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Calculating Steering Force During Static Steering Conditions

tonynguyen_1432

Hi, I'm simulating the steering force and boost force when the car is stationary and simulating steering according to a sinusoidal event. The results show that the steering force when stationary is smaller than when the car is moving according to a sinusoidal event, whereas it should be larger.

I'm wondering where I'm going wrong? Could it be due to incorrect tire modeling? I'm using the MF Swift model for both cases.

I used a vehicle model from the library and ran a sinusoidal steering event with all parameters kept at their default values.

For the stationary steering case, I exported the steering angle profile from the sinusoidal steering event and used it as a motion input through a curve. I deactivated the Altair Driver and set the Differential torque and Brake torque/force to zero. The vehicle remained stationary during this simulation.

Any insights would be greatly appreciated. Thanks in advance!!

I also posted a similar comment here. I apologize if it has caused any inconvenience or annoyance, but I honestly don't know how to delete the comment "https://community.altair.com/discussion/comment/201154?utm_source=community-share#Comment_201154"

standstill_Archive.rar

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Accepted answers

GTT Adam

Hi @tonynguyen_1432,

Typically, this event is completed using the KnC event with the predefined Steering Analysis enabled:

The vehicle will complete a sinusoidal steering event with the magnitude listed under Maximum Steer (deg).

A dry static steer event will need to feature a tire model that has turnslip capabilities enabled. This is achieved with a Use Mode ending in a 5 and the appropriate licensing for that feature.

! USE_MODE specifies the type of calculation performed:
! 0: Fz only, no Magic Formula evaluation
! 1: Fx,My only
! 2: Fy,Mx,Mz only
! 3: Fx,Fy,Mx,My,Mz uncombined force/moment calculation
! 4: Fx,Fy,Mx,My,Mz combined force/moment calculation
! 5: Fx,Fy,Mx,My,Mz combined force/moment calculation + turnslip
! +0: steady state behaviour
! +10: including relaxation behaviour
! +20: including relaxation behaviour (nonlinear)
! +30: including rigid ring dynamics
! +100: smooth road contact
! +200: smooth road contact (circular cross section, motorcycles)
! +400: road contact for 2D roads (using travelled distance)
! +500: road contact for 3D roads
!
! example: USE_MODE = 434 implies:
! -combined slip
! -rigid ring dynamics
! -road contact for 2D roads

Hope this helps!

Adam Reid

All comments

GTT Adam

Hi @tonynguyen_1432,

Typically, this event is completed using the KnC event with the predefined Steering Analysis enabled:

The vehicle will complete a sinusoidal steering event with the magnitude listed under Maximum Steer (deg).

Hope this helps!

Adam Reid

tonynguyen_1432

That's very helpful, thanks!

tonynguyen_1432

Hi @GTT Adam ,
When I try to perform KnC events in run offline mode, I get the following error:

"ERROR: Static analysis failed at time = 0"

However, when I disable run offline and run the same model, it works without any issues.

In addition, other models can run with run offline without this problem.

Could anyone explain what might be causing this issue or suggest where I should start troubleshooting?

Thanks in advance!

GTT Adam

Hi @tonynguyen_1432,

That means your model is failing to settle during the static simulation and usually points to modelling errors. I would recommend reviewing any animations that were created or to simulate your vehicle model using the Default analysis to simply observe how the vehicle settles under gravity with a Transient analysis.

Additional options include increasing the number of static iterations (to give it longer to find equilibrium), to enable the Debug option (which prints integrator error info to the LOG file), and to generate animations during the static portion (to visually observe potential issues in your model)

Hope this helps!

Adam Reid

tonynguyen_1432

Hi @GTT Adam

I still don't understand why the model runs when "Run Offline" is turned off. I thought this option only affects whether the animation is live displayed during the simulation
Thanks!!

tonynguyen_1432

Hi, @GTT Adam
I have a steering assist curve as shown below. I replaced the default curve and modified the force expression from:
.....*CUBSPL(Ax(,), 0, {crv.idstring})
to:
.....*CUBSPL({j.st.wheel.TZ}, 0, crv.idstring})
However, the simulation fails with the warning:
"Exiting - nonlinear solver step is too small.
Smallest force imbalance norm = ...
..................................................................."
Could this issue be caused by an algebraic loop, since the steering assist force is being calculated directly from the steering wheel torque and then fed back into the system? In this case, I already tried to add delay in the signal by SISO to break the loop, but it didn't work. Or is it more likely related to the shape of the assist curve, for example, an excessively steep pressure gradient in the interpolated curve?
I would appreciate any suggestions on what might be causing this issue.
Thank you.

tonynguyen_1432

I've already tried to increase the iteration but it comes with the new ERROR: LineSearch failed inside SolveForGivenRHS