Application of a micro-perforated panel absorber to reduce the curve squeal noise of railways

A micro-perforated panel absorber (MPPA) can reduce noise without the use of sound-absorbing materials. It is made of various materials and is poten- tially applicable in a variety of fields. However, the application of MPPAs is limited owing to the narrow absorption band. In a previous study, to enhance the sound- absorption performance of MPPAs, we proposed a parallel arrangement of multi- layer MPPAs. Based on the results of this previous study, we carried out the present study to apply an MPPA to the curve squeal noise of railways. Squeal noise, which occurs at approximately 500 to 5000 Hz, has high-level peaks. We designed and fabricated an MPPAwith the proposed structure according to the characteris- tics of the squeal noise. The noise reduction was analyzed after an MPPA barrier was installed in the field with a curve radius of 120 m. The reduction in noise level was approximately 17 dB(A) on the first floor and approximately 7 dB(A) on the fourth floor of the building. At 630 to 5000 Hz, the noise reduction level was at least approximately 5 dB(A). To analyze the noise absorption effect of the MPPA bar- rier, a simulation was carried out and subsequently verified by comparing the measurement results with the simulation results. In the simulation, the difference in noise reduction level between the MPPA and reflective barrier was analyzed. The noise reduction level of the MPPA barrier was approximately 7.5 dB(A) higher than that of the reflective barrier on the second and third floors of the build- ing at 630 to 5000 Hz. These results support the viability of MPPA application in re- ducing noise from curve squeal noise.

Light duty automotive duplex drum brake squeal analysis using the finite element method

The brake system creation is an important achievement for automotive production. However there is a secondary response of this system, its noise emission. Brake noise researches started in 1920’s and since then several causes were identified. In addition, many kinds of noises, their frequency range and characteristics were detected. Between these, the squeal is the noise that most concerns the automotive industry by reason of high warranty costs and environmental impact. The squeal noise occurs as a result of three mechanisms that are the stick-slip, the sprag-slip and the modal coupling and these are connected to material parameters of the brake components. This paper proposes a correlation between material and stability parameters of a light duty automotive duplex drum brake to indicate the influence of this on brake squeal. The results suggest that friction coefficient is the most influential parameter and its restrain does make possible to maintain squeal level under emissions regulations.