Model concepts Flashcards
Name some environmental problems where geochemical modelling is useful
High level radioactive waste disposal
Mining-related environmental issues
- Permitting
- Monitoring
- Mine tailings and AMD
Landfills
What is the definition of a model?
A model is an abstract object, described by a set of mathematical expressions and
data, thought to represent natural processes in a particular system
What does the modeller do?
Chooses what data to use
Chooses what computer programme / software to use
Designs the model
Verifies, calibrates and validates the model
Selects the results that seem reasonable and rejects those that do not
Which processes can cause feedback scenarios?
Chemical reactions
Transport
Biological processes
Fluid flow
Heat transport
Name four types of geochemical models?
- Speciation-solubility models
(Batch calculations) - Reaction path models
(Concentration – time models) - Inverse mass balance models
- Coupled mass transport models
(Concentration – time – space models)
What are forcing functions?
External functions/variables that influence the system (e.g. temperature, pH)
What are state variables?
Describe the state of the system (“the model result”, e.g. element concentrations)
What are parameters used in modelling?
Coefficients in the mathematical representation of processes (e.g. equilibrium constants, diffusion coefficients, water flow rates etc.)
What are some universal constants?
E.g., gas constant, atomic weights etc.
How does the modelling procedure look?
Define problem
Define space and time limits
Define subsystem
Select model complexity
Conceptualize model
Formulate mathemathical expressions
Computerize model
Verificate model
Sensitivity analysis
Calibration
Validation
Describe what information is used speciation-solubility models and which questions the models can answer
Speciation–solubility models contain no spatial or temporal information
and are sometimes called zero-dimension models.
Can answer the following questions
1. What are the concentrations and activities of ionic and molecular species in an aqueous solution?
2. What are the saturation states with respect to various minerals in the system, and hence the directions of reactions that might occur toward achieving equilibrium?
3. What is the stable species distribution on surfaces or ion-exchangers that is at
equilibrium with the aqueous solution?
Describe reaction path models
Reaction path models calculate a sequence of equilibrium states involving incremental
or step-wise mass transfer between the phases within a system, or incremental addition or subtraction of a reactant from the system
Describe inverse mass balance models
Using the products in a water to find out the initial minerals which the product came from.
A number of minerals could give the same results
Describe coupled mass transport models
models in which two sets of
equations that describe two types of processes are solved together.
chemical reactions are
evaluated on the temporal and spatial scales.
What is verification of the model?
Checking whether the model reacted as expected
What is sensitivity analysis?
How sensitive the model is to changes in input data
What is calibration?
Optimization of parameters to obtain the best fit to measured data
What is validation?
Testing the model against an independent set of data
Why are models useful even though they are “wrong”?
o Models are useful instruments in the survey of complex systems
o Models can be used to reveal system properties
o Models reveal weaknesses in our knowledge and can therefore be used to set up research priorities
o Models are useful in tests of scientific hypotheses as the model can simulate reactions that can be compared with observations
What is useful with a conceptual model?
o Describes state and forcing functions. Shows in a simplified way how these are connected by processes in the modelled system.
