Appendix D uses notation '\dot{m}' instead of 'm_flow'

[henrikt-ma]

Quoting @HansOlsson in #2643:

… but I realized that there is a major issue in the appendix D: it is using \dot{m} instead of m_flow throughout - without the considerations I gave, whereas chapter 15 uses m_flow. Apart from the problem I stated it's also confusing to have different notations with no explanation.

On the other hand \dot{m} is more common mathematical notation, it's just misleading. I believe we can resolve it by introducing \tilde{m} (or something like that) for m_flow - and have a short explanation for the relation between \tilde{m}and \dot{m}.

[henrikt-ma]

This comment from #2643 could also be of interest here, quoting @HansOlsson:

I finally found the explanation.

Rüdiger Franke did a presentation "Excerpt of Motivation for Modelica stream connectors" as part of "Eurosyslib WP 5.3 Meeting Mannheim, June 9, 2008" (stored in Modelica33 on old svn-server), and used Z instead of m_flow, and included that figure as well.