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comparison between R tria and equilateral tria

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Message 1 of 9
kameshg
3802 Views, 8 Replies

comparison between R tria and equilateral tria

Hi everybody,

Can  anybody suggest me the best type of tria mesh( right angled tria or equilateral triangle) to be used when meshing the part in HM? Does the tria type impact the results? if so how does it affect?

 

 

thanks

kamesh

8 REPLIES 8
Message 2 of 9
xusho
in reply to: kameshg

Hi Kamesh,

Ideally, triangles should be equilateral.

 

Shoudong Xu

Moldflow Meshing Team

Shoudong Xu
Autodesk Moldflow Meshing
Shoudong.Xu@autodesk.com
Message 3 of 9
kameshg
in reply to: xusho

thank you for the reply, i wouldlike to know the reason and how does it affect the accuracy of the results.

 

thanks,

kamesh

Message 4 of 9
madhukeshwart
in reply to: kameshg

Kamesh,

 

It is theoretically proven  Equilateral Trai is better than Right angle triangle

 

 

refer following discussions 

http://forums.autodesk.com/t5/simulation-moldflow-insight/mesh-pattern-related-to-warpage-accuracy/m...

Madhukeshwar Talwar

FORD MOTORS PRIVATE LIMITED, Chennai
mail: madhukeshwart@gmail.com
09600060862
======================================
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Message 5 of 9
sabarinathan1021
in reply to: kameshg

Hello Kamesh,

 

If you are meshing your part in HM for Moldflow analysis always use Equilateral triangle mesh which will give you better results than Right angle trias. Correction & geometrical capturing would be quite difficult but u will get better end results.

 

We tried this for our understsnding & observed the difference in results.

 

Thank you

 

Regards

Sabarinathan. S

Moldflow Analyst

L&T Technology Services

Chennai, India.

Regards
Sabarinathan. S
Core Engineering Specialist - Plastic, Auburn HIlls, USA
eMail : sabi1021@gmail.com
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Message 6 of 9
kameshg
in reply to: sabarinathan1021

Hi everybody,

 

thanks for all the replies, i would like to know if the same tria and equi tria mesh when converted to a 3D tet mesh, produce different results? which gives closer result to reality? has any body tried? i observed 5-10% difference in the results.

Message 7 of 9
sabarinathan1021
in reply to: kameshg

Hello Kamesh,

 

Yes we have tried with equi tria mesh in DD & convert the same to 3D, the results are quite closer to the reality.

There was a slight difference in some results due to poor capturing of some critical regions with equi tria.

In that case what my advice is to use R-trias in the critical regions & perform the analysis you will get much closer results to the reality.

In some critical cases we need to club both R-tria & equi tria meshes if your performing an 3D analysis for the better result capturing.

 

please find the attached image for your reference.

 

Hope this will helps your query.

 

Regards

Sabarinathan. S

Regards
Sabarinathan. S
Core Engineering Specialist - Plastic, Auburn HIlls, USA
eMail : sabi1021@gmail.com
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Message 8 of 9
madhukeshwart
in reply to: kameshg

It has been discussed many times over user forums. summarising the same here. 

==================================================================

A possible reason is due to the method which Mold flow uses to fill the product.

 

Equilateral triangle .jpg

 

you can see that it starts from one point and fills to adjacent points.

 

When equilateral triangles are used the distance between the adjacent points and the starting point are more favorable and in the case of an aspect ratio of 1:1 it's the same distance.

 

When right angled triangular elements are used you always have a side which is longer than the other 2 which may be less favorable.

 

In right angled triangles, With the longest side in the direction of flow, the end node of high aspect ratio elements will add an excessive resistance factor to flow front calculations.

 

The aspect ratio of mesh elements can affect analysis performance. High aspect ratios can cause a slower analysis, and affect results.

we need to avoid very high aspect ratio triangles, which have their longest side in the direction of flow. If very high aspect ratios cannot be avoided, the longest side should, if possible, be at right angles to the flow direction.

 

Warpage is a structural mechanics problem, while the primary calculation methodology that MOLDFLOW follows is a fluids flow-volume control domain problem. Similar mesh discretization differences occur when comparing CFD vs. Structural FEA grid modeling. Being that MOLDFLOW is a volume controlled domain problem, equilateral elements have a similar distance (ie., volume potential) to fill in each node-to-node direction [in above picture from NODE 1 to all other adjacent nodes]. This means there is the same potential for the flow to move in any direction and so take less solver iterations to reach equilibrium (i.e. converging on the correct fill condition prediction).

 

With this in mind, then Right-angled triangles in the flow or cross-flow direction that have an ASPECT Ratio >1.0 to very high, thus differing distances (i.e., control volume increments) make it computationally more difficult to predict the correct flow direction and filling condition.

 

A mesh of Right angled triangles will cause some error in each element as the distance between nodes is not the same. This error is generally not a problem. However, if there are large aspect ratio, right angled triangles, the error may be significant.

 

Right angle triangle mesh will take more time to solve fill analysis & warpage may be results will be different.

 

So It is recommended aspect ratio < 6,  use Equilateral triangles as much as possible, preferably in Base wall.  

Some percentage of right angled triangles are is ok in B-side feature like rib, boss, which contributes much for results.

 

Madhukeshwar Talwar

FORD MOTORS PRIVATE LIMITED, Chennai
mail: madhukeshwart@gmail.com
09600060862
======================================
Please use . Accept as Solution and Give Kudos as appropriate to further enhance these forums. Thank you! .....
Message 9 of 9
kameshg
in reply to: sabarinathan1021

thank you everybody for all the valuable replies.

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