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

Optimal number of Cores

Nophi Biton, modified 6 Years ago.

Optimal number of Cores

Padawan Posts: 38 Join Date: 8/1/13 Recent Posts
Hello everyone,

We are currently using the MPI mode of Delft3D for parallel computation. Is there an optimal number of cores to be used for the specific simulation (depending on the parameters in the model or the phenomenon to be simulated)?

We tried using 8, 24, 48 cores for the simulation and considerable decrease in computing time from 8 cores to 24 cores but as we used 48 cores, there is an increase in computing time? thus the question is how can determine the number of optimal cores to be used.

Adri Mourits, modified 6 Years ago.

RE: Optimal number of Cores (Answer)

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

The optimum number of cores does not only depend on your model, but also on the hardware and operational software used.

Different factors may indeed lead to more than one (local) optimum. For example from 8 to 24 is slower because of increased communication, 24 to 48 is faster because the model now fits better in the memory cache or by accident you are now using other machines having a faster inter-node communication or the system has been upgraded etc.

Because of all these different factors, I don't think there is a general rule that can help you to find the optimum number of cores. Just trial and error.