ◽  
Inspection Strategy ◽  
Extent Of Damage ◽  
Non Destructive

Abstract The development of a robust non-destructive system to detect and monitor the extent of damage in carbon fibre reinforced plastics (CFRP) during service life is a key problem in many practical applications, especially in the aircraft industry. The lack of such technique has severely limited the potentially extensive use of composite materials. In this study a cost and time effective inspection strategy for in-service health monitoring of composites is demonstrated using the fundamental anti-symmetric A 0 Lamb mode at frequencies of 15-20kHz. In principle, this method involves analysis of the transmitted and/or reflected wave after interacting with the test-piece boundaries or discontinuities (defects). In the present work, the applicability of the technique to composite sandwich structures is explored and defects of critical size are successfully detected.

Application of phononic crystals for vibration reduction and noise reduction of wheel-driven electric buses based on neural networks

2021 ◽  
pp. 095440702110359
Author(s):  
Boqiang Zhang ◽  
Penghui Chen ◽  
Huiyong Chen ◽  
Tianpei Feng ◽  
Chengxin Cai ◽  
...  
Keyword(s):  
Noise Reduction ◽  
Band Gap ◽  
Structural Parameters ◽  
Phononic Crystal ◽  
Low Frequency ◽  
Phononic Crystals ◽  
Frequency Noise ◽  
Low Frequency Noise ◽  
System A ◽  
Electric Bus

Because of the position of the motor and the excitation of the suspension system, a wheel-driven electric bus produces low-frequency noise, which is difficult to resolve through traditional sound absorption and noise reduction technology. Through an interior noise test of a wheel-driven electric bus, we found that the interior low-frequency noise had a considerable influence on the driver. In order to solve this problem, a locally resonant phononic crystal was used to meet the requirements of vibration and noise reduction for the wheel-driven electric bus. The intrinsic relationship between the band gap distribution of the locally resonant phononic crystal and the topology was established by training a neural network, so as to achieve the desired effect of the bandgap model on the basis of the input bandgap range. Upon an increase in the number of models, the prediction model error decreased gradually. This method could quickly obtain the structural parameters of the locally resonant phononic crystal with the expected band gap, which made it convenient to apply locally resonant phononic crystals to the vibration and noise reduction of wheel-driven electric buses and in other fields.

scholarly journals Analysis of Composite Scrubber with Built-In Silencer for Marine Engines

2021 ◽  
Vol 9 (9) ◽  
pp. 962
Author(s):  
Myeong-rok Ryu ◽  
Kweonha Park
Keyword(s):  
Noise Reduction ◽  
Transmission Loss ◽  
Flow Characteristics ◽  
Low Frequency ◽  
Frequency Region ◽  
Reverse Direction ◽  
Sulfur Oxide ◽  
Noise Characteristics ◽  
Average Transmission ◽  
Reduction Effect

The International Maritime Organization (IMO) is strengthening regulations on reducing sulfur oxide emissions, and the demand for reducing exhaust noise affecting the environment of ships is also increasing. Various technologies have been developed to satisfy these needs. In this paper, a composite scrubber for ships that can simultaneously reduce sulfur oxide and noise was proposed, and the flow characteristics and noise characteristics were analyzed. For the silencer, vane type and resonate type were applied. In the case of the vane type, the effects of the direction, size, and location of the vane were analyzed, and in the case of the resonate type, the effects of the hole location and the number of holes were analyzed. The result shows that the length increase of the vane increased the average transmission loss and had a great effect, especially in the low frequency region. The transmission loss increased when the vane was installed outside, and the noise reduction effect was excellent when the vane was in the reverse direction. In the resonate type, increasing the number of holes is advantageous for noise reduction. The condition for maximally reducing noise in the range not exceeding 840 Pa, which is 70% of the allowable back pressure, is a vane length of 225 mm in the outer vane reverse type. The pressure drop under this condition was 777 Pa, and the average transmission losses in the low frequency region and the entire frequency region were 43.5 and 54.5 dB, respectively.

