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Old   August 25, 2010, 17:37
Default problem importing mesh into gambit
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Tom McCormack
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Hi all,

I'm currently trying to setup a CFD model for investigating heat transfer for a medical problem. I have some CT and MRI scans from which I have created separate volumes of the head, skull, brain etc. using software called Amira. I now want to import them into Gambit then subtract the skull from the head and so on so that I can form the full head and mesh it. For the subtraction I need each volume to be real.

The problem is most of the time I import a mesh (STL format) it is not recognised as a volume and the faces cannot be stitched together as at least one face cannot be converted to real (often this is the face called boundary wall). Occasionally the mesh is recognised as a volume but cannot be converted to real again because one face cannot be converted.

One of the volumes which is fairly simple did actually fully work and get converted to real. I also tried an experiment where I made a short cylinder in Amira, when I remeshed it and simplified it in Amira (it looked really neat in Gambit) I had the same problem but when I left the cylinder as it was originally (around 70000 triangles) I could make a real volume with it.

From everything I have tried to get it to work the problem occurs almost every time even with simple geometrys apart from the 2 times described. It seems from this an almost random problem but simpler not remeshed volumes are more likely to work.

If anyone has any ideas what might be causing this, has had a similar experience or has a way of getting round this I would be really grateful. It would be a great help to me but also could have some impact on clinical practice in hospitals as well.

Thanks a lot,
Tom
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Old   August 26, 2010, 01:29
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Hi, Tom,
I have ever complete a job similar to yours. I import surfaces from third party CAD software (usually UG, Unigraphics) into Gambit and stitch them to form a solid, then export the solid using parasolid format, and then import it into Gambit again, or sometimes i import the parasolid file into UG and export it out of UG before this step.
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Old   August 26, 2010, 02:20
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Do you have the possibility to export the data with another format? (step, parasolid for instance)
Else try to cut out what you need within your CAD package.
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Old   August 26, 2010, 10:47
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hi,

thanks for your responses.

I tried other the other file formats available - same problem

Tried exporting as a parasolid then importing but only real components are exported hence this does not help.
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Old   August 29, 2010, 21:23
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hi,

I've resolved this problem now, for anyone with a similar issue:

importing stl into solidworks, healing the geometry as much as possible then exporting as parasolid for use in gambit worked for me.
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Old   December 2, 2010, 23:12
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Quote:
Originally Posted by tsm554 View Post
hi,

I've resolved this problem now, for anyone with a similar issue:

importing stl into solidworks, healing the geometry as much as possible then exporting as parasolid for use in gambit worked for me.

Hello tsm555,
I have same problem as you had. I think we are working on similar thing (human body). And my body geometry is created by Poser.
I am gald to hear that you have solved your problem. You mentioned importing STL into solidworks, healing the geometry as much as possible then exporting as parasolid for use in gambit.
I have few questions and hope you can help me (I am new in Gambit, sorry);
1) how can I import STL into solidwork (if I am not wrong, I don't see the option of solidwork),
2) heling geometry: I see only this option (i.e. check or uncheck), but not seeing anywhere that I can type things,
3) what does the meaning of 'exporting as parasolid for use in gambit'? Is that meaning to export to another format and then open again in Gambit?

I am sorry to ask too much questions, but I believe you can understand the frustrated situation of me. I hope you can help me and let me know sooner. Many thanks.
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Old   December 3, 2010, 05:15
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Quote:
Originally Posted by calvin123 View Post
Hello tsm555,
I have same problem as you had. I think we are working on similar thing (human body). And my body geometry is created by Poser.
I am gald to hear that you have solved your problem. You mentioned importing STL into solidworks, healing the geometry as much as possible then exporting as parasolid for use in gambit.
I have few questions and hope you can help me (I am new in Gambit, sorry);
1) how can I import STL into solidwork (if I am not wrong, I don't see the option of solidwork),
2) heling geometry: I see only this option (i.e. check or uncheck), but not seeing anywhere that I can type things,
3) what does the meaning of 'exporting as parasolid for use in gambit'? Is that meaning to export to another format and then open again in Gambit?

I am sorry to ask too much questions, but I believe you can understand the frustrated situation of me. I hope you can help me and let me know sooner. Many thanks.
Hi Calvin,

Yes I can understand your frustration I had to give up on my project but someone else is continuing the work now, If it is similar to mine you will have difficulty doing what is needed in Gambit but it is possible, this was several months ago now so I can't remember exactly but on your questions:

1. Yes you can import stl in Solidworks, I found out how to do it by reading the help file, there is a button or option on the opening/importing part of solidworks which allows you to change what kind of file you are importing.

2. When you import the file into solidworks you will get the option to check the geometry for errors, if you do this and you get no results then the volume is good, if there are problems found you then get the option of trying to heal them. In the Poser programme are you getting your geometry by tracing MRI/CT images or do you have that option? Are you finding errors in the geometry from it and can they all be fixed? Perhaps it is better than what I was using.

3. Yes export it as a parasolid (because it is a "solid" the holes/errors in the geometry get filled in/fixed) then import into Gambit.

Hope this helps.

Tom
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Old   December 3, 2010, 23:15
Default import to gambit
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Hi Tom,

Many thanks for your prompt reply, and thanks for your help. I am sorry to hear that you had to give up that Gambit-body work. But I quite understand how you felt (same as me now)

I just look into the 'solidwork' thing, but I still cannot see whereabout it is. When I open the stl file, I do this;

Import> mesh> (in Type, I take) stl

and this is how I open the stl file.

Do you mean 'Parasolid'?

I also tried like this

Import> Parasolid

and I got error message as the specified file has an incorrect extension.

I got the stl from another guy who used to work in my office. He created the body shape from Poser, but in very simple way; no fancy things.

What he did was just get a body from the Poser library, modified the position of arms, legs etc, then he exported the file to another software (because Poser cannot export file with stl extension), to reaarange the mesh of the body surface and exported to stl file. And I am using this exported stl to Gambit. Do you see what I mean?

I also look at the help file but cannot see 'solidwork'. I can only find things related to 'parasolid'. Or am I reading the wrong help file?

I know you may not use Gambit anymore, but could you please tell me a bit more of the solidwork option. I honestly cannot see where this option is. I am very sorry to trouble so much.

Calvin
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