No abstract

When a railway vehicle moves over a sharply curved section of track, intense high-frequency noises sometimes occur. These are potentially a source of annoyance to those living adjacent to railway tracks. To efficiently identify measures appropriate to reduce curve squeal, it is important to determine the dominant noise type. However, it is difficult to analyze the various noises made over curved sections of railway using general noise measurements. In this study, we analyzed squealing and flange noises using various experimental approaches. We first investigated the noise characteristics of the railway vehicle via structural analysis of the wheel. It was confirmed that a wheel has various natural frequencies and eigenmodes in the high frequency range, i.e. over 1000 Hz. A roller rig test was performed to measure and investigate the characteristics of the noise generated when an actual wheel and the curved section of the railway track come in contact with each other. In this experiment the squeal and the flange noises, in particular, were reproduced by adjustments made to the lateral angle and vertical force, respectively. Results confirmed that the squealing noise occurs in the high frequency region and the flange noise occurs in various modes. A study was also conducted to measure and analyze the noise in the actual curved section of an urban railway. By comparing the frequency analysis and the natural frequency analysis of the noise that was actually measured, the mode by which the wheel caused the squealing noise was confirmed. Furthermore, the influence of the noise generated inside and outside the curved section of the track was investigated based on velocity, and the influence of the former on the noise generated was also examined. This study provides information on the squeal and flange noises generated when a railway vehicle moves over a curved section of a railway using various experimental approaches.

：Volumetric error modelling and compensation has become one of the most cost-effective ways to improve the accuracy and performance of machine tools. However, the time-consuming measurement process limits its application.Hence, a volumetric error rapid modelling and compensation method based on the sensitivity analysis is proposed. Firstly, a generalized kinematic model of the vertical machining center is established. Then the most important key error components are determined according to the sensitivity analysis of the all error components, while the less important angular errors can be neglected. Consequently, all key error components are measured and modelled with Chebyshev polynomials, and further applied in a real time error compensation system. To evaluate the effectiveness of this method, the positioning errors alone each translational axis and body diagonal lines with and without error compensation are compared. The former is greatly reduced from 21.9 μm to 6.5 μm, while volumetric error similarly reduced from 81.6 μm to 35.5 μm. Finally, this method is applied into 20 vertical machining centers, all improved to less than 40 μm. This paper innovatively uses sensitivity analysis as the theoretical basis for simplifying machine tool error models, and proposes a rapid modeling and compensation method for batch of vertical machining centers. This method can effectively improve the error compensation efficiency, which shows great potential in the future industrial applications.

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.

No abstract