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I could solve it. Now I understand the meaning of 'fixed=true'.
Solution is:
Code:
model OpenGasVolume
import Modelica.Units.SI;
parameter SI.Temperature T0=273.15+55 "Start Temperature (K)";
parameter SI.Pressure p0=5e5 "Start pressure (Pa)";
parameter SI.Volume V=1 "Volume (m3)";
SI.Mass m(min = 0.0, start = 1) "Mass in Volume (kg)";
SI.Energy H(min = 0.0) "Enthalpie in Volume (J)";
IdealGas media(T(start = T0, fixed=true), p(start=p0, fixed=true)); <<<=== Correction done here.
initial equation
H = media.h * media.c * V;
does not work as i intend
equation
H = media.h * media.c * V;
media.rho = m / V;
der(m) = 0; // No Mass transfer
der(H) = 0; // No energy transfer
end OpenGasVolume;
Question also posted at: https://stackoverflow.com/questions/697 … n-submodel
Answer on Stackoverflow prefered. Thanks.
In programming Unit-testing of the code is highly recommended.
In order to early detect errors in the code, certain test cases shall be written, to test every submodule.
I think this approach shall be used in modelling as well.
So I'm searching for recommendations on how to apply Unit testing to Modelica modells.
Basically I would need a tool to store lot's of test runs with different models and parameters for batch evaluation.
In each test run one or more acceptance criteria shall be defined. This might need evaluation of simulation data at the end of the run (post processing).
Any recommendations for a tool?
Thanks, Bernd
Hi!
I want to model a thermodynamic system.
This is what I have tried:
Code:
model IdealGas
// Natural Constants
parameter Real R(unit="J/molK") = 8.31446261815324 "Gas Constant J/molK";
// Values of Air used
parameter Real f = 5 "Degrees of Freedom";
parameter Modelica.Units.SI.MolarMass MG = 28.949e-3 "kg/mol";
// Variables
Modelica.Units.SI.Temperature T(start=273.15) "Temperature (K)";
Modelica.Units.SI.AbsolutePressure p(start=1.015e5) "Absolut Pressure (Pa)";
Modelica.Units.SI.SpecificEnthalpy u "spezific energy (J/mol)";
Modelica.Units.SI.SpecificEnthalpy h "spezific Enthalpy (J/mol)";
Modelica.Units.SI.Density rho "Density (kg/m3)";
Modelica.Units.SI.Concentration c "mol/m3";
equation
rho = MG * p / (R * T);
c = p / (R * T);
u = 0.5 * f * R * T;
h = u + R * T;
end IdealGas;
model OpenGasVolume
import Modelica.Units.SI;
parameter SI.Temperature T0=273.15+55 "Start Temperature (K)";
parameter SI.Pressure p0=5e5 "Start pressure (Pa)";
parameter SI.Volume V=1 "Volume (m3)";
SI.Mass m(min = 0.0, start = 1) "Mass in Volume (kg)";
SI.Energy H(min = 0.0) "Enthalpie in Volume (J)";
IdealGas media;
initial equation
media.T = T0;
media.p = p0;
H = media.h * media.c * V; // <--- Somehow this initialization does not work as i intend
equation
H = media.h * media.c * V;
media.rho = m / V;
der(m) = 0; // No Mass transfer
der(H) = 0; // No energy transfer
end OpenGasVolume;
Somehow I do not get the initialization right.
It is mandatory that 'H' is set to a proper start value in 'OpenGasVolume'. Part of the equations are captured in the Model 'media'.
My desired result would be media.T == T0 and media.p=p0 over the whole simulation time.
However I get:
Code:
Simulation process failed. Exited with code 255.
Matrix singular!
The initialization problem is inconsistent due to the following equation: 0 != 55 = T0 - media.T
Error in initialization. Storing results and exiting.
Use -lv=LOG_INIT -w for more information.
How to init the model correctly?
Thanks, Bernd
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