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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** PLEASE TAG YOUR POST! **

 

 

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

 


Message Boards

boundary setup for flow

EA
Ed Atkin, modified 8 Years ago.

boundary setup for flow

Youngling Posts: 2 Join Date: 10/11/11 Recent Posts
Hi All,

Just need verification of where adjacent boundaries should start/end.

Example:

A square domain with 4 astronomically forced boundary cells to each of the doamins edges.

Looking at the southern boundary:

Should the grid indicies specifying the location/extent of the cells have:

A) an overlap (2 to 32, 31 to 62, 61 to 91, 90 to 120):

South_A_____________ Z A 2 1 32 1 7.5000000e+001 S1__________ S2__________
South_B_____________ Z A 31 1 62 1 7.5000000e+001 S2__________ S4__________
South_C_____________ Z A 61 1 91 1 7.5000000e+001 S4__________ S6__________
South_D_____________ Z A 90 1 120 1 7.5000000e+001 S6__________ S8__________

or emoticon meet on the same grid location (2 to 31, 31 to 61, 61 to 90, 90 to 120):

South_A_____________ Z A 2 1 31 1 7.5000000e+001 S1__________ S2__________
South_B_____________ Z A 31 1 61 1 7.5000000e+001 S2__________ S4__________
South_C_____________ Z A 61 1 90 1 7.5000000e+001 S4__________ S6__________
South_D_____________ Z A 90 1 120 1 7.5000000e+001 S6__________ S8__________

or C) should the start of the next cell be last cell+1 (2 to 31, 32 to 61, 62 to 90, 91 to 120)

South_A_____________ Z A 2 1 31 1 7.5000000e+001 S1__________ S2__________
South_B_____________ Z A 32 1 61 1 7.5000000e+001 S2__________ S4__________
South_C_____________ Z A 62 1 90 1 7.5000000e+001 S4__________ S6__________
South_D_____________ Z A 91 1 120 1 7.5000000e+001 S6__________ S8__________

look forward to hearing repsonses

Edeyejedi
Adri Mourits, modified 8 Years ago.

RE: boundary setup for flow (Answer)

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

B: meet at the same grid location.

I expect the GUI to arrange this for you when you use the "Visualisation Area" to add adjacent boundaries.

Regards,

Adri
U
Anonymous Anonymous, modified 6 Years ago.

RE: boundary setup for flow

Interesting comment Adri.

Particularly as DelftDashBoard creates a .bnd file that follows approach C) above

Below is an example from the top of a .bnd file I've just created
North1 Z A 2 182 11 182 0.0000000e+000 North1A North1B
North2 Z A 12 182 21 182 0.0000000e+000 North2A North2B
North3 Z A 22 182 31 182 0.0000000e+000 North3A North3B


This approach is the possible cause of artifacts that appear in my model. Particularly apparent in the depth averaged velocities at the boundary. Still investigating this though. Any thoughts anyone?

Ruairi
Adri Mourits, modified 6 Years ago.

RE: boundary setup for flow (Answer)

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

After discussing this with Bert:
Both B (2-11,11-21, 21-31) and C (2-11,12-21, 22-31) are correct, assuming that correct data is prescribed. For B, data is needed for 4 points (2, 11, 21, 31); For C, data is needed for 6 points (2, 11, 12, 21, 22, 31).

Regards,

Adri
U
Anonymous Anonymous, modified 6 Years ago.

RE: boundary setup for flow

Thanks Adri,

I now see that both approaches can be correct, and in some ways B requires a little less preparatory work.

However, the version of DelftDashBoard I am using appears to be mixing the B and C approach, with the .bnd file using approach C (as mentioned in an earlier post) while the .bca file appears to be based on approach B (the data for a start point bring identical to that of the preceding end point).

Regards
Ruairi
MV
Maarten van Ormondt, modified 6 Years ago.

RE: boundary setup for flow

Padawan Posts: 45 Join Date: 3/11/11 Recent Posts
Mmm. I'm getting confused now. I thought C was the only proper way to go. Otherwise you have overlapping boundary conditions, and then what does the model do? I noticed that the model does run, even if you let boundary conditions overlap with 2 or more grid cells, but not sure how the code deals with it.

Delft Dashboard could do things more accurately. Currently it interpolates TOPEX data to the start and end points of boundary sections. It would be better to have it interpolate to the middle of first and last cell face along a boundary section. I'll see if I can build this into the Dashboard code.

Having said this, I may be all wrong.

Maarten
MV
Maarten van Ormondt, modified 6 Years ago.

RE: boundary setup for flow

Padawan Posts: 45 Join Date: 3/11/11 Recent Posts
Rauiri,
What sort of things are you seeing w.r.t. depth-averaged velocities along your boundaries? Are these boundaries in deep water, or are they over steep bathymetry gradients? Delft3D is known to generate large velocities (jets shooting into the model) over water level boundaries on steep slopes. The easiest way to fix these is to a) locally smooth the bathymetry along those boundary sections, or b) use spatially-varying viscosity (using an *.edy file) with very high viscosity in the problem areas.
Cheers,
Maarten