Simulation Diverging and I cannot tell why

Using SimScale Fluid Flow / CFD
1

My simulation has diverged multiple times. I am not sure why because when I do the mesh no problems arise it all seems ok yet the simulation still diverges. Also I ran another simulation a while ago and the simulation did not diverge in that point that time.

Here is the model if anyone could tell me what exactly is wrong that would be a great help. thanks!

https://www.simscale.com/workbench/?pid=3775219315377088578&mi=spec%3A4c01281b-2560-44cc-b78d-3b7dd91e1651%2Cservice%3ASIMULATION%2Cstrategy%3A3&ps=analysis%2FsimulationControl

3

Hi, this is Bhagyashree from SimScale Support. Thank you for using the forum!

To help users identify and troubleshoot divergence in their simulations, SimScale has a divergence monitor. The following parameters are tracked: velocity, pressure, density, and temperature. Whenever a parameter reaches unrealistic levels in the domain, the simulation automatically stops with an error message:

The error message specifies which parameter diverged and also the exact location in the model. This information is valuable and can be a starting point for the troubleshooting process.

To gain more insight into the causes of divergence, the following basic steps are useful:

  1. Create a ‘probe point‘ result control and input the coordinates displayed in the error message. In doing so, you will see exactly where the divergence occurred;
  2. If the point is close to one of the boundaries, double-check all boundary conditions, making sure they are correct;
  3. If the point is located inside the domain, inspect the mesh around the area. The ‘mesh quality ‘ visualization feature is very useful in this step. Even just a few bad quality cells can create instabilities in the simulation, ultimately leading to divergence.

If you want to learn more and have a look at some trouble-shooting examples too, make sure to read this article:

Divergence in Simulation: How to Tell When and Where? | SimScale

This article explains how to detect divergence in a simulation and provides common troubleshooting workflows.

4

The mesh is failing due to the sharp edges and small parts in the geometry.

2024-01-04_11-41-35
2024-01-04_11-41-351942×680 258 KB

Parts similar to the face highlighted in red are spread across the geometry and this can lead to a bad quality mesh and a subsequent divergence in solution.

I would recommend a geometry cleanup and then perhaps you can try Hex Dominant Parametric Meshing for better accuracy.

1 Like
5

Thank you so much!
And by geometry cleanup do you mean work in cad?

6

Yes, in your native software, you can clean up the sharp edges and perhaps remove the geometry parts that you think are not necessary to the simulation

7

Thanks for the help I was able to fix it.

I have another question on a new simulation diverged without giving any coordinates it says that I need to change my relaxation factors. What should I do.

this is the model

P.S. Please let me know if I should ask this question as part of a new post or if it is okay to attach it here.

8

Hi there,
You can ask this as a new question. :slight_smile: We will answer it soon!