Computation checks in Radioss

Altair Forum User

Could someone tell me the physical meaning of the Explicit calculation error check?  I know the meaning of each term. Internal Energy and External work. But why is it important in an explicit calculation to make sure it stays below 5%?

jiaru72300

Hi，

 

It can be clearly seen from the formula, The error should be negative.
Ideally， the error should be at most -15% and better to have -5%. The closer to 0% error the better.
Any positive energy error means energy has been created which indicates a model issue. An error of 1 or 2% will be acceptable.

Andy_20955

Hi,

The energy error in Radioss is calculated as follows.  Note there is no contact energy or hourglass energy terms included in this formula.  If contact energy or hourglass energy become large usually that energy ends up increasing the internal or kinetic energy in the model and this causes a larger % energy error.  The contact energy or hourglass energy are numerical (not part of the physical problem) and thus for a good simulation they should remain small.  

 

Typically if you have a large energy error you should try to understand why by plotting the energies in the model. 

In simulations with no or small initial energy, a small numerical difference in energy causes a large percent error which can be ignored.  After additional loads are applied the energy error will usually decrease.

In models where contact friction causes a large amount of contact energy, the energy error can be higher.