Unit conversion in Patran after FE Modelling

[jeram123]

Hi all,
I am a beginner in the aerospace domain. I have come across a common and simple error which i think most of the beginners might have experienced.

I was doing the FE Modeling for a secondary structure with lot many sensitive attachments in it.It took 3 days for me to complete the modelling.Now only i got to know that i didn't convert the unit from inches to millimetres.

Is there any way to do this conversion after creation of the FE Model?
Thanking you in advance!

 

[rb1957]

?

you can probably set the default units in FE s/ware, but too late for that now ... it'll convert 1" to 25.4mm, which isn't what you want (i think).

i think you've created a model in inches using mm dim'ns ... something that is meant to 100mm is modelled as 100in.

the "easy" way to fix this is to define your model as 1in model = 1mm reality. anytime your model says inches, read "mm". be carefull with cross-sections ... a X-section of 3mm*8mm should be entered as 3in*8in, and "g" ... on second thoughts, maybe this is getting too confusing ...

what happens in your code if you change units now ? i suspect it'll replace 1" with 25.4mm. so you want to divide all the co-ordinates by 25.4 ... export your model as a bulk data file, read the co-ordinates into excel, divide by 25.4, over-write the .bdf and import back into your FE s/ware. much cleaner than the other fix, but both'll work ...

good experience though, eh?

 

[jeram123]

Thnks rb!

Sure...it s a good experience. Getting the solution for this kind of problems is pretty good.

Second option is more good.....

But it would be nice if some scaling option was there after the fe modeling

 

[Aerodesign]

Patran has no internal units! It reads data and you assign units to suit yourself. What does happen though, and this may be your issue - when reading in external IGES, CATIA (any CAD) data there is a parameter that tells Patran what unit it was created in. You need to ensure that in IMPORT > OPTIONS the correct units are set.

If you did not do the above it is a simple case of scaling the whole model. There are several ways to do this. Example: Assign a GROUP to all entities (geometry and FE) and use Group >Scale.

Easy peazy.

 

[jeram123]

Hi aerodesign,
thanks for your comment, it was truly useful.