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-   -   scaling when importing STL Files (http://www.cfd-online.com/Forums/flow-3d/75879-scaling-when-importing-stl-files.html)

sameer10dulkar May 7, 2010 11:05

scaling when importing STL Files
 
Hi,

I am a new user of flow 3d and am trying to simulate flow through a flow focussing device. I created the geometry using solidworks(dimensions in 'mm') and imported the stl file in flow 3d.

In the model setup--> General tab in flow 3d, i have the simulation units as SI. I was wondering what will be the global magnification factor( Meshing geometry-->geometry->Component1->Subcomponent1-> Transformations-> Magnifications->Global) that I have to use inorder to get the correct units conversion.

Say for example, If I have a solidworks STL file in 'mm', and I have set the units in flow 3d in SI(in the general tab). What magnification factor will I have to use when I import the STL file.


Thanks!

ck5285 May 9, 2010 21:05

Hi Sameer
you need to use the global magnification factor to convert from mm (SolidWorks model) to m (SI units selected by user). the conversion factor from mm to m is 1x10e-3 when you import the model into Flow-3D. Hope this help

sameer10dulkar May 10, 2010 21:24

Quote:

Originally Posted by ck5285 (Post 258102)
Hi Sameer
you need to use the global magnification factor to convert from mm (SolidWorks model) to m (SI units selected by user). the conversion factor from mm to m is 1x10e-3 when you import the model into Flow-3D. Hope this help


Hi ck5285,

Thanks for the info...
I tried it out and it worked..

Although I have one more question regarding the same issue...
Why is it that when i import the file (created in 'm') i get the same X, Y, Z limits as i get when i import a file (created in 'mm'). both times the units for the simulation were selected as SI units.

-Sameer

ck5285 May 10, 2010 21:49

Hi Sameer
If you don't specify the scaling factor then Flow-3D will assumed the model imported is in m/cm (depends on unit system check in Flow-3D). So, the user need to be careful to ensure the unit system from CAD model is consistent with unit system used in Flow-3D. Flow-3D will not automatically detect the unit system used in CAD system. This is unit conversion issue is similar with others CFD program as well. Hope this is clear.

shstyle0 May 12, 2010 03:01

re
 
Flow 3d works like it doesn't care what units you use, so if you don't specify every numbers you use to have the right units, it doesn't convert the units itself.
So if you want to multiply 3mm with 3m/s, you have to put either 0.003 and 3 to use meter, or 3 and 3000 to use mm.

So you have to convert every numbers to match the unit system you've chosen.

sameer10dulkar May 13, 2010 15:07

re
 
Hi,

Here is what i faced in flow 3D...
When i do the whole model that I have in 'm' in solidworks and import the STL file in Flow 3D. The xmin reading shows '0.0' and the xmax reading shows '8.0'

When i do the whole model in 'mm' and import it in flow 3d.
the xmin is still '0.0' and the xmax is '8.0'.

Both the times in the general tab , the units were set to 'm'. All the inputs that i had provided were in converted in 'm' like flow rate and other parameter's.

So that's what was confusing me as in if i am modeling a microchannel and it takes the inputs dimensions like the length in 'm' so instead of the channel length being 0.003mm (which is what i had)it would take it like 0.003m and that would affect my simulation results drastically and then i wasn't sure if the microchannel effects would be modeled correctly.


So now i guess, if i build a model in 'mm' and if the system units are set to 'm' in flow 3D then i will have to use a scaling factor of 0.001 and so on.....Is that correct?


Thanks,

-Sameer

ck5285 May 14, 2010 09:47

Hi Sameer
as mentioned above, Flow-3D don't know what unit system that your CAD model used to build the model. It only read in the numeric value (but not the unit system) from CAD model so that is the reason why Flow-3D shown 0.0 to 8.0 when you are using m or mm from SolidWorks. This value doesn't make sense until you choose the unit system from Generic Tab in Flow-3D to tell the software what unit system been used in the CAD model. Hope this is clear.

Yes you guess on mm to m is correct.

shstyle0 May 16, 2010 11:31

As CK5285 said, Flow3D doesn't import the units from CAD.
So, if you want to model 0.003mm tube, just make the tube to be 0.003 in CAD. doesn't matter what units you use. you can use inch, mm, m, whatever because Flow3D won't import the units, just the number.
and then, since you got 0.003 imported, you have to change the unit system to be mm in general tab, and every numbers you put in that is related to the length (length, speed, acceleration, ...) put in with mm system. For example, if you want 3m/s, put in 3000.
I thought it would be better to use mm system because you are modeling 0.003mm and if you choose m system, then you have to use 0.000003mm, which might make the truncation error to become too big and it could be wrong to ignore the truncation error. Hope now you have the idea how it works.


Quote:

Originally Posted by sameer10dulkar (Post 258682)
Hi,

Here is what i faced in flow 3D...
When i do the whole model that I have in 'm' in solidworks and import the STL file in Flow 3D. The xmin reading shows '0.0' and the xmax reading shows '8.0'

When i do the whole model in 'mm' and import it in flow 3d.
the xmin is still '0.0' and the xmax is '8.0'.

Both the times in the general tab , the units were set to 'm'. All the inputs that i had provided were in converted in 'm' like flow rate and other parameter's.

So that's what was confusing me as in if i am modeling a microchannel and it takes the inputs dimensions like the length in 'm' so instead of the channel length being 0.003mm (which is what i had)it would take it like 0.003m and that would affect my simulation results drastically and then i wasn't sure if the microchannel effects would be modeled correctly.


So now i guess, if i build a model in 'mm' and if the system units are set to 'm' in flow 3D then i will have to use a scaling factor of 0.001 and so on.....Is that correct?


Thanks,

-Sameer



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