Drainage in heterogeneous flow field

[maki]

Hi

 

I’m trying to express the drainage in the heterogeneous flow field in X2t.

Simplified example and flow field tables for the import are attached. Please import the table file by using ‘imported’ function on the Domain pane.

And I attached the supplements for explanation.

 

Q.1 (the supplements 1 and 2)

When the flow field is imported, how should I set the drainage in X2t?

Can I set the open node within the domain?

 

In the example, I set the drainage to the central node of the domain having nine nodes.

Since the flow field seems to be fixed by the imported value, the function of ‘wells’ cannot be used at the same time and I will not use the function.

In the attached file, because all of velocity arrows directs to the central node, the values of Mass H2O, Mass solution, and total moles of node 1, 3, 4, 5, and 7 show much larger than the respective initial ones and the results are not realistic. Their values after the run should be same as initial ones because Bulk volume is not unchanged.

On the other hand, the Cl- concentration (molality) calculated by moles in fluid and Fluid volume seems to be correct.

I think that approximately no change of Mass H2O and Mass solution compared with the initial values of those is practically desirable.

 

Can I set the ‘realistic’ drainage without using the function of ‘wells’ in the heterogeneous flow field?

In other words, because of avoiding such an unrealistic value, can I set the open node within the domain? It will be grateful if you have any good idea to handle this problem.

Or, if I need the molality only, should I ignore the unrealistic values of Mass H2O etc. and adopt the calculation result of molality, which seems to be correct, like the attached example?

 

Q.2 (the supplement 3)

The scale in Xtplot seems not to show an appropriate range corresponding to pasted values. If the maintenance is needed, could you handle it?

 

In addition, Moles in fluid shows a different value from those output in text file of Xtplot. I guess the value in text file of Xtplot is correct. Is it correct?

 

If my explanation is insufficient, could you let me know?

 

Best regards,

 

Maki

drainage.x2t

x_dra.txt

y_dra.txt

the_supplement_drainage_1.pdf

the_supplement_drainage_2.pdf

the_supplement_drainage_3.pdf

[Brian Farrell]

Hi Maki,

 

Sorry I missed this post earlier. The reason you see unrealistic values for the H2O mass in the domain is because the flow field you've specified is not realistic. X and Y discharge cannot have the same magnitude everywhere in the domain. To see what I mean, take a look at this example X2t file, in which I've set the left and right boundaries open to flow, but with no potential drop (no regional flow) but added a production well. Run the model, then plot Hydraulic Potential as contour lines and X or Y discharge as a color map. You'll see how specific discharge is greatest near the well (where the flow converges).

 

When using the "import flow field" option, you should use the results of an actual flow simulation of some sort (like that from the attached X2t file). The program will report an error if you try to specify a constant potential/ head well when using imported flow fields, but I believe you can specify a constant discharge well. Including a well when using the "import flow field" option will not affect the value of discharge or velocity arrows anywhere in the domain, but it will allow water (and solute) to exit the domain through the well (preventing unrealistic H20 mass).

 

Please let me know if this doesn't make sense.

 

Regards,

 

Brian Farrell

Aqueous Solutions

 

P.S. I've moved your post from the archive of old topics to the front GWB page.

2013_09_03_ImportDrainage.x2t

[maki]

Hi Brian,

 

Thank you for your reply.

 

According to your advice, I tried to set a constant discharge well in the imported flow field.

Although the error message ‘Volume imbalance, maximum error of ...’ was shown in the beginning of Results pane, the calculation converged and values of Hydraulic potential in all nodes were zero atm.

My understanding is that I don’t need to mind the error message in the above example. Is this right?

 

Best regards,

 

Maki

[Brian Farrell]

Hi Maki,

 

When you use an imported flow field, X2t uses the values for cell-to-cell discharge directly, so it never calculates Hydraulic potential. That is why you see 0 hydraulic potential everywhere in the domain, even though there is clearly flow in the system.

 

When you set a well, you can adjust the production rate to ensure that the mass of H2O in the nodal block makes sense.

 

Cheers,

Brian

[maki]

Hi Brian,

 

Please let me ask one more question.

 

When the mass of H2O of the well in the imported flow field doesn’t need to be taken into consideration, I don’t need to set the discharge well. Or do I have to set the well in the imported flow field?

 

Thank you for your help.

 

Maki

[Brian Farrell]

Hi Maki,

 

Solutes are transported through the domain by two fluxes. The advective flux is fixed when using an imported flow field because you set specific discharge directly. The dispersive flux (dispersion and diffusion), on the other hand, depends on the concentration gradient between nodes. A problem could potentially arise if the increased mass H2O affected solute concentration enough to alter the concentration gradient between the node with the production well and its neighbors. You'll have to investigate whether or not this is a problem for your particular example. If you're going to look into this further, I would recommend a finer grid than the one you've used in your example to separate the effects of any numerical artifacts.

 

Hope this helps,

Brian