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trouble with medium and connections
trouble with medium and connections
Hi,
im new with Modelica and some things i cant get to run and i Dont know why.
I want to simulate an Air Conditioning therefore i want to use the medium MoistAir but i dont know where exaktly i need to declare the medium. I found, that the ambient (source block) in Thermal has the parameter Medium but as far as i can see, its not working correctly. Is MoistAir broken like the library medium.air and if so how to work around this?
And if im not mistaken its nesseary to have a Ambient block at beginning of the Medium and at the end. Where do i define the Medium? just Input or both?
Another Question i have is: how can i get variables valued from connectors all the courses dont use connection with medium and the thermal examples dont comment well on that matter.
hope you can help me with my Questions
Thank you
Re: trouble with medium and connections
is my question too difficult, is it the wrong place in the forum or is this forum just dead?
i solved my connection problem myself but my question regarding medium.air.moistair is still unsolved ... can anybody explain if the medium.air is usable or bugged.
Re: trouble with medium and connections
You mentioned Medium in the title, so I won't even bother reading the body text
- sjoelund.se
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- 1700 Posts
Re: trouble with medium and connections
People do. I just don't understand it.
- sjoelund.se
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- 1700 Posts
Re: trouble with medium and connections
The issue seems to be that there are different definitions of what a medium is. The Modelica.Media package in the MSL uses packages extended from Modelica.Media.InterfacesPartialMedium as medium, while Thermal instead uses records extended from Modelica.Thermal.FluidHeatFlow.Media.Medium. Same name, but very different things.
MoistAir is one of the medium packages in Media, so it's not meant to be used with Thermal. There are a couple of predefined mediums defined in Modelica.Thermal.FluidHeatFlow.Media that you can use:
Code:
Modelica.Thermal.FluidHeatFlow.Sources.Ambient amb(medium = Modelica.Thermal.FluidHeatFlow.Media.Air_30degC());
If you want to define your own medium you pretty much just extend from Medium and supply your own values:
Code:
record MyMedium
extends Modelica.Thermal.FluidHeatFlow.Media.Medium(
rho = 234,
cp = 100,
cv = 54,
lambda = 0.54,
nue = 94);
end MyMedium;
Modelica.Thermal.FluidHeatFlow.Sources.Ambient amb(medium = MyMedium());
or
MyMedium medium;
Modelica.Thermal.FluidHeatFlow.Sources.Ambient amb(medium = medium);
if you want to be able to use the same medium for multiple components
- perost
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- 114 Posts
Re: trouble with medium and connections
okay thanks for the clarification so i should use fluid if i want to use the predefinded moistair?
since nobody answered i started to change the Connectors and Ambient in the Thermal category like follows in the spoiler:
Code:
connector MoistAir_FlowPort
Modelica.Media.Air.MoistAir medium ;
Modelica.SIunits.Pressure p;
flow Modelica.SIunits.MassFlowRate m_flow;
Modelica.SIunits.SpecificEnthalpy h;
flow Modelica.SIunits.EnthalpyFlowRate H_flow;
annotation (Documentation(info = "<html>
Basic definition of the connector.<br>
<strong>Variables:</strong>
<ul>
<li>Pressure p</li>
<li>flow MassFlowRate m_flow</li>
<li>Specific Enthalpy h</li>
<li>flow EnthaplyFlowRate H_flow</li>
</ul>
If ports with different media are connected, the simulation is asserted due to the check of parameter.
</html>"),
Icon(graphics = {Ellipse(fillColor = {85, 170, 127}, fillPattern = FillPattern.Solid,extent = {{-100, 100}, {100, -100}}, endAngle = 360)}));
end MoistAir_FlowPort;
model MoistAir_Ambient "Ambient with constant properties"
Modelica.Thermal.FluidHeatFlow.Media.Medium medium=Modelica.Thermal.FluidHeatFlow.Media.Medium() "Medium"
annotation(choicesAllMatching=true);
parameter Modelica.SIunits.Temperature T0(start=293.15, displayUnit="degC")
"Initial temperature of medium";
parameter Boolean T0fixed=false
"Initial temperature guess value or fixed"
annotation(choices(checkBox=true));
output Modelica.SIunits.Temperature T_port "Temperature at flowPort_a";
output Modelica.SIunits.Temperature T(start=T0, fixed=T0fixed) "Outlet temperature of medium";
Interfaces.FlowPort_a flowPort(final medium=medium)
annotation (Placement(transformation(extent={{-110,-10},{-90,10}})));
protected
constant Boolean Exchange=true "Exchange of medium via flowport"
annotation(HideResult=true);
Modelica.SIunits.SpecificEnthalpy h "Specific enthalpy in the volume";
equation
T_port=flowPort.h/medium.cp;
T=h/medium.cp;
// mass flow -> ambient: mixing rule
// mass flow <- ambient: energy flow defined by ambient's temperature
if Exchange then
flowPort.H_flow = semiLinear(flowPort.m_flow,flowPort.h,h);
else
h=flowPort.h;
end if;
annotation (Documentation(info="<html>
<p>
Partial model of single port at the left, defining the medium and the temperature at the port.
