| Tramways have become an important and convenient mode of transportation in urban rail transit,because tramways operate safely,have dense and a large amount of traffic,and are also energy-saving and environmentally-friendly.In order to adapt to the development of tramways in urban rail transit and the stringent requirements of environmental protection,the curve squeal noise caused by trams has become an urgent problem to be solved.As a type of vibration-reducing and noise-reducing track structure,embedded rail track which has continuous support without using fasteners has been widely applied to tramway lines,and also applied to subway lines in some countries.But,remarkable curve squeal noise of this track structure still generates.At present,in the operation of tramway lines,there is insufficient understanding of curve squeal noise.For the sake of operational safety only,reasonable control measures against the curve squeal noise have not been taken,so that curve squeal problem is still very significant.Therefore,it is of far-reaching engineering significance to deeply and systematically conduct the study on characteristics and mechanisms,modeling and prediction of curve squeal for controlling the curve squeal noise of trams and further developing tramways in urban rail transit.For trams and embedded rail tracks,the research work on curve squeal noise of wheel-rail contact is mainly carried out in two aspects:measurements and theoretical model simulation.This paper mainly carries out the following research work:(1)The background and significance of the research on curve squeal noise are introduced.The formation mechanism of the curve squeal noise is briefly summarized.The research status of the curve squeal noise is systematically summarized from three aspects:modeling research,experimental research and control measures.(2)The squeal noise measurement of a tram curving an embedded rail track has been described in detail.Time domain and frequency domain characteristics of the curve squeal noise and its effects on the surrounding environment have been analyzed.The control effect of lubrication measures against squeal noise has also been analyzed.Combined with the measured data of wheelside squeal noise,wheel vibration,rail vibration and static resilient wheel dynamics,the formation mechanism of curve squeal noise of tram is understood as follows:based on negative friction characteristics,the wheel/rail lateral instable creep is the main reason for exciting the wheel to generate self-excited vibration and squeal noise.The negative friction characteristic was eliminated after lubrication,and then the squeal noise was significantly reduced,which further proves the above squeal noise excitation mechanism.(3)Simulation prediction models about dynamic characteristics of resilient wheel and embedded rail track are established to predict the wheel and rail mobilities,and the mobilities are also described in the form of state space.The wheel/rail mobilities and their state space forms are applied to the wheel/rail rolling contact curve squeal prediction model and to describe the dynamic characteristics of wheel/rail structure.(4)Based on the SIMPACK multi-body dynamics simulation analysis software,according to the parameters of the tram and the R=50m curve,a dynamic simulation model of tram has been established to predict and analyze the dynamic behaviors of the tram curving the tight curve.At a certain moment when the first wheelset of tram passing the round curve section of R=50m curve,the steady-state dynamic prediction results are used as the input parameters in the prediction of the wheel-rail contact curve squeal,mainly including the wheel-rail normal force,the size of contact patch,wheel-rail contact point position,wheel-rail contact angle and steady-state wheel-rail creepage.(5)The contact zone status of wheel and rail has been described in detail,and the falling friction formula has been introduced to describe the wheel-rail friction coefficient in the sliding state.Based on the mechanism of the wheel-rail self-excited vibration caused by the falling friction characteristic of friction curve,a simplified self-excited vibration model of wheel-rail contact is established,i.e.an ideal mass-on-moving-belt self-excited vibration system model,to simulate the self-excited vibration of wheel with a single wheel mode passing a sharp curved track.This model and its simulation results illustrate the mechanism of squeal noise due to wheel-rail contact self-excited vibration and the control principles of self-excited vibration.(6)The wheel-rail contact curve squeal noise prediction model has been established in time domain and frequency domain based on the wheel/rail dynamic characteristics prediction model,the tram curving dynamics prediction model,the wheel-rail rolling friction model and the wheel-rail rolling contact model.The evolution process of the self-excited vibration response of the wheel-rail contact system and its squeal noise are studied based on time domain analysis model.The stability of the self-excited vibration loop of the wheel-rail contact system is studied based on the frequency domain analysis model,and the wheel modes that are prone to squeal are analyzed.According to the field measurement results,the wheel-rail contact squeal noise prediction model both in time domain and frequency domain are revised,and the effectiveness of the revised models are verified.(7)Based on the wheel-rail contact curve squeal prediction model,a parametric investigation of the influencing factors of curve squeal has been conducted.The influencing factors include the steady-state wheel-rail creepage,wheel-rail friction characteristics,wheel-rail contact point positions,wheel damping,track damping and the track structure stiffness.Through this investigation,the key factors affecting the generation of curve squeal have been clarified.It is found that wheel-rail friction characteristics,wheel/rail damping,track structure stiffness and wheel-rail contact point positions all have significant influences on the wheel-rail self-excited vibration response and the wheel radiated squeal noise.Corresponding squeal noise control measures are proposed for each key factor. |
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