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

*.ssn is not being generated

Tamara Faya, modified 6 Years ago.

*.ssn is not being generated

Youngling Posts: 1 Join Date: 1/6/14 Recent Posts
Hi !
I am running de example of WAVE tutorial 1_siu-lam, it runs with some warnings, finish ok, but it does not generate the file *.ssn. What could it be the problem? I've checked the *.mdw file and the output section is well defined.

The warnings said :
accuracy OK in 79.58 % of wet grid points ( 98.00 % required)

** WARNING : Differences in wave height at the boundary
Relative difference between input and computation >= 0.10

Could this be part of the problem ?
i would appreciate any help.
Adri Mourits, modified 6 Years ago.

RE: *.ssn is not being generated (Answer)

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

The ssn-file is not generated automatically. You have to create it yourself using Delft3D-GPP.

The Delft3D setup contains the manual "Delft3D-GPP_User_Manual.pdf".


Diego Pedrozo-Acuña, modified 6 Years ago.

RE: *.ssn is not being generated

Youngling Posts: 6 Join Date: 4/9/13 Recent Posts
Hello Adri,

I'm having the same warning as Tamara about the difference in wave height at the boundary.
In the print file I just see that a number of warnings of this kind are prompted and then the model just stops.

Do you have any idea what could be wrong? Or what this warning is related to?

Hope you can help.


Diego Pedrozo-Acuña, modified 6 Years ago.

RE: *.ssn is not being generated

Youngling Posts: 6 Join Date: 4/9/13 Recent Posts
Hello again,

I solve this for my case.
As far as I can see this error is related to the spectral resolution, specifically in the directional space.
I was using a complete circle divided into 36 directions, i.e., 36 bins. Increasing the number of directions taken to 40 improves the representation of the distribution hence improving the accuracy on computing Hs at the boundary.

Hope this helps anyone having this issue.