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downstream boundary condition
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TOPIC: downstream boundary condition

downstream boundary condition 4 years 3 months ago #36463

  • doggo3
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Hello,

I'm making a TELEMAC2D v8p1 model,
and have problems with the downstream boundary condition.


The BC Settings are
・upstream(2)(3)(4)： Open boundary with prescribed Q (455)
・downstream(1)： Open boundary with prescribed H (544）
*I have no H and Q data at the downstream(1)　in the feature.

When using
・PRESCRIBED FLOWRATES =0.;587.d0;2932.d0;0.d0
・PRESCRIBED ELEVATIONS=292.d0;0.d0;0.d0;0.d0
(not using rating curve and liq file),
result is good. (Q(1)= -3519.)

But using a rating curve (and liq) file,
results are strange.(case1:H(1)=310, case2:Q(1)=-227000, and so on)

I've tested several solutions in the forum,
but still can't get good results.
・relaxation factor =1.0D0
・hot start after steady flow


I will attach the file.
Where should I modify it?

Regards,
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downstream boundary condition 4 years 3 months ago #36464

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Hello doggo3,

Could you try OPTION FOR LIQUID BOUNDARIES =1;1;1;1 (Dirichlet conditions rather than Thompson conditions) and tell if, at least, at your 1st boundary, you can see what you expect? Thompson conditions are non reflection conditions and may change your boundary conditions for H and/or velocity.

Hope this helps,

Chi-Tuan
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downstream boundary condition 4 years 3 months ago #36465

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Thank you for your quick reply.

Unfortunately, I have tested:
OPTION FOR LIQUID BOUNDARIES =1;1;1;1
but results are strange.

When using the attached liq file, I hope to see a result that match
or is close to the steady state result.(H(1)=292. and Q(1)= -3519.)
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downstream boundary condition 4 years 3 months ago #36466

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Can you try to change the first 3 columns of your 1st liquid boundary: 5 4 4 (prescribed elevation + free velocities) to 5 5 5 (prescribed elevation + prescribed flowrates) in your boundary conditions file?
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downstream boundary condition 4 years 3 months ago #36467

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TELEMAC2D says:

Q : MORE PRESCRIBED FLOWRATES
     ARE REQUIRED IN THE PARAMETER FILE
     AT LEAST      1 MUST BE GIVEN

 PLANTE: PROGRAM STOPPED AFTER AN ERROR
 RETURNING EXIT CODE:            2
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downstream boundary condition 4 years 3 months ago #36468

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Uncomment the line:
PRESCRIBED FLOWRATES = 0.;587.d0;2932.d0;0.d0

It is strange as you should have given e BOUNDARY LIQUID FILE, but try this.
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downstream boundary condition 4 years 3 months ago #36474

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It seems strange, but I understand that this means an initial inflow, in this case.


First, using hot start
・COMPUTATION CONTINUED = YES
・PREVIOUS COMPUTATION FILE ='result/steady_state.slf'
・INITIAL TIME SET TO ZERO = NO
・RECORD NUMBER FOR RESTART = 24 *1Day

・OPTION FOR LIQUID BOUNDARIES =2;1;1;1

and uncomment
・PRESCRIBED FLOWRATES = 0.d0;587.d0;2932.d0;0.d0
================================================================================
 ITERATION    63000    TIME:    1 D  1 H 45 MN   0.0000 S   (    92700.0000 S)
 LIQUID BOUNDARY: Q(2)     =   587.00000000000000
 LIQUID BOUNDARY: Q(2)     =   586.99999999999989
 LIQUID BOUNDARY: Q(3)     =   2932.0000000000000
 LIQUID BOUNDARY: Q(3)     =   2932.0000000000000
 LIQUID BOUNDARY: Q(4)     =   0.0000000000000000
 LIQUID BOUNDARY: Q(4)     =   0.0000000000000000
--------------------------------------------------------------------------------
                          ADVECTION STEP
--------------------------------------------------------------------------------
                    DIFFUSION-PROPAGATION STEP
 EQUNOR (BIEF) :        8 ITERATIONS, RELATIVE PRECISION:   0.7289055E-03
--------------------------------------------------------------------------------
                       BALANCE OF WATER VOLUME
     VOLUME IN THE DOMAIN :   0.4857154E+08 M3
     FLUX BOUNDARY    1:    -175146.8     M3/S  ( >0 : ENTERING  <0 : EXITING )
     FLUX BOUNDARY    2:     587.0000     M3/S  ( >0 : ENTERING  <0 : EXITING )
     FLUX BOUNDARY    3:     2071.070     M3/S  ( >0 : ENTERING  <0 : EXITING )
     FLUX BOUNDARY    4:    -0.000000     M3/S  ( >0 : ENTERING  <0 : EXITING )
Q(1)=-175147, is too large.


