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日期:2021-03-16 10:15

Practical 4 Development of a simple stratigraphic forward model

Note that this practical is assessed and work 50% of the module mark

The aims of this practical session are to:

? Introduce you to the theory and practical considerations involved in constructing a simple

stratigraphic forward model

? Begin to apply the coding skills developed in the module sessions completed so far

? Introduce you to some more basic elements of numerical forward models, including simple

finite difference methods, numerical stability and grid boundary issues

? Develop and assess your ability to use previously developed code fragments in functions to

help construct a coding solution to a particular problem

? Develop and assess your ability to develop code from an algorithm specified in a flowchart

and following other guidance, as specified below

Instructions

1. First, briefly recap the various content of the lecture and seminar session this week that

introduced some of the theory of stratigraphic forward models, and went through an

example of various aspects of one of these models.

2. Pay particular attention to the flowchart and other instructions from the seminar

presentation:

Your main task in this practical is to write code that

implements this flowchart.

And remember, there should also a sub loop within the man time loop that calculates the

diffusional erosion and depositional change to the elevation of a surface, using a shorter

time step than used in the main loop that stores the layers of strata, so

Key elements that the model code completes should be:

? Definition of an initial topography – see the initial topography shown in the seminar

presentation, this is the one you need to use

? Calculation of diffusional erosion and deposition across the topography through multiple

forward-in-time steps

? Representation of the strata produced by this erosion and deposition, including a layer

property such as grain size based on transport distance

? A calculation of total eroded and total deposited volume per time step, with a warning

printed if these two values are not the same – differences could be due to an open grid

boundary…

? Plotting of the results as a 3D final model surfaces, cross-section and chronostratigraphic

diagram

Details of all these elements were given and talked through in the seminar slides, and all of

the initial variable values you need are actually defined for you in the diffusionStratModel.m

code

3. Following this guidance and the various other information provided in this week’s seminar

material, and using all the material from previous practical sessions, you should code the

model, debug, test and run it to produce 100 layers, with a shorter sub-loop iteration to

ensure numerical stability of the diffusion finite difference solution.

4. When the code is complete and working, you need to do some work to explore how the

model behaves and how it produces different results with different input parameters, so:

? Change the grid size to be 100 x 100 cells. Run the model with this new grid size to

check that it works ok

? Now you are going to assess how the strata changes with different values of the

diffusion coefficient ?. Start with a value ?=0.05, but also run examples with

?=0.025, ?=0.10, ?=0.20. Look carefully at the results in each case. Is mass

conserved on the grid for all these diffusion coefficient values? If not, what does this

mean for the validity of the model? Could you still use it to make meaningful

predictions of erosion and deposition?

? Now write a very short report, maximum word limit 200 words, to explain

i. how the modelled strata change with changing values of ?,

ii. Is mass always conserved in the model and does it matter if it is or is not?

You should look at the marking rubric for this work before you complete this report, to

make sure you understand how your report is going to be assessed and marked.

5. Paste this report text into the end of your Matlab code as a comment and save the .m file.

You can then submit your .m file source code via the practical 4 assignment submission on

Canvas. Please make sure the file submitted is a plain text .m file – if you submit any other

file type it might be difficult to mark your work.


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