Module 1: Simulation produces error: Mass is not a number

I found my error. There is a tab in the mesharea exactly looking the same for the viscos layers. Instead of setting it up in at the wall I set it up in the mesh set up in the tab local. That producet the error. Now my Solution converges. Thank you very much for your help :)

hi together,

I have the same issue like you Simon, but I can’t  follow your way of fixing it. I only found the tab from Kathrins screenshot at "simulation"    --> "domain" --> "physics" but there is everything correct.

I also checked the CFL Number part but I have the same settings like you.

Best regards,

Lukas

Hi Lukas,

to my understaning Simon has set up viscous layers not only on the walls but also on inlet and outlet because he used the "local" tab in the mehs setup.

Please try the following:

• Select the mesh setup: Make sure that full hexa mesh and a cell size in domain of 0.0025m has been set.
• Select the mesh setup: Go to the tab local: make sure that viscous layers is deactivated there. The box needs to been unticked. Otherwise the visous layers are inserted on the whole grid.
• Select the boundary of your pipe wall: You are automatically in the tab local. Activate the viscous layers here with the setting from the hand-out: first layer thickness: 9.0e-05 m; target number of layers (fixed): 5

Viscous layers will be a topic in class 2, but here is already some background: Below you see a cutting plane inside the pipe showing the cell intersection (done in the same way as in result analysis; select cells intersection on the cutting plane and activate the wireframe visibility).

The upper screen shot shows a grid with visous layers only on the pipe wall. The lower picture shows a grid with viscous layers on wall, inlet and outlet. A simulation with viscous layers on inlet or outlet will diverge in most of the cases with default numerical parameters. So this is already a very good lessons learned: If your simulation diverges/crashes, check that you don't have viscous layers on inlet & outlet.

Thank you for your explanations! In fact, that was my mistake too.

Do we learn more about the diverging case tomorrow?

Hi Lukas,

thank you for your feedback!

In class 1 we explained already that a simulation can converge and diverge. In all other classes we will quite often address potential divergence issues as the reason for a divergence can be quite difference from on divergence to another.