Troubleshooting the Solution

Some problems that can occur when running a Simcenter STAR-CCM+ simulation are solution divergence and signal segmentation violations or memory errors. Solution divergence is likely to occur when a simulation is not well-posed. SIGSEGV or memory errors are generally unexpected and can require assistance from your support representative.

SIGSEV Error

A SIGSEGV (signal segmentation violation) error or a memory error (memory access exception) both occur when a program attempts to access a memory location that it is not allowed to access. There is a number of reasons why this error occurs.

A SIGSEGV is often a transient fault and can be very difficult to troubleshoot.
  • If the error is infrequent, try making minor changes to the current simulation and re-saving the file with a new name, or in a new location.
  • If it is frequent but limited to a single file, try rebuilding the simulation from scratch.
  • If the error occurs often across a wide range of conditions, the issue could originate either from the computer hardware or software, or it could be that the simulation is regularly exceeding the limits of the computers working memory. It could also be due to a permanent failure of hardware (failure in RAM, hard disk, CPU, mainboard, network, and so on).
  • In some specific circumstances, particularly for a complex or novel setup, the error can stem from a software problem that requires developer investigation.

If this type of error occurs, save the simulation under a different name so you can still use this file for reference. However do not continue working on this file.

Restart Simcenter STAR-CCM+, open the latest available file from a state before the error occurred and try redoing the steps again. Save the simulation file shortly before you reach the critical point. If the memory errors persist, verify that there is enough free memory to load the mesh and run Simcenter STAR-CCM+. In the most general terms, there must be 1 GB of available memory for approximately every million cells in the mesh. If after reviewing the simulation and computing hardware, the problem cannot be identified, then contact your support representative with the following information:

  1. The full output from the Output window: right-click in the output window and select Save As.
  2. The default macro: choose File > Macro > Save Default.
  3. The machine characteristics: see the Knowledge Base article, How to collect relevant computer details for troubleshooting problems?
  4. The last simulation file saved before the error occurred.

Divergence

Divergence of the solution is the situation where cell residuals increase from one iteration to another. If left, it can eventually result in a floating point exception being reported. Generally, the behavior of the residual monitor plots indicates when divergence happens.

An increase in one or more of the residual monitors during the first few iterations is normal and acceptable. For example, consider that a (constant) initial solution often satisfies the discretized equations exactly, everywhere except at the boundaries. The boundary conditions propagate into the interior as the solution iterates, causing the global residuals to increase for several iterations before decreasing. However, if this situation does not change after 5-10 iterations, it is likely to be an indication of divergence.

Solution divergence could be due to one of two reasons:

  • In a case with difficult physics, the initial conditions specify that the initial solution is inappropriate and special steps must be taken to get past a poor initial solution.
  • There is some other fundamental issue with the simulation, such as the mesh quality, the boundary conditions or the solution parameters, and special steps must be taken to debug the simulation setup.

If divergence occurs, you do not need to exit from the simulation. Instead, you can clear the solution and run it again after investigating the cause of divergence and making the required changes to the simulation.