Parametric study of axle box acceleration at squats

Abstract

This paper presents a study of the parameters that influence the detection of squats when using axle box acceleration (ABA) measurements. The analysed parameters include the train speed, the location of the squat in the track relative to the sleeper, and the track design. The study is conducted relying on a validated finite element model. The ABA measurements are found to be highly influenced by train speed. To model this influence, a practical method is proposed to represent the relationship between the train speed and relevant characteristics of ABA (magnitude and frequency) at a given squat. Such practical relationships provide the opportunity to map the ABA signals when it proves impossible to run measuring trains at a constant speed (as is the case with any in-service railway vehicle). The parameter study also indicates that the major frequency characteristics of ABA at squats are strongly related to the natural frequencies of the track. This conclusion is validated by performing hammer tests on the railway track. It is suggested that a proper characterization of the tracks will lead to a better understanding of the ABA signals. Finally, it is claimed that the results presented in this paper can be used as a guideline to calibrate or improve squat detection algorithms based on ABA measurements on a track.