In systems engineering and object-oriented design, encapsulation is a key concept to handle complexity. Interfaces are defined for the external interaction of a component, whereas internal details are hidden. Complex systems such as cars or airplanes consist of many components, which, in turn, consist of many components – hierarchically, through many levels. Therefore composition is built into modelling languages such as Modelica. External interfaces must be defined for external interaction, whereas internal components cannot be accessed if they are not available through these interfaces.
However, in 3D mechanical systems modelling and design, it is natural to be able to connect components whose surfaces are externally available. For example, the motor belonging to a car can be externally accessible in the 3D view, even though it can be regarded as an internal component of the car.
In this paper we compare two modelling approaches, one is Modelica used for systems engineering as well as modelling of multi-body systems and the other one is BEAST which is a specialised multi-body systems tool with good support for contact modelling. The current Modelica approach requires strict interfaces with encapsulation of internal components, whereas BEAST allows connections to internal components which are visible in a 3D view, which is often natural from the 3D mechanical systems point of view. For 3D mechanical systems, Modelica might be too strict, whereas BEAST might be too forgiving. Two different solutions are presented and discussed (in the form of possible Modelica extensions) to combine the advantages of both approaches.
MATHMOD 2012 - 7th Vienna International Conference on Mathematical Modelling, February 15 - 17, Vienna, Austria