Convergence of MPSA for the Sneddon problem

[isakhammer]

Proposed changes

This pull request includes a reimplementation of Sneddon's analytical solution as outlined in https://doi.org/10.1007/s10596-020-10002-5.

Sneddon's solution provides an analytical method to compute the normal jump displacement for a pressurized fracture under linear elasticity conditions. The boundary element method is then integrated to compute semi-analytical boundary values, which are subsequently used to verify the MPSA numerical method for an open fracture. This process serves to validate the accuracy and convergence of the proposed numerical method, making it well-suited as a test case.

Types of changes

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• Minor change (e.g., dependency bumps, broken links).
• Bugfix (non-breaking change which fixes an issue).
• New feature (non-breaking change which adds functionality).
• Breaking change (fix or feature that would cause existing functionality to not work as expected).
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Checklist

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• The documentation is up-to-date.

• Static typing is included in the update.

• This PR does not duplicate existing functionality.

• The update is covered by the test suite (including tests added in the PR).

• If new skipped tests have been introduced in this PR, pytest was run with the --run-skipped flag.
  What types of changes does this PR introduce to PorePy?
  Put an x in the boxes that apply.

• Minor change (e.g., dependency bumps, broken links).

• Bugfix (non-breaking change which fixes an issue).

• New feature (non-breaking change which adds functionality).

• Breaking change (fix or feature that would cause existing functionality to not work as expected).

• Testing (contribution related to testing of existing or new functionality).

• Documentation (contribution related to adding, improving, or fixing documentation).

• Maintenance (e.g., improve logic and performance, remove obsolete code).

• Other:

Checklist

Put an x in the boxes that apply or explain briefly why the box is not relevant.

• The documentation is up-to-date.
• Static typing is included in the update.
• This PR does not duplicate existing functionality.
• The update is covered by the test suite (including tests added in the PR).
• If new skipped tests have been introduced in this PR, pytest was run with the --run-skipped flag.

[IvarStefansson]

This code does not seem to be quite ready for a PR. For the BEM code, documentation and formatting must be updated to current PorePy. For the error computation and convergence testing functionality, we should use the existing framework (see e.g. mandel_biot.py and convergence_analysis.py