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: 
/web/delft3dfm/forum

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

=======================================================

** PLEASE TAG YOUR POST! **

 

 

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

 


Message Boards

Sediment flux at inflow not matching imposed value in bcc

GS
Gerard Salter, modified 2 Years ago.

Sediment flux at inflow not matching imposed value in bcc

Youngling Posts: 3 Join Date: 10/16/14 Recent Posts

Hello,

I am trying to set the upstream sediment flux in conjunction with a discharge per cell boundary condition. However, I am finding that the sediment flux does not match what I'm imposing. The sediment concentration, which I calculate as total sediment load (m^3/s) times sediment density (2650 kg/m^3) divided by total water discharge (m^3/s) should match what I set in the bcc file, but it does not. 

Interestingly, changing the concentration in the bcc file does change the sediment transport rate, but not by the correct factor (i.e., doubling the concentration should double the total transport given that the water inflow is fixed). I found that changing the initial bathymetry but keeping the bcc the same also changes the calculated sediment flux.

I'm running the simulations long enough that this isn't some transient effect. The sediment flux has clearly reached a steady value, which it remains at for the duration of the simulation. 

 In the mor file, EqmBC is set to false, and for good measure I also tried adding NeuBCSand = false just in case, although they should do the same thing. I also discovered adding the keyword UpdInf = true to the .mor file changes the results, but it actually became worse than before. I'm just using a single grain size. I'm running Delft3D 4.02.02 on windows. 

 

Any ideas? Is this a bug in Delft3D?

Thanks,

Gerard

GS
Gerard Salter, modified 2 Years ago.

RE: Sediment flux at inflow not matching imposed value in bcc

Youngling Posts: 3 Join Date: 10/16/14 Recent Posts

I figured out the solution, and thought I'd post it for anyone looking at this in the future. The manual is not clear on this.

 

The .bcc specifies the suspended sediment, but bed load is set independently, even when EqmBC=false. Setting bed load is a bit complicated. 

Append to your .mor file the following:

   
   BcFil            = #mybcm.bcm#                   file containing mophological boundary conditions.
[Boundary]
   Name             = #upstream#
   IBedCond         = 5                             bed load or bed level boundary condition.

Then write a .bcm file with this template, replacing names and values as needed.

 

table-name           'Boundary Section : 1'
contents             'Uniform   '
location             'upstream            '
time-function        'non-equidistant'
reference-time       20180711
time-unit            'minutes'
interpolation        'linear'
parameter            'time                '  unit '[min]'
parameter            'transport excl pores Sediment_sand end A'       unit '[m2/s]'
parameter            'transport excl pores Sediment_sand end B'       unit '[m2/s]'
records-in-table     2
 0.0000000e+000  3.1400000e-004  3.1400000e-004
 3.0960000e+005  3.1400000e-004  3.1400000e-004

 

Notice that this specifies the sediment transport per unit width, but the manual incorrectly says the units are m3/s. 

 

Hope this helps someone!
 

BY
Bing Yuan, modified 1 Year ago.

RE: Sediment flux at inflow not matching imposed value in bcc

Youngling Posts: 5 Join Date: 9/22/17 Recent Posts

Hi Gerard, thanks for sharing! 

For a 2D study domain I did try your method, i.e., set sediment concentration to 0 in bcc file, and use nonzero values for sediment flux per unit width (as you mentioned) in bcm file. However, the resulting total sediment flux at the inflow boundary (remain nearly constant though) did not agree with the specified values at the boundary. May I ask did you get agreed total sediment flux (in time) at the boundary in the end? Thanks! 

ps. I used Engelund-Hansen formulation. 

pps. I did a few 1D simulations using bcc only, the resulting total sediment flux agrees well with the specified value. 

SS
Samuel Schroers, modified 1 Year ago.

RE: Sediment flux at inflow not matching imposed value in bcc

Youngling Posts: 7 Join Date: 9/29/17 Recent Posts

Hi Gerard,

Thx for the work-around! I was wondering about a similar question...

In general- anybody could tell me what is the difference between the .bcc file (which imposes supposedly transport at the boundaries but the results are something different) and the .bcm file?

Which combination would i use is if i know the sediment concentration (kg/s) for a certain inflow (m3/s) and I would like to model suspended and bed load transport?

Thx!

SS
Samuel Schroers, modified 1 Year ago.

RE: Sediment flux at inflow not matching imposed value in bcc

Youngling Posts: 7 Join Date: 9/29/17 Recent Posts

Somehow i managed as you laid out to implement the .bcm file- i changed the values of the time series but the result stays the same...

( i have put

    EqmBc            = false                
   NeuBcSand        = false  )

GS
Gerard Salter, modified 1 Year ago.

RE: Sediment flux at inflow not matching imposed value in bcc

Youngling Posts: 3 Join Date: 10/16/14 Recent Posts

My understanding is that with those two conditions set, the bedload should be set by the .bcm file (make sure you make the above modifications to the .mor file as well) and the suspended load is set by the .bcc. If you know the inflow concentration you want to set, I would do that through the .bcc file, and set the bed load sed flux to 0 in the .bcm. The exact way you set it shouldn't matter (hopefully!) as long as your domain of interest is sufficiently far from your boundaries. If you've checked all of this and are still getting unexpected results, maybe someone with more knowledge of the inner workings of Delft3D could explain why we are getting different results. 

SS
Samuel Schroers, modified 1 Year ago.

RE: Sediment flux at inflow not matching imposed value in bcc

Youngling Posts: 7 Join Date: 9/29/17 Recent Posts

Thank you for your answer-

I have for testing 2 sediment types (specified in .sed file). In the .bcm file i set one sediment inflow to 0 the other some concentration.

Still i get results for both sediments at the inflow - it seems like no matter what i set as inflow sediment / bedload boundary i get always the equilibrium result for the transport formula chosen.

Anyone knows where is the trick?

Jacob A A Morgan, modified 5 Months ago.

RE: Sediment flux at inflow not matching imposed value in bcc

Youngling Posts: 4 Join Date: 4/27/18 Recent Posts
Has there been any resolution to this? We are having what sounds like the exact same problem. We have been testing a model aimed at exploring changes in sediment supply. We are using the .bcm file to specify the volumetric rate of bedload supply. However, when we look at results, the bedload at the upstream boundary is always the same regardless of the values in the .bcm file. It sounds the same as the problem here.