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
Solved! Go to Solution.
Solved by mppkumar. Go to Solution.
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
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
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.
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.
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
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
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 ?
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
Hi @Anonymous
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
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.
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
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.
Hi
To put beams into a separate layer, use the follwoing steps:
1. On main menu, click Mesh.
2. Find Selection, click Prpoperties
3. Click Beam element as below, then all beams will be highlighted.
4. Go to Layer panel (bottom left), click highlighted buttons from left to right
A new layer will be created, and all beams will be in that layer.
5. Turn off that layer.