open TELEMAC-MASCARET The mathematically superior suite of solvers

Hi

I have been trying to figure out the units of the outputs showed in the mass balance portion of the output file:

TRACER 1
ADVECTIVE FLUX THROUGH BOUNDARIES OR SOURCES : -350.2731
DIFFUSIVE FLUX THROUGH THE BOUNDARIES : -203.7670
MASS AT THE PREVIOUS TIME STEP : 0.1915135E+10
MASS AT THE PRESENT TIME STEP : 0.1915136E+10
MASS EXITING (BOUNDARIES OR SOURCE) : -1108.080
ERROR ON THE MASS DURING THIS TIME STEP : -0.1697713E-02

I tried to look for the units in subroutine BIL3D, but I got very strange units for the Fluxes (FLUDI).

Where can I get more information of the units of these variables.

Thanks so much

Viviana

Hello,

Actually the unit is mass if your tracer is in kg/m3, but it may be anything else. What we call mass here is the integral of the tracer over the domain, so actually the unit is (the tracer unit)*m3.

Regards,

Jean-Michel Hervouet

Thank you so much, if I understand you right, the units for the mass are (tracer unit)*m3. What about the units for:

ADVECTIVE FLUX THROUGH BOUNDARIES OR SOURCES
DIFFUSIVE FLUX THROUGH THE BOUNDARIES

Kind Regards

Viviana

Hello,

It is the same principle : the fluxes are the "mass" (as explained in previous post) per unit of boundary (m in 2D and m2 in 3D) that crosses the boundary per second.

JMH

Thank you very much, I got confused while checking subroutine BIL3D in which the calculation for FLUDI (diffusive flux) is:

FLUDI= FLUDI+ATABOS*VOLU2D*TA

The units of ATABOS are = (W/m2.°C)/(J/kg°K)
I assume the units of VOLU2D are m2
The units of TA are °C

So, the units I get for this flux are not °Cm3/m2s, that is why I am getting confused, and I am not sure how FLUDI ends up having the flux units that you mentioned.

Thanks

Viviana

Can you please explain to me how FLUDI in subroutine BIL3D end up having flux units?

Thanks so much

Hello,

OK. You see that in BIL3D the flux has the dimension of :

ATABOF * VOLU2D * TA

We have also :

NUT * D(TA)/DN = ATABOF * TA (boundary condition) then ATABOF is in M/S,

FLUDI is thus in :

M/S * M**2 * TA, that is M**3/S * TA

FLUDI*DT is taken into account in the mass balance, so if TA is given as KG/M**3, FLUDI*DT will be in KG. But TA may be given in any unit by the user (unless it is an active tracer) so this is an example.

With best regards,

Jean-Michel Hervouet

Hello

Thank you very much for your reply. In my case I have temperature which is an active tracer, so for:

DIFFUSIVE FLUX THROUGH THE BOUNDARIES = -FLUDI

which means that the units are m^3*°C/s. I am correct??

Thanks so much

Viviana

That's it!

JMH