Next:
・PRESCRIBED FLOWRATES = -3519.d0;587.d0;2932.d0;0.d0
================================================================================
 ITERATION     3600    TIME:    1 D  0 H  6 MN   0.0000 S   (    86760.0000 S)
 LIQUID BOUNDARY: Q(2)     =   587.00000000000000
 LIQUID BOUNDARY: Q(2)     =   586.99999999999989
 LIQUID BOUNDARY: Q(3)     =   2932.0000000000000
 LIQUID BOUNDARY: Q(3)     =   2932.0000000000000
 LIQUID BOUNDARY: Q(4)     =   0.0000000000000000
 LIQUID BOUNDARY: Q(4)     =   0.0000000000000000
--------------------------------------------------------------------------------
                          ADVECTION STEP
--------------------------------------------------------------------------------
                    DIFFUSION-PROPAGATION STEP
 EQUNOR (BIEF) :        5 ITERATIONS, RELATIVE PRECISION:   0.6934745E-03
--------------------------------------------------------------------------------
                       BALANCE OF WATER VOLUME
     VOLUME IN THE DOMAIN :   0.1342329E+08 M3
     FLUX BOUNDARY    1:    -474551.9     M3/S  ( >0 : ENTERING  <0 : EXITING )
     FLUX BOUNDARY    2:     587.0000     M3/S  ( >0 : ENTERING  <0 : EXITING )
     FLUX BOUNDARY    3:     2932.000     M3/S  ( >0 : ENTERING  <0 : EXITING )
     FLUX BOUNDARY    4:    -0.000000     M3/S  ( >0 : ENTERING  <0 : EXITING )
     RELATIVE ERROR IN VOLUME AT T =       0.8676E+05 S :    0.1543800E-05


relaxation factor=0.5
================================================================================
 ITERATION     7200    TIME:    1 D  0 H 12 MN   0.0000 S   (    87120.0000 S)
 LIQUID BOUNDARY: Q(2)     =   587.00000000000000
 LIQUID BOUNDARY: Q(2)     =   587.00000000000011
 LIQUID BOUNDARY: Q(3)     =   2932.0000000000005
 LIQUID BOUNDARY: Q(3)     =   2932.0000000000000
 LIQUID BOUNDARY: Q(4)     =   0.0000000000000000
 LIQUID BOUNDARY: Q(4)     =   0.0000000000000000
--------------------------------------------------------------------------------
                          ADVECTION STEP
--------------------------------------------------------------------------------
                    DIFFUSION-PROPAGATION STEP
 EQUNOR (BIEF) :        5 ITERATIONS, RELATIVE PRECISION:   0.9450157E-03
--------------------------------------------------------------------------------
                       BALANCE OF WATER VOLUME
     VOLUME IN THE DOMAIN :   0.1431949E+08 M3
     FLUX BOUNDARY    1:    -67341.94     M3/S  ( >0 : ENTERING  <0 : EXITING )
     FLUX BOUNDARY    2:     587.0000     M3/S  ( >0 : ENTERING  <0 : EXITING )
     FLUX BOUNDARY    3:     2932.000     M3/S  ( >0 : ENTERING  <0 : EXITING )
     FLUX BOUNDARY    4:    -0.000000     M3/S  ( >0 : ENTERING  <0 : EXITING )
     RELATIVE ERROR IN VOLUME AT T =       0.8712E+05 S :    0.5138441E-05


