Geometry import problem - extrusion meshing

[Anonymous]

Hello CFD experts,

I'm using simulation cfd 2016. Inventor 2016 is used to create 3D models and I have problem with geometry import into CFD.
I would like to simulate pipe network in CFD in order to obtain the pressure drop. Extrusion meshing for straight sections would be a leverage but there is an edge misalignment between straight section and 180deg bend. There is also misalignment between pipe and water 3D models. (Picture. 1)

Edge merging tool does not solve problem because it is damaging the uniform cross section of the pipe so extrusion meshing can't be used.

- I am importing Inventor .iam file through SimTools
- .dwg format does not work either
- exporting model into .JT with JT Breep output ALMOST worked out with only 2 incorrect spots. (Picture 2.)

Thank you for your help in advance,

[Jon.Wilde]

Hi,

Have you tried just launching direct from Inventor into CFD, or importing the iam from within CFD?

Thanks,

Jon

[Anonymous]

Hi John,

Thank you for your answer. Direct import .iam file from CFD results with the same problem.

[Jon.Wilde]

OK, weird!

Might you be able to share a small example via Pack and Go from Inventor?

[Anonymous]

I have attached a pack and go file.

I also have found a workaround for the time being.

-Assembly is exported to .dwg file. I open it in Autodesk 3D and merge (join) all solid parts into one object. I do the same with water parts.

-Then I make a boolean operations so that straight sections (pipe solid and water solid separately) are cut out from the network pipe and moved away from bend parts (see attached .png file)

-Then the straight section are moved back in their place.

-Next I open .dwg file through SimTools into CFD.

-The merge tool is active and it wants me to merge again those edges, but luckily I am able to assign an extrusion mesh to all straight sections of the pipe network.

I suppose that joining parts in Autocad uniforms the cross section of whole pipe network.

I am very curious what is causing this misalignment and I would be grateful If you could shed some light on the problem.

Maybe it is my improper modeling technique?

[Jon.Wilde]

I only have Inventor 2017 and CFD 2017 installed and it works fine with the direct import from Inventor-> CFD from the Inventor interface.

I did enable 'Surface Refinement' within the meshing window, which seemed to be useful.

I can't see why it wouldn't work in 2016 if 2017 does.

[LKania]

Autodesk CFD includes a kernel-based model healing option performed during the import process. In 2016 this option is disabled by default while in 2017 it has been enabled as the default. This may or may not be relevant to the issue you have reported.

FYI: The relevant flag is AsmHealing. There are two options available under healing (as described in the flag manager) that at times may prove instrumental for successful model import. In addition to the default level of healing, there's a second level of healing that also attempt to address model issues such that parts that ought to be "extrudable" when it comes to meshing remain selectable as such. Some experimentation here might be in order.

[Anonymous]

@Jon.Wilde

I just have tried with direct import from Inventor 2017-> CFD 2017 from the Inventor interface. I did enable 'Surface Refinement'. The problem remains like it was in CFD 2016. Some of straight pipes can be done with extrusion meshing, some can't. 

Please look at the attachment. After selecting all straight pipes, Extrusion button is available to click. But when I check each of the pipe separately, some of them have Extrusion button grayed out.

Jon could you post a screenshot with correctly meshed pipe network I posted earlier? Maybe there is something I am doing wrong when meshing the imported model.

@LKania

Thank you for your answer. Experimenting with this flag (value 1 and 2) did not solve the problem. I have even tried with AsmCoinTol flag, also with no result. 

Whats' more: Even my workaround does not solve the problem with larger pipe network. 

[Jon.Wilde]

Ah, I see what you mean.

This can happen with extruded meshing. My opinion is simply not to use it - especially as you have corners in the model so the flow is not entirely straight through a straight section...

[Anonymous]

"Ah, I see what you mean."
Yes I should've attach this screenshot in the first post, my bad:)

Not entirely straight flow is not a problem because bends will have additional straight pipe at each side of the 180deg bend in order to straighten the flow (Yes, extrusion meshing also does not work properly with this type of 180deg bend 3D model).

Using extruded mesh decreases element count (sometimes even 5x) and in some cases (pipe network longer than > 2m) is irreplaceable.
I'm going to stick to my workaround. Sometimes it works, sometimes don't - what's funny it is really random.

Thank you for your time and support 🙂

[LKania]

Regrettably there are likely sufficient topological differences between the opposite faces of some of the parts on which you are desiring to place an extruded mesh. If you have not already done so, could you upload your CAD model (not the sharefile) as this would be invaluable towards our improving the robustness of the extrusion meshing option.

[Anonymous]

The PipeNetwork-assembly.iam (in the .zip) file does not work properly with direct export to CFD
The PipeNetwork-assembly.dwg file does not work properly with export through SimTools
The PipeNetwork-assembly2.dwg file "remade" in Autocad in a way I described in post #5 works very well (there is a edge Merge tool available but extrusion meshing can be done)

In addition: a .JT file exported from Inventor (option with JT Brep type was chosen) works good with only one row of pipes . CFD does not see problem with edge merging.

[Jon.Wilde]

I opened this into Inventor 2017 and then into CFD 2017 (accidentally through the assessment toolkit, although I don't expect it changed anything).

All seems OK, although there was an error initially:

[Anonymous]

Than you Jon for your answer.
Yes, I understand. However that worked only for water parts. Some of the pipe parts have extruded mesh, some not. 

I exported another pipe network into CFD throught assessment toolkit, merged all edges and autosized. Then I selected all of the straight sections of the network and assigned extruded mesh. You can see the differences.

Currently I run a simulation with all straight sections (pipe and the water part) properly meshed with extrusion meshing. (Thanks to the workaround) I can save a lot of computing time because the pipe parts have prismatic mesh assigned to it.

Is this approach correct?

[Jon.Wilde]

Ah, I see.

I would only apply it to the water anyway. I do see your point though.

Do you even need the solid parts meshed? Only if you have heat transfer through them right?

[Anonymous]

I need only a pressure drop information.

But I thought that pipe material is needed to correctly predict the pressure drop because of the surface roughness. 

However I just opened a material editor and the Wall roughness is set to 0, so:

Which approach is better? 

1. Get rid of the pipe model and use only water parts

2. Use Wall roughness value and check if this makes any difference? (It should right?)

[Jon.Wilde · Accepted solution]

Either is OK.

1. You don't need the pipe material meshed
2. You can apply surface roughness to the fluid if necessary 😉

[Anonymous]

Thank you Jon 🙂

Note for others: When using SST k-omega and wall roughness you should remember to disable Intelligent wall formulation according to this:

https://knowledge.autodesk.com/support/cfd/learn-explore/caas/CloudHelp/cloudhelp/2016/ENU/SimCFD-Us...