Numerous dynamic systems are implemented in Underworld. They may be found within the systems submodule.
Classes are documented with examples using Python docstrings and doctests. This information is available directly in the Python interpreter (using the help() builtin function). However, the rendered version of docstrings is generally more useful, and is available at the Underworld Read the Docs page:
http://underworld2.readthedocs.io/en/latest/underworld.systems.html#underworld.systems.Stokes