Bushing definition in Inspire motion

I use the following python code in the API of Inspire Motion v2025.1 to create a bushing between two imported parts. I applied a force to this system and the bushing displacement was according to the defined stiffness.

I use the same type of definition in a more complicated model, and the solution does not converge.

Is there anything missing? Do I need to define the indipendent variable?

________________________ Python Code:

from hwx import inspire
from hwx.inspire import motionview
from hwx.inspire.motion import Spline
from hwx.inspire import motion
from hw import mview

Start with imported geometry

model = motion.getModel()

subname = ['NAUO'+str(i) for i in range(1, 3)]

extracting the subassemblies:

ass = [model.getChild(i) for i in subname]

extracting the segments as parts

parts = [ass[i].getChild() for i in range(0, len(subname))]

k1 = motionview.Curve(x_type = 'VALUE',y_type = 'VALUE',x_value = [-0.104729072, -0.005496048, -0.002643271, 0.0, 0.002643271, 0.005496048, 0.104729072],y_value = [20000, 350, 100, 0, -100, -350, -20000])

feat_1 = ass[0].getFeature('FeatureCylindrical(Boss-Extrude1.2)')
ref_point = inspire.geometry.Point(feat_1, "CENTER_OF_CIRCLE")
bush1 = motionview.Bushing(name = 'bush'+str(i))

bush1.kx.type = 'CRV'
bush1.ky.type = 'CRV'
bush1.kx.crv = k1
bush1.ky.crv = k1
bush1.kx.int_type = 'CUBIC'
bush1.ky.int_type = 'CUBIC'
bush1.kx.indep_var = 'DX'
bush1.ky.indep_var = 'DY'
bush1.setValues(b1 = parts[0],b2 = parts[1])
bush1.origin = ref_point

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Orestis_YB

Hello @AliH,

as for the bushing the expression you need to use is`-{bushi.DX}`where i is the string of your model. This is also the default set up so in your case I would suggest to just remove this part from your code. As soon as you have defined x and y stiffness with a spline, these variables are automatically set.

Here is what I recommend:

bush1.kx.type = 'CRV'
bush1.ky.type = 'CRV'
bush1.kx.crv = k1
bush1.ky.crv = k1
bush1.kx.int_type = 'CUBIC'
bush1.ky.int_type = 'CUBIC'
bush1.setValues(b1 = parts[0],b2 = parts[1])
bush1.origin = ref_point

Hope this helps!

Best regards,
Orestes

AliH

twoseg-Q1.stmod

Hi @Orestis_YB,

Thanks a lot for your reply. It made sense, but it gave me errors even for a simple model.

I removed those lines from my code and it sets the independent variables automatically as you mentioned (-{bushi.DX}). Now, it is giving me errors:

INFO: Model units are MILLIMETER SECOND NEWTON KILOGRAM.Script file [C:\Program Files\Altair\2025.1\inspiresolvers\2025.1\hwsolvers\motionsolve\bin\win64\mslexicon.py] accessed.

Reading 469 markers...Reading 120 rigid bodies...Reading 1 xy-curves (splines)...Reading gravity vector...Reading 114 action forces...Reading 1 event sensors...Reading 233 marker displacement requests...Reading 233 marker velocity requests...Reading 233 marker acceleration requests...Reading 114 marker force/torque requests...Reading 119 user-expressions requests...Syntax errorERROR: Failure in parsing "CUBSPL( -, 0, Gen5_LG_L1_Altair_thick_elements.sys_Gen5_LG_L1_Altair_thick_elements.Curve_1) - (0.1)*VX(Gen5_LG_L1_Altair_thick_elements.sys_Gen5_LG_L1_Altair_thick_elements.bush0.i, Gen5_LG_L1_Altair_thick_elements.sys_Gen5_LG_L1_Altair_thick_elements.bush0.j, Gen5_LG_L1_Altair_thick_elements.sys_Gen5_LG_L1_Altair_thick_elements.bush0.j)"!License OK.

ERROR: Simulation failed due to error encountered in analysis!

Forced termination from API_SendOffCommandSimulate!

AliH

twoseg-Q1.stmod

Hi @Orestis_YB,

Here is the simple example

Orestis_YB

Hello @AliH,

I tried your simple model and after deleting points, curve and bushing I tried again the script.

I had to change only this
bush1 = motionview.Bushing(name = 'bush'+str(i))
as i is not definied.

After simulating I got the expected behavior of a free falling body as bushings Z trans stiffness is set to zero.

I am using version 2026 Inspire. As you are using Motion Analyst (i.e. bushings) I would suggest to maybe try the latest version as there might be some bug fixes.

Hope this helps!

Best regards,
Orestes

AliH

Hi @Orestis_YB ,

Thanks so much.

You're right. I had v2026 installed on another computer. I tested the same code on that computer, and it worked without any errors.

I preferred the older version because the newer versions usually have more unfixed bugs, but apparently in this case, v2026 is better.

I also tried '{bush1.DX}' instead of '-{bush1.DX}', in v2025 and it worked, but in 2026 both of them work.

Thanks again,

Ali

AliH

The complicated model with contacts still doesn't converge after less than a second from the beggining of the simulation. One of the recommendations is avoiding DX dependency in bushing stiffness.

Do you think using an expression instead of a spline for the stiffness would help?
I'm using the following expression, but it does not work:

bush1.kx.type = 'EXPR'

bush1.kx.expr = "`Poly(DX,0,0,-148372,-2e-8,-4e6)`"

Thanks,

Ali

Orestis_YB

Hello @AliH,

as for the expression I guess you are using DX in the form that we discussed above (Bushing's DX). As for the convergence I would have to see the model. You can either upload it here or better create a support case. Some quick suggestion:

1) Check the log file and look for max penetration depth. If this is significant then you should modify your contact parameters.
2) As per contacts setup you can refer to Best Practices for Running 3D Contact Models in MotionSolve

Hope this helps!

Best regards,
Orestes

AliH

Hello @Orestis_YB ,

When I use a constant stiffness, it runs the simulation without errors.

I'm going to open a support ticket.

Meanwhile, do you have an example of a displacement-dependant expression?

Thanks,

Ali

Orestis_YB

Hello @AliH,

please refer to the other post regarding building the expression.

Defining an expression for the stiffness of a bushing - Altair Community

Hope this helps!

Best regards,
Orestes