how to connect multi-dimensional components with multi-dimensional connectors in Modelica?

Question

I tried to connect a 2-dimensional component array to a 1-dimensional component array including 1-dimensional connectors, but when checking the model, there is an error showing unmatched dimensions. But I could connect a 1-dimensional component array to a component including 1-dimensional connectors, So Why can't this work for multi-dimensional situations? Did I do it wrong?

I checked the code, it seems I can't use

connect(tubeWall.port_b,surface.q_port);

but if I use the following code, it works fine.

for i in 1:x loop for j in 1:y loop connect(tubeWall[i].port_b[j], surface[i,j].q_port); end for; end for;

I did more test, here is the test code which worked fine:

model Unnamed
  gain_1[3] gain_1_1
  Modelica.Blocks.Sources.Sine[3,3] sine
  Modelica.Blocks.Math.Cos[3,3] cos
equation 
  connect(sine.y, gain_1_1.u);
  connect(gain_1_1.y, cos.u);
end Unnamed;

model gain_1

  Modelica.Blocks.Math.Gain[3] gain
  Modelica.Blocks.Interfaces.RealOutput[3] y
  Modelica.Blocks.Interfaces.RealInput[3] u
equation 
  connect(gain.y, y)
  connect(u, gain.u)
end gain_1;

Here is the screenshot of the connections:

So it seems the idea is right, but I am not sure why it doesn't work in my model. Hope someone could give a hint or direction of the unmatched error in my model.

Answer 1

Quoting Fritzon's Principles of object-oriented modeling and simulation with Modelica 3.3:

The connect contruct can be used to directly connect arrays of connectors. For such array connections the following holds:

• The array dimensions of the connected arrays of connectors must match
• Each corresponding pair of elements is connected as a pair of scalar connectors

That is, referring to connect(tubeWall.port_b,surface.q_port);

• it does not know which dimension of surface[:,:] goes to tubeWall[:] and which to port_b[:]
• the for loop works, because you are taking over the task of connecting the pair of elements as scalar connectors

My suggestion for your modeling task is that you create an interface block to put between surface and tubeWall, in which you implement the element-wise connections the way they should be. The connection between surface and interface might then look like:

• connect(surface, interface.surfacePort);

Answer 2

I played around to see if I can figure it out. Here three points that might bring you closer to a canonical answer on why there's a different behavior between physical connections (thermal, in your case) and signal connections (Real input/output, in your case):

1. Real input/output are causal, and declared differently than physical connectors

   connector RealInput = input Real "'input Real' as connector" annotation (...);

   connector PhysConnector
     Real pt;
     flow Real flw;
     annotation (...);
   end PhysConnector;  
   

2. Real input/output look more like functions than connectors. I suppose the rule The array dimensions of the connected arrays of connectors must match does not apply/is not enforced for them. I can think of different reasons for this; two of them could be:

   • There's a general accepted framework to deal with tables, the same way the majority of us agree that looking at a geographical map the top-left corner is north-west. So the connections are sorted automatically according to the sequence: 1st dim, 2nd dim, 3rd dim,... Multidimensional physical connections on the other hand might represent all sorts of scenarios. Better leave the model designer the responsibility to build it up correctly
   • Real input/output generate one assignment instead of a set of equations, therefore they don't mess up too much with the sorting algorithms when figuring out the causality of the system

3. I tried eventually to test a standard connector with only a potential variable, to see if the problem was due to the two equations generated when also a flow variable is present. The flat Modelica shows there's only one equation generated (as expected), but still the connection matrix[:,:],array[:].array[:] is not allowed.

    package MultidimConnections

        connector RealConnector
            Real r;
        annotation(Icon(coordinateSystem(preserveAspectRatio=false)),Diagram(coordinateSystem(preserveAspectRatio=false)));
        end RealConnector;

        partial model RealInterface
            RealConnector realConnector annotation(Placement(transformation(extent={{90,-10},{110,10}})));
        annotation(Icon(coordinateSystem(preserveAspectRatio=false),graphics={Rectangle(extent={{-100,100},{100,-100}},lineColor={28,108,200},fillColor={170,213,255},fillPattern=FillPattern.None)}),Diagram(coordinateSystem(preserveAspectRatio=false)));
        end RealInterface;

