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Particle Data Extraction
Posted 6 févr. 2013, 16:34 UTC−5 Materials, Parameters, Variables, & Functions Version 4.3 3 Replies
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I made a simulation of an electro-kinetic flow within a 2-phase medium, and after computing the currents I wanted to see how particles would behave within the geometry and the resulting fields. I all looked all-right, but what I really need, is a way to extract the particle properties, i.e. for individual particles I want to be able to plot the velocity and the position, as I need to compute the tortuosity.
I tried a great many combinations regarding 1D-plots of individual particles, all of which failed. As a matter of fact everything which one could select from the Charged Particle list failed to result in a plot (besides the global quantities, such as mass and charge, which are steady over the entire domain/time/etc).
I also tried pulling them into Matlab, which again resulted in an errors (of the same kind as the ones in the 1D-plot attempts).
Here is how I tried to extract the data:
q=mpheval(M,{'qx'},'dataset','dset2','complexfun','off','selection','sel1','t',t_list(1:2));
Error using com.comsol.model.impl.NumericalFeatureImpl/getData
Java exception occurred:
Exception:
com.comsol.nativejni.FlNativeException: Failed to evaluate expression
(rethrown as com.comsol.util.exceptions.FlException)
Messages:
Failed to evaluate expression
Undefined post expression
Failed to evaluate variable
- Variable: mod1.qx
- Geometry: 1
- Domain: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25
Failed to evaluate expression
- Expression: real((999999999.99999988*mod1.qx))
Failed to evaluate expression
- Expression: real(9.999999999999999E8*mod1.qx)
Thanks,
Dan.
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www.comsol.com/products/4.3/#particletracing
This allows you to write the numerical value of an expression into a Table for the particles. You can then use the Graph Plot option to plot this data. This means you can plot particle position etc. v.s. time in 1D plots and isolate individual particles. If you want to plot particle position v.s. particle velocity on the same plot you should use a phase portrait. Both are demonstrated in the attached model.
If you want to compute tortuosity for particles you would probably need to add an auxiliary dependent variable and solve an additional ODE for the curvature of the trajectory. This sounds either very difficult or impossible.
Attachments:
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This seems to be just right!
Why ODE? One can use some simple measures for tortuosity of a material (in 2D), like (mean path length)/(shortest possible path), or some other similar arc-length-dependent measures.
Is there by chance also a Matlab link command which would do a similar thing?
Many thanks again,
Dan.
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Here is the matlab code which will allow you to import the particle associated states in your workspace.
%M=mphload(<your model>)
M.result().numerical.create('par1','Particle')
M.result.table('tbl1').clearTableData();
M.result.numerical('par1').set('expr','qx');
M.result.numerical('par1').setResult();
qx=M.result.table('tbl1').getReal();
M.result.table('tbl1').clearTableData();
M.result.numerical('par1').set('expr','qy');
M.result.numerical('par1').setResult();
qy=M.result.table('tbl1').getReal();