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

how to set the bed composition in different layers and spatial variation

Wendy Ni, modified 8 Years ago.

how to set the bed composition in different layers and spatial variation

Youngling Posts: 3 Join Date: 12/20/11 Recent Posts
I am a neophyte of Delft3d in simulating hydrodynamic and sediment transportation process of coastal area. Recently, I have met some questions on the settings of initial bed composition and boundary condition, and if you could help me and give me some suggestion on them, I will really appreciate it.

The region of my investigation located in the coastal tidal flat, and the depth was from about -5m to +3m ODN. The composition of the bed is clay, silt and sand, whose contents varied spatially in tidal flat. The tidal range of this area ranged from 2m to 6m.

My question is:
1.If I want to make the bed composition of tidal flat into two layers, the first (top) layer has a spatially varying thickness and is mixed with mud (cohesive sediment) and sand (non-cohesive sediment). The mud content of this layer has the feature of spatial variation, which means the upper intertidal flat has nearly 70% mud content while the lower intertidal flat only has 5% or less. The second layer composes of uniform coarser sand (350um) without any mud in the uniform thickness.

In the sediment module, I gave three sediment fractions representing the bed composition. Mud1 and Sand1were in the top layer; Sand2 was in the second layer (see below A). To reveal the spatial varying characteristic, I used Delft3d-Quickin to make *.frc and *.thk file and write corresponding keywords in Delft3d-Flow-Additional parameters (see below emoticon. However, when running the simulation, it indicated that there were no thickness and mud content spatial variations at all; the bed composition was just the same as only give the value of the three fractions in Delft3d-Flow-Pysical parameters-Sediment, which meant the additional parameter setting didn’t work.

I was wondering if I wanted to accomplish the bed composition settings of spatial variations in layer thickness and mud content, how should I do?

Fraction1: mud1
Dry density: 380kg/m3
Thickness: 2m
Fraction2: sand1
Dry density: 1600kg/m3
Diameter: 150um
Thickness: 2m
Fraction3: sand2
Dry density: 1600kg/m3
Diameter: 350um
Thickness: 5m
Type: mass fraction
Sediment_mud1: # mud.frc#
Sediment_sand1: # sand.frc#
IniSedThick: #layer1_thick.thk#
Type: mass fraction
Sediment_sand2: 1
IniSedThick: 5

2.For the hydrodynamic boundary input of the model, there were two methods I used to provide: one was a nest grid from the overall grid in open sea; another was from hypothetical harmonic parameters.

In the nesting method, water level condition was acquired from the overall grid; the velocity was up to 1m/s in the Boundary 3. This might cause morphological unstable in the boundary when simulated the sediment transportation process. Under this circumstance, which position should the boundary be settled in?

In the method of providing hypothetical harmonic parameters, when Boundary1 and Boundary2 were set as Neumann Boundary with harmonic parameters (only M2), the velocity near Boundary3 was up to 2m/s. I was wondering the reason and how should I solve the problem.

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Boundary1* *Boundary2
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