DynamicsEnumeration to define definition of balance equations |
Information
This information is part of the Modelica Standard Library maintained by the Modelica Association.
Enumeration to define the formulation of balance equations (to be selected via choices menu):
| Dynamics. | Meaning |
|---|---|
| DynamicFreeInitial | Dynamic balance, Initial guess value |
| FixedInitial | Dynamic balance, Initial value fixed |
| SteadyStateInitial | Dynamic balance, Steady state initial with guess value |
| SteadyState | Steady state balance, Initial guess value |
The enumeration "Dynamics" is used for the mass, energy and momentum balance equations respectively. The exact meaning for the three balance equations is stated in the following tables:
| Mass balance | ||
| Dynamics. | Balance equation | Initial condition |
| DynamicFreeInitial | no restrictions | no initial conditions |
| FixedInitial | no restrictions | if Medium.singleState then no initial condition else p=p_start |
| SteadyStateInitial | no restrictions | if Medium.singleState then no initial condition else der(p)=0 |
| SteadyState | der(m)=0 | no initial conditions |
| Energy balance | ||
| Dynamics. | Balance equation | Initial condition |
| DynamicFreeInitial | no restrictions | no initial conditions |
| FixedInitial | no restrictions | T=T_start or h=h_start |
| SteadyStateInitial | no restrictions | der(T)=0 or der(h)=0 |
| SteadyState | der(U)=0 | no initial conditions |
| Momentum balance | ||
| Dynamics. | Balance equation | Initial condition |
| DynamicFreeInitial | no restrictions | no initial conditions |
| FixedInitial | no restrictions | m_flow = m_flow_start |
| SteadyStateInitial | no restrictions | der(m_flow)=0 |
| SteadyState | der(m_flow)=0 | no initial conditions |
In the tables above, the equations are given for one-substance fluids. For multiple-substance fluids and for trace substances, equivalent equations hold.
Medium.singleState is a medium property and defines whether the medium is only described by one state (+ the mass fractions in case of a multi-substance fluid). In such a case one initial condition less must be provided. For example, incompressible media have Medium.singleState = true.
Enumeration Literals (4)
| DynamicFreeInitial |
DynamicFreeInitial -- Dynamic balance, Initial guess value |
|---|---|
| FixedInitial |
FixedInitial -- Dynamic balance, Initial value fixed |
| SteadyStateInitial |
SteadyStateInitial -- Dynamic balance, Steady state initial with guess value |
| SteadyState |
SteadyState -- Steady state balance, Initial guess value |
Used in Examples (1)
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Modelica.Fluid.Examples Multi-way connections of pipes and incompressible medium model |
Used in Components (10)
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Modelica.Fluid.Examples.DrumBoiler.BaseClasses Simple Evaporator with two states, see Åström, Bell: Drum-boiler dynamics, Automatica 36, 2000, pp.363-378 |
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Modelica.Fluid.Examples.HeatExchanger.BaseClasses Simple heat exchanger model |
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Modelica.Fluid.Examples.HeatExchanger.BaseClasses Pipe wall with capacitance, assuming 1D heat conduction and constant material properties |
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Modelica.Fluid System properties and default values (ambient, flow direction, initialization) |
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Modelica.Fluid.Pipes.BaseClasses Base class for distributed flow models |
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Modelica.Fluid.Pipes.BaseClasses.FlowModels Base class for momentum balances in flow models |
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Modelica.Fluid.Interfaces Lumped volume with mass and energy balance |
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Modelica.Fluid.Interfaces Base class for a lumped momentum balance |
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Modelica.Fluid.Interfaces Base class for distributed volume models |
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Modelica.Fluid.Interfaces Base class for a distributed momentum balance |