Scaling in PrePoMax

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Ok, i have watched some youtube videos that were recommended to me by users on the last thread.

Usually scalling is not an issue, but when your importing a file from another program or creator, it can pose issues.

Here is my current situation.

In my cad software (freecad) i have my file i made. Its a 62 meter in length object i downloaded off of grab cad. (to any users from the freecad forum, this is NOT the NREL blade)

I set the export to meters for the step file in freecad. It is solid, and imports solid into prepomax. however, its HUGE, 62000 meters HUGE. I did set the new file to meters in Prepomax.

Thanks :slight_smile:

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3

Change your default settings in Prepomax.

4

under tools, settings, which category are you referring too?

switching the default units in the general tab still produces the same result : )

5

It might be easiest to export in mm and scale the part in PrePoMax as shown in the tutorial with PrePoMax + FreeCAD CFD.

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6

Latest version of prepomax have a scaling option for parts.
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7

the youtube video number 32 correct?

thanks

8

Step is an Ascii format, and it can be opened in any Text editor. Length units setting can be modified manually but with caution, change $ prefix to .MILLI. to set the model in millimeter units instead of meter in length.

LENGTH_UNIT() NAMED_UNIT(*) SI_UNIT(.MILLI.,.METRE.)

this unit setting is available at the end of block data in Step files,

2024-02-11 12_58_48-box.step - SciTE
2024-02-11 12_58_48-box.step - SciTE788×756 41.7 KB

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9

Yeah, but I realized that there I did the scaling in FreeCAD and used SI(m) unit system in PrePoMax. You can do the scaling in PrePoMax too though.

10

You made those videos?

They are really good.

Yeah, the scale tool in prepomax is just like SketchUps or prusa slicer, so i just scaled by 0.001 in all directions. Now my blade is correct.

Here is what is interesting to me. A 300 by 60mm, 2nd order mesh with constraints etc, took 61 seconds to solve. But if i use a 200 by 60 mm mesh, it takes over 20 minutes to solve haha. Going to try a 100 by 60 and see.

Im comparing deflection values for convergence analysis, but i have a feeling since from 300 to 200, deflection changed by roughly 50mm, that 300 or even 250 mesh size is just fine.

But the cool part, it matches my force analysis i did by hand and my results from openfast.

Hand calcs is 8.44 m deflection
Openfast 7.8
Prepomax 9.65

Now to continue prepomax and also fatlab (at some point haha)