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

In summary, the conversation discusses the results of a small static analysis with one element, where the bottom face is fully constrained and the top is displaced. In the linear analysis, the internal energy and work done are equal, resulting in a total energy of zero. However, in the non-linear analysis, the internal energy is greater than the work done, causing the total energy to increase over time. The conversation raises the question of how this is possible and suggests that the net forces on the element must total to zero for a static analysis. It is also noted that the internal energy should increase during loading and should technically be equal to the external work done on the body. The conversation concludes with a suggestion to check for a mesh problem and potentially use more
  • #1
hari123
8
0
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.
 

Attachments

  • Linear.png
    Linear.png
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  • NonlineAR.png
    NonlineAR.png
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  • Inputfile.txt
    1.8 KB · Views: 585
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  • #2
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?
 
  • #3
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?
 
  • #4
Have you looked to see if this is a mesh problem? Could be that for accurate nonlinear results you need more elements?
 

1. What does it mean when the total energy (ETOTAL) is not zero in Abaqus?

When the total energy (ETOTAL) is not zero in Abaqus, it means that the system is not in equilibrium. This could be due to factors such as external forces, material nonlinearity, or numerical errors. It is important to identify the cause of the non-zero total energy and make appropriate adjustments to ensure accurate results.

2. Why is the total energy (ETOTAL) increasing in my Abaqus analysis?

If the total energy (ETOTAL) is increasing in your Abaqus analysis, it could indicate that there is energy being added to the system. This could be due to factors such as friction, heat generation, or convergence issues. It is important to carefully review your model and make necessary adjustments to prevent an uncontrolled increase in total energy.

3. How can I reduce the total energy (ETOTAL) in my Abaqus analysis?

To reduce the total energy (ETOTAL) in your Abaqus analysis, you can try adjusting the material properties, mesh size, or boundary conditions. It is also important to check for any numerical errors or convergence issues that may be contributing to the increase in total energy. It may require some trial and error to find the most effective solution for your specific model.

4. Can I ignore the non-zero total energy (ETOTAL) in my Abaqus analysis?

No, it is not recommended to ignore the non-zero total energy (ETOTAL) in your Abaqus analysis. This could lead to inaccurate results and potentially cause convergence issues. It is important to identify the cause of the non-zero total energy and make necessary adjustments to ensure reliable and accurate results.

5. How does the total energy (ETOTAL) affect the accuracy of my Abaqus analysis?

The total energy (ETOTAL) is an important factor in an Abaqus analysis as it represents the energy balance in the system. If the total energy is not zero or is increasing, it could indicate that the model is not accurately representing the physical behavior of the system. This could lead to inaccurate results and should be addressed to ensure the accuracy of the analysis.

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