Energy Balance in Crash Analysis- RADIOSS

Altair Forum User

sir, can i know why the total energy is decreasing during full frontal impact with rigid wall? what is the main reason contributing to decrease in Total energy? although by energy error is acceptable contact energies and spring internal energies are acceptable ive observed that it is decling! and what is DTE- Total energy external work force energy ? what we should validate T.E or D.T.E? also where can i read about D.T.E external wrok forces. Please Help me with this theoritical doubts.

Thank you

M. Rama Kiran

Altair Forum User

Hi Ramakiran,Taking into account the external works in a simulation, the total energy must remain constant or can decrease slightly. I recommend you to check the hourglass energy and contact energy of the model due to which this can happen. Normally we have to check the model and find the cause of this issue.Also check the model for intersections or penetrations. We  validate with TE, total energy.

Please search for Time Histories in Help Menu where all the parameters are explained. 

I recommend you to download our free ebook on RADIOSS from http://www.altairuniversity.com/free-ebooks-2/free-ebook-crash-analysis-with-radioss-a-study-guide/  A chapter on Checks During & After Analysis is covered (Page 201 onwards) where validation of results is covered with possible workarounds also suggested.

 

Altair Forum User

Sir, I have checked the hourglass and contact energies and they are less than 8% of T.E. And the total energy varying is still 8% of initial T.E but I want to make it to Almost 0% so what should I do.. Should I change time step I'm using default time step scaling factor 0.9 and Tmin 1e-6..no penetrations are there in my model. Thank you very much 

 

Altair Forum User

Hi Ramakiran,

As mentioned before we need to check the model to find the issue. As a workaround you can check with the hourglass and contact energies in the model.

To avoid hourglass energy use fully integrated elements, and use HEPH (Isolid=24) formulation for solid elements and QEPH (Ishell=24) formulation for shell elements.

For contact energy, please check the interfaces defined in the model. Check the Gapmin defined for the interface and check the contact stiffness. Please review the RADIOSS ebook, page 155 where recommended parameters for the contact definition is explained. Please run the simulation after making these changes and review the energy plots.

Altair Forum User

yes sir i will try and validate the results, ive used rigid wall so no need to define interface between the rigid wall and full vehicle, single surface contact for full vehicle is given though.

shall i remove that rigid wall and make a shell elementys with rigid material properties so that i can define contact properly between vehicle and barrier?

Altair Forum User

Hi Ramakiran,

You can continue with the same model. Review the self interface defined.

Please go through http://www.altairuniversity.com/learning-library/2017-winter-directed-learning-webinar-series-crash-analysis-with-radioss/ which is a webinar on Crash Analysis with RADIOSS which covers post processing part also.

Altair Forum User

thank you sir, i will follow that

Altair Forum User

sir, and in that webinar he is validating the total translational energy only, then if it is so my analysis showing constant translational energy but total energy with rotaional total energy then its showing decling total energy? so which one to validate Total translation or just total energy?

Altair Forum User

Hi Ramakiran,

For TTE, Translational total energy= IE + KE + RKE + CE + HE whereas for total energy, TE=IE + KE. And by validating with Total Energy the physics of conservation of energy is satisfied and normally we validate with TE.

Altair Forum User

okay, thank you sir. where can i see that tte is sum of the energies you mentioned since i need to prove my boss

Altair Forum User

Hi Ramakiran,

Please find the attached image from the Help Menu.

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