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.

Local coating of curved rails by using low friction material for squeal noise reduction

Curve squeal noise is one of the most prominent noises among railway noises. High levels of noise are generated when a train passes through curved sections, resulting in several complaints from the residents and vehicle passengers. To mitigate this problem, the squeal noise was attempted to be mitigated by laser cladding the composite material on the head of the rail. First, the effect of the negative gradient of the coefficient of friction on the squeal noise was theoretically examined. A simple model analysis indicated that the vibration of the wheel increased rapidly when the vibration system involved instability characteristics. In addition, the change in the friction coefficient owing to the local coating of the rail with a low friction material was investigated using a roller rig test equipment. The results demonstrated that the negative friction coefficient did not occur when the contact position between the wheel and rail was locally coated. Furthermore, the effect of the low friction local coating on the squeal noise in the curve section was examined in operational rails. The comparison of the results obtained before and after the local coating confirmed that the local coating of the rail can effectively reduce the squeal noise.