</p>
</html>"), Icon(coordinateSystem(preserveAspectRatio=true, extent={{-100,-100},
{100,100}}), graphics={ Text(
extent={{-150,140},{150,100}},
lineColor={0,0,255},
textString="%name")}));
parameter Boolean usePressureInput = false "Enable / disable pressure input" annotation(
Evaluate = true,
choices(checkBox = true));
parameter Modelica.SIunits.Pressure constantAmbientPressure(start = 0) "Ambient pressure" annotation(
Dialog(enable = not usePressureInput));
parameter Boolean useTemperatureInput = false "Enable / disable temperature input" annotation(
Evaluate = true,
choices(checkBox = true));
parameter Boolean useHumidityInput = false "Enable / disable humidity input" annotation(
Evaluate = true,
choices(checkBox = true));
parameter Modelica.SIunits.Temperature constantAmbientTemperature(start = 293.15, displayUnit = "degC") "Ambient temperature" annotation(
Dialog(enable = not useTemperatureInput));
Modelica.Blocks.Interfaces.RealInput ambientPressure = pAmbient if usePressureInput annotation(
Placement(transformation(extent = {{-20, -20}, {20, 20}}, rotation = 180, origin = {100, 60}), iconTransformation(extent = {{-20, -20}, {20, 20}}, rotation = 180, origin = {100, 60})));
Modelica.Blocks.Interfaces.RealInput ambientTemperature = TAmbient if useTemperatureInput annotation(
Placement(transformation(extent = {{-20, -20}, {20, 20}}, rotation = 180, origin = {100, -60}), iconTransformation(extent = {{-20, -20}, {20, 20}}, rotation = 180, origin = {100, -60})));
Modelica.Blocks.Interfaces.RealInput ambientHumidity annotation(
Placement(visible = true, transformation(origin = {100, 0}, extent = {{-20, -20}, {20, 20}}, rotation = 180), iconTransformation(origin = {110, 70}, extent = {{-20, -20}, {20, 20}}, rotation = 180)));
protected
Modelica.SIunits.Pressure pAmbient;
Modelica.SIunits.Temperature TAmbient;
equation
if not usePressureInput then
pAmbient = constantAmbientPressure;
end if;
if not useTemperatureInput then
TAmbient = constantAmbientTemperature;
end if;
MoistAir_FlowPort.p = pAmbient;
T = TAmbient;
annotation(
Documentation(info = "<html>
<p>(Infinite) ambient with constant pressure and temperature.</p>
<p>Thermodynamic equations are defined by Partials.Ambient.</p>
</html>"),
Icon(coordinateSystem(preserveAspectRatio = true, extent = {{-100, -100}, {100, 100}}), graphics = {Ellipse(lineColor = {255, 0, 0}, fillColor = {0, 0, 255}, fillPattern = FillPattern.Solid, extent = {{-90, 90}, {90, -90}}, endAngle = 360), Text(extent = {{20, 80}, {80, 20}}, textString = "p"), Text(extent = {{20, -20}, {80, -80}}, textString = "T")}));
end MoistAir_Ambient;
Should i rather switch to a fluid model and where do i Define my medium there? in each component individually or once in the Package for all? In the Fluid Library it is nowere stated as an Parameter unlike in Thermal.
Re: trouble with medium and connections
I'm afraid I'm not much of a modeler, so I can't give you an answer on which parts of the MSL you should use for your application. But for Fluid you usually need to redeclare the medium in the components you use, for example:
Code:
Modelica.Fluid.Pipes.StaticPipe pipe(redeclare package Medium = Modelica.Media.Air.MoistAir);
or
package Medium = Modelica.Media.Air.MoistAir;
Modelica.Fluid.Pipes.StaticPipe pipe(redeclare package Medium = Medium);
- perost
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- 114 Posts
Re: trouble with medium and connections
Thanks for your Reply,
maybe you can answer me this question:
What parts of the Ambient declaration (including expands) do you realy need to get a fluid source that gives all the Medium.Air.MoistAir variables? reading some tutorials i get the impression that in the Ambient Thermal declaration there is quite so unnessesary stuff i could just delet. I mean i Get it there is the possibility to use fixed values or imput values which expands the declaration, but whats all the stuff in the expanded class all about. lets say all i Care fore is Temperature and Humidity imputs at a fixed Pressure ... pushing with a imputed massflow through the system, wouldnt that be a rather short declaration or what do i need for shuch a rather limited flowsoruce?
