With the support of the Swiss Federal Office for the Environment (FOEN), the freight wagon leasing company Wascosa and SAVVY Telematic Systems conducted a research project to analyse flat spot detection. Flat spots generate a distinct, thumping sound and contribute to noise pollution.

Flat spots on freight wagon wheel sets are problematic. Not only do they lead to increased noise emissions, they also cause the wheel sets to wear out more quickly. In many cases, the flat spots are detected only after many kilometres on the rails, resulting in increased defects and costs. The new development makes it possible to identify flat spots via acoustic irregularities and eliminate them efficiently.

Methodology

SAVVY’s newly developed flat spot algorithm evaluates the vibrations in the time and frequency range on the telematic system. The measured data is processed directly on the telematic system to calculate different indicators and is compared to historical data. If there is a flat spot on the wagon, this will influence the indicators and trigger an alarm signal.

During operations there are a lot of factors that have an effect on the wheel (imbalance, uneven running surfaces and infrastructure etc.) and the wagon (natural vibrations, load influences etc.). This leads to a wide range of different overlapping frequencies which are perceived as a “whooshing” sound. Not every recurring vibration is a flat spot and, vice versa, not every disturbance on the running surface corresponds to a flat spot. It is therefore important to find significant correlations between the measured data of the affected wagons and the dimensions of the flat spots on the wagon wheels, SAVVY Telematic Systems explained.

A distinct, unnatural periodic sound

In the year 2000, some 265 thousand people were exposed to damaging or annoying railroad noise. To protect them, a comprehensive noise protection plan in accordance with the Swiss Federal Railroad Noise Control Act (14 March 2000) was implemented by 2015. Measures included work on Swiss rolling stock, noise barriers, and sound-proof windows.

Flat spots generate typical acoustic patterns. However, noise perception, especially as it pertains to trains, not only depends on the volume but also on the characteristics of a sound emission. While the sound of a passing freight train can be heard from quite a distance, it is not necessarily annoying; a flat spot on the other hand generates a distinct, unnatural periodic thumping sound. With average kilometrage exceeding 100 thousand, intermodal wagons are some of the most intensely used freight wagons in the business. Correspondingly, flat spots will affect noise emissions, SAVVY Telematic Systems pointed out.