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

bed shear stress in shallow waters

Rachel Allen, modified 1 Year ago.

bed shear stress in shallow waters

Youngling Posts: 2 Join Date: 10/27/18 Recent Posts


I'm looking in to bed shear stress model outputs, and comparing to some ADV data collected in a shallow estuary (1-2 m MLLW, in  San Francisco Bay).  I'm a relatively new user for the Delft models, so I apologize if this is not the correct place for this question...

1) where are the bed shear stresses from currents, waves, and currents and waves reported?  I'm currently running the flow and wave modules in Delft3D4, and I've found that the trim file gives "bed shear stress", "staggered bed shear stress", and "max bed shear stress", and the trih file gives "bed shear stress".  I assume that these are bed shear stresses from currents and waves, tau_m (FLOW manual eq. 9.195) and tau_max (eq. 9.197).  But section 9.7.5 of the FLOW manual discusses tau_c and tau_w,  I'd love to determine if I can output those parameters from the model as well, and I haven't yet figured out how to do this from reading the manual.

2) how does the model account for wave penetration to the bed when computing bed shear stress?  My understanding is that wave spectra are reported for the surface, so tau_peak is the peak wave period at the surface.  But in this shallow estuary with tidal water level changing from 1 m above bed to 3 m  above bed, 2 second waves may penetrate to the bed on low water, but not on high water.  So, since tau_w is computed from u_orb, which is computed from omega (the wave frequency), the relevant omega to use at the bed may not be the same as at the surface where the waves are computed.  I would guess that this is accounted for in the model, but I haven't figured out how yet...  

Thank you for your help!