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##### Meshing Small Fluid Elements Help

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12-01-2017 01:38 PM

Hi FEMAP users,

I've been having a lot of trouble modeling the airflow around a stack of PCBs with very tightly packed (about 2.5mm/0.10inch apart) square capacitors, see picture. My current approach has been to create a separate air volume solid for the space between the components (shown in light blue), and to use very small elements to show the flow between the capacitors in good detail (at least 3 elements across the width).

I realize that the connecting surfaces of the other solids need to have a matching mesh with the air solids, and I haven't been able to get "Adjacent Surface Matching" to work. As a result, I made all of the surface elements of the other solids match the air volumes by using Size On Surface, element size .001. However, I'm encountering meshing errors such as "Unable to link XXX surface to YYYY surface".

I have the curves from the air volume projected on to the mating surfaces, and I've checked that the offending surfaces do not have mismatched curves/seed meshes. I've also done a 2D surface mesh to check for free edges and found nothing.

I've also tried to mesh the entire model using tiny 1mm/.001 elements, but the resulting number of elements is prohibitively large, about 15 million elements.

At this point I'm at a loss for what to do and any help would be greatly appreciated.

Thanks in advance!

16 REPLIES

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12-01-2017 03:39 PM

Match surfaces only works if the boundary of the smaller surface is imprinted on the larger surface.

As an alternative, have you tried making this a single non-manifold body, then set the mesh size for the entire body followed by settting smaller mesh sizes on the surfaces where you want?

Best Regards,

Chip Fricke

Principal Applications Engineer - Femap Product Development

Chip Fricke

Principal Applications Engineer - Femap Product Development

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12-04-2017 09:30 AM

I have the outline curves of the smaller surface projected on to the larger surface - is that what you mean by having the boundary of the smaller surface being imprinted on the larger surface?

I'm not sure how to make it as a non-manifold body. Can you please explain?

Thanks!

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12-04-2017 12:19 PM

To create a non-manifold body, use the command Geometry > Surface > NonManifold Add. Any mesh sizes applied should be reflected in the NonManifold body.

Best Regards,

Chip Fricke

Principal Applications Engineer - Femap Product Development

Chip Fricke

Principal Applications Engineer - Femap Product Development

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12-04-2017 12:26 PM

Thanks again!

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12-04-2017 01:50 PM

Hello!,

This video shows how to use the “**GEOMETRY > SURFACE > NonManifold Add**” command in FEMAP V11.4.1 to create one “General” Solid Body, an option in the Parasolid modelling kernel which creates “General Bodies” as opposed to regular solids (FEMAP solids) and sheet solids (FEMAP surfaces). If you explode the just created body using command “**GEOMETRY > SURFACE > Recover Manifold Geometry**” the imprinted shape remains, not need to proyect manually any curve in surfaces, also you can mesh each solid independenly. Then the Nonmanifold-Add command is a trick to create imprinted surfaces, OK?.

Best regards,

Blas.

Blas Molero Hidalgo, Ingeniero Industrial, Director

IBERISA • 48004 BILBAO (SPAIN)

WEB: http://www.iberisa.com

Blog Femap-NX Nastran: http://iberisa.wordpress.com/

IBERISA • 48004 BILBAO (SPAIN)

WEB: http://www.iberisa.com

Blog Femap-NX Nastran: http://iberisa.wordpress.com/

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12-04-2017 02:53 PM

Hi Blas,

I am able to imprint the smaller surfaces to larger surfaces using Non-manifold Add, but I'm still unable to get smaller mesh on the imprinted surfaces when I mesh the mating solid with smaller elements and use "Adjacent Surface Matching". I can use Size Along Curves if I select the curves individually, but there are hundreds of curves that I'd need to change manually so if there is a way for the imprinted surfaces to automatically take the smaller mesh of the mating solid, I'd much rather do that.

Thanks so much for your help!

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12-04-2017 03:05 PM

Hello!,

Create a simply FEMAP model to see the problem you have and post it here, without the model in hand I don't understand the specific problem, the solution could be so simply, but to be able to help you we need to have something to investigate, OK?.

Best regards,

Blas.

Blas Molero Hidalgo, Ingeniero Industrial, Director

IBERISA • 48004 BILBAO (SPAIN)

WEB: http://www.iberisa.com

Blog Femap-NX Nastran: http://iberisa.wordpress.com/

IBERISA • 48004 BILBAO (SPAIN)

WEB: http://www.iberisa.com

Blog Femap-NX Nastran: http://iberisa.wordpress.com/

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12-04-2017 05:38 PM

Hi Blas,

I've uploaded a simplified version of the model that I'm working on to Google Drive, see below for link. There a total of 2 air volumes in this model - the main air volume and the smaller air volume between the square capacitors that I wish to be meshed from small (.001m) elements. The goal is to have at least 3 elements across the space between the capacitors (the squares arranged in a staggered 3 x 5 array).

Thanks for your help!

https://drive.google.com/open?id=1jD5EmPlPuPyLbPgwtlV2TAmkbHGNp1Ce

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12-05-2017 07:28 AM

Hello!,

This video shows a method to **HEX mesh** the proposed solid assembly using the "**Mesh, Sweep**" command in FEMAP V11.4.2, and next associating the solid mesh to geometry using command "**Modify, Associativity, Automatic**". This command in addition to the nodes and elements being associated to the main SOLID entity, they will then also be associated to the surfaces of solids, curves on those surfaces, and points on those curves allowing you to use geometry based commands in FEMAP (i.e., Loads and Constraints on geometry, any selection method using a geometric entity, etc.).

Best regards,

Blas.

Blas Molero Hidalgo, Ingeniero Industrial, Director

IBERISA • 48004 BILBAO (SPAIN)

WEB: http://www.iberisa.com

Blog Femap-NX Nastran: http://iberisa.wordpress.com/

IBERISA • 48004 BILBAO (SPAIN)

WEB: http://www.iberisa.com

Blog Femap-NX Nastran: http://iberisa.wordpress.com/

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