Page 35 - Mechatronic Systems Modelling and Simulation with HDLs

24 2 PRINCIPLES OF MODELLING AND SIMULATION

allows us to obtain better parameter estimates, as is the case in the weighted
method of least squares.

2.5 Model Verification and Validation

2.5.1 Introduction
As defined in Section 2.1, model verification answers the question of whether the
implementable model reflects the conceptual model within the specified bound-
aries of accuracy, whereas the purpose of model validation is to show whether the
implementable model is suitable for fulfilling the envisaged task within its field
of application. In what follows the most important methods in this field will be
introduced. These originate from a very wide range of fields of application, some
of which lie outside the field of engineering sciences. They are, however, gen-
eral enough to be used in a technical context. Good overviews of the underlying
literature can be found in Kleijnen [193], Cobelli et al. [72] and Murray-Smith
[288], [289].

2.5.2 Model verification

Verification on the basis of the implementation methodology
The most direct form of verification takes place as early as the implementation stage
and aims to ensure that, where possible, the errors to be identified by verification
do not occur at all. This requires intervention into the methodology of model
implementation. In this context, the same boundary conditions often apply as those
for the development of software since, in this field too, a formal description based
upon syntax and semantics is used for the formulation of a given technical content.
Accordingly, most of the mechanisms that are used for software development also
come into play here in order to avoid implementation errors. A few key words
here, see Kleijnen [193], are: Modular modelling, object-oriented modelling or the
‘chief modeller’ principle, in which the actual implementation is as far as possible
performed by a single person, whilst the other colleagues of the ‘chief modeller’
relieve him of all other tasks. In addition, there is the modular testing of submodels,
so that modelling errors are recognised as early as possible and at lower levels. A
further important aspect of verification lies in the correct definition of the scope
of the model and in the ongoing checking to ensure that this scope is adhered
to. Extrapolations beyond the guaranteed range should generally be treated with
extreme caution.

Plausibility tests
Plausibility tests can also make a contribution to verification (and validation), see
also Kramer and Neculau [206]. This is particularly true if they can be performed by