scholarly journals Improvement of transmission loss of bellows through thickness improvement and structural modification

2021 ◽  
Vol 13 (9) ◽  
pp. 168781402110496
Author(s):  
Hee-Min Noh
Keyword(s):  
Simple Model ◽  
Transmission Loss ◽  
Layer Structure ◽  
Low Frequency ◽  
Frequency Region ◽  
Test Results ◽  
Noise Performance ◽  
Actual Performance ◽  
Low Transmission ◽  
Vibration Model

The bellows of the vehicle are vulnerable to noise because of the low transmission loss among the components. Therefore, in this study, we modified the thickness and the structure of the bellows to improve transmission loss. Based on the impedance tube test, the transmission loss of the silicon rubber specimen – the main material of the bellows – was analyzed; the results confirmed low transmission loss in the low-frequency region. An analysis of the natural vibration model of the simple model indicated that in the low-frequency region of the bellows, a number of vibrations occurred because of the vibration of the outer and inner components. Accordingly, to improve transmission loss, the improvement introduced by varying the thickness was analyzed, and the results confirmed that the noise performance improved by more than 3 dB for a thickness of 3.5 mm in the double-layer structure. In addition, the transmission loss improved in the low-frequency region after acoustic-structure coupling analysis was performed based on a simple model. To compare the actual performance between the existing and improved bellows, a noise comparison test was performed. The test results confirm that the existing noise reduction index improved by 3 dB from 30 to 33 dB when the thickness was increased to 3.5 mm; in the frequency domain, the highest noise performance was improved with an improvement of 5.6 dB at 160 Hz.

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.

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.

Low frequency acoustic properties of a honeycomb-silicone rubber acoustic metamaterial

2017 ◽  
Vol 31 (11) ◽  
pp. 1750118 ◽  
Author(s):  
Nansha Gao ◽  
Hong Hou
Keyword(s):  
Silicone Rubber ◽  
Transmission Loss ◽  
Layer Structure ◽  
Low Frequency ◽  
Sound Transmission ◽  
Honeycomb Structure ◽  
Acoustic Properties ◽  
Sound Insulation ◽  
Control Zone ◽  
Acoustic Metamaterial

In order to overcome the influence of mass law on traditional acoustic materials and obtain a lightweight thin-layer structure which can effectively isolate the low frequency noises, a honeycomb-silicone rubber acoustic metamaterial was proposed. Experimental results show that the sound transmission loss (STL) of acoustic metamaterial in this paper is greatly higher than that of monolayer silicone rubber metamaterial. Based on the band structure, modal shapes, as well as the sound transmission simulation, the sound insulation mechanism of the designed honeycomb-silicone rubber structure was analyzed from a new perspective, which had been validated experimentally. Side length of honeycomb structure and thickness of the unit structure would affect STL in damping control zone. Relevant conclusions and design method provide a new concept for engineering noise control.

Observations on the Relations among Occlusion Effect, Compliance, and Vent Size

2002 ◽  
Vol 13 (01) ◽  
pp. 025-037 ◽  
Author(s):  
Roberto Carle ◽  
Søren Laugesen ◽  
Claus Nielsen
Keyword(s):  
Hearing Loss ◽  
Simple Model ◽  
Laboratory Experiment ◽  
Hearing Aid ◽  
Low Frequency ◽  
Minimum Size ◽  
Similar Relationship ◽  
Profound Influence ◽  
Occlusion Effect ◽  
Clinical Experiment

In a clinical experiment, it was found that there is a high correlation between the compliance measured by tympanometry and the minimum size of the earmold vent, which just solves the client's occlusion problem related to his/her own voice when using a hearing aid. For ears with sensorineural hearing losses, compliance explained 59 percent of the variation in vent size, whereas the average low-frequency hearing loss explained as little as 0.3 percent. In a laboratory experiment, the objective occlusion effect measured with the participants' own voices showed a similar relationship with compliance. Whereas the former relationship between compliance and vent size may be explained by a simple model, the latter relationship turns out to be the opposite of what a firstorder model predicts. Hence, compliance must be indicative of another aspect of the occlusion mechanism, which has a more profound influence on the observed occlusion effect than compliance itself.

Fish Attraction with Pulsed Low-Frequency Sound

1968 ◽  
Vol 25 (7) ◽  
pp. 1441-1452 ◽  
Author(s):  
Joseph D. Richard
Keyword(s):  
Acoustic Stimulus ◽  
Low Frequency ◽  
Reef Fishes ◽  
Test Site ◽  
Acoustic Signals ◽  
Commercial Fisheries ◽  
Test Results ◽  
Potential Applications ◽  
Predatory Fishes ◽  
Underwater Television

A series of tests were conducted to determine the effectiveness of pulsed low-frequency acoustic signals for attracting fishes. The acoustic signals were contrived to simulate the hydrodynamically generated disturbances normally associated with active predation. Underwater television was used to observe fish arrivals during both control and test periods. Demersal predatory fishes were successfully attracted although they habituated rapidly to the acoustic stimulus. Members of the families Serranidae, Lutjanidae, and Pomadasyidae were particularly well represented among the fishes attracted. Sharks were also attracted in considerable numbers. Herbivorous reef fishes, although common around the test site, were not attracted. Possible relationships between the test results and the hearing capabilities of fishes are discussed. It is concluded that acoustic attraction techniques have potential applications in certain existing commercial fisheries.

Incoherent inelastic neutron scattering from polyacetylenes in the low-frequency region

1985 ◽  
Vol 10 (4) ◽  
pp. 293-295 ◽  
Author(s):  
M. Tasumi ◽  
I. Harada ◽  
H. Takeuchi ◽  
H. Shirakawa ◽  
S. Suzuki ◽  
...  
Keyword(s):  
Neutron Scattering ◽  
Inelastic Neutron Scattering ◽  
Low Frequency ◽  
Inelastic Neutron ◽  
Frequency Region
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