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Salt intrusion length is wrong
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TOPIC: Salt intrusion length is wrong

Salt intrusion length is wrong 2 months 4 weeks ago #45428

  • giuliaperego
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Hello!
I am running a simulation in Telemac 3D of a channel to model the saltwater intrusion.
According to measures performed in the river, I should observe an intrusion length of a few km.
My simulation observes an almost correct length in the first 8 hours (picture: intrusion length 2 hours.png), and then the intrusion length is pushed downstream (intrusion length 19 hours.png). This is weird because there are no big changes in river discharge and tide level.
Which could be the problem? I am attaching my .cas and .lqd files.
Thank you so much if you can help me


I thought that the problem could be the accuracy, therefore I checked the sortie file. Maybe the Error on the tracer quantity is too hingh? This is an example of a timestep:
ITERATION 1920 TIME 0 D 5 H 20 MN 0.0000 S ( 19200.0000 S)
================================================================================
ELEVATION AT THE BOUNDARY READIN THE ASCII FILE
LIQUID BOUNDARY: SL(1) = 0.17999999999999999
VALUE OF THE TRACER 1 AT THE BOUNDARIES READ IN THE ASCII FILE
T
LIQUID BOUNDARY: Q(2) = 8.5800000000000001
ADVECTION STEP
GMRES (BIEF) : 26 ITERATIONS, RELATIVE PRECISION: 0.7215258E-05
MURD3D_LIPS: 1 ITERATIONS
GMRES (BIEF) : 23 ITERATIONS, RELATIVE PRECISION: 0.8269117E-05
MURD3D_LIPS: 1 ITERATIONS
GMRES (BIEF) : 28 ITERATIONS, RELATIVE PRECISION: 0.9074837E-05
MURD3D_LIPS: 1 ITERATIONS
DIFFUSION OF WN
GMRES (BIEF) : 6 ITERATIONS, RELATIVE PRECISION: 0.8646833E-05
PROPAGATION AND DIFFUSION WITH WAVE EQUATION
GMRES (BIEF) : 19 ITERATIONS, RELATIVE PRECISION: 0.8459467E-06
POSITIVE DEPTHS OBTAINED IN 92 ITERATIONS
DYNAMIC PRESSURE STAGE
GRACJG (BIEF) : 14 ITERATIONS, RELATIVE PRECISION: 0.9030999E-03
VELOCITY PROJECTION STEP
ADVECTION-DIFFUSION OF TRACERS
GMRES (BIEF) : 11 ITERATIONS, RELATIVE PRECISION: 0.9395113E-06
MURD3D_LIPS: 1 ITERATIONS
DIFFUSION OF TRN1
GMRES (BIEF) : 3 ITERATIONS, RELATIVE PRECISION: 0.2478693E-06
MASS BALANCE

WATER
VOLUME AT THE PREVIOUS TIME STEP : 0.2205585E+08
VOLUME AT THE PRESENT TIME STEP : 0.2206117E+08
VOLUME LEAVING DOMAIN DURING THIS TIME STEP : -5325.713
ERROR ON THE VOLUME DURING THIS TIME STEP : 0.1226790E-06
BOUNDARY FLUXES FOR WATER IN M3/S ( >0 : ENTERING )
FLUX BOUNDARY 1 : 435.3834
FLUX BOUNDARY 2 : 97.18786

TRACER 1: SALINITY , UNIT : * M3)

ADVECTIVE FLUX THROUGH BOUNDARIES OR SOURCES : -15591.93
DIFFUSIVE FLUX THROUGH THE BOUNDARIES : -0.000000
QUANTITY AT THE PREVIOUS TIME STEP : 0.2671241E+09
QUANTITY AT THE PRESENT TIME STEP : 0.2672805E+09
QUANTITY EXITING (BOUNDARIES OR SOURCE) : -155919.3
ERROR ON THE QUANTITY DURING THIS TIME STEP : -548.8177
BOUNDARY FLUXES FOR TRACER 1 IN * M3/S) ( >0 : ENTERING )
FLUX BOUNDARY 1 : 15591.93
FLUX BOUNDARY 2 : -0.7874808-174

Here the error is -548.8177, is this causing the wrong results?
And how can I improve my simulation?
Thank you, Giulia
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Salt intrusion length is wrong 2 months 3 weeks ago #45437

  • pham
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Hello Giulia,

When using TELEMAC, I often tell: if you change default values for keywords, you have to wonder why you do it.

I would recommend you to read the recommendations appendix in the TELEMAC-3D user manual (appendix E).
In particular, I would choose an accuracy for diffusion of tracers equal to 1.E-8 (default value) or even less if not too difficult to reach (e.g. 1.E-10 or less down to 1.E-15).

Hope this helps,

Chi-Tuan
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Salt intrusion length is wrong 2 months 3 weeks ago #45455

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Hey, thank you for your answer!
I am now running a simulation with this modification
Giulia
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Salt intrusion length is wrong 2 months 3 weeks ago #45482

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Hi Chi-Tuan,
I ran the simulation with that modification but again salt length becomes zero after a few hours of simulation. I really can't understand why this happens as there are no big changes in water discharge and tide level.
If you have further advice, I would be very hppy to read it.
Thank you again
Giulia
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Salt intrusion length is wrong 1 month 4 weeks ago #45540

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Hello Giulia,

Have you tried to set the different steering files to what is recommended in the appendix E and not only 1 single keyword ACCURACY FOR DIFFUSION OF TRACERS?

Hope this helps,

Chi-Tuan
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Salt intrusion length is wrong 1 month 4 weeks ago #45541

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Yes I did... I tihink I solved that problem, it was in the accuracy
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