I have a question around structuring Modelica code in a re-usable library part and a specific application part. The question concerns medium and equipment that depends on medium and I am inspired by some of the structure in MSL fluid library but I want to make something much smaller and adapted to my needs, but that I also can grow with.
The question is about how to conveniently adapt the library to a new medium defined in the application code. Since there are several models of different pieces of equipment it is natural to have a partial model that defines the type of connectors the equipment should have and then one only make changes in the partial model when adaptation of connectors are needed. To me it looks like I need a three-step adaptation process of the library, instead of one-step that I hope for. I have a detailed example below that makes it possible ask the question more clearly.
The example is a model for pumping liquid from one vessel to another, i.e. we have a feed tank, a pump and a harvest tank. The liquid medium contains originally two substances and now in the application we want to model seven substances.
In the application code the new medium with seven substances are declared as a package Medium7. The adaptation of the library models for pump, feed and harvest tanks are made in the following three steps:
- Define a connector LiquidCon7 as an extension of import of standard connector LiquidCon from the library and redeclare the medium to Medium7
- Define a partial model EquipmentMedium7 as an extension of import of standard partial model EquipmentMedium and where the connector is redeclared LiquidCon to LiquidCon7
- Define a package Equipment7 as an extension of import of the standard package Equipment where the partial model is redeclared from EquipmentMedium to EquipmentMedium7.
First now a system can be defined in the application code that is tailored to Medium7 using equipment from Equipment7. — I wish I could do the adaptation more direct than described above. If I avoid dividing the code in library and application like I do here then it is much more easy to switch from Medium2 to Medium7, by just changing the medium used in the LiquidConType and then that change propagate through the whole system.
When I read text book material on the subject by Tiller and Fritzson or when I try to understand MSL code I find similar structures but still not what I have here. I also think my questions of how to effectively adapt a library to changes in interfaces called for by a new application is not limited to medium, but a much wider range of code.
Just read Tillers paper "Patterns and anti-patterns in Modelica" from 2008 and in section 2.3 "Medium Model Pattern" here is a discussion that relate to my question and think of the last few lines on pg 649.
I just realised that my model structure breaks the Modelica definition, because you are not allowed to extend PumpType, FeedtankType etc from the partial model EquipmentMedium since I need the EquipmentMedium to be replaceable. See Modelica def 3.2 rev 2 section 6.2.1 “Transitively non-Replaceable”.
I would appreciate some comments on the subject and perhaps reading advice. Alternative solutions to my toy-problem is also very wellcome!
Thanks, Jan Peter
I do not know how to append a code file but below I show the application code described above. The library DATA_v04 is straight forward. But note that I need to define models PumpType, FeedtankType etc using extend from a partial model EquipmentMedium...and not allowed.
encapsulated package d4_app7
// ------------------------------------------------------------------------
// Interfaces
// ------------------------------------------------------------------------
import Modelica.Blocks.Interfaces.RealInput;
import Modelica.Blocks.Interfaces.RealOutput;
package Medium7
constant String name = "Seven components" "Medium name";
constant Integer nc = 7 "Number of substances;
type Concentration
= Real[nc] (each min=0, each unit="kg/m3") "Substance conc";
end Medium7;
// ------------------------------------------------------------------------
// Adaptation of library DEMO to Medium7
// ------------------------------------------------------------------------
connector LiquidCon7
import DEMO_v4.LiquidCon;
extends LiquidCon(redeclare package medium=Medium7);
end LiquidCon7;
partial model EquipmentMedium7
connector LiquidConType=LiquidCon7;
end EquipmentMedium7;
package Equipment7
import DEMO_v4.Equipment;
extends Equipment
(redeclare partial model EquipmentMedium=EquipmentMedium7);
end Equipment7;
import DEMO_v4.Control;
// ------------------------------------------------------------------------
// Examples of systems
// ------------------------------------------------------------------------
model Test
LiquidCon7.medium medium;
Equipment7.PumpType pump;
Equipment7.FeedtankType feedtank;
Equipment7.HarvesttankType harvesttank;
Control.FixValueType Fsp(val=0.2);
equation
connect(feedtank.outlet, pump.inlet);
connect(pump.outlet, harvesttank.inlet);
connect(Fsp.out, pump.Fsp);
end Test;
end d4_app7;
