Moldflow Insight Forum
Welcome to Autodesk’s Moldflow Insight Forums. Share your knowledge, ask questions, and explore popular Moldflow Insight topics.
cancel
Showing results for 
Show  only  | Search instead for 
Did you mean: 

Beam L/D ratio

17 REPLIES 17
SOLVED
Reply
Message 1 of 18
OMNI51jkc
1969 Views, 17 Replies

Beam L/D ratio

Hi,

 

I would like to check if 8 mm diameter of cooling channel, what is the correct ratio and the values to set on global edges length.

 

Again, If feed system with various size of from sprue to runner and gating. how do I get the ratio for global edges length setting.

 

Thanks,

Lim

17 REPLIES 17
Message 2 of 18
mppkumar
in reply to: OMNI51jkc

hi

in cooling channels global edge length should be 2.5 or 3 times of diameter

 

 edge length can be set in such a way minimum 3elements formed in gates and runners

 

Thanks

M P Pradeep Kumar

 

Thanks
M P Pradeep Kumar


If my views / comments acceptable, provide "Kudos" as appreciation, if answers your query, please click the "Accept as Solution"
Message 3 of 18
OMNI51jkc
in reply to: mppkumar

Hi Kumar,

Thanks for quick responded.

Does it mean with diameter 8mm of cooling channel whereby ratio 2.5. the edge length values should be 20 mm for each element.

Thanks,
Lim
Message 4 of 18
mppkumar
in reply to: OMNI51jkc

Yes..in your case you need to use edge length of 20mm for cooling channels

 

Significance of L/D ratio

Lower L/D ratios can result in solver convergence warnings in the analysis.

Higher L/D ratios may result in solver convergence warnings and a reduction in solution accuracy.

 

Thanks

M P Pradeep Kumar

Thanks
M P Pradeep Kumar


If my views / comments acceptable, provide "Kudos" as appreciation, if answers your query, please click the "Accept as Solution"
Message 5 of 18
xusho
in reply to: OMNI51jkc

Please be advised that it is not a good idea to choose global edge length based on runner diameters.

As a mesh developer, I would suggest 2 workflows:

 

1. Mesh parts first.
Choose appropriate global edge length for parts. Turn off curves. Geenrate mesh for parts. Curves will not be meshed.

Then turn on curves, mesh curves by appropriate edge length. Beams will connect to cavity automatically.

 

2. Remesh beams after meshing

Choose appropriate global edge length for parts. Generate mesh for parts and curves.

Select runner beams, remesh with different edge length by Mesh-> Mesh Repair -> Remesh Area.

 

Do not sacrifice part mesh for runners. Do not mesh parts and runners together if you need to use different edge length.

Shoudong Xu
Autodesk Moldflow Meshing
Shoudong.Xu@autodesk.com
Message 6 of 18
OMNI51jkc
in reply to: xusho

Hi MF Team,

Thanks for your suggestion.

Does it mean the beam for cooling circuits and feed system should according the mf recommender global edges length to mesh the curve and not based on diameter.
And after to be re-mesh in some regions which is requires with more finer mesh for more accuracy result.

Lim
Message 7 of 18
xusho
in reply to: OMNI51jkc

Hi Lim,

 

What you described is one of the workflows:  mesh parts and curves with one global edge length, and then remesh beams with different edge length.

Another workflow is: make curves invible. Mesh parts first. Then make curves visible and mesh curves separately.

 

Both are OK.

Just do not use global edge length that is good for curves but not for parts if you want to mesh them together.

Shoudong Xu
Autodesk Moldflow Meshing
Shoudong.Xu@autodesk.com
Message 8 of 18
OMNI51jkc
in reply to: xusho

Yes, my practice is turn off the part layer once meshed. Following to import the curve for cooling channel or feed system.
And I will assign the property one by one and generate mesh base on the diameter with 2.5 ratio. With this, bad D/L ratio always shows in log file.

Your advice beams elements should be based on appropriate global edge length whereby system specified and not based on diameter we have it.
Further again re-mesh it if it is finer mesh requires. Correct me if I have any misunderstanding on your suggestion.

Thanks
Lim
Message 9 of 18
mppkumar
in reply to: xusho

Hi Shoudong Xu

 

Agree your methodology of meshing (hiding the curves and mesh part and curves separately)

 

but the question posted here is, about edge length consideration for cooling channels; 

 

for which, the answer would be 2.5D (Moldflow recommended) to avoid bad L/D ratio in cooling analysis calculation

 

Please clarify if I am wrong

 

Thanks

M P Pradeep Kumar

 

Thanks
M P Pradeep Kumar


If my views / comments acceptable, provide "Kudos" as appreciation, if answers your query, please click the "Accept as Solution"
Message 10 of 18
xusho
in reply to: mppkumar

Hi  Kumar,

If you have curves for both feed system and cooling circuits, they need to be meshed separately.

Generally, the edge length for feed system is about half the average diameter, and edge length for circuits is about 2.5 times the diameter.

 

In 2016 release, curves will be meshed based on diameter automatically.

With 2015 release or earlier, you have to mesh them separately by different edge length.

