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

NEFIS Error: Cannot open file

Martin Schueder, modified 6 Years ago.

NEFIS Error: Cannot open file

Padawan Posts: 52 Join Date: 10/8/13 Recent Posts

I have been plagued consistently by the following error that I cannot seem to fix:

*** Deltares, FLOW2D3D Version, Feb 3 2014, 12:22:21
*** built from :
*** runid : C2
*** date,time : 2014-02-07, 11:42:31

*** MESSAGE Executable for 32-bits platform.
*** MESSAGE Double precision computation using reals of kind 8
*** Start of User Defined Model description
- Full Train
*** End of User Defined Model description

*** MESSAGE Using UNESCO density formulation by default
*** MESSAGE Momentum solver cyclic method is specified
*** MESSAGE DRYFLP and DPSOPT both specified in MD-file. Using DPSOPT: MAX

Nefis error:
NEFIS message 8030:
Cannot open file 'trih-C2.dat' for access type 'u' --- Permission denied
While trying to open dat/def-file trih-C2

It is frustrating me because sometimes a model will run, but then I will change something, receive this error, and continue to receive the error on the next run even if I return everything back to a state where the model ran successfully. I have tried deleting all previous com, history, map files between runs and this does not solve the problem.

What does this error mean? I cannot decipher any methodical pattern for when it appears in my model, it seems random to me. How can I get rid of this?

Note: Tutorial files run successfully along with models I have made in the past before I cleared my Deltares directory and re-installed. I do not think I made a mistake in this because models still run sometimes but I could be wrong...

Thanks in advance,

Adri Mourits, modified 6 Years ago.

RE: NEFIS Error: Cannot open file

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

This error appears when Delft3D-FLOW does not have permission to write to the specified file.

The first thing to check is whether you have write permission in the work directory or if the file is blocked in some way (or if your disk is full). You checked this already: if you can delete this file and start a new calculation and it produces output, this is not your problem.

The second thing to check is whether there is another process that blocks Delft3D-FLOW from writing to this file. Examples of possible processes that may cause this:
  • Virus checker/anit virus software
  • Automatic backup systems

Unfortunately this type of problem is difficult to solve. It heavily depends on the system you are using and you can never be sure that you disabled all possible blocking processes.

Some tips:
  • Try to find out what the characteristics are of the problem. Does it always happen at the same time of the day/week? Does it only happen in a directory with a certain name? Or when the file has a certain name?
  • Try to run the calculation on another machine. For example a colleagues one. Preferably a machine as clean/empty as possible.

Hope this helps.


Martin Schueder, modified 6 Years ago.

RE: NEFIS Error: Cannot open file

Padawan Posts: 52 Join Date: 10/8/13 Recent Posts
Hi Adri,

Success! I removed my auto-backup disk and my anti-virus software and now my models can now run and their com files can write successfully. If they cease to do so after I re install my antivirus then I will post back here.

Thank you again for your effective solution!