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May 7, 2021, 01:02 
Divergence detected in AMG solver. VOF.

#1 
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Hi guys. I'm simulating airwater flow through a T pipe with 26mm inner diameter. The pipe was created in a 2D domain, there are two inlets (one for air and the other for water) and one outlet. The two inlets have velocity inlet conditions and the outlet has pressure outlet conditions. The pipe is filled with water and then water and air start to flow from the inlets with their respective inlet velocities. I'm conducting a mesh independence test with four meshes. The timestep for each mesh was calculated based on the CFL condition and the total flow time for each one was 6 seconds. The first three simulations had no problems but the fourth one is presenting the following problems after the bubbles reach the outlet (which occurred approximately in 2,3 seconds):
# Divergence detected in AMG for xmomentum: protective actions enabled! # Divergence detected in AMG for xmomentum, temporarily solve with BCGSTAB! Divergence detected in AMG solver: xmomentum# Divergence detected in AMG for ymomentum: protective actions enabled! # Divergence detected in AMG for ymomentum, temporarily solve with BCGSTAB! Divergence detected in AMG solver: ymomentum# Divergence detected in AMG for pressure correction: protective actions enabled! # Divergence detected in AMG for pressure correction, temporarily solve with BCGSTAB! Divergence detected in AMG solver: pressure correction# Divergence detected in AMG for pressure correction: protective actions enabled! # Divergence detected in AMG for pressure correction, temporarily solve with BCGSTAB! Divergence detected in AMG solver: pressure correction# Divergence detected in AMG for k: protective actions enabled! # Divergence detected in AMG for k, temporarily solve with BCGSTAB! Divergence detected in AMG solver: k# Divergence detected in AMG for omega: protective actions enabled! # Divergence detected in AMG for omega, temporarily solve with BCGSTAB! Divergence detected in AMG solver: omega Divergence detected in AMG solver: xmomentum Divergence detected in AMG solver: ymomentum Divergence detected in AMG solver: pressure correction Divergence detected in AMG solver: pressure correction Divergence detected in AMG solver: k Divergence detected in AMG solver: omega Divergence detected in AMG solver: xmomentum Divergence detected in AMG solver: ymomentum Divergence detected in AMG solver: pressure correction Divergence detected in AMG solver: pressure correction Divergence detected in AMG solver: k Divergence detected in AMG solver: omega reversed flow in 118 faces on pressureoutlet 9. Divergence detected in AMG solver: xmomentum Divergence detected in AMG solver: ymomentum Divergence detected in AMG solver: pressure correction Divergence detected in AMG solver: pressure correction Divergence detected in AMG solver: k Divergence detected in AMG solver: omega Error at host: floating point exception Error at Node 0: floating point exception Error at Node 1: floating point exception Error at Node 2: floating point exception Error at Node 3: floating point exception Error: floating point exception Error Object: #f I checked the mesh quality and it looks good (min orthogonal quality = 0.68; max skewness = 0.60; max aspect ratio = 10.07). I tried to solve the problem by reducing the time step in half and decreasing the relaxation factors, but it didn't work. I don't know how to fix this problem, so I really need some help and I'm open to answering any questions. I'm going to list every piece of information I find relevant about the simulation. General: Parallel Solver type: PressureBased Time: Transient Planar 2D space Gravity on Models: Multiphase VOF with explicit formulation and Surface Tension Force Modeling (CSF) Default Courant number: 0,25 Implicit Body Force Turbulence Model: SST komega Cell Zone Conditions: Specified Operating Density: 1.225 kg/m³ (air density) Boundary conditions: air inlet velocity = 0.123 m/s water inlet velocity = 0.6 m/s outlet Gauge Pressure (pascal) = 0 pipe wall: stationary, no slip Solution Methods: PISO Scheme Least Squares Cell Based Gradient PRESTO! Pressure volume fraction: GeoReconstruct Momentum, Turbulent Kinetic Energy and Specific Dissipation Rate = Second order upwind Transient Formulation = First order implicit Solution Controls: Default Residuals = 10e5 Standard initialization with default initial values 

May 17, 2021, 15:07 

#2 
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Maharshtra
Join Date: May 2021
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You got the solution of this problem ?


August 31, 2021, 20:42 

#3 
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Join Date: May 2020
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Hi Harshad Bhalerao,
I still dont know the answer. It has been months since i posted this and nobody posted a reply. 

September 21, 2022, 05:34 

#4 
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CHEN TING
Join Date: Sep 2022
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can you solve it


September 25, 2023, 08:10 
AMG solver divergence

#5  
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Outside North America
Join Date: Nov 2021
Posts: 14
Rep Power: 4 
Quote:
Hello, I recently encountered the same problem as you. Do you know the reason for this mistake? Thank you! 

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amd divergence; vof; 2d 
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