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## Re: [ff3d-users] How to define a slope domain?

**From**: |
Stephane Del Pino |

**Subject**: |
Re: [ff3d-users] How to define a slope domain? |

**Date**: |
Tue, 6 Mar 2007 21:14:27 +0100 |

**User-agent**: |
KMail/1.9.5 |

Le mardi 6 mars 2007 15:13, Hao a écrit :
>* Hi,*
Hello.
>* > I am trying to solve a slope stability problem with ff3d.*
>* > The surface of space is not flat, but with a slope, such as 10 degree.*
>* > How to define the problem space in FEM? and how to identify the upper*
>* > surface?*
The upper surface of a box is given by 'zmax' or the reference number 5 if
you build the mesh with ff3d.
>* > I know there are two methods implemented in ff3d, one is FEM, another one*
>* > is FDM.*
>* > FEM can only run on regular hexahedral mesh defined by vector a, b, and*
>* > n, is it right(here, FEM used only mesh)?*
No. You can use also tetrahedral meshes build with external meshes in
format 'gmsh' or 'mesh'. Or, if the geometry is simple, you can generate it
with ff3d:
-------8<--------------
// build a cartesian grid of hexahedra
mesh m = structured(n,a,b);
// tetrahedrize it: each hexa is divided into 5 tetra
m = tetrahedrize(m);
// transform your mesh with a field
m = transform([f,g,h],m);
-------8<--------------
f,g and h are functions defining the transformation field
>* > However, FDM can run on other irregular domain with the help of pov ray,*
>* > but the domain must be contained in the Mesh completely, is it true(here,*
>* > FDM used doamin and mesh)?*
Yes.
>* What is the difference between FEM and FDM? Does they use same algorithms*
>* to solve the problem?*
FDM is fictitious domain method. In ff3d, it relies on a Q1 FEM method.
Best regards,
Stéphane.