SimScale CAE Forum

How are units handled?


#1

All physical quantities are measured in SI units. When importing geometries, the units which are encoded in the file, are ignored. For example, a length which is encoded as 1000 mm will be imported as 1000 and displayed as 1000 m in SI units. If the geometry is exported in meters, the same length will be written as 1 m and read as 1. Therefore, the model should be scaled such that the numbers which are written in the geometry file have the desired order of magnitude. After importing a geometry, please check the event log to verify that the size matches your expectations. We generally recommend that you use meters when exporting geometries.


'compliant mounting plate' simulation project by jhahn
#3

When importing from OnShape, it appears that the scaling is automatically applied. I did the drawing in inches and the dimensions in SimScale appear to be correct. Can you confirm this?


#4

Hi @mas985 and thanks for your question.

A very helpful post by @AnnaFless can be found here: Checking The Dimensions .

Let me know if that helps.

Best,

Jousef


#5

Thanks but that doesn’t really answer my specific question above.

Can you confirm that I don’t need to use scale when importing from OnShape? I don’t believe that I do, I just want to make sure I am not missing something.


#6

Hi @mas985,

it indeed answers your question. Also the post of Anna helps quite a bit (“All physical quantities are measured in SI units”). If the dimensions given by the event log are what you wish to have then everything is fine. If not then use the Scaling option in the Mesh tab.

Best,

Jousef


#7

Ok then maybe a follow up.

Is there a way to directly measure a geometry dimension. Using the bounding box is ok but I would prefer to measure a specific piece of the geometry directly. Is that possible? That would give me a much higher level of confidence that the import is correct.


#8

Hi @mas985 and @jousefm,

I would like to jump in to clarify - we are doing a gradual release of our new CAD handling system. Before there were issues that some CAD files were sized incorrectly, usually 1000x too big. Beginning with the new workflow, we will convert all CAD files to meters on upload.

In your case @mas985, I believe the inches would be converted to the appropriate size in meters during the upload/import to SimScale. To be sure, I’m tagging @jprobst who works directly with the CAD handling on SimScale. He can provide more details in this case.

Regarding your follow up question, the bounding box is currently the only measurement available. Our product road map is shaped by our users to please add all of your requests to improve the experience on SimScale in our Vote for Features category.

In the meantime, I will make a note to update this FAQ as well. Thanks for you input :slight_smile:

Cheers,
Anna


#9

Thank you very much. That was the explanation I was looking for.


#10

Thank you for clarifying this @AnnaFless!


#11

Thanks @AnnaFless, what you wrote is correct. We are gradually rolling out a new way of treating CAD where we convert everything consistently to meters on upload. This means that you will see different numbers (unless the geometry was in meters) but the physical size is the same and consistent with the rest of the simulation setup.