Lateral Wheel/rail force oscillations

Simulation of separate railway vehicles, approaches and techniques, wheel/rail contact forces, safety factors, ride comfort, stability, optimization of model parameters

Lateral Wheel/rail force oscillations

Postby jordanhannagan » Thu Aug 24, 2017 7:51 am

Hello

I am trying to simulate a single carriage rail vehicle operating on a flat curve with radius 150 m. The vehicle is to operate at a speed of 5km/hr (1.3999 m/s). Lateral and vertical wheel forces are to be recorded to determine wheel unloading etc.

The vehicle is a model of an Australian Comeng EMU. Vehicle information can be found here ( https://vicsig.net/suburban/train/Comeng ) and here ( https://en.wikipedia.org/wiki/Comeng_(train) )

When I run the simulations, I am seeing a very large oscillation in lateral force between the wheels and rails. The simulation runs as follows
1. Vehicle begins on tangent track for 20m at 1.3999 m/s. Velocity is constant throughout simulation.
2. Vehicle enters left curve. Curve consists of 50m transition length, 70m constant radius of 150m, 50m transition length. Curve does not include cant or rail widening
3. Flange contact is initiated on the right hand wheel of the front axle, the second axle, front axle of the rear bogie.
4. Rear wheelset of rear bogie never engages is flange contact.
5. Rear wheelset of rear bogie begins lateral oscillation. Wheel/rail lateral forces peak at ~20kN. This generally occurs when the vehicle is within the constant radius section of the curve
6. Rear wheelset of front bogie begins lateral oscillation. Same peak forces
7. Front wheelset of rear bogie begins lateral oscillation
8. Front wheelset of front bogie begins lateral oscillation
9. Computation time is drastically slowed.


I have tried running the simulation at higher speed, the problem does not occur during the contant velocity section of the curve.

I am wondering what can be done to prevent this from occurring. I have attached an image below of the lateral forces acting on each of the wheels of the vehicle. The image shows four plots, one for each of the wheelsets. The vertical and lateral forces can seen

Regards
Jordan
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Re: Lateral Wheel/rail force oscillations

Postby Roman Kovalev » Tue Aug 29, 2017 12:54 pm

Hi Jordan,

It is a typical picture of instability of numerical method. For such low speed it is recommended to turn on the [Jacobian for wheel/rail forces] check box, see attachment. Usually turning on [Computation of Jacobian] also helps to improve stability and simulation time. When you faced with such instability it is recommended to make smaller [Error tolerance]. For example, if you used 1E-6 and got instability, try 1E-7. It usually helps.

Roman
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Re: Lateral Wheel/rail force oscillations

Postby jordanhannagan » Thu Oct 12, 2017 12:48 am

Hi Roman,

Thank you so much for your advice, this has worked perfectly! Not only has the instability dissapeared, but also the speed at which the solutions process has increased by around 5x.

Cannot thank you enough

Jordan
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