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! 

 

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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: 
/web/delft3dfm/forum
Post your questions, issues, suggestions, difficulties related to our Delft3D Flexible Mesh Suite on the new forum.

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Sub groups
D-Flow Flexible Mesh
DELWAQ
Cohesive sediments & muddy systems

 

Message Boards

Sediment Simulation - TriDiag File

U
Patrick Specht, modified 6 Years ago.

Sediment Simulation - TriDiag File

Hallo everyone,

within my actual sediment simulation I get follwoing lines in the tri-diag-files:

Sediment erosion shortage at NM 6757 Fraction: 1 Mass available : -0.2684E-04 Mass to be eroded: -0.2684E-04

What does that exactly mean and how can I avoid that problem?

Many thanks and kind regards.
Patrick
Qinghua Ye, modified 6 Years ago.

RE: Sediment Simulation - TriDiag File

Jedi Council Member Posts: 610 Join Date: 3/2/11 Recent Posts
Dear Patrick,

The message means in that cell, there is no sediment left for erosion at this timestep (bare bed, at least seem from the model ). There is possibility that this cell would get sedimentation as well. So it is not a problem, just a message for you to be aware of.

Regards,

Qinghua
U
Patrick Specht, modified 6 Years ago.

RE: Sediment Simulation - TriDiag File

Dear Qinghua,

thank you for your answer.

I get this warnings right after starting the morphological changes and I have an initial sediment layer thickness of 25 m (uniform). That's why I wondered, why there should be no sediment left for erosion.

Kind regards.
Patrick
Qinghua Ye, modified 6 Years ago.

RE: Sediment Simulation - TriDiag File

Jedi Council Member Posts: 610 Join Date: 3/2/11 Recent Posts
Hi Patrick,

I would not expect so as well. Did you observe big shear stress at the points as well? A bit strange and we need more info to analyze it.

Regards,

Qinghua
Ahmed Elkut, modified 1 Year ago.

RE: Sediment Simulation - TriDiag File

Youngling Posts: 11 Join Date: 5/20/14 Recent Posts

Hi everyone

I keep getting the same warning with initial sediment thickness of 5 meters, and I do not get it, I don't understand where is the erosion shortage occur for example if the error states: Sediment erosion shortage at NM 18538 Fraction: 1 Mass available : -0.138E-02 Mass to be eroded: -0.138E-02 

1. Where is that cell (NM 18538), does it mean (n,m)=(185,38) or (18,538)?, which is not either of them for me, or it is something else?

2. How can the mass available is exactly equal to the mass to be eroded?

3. How can I keep getting this error at the early stage of my simulation with maximum cum/erosion/sedimentation not exceeding 0.3m?

4. Does this error impact my simulation results, even though they qualitatively make sense?

I will appreciate any help

Thanks

Richard Measures, modified 1 Year ago.

RE: Sediment Simulation - TriDiag File

Jedi Knight Posts: 178 Join Date: 3/23/11 Recent Posts

Hi Ahmed,

A few thoughts in (partial) answer to your questions:

1. The reference to NM 18538 I think refers to an internal model coordinate system where all cells are given a unique "nm" number. In the source code there is a function called "n_and_m_to_nm.f90" which uses the calculation "nm = n + nmaxddb * (m - 1 + ddb ) + ddb". ddb relates to domain decomposition so assuming you're not using multiple domains this simplifies to: NM = N + Nmax * (M-1). Using this equation you should be able to convert NM back to N & M based on Nmax.

2. I have no idea!

3. Do you have multiple sediment fractions? For multiple sediment fraction beds this warning relates to the amount of sediment available in the active (surface) layer, thus if there is insufficient sediment of a given fraction in the active layer you will get a warning even though there may be sediment available in the subsurface. Fixes can include reducing the timestep or increasing the thickness of the active layer.

4. If the warning is only for 1 or two cells I would tend to ignore it. If it covers large areas of your domains for long periods of time then you probably need to fix it.

Hope that helps.

Richard

warning nm coordinates
Ahmed Elkut, modified 1 Year ago.

RE: Sediment Simulation - TriDiag File

Youngling Posts: 11 Join Date: 5/20/14 Recent Posts

Hi Richard

Thanks a lot for your quick and resourceful reply.

I was able, using the equation of NM, to estimate the location of the error. The problem seems to be located at the boundaries, and it covers few cells. 

I have only one sandy sediment fraction. I will try to reduce the timestep and check on the boundaries to fix this warning.

Thanks again for your help.

 

Ahmed