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Using SYSARY/SYSFNC and MotionSolve functions in CNFSUB/CFFSUB

Hello everyone,

I’m working a contact force problem in MotionSolve where the normal force is implemented via a CNFSUB. I’m trying to confirm whether SYSARY and SYSFNC functions can be used inside CNFSUB (or CFFSUB). From my tests, it seems that these functions always return zero (or no valid value) when called inside CNFSUB. This, combined with the documentation excerpt I've reviewed (which lists the specific subroutines where SYSARY/SYSFNC are supported and does not mention CNFSUB or CFFSUB), led me to the conclusion that they might not be supported here. Could someone please confirm whether this understanding is correct and if such a limitation is officially documented, or if it could instead be related to the way I am using the syntax in my model/routine?

The second issue is with the vector containing input parameters (USER(…)). I attempted to pass MotionSolve functions like WZ, DX and DY, directly inside the USER(…) definition in my contact force, instead of using SYSARY/SYSFNC, for example: "USER(100000, 10, 0.02, 1.7, WZ({b_Gear1.cm.idstring}), DX({b_Gear1.cm.idstring}), DY({b_Gear1.cm.idstring}))". When I include these function calls in USER(…), the "par" array appears empty at runtime. If I remove these expressions, "par" is populated correctly. Could someone please clarify why this is happening? Is this a syntax issue, or is there a different recommended method to access velocities and displacements inside CNFSUB?

Any insight, documentation references, or best-practice recommendations would be greatly appreciated.

Thanks in advance!

Regards,

Nefeli Gkirtziki

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GTT Adam

Hi @Nefeli_gki_02,

For the second issue, I believe you need to pass in the idstrings of the entities and not the WZ function. The computation or calculation is to be carried out inside the User Function.

This is shown in the following example for User Functions:

https://help.altair.com/hwsolvers/ms/topics/solvers/ms/mv_7013_inverted_pendulum_control_using_ms_compose_subs_intro_r.htm

Hope this helps!

Adam Reid

Nefeli_gki_02

Hi ,@GTT Adam

Thank you for the detailed example and explanation. I think there may have been a small misunderstanding about what I was trying.

In my initial tests, I did in fact try to use SYSARY and SYSFNC inside my CNFSUB, and I followed the same syntax you showed (passing in the idstrings of the entities, not expressions like WZ(..)). However, in those cases the functions always returned zero. This, plus the fact that the exact same syntax does return valid values in a GFOSUB, led me to suspect that SYSARY/SYSFNC might not actually be supported inside CNFSUB/CFFSUB.

As an alternative, I then tried a different approach: instead of using SYSFNC inside the subroutine, I attempted to pass functions like WZ, DX, DY directly in the USER(…) definition. My thought was that if these functions could be evaluated up front, I could pass their values in the par array. But when I did that, the par array ended up empty at runtime.

Thanks again for your help and for sharing the example! Any additional insight would be greatly appreciated.

Best regards,
Nefeli

Nefeli_gki_02

Hello everyone,

I wanted to follow up on my original question. After some further testing, I found a workaround that solved the issues I described. In CNFSUB, adding the condition "if iflag == FALSE:" before calling SYSFNC or SYSARY made the functions return valid values instead of zeros. In CFFSUB, adding the condition "if nforce != 0:" resolved the same issue there. With these conditions in place, both SYSARY and SYSFNC work as expected inside CNFSUB and CFFSUB. Hopefully this will be useful to others facing the same problem.

Best regards,
Nefeli