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Volume Mesh Structure

6 REPLIES 6
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Message 1 of 7
Inv_kaos
808 Views, 6 Replies

Volume Mesh Structure

Hey,

 

Surface mesh always looks fine but when I section the part I see very poor volume mesh structure (see attached). For something like this, that is perfectly symmetrical, I should see well structured mesh through the thickness. Is there any way to fix this by changing my inputs? I need to show sections in my design reports and also linearized stress through these regions. I can't use the results with the current structure.

 

Cheers.

Stew

Please mark as "Accept as Solution" if it answers your question or "Kudos" if you found it useful.
---------------------------------------------------------------------------------------------------------------------
Stew, AICP
Inventor Professional 2013, Autodesk Simulation Multiphysics 2013
Windows 7 x64 Core i7 32GB Ram FX2000
6 REPLIES 6
Message 2 of 7
John_Holtz
in reply to: Inv_kaos

Hi Stew,

 

Can you elaborate on why you "can't use the results with the current structure"? Is it just aesthetics?

 

To provide some control on the solid mesh, you can right-click on the part and choose "Create Solid Mesh". (I think it is directly on the right-click menu, but I am away from my work computer. It could be under "CAD Mesh Options > Solid Mesh".) Then one of the tabs let you control the aspect ratio of the solid elements.

 

Keep a couple of things in mind. The solid mesher is creating elements at "arbitrary angles". So once you start to slice the elements at "arbitrary angles", the intersected mesh can look a lot different from reality. Secondly, in the case of cylinders where the elements on the inside surface are the "same size" as the elements on the outside surface. There will be fewer elements on the inside surface than the outside. Therefore, the solid mesh will transition from M elements around the perimeter of the inside to N elements around the perimeter of the outside. If the solid mesher had human intelligence, then it probably would put those transitions at equal locations throughout the perimeter. But we're not close to human intelligence, let alone artificial intelligence.

 

Another option would be to use tetrahedral elements. It is easier to fill a volume with these elements than it is to fill it with mostly 8-node elements, but use 6-, 5-, and 4-node elements to fill the transitions.

 



John Holtz, P.E.

Global Product Support
Autodesk, Inc.


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Message 3 of 7
Inv_kaos
in reply to: John_Holtz

Hi John,

 

Essentially yes but not only. If I were to receive the report I would think the mesh is too unstructured and the elements are distorted, therefore the results can't be accurate. I would like to avoid this impression, and mainly because it is also usually accurate when comparing various results. I am sure my results at the surface will still be acurate but I can't say for sure how many data points used for linearising through the thickness have innacurate stress tensors.

 

I have tried to reduce the aspect ratio, it sometimes fails with warnings when I set it too low. If I don't set it low to avoid any errors then it doesn't change the results much. Out of interest the default 100 seems very high, does Autodesk have a recommendation for this value based on the results of their own validations?

 

The transition from inside to outside shouldn't greatly affect the mesh, even for 75mm plate in my attachment, if the elements stretch across the thickness or increase by an element every n elements along the meridional direction. A slice through the longitudinal axis should look uniform (ideally). Speaking of human intelligence, is there going to be improvements on the auto-volume mesher or options for manually sweeping solid meshes in future releases? The surface meshing works great, just seems like there is some room for improvement through the volume.

 

I know tet elements handle complex shapes better so I had tried that after. However even though the chaos became more uniform, it was still chaos. This was surprising since I have seen other tet automeshers that create very uniform elements through the thickness. Either way I would like to stick to primarily hex elements where possible.

 

What I have done is split my solid at some radius around the nozzle, then apply a part mesh size throughout this solid. It does help improve the structure but because the transition to my global (model) mesh size is too sharp there is a ripple effect back down into my finer mesh control. Is there a way to control the transition of volume mesh or only for the surface meshing? It just seems even if I make the surface mesh transition more gradual the volume mesh still tries to transition over a one element step.

 

Cheers,

Stew

Please mark as "Accept as Solution" if it answers your question or "Kudos" if you found it useful.
---------------------------------------------------------------------------------------------------------------------
Stew, AICP
Inventor Professional 2013, Autodesk Simulation Multiphysics 2013
Windows 7 x64 Core i7 32GB Ram FX2000
Message 4 of 7
Joey.X
in reply to: Inv_kaos

In SW, save your model to CAD neutral formats such as .igs, .step, .sat etc. 

Simulation Multiphysics will read above CAD neutral files.

Jianhui Xie, Ph.D
Principal Engineer
MFG-Digital Simulation
Message 5 of 7
Inv_kaos
in reply to: Joey.X

Was this posted in the wrong thread Joey? I am not using SolidWorks..

Please mark as "Accept as Solution" if it answers your question or "Kudos" if you found it useful.
---------------------------------------------------------------------------------------------------------------------
Stew, AICP
Inventor Professional 2013, Autodesk Simulation Multiphysics 2013
Windows 7 x64 Core i7 32GB Ram FX2000
Message 6 of 7
Joey.X
in reply to: Inv_kaos

Sorry, inv_kaos, last post should not be in this thread.

Jianhui Xie, Ph.D
Principal Engineer
MFG-Digital Simulation
Message 7 of 7
hupn
in reply to: Inv_kaos

Hi,

 

For tetrahedral mesh, you can modify the "transition rate" to control the transition of volume mesh from surface to inside. I attached one picture for your reference.

 

hup

 

 

 

 

 

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