Message Boards

Back

Outlet water quality boundary conditions

Martin Schueder, modified 5 Years ago.

Outlet water quality boundary conditions

Padawan Posts: 52 Join Date: 10/8/13 Recent Posts
Hello,

I am modeling a waste stabilization pond with a flow inlet and a flow outlet. I have my initial conditions for my chemical species of interest (I am modeling pH so mostly those in the dissolved inorganic group + some I added) and the water quality inlet boundary conditions as concentrations of the chemical species entering the pond.

What I do not understand is how I could specify the outlet boundary conditions for these chemical species as concentrations. I am modeling the pond to determine its treatment efficiency, a reflection of how much the concentration of these components has been reduced in the outlet relative to what the concentration was in the inlet.

How is it that I can specify the very thing I am trying to model, which is the outlet concentration of my components as they undergo change within the pond as a result of chemical and biological processes, as a boundary condition?

I understand that for the numerical scheme to function I need 2 boundary conditions, but I do not seem to be able to define the boundary as anything other than a Dirichlet condition. What about a Neuman condition? Is there any way to get around the need to specify the outlet concentrations of the chemical species in the pond?

Many thanks,

Martin
Christophe Thiange, modified 5 Years ago.

RE: Outlet water quality boundary conditions (Answer)

Jedi Knight Posts: 125 Join Date: 11/15/12 Recent Posts
Hi Martin,

Concentration values at boundaries won't influence the mass of your modelled substances unless those boundaries have an incoming flow.
In your case it seems like the flow at the outlet is unidirectional, hence the conditions you specify there will have no effect, you might as well set them to -999.

Hope this helps.
Christophe
Martin Schueder, modified 5 Years ago.

RE: Outlet water quality boundary conditions

Padawan Posts: 52 Join Date: 10/8/13 Recent Posts
Thank you Christophe, this clears things up for me.

Martin