scholarly journals Effect of Cavity Structure on Acoustic Characteristics of Phononic Crystals Based on Double-Layer Plates

Crystals ◽  
2020 ◽  
Vol 10 (11) ◽  
pp. 995
Author(s):  
Chuanmin Chen ◽  
Zhaofeng Guo ◽  
Songtao Liu ◽  
Hongda Feng ◽  
Chuanxi Qiao
Keyword(s):  
Noise Reduction ◽  
Band Gap ◽  
Double Layer ◽  
Transmission Loss ◽  
Low Frequency ◽  
Phononic Crystals ◽  
Frequency Noise ◽  
Structural Factors ◽  
Low Frequency Noise ◽  
Cavity Structure

Localized resonance phononic crystals (LRPCs) are increasingly attracting scientists’ attention in the field of low-frequency noise reduction because of the excellent subwavelength band gap characteristics in the low-frequency band. However, the LRPCs have always had the disadvantage that the noise reduction band is too narrow. In this paper, in order to solve this problem, LRPCs based on double-layer plates with cavity structures are designed. First, the energy bands of phononic crystals plate with different thicknesses were calculated by the finite element method (FEM). At the same time, the mechanism of band gap generation was analyzed in combination with the modalities. Additionally, the influence of structure on the sound transmission loss (STL) of the phononic crystals plate and the phononic crystals cavity plates were analyzed, which indicates that the phononic crystals cavity plates have notable characteristics and advantages. Moreover, this study reveals a unique ”cavity cave” pattern in the STL diagram for the phononic crystals cavity plates, and it was analyzed. Finally, the influence of structural factors on the band structure and STL of phononic crystals cavity plates are summarized, and the theoretical basis and method guidance for the study of phononic crystals cavity plates are provided. New ideas are also provided for the future design and research of phononic crystals plate along with potential applications in low-frequency noise reduction.

scholarly journals Improvement of noise reduction performance in bellows using multilayer perforated panels

2021 ◽  
Vol 13 (1) ◽  
pp. 168781402098625
Author(s):  
Hee-Min Noh
Keyword(s):  
Noise Reduction ◽  
Multilayer Structure ◽  
Transmission Loss ◽  
Low Frequency ◽  
Frequency Region ◽  
Design Parameters ◽  
Railway Vehicle ◽  
Noise Performance ◽  
Analysis Model ◽  
Railway Vehicles

When the speed of a railway vehicle increases, the level of noise inside the vehicle inevitably increases as well, which is a major cause of discomfort to passengers. The most effective method is to improve the overall noise reduction performance of a vehicle. In particular, the gangway of the railway vehicle is made of silicone rubber; therefore, its noise reduction performance is inferior to that of other components of the vehicle. Thus, it is essential to improve the interior noise performance of railway vehicles. This study aims to reduce the noise in the low-frequency region of a railway vehicle gangway. It examines the applicability of the multi-layered resonance type panel, which has not been previously applied to the bellows in railway vehicles. In particular, the transmission loss was improved by changing the structure without filling the bellows with sound-absorbing material. First, a theoretical review of the noise reduction performance of a perforated multilayer structure was performed. Based on this, the major design parameters of the perforated multilayer structure that are effective in reducing noise in the low-frequency region of the bellows were derived. Through this, it was confirmed that in the multilayered structure, the hole diameter of 1 mm was effective in increasing the transmission loss in the low-frequency region, and the transmission loss was improved at 1% of the porosity. In addition, through a simple two-dimensional analysis model, it was confirmed that the transmission loss of the porous panel was improved at low frequencies of 100 to 400 Hz. Based on this result, a gangway with perforated multilayer structures was developed and tested. Through this verification test, it was confirmed that the noise performance of 9.2 dB was an improvement in the low frequency range of 100 Hz.

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