Poor solute balance

A discussion forum for users of the new HYDRUS 2D/3D. HYDRUS is a software package for simulating water, heat and solute movement in two- and three-dimensional variably saturated media. Happy Posting!
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David Radcliffe
Posts: 25
Joined: Wed Oct 07, 2009 3:32 pm

Poor solute balance

Post by David Radcliffe » Mon Apr 01, 2019 3:34 pm

I am working on a hillslope model of Cl movement from a septic system to a lake at the bottom of the slope. Input concentrations of Cl are 40. With a simplified geometry (a parallelogram, Model 56) the water and Cl balance is very good. But with more detailed geometry, the solute balance is poor with large negative concentrations (Model 57). I have tried to make the model settings as close as possible in terms of mesh.

I attach images of the models.
Attachments
Model 56 & 57 images.docx
(1.71 MiB) Downloaded 17 times

Jirka
Posts: 4712
Joined: Sat Mar 16, 2002 3:47 pm
Location: USA
Location: Riverside, CA

Re: Poor solute balance

Post by Jirka » Mon Apr 01, 2019 3:43 pm

The computational module solves exactly the same equations and uses the same numerical techniques/algorithms for both simplified (2D-Simple) or general (2D-General) geometries. Differences are only in how the two geometry types are handled by the GUI, not by the computational module. The reason for the nonstability of the numerical solution thus must be in the definition of the problem, not the geometry. J.

David Radcliffe
Posts: 25
Joined: Wed Oct 07, 2009 3:32 pm

Re: Poor solute balance

Post by David Radcliffe » Tue Apr 02, 2019 1:16 pm

Sorry I did not make myself clear. Both models use the 2D General Geometry for mesh. So I know something else is causing the differences in solute balance. I was hoping you might be able to take a look at the 2 models (sent by email) and make suggestions. Thanks so much.

Jirka
Posts: 4712
Joined: Sat Mar 16, 2002 3:47 pm
Location: USA
Location: Riverside, CA

Re: Poor solute balance

Post by Jirka » Tue Apr 02, 2019 3:34 pm

I have not received any email related to this posting. J.

Jirka
Posts: 4712
Joined: Sat Mar 16, 2002 3:47 pm
Location: USA
Location: Riverside, CA

Re: Poor solute balance

Post by Jirka » Wed Apr 03, 2019 1:02 am

You had no solute transport boundary conditions specified in the Model 57. Once I added Cauchy Boundary Conditions on all boundaries with specified water flow BCs (seepage face and variable head), the programs runs just fine with a solute mass balance error of about 2.5%. J.

David Radcliffe
Posts: 25
Joined: Wed Oct 07, 2009 3:32 pm

Re: Poor solute balance

Post by David Radcliffe » Wed Apr 03, 2019 12:54 pm

That is wonderful! Can you please send the program back by email with the changes you made? This has been driving me nuts for 2 weeks...

Jirka
Posts: 4712
Joined: Sat Mar 16, 2002 3:47 pm
Location: USA
Location: Riverside, CA

Re: Poor solute balance

Post by Jirka » Wed Apr 03, 2019 1:06 pm

I have copied those two projects (which I ran for few hundred years and thus they are on the order of 200 MB) to DropBox, together with the computational module that I used. J.

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