 

By the way, when you see warning message re: "Low beam L/D ratio", refer to this:

http://forums.autodesk.com/t5/simulation-moldflow-insight/beam-l-d-ratio/td-p/5413153

 

 

Shoudong Xu
Autodesk Moldflow Meshing
Shoudong.Xu@autodesk.com
Message 11 of 18
psofiagida
in reply to: OMNI51jkc

that's an old post, but i am having trouble with sth similar here. So i have a model of 2mm wall thickness. I imported in DD, used an edge length of 4mm and meshed. Then i created a sprue, using a 4mm edge length again. I also ensured the "remesh already meshed parts" was unchecked. Fill + pack analysis runs successfully. Now i change it to fill + pack + cool analysis. So i create a cooling circuit, with a channel diameter of 6mm. But according to what u have said in this post, i should mesh these channels. So i go to mesh panel --> remesh area --> i select the beam elements of the cooling circuit (excluding the arrows that indicate the coolant inlet) and apply a target edge length of 15mm (L/D = 2.5). Truth is nothing changed on beam elements. They are shown as they were  before the mesh.

 

So i am running the new analysis, and i get the warning L/D ratio very bad. I right click on the warning --> and moldflow shows that the error is on the beam elements of my sprue gate !!! How is this even possible ? Am i doing sth wrong on the mesh here ?

Message 12 of 18
mppkumar
in reply to: psofiagida

Hi

 

Warning messages on L/D ratio on feed system beam elements need to be ignored

 

L/D ratio need to be maintained only on cooling circuits

 

for example, in gate regions you can't maintain L/D ratio, as we may be need minimum three elements on the gates

 

Hope i answered your query

 

Thanks
M P Pradeep Kumar


If my views / comments acceptable, provide "Kudos" as appreciation, if answers your query, please click the "Accept as Solution"
Message 13 of 18
bernor_mf
in reply to: mppkumar

Hi @psofiagida

 

The length to diameter ratio (L/D ratio) for all beam elements should be about 2.5:1 to 3:1, as a minimum ,
and no more than about 5:1 as a maximum for the BEM (Cool Boundary Element Method).
This includes cooling channels and all other beam elements.
If the mesh density is too fine, the temperature solution may have a difficult time solving. There could be errors indicating elements cannot freeze.
If the mesh is too coarse, the same thing could happen.
When there are many different diameters of cooling lines, the different diameters should be meshed at different densities.

It is normally impossible to get this ratio for gates. There must be at least 3 elements in the gate.
This forces the L/D ratio to be much smaller.
The requirements of the flow analysis will outweigh the needs of cooling. There will be warnings about those beam elements.

In cases where there is an important but short circuit component, such as a baffle, the 2.5:1 ratio may only have one element on the feature.
If there is a high heat load in that area, more elements should be created.
There should be a minimum of two or three elements for a cooling line component in a high heat load area.

The L/D ratio is most important when the beams are not in a straight line.
If the L/D ratio is too short a condition called "a trapped beam" can occur. (Typically when the cooling circuit turn, often like a 90dgr turn and when beams are overlaid in a turning corner.)
Hence the L/D ratio to be 2.5*D rule of thumb.
There are two diagnostics that can help find potential problems :
- Beam L/D ratio diagnostic.
- Trapped beam diagnostic.

Hope this helps.

Regards,
Berndt

( If my comments are accepted, provide "Kudos" as appreciation. If your request is answered/resolved, please click the "Accept as Solution" button. Thanks.)
Message 14 of 18
psofiagida
in reply to: bernor_mf

Hello,

 

thx for your quick response. After checking this warning over and over again, i understood that moldflow considered my sprue gate as "too fine", as it was consisted of 12 elements. Truth is i had meshed my sprue with an edge length of 4mm (very small for a dual domain analysis). So i selected the specific beam elements, went to mesh--> remesh area--> and entered a larger "target edge length". The 1st beam element of my sprue had D=3mm, while the last beam had D=5mm. So the target edge length was set to about 8mm (beam elements were reduced to 6 now). After that, warning messages stopped appearing. Isn't that the correct way to do a remesh ?

 

For the cooling circuit, i didn't change sth. 

 

My second question concerns the 3D mesh conversion. How could i mesh seperately my part (edge length of 2mm now) , while keeping my sprue & cooling channel the same ? Something with the visible layers must be the answer, but i can't get it right.

 

thanks a lot for your time.

Message 15 of 18
mppkumar
in reply to: psofiagida

Hi

 

When you change mesh type to DD to 3D and meshing the elements with specified edge length.....it won't affect your already meshed beam elements

 

 

Thanks
M P Pradeep Kumar


If my views / comments acceptable, provide "Kudos" as appreciation, if answers your query, please click the "Accept as Solution"
Message 16 of 18
psofiagida
in reply to: mppkumar

hello sir,

when i try to convert the dd to 3d, my only option is to remesh the already meshed parts of my model. That means both the sprue & cooling channels will be meshed. So yes the beam elements are affected. How can i put the beam elements into a different layer and make the invisible ? (so i can mesh only the part itself).

 

P.S. I am using Moldflow Insight 2012.

Message 17 of 18
mppkumar
in reply to: psofiagida

Hi

 

 

remesh.png

Thanks
M P Pradeep Kumar


If my views / comments acceptable, provide "Kudos" as appreciation, if answers your query, please click the "Accept as Solution"
Message 18 of 18
xusho
in reply to: mppkumar

To put beams into a separate layer, use the follwoing steps:

1. On main menu, click Mesh.

2. Find Selection, click Prpoperties

Sel.PNG

 

3. Click Beam element as below, then all beams will be highlighted.

b.PNG

 

4. Go to Layer panel (bottom left), click highlighted buttons from left to right

l.PNG

A new layer will be created, and all beams will be in that layer.

 

5. Turn off that layer.

 

Shoudong Xu
Autodesk Moldflow Meshing
Shoudong.Xu@autodesk.com

Can't find what you're looking for? Ask the community or share your knowledge.

Post to forums  

Autodesk Design & Make Report