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Fail to converge when solving with a fabricated solution

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Old   March 22, 2021, 06:33
Default Fail to converge when solving with a fabricated solution
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zizhou huang
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Hi,

I got "Divergence detected in AMG solver" when trying to solve with the exact solution on the domain [0,1]^3 as follows, it's from paper http://tarjomefa.com/wp-content/uplo...-TarjomeFa.pdf.
u(x,y,z,t)=-a e^{-d^2\nu t} (e^{ax}\sin(ay+dz)+e^{az}\cos(ax+dy))
v(x,y,z,t)=-a e^{-d^2\nu t} (e^{ay}\sin(az+dx)+e^{ax}\cos(ay+dz))
w(x,y,z,t)=-a e^{-d^2\nu t} (e^{az}\sin(ax+dy)+e^{ay}\cos(az+dx))
where a=d=\nu=1

Here's the log.

Code:
Updating solution at time levels N and N-1.
 done.

  iter  continuity  x-velocity  y-velocity  z-velocity     time/iter
        Stabilizing x-momentum to enhance linear solver robustness.
        Stabilizing x-momentum using GMRES to enhance linear
Error at Node 1: floating point exception

Error at Node 0: floating point exception

Error at Node 2: floating point exception

Error at Node 3: floating point exception
        Stabilizing x-momentum to enhance linear solver robustness.
        Stabilizing x-momentum using GMRES to enhance linear solver robustness.

Divergence detected in AMG solver: x-momentum        Stabilizing y-momentum to enhance linear solver robustness.
        Stabilizing y-momentum using GMRES to enhance linear solver robustness.

Divergence detected in AMG solver: y-momentum        Stabilizing z-momentum to enhance linear solver robustness.
        Stabilizing z-momentum using GMRES to enhance linear solver robustness.

Divergence detected in AMG solver: z-momentum        Stabilizing x-momentum to enhance linear solver robustness.
        Stabilizing x-momentum using GMRES to enhance linear solver robustness.

Divergence detected in AMG solver: x-momentum        Stabilizing y-momentum to enhance linear solver robustness.
        Stabilizing y-momentum using GMRES to enhance linear solver robustness.

Divergence detected in AMG solver: y-momentum        Stabilizing z-momentum to enhance linear solver robustness.
        Stabilizing z-momentum using GMRES to enhance linear solver robustness.

Divergence detected in AMG solver: z-momentum        Stabilizing x-momentum to enhance linear solver robustness.
        Stabilizing x-momentum using GMRES to enhance linear solver robustness.

Divergence detected in AMG solver: x-momentum        Stabilizing y-momentum to enhance linear solver robustness.
        Stabilizing y-momentum using GMRES to enhance linear solver robustness.

Divergence detected in AMG solver: y-momentum        Stabilizing z-momentum to enhance linear solver robustness.
        Stabilizing z-momentum using GMRES to enhance linear solver robustness.

Divergence detected in AMG solver: z-momentum        Stabilizing x-momentum to enhance linear solver robustness.
        Stabilizing x-momentum using GMRES to enhance linear solver robustness.

Divergence detected in AMG solver: x-momentum        Stabilizing y-momentum to enhance linear solver robustness.
        Stabilizing y-momentum using GMRES to enhance linear solver robustness.

Divergence detected in AMG solver: y-momentum        Stabilizing z-momentum to enhance linear solver robustness.
        Stabilizing z-momentum using GMRES to enhance linear solver robustness.

Divergence detected in AMG solver: z-momentum        Stabilizing x-momentum to enhance linear solver robustness.
        Stabilizing x-momentum using GMRES to enhance linear solver robustness.

Divergence detected in AMG solver: x-momentum        Stabilizing y-momentum to enhance linear solver robustness.
        Stabilizing y-momentum using GMRES to enhance linear solver robustness.

Divergence detected in AMG solver: y-momentum        Stabilizing z-momentum to enhance linear solver robustness.
        Stabilizing z-momentum using GMRES to enhance linear solver robustness.

Divergence detected in AMG solver: z-momentum        Stabilizing pressure correction to enhance linear solver robustness.
        Stabilizing pressure correction using GMRES to enhance linear solver robustness.

Divergence detected in AMG solver: pressure correction        Stabilizing pressure correction to enhance linear solver robustness.
        Stabilizing pressure correction using GMRES to enhance linear solver robustness.

Divergence detected in AMG solver: pressure correction        Stabilizing pressure correction to enhance linear solver robustness.
        Stabilizing pressure correction using GMRES to enhance linear solver robustness.

Divergence detected in AMG solver: pressure correction        Stabilizing pressure correction to enhance linear solver robustness.
        Stabilizing pressure correction using GMRES to enhance linear solver robustness.

