open TELEMAC-MASCARET The mathematically superior suite of solvers

Hi all,

I am having some trouble trying to create the geometry of a rectangular basin filled with 10 or so scattered islands - that is, isolated objects with solid boundaries where flow cannot penetrate. I have generated my mesh already within the basin and hope to set boundary conditions for the sides of the basin as well as each island.

I've tried creating one giant constraint line that includes the basin sides and the islands, but BlueKenue doesn't recognize the islands as part of the boundary, and there is flow going into them. Is there a way to help BlueKenue recognize that the islands require boundary conditions too? Or perhaps a method to concatenate all the islands together after setting each one as a boundary condition separately? Any help would be greatly appreciated!

On an unrelated note, I am trying to experiment with different types of mesh - would you happen to know how to generate an unstructured mesh? For example, perhaps generating equilateral triangles of specified size. Thanks!

Best regards,
Alex

Hi Alex,

In BlueKenue, islands can be integrated at the mesh generation step, through hardlines. Indeed closed hardlines (in a T3 Mesh Generator) are interpreted differently and used to define islands (the drawnback is that the hardlines can not be resampled automatically).
However the regular channel mesher (T3 Channel Mesher) do not provide this feature (hardline and hardpoint can not be integrated, this is a "basic" tool).

The other approach is to remove some triangles from an already generated mesh. This can be done by :
1. Selecting a mesh object
2. In the menu : Edit > T2 Mesh > Delete Elements in Polgon
3. Select a closed polyline
Only stricly included elements/triangles are removed, and there is no direct control on the shape of the island.

Regards,
Luc

Hi Alex,

If you post the t3m file here it will be easier to help you.
A picture is also worth a thousand words.

The outline object should contain only 1 closed line.

Islands are created by supplying closed lines as either:
1. SoftLines in which case the node spacing along the island outline is computed from the Density object, or as
2. HardLines in which case the user must explicitly supply the geometry (nodes)

The Boundary Conditions editor will automatically detect the islands and allow you to specify the type of boundary.

Cheers... Martin

Hi,

Thank you both for your help! It has been really helpful and I've made progress on the problem. I just have 2 quick follow-up questions: how does one create a Density object, and what's the format of a Density object file?

Also, how can I smoothen out or refine the nodes around my island in more detail? The T3 Mesh Generator is adding space around the island so that the boundary is getting distorted - I've attached a screenshot and my t3m file. Would specifying a Density perhaps help fix this?

Thank you again for your help!

Best regards,
Alex

Hi Alex,

You can think of the density object as a kind of "virtual surface"
It is composed of any number of sub-objects that may be point-sets, line-sets, regular grids or triangular meshes. The mesher queries this object to retrieve the local edge length anywhere in the domain. In the case of overlap the smallest value is always taken. You add the sub-objects by dragging and dropping them to the "Density" object in the Workspace.
See page 138 in the reference manual.

You have provided your slf file NOT the t3m file. The t3m file is the complete specification to the mesher. The slf file is only the output in the telemac format.

Cheers... Martin