Re: trouble with medium and connections
i tried to get some tests done but i dont get why folloing code compiles but the code below doesnt anymore. Why does setting variables doesnt Work with .BaseProperties
This compiles:
Code:
model TestModel
Modelica.SIunits.Temp_K t = 294;
Real p = 1.0e5;
Real AbsHumid= 0.01;
Modelica.Media.Air.MoistAir.BaseProperties Medium(
T(start=294, fixed=false),
X(start={0.95,0.05}),
p(start=1.0e5, fixed=false));
equation
end TestModel;
this Doesnt anymore:
Code:
model TestModel
Modelica.SIunits.Temp_K t = 294;
Real p = 1.0e5;
Real AbsHumid= 0.01;
Modelica.Media.Air.MoistAir.BaseProperties Medium(
T(start= t, fixed=false),
X(start={0.95,0.05}),
p(start=1.0e5, fixed=false));
equation
end TestModel;
Error Message:[Test: 21:9-21:17]: Component start of variability parameter has binding 't' of higher variability continuous
neither does this compile:
Code:
model TestModel
Modelica.SIunits.Temp_K t = 294;
Real p = 1.0e5;
Real AbsHumid= 0.01;
Modelica.Media.Air.MoistAir.BaseProperties Medium(
T(start= 294, fixed=false),
X(start={0.95,0.05}),
p(start= p, fixed=false));
equation
end TestModel;
Same Error
Changing variables to Integer gives another error but at last still similar
Can somebody pleas explain, how to get variables into Baseproperties and how to change BaseProperties after setting them initially? If there is any tutorial on that please show me where 
Re: trouble with medium and connections
The attributes in the builtin types are parameters, see the specification. So this works:
Code:
model M
parameter Real s = 1.0;
Real x(start = s); // ok, s is a parameter expression
end M;
while this doesn't:
Code:
model M
Real s = 1.0;
Real x(start = s); // s is continuous, not parameter
model M;
- perost
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- 114 Posts
Re: trouble with medium and connections
Okay, that was Easy, Thanks for the explanation
is it possible that this variable is given to the model via a connector from an
means Connector has parameter Real s=1;
and Model2 has
connector.s y;
Real x(start=y);
or is it important that the parameter definition is within the model itself.
As far as i understand the definition this attribute can be passed through a connector, correct?
Re: trouble with medium and connections
The modifier expression just needs to be a parameter expression, where the parameter in question is declared doesn't matter as long as it's accessible in the scope where the modification occurs.
- perost
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- 114 Posts
Re: trouble with medium and connections
Okay, Im at the next point where i dont understand, whats wrong with my code:
as in my former posting i declared the ... .BaseProperties medium (...)
then the code compiles and if i type medium. its recognised and i get things like medium.x_sat as a posibility. But if i type abc = medium.x_sat
i get the errror Code:Variable medium.x_sat not found in scope TestModel.
How can i work with the MoistAir i defined above?
Re: trouble with medium and connections
x_sat is a protected member of MoistAir.BaseProperties, so you're not supposed or allowed to modify it. If you want to change the definition of x_sat you'd have to either make your own BaseProperties model or make one that extends from one of the existing BaseProperties, but I don't really know how Media is supposed to be used.
- perost
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- 114 Posts
Re: trouble with medium and connections
well than i have to test some more ... a other question that sometimes bothers me is: in many examples (even in the language declaraiton ModelicaSpec34.pdf ) things like follows seem to compile but not if i try 
Code:
import SI= Modelica.SIunits;
SI.Mass x;
or
Code:
package Medium = Air.MoistAir "Medium model";
with following package definition
Code:
package Medium = Air.MoistAir "Medium model";
As far i can say it at least the Import shoud work but it doesnt the question is why?
and shouldnt even:
Code:
import Medium = Modelica.Media.Air.MoistAir
Medium.BaseProperties
work?
Re: trouble with medium and connections
Something like this should work:
Code:
model M
import Medium = Modelica.Media.Air.MoistAir;
Medium.BaseProperties medium;
end M;
You can't import the name Air.MoistAir though, because import requires a fully qualified name. I.e. you must give the full path to the name, so Modelica.Media.Air.MoistAir instead of Air.MoistAir.
- perost
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- 114 Posts
Re: trouble with medium and connections
okay my last question is still not answered but i think i finally understood how medium is meant to be used. Following code does Run but "RelHumid= Modelica.Media.Air.MoistAir.relativeHumidity (state1);" is alsways =1 which it shouldnt be. I checked with hx-diagramm (by hand not modelica) that at 14°C and 1bar pressure the absolute humidity is about 10g (and Modelica gets this value right so it should be true and something is obviously working)
but if i define the mass of water to 1g the Relative humidity shoud be 10% but the equation always says 1 (100%) regardless of any parameters
Is my understanding of this function wrong or is there a bug with that one?
Code:
model TestModel1
parameter Modelica.SIunits.Temp_C t = 14;
constant Real p = 1.0e5;
parameter Modelica.SIunits.Mass water=0.001;
Real AbsHumid[2];
Real AbsHumidMax;
Real RelHumid;
Modelica.Media.Air.MoistAir.ThermodynamicState state1;
equation
AbsHumid[1]= 1-water;
AbsHumid[2]=water;
state1.p = p;
state1.T = Modelica.SIunits.Conversions.from_degC(t);
state1.X = AbsHumid;
AbsHumidMax = Modelica.Media.Air.MoistAir.xsaturation(state1);
RelHumid= Modelica.Media.Air.MoistAir.relativeHumidity (state1);
end TestModel1;
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