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

odd/even refinement

Ed Atkin, modified 6 Years ago.

odd/even refinement

Padawan Posts: 27 Join Date: 3/27/12 Recent Posts

I have successfully been running a complex 3 domain model, no errors.
I do get the following warning from all domain logs:

*** WARNING The following line in the ddb-file defines a 1 to even domaindecomposition boundary:
Odd refinement is strongly advised

I am indeed running even refinements (5m to 10m, 10m to 20m).

This post is much like this post from 2011 by Murray Burling that received no replies:;jsessionid=CEAA63133C61B9D20218A1F39C47A873

From the post Murray explains he ran odd refinements and still got the same message.

I checked the tri-diag.zz(n) files from the domain decomp example and there is no such warning (so perhaps Murray didn't quite get his odd refinements right)

Is it an issue using even refinements???

Adri Mourits, modified 6 Years ago.

RE: odd/even refinement (Answer)

Yoda Posts: 1221 Join Date: 1/3/11 Recent Posts
Hi Ed,

Odd refinements are (still) strongly advised. The algorithm is developed on this assumption. After that, bugs related to even refinements are solved. So with odd refinements you are on the safe side.

But even refinements might work correctly if they are not a critical part of your model and if it is "smoothly" modelled (small bed level gradient along the boundary, preferably additional local eddy viscosity). But as soon as you see strange results, you should switch to odd refinement.