Today, at the 29^th design meeting of the Modelica Association, in Lund, Sweden, the second major release of Modelica, version 2.0, was completed and formally approved.

The major design goal of this release was to enhance the development of application libraries, incorporating the experience and feedback of library developers, while keeping backward compatibility. A number of language enhancements have been added, significantly facilitating library development. In particular, Modelica 2.0 introduces the following improvements:

• A mathematically rigid specification of the initialization of hybrid differential-algebraic equations in order to compute consistent initial values of all variables appearing in a model before performing an operation, such as simulation or linearization. This new initialization technique permits the correct solution of difficult, non-standard initialization problems occurring in industrial applications, e.g.:
  • Stationary initialization around a constant reference velocity of an aircraft.
  • Determination of stationary periodic solutions for the initial states, needed in power systems or in detailed engine models.
  • Stationary initialization of continuous systems controlled by sampled data systems (the states of the discrete controllers are computed in such a way that the overall system is in a steady state when simulation starts).
  • Stationary initialization of discontinuous or variable structure systems, e.g., systems containing friction or backlash, by using smooth approximations of such elements during initialization.
     
• Enhance control of the selection of state variables in order that a modeler can incorporate application specific knowledge to guide the solution process. Examples occur in:
  • Thermodynamic systems where nonlinear algebraic loops can be avoided by defining states which are appropriate for the utilized property functions.
  • Three-phase power systems where the selection of states according to the Park transformation leads to linear instead of nonlinear differential equations, which can be solved much more accurately and efficiently.
  • Preference selection of relative over absolute positions in rotating machinery, to significantly improve the accuracy.
  • Avoiding dynamic state selection in simulations of mechanical systems with closed kinematical loops by explicitly defining the, usually known, driving joints of kinematical loops.
     
• Support for generic formulation of blocks applicable to both scalar and vector connectors, connection of (automatically) vectorized blocks, and simpler input/output connectors. This allows significant simplifications of the input/output block library of Modelica, e.g., since only scalar versions of all blocks have to be provided. Furthermore, new library components can be incorporated more easily.
   
• Additional utilities for external C-functions that are interfaced to Modelica models, especially supporting external functions with internal memory (e.g., to interface user-defined tables, property databases, sparse matrix handling, hardware interfaces).
   
• Support for data sheet libraries based on the Modelica package concept, data records and the new record constructor.
   
• Enumerated types, to allow the definition of options and properties in an understandable, safe and efficient way.
   
• Functions with mixed positional and named arguments. Optional results and default arguments make the same function fit for beginners and expert users.
   
• Iterators in array constructors and reduction operators, to support more powerful expressions, especially in declarations, in order to avoid inconvenient and less efficient local function definitions.
   
• Specifying a graphical appearance of Modelica object diagrams, thereby ensuring portability of model topology information and improving the previous informal graphical description.
   
• Additional built-in operators to access system resources in an operating-system independent way.

For further information, you may contact:

• Dr.-Ing. Martin Otter, German Aerospace Center, Germany (Chairman of the Modelica Association), +49/8153/28-2473, Martin.Otter@dlr.de.
• Prof. Peter Fritzson, Linköping University, Sweden (Vice-Chairman of the Modelica Association), +46-13-281484, petfr@ida.liu.se.
• Dr. Hilding Elmqvist, Dynasim AB, Sweden (Former Chairman, Secretary of the Modelica Association), +46-46-2862500, Elmqvist@Dynasim.se.
• Dr. Michael Tiller, Ford Motor Company (Treasurer of the Modelica Association),+1 (313) 337-1235, mtiller@ford.com.