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

Baroclinic simulation with sigma layers

Fernando Barreto, modified 3 Years ago.

Baroclinic simulation with sigma layers

Padawan Posts: 74 Join Date: 6/21/12 Recent Posts
Hi all,

I am performing a 3D baroclinic simulation using 37 vertical sigma layers, in which the boundary and initial conditions were build from a
3D gaussian feature model representing the Brazil Current with a maximum core velocity of 0.2 m/s. Therefore, the boundary conditions are stationary.
The jet is in thermal-wind balanced.
The problem is, right after the simulation begins the velocity field gets completely destabilized, with peak velocities of 3 m/s, mainly
along continental slope.
Therefore my question is: is there any optimum set up for boundary and initial conditions and parameters when establishing a 3D baroclinic simulation with sigma layers?
I'm using Current boundary condition, with alpha=10000, nudge=#y#, and a sponge layers along boundaries. Attached is a figure with the initial condition for the surface velocity field, and the velocity field after 14 ts.
When simulating with uniform temperature and salinity (barotropic) the simulation runs much smoother. Time step is not the issue, I've run some tests.

Thank you in advance a lot in advance.

Fernando Tulio Camilo Barreto
baroclinic sigma layers

Attachments:

Qinghua Ye, modified 3 Years ago.

RE: Baroclinic simulation with sigma layers (Answer)

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

In general, Delft3D sigma layer have baroclinic mode simulation, which has been proved by several validation cases, such as lock exchange, salt intrusion in an estuary (3d sigma) etc. For your question, I guess it might be related to the improper combination of initial condition and boundary condition. Most probably it is because of the salinity/temperature data in the initial condition.

One possible walk around might be using nesting. Not sure how difficult to get a good initial condition from a nested model.

Hope this is helpful,

Greetings,

Qinghua
Fernando Barreto, modified 3 Years ago.

RE: Baroclinic simulation with sigma layers

Padawan Posts: 74 Join Date: 6/21/12 Recent Posts
Thanks for your reply Qinghua ,

After some tests I realized that, for the sigma case, bottom slope is the key when stabilizing the model (for my specific case). After I removed the bottom slope, velocity magnitudes got much more "tamed", ranging around the input velocity (what is a very good thing). In this case, the stability seems to be controlled by vertical layers configuration. I'm still working on this but I think that few layers, as well as many layers, are both bad for the model stability (there is an ''inbetween''). After finding the best configuration for the number of layers and bottom slope I will play with the physical and numerical parameters.
In relation to initial conditions I will check my input and output data, and also smoothing time (I hope might help with this). Thanks, even a small perturbation can spoil the simulation, so we need to pay attention in every detail

Regarding Z baroclinic case, I found out that the best results were achieved when refining both the surface and the bottom.

For whom may concern, I will update any information in this thread so It can help others in the future


Regards,


Fernando Túlio Camilo Barreto