Divergence detected in AMG solver: pressure correction        Stabilizing pressure correction to enhance linear solver robustness.
        Stabilizing pressure correction using GMRES to enhance linear solver robustness.

Divergence detected in AMG solver: pressure correction        Stabilizing pressure correction to enhance linear solver robustness.
        Stabilizing pressure correction using GMRES to enhance linear solver robustness.

Divergence detected in AMG solver: pressure correction        Stabilizing pressure correction to enhance linear solver robustness.
        Stabilizing pressure correction using GMRES to enhance linear solver robustness.

Divergence detected in AMG solver: pressure correction        Stabilizing pressure correction to enhance linear solver robustness.
        Stabilizing pressure correction using GMRES to enhance linear solver robustness.

Divergence detected in AMG solver: pressure correction        Stabilizing pressure correction to enhance linear solver robustness.
        Stabilizing pressure correction using GMRES to enhance linear solver robustness.

Divergence detected in AMG solver: pressure correction        Stabilizing pressure correction to enhance linear solver robustness.
        Stabilizing pressure correction using GMRES to enhance linear solver robustness.

Divergence detected in AMG solver: pressure correction        Stabilizing pressure correction to enhance linear solver robustness.
        Stabilizing pressure correction using GMRES to enhance linear solver robustness.

Divergence detected in AMG solver: pressure correction        Stabilizing pressure correction to enhance linear solver robustness.
        Stabilizing pressure correction using GMRES to enhance linear solver robustness.

Divergence detected in AMG solver: pressure correction        Stabilizing pressure correction to enhance linear solver robustness.
        Stabilizing pressure correction using GMRES to enhance linear solver robustness.

Divergence detected in AMG solver: pressure correction        Stabilizing pressure correction to enhance linear solver robustness.
        Stabilizing pressure correction using GMRES to enhance linear solver robustness.

Divergence detected in AMG solver: pressure correction        Stabilizing pressure correction to enhance linear solver robustness.
        Stabilizing pressure correction using GMRES to enhance linear solver robustness.

Divergence detected in AMG solver: pressure correction        Stabilizing pressure correction to enhance linear solver robustness.
        Stabilizing pressure correction using GMRES to enhance linear solver robustness.

Divergence detected in AMG solver: pressure correction        Stabilizing pressure correction to enhance linear solver robustness.
        Stabilizing pressure correction using GMRES to enhance linear solver robustness.

Divergence detected in AMG solver: pressure correction        Stabilizing pressure correction to enhance linear solver robustness.
        Stabilizing pressure correction using GMRES to enhance linear solver robustness.

Divergence detected in AMG solver: pressure correction        Stabilizing pressure correction to enhance linear solver robustness.
        Stabilizing pressure correction using GMRES to enhance linear solver robustness.

Divergence detected in AMG solver: pressure correction        Stabilizing pressure correction to enhance linear solver robustness.
        Stabilizing pressure correction using GMRES to enhance linear solver robustness.

Divergence detected in AMG solver: pressure correction        Stabilizing pressure correction to enhance linear solver robustness.
        Stabilizing pressure correction using GMRES to enhance linear solver robustness.

Divergence detected in AMG solver: pressure correction        Stabilizing pressure correction to enhance linear solver robustness.
        Stabilizing pressure correction using GMRES to enhance linear solver robustness.

