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

Question

The problem I have with the first challenge might be a problem with my PC. When ever I start the simulation of the in the handout specified numbers, the simulation ends after some time and gives out the error message - S_Simulation 1 Error: ERROR: residual of Mass is Not A Number: the solver has been stopped and the message - The simulation Simulation 1 has failed: some NaN have been detected during the computation.
ERROR: residual of Mass is Not A Number: the solver has been stopped I don´t know if my PC´s CPU is maybe not good enough or if there might be a problem with my pre-processing in this challenge. What worked is to set the CFL Number to 1.5 instead of 3.0, but the challenge requires running the simulation with a CFL of 3.0.

SimonGohle · Accepted Answer

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 :)

Manuel NIB · Answer

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.

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

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