Translational total energy(TTE) and Global external force work (EFW) are same?

gslee

Hi,

 

Translational total energy and External force work are same?

In referernce guide, energy is as follows.

 

https://community.altair.com/community?id=community_question&sys_id=bb4644b61b2bd0908017dc61ec4bcb09

 

In this topic, 

<?xml version="1.0" encoding="UTF-8"?>

However, in my case,

<?xml version="1.0" encoding="UTF-8"?>

 

Why are they different??

 

Thanks

 

 

 

Andy_20955

Hi,

There was some incorrect information in the post you linked to.

 

External Work includes the work from Imposed movement (displacement, velocity or acceleration), force (/CLOAD or /GRAV), and pressure.  It also include the frictional energy from a /RWALL (when FRIC!=0.0)

 

What loads are applied in your model? 

 

Do you have Friction defined in the contacts or rigid wall?

 

Also plot, contact energy, internal energy, kinetic energy, and hourglass energy.  Also plot DTE which is TTE - external Work. 

 

Thank,

Andy

gslee

Thank you for your answer.

 

Loading condition is as follows. (/CLOAD)

  <- loading curve

Unit system is  ton,mm,s. In my model, there is a contact interface between Yellow component and Green component. (TYPE 7)

TYPE 7 setting is as follows.

 

In the model, there is a rayleigh damping applied on the Yellow and Green component.

-> Total energy decrease graudally.

 

 

 Plotting result is as follows.  

<?xml version="1.0" encoding="UTF-8"?>

 

 In the output file, negative energy error is -34.4%. 

Why is this so high?  

 

 

Thanks

 

gslee

@Andy

I wonder that my result is reasonable.

 

Thanks.

Andy_20955

Hi @gslee

Thanks for the detailed information.  The issue is that the damping energy is not included in any of the global energy output.  The damping energy is also not included in the % energy error which is why your energy error is -34.4%. 

 

Since the total energy in your model is small (this is reasonable since your only load is the /CLOAD) thus the small amount of damping energy added creates a larger % energy error. 

 

Thanks,

Andy

gslee

Hi, @Andy

 

Thank you for your answer.

 

You mean that the damping energy from rayleigh damping causes the energy error.

 

To check the energy error on the model which doesn't have contact (sliding and crash), I compare the 2 models. (No contact, Tied contact)

In 3 models, the same rayleigh damping, boundary condition and same loading condition is applied.

 

 No contact (Only Yellow component)

The energy output is as follows.

<?xml version="1.0" encoding="UTF-8"?>

 

 Tied contact (No sliding and No crash)

The energy output is as follows.

<?xml version="1.0" encoding="UTF-8"?>

 

 

In the results, although the same rayleigh damping is applied, the %energy error is very small.

The high %energy error occurs in the model which has TYPE7 contact.

 

How can I do to reduce the %energy error?

 

How do you think about that??

 

Thanks.

 

 

 

 

 

Andy_20955

Hi,

The friction energy is also not included in the energy calculations.  In the TYPE7 contact model try setting FRIC=0 to see if the energy error is low.  If it is low, then the energy error is from the friction and it is OK to have that large of an energy error.

Thanks,

Andy

gslee

Hi, @Andy

 

Thank you so much for your answer. I appreciate that.

Contact energy output and other energy output are as follows. (Left is setting FRIC=0.2, Right is setting FRIC=0.0)

<?xml version="1.0" encoding="UTF-8"?>

<?xml version="1.0" encoding="UTF-8"?>

 

<?xml version="1.0" encoding="UTF-8"?>

Firstly, as you said, I thought high %energy error is the result from contact energy (friction and crash) because the contact energy is not included in %energy error.

So I plot the IE, KE, HE, CE, DTE. 

 

1) I thought DTE is the result from the contact energy, but contact energy is very small. 

2) In your answer,

'In the TYPE7 contact model try setting FRIC=0 to see if the energy error is low.  If it is low, then the energy error is from the friction and it is OK to have that large of an energy error.'

 

I think that contact energy is so high that %energy error is high.

But contact energy is so small. I don't know why %energy error is so high.

 

Please let me know if the opinion is wrong.

 

How do you think about that?

 

Thanks

 

Andy_20955

Hi,

Thanks it doesn't seem to be the friction causing the issue.  Can you run the model without damping and see how that changes the results?

Also try setting in the model with FRIC=0 also set VISs = 1e-30 which will remove damping applied to the interface stiffness. 

 

Or if you can share the model, I can review it.

Thanks,

Andy

 

 

gslee

Hi, @Andy

 

Thank you for your answer. I appreciate that.

 

The factors which have an effect on friction force are 'FRIC' and 'VISF'??

 

'VISS' is a factor which has an effect on normal force of interface??

 

I attach the model in which contact interface is TYPE7.

 

Thanks

Unable to find an attachment - read this blog

gslee

Hi, @Andy

 

I have the two questions.

 

The factors which have an effect on friction force are 'FRIC' and 'VISF'??

 

'VISS' is a factor which has an effect on normal force of interface??

 

Thanks.

Andy_20955

Hi,

Yes VisS is a damping coefficient on the interface stiffness which would effect the normal force.  After reviewing your model, I am unable to find the source of the lost energy.  Since the error only occurs with the contact model, there must be some part of the energy from the contact force that is not being tracked correctly.  I'm not sure what you are simulating but if the results look reasonable to you then it is OK ignore the energy error. 

 

Thanks,

Andy