Boundary Numerical Instability  Delwaq  Delft3D
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DELWAQDELWAQ is the engine of the DWater Quality and DEcology programmes of the Delft3D suite. It is based on a rich library from which relevant substances and processes can be selected to quickly put water and sediment quality models together. The processes library covers many aspects of water quality and ecology, from basic tracers, dissolved oxygen, nutrients, organic matter, inorganic suspended matter, heavy metals, bacteria and organic micropollutants, to complex algae and macrophyte dynamics. High performance solvers enable the simulation of long periods, often required to capture the full cycles of the processes being modelled. The finite volume approach underlying DELWAQ allows it to be coupled to both the structured grid hydrodynamics of the current Delft3DFLOW engine and the upcoming DFlow Flexible Mesh engine (1D2D3D) of the Delft3D Flexible Mesh Suite (or even other models such as TELEMAC). 'DELWAQ in open source' is our invitation to all leading experts to collaborate in further development and research in the field of water quality, ecology and morphology using Delft3D. Feel free to post your DELWAQ related questions or comments in this dedicated forum space. If you are new to DELWAQ, the tutorial (in the user manual) is a good place to start. A list of DELWAQ related publications is available here. ** PLEASE TAG YOUR POST! **  Sub groups

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Boundary Numerical Instability
Fernando Barreto, modified 6 Years ago.
Boundary Numerical Instability
Padawan Posts: 74 Join Date: 6/21/12 Recent PostsIn another configuration I imposed current in north bound., and in the half of the east boundary; the remaning sections was elevation type (south and the rest of east). In this configuration was also generated a jet in the interface between bound types (fig). The jet can be seen in the east boundary.
Someone knows how to solve this. Can this be related with the zmodel? if not, any advice?
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Steven Ayres, modified 6 Years ago.
RE: Boundary Numerical Instability
Padawan Posts: 33 Join Date: 4/21/11 Recent PostsWere you able to resolve the boundary problems in your model? I have something similar going on in my 18level Zmodel with salinity. The model is creating velocity jets in the middle of an open stage boundary. I assume this has something to do with the salinity constituent but I'm not sure how to go about fixing the problem.
Thanks,
Steve
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Fernando Barreto, modified 6 Years ago.
RE: Boundary Numerical Instability (Answer)
Padawan Posts: 74 Join Date: 6/21/12 Recent Postsmy problem was the input of different boundary conditions (velocity and wl) in adjacent boundaries. This was resolved when I used riemann boundary conditions. What's your model configuration? boundary type, dimension?
regards,
Fernando
Steven Ayres, modified 6 Years ago.
RE: Boundary Numerical Instability
Padawan Posts: 33 Join Date: 4/21/11 Recent PostsA formula is given in the manual to determine the alpha coefficient 
Equation 9.76, Water level boundary: alpha = Td * sqrt(H/g), where Td is the time it takes for a free surface wave to travel from the left boundary to the right boundary of the model area.
Since the model is around 30 miles (48 km) across the shortest open tide boundary, and assuming the tidal wave travels around 30 miles/hour or 13.4 m/s, Td would equal 3600 seconds. Using a typical depth of 200 meters at the open boundary, alpha would be on the order of 16,000. Does that sound right?
Fernando Barreto, modified 6 Years ago.
RE: Boundary Numerical Instability
Padawan Posts: 74 Join Date: 6/21/12 Recent PostsWhen I use WL boundaries I usually put alpha as 1000. I didn't know how to calculate alpha, it's really to know. In Riemman we didn't use alpha, Riemann is a weaky reflective boundary condition, so I don't know a lot about alpha.
There are many possibilities to cause your error. Could you attach your model ?, I think it's easier to help.
Regards,
Fernando Barreto