Unexpected progresive rollover in Vehicle Simulation
Hi,
I'm reaching out for help because it's been a couple of months, and I still can't find a solution or even an explanation for what's happening.
I'm simulating a constant-radius turn with constant acceleration, and at some point, the car starts to roll over. I've reviewed all the data and parameters, but I still don't understand the cause. The simulation shows a progressive rollover, so nothing seems technically wrong with the simulation calculation.
The center of gravity is extremely low (lower than in real life), and in reality, our car cannot flip, it even handles the same corner at higher speeds without issue. Nearly all real-world data has been imported, except for the moments of inertia and tires. Interestingly, when I adjust the weight of the steering column, the simulation becomes unstable, making it the only body assembly with incorrect mass properties.
If you could provide any explanation or insight into why this is happening, it would be a huge help.
Thanks in advance, have a nice day
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Altair EmployeeAttached the modified model for your reference
Hi,
Thank you very much! I was surprised that it worked, I had tried it before with the same idea, but I didn’t experiment with a wide enough range. Also, since inertia resists changes in rotation, we thought it had to be increased, which didn’t seem realistic for our car. Another small question: the car reaches a maximum speed, which isn't the same as the final speed set in the simulation parameters. Is this also due to the inertia, the tire model or is there some type of traction control in the solver of the driver?
Have a nice day
Altair EmployeeHello @MBURE,
The reason for not reaching the final velocity might be primarily related to the tire property file. As the speed increases, the required lateral acceleration increases, eventually, the tires reach their maximum lateral grip—at that point, any further increase in speed would exceed the tire’s friction ellipse (combined slip), and the car would understeer or slide.
This is likely what's capping your speed. You can try by modifying few parameters related to this in the tire file, and you may see some differences in the results.
Altair EmployeeIf you don't have actual tire data from the supplier, Altair FIALA tire model might be a good place to start with as it needs very basic inputs which can be easily obtained from testing.
FIALA TIRE
Hi,
Thank you for your quick reply. Yes, I’ve already implemented our tire model. However, is there a way to deactivate the function that prevents the car from spinning?
In real life, when the car goes outside the friction ellipse, it would start to spin. Allowing this behavior in the simulation would also help us identify the maximum grip of the tire.
Thanks in advance!
Hi,
I found it, thank you! Are the GIFs automatically generated, or are they just made using screen recording?
Thanks in advance!
Sorry this was a mistaken chat
Altair EmployeeHello @MBURE,
I have gone through your model and I see couple of issues. The Wheel bodies in the front and rear suspension have 0 mass, but high inertias. I understand you have added the mass to the Autotire entities, but a very low mass (about 0.005 kg) is recommended to these bodies.
Also the Vehicle Body and Chassis Body have incorrect inertias. You can see the warning for those bodies in the .log file as well. I just reduced them completely to 5 kgmm2 to test it out, and I am seeing much stable results. (See below image, at same time step for different inertias)
So in conclusion, the incorrect inertias are causing the rollover. Please try to get the accurate inertia values for these bodies. That should resolve the issues. Overall the model looks great!
Hope this helps!
Hello @MBURE,
I have gone through your model and I see couple of issues. The Wheel bodies in the front and rear suspension have 0 mass, but high inertias. I understand you have added the mass to the Autotire entities, but a very low mass (about 0.005 kg) is recommended to these bodies.
Also the Vehicle Body and Chassis Body have incorrect inertias. You can see the warning for those bodies in the .log file as well. I just reduced them completely to 5 kgmm2 to test it out, and I am seeing much stable results. (See below image, at same time step for different inertias)
So in conclusion, the incorrect inertias are causing the rollover. Please try to get the accurate inertia values for these bodies. That should resolve the issues. Overall the model looks great!
Hope this helps!