Learning Forum

[Cameron Harris]

Hi there,

I am trying to complete thermal analysis for a brake disc and pad system, but encountering errors that I can't get past. I have spent hours on YouTube to search for resources, but had no success. If anyone could lend me any advice, I would really appreciate it. I have been following the official Ansys tutorial step-by-step (/courses/index.php/courses/automotive-components-design-structural-analysis/lessons/thermo-structural-analysis-of-a-brake-lesson-3/).

Thank you very much

[Erik Kostson]

 

 

Hi

Is it not possible to use the file and model we provide in our tutorial (thermo-structural-analysis-of-a-brake-lesson-3/) because that solves and works fine on the release we made it with (think 2020 R2).

Thank you

Erik

Otherwise we can only provide some general advice.

Some general advice is given below for troubleshooting nonlinear convergence.



Training Chapter on Diagnostics in the Basic Structural Nonlinearities Training (Ansys Learning Hub).

Overcoming Convergence Difficulties in ANSYS Workbench Mechanical, Part I: Using Newton-Raphson Residual Information
https://www.padtinc.com/2012/10/10/overcoming-convergence-difficulties-in-ansys-workbench-mechanical-part-i-using-newton-raphson-residual-information/

Overcoming Convergence Difficulties in ANSYS Workbench Mechanical, Part II: Quick Usage of Mechanical APDL to Plot Distorted Elements
https://www.padtinc.com/2012/10/18/overcoming-convergence-difficulties-in-ansys-workbench-mechanical-part-ii-quick-usage-of-mechanical-apdl-to-plot-distorted-elements/

Nonlinear Convergence Tips
https://www.ansystips.com/2018/06/non-linear-convergence.html

1. Align nodes between contact and target if possible in the sliding direction (link)
2. Save Newton-Raphson Residuals & Identify Element Violation before analysis starts (link)
3. Use MPC for bonded contacts if needed (link).
4. Set small initial time steps. Here is my default setting for difficult problems:
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The first step would thus be 1/100= 0.01s with a minimum time step of 1/1000= 0.001s. Apply this to all “Current Step Number” of interest.

5. Have similar size mesh at contacts. If not, Contact has finer mesh while Target is coarser.
6. Slice and dice geometry such that the volumes adjacent to contacts can be Hexahedron elements. 
         – Starting with pretty mesh by the contacts reduces the distortion during the analysis. 
         – Hexahedron elements are less distorted when capturing curved geometries (e.g. holes). 
7. Drop Contact Normal Stiffness Factor (i.e. FKN) to 0.01. Watch out for excessive penetration.
8. Use Contact Tool to see if any contacts are open. Pinball radius may need tweaking. 
9. Switch model to Displacement driven instead of Force driven for better stability. 
10. Avoid over-constrained model whenever possible (e.g. symmetry and bonded contacts) 
11. Move the body to be just in contact so that it doesn’t ‘fly’ a small distance before touching. 

 

 

 

 

[Cameron Harris]

Thank you Erik for the tips. I will give them a go!