Using Blender to create solids for Gerris

From Gerris

This is a short introduction to using Blender for creation of solid bodies for inclusion in Gerris simulation.

Contents 1 How to create a wing 1.1 Start with an empty scene (camera and light is OK) 1.2 Add Bezier curve 1.3 Close the curve 1.4 Subdivide it 1.5 Disable the Back and Front for the curve 1.6 Extrude the curve 1.7 Convert the curve to mesh 1.8 Close the top and bottom parts of the mesh 1.9 Recalculate normals 1.10 Export the mesh in STL format 2 STL to GTS 2.1 Convert from .stl to .gts 2.2 Transform the wing.gts 3 Example simulation

How to create a wing

Start with an empty scene (camera and light is OK)

Add Bezier curve

<space> -> add -> curve -> bezier curve

Close the curve

<TAB>
<C>

Subdivide it

(curve) -> segments -> subdivide

Disable the Back and Front for the curve

De-select "Back" and "Front" (this is done in bottom window in blender)

Extrude the curve

Set the extrude level to 1

Convert the curve to mesh

<TAB> - Switch to object mode

(object) -> convert object type: Mesh

Close the top and bottom parts of the mesh

numpad<3> - switch to the side view
<Tab>
<B> - border select (select the top nodes)

(mesh) -> faces -> fill

<A>
<B> - border select (select the bottom nodes)

(mesh) -> faces -> fill

Recalculate normals

<A>
<A>

Now you should have all mesh nodes selected.

(mesh) -> normals -> recalculate inside

Export the mesh in STL format

<TAB> - go to object mode

Select the wing...

(File) -> Export -> STL

Save the file as wing.stl

STL to GTS

Convert from .stl to .gts

 stl2gts < wing.stl > wing.gts

Transform the wing.gts

 transform -o < wing.gts | transform -t 1 > blender_1.gts 

The first transform normalizes the wing, the 2nd one moves it to 2nd cell along X axis. The resulting file "blender_1.gts" is ready for use in Gerris simulation.

Example simulation

(download links below)

4 3 GfsSimulation GfsBox GfsGEdge {} {
  Time { end = 100 }
  Solid blender_1.gts
  Refine 6
  RefineSolid 8
  Init {} { U = 1 }
  OutputTime { istep = 10 } stderr

  OutputSimulation { istep = 4 } stdout

#  EventScript { istep = 4 } { echo "Save stdout { width = 1024 height = 768 }" }

}
GfsBox { left = BoundaryInflowConstant 1 top = BoundaryOutflow bottom = BoundaryOutflow }
GfsBox { top = BoundaryOutflow bottom = BoundaryOutflow }
GfsBox {  top = BoundaryOutflow bottom = BoundaryOutflow }
GfsBox { right = BoundaryOutflow  top = BoundaryOutflow bottom = BoundaryOutflow }
1 2 right
2 3 right
3 4 right

Simulation files (use "right click" + "save as" to download):

gfs gfv gts

To run the simulation:

gerris2D blender_1.gfs | gfsview2D blender_1.gfv