Learning Forum

[Clarkt]

Greetings,

I am trying to perform a geometry condensation of an assembly consisting of two bodies. The connection between the two bodies should be modeled as a constant 6x6 stiffness matrix between two remote points. 

The modal analysis was performed with MPC184 elements whose formulation is not supported by the geometry condensation feature. Using a bushing connection or a COMBI250 element is not sufficient because it covers only the diagonal terms of the stiffness matrix and in my case the off-diagonal terms do play an important role.

Is there anything I could do to overcome this issue in Workbench? 

Thanks in advance!

 

 

 

[peteroznewman]

I had some advice on a related topic in this discussion.

If you share some more details about your model, you might get some suggestions specific to your model.

[Erik Kostson]

 

 

 

 

 

Hi

By geometry condenstaion I assume here you mean about creating super elements via condensed parts.

If that is the case then

Use bushing type of joint (formulation: MPC and 6×6 matrix - needs radians as units) and that goes well with condensed parts (at least it runs with no errors)
https://innovationspace.ansys.com/forum/forums/topic/how-to-parameterize-stiffness-coefficients-for-a-bushing-joint/

 

All the best

Erik

 

 

 

 

 

[Clarkt]

Thank you for your answers guys. To give you some further insight on the application, it's about a shaft and housing system and the matrix represents the bearing stiffness. Indeed, I am trying to derive a superelement using modal reduction.  So if I understand properly I should create a dummy line element that I will convert into MATRIX27. Then I should define bonded contacts between the line element's vertices and the shaft and bearing faces. Are there any recommendations regarding the bonded contact formulation? Should I go for MPC? If yes, with what constraint type?

[Erik Kostson]

 

Thiink best to skip Matrix27 – take that back as it is tricky to use.

See below what I suggest:

 

In workbench mech., create a bushing type of joint between parts (formulation: MPC – and 6×6 matrix in worksheet – needs radians as units to see 6×6) and that goes well with condensed parts (at least it runs with no errors) – I have tried it in 2024 R2 and worked

 

All the best

Erik

 

[Clarkt]

Dear Erik,

Just tried exactly what you said but (surprisingly) it didn't work. Here's the message I got:

This Condensed Part is invalid due to MPC formulation Bushing joint(s) completely contained inside the condensed part.

Maybe it's because the joint is completely within the assembly that I am trying to reduce.

What could go wrong with the matrix element?

[Erik Kostson]

Hi

 

Tried it between two parts and it worked fine.

Can you show a bit how you use the bushing between parts.

All the best

Erik

[Clarkt]

Here's what I've done so far. :

 

 

 

[Erik Kostson]

 

Hi

Can not do like that.

So create 4 different/separate condensed parts and not only one with all 4 bodies in it as that does not work.

All the best

Erik

 

[Clarkt]

Hi Erik,

Thanks for your answer once again. Do you think that creating 4 matrices separately and then combining them (properly of course) into one would be equivalent to extracting the matrix from the complete assembly?

Also, if I still need to go for the full assembly, the MATRIX27 method is the only way to go right?

[Alfred Stanton]

In your Workbench model, identify or create the two remote points where the connection is to be modeled.

Use the MATRIX27 element in ANSYS Mechanical APDL, which supports a full 6x6 stiffness matrix (diagonal and off-diagonal terms).

You can refer to this link: https://innovationspace.ansys.com/forum/forums/topic/2d-structural-analysis-of-a-rocket-fairing/snow rider 3d