fiala cornering force saturation value

Luca Cavagna_21621

Hello,

 

I am testing my model with FIALA tires for some turning cases. I notice something I cannot explain.

I set a relatively high steer angle to see the Fy generated by tires when slip angle is more than the critical value.

I compared the Fy force I get from the output with mu * vertical force.

Considering I have a max mu of 0.8, I get a Fy which is 0.83 times the vertical force.

 

As example: The red line if the Fy force generated by the tire (from the autotire ouput in C-axis system). The blu curve is my user defined output taking 0.8 * vertical force (from {ts_18.sys_varsub.sv_cp_force_z.VARVAL}).

How is this possibile? 

 

The force should be:

 

I set Fyc (CGAMMA in tir file) to zero.

 

GTT Adam

Hi Luca,

There are different inputs for the road and tire when it comes to mu.

The road property file will commonly have a MU in the [PARAMETERS] header and the FIALA tire property file will also have a MU, either as a constant or as a table with respect to slip and/or a table with respect to vertical force:

Tire File Example:

FIALA TPF Example:

Depending on your tire and road file assignments, the calculation may be more detailed than just the 0.8*FZ

Does your tire file have similar tables?

At what speed are you running this cornering event?

 

Hope this helps!

Adam Reid

GTT Adam

Hi Luca,

There are different inputs for the road and tire when it comes to mu.

The road property file will commonly have a MU in the [PARAMETERS] header and the FIALA tire property file will also have a MU, either as a constant or as a table with respect to slip and/or a table with respect to vertical force:

Tire File Example:

FIALA TPF Example:

Depending on your tire and road file assignments, the calculation may be more detailed than just the 0.8*FZ

Does your tire file have similar tables?

At what speed are you running this cornering event?

 

Hope this helps!

Adam Reid

Luca Cavagna_21621

Hello Adam ,

good points as usual. I am running at 40kts and the steer angle is not small

This is from my simple road:

 

 

and this is an excerpt of my tir

 

 

 

GTT Adam

Luca Cavagna_21621 said:

Hello Adam ,

good points as usual. I am running at 40kts and the steer angle is not small

This is from my simple road:

 

 

and this is an excerpt of my tir

 

 

 

Hi Luca,

In your TIR is there a MU parameter, and is it set to MU_SLIP or MU_FZ?

https://help.altair.com/hwdesktop/hwx/topics/motionview/fiala_tire_force_calculation_r.htm

 

Hope this helps!

Adam Reid

Luca Cavagna_21621

Hello Adam,

my fault

My nose gear tir file was pointing to one with wrong parameters, so the umax and umin were not 0.8.

I am very sorry for this.  Thanks for the help!!

 

GTT Adam

Luca Cavagna_21621 said:

Hello Adam,

my fault

My nose gear tir file was pointing to one with wrong parameters, so the umax and umin were not 0.8.

I am very sorry for this.  Thanks for the help!!

 

Hi Luca,

Not a problem! Always happy to help.

 

Thanks,

Adam Reid

Luca Cavagna_21621

Hello Adam, sorry I deleted the question regarding how to make MU_SLIP block work because I found the way and did not want to bother you again.

Actually I am using V2021 and the manual is misleading. It mentions MU_SLIP and then proposes MU_SLIP_CURVE.

The solution came when I checked user's guide V2022:

 

So to recap with v2021 you do not need to use MU = 'MU_SLIP' in parameters section and the table must be formatted similarly to Adams tire.

I tried to comment out UMIN and UMAX but the solver complains and halts.

So for those still using V2021 this is the solution. Unfortunately the tir files in the example folder already refer to the new format with MU_SLIP and the subcommands 

 

If you do not use the old format, MW will skip MU_SLIP and you do not realize it.

I hope this helps.

Cheers

GTT Adam

Luca Cavagna_21621 said:

Hello Adam, sorry I deleted the question regarding how to make MU_SLIP block work because I found the way and did not want to bother you again.

Actually I am using V2021 and the manual is misleading. It mentions MU_SLIP and then proposes MU_SLIP_CURVE.

The solution came when I checked user's guide V2022:

 

So to recap with v2021 you do not need to use MU = 'MU_SLIP' in parameters section and the table must be formatted similarly to Adams tire.

I tried to comment out UMIN and UMAX but the solver complains and halts.

So for those still using V2021 this is the solution. Unfortunately the tir files in the example folder already refer to the new format with MU_SLIP and the subcommands 

 

If you do not use the old format, MW will skip MU_SLIP and you do not realize it.

I hope this helps.

Cheers

Hi Luca,

Interesting, I did not know that the call for that table had been changed in recent years.

Thanks for the response!

 

Adam Reid