efforts on a sail

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7 years 9 months ago #6150 by Panloup
Replied by Panloup on topic efforts on a sail
Hi ! Thank you for your answer. I got the sum of the efforts on the sail :-) . However, I have a litte problem: 10-⁸ (Newton I think) is obviously incoherant.... But links between efforts on "x", and efforts on "y" are logical. That's why I suppose that there is an issue with units. Does salome work in mm ? I found a post which said that we can choose units, but I didn't find how. I'd like to make several simulations to show the importance of the sail adjustment. Shall I create a new mesh for each case ? Or is there a way to build a mesh with settings ?
Thanks

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7 years 9 months ago #6151 by Claus
Replied by Claus on topic efforts on a sail
Salomé is unit-less, but I think Code_Saturne uses meters unless other is specified in a subroutine - but this is just from memory. Search the CS forum, Im positive I asked that particular question at some point :)

Mesh creation can be python driven with Salomé, so it's possible to create iterations of a geometry and automatically mesh it. Try to 'dump' a study and look at the resulting files.

/C

Code_Aster release : STA11.4 on OpenSUSE 12.3 64 bits - EDF/Intel version

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7 years 9 months ago #6152 by Yvan Fournier
Replied by Yvan Fournier on topic efforts on a sail
I confirm that Code_Saturne assumes meters.

What is the integral surface of the sail (computed with ParaVie in the same way as the efforts, as an additional check ?

Also, if viscous efforts are underestimated, pressure efforts could balance out, though that seems quite improbable. What is the range of efforts per unit surface on the sail ?

Best regards,

Yvan

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7 years 9 months ago - 7 years 9 months ago #6157 by Panloup
Replied by Panloup on topic efforts on a sail
Hi ! I scaled the sail, new results are coherant and the efforts are linked to the selected surface. I kept the viscosity of air for the simulation. I will create new cases and confront results with our real measures (we built a model and have got a wind tunnel).
Shall I make a script to create new geometries and mesh them after ? In this case should I create a whole geometry (I don't know salome commands)? Or have I just to change a ready made file (I can't open salome files in "text" mode to see its construction) ?
Can I make a script which work only with meshes ?

Anyway, I'm going to learn Python only if I have enought time. Four or five simulations are enought for my project.

Thank you for your help :-)
Last edit: 7 years 9 months ago by Panloup. Reason: mistakes

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7 years 9 months ago #6158 by Yvan Fournier
Replied by Yvan Fournier on topic efforts on a sail
Hello,

You can easily scale the mesh under SALOME, even if you did not scale the geometry, so tere is probably no good reason to modify the geometry if it fits your purpose. You can also scale the mesh under Code_Saturne (using preprocessor mesh meta-files or the usmodg.f90 user subroutine for Code_Saturne 2.0, using cs_user_mesh_input.c or cs_user_mesh_modify unde version 2.1)

In any case, for Code_Saturne developpers, it is quite common to buid a geometry in millimeters (if the data it is based on is available in millimeters, this allows for easier verification), then scale the mesh to meters once finished, just before running the calculation. In this case, the preferred method is to scale the mesh in the meshing tool (using the Code_Saturne solution as a backup).

If we forget to scale the mesh, there are several signs showing the mistake (min/max coefficients range when checking the preprocessor.log or listing file, checkerboard patterns in the pressure, convection of optional tracer scalars showing the time step does not match the mesh scale, very small CFL numbers, etc.) which can be easily detected by experienced users, for for which there is no simple automatic check, but running a few iterations and checking the results is always good practice before running to convergence.

Best regards,

Yvan

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7 years 6 months ago #6330 by Panloup
Replied by Panloup on topic efforts on a sail
Hi !
The last simulations gave me coherent results (compared to a real study), so I will run other one with a bigger sail.
I'd like to see the stream lines, but the stream tracer tool is never available... and I don't really understand how to use the Glyph tool: all arrows are parallel =S, I didn't find how to associate them to the local velocity.
Does anyone has an idea ?
Thanks a lot.

Romain P

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