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Wheel/rail contact analysis of tramways and LRVs against derailment
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Yasuhiro Satoa,∗, Akira Matsumotoa, Hiroyuki Ohna National Traffic Safety and Environment Laboratory (NTSEL), 7-42-27 Jindaiji-higashib Sumitomo Metal Technology, Inc., 1-8-11 Harumi, Chuo-ku, Tokyo 104-6109 Japan
a r t i c l e i n f o
Article history:Accepted 6 December 2007Available online 6 June 2008
Through the developmentprecision data of the profiof rail or wheel profile maespecially to identify the loa simulation tool whichsimulate the situations sucondition of derailment pthe analysis of derailment
1. Introduction
In recent years, some cities in Japan introduced LRVs to the con-ventional tramlines as LRV is environmental friendly and passengerkindly, and some other cities are going to introduce LRT systems.
Most of the LRVs adopted in Japan have the latest low floor tech-nology from Europe as European countries have long experience inusing LRT systems. In order to realize the low floor configuration,most of the LRVs have independent rotating wheel-set system. Thisconstruction makes the different running characteristics of wheelsto negotiate on rail from those of solid wheel-set systems.
On the other hand, the tracks and switches in most tramwaylines are not upgraded when LRVs are introduced. The conventionaltracks and switches have been constructed for traditional tramvehicles and the top of rails and switches may be worn to a contourto fit with the profile of conventional wheels. In the extreme case,LRVs are put into through-operation both on tramway system andheavy railway system, although both systems have different regu-lations, for example, “back wheel flange clearance”, “wheel flangeheight”, “wheel diameter” and so on.
For those reasons, it is very important to investigate the contactproperty between wheel and rail, especially in switch section, inorder to prevent the risk of derailment before the LRV is put intooperation. Unfortunately, the analysis using digital profile data hasnever been done for such purpose until now. One of the reasons
easurement tool of rail and wheel profiles, it is much easier to acquire thelthough most of the digital data are used independently for the purposesment at present, such data make it possible to analyze the contact statusn of the contact point between rail and wheel tread. The authors developedot only simulate the normal wheel/rail contact condition, but can alsoback-wheel flange contact in switching section and the critical contact
mena. In this paper, the data processing method and the applications toess of LRV vehicles are introduced.
for this situation is, most of the conventional tools for wheel/railcontact analysis are developed for the purpose of new wheel profiledesign [1]. They consider mainly on the profile of wheel tread butnot of wheel flange, especially of the back flange of wheel whichwill contact with guard rail in switch section or in curved sectionof tramway lines.
In order to deal with this problem, a wheel/rail contact sim-ulation tool is developed. This tool can deal with not only theconventional contact problem of wheel tread contact including two
point contact (wheel tread and wheel flange), but with the backflange contact problem including three points contact (wheel tread,wheel flange and back of wheel flange which may happen in switchsection). This tool can also deal with wheel-set roll over situationwhich may happen in the lateral turn over derailment.
In this paper, the details of the newly developed wheel/rail con-tact analyzing tool and its application to the investigation of LRVderailment is reported, and the proposal to evaluate the derailmentsafety by concerning the contact location on wheel is explained.
2. Contact analyzing tool
2.1. Profile data
The digital profile data of rail and wheel are measured by usingMiniProf developed by GREENWOOD Engineering [2]. As the pro-files of wheel and rail are measured respectively, they are combinedand deployed into the same plane coordinate by considering theback flange distance of wheel-set and the geometry of track. Thecoordinate is defined by the top level of rails and the center axis of
Fig. 1. Combined matrix of wheel and rail coordinate.
Fig. 2. Contact point analysis model.
wheel-set. The cant elevation of track is neglected. A given verti-cal distance is added to the wheel profile matrixes. Fig. 1 shows
the typical combined matrixes of wheels and rails in the planecoordinate.
2.2. Contact points analyzing process
Contact points analysis is done for given lateral displacementof wheel-set. The yawing angle of wheel-set is neglected because3D contact analysis is necessary for the yawing movement ofwheel-set, and the analysis will be much more complicated. Elasticdeformation and displacement are also neglected.
At first, the shortest vertical distance between wheel and rail ofeach pair is calculated as shown in the model of Fig. 2. The short-est vertical distance of left wheel/rail pair may not be the same asthat of right wheel/rail pair. Fig. 3 shows the case where the leftwheel/rail pair may still remains a certain distance to get in con-tact when the wheel-set moves vertically down through the samedistance as the shortest distance of right wheel/rail pair. In thiscase wheel-set is rotated around the wheel-set center by consider-ing the distance difference between left side and right side pairs.Coordinates of wheel profile matrix are recalculated according to
Fig. 3. Vertical distance difference.
