BondLib.UsersGuide.Overview.SystemDynamics

# .BondLib.UsersGuide.Overview.SystemDynamics

The System Dynamics library

## Information

System Dynamics is a methodology that was designed to describe mass and information flows in dynamical systems. Since there are no energy flows, bond graphs seem to be the wrong methodology for implementing System Dynamics models.

Yet, masses being transported across a system carry their own internal energy along with them, and it may make sense to enhance the System Dynamics methodology to encompass those internal energy flows as well. In that context, the Levels of the System Dynamics methodology turn into mass capacitances of the bond graph methodology.

Mass capacitances are non-linear. Analogous to the thermal capacitances, they are inverse proportional to the effort, which in the case of a mass capacitance happens to be an enthalpy. We know that from the chemical domain, where we also deal with these types of mass capacitances.

Masses in System Dynamics are measured in all kinds of units. These can be numbers of people, money in a bank account, or frustration level in a relationship. Hence the "enthalpy" that accompanies the mass flow can also assume a variety of different measurement units.

System Dynamics has been designed for coarse-grain modeling, i.e., for modeling at a macroscopic level without delving down into all of the gory details of physics. Bond graphs on the other hand have been designed for fine-grain modeling, i.e., for capturing physical knowledge down to the basics.

Hence for modeling System Dynamics using bond graphs, we'll need to introduce a concept of sloppy bond graphs.

As System Dynamics is a world of its own, the SystemDynamics library comes with its own User's Guide.

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