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Boundary effect

SL
S L, modified 3 Years ago.

Boundary effect

Youngling Posts: 8 Join Date: 8/13/15 Recent Posts
Hi there,

I've been using Delft3D to run water quality modelling. I've been playing with the input at the boundaries and notice that the loading at the boundary tend to be lower than my input. For example, I have put 5000000 g/m3 at my boundary but the value seem to drop to approximately 12 g/m3 overtime at the boundary area. I would like to understand the mechanisms or boundary effect within the water quality model simulation. Can anyone help?
AM
Arjen Markus, modified 3 Years ago.

RE: Boundary effect (Answer)

Jedi Knight Posts: 222 Join Date: 1/26/11 Recent Posts
This might happen if the flow at the boundary is outward - then the substance would enter the model area only through dispersion _against_ the flow.

What kind of water system are you modelling? Can you check that the flow is indeed pointing out of the model area?
SL
S L, modified 3 Years ago.

RE: Boundary effect (Answer)

Youngling Posts: 8 Join Date: 8/13/15 Recent Posts
Hi Arjen,

Thanks for your response. I'm actually modelling a coastal system with inputs from a few rivers. To be more exactly it is a strait/channel that opens up to the sea on one side and blocked by a causeway on the other side. The flow is pointing into the model area. Would the force or magnitude of the flow influence the boundary discharge?

Thanks in advance.
AM
Arjen Markus, modified 3 Years ago.

RE: Boundary effect (Answer)

Jedi Knight Posts: 222 Join Date: 1/26/11 Recent Posts
The flow rate will most definitely influence the amount of substance that enters the model area, but we are talking about differences of several orders of magnitude. So the flow rate seems to be very small wrt the ambient flow in the main part of the model. What you could do is put a monitoring point or a monitoring area around the inflows and turn on the mass balance output. This ought to help identifying the problem.

Be sure to use "continuity"| as one of the substances, as that helps with visualising the flows.