River Modelling

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andersonsoares
Posts: 4
Joined: Wed Oct 18, 2017 5:53 pm
Location: Federal University of Rio de Janeiro, LAMCE- COPPE

River Modelling

#1 Unread post by andersonsoares »

Hi, I'm a graduate student and I am trying to modelling a river that goes from east to west of my grade, i put the flow as a point source (22 point sources side by side) and i am using roms_iview to check if the velocities corresponds with my input( river_transport), and this part its ok, but in the end of my river the u velocities sometimes is negative this represent a flow entering in the end of my river, and this is not expected.
I tried many lateral boundaries, I had the better result with this one:

! W S E N
! e o a o
! s u s r
! t t t t
! h h
!
! 1 2 3 4

LBC(isFsur) == Clo Clo Cha Clo ! free-surface
LBC(isUbar) == Clo Clo red Clo ! 2D U-momentum
LBC(isVbar) == Clo Clo red Clo ! 2D V-momentum
LBC(isUvel) == Clo Clo Rad Clo ! 3D U-momentum
LBC(isVvel) == Clo Clo Rad Clo ! 3D V-momentum
LBC(isMtke) == Clo Clo gra Clo ! mixing TKE

LBC(isTvar) == Clo Clo rad Clo\ ! temperature
Clo Clo rad Clo ! salinity

Physical Parameters, Grid: 01
=============================

388800 ntimes Number of timesteps for 3-D equations.
20.000 dt Timestep size (s) for 3-D equations.
30 ndtfast Number of timesteps for 2-D equations between
each 3D timestep.
1 ERstr Starting ensemble/perturbation run number.
1 ERend Ending ensemble/perturbation run number.
0 nrrec Number of restart records to read from disk.
T LcycleRST Switch to recycle time-records in restart file.
72 nRST Number of timesteps between the writing of data
into restart fields.
10 ninfo Number of timesteps between print of information
to standard output.
T ldefout Switch to create a new output NetCDF file(s).
100 nHIS Number of timesteps between the writing fields
into history file.
0 nQCK Number of timesteps between the writing fields
into quicksave file.
F LuvSponge Turning OFF sponge on horizontal momentum.
F LtracerSponge(01) Turning OFF sponge on tracer 01: temp
F LtracerSponge(02) Turning OFF sponge on tracer 02: salt
5.0000E-06 Akt_bak(01) Background vertical mixing coefficient (m2/s)
for tracer 01: temp
5.0000E-06 Akt_bak(02) Background vertical mixing coefficient (m2/s)
for tracer 02: salt
5.0000E-05 Akv_bak Background vertical mixing coefficient (m2/s)
for momentum.
3.0000E-04 rdrg Linear bottom drag coefficient (m/s).
3.0000E-03 rdrg2 Quadratic bottom drag coefficient.
2.0000E-02 Zob Bottom roughness (m).
2 Vtransform S-coordinate transformation equation.
4 Vstretching S-coordinate stretching function.
5.0000E+00 theta_s S-coordinate surface control parameter.
4.0000E-01 theta_b S-coordinate bottom control parameter.
20.000 Tcline S-coordinate surface/bottom layer width (m) used
in vertical coordinate stretching.
1000.000 rho0 Mean density (kg/m3) for Boussinesq approximation.
157.000 dstart Time-stamp assigned to model initialization (days).
20170101.00 time_ref Reference time for units attribute (yyyymmdd.dd)
0.0000E+00 Tnudg(01) Nudging/relaxation time scale (days)
for tracer 01: temp
0.0000E+00 Tnudg(02) Nudging/relaxation time scale (days)
for tracer 02: salt
0.0000E+00 Znudg Nudging/relaxation time scale (days)
for free-surface.
0.0000E+00 M2nudg Nudging/relaxation time scale (days)
for 2D momentum.
0.0000E+00 M3nudg Nudging/relaxation time scale (days)
for 3D momentum.
0.0000E+00 obcfac Factor between passive and active
open boundary conditions.
F VolCons(1) NLM western edge boundary volume conservation.
F VolCons(2) NLM southern edge boundary volume conservation.
F VolCons(3) NLM eastern edge boundary volume conservation.
F VolCons(4) NLM northern edge boundary volume conservation.
14.000 T0 Background potential temperature (C) constant.
35.000 S0 Background salinity (PSU) constant.
1027.000 R0 Background density (kg/m3) used in linear Equation
of State.
1.7000E-04 Tcoef Thermal expansion coefficient (1/Celsius).
0.0000E+00 Scoef Saline contraction coefficient (1/PSU).
1.000 gamma2 Slipperiness variable: free-slip (1.0) or
no-slip (-1.0).

