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! 


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: 

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





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


Message Boards

numerical instability in domain decomposition with inclined bathymetry

Markus Gross, modified 2 Years ago.

numerical instability in domain decomposition with inclined bathymetry

Youngling Posts: 7 Join Date: 12/10/11 Recent Posts



We are trying to run a domain decomposition model but run into several difficulties. Attached one of our problems as Smallest Possible Case.


It is a cut out rectangle and inside it is a higher resolution grid with a 1:3 ratio.


It is currently setup as spherical, but I converted it into Cartesian at some point and it did not change anything. We also tried the recent trunk version.


In this case there are no open boundaries. So everything should stay within the numerical noise of the solver. The bathymetry is inclined, with a constant gradient.


In a relatively short period it spins up a significant instability, originating from the domain decomposition boundary, which eventually leads to model failure. For me:


 Time to finish   2m 14s,   33.5% completed, time steps left  766
 Flow exited abnormally


We must be missing something obvious, but with now two weeks of searching I cannot find it.


Does anybody have any advice? Is there something really silly in the setup?


I feel that without resolving this, going to more complex bathymetries and boundary conditions would not make any sense.


Any help/advise would be greatly appreciated!!


Best wishes,



Frank Platzek, modified 2 Years ago.

RE: numerical instability in domain decomposition with inclined bathymetry

Youngling Posts: 3 Join Date: 3/24/11 Recent Posts

Hi Markus,

Thanks for your post. I will have a look at your model to see what goes wrong.

Best regards,