The standard acceleration of gravity gn not working correctly in Imperial Units within Karamba

The standard acceleration of gravity gn is defined to be exactly 9.80665 meters per second per second (m s-2), or about 32.174 05 feet per second per second. There is a typo in the karamba ini file. But even when I change the gravity to 32.174 and the units to imperial, the calculations do not work correctly. See attached images.

For a beam of 6" x 2", the displacement should be 0.009" in imperial or 0.000228 in meters according to my calculations. This works when everything is set to SI units in Karamba and Meters in Rhino, but does not work when Karamba is set to imperial units and Rhino is set to Feet even after updating the gravity in the INI file to 32.174

We work in imperial units and feet and would like this to work in those units. Any suggestions of how to make this work?

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Replies to This Discussion

Permalink Reply by Shivang Patwa on July 26, 2018 at 3:15pm

These are the hand calculations for your reference. We would like to get the professional license of Karamba, but everything needs to work in imperial units within Karamba and Feet/Inches in Rhino. Thank you for your time.

Attachments:

Displacement Calculation 07.26.18.jpg, 1.7 MB

Permalink Reply by Shivang Patwa on July 27, 2018 at 9:41am

Is someone from Karamba going to respond to this? We need to make a determination whether we should invest in getting the Karamba license for our company depending on whether this works with imperial units. Hope to hear from someone soon. Thanks.

Permalink Reply by Karamba3D on July 27, 2018 at 2:16pm

Dear Shivang Patwa,

'g' in the ini-file is always interpreted in SI units irrespective of the setting of 'UnitsSystem'. When working in SI units one usually assumes g=10m/s2. When you set g=9.80663520001m/s2 you should get the 'exact' value. Make sure to restart Rhino so that the changes in the ini-file take effect.

Thanks for pointing out the typo in the ini-file.

Best,

Clemens

Permalink Reply by Shivang Patwa on July 27, 2018 at 3:43pm

Thanks for your reply. Everything works correctly now. Though the ini file is a little confusing when it says that "In the imperial system g needs correspond to 32.174ft/s2 otherwise the conversion from lbf to lbf does not work". This is automatically taken care of when we change the units from SI to imperial.

On another note, would it not be better to have the factor of the input units and output units the same? For instance, currently the input units are in inches and the output units are in feet, which again throws us off a bit. Moreover, displacement would be better in smaller units rather than larger units. It would be better to have everything in inches or everything in feet. Just a suggestion.

Permalink Reply by Karamba3D on July 30, 2018 at 1:17pm

Dear Shivang,

I have corrected the text in the karamba.ini-file - thanks for pointing that out.

In the next version of Karamba3d the displacements will be output in cm and inch repectively.

Best,

Clemens

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