TELEMAC-MASCARET Forum: Tracer with negative value ? (1/1)

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TOPIC: Tracer with negative value ?

Tracer with negative value ? 11 years 3 weeks ago #10848

csee

Hello,

I'am running a simulation with tracers (actually sediment) and at the surface or sometimes at the sides of the mesh I get slightly negative values (those points are far from the entrance).

I'am using advection scheme 5 for tracers, and am really surprised to get negative values (not huge but definitvely negative).

Where are possible causes for this ? Should I use a different advection scheme?

I guess I really need some hints here,
kind regards
csee

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Tracer with negative value ? 11 years 2 weeks ago #10943

jmhervouet

Hello,

Yes, this is surprising, unless:

* You have tidal flats, in which case the PSI scheme is not guaranteed to work (use scheme 14 instead).

* You have only a partial mass-lumping of depth, and consequently a partial mass-lumping of the tracer diffusion, and this could be the problem.

* it is due to the settling velocity step (so far an upwind scheme without guaranteed positivity, we are working on several others for the next version).

With best regards,

Jean-Michel Hervouet

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