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Negative total energy for screw

User: "Girish Kulkarni"
Altair Community Member
Updated by Girish Kulkarni

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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    User: "PaulAltair"
    Altair Employee
    Updated by PaulAltair

    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

    User: "Girish Kulkarni"
    Altair Community Member
    OP
    Updated by Girish Kulkarni

    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.

    User: "PaulAltair"
    Altair Employee
    Updated by PaulAltair

    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