Salinity variation for 2D model

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lilianseiler@yahoo.com.br
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Salinity variation for 2D model

Postby lilianseiler@yahoo.com.br » Mon Oct 03, 2011 14:46

Hello!

Im trying simulate a water quality process on my estuary. For this, im using a 2D model.
My estuary circulation is dominated by wind and discharge (for both, my input data is a time serie ).
Like the model is 2D, i got the parameters results of water column integration.

For vertical turbulence im using a constant model and for horizontal turbulence the smagorinsky model, like this:

MODTURB : constant
VISCOSITY_V : 0.0010
MODVISH : smagorinsky
HORCON : 0.2
VISH_REF : 1
VISCOSITY_H : 10.000


Analysing the results, when i compared the model results with real results i got a good tendency line, but with bad results for lowest salinity values.
As i told, i understand that using a 2D model ill have a water column integration, but is possible change some thing to have best results, like change the horizontal turbulence model, for example?

Thanks!

Lilian

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Re: Salinity variation for 2D model

Postby luis_at_mohid.com » Wed Dec 07, 2011 12:10

Hi Lilian,

Several things may influence your results. Depending on the exact characteristics of your model:

1) the river flow does not have the correct values or it's values do not have the needed update frequency. What's the average river flow?
2) the grid resolution in the upper estuary is insufficient
3) the estuary is stratified and thus a 2D approach is insufficient especially in the low salinity areas
4) what's your grid resolution? maybe reduce the horizontal viscosity might help? are you using the TVD scheme for advection?


Hope this helps,
Luis

lilianseiler@yahoo.com.br
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Posts: 24
Joined: Thu Jan 01, 1970 00:00

Re: Salinity variation for 2D model

Postby lilianseiler@yahoo.com.br » Mon Dec 12, 2011 13:26

Hi Luis,

First of all, thanks for you help.

So..

1) The rivers discharges has a a average flow about 1700m³/s. But as i told you, is a tim serie with time step of 3600s (1h/1h).

2) im doing a simulation for all Lagoon body, not only the estuary part. The river discharge point is located far from estuary part, where the resolution is lower (i have a non regular grid, with highest resolution at estuary part).

3)The lagoon has a estuary that is a ''strangled'' type, so the variation between strafied and mixed is so fast. I think that is the problem.

4) The lowest resolution is 90000m² and the highest is 4000000 m². My horizontal viscosity is 10m/s.


I dont know if i should change the grid size, its because even that the salinity had some problemas with lowest values, my water quality results are ok.
I think i'll just change the horizontal viscosity. Other question about it, im using a smagorinsky scheme for turbulence. Is that ok for a 2D model, or use a constant value or estuary scheme is better? Does the turbulence schem could change the results?

Thanks one more time

cheers

luis_at_mohid.com
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Posts: 553
Joined: Thu Jan 01, 1970 00:00
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Re: Salinity variation for 2D model

Postby luis_at_mohid.com » Mon Dec 19, 2011 15:45

Hi Lilian,

Most likely the problems come from grid resolution and vertical resolution to solve the vertical mixing correctly and thus have the horizontal salinity mixing well resolved.

What's the name of the lagoon? I can take a look and make a quick suggestion of the grid resolution you should use.

Cheers,
Luis


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