Scaling and units in HyerMesh

Altair Forum User

Hello,

 

my latest optimization results with OptiStruct always seem to be a few decimal powers away from a realistic result, so i started thinking about scaling and units.

I changed the units in HyperMesh to SI units, so KG, N, M, S

 

Now, when I import my model, which I have created with Catia in the mm scale (one distinctive length is 550 mm), and check this length in HyperMesh via the distance tool, it shows a distance of 550... I changed the units before the geometry import, so is this distance not displayed in m? Which means I would have to import the model with a scale of 0.001 in order so get the right scale?

 

Further, I create a material (aluminum in this case), and the field shows the default 210000 for steel. Now, 210000 is in MPa. Why is this not in Pa when m and kg are my chosen units? It should read 2.1e11 with these settings, shouldn't it?

 

Now when I apply a moment to one end of my part, I should state the value in Nm, correct?

 

Is there any way to really see which values have which unit? At least in OptiStruct in the legend?

 

Thank you for your answeres, I am really confused right now.

Altair Forum User

Hi,

Please scale the model in HyperMesh (Tools>Scale) in order to work in the required unit system.

Normally most of them follow Tonnes,mm and sec unit system. Hence the default material value was provided with this unit system.  Please change it accordingly.

The attached image shows the basic unit consistency followed. Example reference values are also there.

Hope this helps.

 

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Altair Forum User

Hello George,

thanks for your answer! I will keep with one consistent unit system, so I don't run into any more problems. The reference values really helped, I was able to identify one wrong statement.

 

Best,

Chris