Negative total energy for screw

Girish Kulkarni
Girish Kulkarni Altair Community Member
edited April 2022 in Community Q&A

Hello,

I am plotting energy curves for my Head Impact model. 

I am seeing -ve Internal energy. When I plot TE for each parts, I observed that many screws are having -ve energy plot.

Please let me know the cause for this -ve energies.

 

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Answers

  • PaulAltair
    PaulAltair
    Altair Employee
    edited April 2022

    Are your 'screws' modelled as pretension springs? The pretension can manifest itself as negative internal energy in the springs depending on the set up (nothing to worry about though, you should see the equivalent internal energy increase in whatever they are attached to) example below is a pre ten spring (purple curve) connected in series with a 'normal' spring during the pretension then lock phase.

    image

  • Girish Kulkarni
    Girish Kulkarni Altair Community Member
    edited April 2022
    Paul Sharp_21301 said:

    Are your 'screws' modelled as pretension springs? The pretension can manifest itself as negative internal energy in the springs depending on the set up (nothing to worry about though, you should see the equivalent internal energy increase in whatever they are attached to) example below is a pre ten spring (purple curve) connected in series with a 'normal' spring during the pretension then lock phase.

    image

    Thank you for reply. Yes. Scews are having pre-tensions.

    If you see attached pic which has energy plots, it shows -ve IE and TE is less than KE.

    Which is not typical energy plot for impact problem.

  • PaulAltair
    PaulAltair
    Altair Employee
    edited April 2022
    Paul Sharp_21301 said:

    Are your 'screws' modelled as pretension springs? The pretension can manifest itself as negative internal energy in the springs depending on the set up (nothing to worry about though, you should see the equivalent internal energy increase in whatever they are attached to) example below is a pre ten spring (purple curve) connected in series with a 'normal' spring during the pretension then lock phase.

    image

    'Total Energy' (TE) doesn't include contact energy though and that looks to be more than the difference you have between KE and TE, in fact, your CE looks too high to me, If you plot 'Total Translational Energy' (TTE, which includes TE and adds CE and HE and RKE) then it will be greater than KE alone

     

     

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