1. Extending SysML for Integration with Solver-based Simulation Tools
SysML/Modelica Team Discussion

2. Next Steps Alternative extensions and transformations to simulators.
Conrad had side discussion with Nicolas.
Signal processing / directed flow example.
Modeling tool testing (NoMagic, etc).
SysML/Modelica profile
Based on the simulator-independent profile?
Populated from this profile?
Other aspects of SysML useful in simulation
State machines, etc.
Use cases? How much of the simulation languages to include?
RFC? Into SysML or separately.
Spec should cover generation to simulators.
Simulator-independent libraries.
Generate to use simulator-specific libraries.
Other languages: VHDL-AMS (similar to Modelica).
Axel: Other extensions: geometry.
Chris: Solvers constrain states to have the same number of equations/unknowns in each state, modelers use conditionals in equations. Conrad: Generate conditionals from state machines when constraint is violated.
Axel: Dassault concerned with SE/Eng integration (bought Dymola), and others, offering proprietary solutions. Conrad: Start with smaller players. Axel: Multiple disciplines involved. Conrad: Yes, but with same underlying mathematics.

3. Other comments / questions
Separation of descriptive and analysis model.
Not necessarily one-to-one from descriptive to analysis.
Time modeling
Physical vs clocks vs simulation.
Generation from time parameters.
Type system differences
See Nicolas messages on subtyping.
12/05/12
Conrad: Profile is limited to solver-based simulators, rather than analysis in general. It is simulator-independent, so is more appropriate for so-called descriptive models, because it is widely applicable. The extensions can also be applied in specialized models if complete separate is needed (or using views if its a matter of presentation). We found the descriptive and simulation models to be very close to one-to-one. SysML already contains information need for simulation (connectors, direction of flow) and describes flows (kind of thing that flows). The flow rate and flow potential are just additional information about flows that the SE modeler happens to not be interested in immediately.
Roger: Some descriptive information is in analysis models that should be carried back to SE models. Chris: Dependencies between descriptive and analytical models. Facilitates considering the system from different analysis perspectives, eg, mechanical, heat, etc. Conrad: This could be views, rather than separate models, to avoid redudancy and the associated transformation and synchronization burden. Sandy: Specialized descriptive models for analysis. Alex: Support degrees of separation of description and analysis. Chris: Conflicting semantics between SysML and simulation tools. Conrad: Not clear there are conflicts yet. Purpose is to integrate simulation into overall SysML-based SE process, so alignment is needed, perhaps in both SysML and the simulators.
Chris: Not simulator-independent due to acausal modeling. Conrad: True, it’s as only as independent as it can be, and includes acausal because its so important. It’s more independent than extension for individual simulators or simulation languages.
Chris/Roger: Should define semantics in terms of SysML. Conrad: Perhaps in the long-run, but in the short run, the semantics can be defined by mapping to popular simulation languages, and perhaps DE’s.
Roger: Modelica does not support creation/destruction of objects during a simulation run.
Nicolas: Time property in example. Ion: Binding to properties on blocks representing clocks (global or otherwise). Should be a regular property, not parameter, because it changes during simulation run. Nicolas: How does generator know this is a simulation time property? Ion: Profile should have a way to indicate it. Modelica has a “time” keyword.
Nicolas: For a comprehensible introduction to the distinction between nominal vs. structural subtyping, see:
12/19/12, About Sandy’s example, Chris: Until recently Simulink was used for physical modeling (by writing the additive Kirchoff law themselves, etc, using intermediary component). Simscape has only been around a few years. Conrad: Dymola also prominent. Nicolas: DARPA META using combination of Modelica + GME.

4. Alternative Extensions

5. SimVars on Flow Prop Types?
«block»
Electron
sim variables
«isConserved» i :
Current
v : Voltage
«block»
SomePortType
«block»
HeatEnergyQ
flow properties
inout electricity : Electron
inout heat : HeatEnergyQ
inout fluid : WaterMolecule
sim variables
«isConserved» hq :
HeatFlowRate
t : Temperature
«block»
WaterMolecule
sim variables
«isConserved» fq :
VolumeFlowRate
p : Pressure
i = 43
Do individual electrons or molecules of water (items) have flow rates and potentials to flow independent of their ports?

