Page 53 - Biosystems Engineering

34 Chapter Two

all living organisms (human, animal, microorganisms, and
even plants) are also dynamic systems because they change
over time.
• A system can constitute different subsystems that interact with
each other (e.g., organs in a human body) or can be part of a
larger system (e.g., individual organisms in a population). Often,
complex systems can be decomposed in subsystems on different
levels or scales and are, therefore, called multiscale systems.

Example A combine harvester is a highly complex biologically related dynamic
system, which can be split into different subsystems such as the header, the straw
elevator, the threshing, the separation, the cleaning and the grain elevator. These
subsystems themselves contain smaller subsystems. The cleaning section, for
example, consists of a number of shaking sieves and a fan, which are dynamic
systems themselves.

Goal The aim of biosystems analysis is to gain insight into the behavior of a
system, such that we can predict the system behavior and eventually control it
by actively adapting its dynamics.

This chapter is dedicated to the application of systems analysis to
biologically related problems. The reader is introduced to the methods
for model building, system analysis through computer simulations,
system identification, and optimization methods.
The examples given in this chapter are limited to biotechnical
systems (agricultural machinery). Some examples of biotechnical
systems where we have applied the principles described in this
chapter are control of slurry injectors (Saeys et al. 2007, 2008a, 2008b),
cab suspension design (De Temmerman et al. 2004, 2005), spray
boom suspension design (Ramon et al. 1998; Anthonis and Ramon
2003; Deprez et al. 2003), cruise control (Coen et al. 2008a, 2008b),
and an autopilot (Coen et al. 2008c) for a combine harvester, and
modeling and control of pasta drying (De Temmerman et al. 2007,
2009). However, the methods described can also be applied to purely
biological systems.

2.2 System Representation

2.2.1 Block Diagram Representation
Throughout history, engineers have always sought to describe reality
in a structured way. A common form of representation for dynamic
systems is to use block diagrams. These diagrams are meant to repre-
sent the system as a block or a box where all signals entering (inputs)
and exiting (outputs) the system are represented as directed lines.