Draft: Preconditioner freezing for ContField::GlobalSolve

Issue/feature addressed

Time-dependent matrix system require re-building of local matrices at every time step. This also requires re-building the preconditioner and is computationally expensive. In particular, for the IncNavierStokesSolver with VCSImplicit.

Proposed solution

Separate initialising the GlobalLinearSystem (matrix) and the preconditioner, and add the possibility to save the preconditoner in ContField.

Implementation

Added a function InitPreconditioner in GlobalSolve which builds the preconditioner. Additionally, the ContField holds a reference to the preconditioner via shared_ptr. InitPreconditioner additionally checks whether a non-Null preconditioner ptr is available.

Tests

• All previous iterative tests with VCSImplicit that use a Block or LowEnergyBlock preconditioner.
• For example Tet_Kovasnay_PreconditionerBlock.xml and Tet_Kovasnay_PreconditionerLowEnergyBlock.xml
• Added a test for IterativeFull Tet_Kovasnay_VCSImplicit.xml

Suggested reviewers

@CFD-Xing

Notes

Checklist

• Functions and classes, or changes to them, are documented.
• User guide/documentation is updated.
• Changelog is updated.
• Suitable tests added for new functionality.
• Contributed code is correctly formatted. (See the contributing guidelines).
• License added to any new files.
• No extraneous files have been added (e.g. compiler output or test data files).