How to Resolve Singular Matrix Error in COMSOL Transient Solver?

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SUMMARY

The discussion focuses on resolving a singular matrix error encountered in COMSOL 3 while solving a 3D incompressible flow problem. The user, Akshay, experiences issues with the direct solver, specifically a failure in residual computation due to a relative error exceeding the tolerance. Despite refining the mesh to a maximum element size of 0.002 and utilizing the GMRES method with a preconditioning quality of 0.01, the problem persists. Solutions proposed include adjusting solver settings and refining mesh further.

PREREQUISITES
  • Familiarity with COMSOL Multiphysics 3.0
  • Understanding of 3D incompressible flow simulations
  • Knowledge of numerical methods, specifically GMRES
  • Experience with mesh refinement techniques
NEXT STEPS
  • Investigate alternative solver settings in COMSOL, such as switching to iterative solvers.
  • Explore advanced mesh refinement strategies to improve convergence.
  • Learn about preconditioning techniques specific to GMRES in COMSOL.
  • Review documentation on handling singular matrix issues in COMSOL simulations.
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Engineers and researchers working with fluid dynamics simulations in COMSOL, particularly those facing convergence issues in transient solvers.

timjm
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I am currently just running a normal 3D incompressible flow problem in COMSOL 3, and end up with the following error:

Error:
Time 0:
Error in residual computation:
The_relative_error_is_greater_than_the_relative_tolerance
For the direct solver.
Last time step is not converged.

How do I go about resolving this issue?

Thanks.
 
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Hi All,

I am trying to solve a problem where the solutions are expected to be zero for a very long time.

I have refined the mesh with the maximum element size of 0.002 and am using the GMRES method with preconditioning quality of 0.01.

However, inspite of it, the system is unable to process the solution and gives an error for residual computation citing singular matrix as the problem.

Can anyone please suggest some ways to solve the problem?

Akshay
 

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