Page 29 - Mechatronic Systems Modelling and Simulation with HDLs

18 2 PRINCIPLES OF MODELLING AND SIMULATION

also called meshing, and both geometric dimensions and topological information
are important. The element matrices of the individual finite elements are found
from their material parameters and geometry, whereas the connection structure
between the elements, and consequently the system matrix, is derived from the
topology. Often the meshing has to be checked manually in order to ensure that the
elements have the correct form, the grid is sufficiently fine and available symmetries
are exploited.

2.4.3 Physical modelling

Introduction

In physical modelling the laws of physics are used to describe the behaviour and
inner action mechanism of a system or a component. The selection of the relevant
relationships depending upon suitability and efficiency and the establishment of
cause and effect chains, requires a comprehensive understanding of the system and
remains an engineering task. Computer support for this form of modelling is at
best rudimentary.
In the following, some classifications will be undertaken for the characterisation
of the physical modelling based upon various criteria. These consider the perspec-
tives of modelling and the nature of the yielded equations. Otherwise the reader is
referred at this point to Chapters 5 and 6 on modelling, and also to Chapters 7 and
8 on applications, which contain a whole range of examples of physical modelling
and electro-mechanical systems.

Perspectives of modelling

The perspectives of modelling offer a coarse division of the physical models which,
however, runs through all disciplines like a red thread. We should differentiate here
between whether the system perspective or the component perspective has been
selected. In one case the system-oriented modelling formulates the system in the
overall context; in the other case object-oriented modelling describes components,
which only form a system by their connection together, i.e. by structural modelling.
The decisive factor is that in object-oriented modelling no system knowledge is
fed into the component model. This ensures that the components can be used in
any desired context, so that modelling work only has to be performed once and
not for each system.
Hitherto in electronics, more significance has been attached to object-oriented
modelling. The physical models for electronic components provide the classic
example of this. These are formulated independently of the circuit in which they
are used. The connection structure is determined in a circuit diagram, which forms
a structural model. Thus the validation of the circuit model is in principle achieved
by a validation of the component model. This is particularly worthwhile if the