Error: "Analysis has stopped because the Solver has exited Unexpectedly" in Simulation CFD

Jan 14, 2015


While solving an analysis, the following error message is issued:

The analysis has stopped because the solver has exited unexpectedly



While there are several factors that can cause this behavior, these are the primary causes:

  1. Memory Problems - The solver exits if enough memory is not available.
  2. Poorly Posed Setup Parameters - The solver exits and/or diverges if the model is not properly set up.
  3. File I/O Errors - The solver exits if errors are encountered while reading or writing solver and results files.
  4. Incompatible Scalar Diffusion Coefficient value – If the General Scalar formulation is invoked, the value of Diffusion Coefficient may be numerically incompatible with other settings in the simulation.


As a first solution, simply attempt to run the simulation again after encountering this error. If the error occurs again, more investigation is needed.

Problem 1: Memory Problems

1. The mesh and/or physics being modeled may simply exceed the memory resources of the machine. To reduce the amount of required RAM:       

  • Ensure the setup (boundary conditions, domain size, etc) follows the best practices outlined in the Help system. (Review the “Analysis Guidelines” and “Application Best Practices” sections in particular.)
  • Coarsen the mesh where appropriate to reduce the number of elements.
  • Improve mesh quality by keeping nodal aspect ratios below 2000.
  • For a steady state thermal analysis, the thermal solver may attempt to change the solution too rapidly, which can exceed the resources of the computer. To force a more gradual solution of the thermal field, add the flag shown below. The Flag Manager can be accessed through the interface (Design Study Tools -> Flags).

    Max_Pseudo_Time_Step_Size 60

    This slows the evolution of the thermal solution, and generally requires less memory.

2. Other applications may take up a significant amount of RAM. Close other applications (CAD, web browser windows, email, etc.) and, optionally, reboot the computer to initiate a more efficient memory allocation within Windows.

3. There may be multiple RAM boards installed that operate at different speeds. This can lead to errors within the HPC (parallelization) routines. Either remove the additional RAM board or replace one or more to ensure that all operate at the same speed.

4. The Windows 3GB switch has caused difficulty in several cases due to improper memory allocation of solver processes. If the Solver exits unexpectedly during an analysis, try disabling the 3GB switch.

Problem 2: Check the setup for poorly posed setup parameters and other problems

A combination of material properties (density, viscosity and several other properties) may prevent a successful solution. The numerical matrix containing the mathematical representation may be "poorly posed," meaning that the solvers are unable to calculate the results based on the specified model parameters. This can be caused by several issues, including:

  • Unrealistic material properties or boundary conditions
  • Blowers with incorrectly assigned inlet and outlet surfaces
  • Non-physical scalar diffusion coefficients

Check the boundary condition assignments of the model to ensure that all use realistic values and are assigned to the correct locations. There should be no surface boundary conditions internally (a scalar = 1 on a fire is the exception) as this will cause the above error.

Check the mesh distributions to ensure that small details are meshed adequately to resolve flow and temperature gradients.

Problem 3: File I/O Errors

Antivirus or firewall applications may prevent the solver from running smoothly. Ensure that firewalls have exceptions for SimCFDSolver.exe, smpd.exe, mpiexec.exe, and mpich2.exe.

Ensure the Autodesk® Simulation CFD application and working folders (folders where analysis data are saved to) are not actively scanned while the analysis is running.

Make sure that your design study is located on a local drive (internal, not external) and not a network drive.  Many networks will block the I/O communication between the user interface and solver.  The error will usually display as soon as the solve button is pressed.

Problem 4: Incompatible Scalar Diffusion Coefficient value

A combination of material properties (density, viscosity and several other properties) is preventing the Solver from solving the analysis model. The numerical matrix that contains the mathematical representation is "poorly posed," meaning that the solvers are unable to calculate the results based on the specified model parameters.

To resolve the issue, increase the Scalar Diffusion Coefficient to a slightly higher value. This should eliminate the numerical problems that are causing the problem. We recommend using a value of 1e-4 m2/s, as this has resolved several instances of this issue.

To do this:

  1. Right click off the model, and select Solve.
  2. Select the Physics tab, and click the Advanced button.
  3. Specify the value in the Diffusion coefficient field.

This solution applies to models in which the General Scalar is selected. It will not resolve issues with the other scalar models (such as humidity and steam quality).

Note: If the analysis is transient, increase the number of Inner Iterations (on the Solve dialog) to be greater than 1.


Simulation CFD