Acceleration units

[gutboy17]

I'm getting back into the FEM world with a simple structural analysis undergoing acceleration loads. I thought the acceleration units were in inches/sec/sec (32.2"/sec/sec = 1g). However, when I apply the acceleration loads to the model, the freebody resultant loads are a factor of 12 greater than one would expect. Did the units change to feet/sec/sec or do I have a setting incorrect in the software? Thanks.

 

[ThomasH]

Hi

Depends on what software you are using probably more on the remaing units in your model. If you are using a general FEM software there typically are no "built-in" unit system. It's your choice. Just remember, they have to be consistent.

So answering you questing like this is not possible. In my world acceleration is meters/sec/sec, but that's my choice.

Regards

 

[ESPcomposites]

As ThomasH mentioned, it will depend on the "base" units that you choose. You may have chosen a standard IPS (inches, lbs-force, second). If so, then:

1 lb-force = 1 slug*ft/s^2 = 32.2 lb-mass*ft/s^2 = 386 lb-mass * in/s^2.

Perhaps the difference is from in to ft in your conversion. This is a common one that trips many users.

Brian

http://www.espcomposites.com

 

[ZeroExperience]

You can find more information regarding units in the following Nastran blog.

http://mscnastrannovice.blogspot.com/2011/12/what-units-does-nastran-use.html