Approximation of the finite line source

[MassimoCimmino]

This issue is to implement the approximation of the finite line source solution introduced in [1]. An option will be added to choose to evaluate the FLS using the current quadrature method or the approximation.

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[1] Cimmino, M., 2021. An approximation of the finite line source solution to model thermal interactions between geothermal boreholes. International Communications in Heat and Mass Transfer, 127, p.105496.

[j-c-cook]

Would it be possible to get this into master for the v2.1.0 release? Given that Cimmino (1) mentions a 1000x speed increase, this should provide a nice increase to calculating g-functions with accuracy.

I'd be happy to help make this happen. If you'd want to open a draft PR, I can work on it.

[MassimoCimmino]

equivalent solver : Rectangular fields up to 400 boreholes

Results labeled with 'PR-189' use the approximation of the FLS and nFLS=10 terms.

[MassimoCimmino]

similarities solver : Rectangular fields up to 400 boreholes

Results labeled with 'PR-189' use the approximation of the FLS and nFLS=10 terms. We can see that the calculation time is only decreased for smaller bore fields. This is expected since the solution of the system of equations is the major part of the calculation time for larger bore fields.