intro story D-Flow FM

 

D-Flow Flexible Mesh

D-Flow Flexible Mesh (D-Flow FM) is the new software engine for hydrodynamical simulations on unstructured grids in 1D-2D-3D. Together with the familiar curvilinear meshes from Delft3D 4, the unstructured grid can consist of triangles, pentagons (etc.) and 1D channel networks, all in one single mesh. It combines proven technology from the hydrodynamic engines of Delft3D 4 and SOBEK 2 and adds flexible administration, resulting in:

  • Easier 1D-2D-3D model coupling, intuitive setup of boundary conditions and meteorological forcings (amongst others).
  • More flexible 2D gridding in delta regions, river junctions, harbours, intertidal flats and more.
  • High performance by smart use of multicore architectures, and grid computing clusters.
An overview of the current developments can be found here.
 
The D-Flow FM - team would be delighted if you would participate in discussions on the generation of meshes, the specification of boundary conditions, the running of computations, and all kinds of other relevant topics. Feel free to share your smart questions and/or brilliant solutions! 

 

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We have launched a new website (still under construction so expect continuous improvements) and a new forum dedicated to Delft3D Flexible Mesh.

Please follow this link to the new forum: 
/web/delft3dfm/forum

Post your questions, issues, suggestions, difficulties related to our Delft3D Flexible Mesh Suite on the new forum.

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** PLEASE TAG YOUR POST! **

 

 

Sub groups
D-Flow Flexible Mesh
DELWAQ
Cohesive sediments & muddy systems

 


Message Boards

Bubble plume boundary conditions not working in z-model

DG
Dougal Greer, modified 8 Years ago.

Bubble plume boundary conditions not working in z-model

Youngling Posts: 4 Join Date: 10/28/11 Recent Posts
Hi,

I am using bubble plume boundary condition in simulation of a lake. For now I have nothing else driving the model so any induced velocities are from the bubble plume boundary conditions (.bub, .scr, .dis files). I set it up as a sigma model and it seems to run OK. The bubble plume induces vertical and horizontal velocities that look reasonable. However I get the following warning in my .diag file:

*** WARNING Combination of sigma-model and bubble screens has not yet been tested

So I change my setup to be a z-model with a similar setup to my sigma model. I get vertical velocities in the right place, but they don’t induce any horizontal velocities which doesn’t really make any sense physically. There does not appear to be any documentation suggesting that a sigma or z-model should be used preferentially. Has anyone got any idea why the z-model (which appears to be the one that has been tested) would not work?

Many Thanks,

Dougal.
Erik de Goede, modified 8 Years ago.

RE: Bubble plume boundary conditions not working in z-model

Youngling Posts: 13 Join Date: 1/7/11 Recent Posts
Dear Dougal,

The warning "Combination of sigma-model and bubble screens has not yet been tested" is in my opinion outdated. In recent years we have done important studies with bubble screens in Dutch rivers, in whcih sigma models were used. Our Delft3D-FLOW test bench contains test cases for this. So, there is no reason to have any doubts about the implementation. This hods for both the sigma model and the Z-model.

By the way, extensive documentation about bubble screens can be found in Appendix B.22 of the User Manual.

You seem to have a problem when you switched from sigma-model to Z-model. Unfortunately, the layer numbering in both systems is different (layer 1 is the top layer in a sigma model, but is the bottom layer in a Z-model). Did you perhaps forget to adapt the layer number at which the bubble screen discharges? Or to adapt the initial vertical stratification (if present)?

With kind regards,

Erik de Goede
Deltares
DG
Dougal Greer, modified 8 Years ago.

RE: Bubble plume boundary conditions not working in z-model

Youngling Posts: 4 Join Date: 10/28/11 Recent Posts
Dear Erik,

Thanks very much for your reply. I am not entirely sure what changed but the z-model is now working. However...

...I have realised that the velocities that are being generated are definitely not sensible. I have created a very simple test scenario to illustrate the problem (attached to this post). I am using a really big plume just to try and move some water. Horizontal velocities are of the order of 10E-13 m/s which are in the right direction but obviously way way too small (almost round off error). Vertical velocities are being generated in the range of -0.1 to -1 m/s (wrong direction?) but only at the cell where the bubble plume is placed, vertical velocities are zero everywhere else for all except the top layer where they are very small. And this raises a concern about mass conservation.

I have been using appendix B.22 but I can't see anything that helps. The problem persists with the latest version of the code.

If anyone feels like checking the test run attached I would really appreciate it (the problems appear almost immediately so its quick to test).

Thanks again Erik,

Dougal.

Attachments: