How to output force of a User Subroutine Bushing (difined by GFOSUB)?

User: "Garand"
Altair Community Member

Hello everyone,

I difined a Bushing with user subroutine GFOSUB in Python, the input is Bushing velocity and displacement and returns six-point force, like:

def GFOSUB(id, time, par, npar, dflag, iflag):
…
return [FX, FY, FZ, MX, MY, MZ]

The simulation performed correctly, but the output of Bushing force is zero. As shown in Figs below. Bushings in Fig. 1 are all general Bushings, the force in the middle is an external force

1c74d636-95fe-453e-9bff-759116fa5083.png

In Fig.2, GFOSUB Bushing on the left and general Bushing on the right. The GFOSUB Bushing force has vanishes, but force of another Bushing seems similar, means there is no error in the model setup.

b1d4deef-91f2-4237-b7ee-9396f1c9bb00.png


The problem is I need the GFOSUB Bushing force for debugging, so how can I get it to output correctly?

Sincere gratitude,

Garand

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    User: "Praful"
    Altair Employee

    Hello Garand - Have you tried defining an Output of type Force using the Bushing ?

    image.png

    Regards
    Praful

    User: "Garand"
    Altair Community Member
    OP

    Hello Praful

    Thank you for the reply.

    Yes, I've tried this, but the result is all zero. Shows in figs. below:

    image.png image.png

    Above belongs the GFOSUB Bushing. Just like in HyperView, the bushing force vanishes.

    Does this means GFOSUB Bushing is not allowed to be output in MotionView?

    Sincerely,

    Garand

    User: "Praful"
    Altair Employee
    Accepted Answer

    Hello Garand - I think I found the problem. This could be a bug in MotionView where it is not writing the correct marker id for j_marker_id in the <Post_Request statement. (I am presuming you are using xml)

    image.png

    There are couple of workarounds you can use to get around this problem.

    1. Use a Force entity instead of Bushing with the same GFOSUB. and define an output on the Force. (Actually, when Bushing is made anything but Linear, it goes as a Force to the solver.)
    2. if you are very particular about using the Bushing entity, you may define the output <Post_Request statement in a Template
    image.png

    Hope this helps.

    Praful