[CAD formats] Mesh for a solid described by parametric surfaces

Align · August 16, 2016, 19:50

Hi all,

I'm sorry if this has been asked before, but I'm new at CFD and maybe I'm not searching with the appropriate language.

I need to describe the geometry for a problem were both the top and bottom layer of a solid are given by the parametric equations of an orientable surface (as defined in https://en.wikipedia.org/wiki/Parametric_surface)

For simplicity right now I can assume that:
1) The top and bottom layer are equal in shape (related by a simple vertical translation) and don't intersect, so that
2) The solid has constant "width" between the top and the bottom layer.
3) The bottom and top layers are in the simplest form r(x,y) = (x, y, f(x,y)) (i.e., both surfaces are graphs of functions)

My problem is that in practice the solid's limiting surface may end up being too complicated to be described using direct methods and I also may need to change the function f with relative ease. Later I'll need to mesh this surface (solid?), let's say to simulate fluid flow around it.

The simplest example would be describing a solid cube knowing the equations of the limiting planes. Then maybe I'd try to do a solid cylinder. My first guess is that it would be easy to describe the solid limits using a numerical software, let's say Octave, but I'm still not to sure on what to read to proceed or if this is the easiest way to achieve my goal.

My question is:
A) Starting with the parametric equations, how do you recommend I generate the solid? (software, method, format, ...)
B) What kind of mesh should I use?
C) How do I generate this mesh starting from the solid as in (A)?

Any help is greatly appreciated. Thank you for your time.

cutter · August 24, 2016, 04:37

Hi,

just an idea (haven't done it myself yet):

You may use something like K3DSurf (http://k3dsurf.sourceforge.net/) to define your surface. The tool allows to export the generated surfaces as OBJ file, which is similar to STL. Both formats can be used in may 3D software packages. They can also be used in OpenFOAM meshers such as cfMesh (recommended because of ease of usage) or snappyHexMesh. There are probably other [OSS] programs that are capable of this too.

Good Luck!
Cutter

August 16, 2016, 19:50	Mesh for a solid described by parametric surfaces	#1
Align New Member Join Date: Aug 2016 Posts: 1 Rep Power: 0	Hi all, I'm sorry if this has been asked before, but I'm new at CFD and maybe I'm not searching with the appropriate language. I need to describe the geometry for a problem were both the top and bottom layer of a solid are given by the parametric equations of an orientable surface (as defined in https://en.wikipedia.org/wiki/Parametric_surface) For simplicity right now I can assume that: 1) The top and bottom layer are equal in shape (related by a simple vertical translation) and don't intersect, so that 2) The solid has constant "width" between the top and the bottom layer. 3) The bottom and top layers are in the simplest form r(x,y) = (x, y, f(x,y)) (i.e., both surfaces are graphs of functions) My problem is that in practice the solid's limiting surface may end up being too complicated to be described using direct methods and I also may need to change the function f with relative ease. Later I'll need to mesh this surface (solid?), let's say to simulate fluid flow around it. The simplest example would be describing a solid cube knowing the equations of the limiting planes. Then maybe I'd try to do a solid cylinder. My first guess is that it would be easy to describe the solid limits using a numerical software, let's say Octave, but I'm still not to sure on what to read to proceed or if this is the easiest way to achieve my goal. My question is: A) Starting with the parametric equations, how do you recommend I generate the solid? (software, method, format, ...) B) What kind of mesh should I use? C) How do I generate this mesh starting from the solid as in (A)? Any help is greatly appreciated. Thank you for your time.

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August 24, 2016, 04:37		#2
cutter Senior Member Join Date: Mar 2010 Location: Germany Posts: 154 Rep Power: 16	Hi, just an idea (haven't done it myself yet): You may use something like K3DSurf (http://k3dsurf.sourceforge.net/) to define your surface. The tool allows to export the generated surfaces as OBJ file, which is similar to STL. Both formats can be used in may 3D software packages. They can also be used in OpenFOAM meshers such as cfMesh (recommended because of ease of usage) or snappyHexMesh. There are probably other [OSS] programs that are capable of this too. Good Luck! Cutter