Optimization and Computational Fluid Dynamics - Department of ...

9 CFD-based optimization for papermaking 287
intelligent decision support system [20]. As we can see from presented examples,
handling even a few conflicting targets at the same time is too complex
for the human mind and therefore multi-objective optimization methods are
needed. Furthermore, when the papermaking process can be controlled as a
whole, relationships between the targets can be seen clearer. By means of such
a system, a papermaking expert can take into account not only the individual
requirements of the paper to be produced, but, at the same time, all the
related aspects beginning from choice of raw materials and control of wood
fiber pre-processing to as far as market situation and customer demands –
all the facts affecting decision making in real life.
This kind of virtual papermaking line and decision support system demands
a lot of convenience from the models used. When the main focus has
extended to handle larger systems, even the whole papermaking process, the
number of models as a chain and sub-ensembles gets bigger. This poses a
real challenge since the CPU times cannot be extended too much. The CFDmodels
are usually time-consuming and that is why it is important to develop
new computationally effective ways to model phenomena occurring in the systems
such as virtual papermaking line. The accuracy of the CFD-models has
to be reduced in order to shorten the computing time or the CFD-model
might even sometimes need to be replaced with a statistical or stochastic
model, for instance.
A flexible decision support tool is required for different types of usage
and different users: from research and development engineers to managers of
a paper mill. Moreover, the system must include interactive interfaces with
automation and control softwares as well as direct connections to on-line measurements.
This trend sets new challenges for modeling and optimization. At
its best, the decision support system is able to provide new knowledge on the
physical and economical mechanisms affecting papermaking, and ultimately
leads to considerable financial benefits.
9.6 Conclusions
Depending on the requirements of the software tool to be developed, the
choice of appropriate modeling approach is essential. This means making
compromises between accuracy and extent of CFD, especially when coupled
with optimization. In phenomenological research the road leads towards more
detailed and accurate modeling, such as DNS, but when the aim is to control
larger ensembles, there is a need for decision support systems.
In this chapter some examples of coupling optimization with CFD in the
field of papermaking have been presented. They are chosen to represent different
categories of modeling extent and accuracy. Decision support systems
are coming in the near future, but optimal shape design and optimal control
are possible today, and in fact, are in everyday use in the industry. All the