Create multiple coordinate system with CBUSH

Ricardo_Assis

Hi all
I need to create CBUSH elements connecting surfaces with multiple curvatures. In general, I use to create these CBUSH automatically using connectors tool but, to have the CBUSH axis aligned to a local coordinate system normal to the curvature, I still need to create the CSys manually.
Is there any simpler and faster way to create multiple local the coordinate system with the CBUSH?

Fred_Juras

Hi Ricardo,

Could you please tell me which version of HyperMesh you're using and which connector control you're interested in?

Regards,
Fred.

Ricardo_Assis

Hi Fred
I'm using HyperMesh version 2022.3 (Nastran solver preference).
In general, I use spot connectors, type "rbe3-cbush-rbe3". That's why I need to align the cbush axis to a local csys x-direction normal to the curvature at each spot point.
I can create several connectors at one shot but I still need to create the local coordinate systems manually at each point and associate them to the cbush elements.

Regards,
Ricardo

Fred_Juras

Hi Ricardo,

Ok, thanks for sharing this info.

Indeed, in that case and by default it is not possible to use an existing local system during the creation or realization of a connector. But you should be able to request the creation of a local system for each cbush. Let me explain.

The orientation of the cbush depends on the chosen 'projection control method'. By default this option is set to 'normal to links'.

In order to better control this projection (orientation of the cbush), and if you have for instance a part with a finer mesh catching the curvature nicely, then you can change this parameter to 'normal to closest link' or 'normal to furthest link' or even 'normal to specific link'.

Regarding the system, you can ask to create and assign a local system for each cbush with this 'system' option:

FYI, in v2022.3, the Y axis of the created system is aligned with the cbush orientation. We added this axis assignment as a parameter in the latest v2024.1:

Regards,
Fred.

Ricardo_Assis

Hi Fred

Thank you for your prompt answer.
I still have some questions I would like to discuss with you.

You've mentioned the 'projection control method' options to define the orientation of the cbush, but the differences between the default 'normal to links' and the other options 'normal to closest link', 'normal to furthest link' or 'normal to specific link' are not so clear to me yet. Can you give me more explanations on this?

You've mentioned also that it is possible to create and assign a local system for each cbush with this 'system' option and that the csys axis assignment can be selected as needed in v2024.1. However, in v2022.3, only the Y axis of the created system is aligned with the cbush orientation.

From the remarks on the Reference Guide cbush input data (it is almost the same for OptiStuct and Nastran), I understand that the element x-axis is along T1 (or the X direction of the CID coordinate system), the element y-axis is along T2 (or the Y direction of the CID coordinate system), and the element z-axis is along T3 (or the Z direction of the CID coordinate system). If the Y axis of the created system is aligned with the cbush orientation instead of the X axis, it would be enougth only to play with the appropriate directional parameters (K,B,GE...) to set the springs correctly? If not, is there any alternative means (an script, for ex.) to solve it? Are there any additional concerns about that for both coincident and noncoincident GA and GB grids?

And what about defining the correct orientations when the cbush must refer to a cylindrical or a spherical coordinate system?

Thank you again.
Best regards!

Ricardo

Fred_Juras

Hi Ricardo,

Regarding Pojection Control Methods, please take a look at this page:
https://help.altair.com/hwdesktop/hwx/topics/pre_processing/connectors/connector_controls_create_edit_t.htm#behavior_options_r

Regarding the system axis, indeed before v2024, the system Y axis was aligned with the cbush. Now, since v2024.0, you can decide how to align the system to the cbush (x axis by default).

Regarding cylindrical or a spherical coordinate system, you can't create one system per connector but you can select an existing cylindrical or a spherical coordinate system and assign it to all cbush entities.

Regards,
Fred.