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

Have a time step less of less than 1 minute

Martin Schueder, modified 6 Years ago.

Have a time step less of less than 1 minute

Padawan Posts: 52 Join Date: 10/8/13 Recent Posts

I recall reading it is possible to make your time step less than one minute, and from reading papers I have seen that some users are able to do so. So far I cannot find out how to do this from searching the forums and manuals. How can I make my time step less than one minute?

Thank you!

Martin Schueder, modified 6 Years ago.

RE: Have a time step less of less than 1 minute (Answer)

Padawan Posts: 52 Join Date: 10/8/13 Recent Posts
I was able to answer my own question but will leave the question up in case it may help someone else.

All I had to do was delete the .def and .dat files that were generated in previous runs of the same model but at different time steps. If the files remained in the working directory, FLOW would try to use the TSCALE used in the last run recorded in those files, which would then conflict with the new specified time step of <1 minute. I think deleting those files made FLOW generate new .def and .dat files which contained the new specified timestep. This may not actually be what is happening, but I was able to successfully set a time step of 6 second.

Adri Mourits, modified 6 Years ago.

RE: Have a time step less of less than 1 minute

Yoda Posts: 1224 Join Date: 1/3/11 Recent Posts
Hi Martin,

Very good.

It's a good habit to clean the work directory as much as possible before doing a calculation.

FLOW cannot delete the com-files, because they might contain data created by another application (WAVE for example), possibly used as input somewhere.