1. System Dynamics
MCT 3113
Lecture #1: Introduction to System Dynamics
Dr. Shahrul Naim Sidek
Department of Mechatronics Engineering
International Islamic University Malaysia

2. What is system?

3. Definition of System
“An object or collection of objects whose properties we
would like to study”
It contains of interacting components connected together in
such away that the variation in one component affects the
other components

4. Definition of System
System and Surroundings
We scope a system by defining
its boundary; this means
choosing which entities are
inside the system and which
are outside the boundary -
part of the environment.

5. Definition of System
input output
System
The environment affects the system through the input (cause)
and system responds (effect) due to the input.

6. Definition of System
Way to structure a system
• what belongs to the system, and what does not
• inputs, outputs and internal dynamics
Example: System’s view of cruise control in a car

7. System Classifications
Static vs. Dynamic Systems
Static System
The output of the system depends only on the current
input.
The output does not change with the time if the input is
held constant (time-invariant).
Dynamic System
The output of the system depends on the current and the
previous input.
The output changes with the time even if the input is
constant (time varying).

8. System Classifications
Dynamic systems are found in all major
engineering areas.
Mechanical Systems
Electrical Systems
Thermal Systems
Fluid Systems
Mixed Systems

9. Mechanical Systems
What is mechanical system?
Mechanical systems are concerned with the behavior
of matter under the action of forces/torques.
Governed by Newton’s 2nd Law

10. Electrical Systems
What is electrical system?
Electrical systems are concerned with the behavior of
three fundamental quantities: charge, current and voltage.
Two Kirchoff’s laws are used to model the electrical
system:
1. ?
2. ?

11. Thermal Systems
What is thermal system?
Thermal systems involves heating of objects and
transports of thermal energy.
Example of thermal system ?

12. Fluid Systems
What is fluid system?
Fluid system involves connection of fluid flows in tube and
tank.
Example of fluid systems ?

13. Mixed Systems
What is mixed system?
System which consists of two or more of previously
mentioned systems.
Electro-mechanical system
Fluid-mechanical system
Thermo-mechanical
Electro-thermal
Mechatronics system !

14. What system is this?

15. What system is this?

16. What system is this?

17. What is system dynamics?

18. Definition of System Dynamics
System dynamics is the study of the time-behavior of a system
and includes the followings:
System definition
System boundaries, input and output variables
Modeling of the system
Usually in the form of mathematical or graphical relationship determined
analytically or empirically
Determination of the behavior of the system (i.e.
Analytical/Simulation)
Effect of the inputs to the system outputs
Formulation of recommendation
To improve system performance through modification of the
system structure or parameter values

19. Definition of System Dynamics
System Definition
Modeling
Simulation
Recommendation
System dynamics

20. System Dynamics
Actual System
System Definition
Modeler’s Perception
Modeling
Mathematical
Simulation Representation
Validation
Recommendations

21. What is model?
The word “model” is derived from a Latin word which
originally means pattern or mold.
Model of a system is basically a tool to study the behavior
of a system without having experiment on the real
system.
Model can be: physical model, mental model, verbal model
and also mathematical model.
We concern ONLY mathematical model.

22. What is mathematical model?
Model is a collection of mathematical equations which
represent behavior/characteristic of real system
&
x, x
f m1
T = fr
(m1 + m2 )&& + m2l (θ& cosθ − θ& 2 sin θ + 2ml&θ& cosθ + m&&sin θ ) =
x & l f
θ l lθ& + 2l&θ + && cos θ + g sin θ = 0
& & x
m2

23. Why do we need mathematical model?
• To avoid physical system
– Can treat new designs/technologies without physical
prototype
– Do not disturb operation of existing system
• Easier to work with than real world
– Easy to check many approaches, parameter values,…
– Flexible to time-scales
– Can access immeasurable quantities
• Support safety
– Experiments may be dangerous
– Operators need to train for extreme situations
• Help to gain insight and understanding

24. Why do we need mathematical model?
The first step in understanding a
problem is to model its
behavior.
“If it works on paper, it will
work in real life”
<Susan Koerner Wright>
mother to Wright ‘s brothers
Model can be simulated
Fast-time simulation save time.

25. Model Characteristics
A model captures only some aspects of a system
Important to know which aspects are modeled and
which are not.
Make sure that model is valid for intended purpose
All-encompassing models often a bad idea
Large and complex – hard to gain insight
Cumbersome and slow to manipulate
Good models are simple, yet capture the essentials!

26. Simulation
Model can be used to compute how the system would
react upon certain inputs.
This can be done mathematically solve the equations that
describe the system and study the answer.
OR
With the power of computer we can perform a
numerical computation to solve the equations.

27. Simulation
Simulation is derived from Latin world simulare which
means pretend.
We may define simulation as a process of imitation the
dynamic system using a computer in order to evaluate
and/or improve the system performance.