6. SimVars on Port Types?
«block»
SomePortType
connector EF
flow Current i;
Voltage v;
flow HeatFlowRate hq;
Temperature t;
flow VolumeFlowRate fq;
Pressure p;
end EF;
flow properties
inout electricity : Charge
inout heat : HeatEnergy
inout fluid : Water
sim variables
«isConserved, referTo=electricity» i : Current
«referTo=electricity» v : Voltage
«isConserved, referTo=heat» » hq : HeatFlowRate
«referTo=heat» t : Temperature
«isConserved, referTo=fluid» fq : VolumeFlowRate
«referTo=fluid» p : Pressure
SysML+
Modelica
SimVariables for all flow properties on the port type.

7. SimVars on Port Types?
Instances of port types are structural elements of as-built systems.
They are not flowing items.
«block»
GasIntake
«block»
Car
value properties
diameter : cm
temp : Celsius
flow properties
in fuel : Gas
sim variables
«isConserved, referTo=fuel» fq : VolumeFlowRate
«referTo=fuel» p : Pressure
«isConserved, referTo=fuel» hq : HeatFlowFlowRate
«referTo=fuel» t : Temperature
ports
gasIntake : GasIntake
Sandy: Similar conceptual problem as atomic flow ports (treating a structural thing as behavioral).
Nicolas: Modeling is simpler in SysML, but not close to simulation language (Conrad: doesn’t necessarily need to be) and don’t have instances representing the flows. Harder to separate the analysis from descriptive aspects of the model. Eg, want separate heat going out with the fuel vs heat going out the gas intake part.
Structural elements don’t have flow rates and potentials to flow.

8. SimVars on SimBlock
Instances of SimBlocks are the flows themselves (not the ports instances or things flowing)
«block»
GasIntake
«simBlock»
EHF
«block»
Car
value properties
diameter : cm
temp : Celsius
flow properties
in fuel : Gas
sim properties
«referTo=fuel» fsb : EHF
sim variables
«isConserved» fq : VolumeFlowRate
p : Pressure
«isConserved» hq : HeatFlowFlowRate
t : Temperature
ports
gasIntake : GasIntake
Chris: The Modelica profile separates the properties of the port object from the flows through it.
Nicolas/Chris/Axel: Agreed best to add SimBlock indirection.
Chris: About flow property direction, “in” could constrain pressure to be always positive in an acausal simulator, so the SimBlock could have conserved variables.
SimBlock instances have flow rates and potentials to flow.

9. Alternative Transformations

10. SimVars Generated By SimBlock
SomePortType
connector EF
flow Current i;
Voltage v;
end EF;
connector HF
flow HeatFlowRate hq;
Temperature t;
end HF;
connector FF
flow VolumeFlowRate fq;
Pressure p;
flow properties
inout electricity : Charge
inout heat : HeatEnergy
inout fluid : Water
sim properties
«referTo=electricity» var : ElectricityFlow
«referTo=heat» var : HeatFlow
«referTo=fluid» var : FluidFlow
«simBlock»
FluidFlow
«simBlock»
HeatFlow
«simBlock»
ElectricityFlow
sim variables
«isConserved» fq :
VolumeFlowRate
p : Pressure
sim variables
«isConserved» hq :
HeatFlowRate
t : Temperature
sim variables
«isConserved» i : Current
v : Voltage
Pin => EF
Modelica nested connectors (eg, electrical and mechanical).
Alec/Nicolas: Multiple SysML connectors with different matching generate Modelica lines between connectors that match.
SysML issue: What if association block has different flow property matching than its usage on a connector?
SysML+
Modelica
SimVariables generated to separate Modelica connectors.

11. SimVars Generated Together
«block»
SomePortType
flow properties
inout electricity : Charge
inout heat : HeatEnergy
inout fluid : Water
sim properties
«referTo=electricity» var : ElectricityFlow
«referTo=heat» var : HeatFlow
«referTo=fluid» var : FluidFlow
connector EHFF
flow Current i;
Voltage v;
flow HeatFlowRate hq;
Temperature t;
flow VolumeFlowRate fq;
Pressure p;
end EHFF;
«simBlock»
FluidFlow
«simBlock»
HeatFlow
«simBlock»
ElectricityFlow
sim variables
«isConserved» fq :
VolumeFlowRate
p : Pressure
sim variables
«isConserved» hq :
HeatFlowRate
t : Temperature
sim variables
«isConserved» i : Current
v : Voltage
Axel: Modelica checks that there are the same number of flow as non-flow variables. Conrad: Can’t use just non-flow variables? Wladimir: Can have just non-flow variables, but they must have direction. On non-directed connectors, must have as Axel said.
Nicolas: This optimization not worth doing so early.
Modelica
SysML+
Could generate SimVariables to one Modelica connector if lines are not needed to separate connectors.

