# 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!

## Message Boards

### Problem to run flow model

VT

#### Problem to run flow model

Youngling Posts: 12 Join Date: 11/26/13
Hi everybody,

I was running a model with two open boundary (water level - time series south and neumann time series north). I'm using data from MyOcean to generate time series.
For these conditions the model runs correctly, but if I change the north condition (now I want water level time series in the north too) I have problems when I run the model.
tri-diag says:
*** WARNING Velocity change too high > 5.00 m/s (per 0.5 DT) after 16658 timesteps in the following points:
(m,n,k) = (2,58,2), v0, v1, abs(v0-v1): -0.857E+02 , -0.908E+02 , 0.504E+01

I know this message appears when your time step is high, but I'm using the same that in the first case (water level south and neumann north), even i'm using a smaller time sep.

Any suggestion?

Thanks

#### RE: Problem to run flow model

Jedi Council Member Posts: 612 Join Date: 3/2/11
Dear VIRGINIA ,

Yes, as we learned in the textbooks, the boundary conditions are so important. The error message says the computation is not stable, due to some reasons. Too bit time step is one of the reasons, and bad boundary conditions is another.

Regards,

Qinghua
VT

#### RE: Problem to run flow model

Youngling Posts: 12 Join Date: 11/26/13
Dear Qinghua,