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asingle look up table representing the two draft gear springs in series and then tuning draft gear
modelparameters to suit adraft gear pair.The slack element can be added either in the look up table
or added in series.Different parameterscan be chosenfor loading and unloadingcurves. The small
kick in the unloading curve is observed in some test data. The dynamicist can also implement
slightly different values of, f , V f , m s and m k for the unloading curve if required toobtain agood fit
to the experimental data.
There is always room for debate as to whether acomplex model asdescribed here is justified
whencomparedtothe simpler yetdetailed work by Duncan and Webb. 1 Theuser may decide on the
complexity of the model according to the purpose and accuracy required for the simulation studies
being completed. While the wedge friction model adjusts for different impact conditions, its use is
really justified for simulations where these conditions are expected to vary. The use of the wedge
model for the unloading curve is an area where asimple lookup table may suffice, as it is only
the loading curve data that shows large variations in stiffness. The following figures show
the response of the model with sine wave inputs with frequencies of 0.1, 1.0, and 10.0 Hz. This
frequencyrange covers both normal train operation and loose shunt impact conditions, Figures 9.19
to 9.21, inclusive. These results were obtained byapplying the friction wedge model only to the
loading curve. 9
Train simulations using this model are given in Figure 9.22 and Figure 9.23. Force and
acceleration traces are plotted for train positions: first and last connected couplers and wagons
positioned at intervals of 20% of train length. Both simulations are for adistributed powertrain for
which athrottle disturbance is added at time ¼ 38 sec. The first result showing sinusoidal locked
behaviourhas the train situated on acrest with the top of the crest situated in the first wagon group.
The second result uses exactly the same control input on flat track. It will be noted inFigure 9.22
that while longitudinal forces behave sinusoidally between time ¼ 40 sec and time ¼ 100 sec,
wagon accelerations are steady demonstrating locked draft gear behaviour. This is contrasted with
the oscillatory nature of wagons longitudinal behaviour for the sameperiod and control input on flat
track, Figure 9.23. The difference between what Duncan and Webb referred to as sustained
longitudinal vibration and cycle vibration can be identified in Figure 9.22 and Figure 9.23,
respectively.
Force, kN
2500
2000
1500
1000
500
0
- 500
- 1000
- 1500
- 2000
Model Output
Full Drop Test Data
Friction Wedge model
- 2500
- 200 - 150 - 100 - 50 0 50 100 150 200
Deflection, Incl, Slack, mm
Handbook of Railway Vehicle Dynamics
FIGURE 9.19 Draft gear model response —slow loading (0.1 Hz). 9 Source:From Cole, C., Improvements to
wagon connection modelling for longitudinal train simulation, Conference on Railway Engineering,
Rockhampton, Institution of Engineers, Australia, pp. 187–194, 1998. With permission.
© 2006 by Taylor & Francis Group, LLC