Feature expressions

Summary

This branch represents an implementation of what is considered to be the most useful aspects of swak4Foam (Swiss-Army-Knife for FOAM) from Bernhard Gschaider, namely the ability to use text-based expressions instead of coding in C++ for the following cases:

• expression-based boundary conditions (also known as groovy boundary conditions)
• expression-based setFields (also known as funky set fields)

The idea of what we currently term expressions was pioneered by (Bernhard Gschaider) and is now firmly established in swak4Foam. Among other things, expressions attempt to bridge the gap between using standard, predefined boundary conditions and writing dedicated, special-purpose ones. Although part of this gap is now covered within OpenFOAM by using dynamically compiled user coding (eg, coded boundary conditions), there remains substantial areas where it can be significantly more convenient to have a series of predefined functions and expression sytax with some access to base OpenFOAM field functionality that enables rapid deployment of boundary conditions, or custom-defined setFields without writing code. A significant portion of swak4Foam expressions has been adapted for direct integration into OpenFOAM. During the integration and rewrite, we have tried to pare things down to a smaller subset with the aim of covering 90% or more of the common cases. The remaining cases are left to be reassessed for extending the expressions functionality in the future, but they also may be better served with other approaches (eg, with coded conditions) that were not available when swak4Foam was originally conceived.

To the greatest extent possible, the integrated expressions have been designed to avoid name clashes with swak so it should remain possible to use the most recent versions of swak without problem.

Risks

• New functionality, so low chance of regression.
• The scope of the functionality will be revised in the future

Naming (for swak4Foam users)

The following are the expressions correspondences to swak:

• The exprFixedValue and exprGradient boundary conditions are roughly equivalent to the groovy boundary conditions.

• The utilities setExprFields and setExprBoundaryFields are roughly equivalent to the funky utilities of similar name.

The naming of the boundary conditions and utilities not only reflects the slightly different input requirements, but simultaneously seeks to avoid any potential name-clash with swak4Foam in a mixed environment.

The names for the boundary condition dictionary entries tend be shorter and slightly different (eg, valueExpr vs valueExpression) to serve as a small reminder that the expressions syntax is slightly different than the groovy equivalents. It also allows the user to fashion dictionary entries that are sufficient for both boundary condition variants and quickly toggle between them simply by changing the boundary condition type.