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Fiala relaxation length

Description: On the user guide I read " The FIALA tire with and without relaxation effects can be used with the AutoTire AutoEntity

Product/Topic Name : MotionSolve 2023.2

I wonder if there is a flag to avoid providing the relaxation length and use a static response for tire. If not given in the .tir file, error occours

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GTT Adam

Hi @Luca Cavagna,

The documentation mentions that the relaxation lengths are "…to predict the transient behavior of tire…", and are included whenever completing a transient analysis.

Technically speaking, you could set the rlenx and rleny to extremely small values to 'turn them off', but I suspect a value of 0 may throw an error.

Why are you interested in disabling the relaxation lengths?

Hope this helps!

Adam Reid

Luca Cavagna

Correct. A zero kicks me out of the simulation. I am doing some drop test simulations. The gear is made of rigid elements. So the springback I see is simply due to the tire and the relaxation length strongly affects the entity of the drag force. This is clearly a fake. So I reduced the relx to avoid this force to show up, because in reality is mostly due to the elasticity of the strut.

GTT Adam

Hi @Luca Cavagna,

Interesting! If you are purely looking for a simplified tire model, does it make sense to remove the autotire and instead use an IMPACT force or a SpringDamper entity? Does the tire need to accomplish anything other than vertical stiffness and damping in this simulation?

Hope this helps!

Adam Reid

Luca Cavagna

Hello Adam, not a bad idea to replace the tire with a simplified SpringDamper. That would remove the strange effect I see at the springback. See the attached picture (tire force should be changed in sign). The second peak is simply due to tire relax length. In reality should come from strut flexibility but here the model is rigid, so that peak is fake