modelSystem
Information
A system component is needed in each fluid model to provide system-wide settings, such as ambient conditions and overall modeling assumptions. The system settings are propagated to the fluid models using the inner/outer mechanism.
A model should never directly use system parameters. Instead a local parameter should be declared, which uses the global setting as default. The only exceptions are:
- the gravity system.g,
- the global system.eps_m_flow, which is used to define a local m_flow_small for the local m_flow_nominal:
m_flow_small = system.eps_m_flow*m_flow_nominal
The global system.m_flow_small and system.dp_small are classic parameters. They do not distinguish between laminar flow and regularization of zero flow. Absolute small values are error prone for models with local nominal values. Moreover dp_small can generally be obtained automatically. Consider using the new system.use_eps_Re = true (see Advanced tab).
Parameters
| Type | Name | Default | Description |
|---|---|---|---|
| Environment | |||
| SI.AbsolutePressure | p_ambient | 101325 | Default ambient pressure |
| SI.Temperature | T_ambient | 293.15 | Default ambient temperature |
| SI.Acceleration | g | Modelica.Constants.g_n | Constant gravity acceleration |
| Assumptions | |||
| Boolean | allowFlowReversal | true | = false to restrict to design flow direction (port_a -> port_b) |
| Assumptions › Dynamics | |||
| Modelica.Fluid.Types.Dynamics | energyDynamics | Modelica.Fluid.Types.Dynamics.DynamicFreeInitial | Default formulation of energy balances |
| Modelica.Fluid.Types.Dynamics | massDynamics | energyDynamics | Default formulation of mass balances |
| Modelica.Fluid.Types.Dynamics | substanceDynamics | massDynamics | Default formulation of substance balances |
| Modelica.Fluid.Types.Dynamics | traceDynamics | massDynamics | Default formulation of trace substance balances |
| Modelica.Fluid.Types.Dynamics | momentumDynamics | Modelica.Fluid.Types.Dynamics.SteadyState | Default formulation of momentum balances, if options available |
| Initialization | |||
| SI.MassFlowRate | m_flow_start | 0 | Default start value for mass flow rates |
| SI.AbsolutePressure | p_start | p_ambient | Default start value for pressures |
| SI.Temperature | T_start | T_ambient | Default start value for temperatures |
| Advanced | |||
| Boolean | use_eps_Re | false | = true to determine turbulent region automatically using Reynolds number |
| SI.MassFlowRate | m_flow_nominal | if use_eps_Re then 1 else 1e2*m_flow_small | Default nominal mass flow rate |
| Real | eps_m_flow | 1e-4 | Regularization of zero flow for |m_flow| < eps_m_flow*m_flow_nominal |
| Advanced › Classic | |||
| SI.AbsolutePressure | dp_small | 1 | Default small pressure drop for regularization of laminar and zero flow |
| SI.MassFlowRate | m_flow_small | 1e-2 | Default small mass flow rate for regularization of laminar and zero flow |
Contents
| Name | Description |
|---|---|
 Medium | Medium model for default start values |