open TELEMAC-MASCARET The mathematically superior suite of solvers

Dear all,

I met some problem about measuring residence time in a bay using telemac2d.

First,I release the tracer in the whole Bay domain, and measure the mean tracer concentration in the bay domain. Then I found that the tracer mass are not conservative which might because of the default setting of tracer advection scheme = 1.
So I try to repeat the suggestion setting from Mr. Hervouet in previous post:

TIDAL FLATS : YES
OPTION FOR THE TREATMENT OF TIDAL FLATS : 1
TREATMENT OF NEGATIVE DEPTHS : 2
SCHEME FOR ADVECTION OF TRACERS : 13/14
COEFFICIENT FOR DIFFUSION OF TRACERS = 0.1
MAXIMUM NUMBER OF ITERATIONS FOR DIFFUSION OF TRACERS : 200

But there is always error of ‘GRACJG (BIEF) : EXCEEDING MAXIMUM ITERATIONS:’ happening. I have tried reduce the time step and increase MAXIMUM NUMBER OF ITERATIONS but the model always 'EXCEEDING MAXIMUM ITERATIONS:'. I think the potential reason might be the large tidal flat area in this bay. Is there any suggestion to fix this problem? Many thanks.

Another question is that how could I chose the COEFFICIENT FOR DIFFUSION OF TRACERS? Since this value linked with mesh resolution and I have high resolution in this bay area, should I apply different tracer diffusion coefficient regarding different mesh resolution?
Any advice will be welcome.

Best Wishes,
Bin