12. Port Type Name => Connector Name
«block»
SomePortType
flow properties
inout electricity : Charge
inout heat : HeatEnergy
inout fluid : Water
sim properties
«referTo=electricity» var : ElectricityFlow
«referTo=heat» var : HeatFlow
«referTo=fluid» var : FluidFlow
connector SomePortType
flow Current i;
Voltage v;
flow HeatFlowRate hq;
Temperature t;
flow VolumeFlowRate fq;
Pressure p;
end SomePortType;
«simBlock»
FluidFlow
«simBlock»
HeatFlow
«simBlock»
ElectricityFlow
sim variables
«isConserved» fq :
VolumeFlowRate
p : Pressure
sim variables
«isConserved» hq :
HeatFlowRate
t : Temperature
sim variables
«isConserved» i : Current
v : Voltage
Modelica
Pin => EF
Modelica nested connectors (eg, electrical and mechanical).
SysML+
Generate connector name from port type name.
Does not mean instances of SyML port types have flow rates or potentials to flow.

13. Nested Connectors are Syntax Only
connector EF
flow Current i;
Voltage v;
end EF;
connector HF
flow HeatFlowRate hq;
Temperature t;
end HF;
connector FF
flow VolumeFlowRate fq;
Pressure p;
connector EHFF
ef : EF
hf : HF
ff: FF
end EHFF;
connector EHFF
flow Current i;
Voltage v;
flow HeatFlowRate hq;
Temperature t;
flow VolumeFlowRate fq;
Pressure p;
end EHFF; =
Pin => EF
Modelica nested connectors (eg, electrical and mechanical).
Modelica expandable connectors can take on properties by having lines to connectors that have properties defined.
Modelica
Simulation is the same with and without nested connectors.

14. SysML Port => Compound Connector
connector EF
flow Current i;
Voltage v;
end EF;
connector HF
flow HeatFlowRate hq;
Temperature t;
end HF;
connector FF
flow VolumeFlowRate fq;
Pressure p;
connector SomePortType
ef : EF
hf : HF
ff: FF
end SomePortType;
«block»
SomePortType
flow properties
inout electricity : Charge
inout heat : HeatEnergy
inout fluid : Water
sim properties
«referTo=electricity» var : ElectricityFlow
«referTo=heat» var : HeatFlow
«referTo=fluid» var : FluidFlow
«simBlock»
FluidFlow
«simBlock»
HeatFlow
«simBlock»
ElectricityFlow
sim variables
«isConserved» fq :
VolumeFlowRate
p : Pressure
sim variables
«isConserved» hq :
HeatFlowRate
t : Temperature
sim variables
«isConserved» i : Current
v : Voltage
Pin => EF
Modelica nested connectors (eg, electrical and mechanical).
SysML+
Modelica
Generating port type as connector with nested connectors.

15. SysML Port => Simple Connector
«block»
SomePortType
flow properties
inout electricity : Charge
inout heat : HeatEnergy
inout fluid : Water
sim properties
«referTo=electricity» var : ElectricityFlow
«referTo=heat» var : HeatFlow
«referTo=fluid» var : FluidFlow
connector SomePortType
flow Current i;
Voltage v;
flow HeatFlowRate hq;
Temperature t;
flow VolumeFlowRate fq;
Pressure p;
end SomePortType;
«simBlock»
FluidFlow
«simBlock»
HeatFlow
«simBlock»
ElectricityFlow
sim variables
«isConserved» fq :
VolumeFlowRate
p : Pressure
sim variables
«isConserved» hq :
HeatFlowRate
t : Temperature
sim variables
«isConserved» i : Current
v : Voltage
Modelica
Pin => EF
Modelica nested connectors (eg, electrical and mechanical).
SysML+
Generating port type as connector without nested connectors.
Simulation is the same as previous slide.