Particle tracker utilitiy using equation system infrastructure

Issue/feature addressed

Please provide a description of the problem your changes address. Be sure to link to any related items in the issue tracker.

Some post-processing module needs a time-dependent flow field, such as phase averaging, and Lagrangian point tracking in a subdomain. To do these post-processings, one can call filter modules when running the simulation. However, people cannot always know which post-processing is needed when submitting the job and re-run the simulation can be very expensive sometimes.

Proposed solution

A summary of the proposed changes and how they address the issue/feature at hand. Whenever possible, describe alternatives your considered and decisions you made.

To solve this problem, this MR introduces a utility tool ReviewSolution to recreate the time-continuous solution. This ReviewSolution is a derived class of UnsteadySystem. It reads the discrete check-point files and interpolates the check-point files into a continuous field. The ReviewSolution pretends to output the interpolated field at the integration time as the time-integration result of the unsteady system. All filter modules can be applied to this utility tool.

Implementation

A more detailed description of the changes. Please include any details necessary for reviewers to understand your work, and point out particular points would like them to pay particular attention to.

In the ReviewSolution, the key module is field interpolation using evenly-spaced Lagrange polynomials or Fourier transformation (periodic only). This module repeats the baseflow-interpolation module in LinearisedAdvection class. Merging them together needs another merge request.

Tests

Notes

Please add any other information that could be useful for reviewers.

Checklist

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