ferrossi
Subscriber

Hi Peter,

After following your suggestion (together with some geometry changes to the model) I was able to get the simulation to converge. Thank you for the hint!
However, now that it converged, I want to better understand what I was doing wrong, so that I have a complete understand of what I am doing.

See below the questions I have, I hope you can respond (or redirect me to other sources) so that I can clear out my doubts.

Question 1: I didn't understand your statement "I can tell from the graphs that the solver is trying (but failing) to accommodate the entire load in one step". How do you tell this is the case by looking at the Force Convergence chart?

Question 2: For what concerns the simulation results, what is the difference between "accommodating the entire load in one step" versus using substeps as you suggested?                                                                                                                                                                                                I am not familiar with the concepts that you asked me to apply (initial substeps, min substeps, max substeps). Do you have an explanation or some material that I can read to better understand the effects of using substeps in a simulation?

Question 3: The simulation converged when the values of the two forces applied to the model was +100 and -100 N. Then, I tested the same model with greater forces (200 N, 250 N, 300 N, and 400 N). See below the stress results for each simulation:

100 N -->    247 MPa     (converged)                                                                                                                                                                                                     200 N -->    548 MPa     (converged)                                                                                                                                                                                                     250 N -->    740 MPa     (converged)                                                                                                                                                                                                   300 N -->    958 MPA              (partial results, NOT converged)                                                                                                                                                           400 N -->    927 MPA               (partial results, NOT converged)  (mesh is finer than previous meshes, so maybe this is why it's slightly lower than 300 N).

As you can see, as the force increases, the stress becomes greater (makes sense). Please consider that the material I am using is a Carbon Fiber which fails at 513 MPa (in tension) and -437 MPa (in compression). Therefore, you can see how the results for 200 N and 250 N would cause the material to fail already. My question concerns the reason why the 300 N and 400 N simulations do not converge: is it because the stress is so much above the failure limit of the material, or is it because my mesh is not fine enough (good elements quality)? I am trying to understand if the non-convergence is due to unrealistic loads (out of my control), or to the mesh which is not good enough (which would be equal to saying: ANSYS will always give a results, even if the value is extreme and clearly beyond the failure limit of the material). See here a picture of the 400 N results:

Question 4: I am not understanding how to interpret the Force Convergence chart and the Newton Raphson plots. See for example the chart and plot for the unconverged solution at 400 N force.

What does the Y axis represent? are those the errors (residuals) calculated by the solver when solving the equations? I fear they might be something else though, since the force convergence chart reaches values of 34,062.00 N (which is incredibly high) so I find it hard to believe that this is a residual error. And what does the X axis represent? It would be great if you can share some material where I can read about it.

What about the Newton Raphson plots below? The are showing units of force (N) applied to the trailing edge cap. I understand that that they are indicating some kind of error, but I can't understand why they would indicate 38 N on the trailing edge. What do these plots mean physically?