KR373: Why am I getting divergence on the first iteration for an axisymmetric problem?
I am running a 2d axisymmetric simulation but it diverges on the first iteration with the following message:
Divergence detected in AMG solver: x-momentum -> Increasing relaxation sweeps!
Error: Divergence detected in AMG solver: x-momentum
Error Object: #f
One reason could be that the geometry is not correct. Do a Mesh->Check to make sure you don't get
Checking for nodes that lie below the x-axis.
WARNING: Invalid axisymmetric mesh: 6 nodes lie below the x-axis.
WARNING: Mesh check failed.
For axisymmetric, the axial direction should be x and radial is positive y. Even if the y starts with -1e-32, it will fail.
To fix this:
Use Mesh->Translate and move the geometry so ymin is +ve.