        model Source
            extends RealInterface;
            parameter Real k = 0;
        equation 
            k = realConnector.r;
        annotation(Icon(coordinateSystem(preserveAspectRatio=false),graphics={Rectangle(extent={{-80,80},{80,-60}},lineColor={28,108,200},fillColor={151,226,75},fillPattern=FillPattern.Solid), Text(extent={{-100,-60},{100,-100}},lineColor={28,108,200},fillColor={151,226,75},fillPattern=FillPattern.Solid,textString="%name")}),Diagram(coordinateSystem(preserveAspectRatio=false)));
        end Source;

        model User
            extends RealInterface;
            Real double;
        equation 
            double = 2*realConnector.r;
        annotation(Icon(coordinateSystem(preserveAspectRatio=false), graphics={Rectangle(extent={{-80,80},{80,-60}},lineColor={28,108,200},fillColor={85,170,255},fillPattern=FillPattern.Solid), Text(extent={{-100,-60},{100,-100}},lineColor={28,108,200},fillColor={85,170,255},fillPattern=FillPattern.Solid,textString="%name")}),Diagram(coordinateSystem(preserveAspectRatio=false)));
        end User;

        model User_multi
            MultidimConnections.User user annotation(Placement(transformation(extent={{-10,40},{10,60}})));
            MultidimConnections.User user1 annotation(Placement(transformation(extent={{-10,-10},{10,10}})));
            MultidimConnections.User user2 annotation(Placement(transformation(extent={{-10,-60},{10,-40}})));
            RealConnector realConnector[3] annotation(Placement(transformation(extent={{110,-10},{90,10}})));
        equation 
            connect(user.realConnector, realConnector[1]) annotation(Line(points={{10,50},{98,50},{98,-6.66667},{100,-6.66667}}, color={0,0,0}));
            connect(user1.realConnector, realConnector[2]) annotation(Line(points={{10,0},{98,0},{98,4.44089e-16},{100,4.44089e-16}}, color={0,0,0}));
            connect(user2.realConnector, realConnector[3]) annotation(Line(points={{10,-50},{98,-50},{98,6.66667},{100,6.66667}}, color={0,0,0}));
        annotation(Icon(coordinateSystem(preserveAspectRatio=false), graphics={Rectangle(extent={{-80,80},{80,40}},lineColor={28,108,200},fillColor={85,170,255},fillPattern=FillPattern.Solid),Text(extent={{-100,-60},{100,-100}},lineColor={28,108,200},fillColor={85,170,255},fillPattern=FillPattern.Solid,textString="%name"),Rectangle(extent={{-80,28},{80,-12}},lineColor={28,108,200},fillColor={85,170,255},fillPattern=FillPattern.Solid),Rectangle(extent={{-80,-20},{80,-60}},lineColor={28,108,200},fillColor={85,170,255},fillPattern=FillPattern.Solid),Rectangle(extent={{-100,100},{100,-102}}, lineColor={28,108,200})}),Diagram(coordinateSystem(preserveAspectRatio=false)));
        end User_multi;

        model TestCustomReal
            extends Modelica.Icons.Example;
            Source source(k=1) annotation(Placement(transformation(extent={{-60,40},{-40,60}})));
            User user annotation(Placement(transformation(extent={{60,40},{40,60}})));
            User_multi user_multi annotation(Placement(transformation(extent={{60,-10},{40,10}})));
            Source source_arr[3](k=1) annotation(Placement(transformation(extent={{-60,-10},{-40,10}})));
            User_multi user_multi_array[3] annotation(Placement(transformation(extent={{60,-60},{40,-40}})));
            Source source_mat[3,3](k=1) annotation(Placement(transformation(extent={{-60,-60},{-40,-40}})));
        equation 
            connect(source.realConnector, user.realConnector) annotation(Line(points={{-40,50},{40,50}}, color={0,0,0}));
            connect(source_arr.realConnector, user_multi.realConnector) annotation(Line(points={{-40,0},{40,0}}, color={0,0,0}));
            connect(source_mat.realConnector, user_multi_array.realConnector) annotation(Line(points={{-40,-50},{40,-50}}, color={0,0,0}));
        end TestCustomReal;

    annotation(uses(Modelica(version="3.2.3")));
    end MultidimConnections;

Answer 3

The connect construct works only if the array dimensions match.

• You could provide indices on the create connection window, to make the connection right between tubeWall and surface. which is exactly what the code is doing.
• The model Unnammed works because gain_1_1.u is a connector with sizes [3,3]. If you change the size of the instance gain_1, you will see the difference.

Therefore you can either connect same size arrays or explicitly mention the indices during the connection.

Hope this helps.