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

Boundary conditions for z-model

Fernando Barreto, modified 7 Years ago.

Boundary conditions for z-model

Padawan Posts: 74 Join Date: 6/21/12 Recent Posts
Hy everyone,

I'm performing a 3D simulation for a region using z-model. I intend to use boundary conditions from HYCOM. HYCOM has 33 layers at greater depths. If I want to begin the simulation from this region, how would be the boundary conditions. Should I put in delft3d 33 layers (the most superficial at z = 0) and one more for the atmosphere, for example (34 in total). In this atmospheric layer I put all vaues iqual 0?. In regions closer to the shore, when the layers are truncated, and there are no more data, what do I put in the . Bct file [any flag (-999, for example) or 0?].

Qinghua Ye, modified 7 Years ago.

RE: Boundary conditions for z-model (Answer)

Jedi Council Member Posts: 610 Join Date: 3/2/11 Recent Posts
Hi Fernando,

You may notice that z-layer in Delft3D starts to count the layers from bottom. And I won't expect there is necessary for one layer extra for atmosphere. The layers in Delft3D is given as the following: (ztop-zbot) as the whole layer thickness and distributed as the ratio you specified in the mdf file.

And you can specify the values at the boundary the same way as in sigma layer model. For example, if you have a discharge at the boundary, you can just give one value and the model can judge how many layers are active in this time step and distribute the discharge vertically.

In case if you want to specify a velocity boundary, it is more complicated. You might have to find out which layer is active at first time step and specify the velocity at that layer. For other layers, you can just set to 0. There is a risk here. A miss-setting may lead a jet at the boundary.

I hope this might be a bit helpful.