Systems modelling concepts

System modelling conceptsWhat is a modelling?Model classificationDynamical SystemsSystem analysis-System dynamics and thinkingIntroduction to course litterature

What is modelling?

Mind modelling

So, thinking is modelling

If the thought is clear and can be

communicated, then we can always model it.

Modelling is to get an idea of how

things are or work.

What is a model?

A model - a replica- an ideal- to display

- a simplified representation of the world around us or a material, conceptual or formal representation

Book: section1.2

Dictionary

SMHI, developed by Sten

Bergström and colleagues.

Semi-distributed modelHBV

z

TR

gpp

a

EXP0

A model is:

- A model is any understanding which is used to reach a conclusion or a solution

- There are no computer models, these are mere mechanical and mathematical translations of mental models

- If a model is ’wrong’, then the underlying understanding is wrong

The value of models:

- Forces us to examine a system carefully and define key variables, relationships, processes, structures and scales

- Helps us to understand the functioning

- Enables us to extrapolate in – scale and space

- future (forecasts)- past(hindcast)

- Enables us to interpolate

- Allows us to obtain or infer information about unmeasurable variables

Models have the potential to:

- Quantify expected results

- Compare the results of two alternative theories

- Describe the effect of complex factors, such as

random variation in inputs

- Explain how the underlaying processes

contribute to the result

- Extraplota results to other situations

- Predict future events

- Translate our science into a form that can be

easily used by non-experts Book: section 1.3

Models

Conceptuel

Probabilistic

Deterministic

Analogue

Scale

Hardware

Matematical

Incr

easi

ng

ab

stra

ctio

n

Types of models

z

TR

gpp

a

EXP0

Example; light absorbtion in a canopy

Model classification

Question

Hypothesis

Output Input Scope

ApplicationOutputQualitative / quanitiative?

Deterministic / stochastic?

InputStatic / dynamic?

ScopeDescriptive / predictive?

ApplicationFunctional /

mechanistic?Book: section 1.4

Model classifi cation

Question

Hypothesis

Output I nput Scope Application

OutputQualitative / quanitiative?Deterministic / stochastic?

I nputStatic / dynamic?

ScopeDescriptive / predictive?

ApplicationFunctional / mechanistic?

Discuss examples:1. A stylist use a model to suggest what colours dress you best2. A weather forecast model3. Betsson (a betting company) needs a model to set odds for which

song will win the Eurovision song contest

Dynamical systems

Systems in the societyWhat do they have in common?Football formation

system Education system Transport system

Defence system

Systems in nature:

Closed system

Energy

Open system

Matter

Isolated system: no exchange with its environment

Closed systems: only exchange of energy

Open systems: exchange of both energy and matter with its surroundings

Isolated system

Representation of a part of reality that is bounded in its surrounding

Consist of a number of elements (entities, components) The state of the elements effects each other, which

makes the system functioning (or work)

Systems

Simple

Complicated

Simple representation of a complicated system

Ecosystem:

An ecosystem is a biotic and functional system or unit, which is able to sustain life and includes all biological and non-biological variables in that unit. Spatial and temporal scales are not specified a priori, but are entirely based upon objectives of the ecosystem study

(Jorgensen & Bendoricchio, 2001)

A system:

A system is a group of independent but interelated elements comprising a unified whole

But:

The properties of the whole can only be understood through the interaction and the relationships among the parts within the systemFor example: a forest stand

In isolation the parts can not be considered as a forest. It is the interaction between the parts that makes it a forest

+ +

=

A system element:

can be specified by its properties (a tree: height, leaf area)

The State of a system:

the value of relevant properties at a moment in time

Process:

a (time dependent) relation that changes the state of a system

1. All descriptions or models of systems are to some extent generalizations, abstractions or idealization of the real world.

2. Systems have some kind of structure or organization of its objects and a boundary.

3. A system is functioning in some way

4 Because it is functioning, there are functional as well as structural relationships between the objects in the structure.

5. The functioning implies some flow and transfer of material or energy through the system

6. This means that there is a driving force, or a source of energy that support the functioning, or drives the system

To summarize the characteristics of a system:

System thinking as a discipline

for seeing systems as a wholes, it counteracts reductionism looks at relationships between system elements

looks at dynamic changes

It focus on how the system ’works’: the processes and inter-relations – as a mean to understand the system

System dynamics = analysis and understanding of the behavior of systems: a methodology for studying and managing complex systems or any feedback system. It uses simulation (computer) models.

It is seeing the whole (holism) versus Reductionism

The discipline of System dynamics and system thinking

System dynamics

Originated in 1960’s from work of Jay Forrester et al of Massachusetts Institute of Technology’Industrial Dynamics’ (1961), ’Urban dynamics’ (1969) and ’World dynamics’ (1971)

System dynamicsOther examples

Limits to GrowtDonella L. Meadows et al, 1972 (World3-model)

Club of Rome (1968)http://www.clubofrome.org/

Our common future (1987)United Nations World Commission on Environment and Development, headed byGro Harlem Brundtland, Previous Prime Minister of Norway

Informal association of leading long-term thinkers contributing in a systematic interdisciplinary and holistic manner to a better world

It targets multilateralism and interdependence of nations in the search for a sustainable development path, and aims to discuss the environment and development as one single issue.

Basic elements in system modelling

ParametersConstantsVariables

FlowsStocks

Processes

Stages in making a model

Research question

Answer

Picture

Hypothesis & assumptions

Mathematical model

Measurements

Evaluation

Book: section 1.6

Conceptual model

LitteratureSmith & Smith: Environmental Modellingwww.oxfordtextbooks.co.uk/orc/smith_smith/

1: Introduction (22 Jan)

2: Model Development (30 Jan)

3: Model Evaluation (8 Feb)

4: Application of Models (15 Feb)

LitteratureSmith & Smith: Environmental Modellingwww.oxfordtextbooks.co.uk/orc/smith_smith/