Improvement of noise reduction performance in bellows using multilayer perforated panels

Abstract

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.

Analysis of Noise Levels in Typical Passenger Cars

“…Hence, in the mentioned case, it would be advisable to use a thermal screen in the form of a thin layer of extruded aluminum. Similarly, Noh [41] used a solution with extruded aluminum. Generally, to minimize the level of noise emitted by internal combustion engines, the solution, in short, is a gradual increase in the number of electric cars in use.…”