# 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

### Riemann boundaries: inflow/outflow coefficient

FM

#### Riemann boundaries: inflow/outflow coefficient

Youngling Posts: 21 Join Date: 3/12/13
Hi,

I am working on the Riemann boundaries from coarser model conditions and I have a doubt about the conventions used by d3d.

In the user guide, the riemann variable is defined as: U +- zeta * ((g / depth) ^ 0.5)
In the nesthd codes, I have seen that you use a coeffcient(-1 or +1) defined if it considered as inflow or outflow boundary.

So, it means that if it is a west or a north boundary, the coefficient will be (+1) and if it is a east or a south boundary, the coefficient will be (-1), isn't it?
Or, maybe I just have to sum the velocity with the water elevation without any other coefficient...I am not sure.

Regards,

Florian Monetti

#### RE: Riemann boundaries: inflow/outflow coefficient (Answer)

Jedi Council Member Posts: 612 Join Date: 3/2/11
Beste Florian,

No. The sign follows the MN directions. If it is to the positive M, it is positive, otherwise it is negative.

I don't fully understand this: Or, maybe I just have to sum the velocity with the water elevation without any other coefficient.

Hope this will be a little bit helpful,

Qinghua
FM

#### RE: Riemann boundaries: inflow/outflow coefficient

Youngling Posts: 21 Join Date: 3/12/13