And my .h file:

/* momentum equations */

#define UV_ADV /* use to turn ON or OFF advection terms */
#define UV_LDRAG
#define ANA_BTFLUX
#define ANA_BSFLUX
#define ANA_HMIXCOEF

/* general options */
#define SOLVE3D
#define MASKING

#define ANA_STFLUX
#define ANA_SMFLUX

#define ANA_INITIAL
#define ANA_FSOBC

But sometimes the velocity in u direction (in top levels) get negative. And I am assuming that in the bottom the velocity can be negative.
what should i have to do to get a right distribuition of velocities in the end of my river (west side)?
Attachments
grade.png

User avatar
kate
Posts: 4088
Joined: Wed Jul 02, 2003 5:29 pm
Location: CFOS/UAF, USA

Re: River Modelling

#2 Unread post by kate »

If you are imposing a river inflow on the eastern end, then you don't want a radiation condition there. If the western end is outflow, then that should have a radiation condition. Since your inflow is at the edge of the domain, you can use the river sources with a closed wall boundary condition or you can use a clamped boundary condition. Either way, you enforce the velocity as being purely incoming and you have to specify all the tracer values there.

andersonsoares
Posts: 4
Joined: Wed Oct 18, 2017 5:53 pm
Location: Federal University of Rio de Janeiro, LAMCE- COPPE

Re: River Modelling

#3 Unread post by andersonsoares »

Sorry, the inflow is on the west end. As you can see in the figure, the west end is closed ( the inflow is right).
When I put radiation condition on the eastern end, the outflow get wrong direction.



kate wrote:If you are imposing a river inflow on the eastern end, then you don't want a radiation condition there. If the western end is outflow, then that should have a radiation condition. Since your inflow is at the edge of the domain, you can use the river sources with a closed wall boundary condition or you can use a clamped boundary condition. Either way, you enforce the velocity as being purely incoming and you have to specify all the tracer values there.
Attachments
The inflow (figure to the left) is right (all positive) but the outflow (figure to the right) get wrong direction.
The inflow (figure to the left) is right (all positive) but the outflow (figure to the right) get wrong direction.

User avatar
kate
Posts: 4088
Joined: Wed Jul 02, 2003 5:29 pm
Location: CFOS/UAF, USA

Re: River Modelling

#4 Unread post by kate »

Is it going unstable? There's nothing in the radiation condition that guarantees outflow in all cells. The outgoing transport should match (roughly) the imposed inflow from the other end.

andersonsoares
Posts: 4
Joined: Wed Oct 18, 2017 5:53 pm
Location: Federal University of Rio de Janeiro, LAMCE- COPPE

Re: River Modelling

#5 Unread post by andersonsoares »

kate wrote:Is it going unstable? There's nothing in the radiation condition that guarantees outflow in all cells. The outgoing transport should match (roughly) the imposed inflow from the other end.
Kate, i would like to thank you for your help.

I will share what i choose as Lateral Boundary Condition and maybe this can be useful for someone.

LBC(isFsur) == Clo Clo Cha Clo ! free-surface
LBC(isUbar) == Clo Clo Fla Clo ! 2D U-momentum
LBC(isVbar) == Clo Clo Fla Clo ! 2D V-momentum
LBC(isUvel) == Clo Clo Rad Clo ! 3D U-momentum
LBC(isVvel) == Clo Clo Rad Clo ! 3D V-momentum
LBC(isMtke) == Clo Clo gra Clo ! mixing TKE

LBC(isTvar) == Clo Clo rad Clo\ ! temperature
Clo Clo rad Clo ! salinity

And now, the u velocity looks better on eastern end (outflow).
Attachments
Screenshot.png

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