Figure 25: Constraint block for signal flow in SysML


model Spring
  input Real u;
  output Real y;
  Real position;
  parameter Real springcst = 1;
  Real velocity;
  parameter Real mass = 10;
equations
  der(velocity)=(u-springcst*position)/m;
  der(position)=velocity;
  y=position;
end Spring;

SysPhS-1.1: p.38: 10.9.4 Modelica modeling, signal flow: Example Modelica model should be for SpringMassSys not Spring

SysPhS-1.1: p.38: 10.9.4 Modelica modeling, signal flow: Modelica code: the keyword should be 'equation' not 'equations'.

SysPhS-1.1: p.38: 10.9.4 Modelica modeling, signal flow: Modelica code: the equation 'der(velocity)=(u-springcst*position)/m;' should use variable 'mass' not 'm'

And the referenced flow properties in the spec version of the figure should be rSig not rsig:

SysPhS-1.1: Typos: Numerous references to 'rsig' lower case should be 'rSig' (including Figure 25 and Figure 29)

Also, the model as given in the spec not very useful, if you run it you just get a flat line for the position, it would be better to at least kick start the spring with something like:


  Real position(start=5);

Note also this suggestion (which corresponds with how the MagicDraw SysML Plugin and Magic Cyber-Systems Engineer^® (Cameo Systems Modeler^®) export it):

SysPhS-1.1: Suggest use connector forms 'Modelica.Blocks.Interfaces.RealInput u;' and 'Modelica.Blocks.Interfaces.RealOutput y;' not 'input Real u;' and 'output Real y;' in Modelica code examples (otherwise not connectable).

Note that the Parametric diagram named 'SpringMassSys' is owned by a context block SpringMassSys. Export of block SpringMassSys to Modelica from the MagicDraw SysML Plugin or Magic Cyber-Systems Engineer ^® (Cameo Systems Modeler^®) gives:


model SpringMassSys
  Modelica.Blocks.Interfaces.RealInput u;
  Modelica.Blocks.Interfaces.RealOutput y;
  Real position;
  Real velocity;
  parameter Real springcst(start=1.0,fixed=true);
  parameter Real mass(start=10.0,fixed=true);
equation
  der(velocity)=(u-springcst*position)/mass;
  der(position)=velocity;
  y=position;
end SpringMassSys;

Note the use of the explicit start attribute along with the explicit attribute fixed=true.

And on a minor modelling matter:

MagicDraw/SysML vs SysPhS-1.1: Can't reproduce the "shortcut" property path representation of some properties nested within Ports as shortcut symbols fully inside the diagram frame. (Might be a specification diagram style issue.)

In the MagicDraw SysML Plugin and Magic Cyber-Systems Engineer^® (Cameo Systems Modeler^®) implementation of the SysPhS library the FlowProperty rSig has AggregationKind 'none':

SysML-1.6: 'A reference property is shown by a dashed-outline box, consistent with UML.'

SysML-1.6: 'If any of the properties named in the path name string identifies a reference property, the property box is shown with a dashed-outline box, just as for any reference property on an internal block diagram.'

The spec version of Figure 25 shows rSig as AggregationKind 'composite'.

Up next

Figure 26: Constraint block for physical interaction in SysML

Notes

[ISSUE]{INFORMATIVE} SysPhS-1.1: p.38: 10.9.4 Modelica modeling, signal flow: Example Modelica model should be for SpringMassSys not Spring

[ISSUE]{INFORMATIVE} SysPhS-1.1: p.38: 10.9.4 Modelica modeling, signal flow: Modelica code: the keyword should be 'equation' not 'equations'.

[ISSUE]{INFORMATIVE} SysPhS-1.1: Typos: Numerous references to 'rsig' lower case should be 'rSig' (including Figure 25 and Figure 29)

[ISSUE]{INFORMATIVE} SysPhS-1.1: p.38: 10.9.4 Modelica modeling, signal flow: Modelica code: the equation 'der(velocity)=(u-springcst*position)/m;' should use variable 'mass' not 'm'

[ISSUE, PROPOSAL]{INFORMATIVE} SysPhS-1.1: p.38: 10.9.4 Modelica modeling, signal flow: Suggest kick start Spring with something like 'position=5' (otherwise get flat line when run).

[ISSUE, PROPOSAL] SysPhS-1.1: Suggest use connector forms 'Modelica.Blocks.Interfaces.RealInput u;' and 'Modelica.Blocks.Interfaces.RealOutput y;' not 'input Real u;' and 'output Real y;' in Modelica code examples (otherwise not connectable).