Simulation Of Longitudinal Train Dynamics Considering The Variation Of Adhesion

The developing trend of heavy haul railway transportation is the constantly increasing of traction weight and marshalling length of trains,and the longitudinal impulse problem is becoming more and more prominent.The tracting force and electrical braking force of locomotive are important contents to be considered in the calculation of longitudinal train dynamics,and adhesion is an important factor restricting the exertion of locomotive force.The longitudinal dynamic performance of locomotives will have some differences under the consideration of varying adhesion.This paper established the longitudinal dynamic calculation model of 20,000 t heavy haul combined train with "1+1" mode using the TDEAS package developed by the Traction Power State Key Laboratory of Southwest Jiaotong University.The longitudinal train dynamic calculations considering the influence of adhesion reduction on sharp curve,curve lubrication and locomotive sanding were carried out.The results were shown that:1.On the tracting condition of train on straight track,the traction would be raised a notch per 5s until the maximum without considering the varying adhesion limitation,the remaining adhesion force of the locomotive would be in a negative state for a long time which would cause the wheel skidding.The maximum coupler-pulling force was 800 kN,and train could accelerate to 70km/h within 7.8 minutes,the traveling distance was 4.85 km.2.This paper carried out the longitudinal train dynamic calculations for 8 conditions on straight line considering the varying adhesion coefficients from large to small to avoid the skidding of locomotive.The lower the adhesion coefficient was,the lower the tracting force of locomotive would be,the slower the acceleration would be,and the longer the running distance would be.For the condition 7 and 8 with poor wheel-rail adhesion coefficient,the initial remaining adhesion forces of locomotive were lower which valuing 103 kN and 68 kN respectively.The notches that could be rapidly raised were smaller,which were the 3rd and2 nd respectively.Train under single tracting operation could not get to the expected speed values,train speeds under condition 7 and 8 could be increased to 53km/h and 29km/h respectively.As for conditions 7 and 8,2 schemes were proposed to improve the tracting performance of train,i.e.high axle-load locomotive tracting and assisting locomotive tracting.For condition 7,the train speed could be accelerated to 62 km/h under high axle-load locomotive tracting scheme,and the train speed could be accelerated to 70 km/h under assisting locomotive tracting scheme.For condition 8,the train speed could be raised to 40 km/h under high axle-load locomotive tracting scheme,and the train speed could beaccelerated to 52 km/h under assisting locomotive tracting scheme.Accelerating time had also been shortened to a certain extent.Remaining adhesion force had been improved a little,but the tracting notch could not be raised further.3.As for the calculation of cyclic braking condition on-11‰ long heavy down grade section,if the varying wheel-rail adhesion was not taken into account,the remaining adhesion force of locomotive would be insufficient if 100% electrical braking force was applied in traditional calculation.This paper carried out the longitudinal train dynamic calculations for 3 conditions considering the varying adhesion coefficients from large to small.The corresponding adhesion coefficients were 100%,90% and 80% respectively.The maximum electrical braking forces applied to locomotive were 80%,70% and 60%respectively.The corresponding maximum values of coupler-pressing force were 586 kN,538kN and 490 kN,respectively.4.The following tracting calculations had been carried out for curve passing conditions with or without consideration of curve lubrication.Tracting calculations were carried out for train passing through curves of 400 m,500m and 600 m without considering curve lubrication,due to the different degrees of adhesion reduction on curves with different radius,there were differences in tracting operation control when the middle locomotives passing through curves.When passing through the R400 m curve,the tracting notch needed to be reduced from 7th to 6th notch.When passing through the R500 m curve,the tracting notch did not need to be reduced.When passing through the R600 m curve,there was no adhesion reduction,and the locomotive could pass the curve with the 8th tracting notch.Tracting calculation was carried out for train passing through R400 m curve considering the curve lubrication.Because of the lubrication,the adhesion coefficient on curve was obviously reduced.The leading locomotive and middle locomotive needed to be reduced from the 7th to 3rd notch to ensure some remaining adhesion force.Because the maximum tracting forces on each condition were the same,there was no difference between the maximum values of the coupler-pulling force.5.The tracting calculation was carried out for the starting condition considering locomotive sanding.Due to the obvious increasing of adhesion coefficient after locomotive sanding,the locomotive could be quickly raised to the maximum notch in a short time,the accelerating time could be shortened about 2.7 minutes,and the accelerating distance could be shortened by 1.6km.But the maximum value of coupler-pulling force increased from595 kN to 787 kN.6.Finally,taking the long downhill section of the Shuohuang Railway from Ningwu West to Yuanping South as an example,the longitudinal train dynamic of train was calculated,and 2 conditions corresponding to without considering the varying of wheel-rail adhesion or considering the varying of wheel-rail adhesion were compared.In the process of locomotive starting from Ningwu West Station,the locomotive notch of the former could reach the 10 th without considering the varying adhesion limitation.The locomotive could basically exert its full traction capacity(368kN),and the maximum coupler-pulling force occurred at the leading locomotive(722kN).In fact,the latter locomotive notch increasing would be limited by varying adhesion,and the maximum notch could only be limited to 8th,and locomotive's tracting ability,in fact,could not fully exert(265kN).The maximum coupler-pulling force occurred at the middle locomotive(560kN).When the train running on long down grade section,the former train's locomotive could apply 100% electrical braking force without considering the varying adhesion limitation.The latter train's locomotive could only apply 80% electrical braking force because of the varying adhesion limitation.On the process of electrical braking condition,the maximum coupler-pressing forces for 2 cases occurred at the middle of train,the former was 947 kN,and the latter was 809 kN.