Page 25 - Mechatronic Systems Modelling and Simulation with HDLs

14 2 PRINCIPLES OF MODELLING AND SIMULATION

displayed in a debugger that shows the current status of the software, i.e. program
line and variable values, plus their outputs on the terminal. Without this type of
simulation, software development would be unthinkable.
Like electronics, the construction of mechanical systems in reality is very expen-
sive in terms of time and costs. In many of the industries in question the answer
to this problem lies in the increased use of simulation. The automotive industry
is particularly advanced in this field. The two main key words here are digital
mock-up and virtual prototype, see for example Paulini et al. [317] or Schweer
et al. [376]. A digital mock-up is as complete as possible a description of a single
product on the computer and thus represents a limited data quantity. All the various
tools check the design on the basis of this data. The digital mock-up thus primarily
represents a medium for information exchange, which links together data sources
and data sinks in the design process. At regular intervals, for example every two
weeks [376], new data are put in and thus are available to all possible users. A vir-
tual prototype is extracted from the data of the digital mock-up, which can then be
used for experiments on the computer. A classic example of this is the simulation
of crash tests. In this application, a finite-element model is obtained from the CAD
data of the body by automatic meshing, which can then be subjected to any desired
crash situations. Although the simulation requires several hours of processing time
even on the fastest computer, it means that the majority of real crash tests can be
dispensed with. Furthermore, simulations are also run in virtually all other sectors
of the automotive industry, such as for example in the development of running
gear, engine, drive train and the associated electronics.

2.4 Model Development

2.4.1 Introduction

The following section provides an overview of the most up-to-date methods for
model development in electronics and mechanics, looking at both the common
ground and differences. We can make an initial classification by asking whether
the model describes the structure or the behaviour of a system.
Taking the first case, in classic modelling the model establishes only which com-
ponents make up the system and how these are connected together. Alternatively,
however, the term structural modelling can also be expanded and, for example, take
in the description of the structure of an equation system or a finite state machine.
In such cases the following forms of model description may be called structural:
electronic circuit diagrams, state graphs, multibody diagrams, meshes of finite ele-
ments, block diagrams, bond graphs and Petri nets. The common factor of all these
descriptive forms is that they are all graphical in nature.
If, on the other hand, it is the behaviour of a system that is to be described
then this can be achieved on the basis of the underlying physics or the measured
input/output behaviour. In the former case the development of such models is