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 cfd seeker September 20, 2012 02:17

How to tackle this problem?

2 Attachment(s)
I need to mesh the simple rectangular wing using Unstructured Mesh. I have to set finer node distributions near the leading edge all along the span. There is only one surface on suction side(upper), one surface on the pressure side(lower) and one surface in the wing tip region. I have set the finer node distribution on wing root curves and wing tip curves(shown in images) to get finer bunching on the leading edge but only these curves(wing root curve and wing tip curve) are respecting the finer node distribution not the whole span(from root to tip) as shown in attached images. I think I need to do some geometry operations on the upper and lower side of wing to tackle this problem but I have no idea about these operations. So how to tackle this? Thanks
Waiting for expert opinions of Diamondx and Simon :D

Regards

 Manigandan September 20, 2012 02:55

Quote:
 Originally Posted by cfd seeker (Post 382688) I need to mesh the simple rectangular wing using Unstructured Mesh. I have to set finer node distributions near the leading edge all along the span. There is only one surface on suction side(upper), one surface on the pressure side(lower) and one surface in the wing tip region. I have set the finer node distribution on wing root curves and wing tip curves(shown in images) to get finer bunching on the leading edge but only these curves(wing root curve and wing tip curve) are respecting the finer node distribution not the whole span(from root to tip) as shown in attached images. I think I need to do some geometry operations on the upper and lower side of wing to tackle this problem but I have no idea about these operations. So how to tackle this? Thanks Waiting for expert opinions of Diamondx and Simon :D Regards
In this problem you want to change the value
1. in Global mesh parameter -> Volume meshing parameters->reduce the edge criterion try it once or
2. sweep the surface mesh by Edit mesh-> Extrude mesh-> select mesh-> Give volume element name->give ->side surface mesh name->topsurface mesh name
on tht time you can the on two side will be tri surface mesh and top and bottom side quad mesh on it

 cfd seeker September 20, 2012 04:37

Quote:
 2. sweep the surface mesh by Edit mesh-> Extrude mesh-> select mesh-> Give volume element name->give ->side surface mesh name->topsurface mesh name on tht time you can the on two side will be tri surface mesh and top and bottom side quad mesh on it
Didn't get this point?

 diamondx September 20, 2012 08:50

what do you mean by geometry reparation, splitting the upper and bottom surfaces ?? i'm not much of an expert when it comes to unstructured mesh :o ! i can help you with geometry changing tough

 diamondx September 20, 2012 09:04

i have a memory of a similar thread, may be you can find if make and advanced search, filter prefix "icem" and look for wing unstructured.... may be ...

 cfd seeker September 20, 2012 10:27

Quote:
 hat do you mean by geometry reparation, splitting the upper and bottom surfaces ??
Yup by geometry operations I mean making many surfaces out of a single and also make extra curves on the surfaces for your needs....any suggestions?

Quote:
 i'm not much of an expert when it comes to unstructured mesh
I myself don't like this but for a particular project of Flapping Wing Analysis I have it use it

 yonchong September 20, 2012 10:31

Try adding density to the leading edge line.

Mesh -> Create Mesh Density

In fact, if you go to the Ansys help on Create Mesh Density, it has leading edge on wing example. In that example, the density line was created in front of the leading edge but, in your case, you can just use the line dividing the upper and lower surface.

 cfd seeker September 20, 2012 10:41

Quote:
 Originally Posted by yonchong (Post 382788) Try adding density to the leading edge line. Mesh -> Create Mesh Density In fact, if you go to the Ansys help on Create Mesh Density, it has leading edge on wing example. In that example, the density line was created in front of the leading edge but, in your case, you can just use the line dividing the upper and lower surface.
If I am not wrong the Mesh Density Box only affects the Volume Mesh not the Surface Mesh isn't it? I am having problem with the Surface Mesh

 yonchong September 20, 2012 10:51

If you use the patch independant option the shell mesh will be affected as ICEM uses Octree volume mesher to create volume and surface mesh together and delete the volume mesh to leave the surface mesh.

If you use the patch dependant option then the density box will not do anything as the shell mesh is generated using surfaces.

 cfd seeker September 20, 2012 12:26

Quote:
 If you use the patch independant option the shell mesh will be affected as ICEM uses Octree volume mesher to create volume and surface mesh together and delete the volume mesh to leave the surface mesh
Thanks nice information

 PSYMN September 22, 2012 19:53

Some users like to run iso parametric curves along curving surfaces like this (or along fillets) to control the way the nodes fall... I am guessing that is what you are looking for.

