Why is the total energy dropping so drastically ? It should remain constatn
Hello Everyone,
I am performing a crash of simple component on the rigid wall. I want to understand the basics of the Energy Curves. When I plot the curves of the energies. It is seen that the Total Energy is dropping significantly, as per my knowledge the energy should stay constant or change negligible. The energy error and mass error are in acceptable range. Can anyone help me understand this. I have attached the model and following are the energy curves.
Best Answer
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Akshay Dengwani said:
Hello Paul,
Thank you for the answer. Now I get why the sudden drop was occurring and this will help me to get to know about the usage of added mass, incompatible condition. Thank you again. If you have any material on this topic or any leads would be much appreciated.
Thank you again
Kind Regards,
Akshay Dengwani
I spoke with someone else, maybe my explanation was not 100% correct, apparently the masses are not removed or incompatible, simply in this case the energy/work is accounted for in the EFW measure, we can see the structural result is the same/similar with either the RWALL or meshed wall. Either way, the conclusion is that your model is OK as it is and you just need to consider EFW as part of the energy balance, the error is low as EFW is used in the calculation.
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Altair EmployeeAnswers
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Hi Akshay,
First, please keep the part close to the rigid wall and then run the simulation. The part is freely moving for 65ms. There will be clear picture once you keep the part closer to the wall.
If you dont have clear picture, please share the energy plots and animation again.
Regards,
Prasad.
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Hello Prasad,
Thank you for your reply and the suggestion. After your given recommendation, I made the changes and ran the simulation.
So As it can be seen that after certain time after the contact with the rigid wall the total energy is constant. But as soon as the contact happens the sudden drop is something which I dont why it is so. Could you please throw some light or what kind of aspect I am not aware of. Because the value of Kinetic Energy is correct.
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Akshay Dengwani said:
Hello Prasad,
Thank you for your reply and the suggestion. After your given recommendation, I made the changes and ran the simulation.
So As it can be seen that after certain time after the contact with the rigid wall the total energy is constant. But as soon as the contact happens the sudden drop is something which I dont why it is so. Could you please throw some light or what kind of aspect I am not aware of. Because the value of Kinetic Energy is correct.
TE (despite its name) doesn't include Rotational Kinetic Energy, I am guessing your 'missing' kinetic energy has been converted into that (otherwise energy error measure would be off, and you say it is ok?)
If you Plot TTE (Total Translational Energy), it should make more sense
That said, it does seem you are getting an unusual result here, I would expect RKE to be a relatively low component of the energy.
Can you share the model so I can take a look?
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Hello Paul,
Thank you for your reply. Yes the Rotational Kinetic Energy is very low. And the plot for the TTE is coincident to Total Energy plot. The energy error is -4.5%. I have attached the model file.
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Akshay Dengwani said:
Hello Paul,
Thank you for your reply. Yes the Rotational Kinetic Energy is very low. And the plot for the TTE is coincident to Total Energy plot. The energy error is -4.5%. I have attached the model file.
Ok, the reason is that 75% of the mass (and therefore kinetic energy) of your model is in added masses (non structural mass) once these 'contact' the rigid wall they are effectively deactivated (as the added mass and the rigid wall are incompatible) and their energy is no longer accounted for (the added masses themselves do not have internal energy) if you plot External Forces Work, you can see it reflected in that as they are removed
If instead, you mesh a wall and crash into that there is no incompatibility between the masses and the other mesh, (here I made one 10mm thick out of the same material as your part) then the energy balance is far more as you might expect
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Hello Paul,
Thank you for the answer. Now I get why the sudden drop was occurring and this will help me to get to know about the usage of added mass, incompatible condition. Thank you again. If you have any material on this topic or any leads would be much appreciated.
Thank you again
Kind Regards,
Akshay Dengwani
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Akshay Dengwani said:
Hello Paul,
Thank you for the answer. Now I get why the sudden drop was occurring and this will help me to get to know about the usage of added mass, incompatible condition. Thank you again. If you have any material on this topic or any leads would be much appreciated.
Thank you again
Kind Regards,
Akshay Dengwani
I spoke with someone else, maybe my explanation was not 100% correct, apparently the masses are not removed or incompatible, simply in this case the energy/work is accounted for in the EFW measure, we can see the structural result is the same/similar with either the RWALL or meshed wall. Either way, the conclusion is that your model is OK as it is and you just need to consider EFW as part of the energy balance, the error is low as EFW is used in the calculation.
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Hello Paul, Ok understood. Can you throw some light on how or what is significance of the EFW. A bit explanation on this would be helpful. I tried to get in the manual but didn't find it. What exactly that resonates. Kind Regards, AkshayPaul Sharp_21301 said:I spoke with someone else, maybe my explanation was not 100% correct, apparently the masses are not removed or incompatible, simply in this case the energy/work is accounted for in the EFW measure, we can see the structural result is the same/similar with either the RWALL or meshed wall. Either way, the conclusion is that your model is OK as it is and you just need to consider EFW as part of the energy balance, the error is low as EFW is used in the calculation.
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Akshay Dengwani said:
Hello Paul, Ok understood. Can you throw some light on how or what is significance of the EFW. A bit explanation on this would be helpful. I tried to get in the manual but didn't find it. What exactly that resonates. Kind Regards, Akshay
It is a catch all for all energy/work added/removed from the model that doesn't neatly fit in the KE/IE categories (e.g. Imposed kinematic conditions would end up here too), it is mentioned in the help energy balance section:
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Thank you so much ! I appreciate that you and Prasad replied to my doubt and gave your valuable time for the discussion.
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