An assessment of mode-coupling and falling-friction mechanisms in railway curve squeal through a simplified approach

Abstract

Curve squeal is one of the most annoying types of noise caused by the railway system. It usually occurs when a train or tram is running around tight curves. Although this phenomenon has been studied for many years, the generation mechanism is still the subject of controversy and not fully understood. A negative slope in the friction curve under full sliding has been considered to be the main cause of curve squeal for a long time but more recently mode coupling has been demonstrated to be another possible explanation. Mode coupling relies on the inclusion of both the lateral and vertical dynamics at the contact and an exchange of energy occurs between the normal and the axial directions. The purpose of this paper is to assess the role of the mode-coupling and falling-friction mechanisms in curve squeal through the use of a simple approach based on practical parameter values representative of an actual situation. A tramway wheel is adopted to study the effect of the adhesion coefficient, the lateral contact position, the contact angle and the damping ratio. Cases corresponding to both inner and outer wheels in the curve are considered and it is shown that there are situations in which both wheels can squeal due to mode coupling. Additionally, a negative slope is introduced in the friction curve while keeping active the vertical dynamics in order to analyse both mechanisms together. It is shown that, in the presence of mode coupling, the squealing frequency can differ from the natural frequency of either of the coupled wheel modes. Moreover, a phase difference between wheel vibration in the vertical and lateral directions is observed as a characteristic of mode coupling. For both these features a qualitative comparison is shown with field measurements which show the same behaviour.

Modelling and mitigation of wheel squeal noise under friction modifiers

“…The magnitude of all these effects are dependent upon the exact cornering conditions such as the train configuration, creep law and wheel/rail contact geometries. Recent research has investigated the possibility of mode coupling in these conditions [10]. Other effects on creep behaviour can also be captured by the present model.…”

“…Mode coupling has also been investigated as a mechanism of rail corrugation [9]. However experimental and field evidence of this mechanism in railways is only qualitative at this stage [10].…”

Squeal Noise Analysis Using A Combination of Nonlinear Friction Contact Model

“…Brunetti developed a method to predict unstable mode selection by modal absorption index from CEA [20]. Ding developed the assessment of the unstable vibration by mode coupling and nonlinear falling friction mechanism [21]. Oberst also modelled the brake pad contact by pressure-depended material properties of lining [22], and Tison had the integration of ABSTRACT -Squeal noise is generated by an unstable friction-induced vibration in a mechanical structure with friction load.…”

Numerical modeling of wheel-rail squeal-exciting contact

“…To consider the influence of the vertical dynamics on friction, the 'mode-coupling dynamic instability' mechanism have been employed in combination with falling-friction theories to predict friction-induced instability [8,[11][12][13] . Chiello , et al [14] concluded that the two types of destabilization caused by the falling-friction mechanism and by the mode-coupling mechanism may be combined in each particular situation of squeal; thus, both mechanisms should be explored [15] .…”