Total energy (ETOTAL) is not zero and increasing (Abaqus)?

[hari123]

Hi all,

I have performed a small static analysis with one element (C3D8). The bottom face of element is completely constrained, and the top part is displaced.

In the geometrical linear analysis, the internal energy (ALLIE) and the work done (ALLWK) are equal. So, with ETOTAL = ALLIE - ALLWK, the total energy was zero. But in the case of geometrical non-linear analysis, ALLIE > ALLWK and the total energy (Etotal) was increasing over the time.

How is this possible ??, the total energy has to be constant, and should be zero for the case of static analysis.

Note:
Please find the attached inp file, and the energy plots for the linear and non-linear cases.

 

[Mech_Engineer]

As a point of clarification, the net forces on the element must total up to zero if it's a static analysis. The internal energy should increase if the simulation is doing work on the part, right?

 

[hari123]

Yup, the internal energy will increase (due to increase in strain energy) during loading. And it should be technically equal to the external work done on the body. (assuming no dissipations and other factors).

This law (internal energy = workdone) can be observed in the geometrical linear version of my model (attached above). But in the case of geometrical no linear analysis, this law (internal energy ≠ workdone) is not satisfied, and i would like to know why?

 

[DrBwts]

Have you looked to see if this is a mesh problem? Could be that for accurate nonlinear results you need more elements?