.Modelica.UsersGuide.Connectors

Information

The Modelica standard library defines the most important elementary connectors in various domains. If any possible, a user should utilize these connectors in order that components from the Modelica Standard Library and from other libraries can be combined without problems. The following elementary connectors are defined (the meaning of potential, flow, and stream variables is explained in section "Connector Equations" below):

domain potential
variables
flow
variables
stream
variables
connector definition icons
electrical
analog
electrical potential electrical current Modelica.Electrical.Analog.Interfaces
Pin, PositivePin, NegativePin
electrical
multi-phase
vector of electrical pins Modelica.Electrical.MultiPhase.Interfaces
Plug, PositivePlug, NegativePlug
electrical
space phasor
2 electrical potentials 2 electrical currents Modelica.Electrical.Machines.Interfaces
SpacePhasor
quasi
stationary
single phase
complex electrical potential complex electrical current Modelica.Electrical.QuasiStationary.SinglePhase.Interfaces
Pin, PositivePin, NegativePin
quasi
stationary
multi-phase
vector of quasi stationary single phase pins Modelica.Electrical.QuasiStationary.MultiPhase.Interfaces
Plug, PositivePlug, NegativePlug
electrical
digital
Integer (1..9) Modelica.Electrical.Digital.Interfaces
DigitalSignal, DigitalInput, DigitalOutput
magnetic
flux tubes
magnetic potential magnetic flux Modelica.Magnetic.FluxTubes.Interfaces
MagneticPort, PositiveMagneticPort,
NegativeMagneticPort
magnetic
fundamental
wave
complex magnetic potential complex magnetic flux Modelica.Magnetic.FundamentalWave.Interfaces
MagneticPort, PositiveMagneticPort,
NegativeMagneticPort
translational distance cut-force Modelica.Mechanics.Translational.Interfaces
Flange_a, Flange_b
rotational angle cut-torque Modelica.Mechanics.Rotational.Interfaces
Flange_a, Flange_b
3-dim.
mechanics
position vector
orientation object
cut-force vector
cut-torque vector
Modelica.Mechanics.MultiBody.Interfaces
Frame, Frame_a, Frame_b, Frame_resolve
simple
fluid flow
pressure
specific enthalpy
mass flow rate
enthalpy flow rate
Modelica.Thermal.FluidHeatFlow.Interfaces
FlowPort, FlowPort_a, FlowPort_b
thermo
fluid flow
pressure mass flow rate specific enthalpy
mass fractions
Modelica.Fluid.Interfaces
FluidPort, FluidPort_a, FluidPort_b
heat
transfer
temperature heat flow rate Modelica.Thermal.HeatTransfer.Interfaces
HeatPort, HeatPort_a, HeatPort_b
blocks Real variable
Integer variable
Boolean variable
Modelica.Blocks.Interfaces
RealSignal, RealInput, RealOutput
IntegerSignal, IntegerInput, IntegerOutput
BooleanSignal, BooleanInput, BooleanOutput
complex
blocks
Complex variable Modelica.ComplexBlocks.Interfaces
ComplexSignal, ComplexInput, ComplexOutput
state
machine
Boolean variables
(occupied, set,
available, reset)
Modelica.StateGraph.Interfaces
Step_in, Step_out, Transition_in, Transition_out

In all domains, usually 2 connectors are defined. The variable declarations are identical, only the icons are different in order that it is easy to distinguish connectors of the same domain that are attached at the same component.

Hierarchical Connectors

Modelica supports also hierarchical connectors, in a similar way as hierarchical models. As a result, it is, e.g., possible, to collect elementary connectors together. For example, an electrical plug consisting of two electrical pins can be defined as:

connector Plug
   import Modelica.Electrical.Analog.Interfaces;
   Interfaces.PositivePin phase;
   Interfaces.NegativePin ground;
end Plug;

With one connect(..) equation, either two plugs can be connected (and therefore implicitly also the phase and ground pins) or a Pin connector can be directly connected to the phase or ground of a Plug connector, such as "connect(resistor.p, plug.phase)".

Connector Equations

The connector variables listed above have been basically determined with the following strategy:

  1. State the relevant balance equations and boundary conditions of a volume for the particular physical domain.
  2. Simplify the balance equations and boundary conditions of (1) by taking the limit of an infinitesimal small volume (e.g., thermal domain: temperatures are identical and heat flow rates sum up to zero).
  3. Use the variables needed for the balance equations and boundary conditions of (2) in the connector and select appropriate Modelica prefixes, so that these equations are generated by the Modelica connection semantics.

The Modelica connection semantics is sketched at hand of an example: Three connectors c1, c2, c3 with the definition

connector Demo
  Real        p;  // potential variable
  flow   Real f;  // flow variable
  stream Real s;  // stream variable
end Demo;

are connected together with

   connect(c1,c2);
   connect(c1,c3);

then this leads to the following equations:

  // Potential variables are identical
  c1.p = c2.p;
  c1.p = c3.p;

  // The sum of the flow variables is zero
  0 = c1.f + c2.f + c3.f;

  /* The sum of the product of flow variables and upstream stream variables is zero
     (this implicit set of equations is explicitly solved when generating code;
     the "<undefined>" parts are defined in such a way that
     inStream(..) is continuous).
  */
  0 = c1.f*(if c1.f > 0 then s_mix else c1.s) +
      c2.f*(if c2.f > 0 then s_mix else c2.s) +
      c3.f*(if c3.f > 0 then s_mix else c3.s);

  inStream(c1.s) = if c1.f > 0 then s_mix else <undefined>;
  inStream(c2.s) = if c2.f > 0 then s_mix else <undefined>;
  inStream(c3.s) = if c3.f > 0 then s_mix else <undefined>;

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