Divergence detected in AMG solver: pressure correction
Divergence detected in AMG solver: x-momentum
Divergence detected in AMG solver: y-momentum
Divergence detected in AMG solver: z-momentum
Divergence detected in AMG solver: x-momentum
Divergence detected in AMG solver: y-momentum
Divergence detected in AMG solver: z-momentum
Divergence detected in AMG solver: x-momentum
Divergence detected in AMG solver: y-momentum
Divergence detected in AMG solver: z-momentum
Divergence detected in AMG solver: x-momentum
Divergence detected in AMG solver: y-momentum
Divergence detected in AMG solver: z-momentum
Divergence detected in AMG solver: x-momentum
Divergence detected in AMG solver: y-momentum
Divergence detected in AMG solver: z-momentum
Divergence detected in AMG solver: pressure correction
Divergence detected in AMG solver: pressure correction
Divergence detected in AMG solver: pressure correction
Divergence detected in AMG solver: pressure correction
Divergence detected in AMG solver: pressure correction
Divergence detected in AMG solver: pressure correction
Divergence detected in AMG solver: pressure correction
Divergence detected in AMG solver: pressure correction
Divergence detected in AMG solver: pressure correction
Divergence detected in AMG solver: pressure correction
Divergence detected in AMG solver: pressure correction
Divergence detected in AMG solver: pressure correction
Divergence detected in AMG solver: pressure correction
Divergence detected in AMG solver: pressure correction
Divergence detected in AMG solver: pressure correction
Divergence detected in AMG solver: pressure correction
Divergence detected in AMG solver: pressure correction
Divergence detected in AMG solver: pressure correction
Divergence detected in AMG solver: pressure correction
Divergence detected in AMG solver: pressure correction
Divergence detected in AMG solver: pressure correction
Divergence detected in AMG solver: pressure correction
Divergence detected in AMG solver: x-momentum
Divergence detected in AMG solver: y-momentum
Divergence detected in AMG solver: z-momentum
Divergence detected in AMG solver: x-momentum
Divergence detected in AMG solver: y-momentum
Divergence detected in AMG solver: z-momentum
Divergence detected in AMG solver: x-momentum
Divergence detected in AMG solver: y-momentum
Divergence detected in AMG solver: z-momentum
Divergence detected in AMG solver: x-momentum
Divergence detected in AMG solver: y-momentum
Divergence detected in AMG solver: z-momentum
Divergence detected in AMG solver: x-momentum
Divergence detected in AMG solver: y-momentum
Divergence detected in AMG solver: z-momentum
Divergence detected in AMG solver: pressure correction
Divergence detected in AMG solver: pressure correction
Divergence detected in AMG solver: pressure correction
Divergence detected in AMG solver: pressure correction
Divergence detected in AMG solver: pressure correction
Divergence detected in AMG solver: pressure correction
Divergence detected in AMG solver: pressure correction
Divergence detected in AMG solver: pressure correction
Divergence detected in AMG solver: pressure correction
Divergence detected in AMG solver: pressure correction
Divergence detected in AMG solver: pressure correction
Divergence detected in AMG solver: pressure correction
Divergence detected in AMG solver: pressure correction
Divergence detected in AMG solver: pressure correction
Divergence detected in AMG solver: pressure correction
Divergence detected in AMG solver: pressure correction
Divergence detected in AMG solver: pressure correction
Divergence detected in AMG solver: pressure correction
Divergence detected in AMG solver: pressure correction
Divergence detected in AMG solver: pressure correction
Divergence detected in AMG solver: pressure correction
Divergence detected in AMG solver: pressure correction
Divergence detected in AMG solver: x-momentum
Divergence detected in AMG solver: y-momentum
Divergence detected in AMG solver: z-momentum
Divergence detected in AMG solver: x-momentum
Divergence detected in AMG solver: y-momentum
Divergence detected in AMG solver: z-momentum
Divergence detected in AMG solver: x-momentum
Divergence detected in AMG solver: y-momentum
Divergence detected in AMG solver: z-momentum
Divergence detected in AMG solver: x-momentum
Divergence detected in AMG solver: y-momentum
Divergence detected in AMG solver: z-momentum
Divergence detected in AMG solver: x-momentum
Divergence detected in AMG solver: y-momentum
Divergence detected in AMG solver: z-momentum
Divergence detected in AMG solver: pressure correction
Divergence detected in AMG solver: pressure correction
Divergence detected in AMG solver: pressure correction
Divergence detected in AMG solver: pressure correction
Divergence detected in AMG solver: pressure correction
Divergence detected in AMG solver: pressure correction
Divergence detected in AMG solver: pressure correction
Divergence detected in AMG solver: pressure correction
Divergence detected in AMG solver: pressure correction
Divergence detected in AMG solver: pressure correction
Divergence detected in AMG solver: pressure correction
Divergence detected in AMG solver: pressure correction
Divergence detected in AMG solver: pressure correction
Divergence detected in AMG solver: pressure correction
Divergence detected in AMG solver: pressure correction
Divergence detected in AMG solver: pressure correction
Divergence detected in AMG solver: pressure correction
Divergence detected in AMG solver: pressure correction
Divergence detected in AMG solver: pressure correction
Divergence detected in AMG solver: pressure correction
Divergence detected in AMG solver: pressure correction
Divergence detected in AMG solver: pressure correction
For boundary conditions, the "velocity-inlet" boundary condition is used for all boundaries. Both the boundary condition and the initial condition is set to the exact solution. For the mesh, I'm using a uniform grid with size 40\times 40\times 40. For the model and solver, I use the laminar model, piso/simple/coupled methods with default parameters and schemes, and various CFL numbers, but none of them converge.

I also tried with the taylor green vortex solution (as shown below) with the same settings, and it works. However, I really want to try something non-trivial in the third dimension.
u(x,y,z,t)=\cos(x)\sin(y)e^{-2\nu t}
v(x,y,z,t)=-\cos(y)\sin(x)e^{-2\nu t}
w(x,y,z,t)=0

I'm wondering whether it's because fluent cannot solve with this solution? Or did I make any mistake? Thanks a lot!
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