ABSTRACT
The key idea in any modeling approach that starts from the a priori knowledge about the physics properties of the system to be modeled is that a conceptual separation is made between various fundamental behaviors that are (considered to be) relevant for a given problem context. Although this step is always present, it is often preceded by a step in which the system to be modeled is subdivided into subsystems on the basis of aspects of function or configuration. A pump (drive) system, for example, can be seen as an interconnection of an electric power source (an amplifier), an electric motor, a transmission, and a mechanism for displacement of a fluid (a gear box and a load). This is the first conceptual level of observable, functional components. The total behavior consists not only of the observable dynamic interaction between these subsystems, but also of the conceptual interaction between the fundamental behaviors that constitute the behavior of these subsystems. Already when modeling at this level, it is useful to consider both forms of interaction from the point of view of bilateral relations, instead of the unidirectional input-output relations that are often used, thus implicitly assuming no “back-effect” (Figure 26.1). This bilateral relation
and its relation to the concept of energy is the key idea behind a port-based modeling approach, as will be one of the main objectives of this chapter.
