Using body subtract leads to duplicate bodies with identical names

[philipp-tty]

🔍 Before submitting the issue

• I have searched among the existing issues
• I am using a Python virtual environment

🐞 Description of the bug

I have a question about modelling in py_ansys and py_fluent.

I create my geometry in py_ansys, which is then supposed to be simulated in py_fluent.

In the process, three bodies are created using body.subtract. However, when the exported .pmdb file is loaded into Design Modeler, five bodies are displayed.

Some of these have the same name, which causes problems in Fluent. Fluent refuses to mesh bodies that have the same name.

I have reproduced the issue in a minimal script.

from ansys.geometry.core import launch_modeler, Modeler
from ansys.geometry.core.designer import Design, Body
from ansys.geometry.core.math import Point2D
from ansys.geometry.core.sketch import Sketch

modeler: Modeler = launch_modeler(mode="geometry_service")
design: Design = modeler.create_design("test_domain")

sketch: Sketch = Sketch()
sketch.box(Point2D([0,0]),1,1)
body1: Body = design.extrude_sketch("body1", sketch, 0.1)

sketch: Sketch = Sketch()
sketch.box(Point2D([0,0]),1,0.2)
body2: Body = design.extrude_sketch("body2", sketch, 0.1)

sketch: Sketch = Sketch()
sketch.box(Point2D([0,0.3]),0.2,0.4)
body3: Body = design.extrude_sketch("body3", sketch, 0.1)

body1.subtract(body2, keep_other=True)
body1.subtract(body3, keep_other=True)

design.export_to_pmdb()

for body in design.bodies:
    print(f"Body Name: {body.name}")
    print(f"Body ID: {body.id}")
    print("-" * 40)

modeler.close()

Script output:

Body Name: body1
Body ID: 0:22
----------------------------------------
Body Name: body2
Body ID: 0:85
----------------------------------------
Body Name: body3
Body ID: 0:148
----------------------------------------

Process finished with exit code 0

📝 Steps to reproduce

Run the script, import the geometry either in Design Modeler or Fluent.

Fluent volume meshing will fail, due to duplicate body names

💻 Which operating system are you using?

Windows

📀 Which ANSYS version are you using?

Ansys 25R2
py_ansys geometry core 0.10.9

🐍 Which Python version are you using?

3.11

📦 Installed packages

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[RobPasMue]

Ha interesting.. let me try to reproduce and investigate @Cerberus-ik - thanks for opening this issue!

[RobPasMue]

Okay ... so if I understand the problem...

What's going on is that your subtract operation is causing your body 1 to be "divided" into 3 disconnected pieces. The other 2 pieces that are getting created and that you see named as "Solid".

The problem is that the "Solid" bodies seem to not be properly linked to the actual body...At least not after the boolean operation is performed.

Couple of questions:

• are you intending to keep body2 and body3? This seems odd to me - my feeling is that you would want to get them consumed after the subtraction operation. For that, please set keep_other=False or just remove the keep_other assignment since False is the default behavior.
• For this specific case, we might need to fix a couple of things in the backend so that things work seemlessly... but there are some good news, I think the following could solve your problems:

...

sketch: Sketch = Sketch()
sketch.box(Point2D([0,0.3]),0.2,0.4)
body3: Body = design.extrude_sketch("body3", sketch, 0.1)

body1.subtract(body2)
body1.subtract(body3)

design._update_design_inplace()

counter = 0
for body in design.bodies:
    if body.name == "Solid":
        # Rename it
        body.name = f"Solid_{counter}"
        counter += 1

for body in design.bodies:
    print(f"Body Name: {body.name}")
    print(f"Body ID: {body.id}")
    print("-" * 40)

modeler.close()

The new part I added is specifically the design._update_design_inplace() call after the subtract operation. This basically cleans up the current design. It's a fallback mechanism whenever something gets corrupted in the Python client side (and we are working on solving it).

The next part I added is this small loop:

counter = 0
for body in design.bodies:
    if body.name == "Solid":
        # Rename it
        body.name = f"Solid_{counter}"
        counter += 1

It's just a hack so that all bodies named "Solid" now have a different name and you are not impacted on the Fluent processing. We definitely need to solve this but, for your current release that's not possible.. so we will need to do this workaround for now. Let's try to fix this for 26R1.

[philipp-tty]

Firstly, thank you for the response.

Maybe as a clarification: I do indeed want keep_others you can think of my geometry as a large aluminum block that I mill out paths for my fluid. The new bodies will be part of the fluid domain in Fluent in the next simulation step.

design._update_design_inplace()

Fixed the issue, I was aware that I can rename bodies, but the issue laid with the two Solid bodies. Which did not appear under design.bodies.

So the underlying issue seems that py_ansys and the server are out of sync. So this can be labeled as a bug?

_update_design_inplace()

Is a nice workaround but shouldn't be required from a user perspective, especially since it is a protected method.

Anyway, thank you again. Should we close this issue or leave it open for now?

[RobPasMue]

Ah awesome, then please keep the other bodies if they are needed. That was just my inner-self thinking whether they were necessary or not.

This is definitely a bug and we are keeping track of it in #1528 and #1539. But we can add this one to the list as well. Efforts going on in #1881 and #1992 will solve this problem but it is a bit complicated...

In the meantime, the _update_design_inplace() call is a brute-force operation that cleans up the local model on the Python side and updates it with the server side snapshot. Typically it is not needed, and that's why we are not calling it by default in the boolean operations but, if your boolean operation partitions the body into several bodies.. then you get this behavior.

We know it's a protected method and users shouldn't be using it. We are working on getting rid of this workaround for sure so that it is done for you. Really sorry for the inconveniences.

We have only seen this to happen in boolean operations and some repair_tools/geometry_commands/prepare_tools. But, for the latter we went with the safe approach and always call the _update_design_inplace(). It is just the boolean op. where disconnected bodies are created when this is needed.