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Fig. 4. Definition of contact angle.
the wheel-set rotation angle. The shortest distances between wheeland rail pair are analyzed again. This process is repeated again andagain until the distance difference is small enough to an acceptablevalue. At this state, the coordinates which have the shortest verticaldistance are considered as the contact points.
Contact angle is obtained after the contact point is fixed. Fig. 4shows the definition of contact angle between rail and wheel. Thisfigure shows the enlargement of the digital rail profile coordinatesincluding the contact point. The inclination angle of the approxi-mate line of 5 continuous coordinates around the contact point isdefined as the contact angle.
For high rail side, the vertical distance between wheel flangeand rail is also analyzed when wheel-set lateral displacement islarge enough that the wheel flange may get in contact. With theincrease of wheel-set lateral displacement, the contact point onwheel may jump from tread section to wheel flange. The transfer
state is defined as two points contact.
For low rail side, the vertical distance between wheel back flangeand guard rail is also calculated if guard rail exists. Sometimes thewheel tread of low rail side is going to be elevated from rail oncethe wheel back flange get in contact with the guard rail. The contactanalysis of low rail will be done just between the wheel back flangeand the guard rail.
Wheel rolling radius and altitude from top of flange to the con-tact point can be calculated once the contact point coordinate isobtained.
The analyzing tool is extended to analyze the state of the wheel-set of train overturning process. In the state of train overturningprocess, just one side of wheel/rail pair engaged in the contactand the analysis is done for one side. As shown in Fig. 5, atfirst, the contact point for the shortest vertical distance betweenwheel and rail is detected, and after that wheel-set is rotated lit-tle by little around this contact point until another contact pointappeared. The angle of the wheel-set at this state is the overturningangle.
Fig. 5. Wheel-set rolling over analysis model.
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Fig. 6. The derailed switch section.
3. Application in derailment investigations
3.1. LRV derailment investigation
3.1.1. Derailment site investigationThis analyzing tool was applied to the derailment accident inves-
tigation of new LRV systems. The line where new LRVs were put intooperation is basically a tramway line, but the vehicles were used forthrough-operation to a conventional railway line. For this reason,the conventional vehicles are constructed under the regulation ofrailway line. On the other hand, LRVs are designed under the reg-ulation of tramway. Before the first LRV fleet was put into service,many running tests were done in depot and in the tramway section.The wheel flange of the first fleet had been worn in this period andafter that it was put into service operation. Not so many test runwas carried out for the second fleet because the performances ofLRVs were considered equal to the results of test runs of the firstfleet.
Fig. 8. Contact simulation in railway section (
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Fig. 7. Contact with “wheel-set gauge”.
The accident happened in curved section of railway line just oneday after the new LRV of second fleet was put into service, wherethe first fleet had operated for months. After the derailment “GuardRail” was installed to the derailed section in order to prevent thewheel from derailment. Derailment happened again in a switch oftramway section just one trip after the re-operation. Fig. 6 shows
the section of the switch where the derailment happened. From thefigure it can be found, this section is tramway and the switch hasonly one tongue rail in it.
Top of rail profiles in the derailed section are measured. Wheelprofiles of LRV fleets and the typical conventional fleet are also mea-sured. At the same time, a “wheel-set gauge of LRV” is manufacturedand taken to site for contact state identification. Fig. 7 shows oneof the contact states by using the “wheel-set gauge”.
3.1.2. Contact simulation of derailment processWheel/rail contact simulations between those measured data
and designed profiles are carried out. The simulation results showperfect agreement with the phenomena observed at the derail-ment site. Figs. 8 and 9 show the simulation results in conventionalrailway section and Fig. 10 in tramway line.
From these simulation results it can be found, the contact char-acteristics between first fleet and second fleet are quite different,especially in the wheel flange contact region. For the first fleet, thecontact angle reaches to the maximum value of about 70◦ once thewheel flange enters into contact region. For the second fleet, wheelflange enters into contact region by much less lateral displacement
leading wheel-set of the first LRV fleet).
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ion (le
lation
Fig. 9. Contact simulation in railway sect
Fig. 10. Contact simu
of the wheel-set and the contact angle is much smaller at the firststage of flange contact. According to the Nadal’s equation [3], thecritical value of derailment coefficient become smaller for small
wheel flange contact angle, and it means easier to derail.
Another fact found from the simulation results is: the verticaldistance between the contact point at wheel flange and the top ofrail is much small for the second fleet compared with that of thefirst fleet. Shallow contact position means less friction energy isneeded for the contact point transporting to the top of rail (derail).
