BDD & PD: HumidityBalance

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Tutorial
TRAIL: SysPhS-1.1 Annex A examples in MagicDraw/Cameo SysML vs Modelica (Wolfram SystemsModeler)
Section
Annex A.5: Humidifier (with Units)
Topic level
INTERMEDIATE
UML keywords
Property::redefinedProperty
ports compartment
Port
SysML keywords
Block
:values compartment
BindingConnector
constraint parameter
Keywords
Slide kind
hybrid diagram
SysML Block Definition Diagram (BDD)
SysML Parametric Diagram
This diagram shows the Block HumidityBalance with a supporting ConstraintBlock HumidityBalanceConstraint:
Click on the image to view it full size
Noting that:
Webel vs SysPhS-1.1: Annex A.5: Humidifier: Dimensional analysis of RelativeHumidityCalculationConstraint implies constraint parameter 'change' in {der(x)=((press/satVap)-change)/c2} is a unitless relative humidity, given that 'c2' is a Time.
It is concluded that:
Webel vs SysPhS-1.1: Annex A.5: Humidifier: Dimensional analysis of HumidityBalanceConstraint implies constraint parameter 'airExRate' in {change=((humidity-envH)*(volume*airExRate))} is per-volume, assuming that 'volume' is a fixed Volume.

This is based on the assumption that volume is indeed a fixed Volume (does not depend on time).

The use of suffix "Rate" in the names airExRate and airExchangeRate is not entirely clear. But it's not a big deal because it is clear that the output is simply a unitless relative Humidity.

There are the following main candidates for the units of volume based on the startup value '25,000':

  • If the volume is stated in cubic metre 25,000 m^3 it would correspond to a cube of length about 29.24 m, which is possible for a large office building, but much larger than a typical "room".
  • If the volume is stated in litres 25,000 L it would correspond to a cube of length about 2.924 m, which would be realistic for a small room.

We'll see also later that it turns out that if the volume here is in fact the same quantity as the volume under VaporPressureCalculation (i.e., they are both the volume of the "humidified space") and if you assume litres (L) here, you get trouble during dimensional analysis of VaporPressureCalculation.

The WaterTank::tankVolume gives us another hint:

Webel vs SysPhS-1.1: Annex A.5: Humidifier: If the WaterTank::tankVolume 50,000 is measured in litres (L) the VaporPressureCalculation::volume within the HumidifiedRoom can't possibly be 25000.0 litre (L), it has to be 25000.0 (m^3), which is NOT a "room"

And the term VaporGenerationPlant seems overkill for a mere humidified room.

If this is analysis is correct, the block name HumidifiedRoom is ill-chosen. Something like "HumidifiedSpace" would have been better:

Webel vs SysPhS-1.1: Annex A.5: Humidifier: In the Webel version it will be tentatively assumed we are in fact dealing with a large humidified space like an office building NOT a single "humidified room" - despite the block name HumidifiedRoom in the spec
Up next
BDD & PD: VaporPressureCalculation
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.
[MODELLING, NAVIGATION, PATTERN, TIP, TOOL]{STRONG} Webel: UML/SysML: Navigation: ALWAYS offer a way out of a diagram (usually up a hierarchy, but possibly across) using a navigable symbol (linked to a diagram) and/or a diagram symbol. Avoid "cul-de-sacs"! [But beware of shared package cross-dependencies]
[MODELLING, PATTERN, TIP]{RECOMMENDED} SysML: When using Property::defaultValue and Property::redefinedValue to carry a "shadow hierarchy" of redefinitions across an entire system hierarchy, considering using a user-defined keyword such as «configuration» or «scenario» on each redefining Block
[CAPABILITY, FEATURE, TOOL] MagicDraw/Cameo: Supports embedding of one or more Diagrams in another via the Diagram Overview feature. Awesome!
[CONVENTION, DISPLAY, MODELLING, STYLE, TIP]{STRONG} Webel: SysMLv1: Highly recommend creating a "focus" Block Definition Diagram (BDD) for each main Block with expanded feature details and relationships to at least nearest neighbours
[NAMING, TIP]{OPTION} Optionally suffix the "focus" BDD for a Block with '.bdd' so that it won't clash with a corresponding IBD on diagram export. This is not a SysMLv1 concern, it is purely a workflow concern. It has the slight disadvantage that BDD may "indicated" twice.
[DISPLAY, STYLE, TIP, TOOL]{SUGGESTED} Style: use line width 2 or 3 on the border of the "focus" element in "focus" diagrams (such as the main Block or Class of a dedicated Block Definition Diagram or Class Diagram)
[CONVENTION, MODELLING, NAMING, TIP]{STRONG} Webel: If you must name your Ports or Pins, name them simply 'i', 'o', or 'io' (or 'oi') to indicate direction UNLESS you have to indicate a special role like 'iRole', 'oAuxiliary'. DO NOT use Port or Pin names like 'input', 'output', etc.
[CAPABILITY, FEATURE, STYLE, TIP]{RECOMMENDED} TIP: UML/SysML: MagicDraw/Cameo: Consider showing the constraint parameter name and type label inside the small rectangular parameter symbol on SysML Parametric Diagrams. Dr Darren swears by it!
[ASSERTION] Webel vs SysPhS-1.1: Annex A.5: Humidifier: Dimensional analysis of HumidityBalanceConstraint implies constraint parameter 'airExRate' in {change=((humidity-envH)*(volume*airExRate))} is per-volume, assuming that 'volume' is a fixed Volume.
[ASSERTION] Webel vs SysPhS-1.1: Annex A.5: Humidifier: If the WaterTank::tankVolume 50,000 is measured in litres (L) the VaporPressureCalculation::volume within the HumidifiedRoom can't possibly be 25000.0 litre (L), it has to be 25000.0 (m^3), which is NOT a "room"
[ASSERTION] Webel vs SysPhS-1.1: Annex A.5: Humidifier: In the Webel version it will be tentatively assumed we are in fact dealing with a large humidified space like an office building NOT a single "humidified room" - despite the block name HumidifiedRoom in the spec
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Figure 27: Default values and initial value in SysML
BDD & PD: VaporPressureCalculation
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