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Query regarding Error (ERR) percent during solving the problem

Dear all

I have a query regarding the ERR percent which can be seen in 'HyperWorks Solver View' while running an analysis in Radioss (Image attached below). While solving a problem, at the start of solution I was getting ERR ' 0%' but as the process continued the ERR keep on increasing towards 'negative value' and at the end of the solution I found ERR as '- 29.3%'. I can see the results, animations and plot the variables and it seems fine with the expected outcome. But I am unable to understand few things which I have listed below:

1. What does ERR signifies?

2. Does this ERR percentage shows that my result is deviated by ' - 29%' as per software.

3. Since it has a negative sign, does it shows that my error percentage is decreasing? or should it be seen as an absolute value?

4. What should be the ideal scenario of ERR Values we should expect while running a solution?

Regards

Pritish

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Pranav Hari

Hi Pritish Shubham

1. What does ERR signifies?

ERR signifies the Energy error percentage

Does this ERR percentage shows that my result is deviated by ' - 29%' as per software.

It doesn't mean the deviation from the result. Negative Energy Error represents energy dissipated from the system and this can be from many sources including plastic deformation and Hourglass energy.

Please check the hourglass energy of the model.Keep Isolid=24 and try running the simulation.

If the components penetrate each other due to the loads applied the user need to define an interface/contact between them for achieving a realistic simulation. The master segment can be parts, elements, contact surface, node sets and similarly for slave the selection can be parts and node sets. Once these master slave sets are identified the algorithm will check these locations for potential penetration of a slave node through a master segment, and this check is done in every time step

Since it has a negative sign, does it shows that my error percentage is decreasing? or should it be seen as an absolute value?

Negative Energy Error represents energy dissipated from the system and positive energy error means energy absorbed in the system

4. What should be the ideal scenario of ERR Values we should expect while running a solution?

You should check hourglass energy and contact energy in your model. ideally (Hour glass energy + contact energy)/Total energy < 15%

Also, check the Radioss explicit e-book( https://altairuniversity.com/free-ebooks-2/free-ebook-crash-analysis-with-radioss-a-study-guide/) Page 283 onwards

Check this forum post also

https://community.altair.com/community?id=community_question&sys_id=11464c761b2bd0908017dc61ec4bcbb1

Andy_20955

Hi,

Adding some more information, if you could share the global energy plots for your model and some information about the type of simulation and loads that exist in the model.

Please plot kinetic energy, Internal, Energy, Translational total energy (TTE) , Hourglass, energy, Contact energy, and External Work.

If the contact energy is large relative to TTE, then you can get a large energy error. The energy due to friction is stored in the contact energy and this is sometimes the reason why you get the negative energy error. If the energy error is caused by Friction, then it is OK to ignore the energy error.

Thanks,

Andy

Altair Forum User

Hi Pritish Shubham

ERR signifies the Energy error percentage

It doesn't mean the deviation from the result. Negative Energy Error represents energy dissipated from the system and this can be from many sources including plastic deformation and Hourglass energy.

Please check the hourglass energy of the model.Keep Isolid=24 and try running the simulation.

If the components penetrate each other due to the loads applied the user need to define an interface/contact between them for achieving a realistic simulation. The master segment can be parts, elements, contact surface, node sets and similarly for slave the selection can be parts and node sets. Once these master slave sets are identified the algorithm will check these locations for potential penetration of a slave node through a master segment, and this check is done in every time step

Negative Energy Error represents energy dissipated from the system and positive energy error means energy absorbed in the system

4. What should be the ideal scenario of ERR Values we should expect while running a solution?

You should check hourglass energy and contact energy in your model. ideally (Hour glass energy + contact energy)/Total energy < 15%

Also, check the Radioss explicit e-book( https://altairuniversity.com/free-ebooks-2/free-ebook-crash-analysis-with-radioss-a-study-guide/) Page 283 onwards

Check this forum post also
https://community.altair.com/community?id=community_question&sys_id=11464c761b2bd0908017dc61ec4bcbb1

Dear Pranav

Thanks for giving me such a detailed insight on the queries I had put on ERR Percentage. Its great to know these things which can help me understand the outcome of analysis in much better way.

Thanks and regards

Pritish

Altair Forum User

Hi,

Adding some more information, if you could share the global energy plots for your model and some information about the type of simulation and loads that exist in the model.

Please plot kinetic energy, Internal, Energy, Translational total energy (TTE) , Hourglass, energy, Contact energy, and External Work.

If the contact energy is large relative to TTE, then you can get a large energy error. The energy due to friction is stored in the contact energy and this is sometimes the reason why you get the negative energy error. If the energy error is caused by Friction, then it is OK to ignore the energy error.

Thanks,

Andy

Thanks Andy for giving some useful tips. I checked the plots and animation results, which seems fine and as expected. However, my analysis results shows a bit higher Hourglass. Can you advice me how to minimize it? Does it depends on selection of 'Master's and Slave's' or it is dependent on meshing quality?

Regards

Pritish

Andy_20955

Hi Pritish,

If your global hourglass energy is high, then switch your shell elements to the /PROP/SHELL, Ishell=24 and solid elements to /PROP/SOLID, Isolid=24. Your analysis will take a little longer to run but you should get lower global hourglass energy.

Thanks,

Andy