relaxation factor=0.2
================================================================================
 ITERATION     5400    TIME:    1 D  0 H  9 MN   0.0000 S   (    86940.0000 S)
 LIQUID BOUNDARY: Q(2)     =   587.00000000000000
 LIQUID BOUNDARY: Q(2)     =   587.00000000000000
 LIQUID BOUNDARY: Q(3)     =   2932.0000000000000
 LIQUID BOUNDARY: Q(3)     =   2932.0000000000000
 LIQUID BOUNDARY: Q(4)     =   0.0000000000000000
 LIQUID BOUNDARY: Q(4)     =   0.0000000000000000
--------------------------------------------------------------------------------
                          ADVECTION STEP
--------------------------------------------------------------------------------
                    DIFFUSION-PROPAGATION STEP
 EQUNOR (BIEF) :        3 ITERATIONS, RELATIVE PRECISION:   0.9248101E-03
--------------------------------------------------------------------------------
                       BALANCE OF WATER VOLUME
     VOLUME IN THE DOMAIN :   0.1365805E+08 M3
     FLUX BOUNDARY    1:    -24586.49     M3/S  ( >0 : ENTERING  <0 : EXITING )
     FLUX BOUNDARY    2:     587.0000     M3/S  ( >0 : ENTERING  <0 : EXITING )
     FLUX BOUNDARY    3:     2932.000     M3/S  ( >0 : ENTERING  <0 : EXITING )
     FLUX BOUNDARY    4:    -0.000000     M3/S  ( >0 : ENTERING  <0 : EXITING )
     RELATIVE ERROR IN VOLUME AT T =       0.8694E+05 S :    0.3153529E-05

relaxation factor=0.03
================================================================================
 ITERATION     3600    TIME:    1 D  0 H  6 MN   0.0000 S   (    86760.0000 S)
 LIQUID BOUNDARY: Q(2)     =   587.00000000000000
 LIQUID BOUNDARY: Q(2)     =   586.99999999999989
 LIQUID BOUNDARY: Q(3)     =   2932.0000000000000
 LIQUID BOUNDARY: Q(3)     =   2932.0000000000000
 LIQUID BOUNDARY: Q(4)     =   0.0000000000000000
 LIQUID BOUNDARY: Q(4)     =   0.0000000000000000
--------------------------------------------------------------------------------
                          ADVECTION STEP
--------------------------------------------------------------------------------
                    DIFFUSION-PROPAGATION STEP
 EQUNOR (BIEF) :        3 ITERATIONS, RELATIVE PRECISION:   0.3396643E-03
--------------------------------------------------------------------------------
                       BALANCE OF WATER VOLUME
     VOLUME IN THE DOMAIN :   0.1251125E+08 M3
     FLUX BOUNDARY    1:    -5978.220     M3/S  ( >0 : ENTERING  <0 : EXITING )
     FLUX BOUNDARY    2:     587.0000     M3/S  ( >0 : ENTERING  <0 : EXITING )
     FLUX BOUNDARY    3:     2932.000     M3/S  ( >0 : ENTERING  <0 : EXITING )
     FLUX BOUNDARY    4:    -0.000000     M3/S  ( >0 : ENTERING  <0 : EXITING )
     RELATIVE ERROR IN VOLUME AT T =       0.8676E+05 S :    0.1638698E-05
 DEBIMP: PROBLEM ON BOUNDARY NUMBER      2

         GIVE A VELOCITY PROFILE
         IN THE BOUNDARY CONDITIONS FILE
         OR CHECK THE WATER DEPTHS.

         OTHER POSSIBLE CAUSE:
         SUPERCRITICAL ENTRY WITH FREE DEPTH
         IN THIS CASE GIVE A POSITIVE DEPTH
         IN THE INITIAL CONDITIONS
         OR PRESCRIBE THE DEPTH AT THE ENTRANCE.
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downstream boundary condition 4 years 3 months ago #36469

  • c.coulet
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Hi
Just to add a comment.
Using a relaxation factor of 1 is not a good option in my opinion.
this means you modified the actual value (which is 0.02) in sta_dis_cur.f
This probably leads to oscillation of the BC.

Regards
Christophe
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downstream boundary condition 4 years 3 months ago #36475

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Thank you for your comment.

At first, I calculated with 0.02, but sometimes an error occurred and the calculation stopped.(Like the reply above.)

Then I started using 1.0 for a different purpose, the calculation was stable (often ran to the last time step).
However, as you pointed out, there were cases where oscillation were seen on the water surface near BC.
(Fortunately there is no noticeable vibration in steady state result).

I'll try to make it smaller without error.

Regards
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downstream boundary condition 4 years 3 months ago #36476

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Did you try to put the value of discharge positive in your stage-discharge curve file?
I don't remember we have to put negative value...

Regards
Christophe
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