Go into Geometry (tab) => Create/Modify Curves => Create Iso-Parametric curve... (or something similar to that, I don't have ICEM up to check the command)

An iso parametric curve is one that follows the UV space of a surface. If you set it to 0.5, it will create a curve exactly down the middle of the surface. In your case, you might want to try 0.05 (or 0.95) to get it just 5 percent from the edge... You may even want to create a few of these near each other...

If the curves are perpendicular to what you expect, then switch between u and v.

Then when you generate octree tetra mesh, it will be controlled by the curves... It is sort of like forcing the tetras to line up along the leading edge of the wing.

The downside is that the curves also constrain the smoother, etc. so you could have some reduced quality (but still good enough).

Post a pic when you are done so people can see what this did for you.

 cfd seeker September 23, 2012 02:18

Quote:
 Originally Posted by PSYMN (Post 383135) Some users like to run iso parametric curves along curving surfaces like this (or along fillets) to control the way the nodes fall... I am guessing that is what you are looking for. Go into Geometry (tab) => Create/Modify Curves => Create Iso-Parametric curve... (or something similar to that, I don't have ICEM up to check the command) An iso parametric curve is one that follows the UV space of a surface. If you set it to 0.5, it will create a curve exactly down the middle of the surface. In your case, you might want to try 0.05 (or 0.95) to get it just 5 percent from the edge... You may even want to create a few of these near each other... If the curves are perpendicular to what you expect, then switch between u and v. Then when you generate octree tetra mesh, it will be controlled by the curves... It is sort of like forcing the tetras to line up along the leading edge of the wing. The downside is that the curves also constrain the smoother, etc. so you could have some reduced quality (but still good enough). Post a pic when you are done so people can see what this did for you.
Yah Friday evening I was trying something like that but I was projecting curves on the already existing surface, that option seems to divide the surface into two parts by creating a curve at 50% location(using leading and trailing edge curves), again I applied the same process on the two parts separately to get four parts in total, then I deleted the main surface and with the help of created curves I made separate surfaces but this process was not giving me my desired result as I want a separate surface 30% from the leading edge. of course I don't have pics or geometry here to post my effort but I will post some pics what I was doing and will also try to implement what you said. Thanks

 diamondx September 23, 2012 08:59

Quote:
 separate surface 30% from the leading edge
Another thing to try, i usually go to the create point option.
there is a very handy tool there, you can create point depending on a parameter of a curve, 30%=0.3 50%=0.5. when you create your point, you can project that point to several other parallel edges again using the option "project point on curve". once projected, create an edge with those point, then slice the surface using those edge in the option "split surface using edge" i hope it can help.

 PSYMN September 23, 2012 18:52

Quote:
 curve at 50% location
Iso parametric doesn't have to be 50%, you can use any percentage you want. And it doesn't have to cut the other surface... Just don't build topo...

You don't need to cut the surfaces for it to work.

 cfd seeker September 24, 2012 09:50

Quote:
 Then when you generate octree tetra mesh, it will be controlled by the curves...
octree tetra mesh using Patch Dependent or Patch Independent method for surface mesh?

 PSYMN September 24, 2012 11:13

Octree tetra uses the patch independent method... In fact, Octree tetra starts with the volume mesh (it is a top down method) and then figures out the surface mesh from there.

When you start with a patch conforming method, it actually generates the patch independent mesh as part of its process and then dumps it to make the octree volume mesh conformal with the surface mesh. This really combines the worst of both worlds, like having German Police and French Mechanics, instead of the other way around. There isn't really much good reason to do all the work required to get a good patch conforming surface mesh if you are going to fill it with Octree... The one good exception is when you have just a few patch conforming surfaces (perhaps coming from an adjacent model) that you want the octree to align with. Octree would then create all the other surface mesh that you need...

But in the end, I might still delete the octree mesh, smooth the surface mesh (alternating rounds of laplace and regular smoothing, ending with regular smoothing) and regenerate the volume mesh with a Delaunay Fill (with the TGlib and AF options).

In your case, patch conforming mesh on the difficult thin surfaces may be easier than octree (PI surface mesh) and then you can fill with delaunay.

If you have trouble with other surfaces in the model, just skip them with PI, and use Octree to capture them...

 BrolY September 25, 2012 03:39

You are right, German Police is awful ;)

 Far September 25, 2012 05:47

Quote:
 Originally Posted by BrolY (Post 383455) You are right, German Police is awful ;)
Are they going to teach us unstructured meshing using ICEM :p

 diamondx September 25, 2012 09:09

Broly, always there to start spaming threads and diverting subject, keep up the good work ;)
Far, always there to support him.

 Manigandan October 3, 2012 08:31

Contact me in my mail ID manirainbow61@gmail.com i can help u from thr.

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