As the thickness of flange and the back flange distance of thetwo fleets are different, the low rail side wheel of the first fleet ismuch easier to be guided by the guard rail in tramway comparedwith the second fleet shown in Fig. 10. In Fig. 10, the back flangeof low rail side wheel has not been guided by guard rail even theflange of high rail side wheel has contacted with rail. This means,some unguarded blank exists between the back flange and guardrail for the wheel-set of the second fleet, and wheel-set cannot beguided by the guard rail even in sharp curve section of tramway.
According to the simulation and other analysis results, solutionsto prevent derailment had been proposed to the railway companyand the vehicle manufacture. The proposals were accepted andalternation of wheel-set design was carried out. Now the secondfleet is in operation on tramway and conventional railway line with-out problem.
ading wheel-set of the second LRV fleet).
in tramway section.
3.2. Rolling over derailment simulation
In case of over speed operation at curve section or in strong
lateral wind blowing, vehicle may be put into the danger of turnover derailment. In this situation, wheel-set may roll over on thetrack. Sometimes, the contact traces on top of rail can be found inthe derailment section (Fig. 11). It is not easy to identify whetheror not the trace is printed by the derailed wheel.
This analyzing tool can help to verify the practice. Fig. 12 showsone of the simulation results to identify the contact trace printedby the rolling over wheel. Zero point in this figure is the point todefine the track gauge and is used to calculate the lateral positionof contact point.
4. Derailment measuring concept
Nadal’s limit is dependent on wheel/rail profiles and the coef-ficient of friction between them, which is generally believed to beconservative. Measured lateral-to-vertical load values or recordedvalue during test [4] often exceeded Nadal’s limit without anyapparent danger of wheel climbing. In recent years, safety criteriawere examined at a field test in turnout in Japan [5]. They inves-tigate the behavior of the wheel-set and the relationship between
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the situations such as back-wheel flange contact in switching sec-
Fig. 11. Contact trace on top of rail.
Fig. 12. Rolling over and contact trace.
some kinds of parameters and the wheel rise. In another research,the relationship between the friction coefficient and wheel climbderailment is particularly discussed [6]. In both of the papers, thewheel rise similar to vertical displacement of the wheel is inves-tigated. It is needless to say that the vertical displacement of thewheel is directly connected with the risk of wheel climb derailment.We look at the wheel rise in a new light. The wheel rise is related tothe quantity of the shift of contact point between wheel and rail. Sothe location of contact point on wheel flange or back flange has greatinfluence on the derailment crisis. Apart of the derailment coeffi-cient (lateral force/wheel load), which is commonly used in Japanto evaluate the safety of vehicle in curve section, a new evaluationparameter which concerns with contact point location is proposed.This parameter is named “derailment energy”. This parameter isthe function of “the altitude of contact point to the critical pointon rail gauge corner”, “wheel load”, “lateral contact force”, “frictioncoefficient” and so on. Fig. 13 shows one of the examples of move-ment of contact point on wheel and on top of rail. In the derailment
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Fig. 13. Contact simulation of derailment process.
of wheel climbing, the movement of contact point involves the fric-tion energy. Total energy from the state of first wheel flange or backflange contact to the critical point on rail or guard rail will be eval-uated by this parameter. The detail of the evaluation methodologyis still under verification.
5. Conclusions
In order to analyze the derailment process of LRV in tramway andin conventional railway, a simulation tool which can not only simu-late the normal wheel/rail contact condition, but can also simulate
tion or the contact at critical condition of derailment is developed.This tool is applied to the derailment investigation of LRV. Simula-tion results agree well with the practical measurements. From theanalysis by using this tool, the reasons of derailment are illumi-nated. Solutions were proposed to the railway company and themanufacture. After the improvement according to our proposal,derailment risk of the LRV is greatly reduced.
From the process of derailment investigation, a new parameterwe call “derailment energy”, that can evaluate the derailment riskis proposed.
References
1] I.Y. Shevtsov, V.L. Markine, C. Esveld, Wear 258 (2005) 1022–1030.2] http://www.railway-technology.com/contractors/track/greenwood/.3] M.J. Nadal, Ann. Mines 10 (1896) 232–288.4] W.C. Shust, J.A. Elkins, S. Kalay, M. ElSibaie, Wheel Climb Derailment Test Using
AAR’s Track Loading Vehicle, AAR report R-910, Pueblo, CO, 1997.5] H. Ishida, K. Ueki, Y. Yamashita, K. Asano, H. Kaneko, Proc. Jpn. Soc. Mech. Eng.
(95–36) (1995) 391–393 (in Japanese).6] K. Nagase, Y. Wakabayashi, H. Sakahara, Proc. Inst. Mech. Eng. 216 (2002) 237–247
