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

Non-hydrostatic pressure solver

SD
Steven Douglas, modified 7 Years ago.

Non-hydrostatic pressure solver

Youngling Posts: 6 Join Date: 10/22/13 Recent Posts
Hello,

I am interested in developing a numerical model for scouring around different structures. In particular, tsunami-induced scouring, which would be simulated by creating a dam break wave. I've already began some initial simulations with hydrodynamics only, just to begin familiarizing myself with defining scenarios and the available functions that the open source Delft3D offers.

In the deflt3D-flow manual, it describes a non-hydrostatic pressure solver that can be invoked when vertical accelerations are significant. In my case, I think that this would be very important. However, I have not found a way to enable this function. Currently, I am using Delft3D tag version 5.01.00.2163 with the Delft3D 4.00.02 GUI.

As of right now, I have been simulating a circular column as "dry points" which as far as I can tell is the only way to implement a structure that causes a change in the flow field. Again, the manual describes insertion of hydraulic structures such as piers. Is this functionality not yet supported by open source versions? Also, my simulations have been defined with no open boundaries, such that the dam break wave reflects off the back wall of the wave flume. In the experimental setup, there is a drain that allows all the water to leave the flume at the downstream end. I've tried several boundary conditions to mimic this effect but have not yet had any success. Is there any way to allow water to simply leave the computational domain at the downstream end of the flume?

Lastly, I understand that there is two ways of defining the vertical layers of the computational grid, namely the Z-layers or Sigma-Layers. When I generate a grid using RGFGRID and define the number of layers I need in Flow Input>Grid Parameters, it is unclear which definition is being used. Are the vertical layers of grid automatically fitted to the bathymetry and free surface by default? Or are the layer elevations constant based on your initial water surface elevation?

I would appreciate any insight to these issues.

Steven
Adri Mourits, modified 7 Years ago.

RE: Non-hydrostatic pressure solver

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

To switch on Non-Hydrostatic: See the manual, section "B.12.6.1 Switches in MDF-file". Non-Hydrostatic is only implemented for Z-layers.

Please use the latest tagged version, currently https://svn.oss.deltares.nl/repos/delft3d/tags/3058. A major improvement of the Z-model is merged in January 2013.

I'm not sure what you mean with the "pier structure". The only "pier" in the manual is related to bridge pillars.

There is only one Delft3D-FLOW version, being the open source version. There is no hidden/closed/extended version.

What about prescribing a spatially varying initial water level being zero everywhere, except in a few points where a (much) higher waterlevel is prescribed? See section "A.2.9 Initial conditions" in the manual.

I expect that a water level boundary as outflow condition should do.

Sigma-layers are used by default. To turn your model into a Z-layer model, see section "B.11.2 Defining the keywords in the FLOW-GUI".

"Figure B.14 Vertical grid construction, Z-model" and "Figure 12.2: Vertical computational grid Z-model (left) and sigma-model (right)" should clarify the differences.

Regards,

Adri
Adri Mourits, modified 7 Years ago.

RE: Non-hydrostatic pressure solver

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

A few additions:
We have performed research on scouring around cylindrical structures but were not very successful yet. I will forward your questions to a few colleagues.

Forget my misinterpretation of the piers. You are thinking about using them as the structure to investigate. But the "bridge pier" in Delft3D can not be used for that. They are modelled as sub-grid structures while you want to know in detail what is going on around them. You have to model your structure with dry points. And that will be difficult when your structure is cylindrical.

Regards,

Adri
SD
Steven Douglas, modified 7 Years ago.

RE: Non-hydrostatic pressure solver

Youngling Posts: 6 Join Date: 10/22/13 Recent Posts
Hi Adri,

I really appreciate your responses.

Somehow I missed that section while reading through the non-hydrostatic pressure solver in the manual, thank you for pointing this out. I believe that the z-model will not pose any problems for my particular application, unless any of the sediment transport/morphology formulations require a deformable mesh (I have not yet looked into it this far).

So far I have specified an initial spatially varying water surface elevation. In my model I have an upstream reservoir filled to a certain elevation with the downstream end of the flume initially dry. The only problem I foresee with a water level boundary is that I will have an initial inflow of water into the flume from the downstream boundary until the dam break wave reaches it. Perhaps I could lower the bathymetry at the downstream to avoid this. I will test this out.

I would appreciate the forward to your colleagues. Thank you for your help Adri.

Steven