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

Nature of C_{loss} coefficient for porous plate

Simon Waldman, modified 5 Years ago.

Nature of C_{loss} coefficient for porous plate

Youngling Posts: 4 Join Date: 7/16/14 Recent Posts
Dear forum,

Like a number of other forum users before me, I'm looking at representing tidal turbines in Delft3D-FLOW using porous plates.
Based on the information given in the manual, my understanding is that the c_{loss} parameter can be stated as,

c_{loss} = (- C_t A_t) / 2 dydz

where C_t is the thrust coefficient of the turbine(s), A_t is the total cross-sectional area of turbine rotor in the cell when viewed in the appropriate direction (total, because there may be more than one turbine), and dydz is the cross-sectional area of the cell in the direction being considered.

Intuitively, I think that this can be thought of as representing the proportion of the momentum passing through the cell that is removed, and on this basis must be between zero and one. (actually between zero and 0.5, given the division by two above)

However, the example values given in the manual are 800 and 1000, a discrepancy of some orders of magnitude! Some initial testing suggests that using values <0.5 in a model gives plausible results, wheras using values a thousand times higher looks more like a brick wall has been placed in the flow.

A number of people have asked the same, or substantially similar questions, before, but none has received a full answer[1]. Please can anybody clarify whether I have misunderstood somewhere, or whether the example values in the manual are implausible? Alternatively, any pointers as to how this is handled in the code might be helpful.

Many thanks

[1] Previous questions on the same topic: