open TELEMAC-MASCARET The mathematically superior suite of solvers

Hello,
I am carrying out 3D simulation using a rectangular domain, with TEMPERATURE as TRACER at a SOURCE POINT. I have used the following KEYWORDS in the STEERING FILE

INITIAL VALUES OF TRACERS = 0.0
VALUES OF THE TRACERS AT THE SOURCES = 215

The simulation time is 4 hours. In the result, i could observe that the solution contains tracer concentration (at source point) to be lesser than that of the value provided (215).
I would like to know
a)why does this happen?
b)How to control the tracer value at source point in case if i want to have source point tracer concentration to be 215 for the entire 4 hours of simulation?

Thanks
Sathya

Hello,

This is due to the fact that sources bring the correct flux, i.e. the correct quantity of tracer: discharge*(tracer value)*dt at every time step. Then as this is averaged over the basis of the point, which is like a volume around the point, the prescribed value is like diluted. The larger the mesh around the source point, the more it is diluted, so you never see the prescribed value at the source point but you get the correct quantity in the domain, which is what you want.

With best regards,

Jean-Michel Hervouet

Hello,
I would like to know the name of the subroutine which does the calculation of correct quantity of tracer.

Thanks
Sathya

Hello,
I understand that the correct quantity of tracer is given by the formula : discharge*(tracer value)* dt

1) Is the discharge used here include tracer discharge also (i.e water discharge + tracer discharge)?

2) At every time step, is it the previous time tracer value applied to find the correct quantity of discharge?

3)"The larger the mesh around the source point, the more it is diluted" - This implies that the concentration of tracer at SOURCE POINT will be MESH SIZE DEPENDENT! .
If the mesh element area around the source point tends to become zero, will the dilution also tend to get reduced?

Thanks in advance
Sathya

Hello

You can edit subroutine source_trac.f (folder sources/telemac3d) in which is given some exemples of sources.
Otherwise, all the advection-diffusion process is achieved through subroutine cvdf3d.f. Source terms are computed and managed in subroutine diff3d.f

I hopte that this helps

with my best regards

Riadh ATA

Hello,

To complement the information given by Riadh, the mass of tracer is computed in subroutine mass3d, it is the dot product between the nodal values of the tracer and the volumes around points. The volume around points are the integrals of the test functions. They must be taken at the right time because the mesh evolves with time, VOLUN for the old time and VOLU for the new time.

With best regards,

Jean-Michel Hervouet