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Complex Structure in Salome

  • Alex
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15 years 1 month ago #2990 by Alex
Complex Structure in Salome was created by Alex
Hi Forum



I want to use Salome to export a mesh to be analyzed in Aster 9.4

The structure to be analyzed is a complete ( well... sort of... :-) ) aircraft, modeled as an assembly of beams, plates and shells... :

The wings are modeled as structural elements loaded in bending and torsion ( it is a tappered wing with a sweep and a dihedral angle ), and are made of longitudinal beams with shape factor ( L beams ) stiffened to eachother by plates with the wing's profile shape, and these later are fully covered by the wing's skin, made of shells.

All these structural elements are joined to eachother by bolts ( probably modeled as discrete axial spring elements between nodes ) and rivets ( same as before, but with shear ).

The "beams axis" of the wing is supposed to join the aircraft body at the central stiffening plates, and the bodywork of the aircraft is made of shells.

I know that Salome can successfully mesh 1d ( beams, bars, shafts ) structural elements, as well as 2d ( plates, shells, membranes ) and 3d.

I Can obtain the values of Cx, (Cy=Cz=0) CMx, CMy and CMz for a specified flight condition from OpenFOAM; Having these data, as well as my ( calculated ) lift and Moment distribution over the wingspan, I plan to feed my structure, as well as the calculated loads in flight condition, to Aster.

My questions are two:

Once I build the "thing", will I export it as a MED file with several physical groups ( Like with GMSH ), or will I export it as several meshes ( one per structural element ) with groups defined on which to impose boundary conditions ( Contact faces, bolted connetctions between nodes, etc... ) ?

I spoke about a tappered sweptback wing... its surface cannot be built from an extrusion or a boolean operation... Is there something in Salome that can be compared to a multi section loft, or even a way to generate a ruled surface between splines ( my wing profiles ) at wing sections...?

I never understood what the "filling" command is about anyway... And Salome interface for 3d modeling is different from Pro Engineer's... Can I do this in Salome Platform ( I am using 4.1.4 in Debian )...?

Is it possible ( or somehow easier ) to do all this in GMSH...?

What would you consider the best solver to undertake the kind of analysis ( A static flight condition, and a modal analysis ) that I want...? Calculix ( does it allow modelling of assemblies ) , or Code Aster...?

As you may have seen, I want to design my airplane using only OSS tools...

best regards

Alex
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15 years 3 weeks ago #3129 by Xavier DURIEUX
Replied by Xavier DURIEUX on topic Re:Complex Structure in Salome
Hello Alex,

I'm not able to answer all your questions but I'd like to point out that you're in front of an AEROELASTICITY problem. You should take into account the coupling between the air and the dynamic (=flexible) model of your structure.

Please, do not consider my answer if you work with an infinitely rigid airplane.

Regards,

Xavier
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15 years 3 weeks ago #3143 by Alex
Replied by Alex on topic Re:Complex Structure in Salome
Hello Xavier

Thanks for your answer,

I am aware of this kind of coupling, and I will not try to solve it directly ( bi directional coupling ) ;

In my preliminary study, what I want is to evaluate, to what extent the first bending mode of the wing is far apart ( frequency-wise ) from the first torsion mode of the wing... and provide that ( playing with structural moduli of bending and torsion ) they have a nonrational ratio of frequencies ( ie bending freq not a multiple of torsion freq )

Since I am considering only the symmetrical modes ( trimmed steady horizontal flight condition, no ailerons actuated ) my analysis should guarantee some insight on a safe design, at least for the airspeed that i consider ( and the corresponding fluctuation spectrum of turbulent quantities at wing tip, where the trailing vortex formation triggers the flutter codition at the critical speed )... which I can obtain in a LES run in OpenFOAM...

I want to adress the issue of static aeroelasticity first, since dynamic aeroelasticity is way more complex, requiring me to solve for the flow stagnation pressures over the control surface, as well as for structural dynamics of my airframe... not easy...


Anyway, I have been "playing" with Salome Meca, so as to evaluate if it can represent my structure, and I have failed so far...

In ADINA ( or Abaqus, or ANSYS Classic ) I would define my layout begining with geometrical points, used to define my beams ( in wing spars, and fuselage ), plates ( in wing ribs and fuselage bulkheads ) and shells ( in my fuselage, wings and control surface skins )

From these geometric definitions, I would define material properties ( either isotropic (non)linear models, or orthotropic (non)linear models ), and finite element families ( Beams, plates shells ) each with its specific material and modulus.

Then I would define loading spectra, boundary conditions, and proceed with my analysis, static, and eigenmode.



In Salome Meca, I don't even know hoy to analyze a sinple 3d frame with beams... :-)

After defining my geometry, ( beams ) and meshing , Aster wizard does not allow me to make a 3D analysis, saying that I should select 3D mesh to complete the analysis... :-(

My frame IS 3D, each of its nodes ( except pinned DOFS ) has full set of 6 degrees of freedom 3 translations, and 3 rotations... I am considering beams here...


Can I use Salome meca to build make my aircraft structure, or it has no capability to perform what I want...?
Can I use Salome to build the structure, and hack my .comm file to set things how they "should" be, before "feeding" it to Aster...as well as my "assembly" mesh ( full set of beams plates and shells ) ?


Thanks in advance

Best regards,

Alex
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