Increase of Total Energy in Bird Strike

[Teru1212]

Hello,

I madea Bird strike simulation on a wing with Lagrange Methode. Everything works fine and I use a Tabular EOS for the bird with element deletion. Now I got the plot of the Energies and something is strange. As you can see the Total Eneryg is increasing even thoguh it should be constant. Can someone explain this to me? I thought ETOTAL cant get bigger, because there should be no Energy coming from outside. Is it becasue of the artificial Energy that increases?

Thanks for your help.

 

[FEA way]

There seems to be significant hourglassing. Compare ALLAE with ALLIE and take a closer look at the mesh. It might need some refinement.

 

[Teru1212]

Yes youre right, the ALLAE is so high that Etotal is increasing. Now I have this plot, where ETotal is constant but ALLAE goes beyond ETOTAL. How is that even possible? Shouldnt ETotal be the highest Energy?

 

[FEA way]

It’s better to plot energies individually and in pairs for easier interpretation. Most importantly, ALLAE needs to be taken care of here.

ETOTAL has many contributions (some added and some subtracted). Check the documentation chapter Getting Started with Abaqus/CAE —> Nonlinear Explicit Dynamics —> Energy balance —> Statement of energy balance.

 

[Teru1212]

Yes I understand the chapter. and I see that ETOTAL = EI+ EV+EFD+EKE-EW and EI = EE+EP+ECD+EA. So if EA is High EI is high as well. And ETOTAL should be higer as well. So how can it be that Etotal is still constant while the INternal Energy is higher than ETOTAAL?

 

[FEA way]

Internal energy increases but on the other hand, kinetic energy decreases accordingly (which is expected). Use Create XY Data --> Operate on XY data to add those energies like in the equation and compare with ETOTAL.

 

[rb1957]

"surely" total energy remains constant in the FEA world ?

"Hoffen wir mal, dass alles gut geht !"
General Paulus, Nov 1942, outside Stalingrad after the launch of Operation Uranus.

 

[Teru1212]

Yes INternal Energy Increases while kinetic Energy decreases. I added the Energies plots and they are above the ETOTAL I get from the History output. Is there something wrong with Etotal?

""surely" total energy remains constant in the FEA world ?"
In Lagrangian formulation i thougt so. But if not, in my case it should increase or not?

 

[rb1957]

"surely" total energy remains constant in the FEA world ?

it's simply physics, no? In the real world you're going to lose some energy from the impact (like noise). In the FEA world, you have to make sure you're including all the necessary terms.

"Hoffen wir mal, dass alles gut geht !"
General Paulus, Nov 1942, outside Stalingrad after the launch of Operation Uranus.

 

[Teru1212]

I did. The problem is not that ETotal isnt constant my problem ist that Einternal is way above Etotal. And that makes no sense for me. How can there be more Internal Energy than the total amount of energy that is avaiable?

 

[rb1957]

agreed the individual components of energy should never exceed the total energy. But I see other issues ...

1) why the small hitch up in total energy about 1 second in ? around off error ?? one would expect more steps if that were the case.
2) at about 4 sec and again at 5.5 sec, where there is a step up in strain energy, why isn't there a step down in KE ?



"Hoffen wir mal, dass alles gut geht !"
General Paulus, Nov 1942, outside Stalingrad after the launch of Operation Uranus.

 

[Teru1212]

1) I thought thats normal because Etotal is constant with a deviation of 1%
2) I thought the step up is due to the step up in artificail energy, thats why there is also a step up in Internal Energy