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#1 2022-06-03 02:06:26

aep93
Member
Registered: 2020-02-21
Posts: 103

Orientation of faces in FLUI_STRU

Hello all,
I have a question regarding the orientation of faces of elements FLUI_STRU. These elements are the intersection of solid and fluid elements. My question is this: Should the normal of the FLUI_STRU faces be toward solid volume or they should be toward fluid volume?

I get different results when I change the reverse orientation of faces and I am not sure which result is correct.

The documentation (U3.14.02) mentions this:
"It is imperative that the normal external with the fluid field is always directed in the same
direction. It is strongly advised to keep the convention of orientation of the structure towards
the fluid for all modelings of interface fluid-structure, in particular FLUI_STRU ."

The explanation is not very clear to me. Does it mean that ALWAYS normals of the FLUI_STRU face should be toward fluid elements or there are other considerations in this regard?

Last edited by aep93 (2022-06-27 23:35:27)

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#2 2022-06-06 15:12:15

CLF
Member
From: Sweden
Registered: 2009-01-27
Posts: 136
Website

Re: Orientation of faces in FLUI_STRU

Hi

Good question.

My guess - I don't think it matters - as long as the element normals are consistent, ie either in or out.

The latter is based on work with software other than CA, such tend to be a bit grumpy wrt consistent normals.

Hope this helps.

Claes

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#3 2022-06-07 19:31:53

aep93
Member
Registered: 2020-02-21
Posts: 103

Re: Orientation of faces in FLUI_STRU

Thank you very much for your reply @CLF.
I tried multiple cases and based on my observations also, as long as the normals are consistent, the results are the same.

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#4 2022-06-28 00:26:59

aep93
Member
Registered: 2020-02-21
Posts: 103

Re: Orientation of faces in FLUI_STRU

Hello all,
I thought this problem has been solved and always the normals should be consistent no matter whether they are toward the fluid or not.
But I encountered a weird situation when I was reviewing one of the test cases.
In a test case, FDLV111A, the directions of FLUI_SRTU elements are not consistent with respect to fluid elements!!! Some of the faces are toward the fluid and some others are not!!!

So I think either my understanding of the direction of FLUI_STRU, which I mentioned previously here, is wrong or there is an error in this test case. Can someone please check it?

I attached the mesh and comm files as well. The FLUI_STRU elements in the mesh are groups 'IFLUSOL' and 'IPRES' and the 3D_FLUID elements is group 'FLUIDE'.


Attachments:
FDLV111A.zip, Size: 8.53 KiB, Downloads: 40

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#5 2022-07-29 14:25:41

CLF
Member
From: Sweden
Registered: 2009-01-27
Posts: 136
Website

Re: Orientation of faces in FLUI_STRU

Hi

Happy it helped.

If this is so - good catch. Congrats. smile

I never ran the test cases, just looked at them & checking for consistent normals in the preprocessor is second nature for me. 

If I may add a practical note to CA developers?

For what it is worth. I believe there are two ways to go about it.

Either CA handles it internally and is forgiving, ie normals do not matter. This would be the better way to produce accurate results. Might make the code more sensitive tho and is likely to goof up postprocessing, so I'd consider it to be a double edged sword.

Or, normals have to be consistent. If so, I would, by defualt, expect CA to check normals and, at least, issue a warning when not consistent within a group. It is useful to be able to turn off such checks.

That said. Such a check would not be enough.

Ideally, the group that is checked should have a normal to normal check and automatically create groups within which consistent normals are expected, eg the six sides of a box should be six groups.   

Consistency of normals can be tracked from one element to the next. Most preprocessors can do this, so perhaps the algorithm for this can be borrowed from there?

The above is relatively straightforward. However, once we start to get multiple independent groups, then checking would have verify groups to be independent, next ensure consistency within that group.

/Claes

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#6 2022-07-31 21:37:59

AsterO'dactyle
Administrator
Registered: 2007-11-29
Posts: 421

Re: Orientation of faces in FLUI_STRU

Hello,

VERI_NORM_IFS in AFFE_MODELE check normals are consistent for FSI analysis


Code_Asterの開発者

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#7 2022-08-03 22:30:35

aep93
Member
Registered: 2020-02-21
Posts: 103

Re: Orientation of faces in FLUI_STRU

@AsterO'dactyle, Thanks. I found that this command (VERI_NORM_IFS) is relatively new and it exists in version 15.4. When I use it, I get the following message:

<A> <FLUID1_4>                                                                                 ║
║                                                                                                ║
║ Certaines normales entre fluide et structure ne sont pas orientées dans le bon sens.           ║
║                                                                                                ║
║ This is a warning. If you do not understand the meaning of this                                ║
║  warning, you can obtain unexpected results!           


But, it does not show the id of elements that have problems.
When I check my mesh in Salome, it seems that all normals are consistent. So I am wondering why I am getting this warning.
I cannot find out which elements cause this warning. Is there a way to find out which elements have bad orientations?

Last edited by aep93 (2022-08-04 01:47:58)

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