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

Delft3D-FLOW "Mass closure error" warning

Abdulla Mohamed, modified 6 Years ago.

Delft3D-FLOW "Mass closure error" warning

Youngling Posts: 16 Join Date: 6/12/13 Recent Posts

I was wondering if anyone might be help me out with what this warning means. I tried to look at the flow manual but am unable to find this warning in there.

*** WARNING Mass closure error exceeds 0.450E-04 after 69 timesteps.

I was getting this warning for every time step of my run.
I am trying to run my model with two open boundaries, Downstream and Upstream of the model.
Time series water levels are imposed on the down stream boundary.
Time series water levels and flow are imposed on the upstream boundary.

Any help on this will be much appreciated.

Thanks very much
Anas Rahman, modified 6 Years ago.

RE: Delft3D-FLOW "Mass closure error" warning

Youngling Posts: 21 Join Date: 10/4/13 Recent Posts
Hi Abdulla,

I had the same problem with my model. I am using domain decomposition for my models, and one of the domains gives the same warning " WARNING Mass closure error exceeds ...."

However, the simulation finished without any errors, and I am currently analysing the results.

So far I noticed that my results produces a lot of "noise" i.e. not smooth when compared to measured data.

I am going to re-run again my model with new parameters setting.

Anyone who can help us on this matter will be greatly appreciated

Best regards

Abdulla Mohamed, modified 6 Years ago.

RE: Delft3D-FLOW "Mass closure error" warning

Youngling Posts: 16 Join Date: 6/12/13 Recent Posts
Hi Anas,
thanks for your response
I have been trying different things, but have not been able to get rid of this warning just yet. But If I do find out something I will be sure to let you know.
Could you also let me know if you are able to find out why this warning happens.

Rodrigo da Silva, modified 3 Years ago.

RE: Delft3D-FLOW "Mass closure error" warning

Youngling Posts: 1 Join Date: 5/28/17 Recent Posts

have any of you solved this warning? It seems like a problem of vertical decomposition, and I can only solve it when I change the number of layers.

I'll be glad with any help,
Adri Mourits, modified 2 Years ago.

RE: Delft3D-FLOW "Mass closure error" warning

Yoda Posts: 1224 Join Date: 1/3/11 Recent Posts
Hi Rodrigo,

1. Try to locate where the problems start (in space and time) and look if there is a reason for it. Try to solve it locally:
When it starts at a DomainDecomposition boundary, check that the grids are connected smoothly, without big jumps in the vertical, without big jumps in cell sizes.
2. What happens when you decrease the timestep? It should run more smoothly.
3. (Not nice, but may be helpfulemoticon When the problems occur on a specific spot at a DomainDecompostion boundary, you can add viscosity locally to "damp" the effects.