Fixing ANSYS CFX Error: Subroutine MATIN2 & ERROR #001100279

Troubleshooting initial solver loop crashes on thin 2mm extrusions, tetrahedral inflation meshing, and multiphase flows.

If your ANSYS CFX simulation crashes during the very first iteration with an unhelpful solver log referencing MATIN2 and MESG_RETRIEVE, you are dealing with one of CFX's lesser-documented matrix inversion failures.

Typical Solver Error Log:

ERROR #001100279 has occurred in subroutine ErrAction.
Message: Stopped in routine MATIN2

ERROR #001100279 has occurred in subroutine MESG_RETRIEVE.
Message: Stopping the run due to error(s) reported above

What Does Subroutine MATIN2 Mean?

In CFX’s underlying solver architecture (derived from Fortran routines), MATIN2 stands for Matrix Inversion (2D / Phase Sub-Matrix). It is responsible for inverting localized element matrices and phase-coupling equations prior to starting numerical iterations.

When the run stops inside MATIN2 on Loop 1, CFX attempted to invert a matrix that is singular (determinant = 0) or contains invalid numbers (NaNs). The secondary error (MESG_RETRIEVE) is simply the solver error handler shutting down parallel processes.

Root Causes for Thin Extrusions (2mm) with Air/Water Setup

• Inflation Layer Collision Across the 2mm Thickness: Tetrahedral meshing on a 2mm domain with inflation layers often causes prismatic elements growing from opposing walls to overlap, pinch, or invert. This creates elements with zero or negative Jacobian volume.
• Uninitialized Multiphase Volume Fractions: In two-phase flow (air/water), if initial fluid volume fractions are left unassigned or conflicting under Global Domain Initialization, the phase matrix initialization in MATIN2 fails due to division-by-zero.
• Inflation Applied to Inlets or Outlets: If inflation layers were assigned to boundary walls and accidentally selected the 2 air/water inlet or outlet faces, high-aspect-ratio elements at open boundaries cause matrix singularity.

Step-by-Step Solutions

1. Switch from Tet Mesh to Sweep/Hex Mesh (Recommended)

Tetrahedral elements perform poorly on thin extruded geometries (2mm gap). Instead of using tetrahedral meshing with inflation layers:

• Use Sweep Meshing (Hexahedral) across the 2mm extrusion direction.
• Set at least 4 to 6 divisions across the 2mm thickness gap.
• If using tetrahedral mesh is mandatory, change Inflation Collision Handling to Layer Compression or Stair-step in ANSYS Meshing.

2. Check Mesh Metrics in ANSYS Meshing

Inspect your mesh before opening CFX-Pre:

• Orthogonal Quality: Ensure the minimum value is strictly > 0.1 (aim for > 0.15).
• Skewness: Ensure the maximum value is < 0.95.
• Verify there are no negative-volume elements near the inflation-to-tet transition zone.

3. Explicitly Define Air & Water Volume Fractions

In CFX-Pre:

• Open Flow Analysis > Global Domain > Initial Values.
• Set explicit initial values for fluid phases (e.g., Water Volume Fraction = 1.0, Air Volume Fraction = 0.0).
• Avoid leaving phase volume fraction fields empty or set to unassigned defaults.

4. Verify Boundary Face Assignments

Double-check your Named Selections in ANSYS Meshing / CFX-Pre. Ensure that inflation layers are assigned exclusively to solid wall surfaces and do not touch or include the 2 inlet and 2 outlet faces.

Quick Diagnostic Checklist

1. Is minimum Mesh Orthogonal Quality greater than 0.1?
2. Are inflation layers crashing into each other across the 2mm thickness gap?
3. Are both Air and Water volume fractions initialized in CFX-Pre?
4. Are inlet/outlet faces excluded from inflation layer scope?