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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
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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
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Types of models
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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/