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> Derivative functions for external medium model
post Jan 14 2010, 10:33 AM
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Hi everyone,

I am currently trying to implement a medium model in Modelica. The medium model is based on external data, available in a .dll file.
My idea is to implement the medium model similar to the Modelica.Media Library, with a BaseProperties object describing the thermodynamic relationship between the 5 primary medium variables p, T, d, u, h (assuming a single component fluid here). From within the BaseProperties object I want to call the respective functions of to retrieve the data provided with the external medium model.

The problem that occurs now, is that Dymola is unable to symbolically differentiate these functions (as they are external I suppose) and thus fails at DAE Index reduction. Unfortunately, as of now, there are no derivative functions provided with the external media model.

I now hope to find answers to the Questions:
  1. Would it be possible for Dymola to translate the model if the necessary derivative functions were also provided by the external .dll file and communicated to dymola with the annotation(derivative= ... ) command?
  2. Which derivative and partial derivative functions would then be needed if, for example p and T are state variables and Volume balance equations written in a way it is done in the Modelica.Fluid library?

Thankful for any input on the matter

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