REFERENCE: A.5 Humidifier: Webel: ValueTypes and Units

The diagram shows all ValueTypes and Units used in the Webel IT version of the Humidifier example, as gleaned using dimensional analysis (and yes this diagram is much larger than usually recommended):

Click on the image to view it full size

First, a big fat DISCLAIMER:

Webel: In some SysML trails ValueType names with Unit indicator suffixes have been used for dimensional analysis and illustrative purposes. This practice is NOT otherwise recommended here. Instead just use consistent custom ValueTypes across your system!

Note also that the Unit symbols (mostly) use Modelica-friendly syntax:

Webel vs SysPhS-1.1: Annex A.5: Humidifier: Where custom ValueTypes are defined, Modelica-friendly Unit symbols are used. Examples: "m3" not "m^3"; "degC" not "°C"; "J/(K.L)" (full stop as multiplier) not "J/(K⋅L)"; (EXCEPT "L" for litre not "l").

There is one Aussie-friendly exception:

Webel vs SysPhS-1.1: Annex A.5: Humidifier: Where ValueTypes involving litre are defined, the Unit symbol "L" is used rather than the Modelica-preferred "l" (in combination with an explicit additional unit converter).

And a unit symbol "%" is introduced for percent.

The following are the keys to un-ravelling the units for the equations across the system:

Webel vs SysPhS-1.1: Annex A.5: Humidifier: It is assumed that "vapor" is a volume rate corresponding to the rate of consumption OF HEATED LIQUID WATER (from a tank) used to create the vapor.

And yes, it took a while to figure that one out, as it's not at all obvious from the naming of the value properties and parameters in the spec version. Also:

Webel vs SysPhS-1.1: Annex A.5: Humidifier: It is assumed that "energy" is a rate (equivalent to a power).

Webel vs SysPhS-1.1: Annex A.5: Humidifier: It is assumed that "radiation" is a rate (equivalent to a power).

The "vapor" is in fact handled with 3 different units in different parts of the system, denoted here VaporRate_mL_per_h, VaporRate_mL_per_s, and VaporRate_L_per_s, and we'll see it actually corresponds to the volume rate of the liquid water required to create the vapor (it is not a measure of steam volume).

The use of Integer as the base for FanPowerRatio (which is used in the system essentially as a 0/1 switch) is as a workaround for this:

Modelica does not support comparison of Real values using == outside of functions (so not directly inside state machines)

To make the use of symbols and names more consistent - and to help tracing during dimensional analysis - this trail model uses either SysPhS versions of ValueTypes and Units, or introduces custom ones, although one could easily re-use ones from the ISO-80000 ModelLibrary where appropriate.

Make sure your custom ValueTypes either directly or indirectly extend Real:

GOTCHA: MagicDraw SysML/Cameo 19SP3: Export to Modelica: The name of a redefining Property must be exactly the same as the Property it redefines or it will not export properly!

Up next

REFERENCE: A.5 Humidifier: Webel: Block overview

Notes

[ASSERTION]{STRONG} Webel vs SysPhS-1.1: Annex A.5: Humidifier: It is assumed that "vapor" is a volume rate corresponding to the rate of consumption OF HEATED LIQUID WATER (from a tank) used to create the vapor.

[ASSERTION] Webel vs SysPhS-1.1: Annex A.5: Humidifier: It is assumed that "energy" is a rate (equivalent to a power).

[ASSERTION] Webel vs SysPhS-1.1: Annex A.5: Humidifier: It is assumed that "radiation" is a rate (equivalent to a power).

[GOTCHA] Modelica does not support comparison of Real values using == outside of functions (so not directly inside state machines)

[GOTCHA, ISSUE, MODELLING, TIP, WARNING]{INFORMATIVE} GOTCHA: MagicDraw SysML/Cameo 19SP3: Export to Modelica: The name of a redefining Property must be exactly the same as the Property it redefines or it will not export properly!

[ANTI-PATTERN, NAMING, POLICY]{STRONG} Webel: In some SysML trails ValueType names with Unit indicator suffixes have been used for dimensional analysis and illustrative purposes. This practice is NOT otherwise recommended here. Instead just use consistent custom ValueTypes across your system!

[CONVENTION, MODELLING, NAMING]{STRICT} Webel vs SysPhS-1.1: Annex A.5: Humidifier: Where custom ValueTypes are defined, Modelica-friendly Unit symbols are used. Examples: "m3" not "m^3"; "degC" not "°C"; "J/(K.L)" (full stop as multiplier) not "J/(K⋅L)"; (EXCEPT "L" for litre not "l").