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**todd_alan_martin****Member**- Registered: 2008-03-06
- Posts: 131

Hi

Can someone please advise me where to look in the source code as a starting point for implementing buckling for DKT/DST plate elements?

I'm aware that buckling of isotropic and orthotropic plates is already handled by COQUE_3D, but I'm interested in using DEFI_COQU_MULT.

I'm thinking buckling of a DKT/DST plate, defined by an in-plane stiffness matrix, a bending stiffness matrix, a bending-stretching coupling matrix and a transverse shear matrix (presumably already generated by DEFI_COQU_MULT), could be solved by extending the governing differential equations to take account of the extra stiffness terms.

Also, since modal analysis is handled for DKT/DST plate elements already, there must be some cross-over there. Any comments?

Thanks,

Todd.

*Last edited by todd_alan_martin (2008-08-28 08:44:07)*

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**plegat****Member**- Registered: 2007-11-23
- Posts: 184

Hello

Very good question and initiative!

I suppose you would implement buckling for all kind of materials (isotropic, anisotropic, composite...).

I don't know where and how to start with the source code, but as I am interested in composite DKT/DST buckling, don't hesitate to contact me if you need some help for the new code.

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**Thomas DE SOZA****Guru**- From: EDF
- Registered: 2007-11-23
- Posts: 3,066

Hi,

In order to implement buckling for plates, one needs to instruct Code_Aster how to calculate a geometric stiffness matrix (I don't know the exact term in english, maybe initial stress matrix) for DKT, DKQ elements.

One therefore needs to derive such matrix from the finite element formulation (manual R3.07.03).

Suppose you are there, then this matrix may be inputed in a fortran routine. For each element in Code_Aster there is a file which tells it what options it can calculate.

For DKT and DST these files are

```
/opt/aster/STA9.3/catalo/typelem/gener_medkg1.cata
/opt/aster/STA9.3/catalo/typelem/gener_medkt2.cata
```

The option you are interested in is RIGI_MECA_GE (for GE for geometric, i.e. buckling analysis). If you have a look in each of these files, you'll see :

```
RIGI_MECA_GE -1 IN__ XXXXXX XXXXXX
OUT__ XXXXXX XXXXXX
```

You'll have to replace -1 with a free slot since if you give for example 123, the fortran routine te0123 will be called (if you look in /opt/aster/STA9.3/bibfor/*/* you can see which te0xxx is not already taken).

The XXXXX are a bit tricky to figure out. These are the input arguments you'll need to achieve the calculus of the matrix. You should learn from other element which know how to calculate the geometric matrix (beams for examples, just grep in /opt/aster/STA9.3/catalo/typelem/*.cata).

You should also read the slides for developement learning in Aster (in french in the wiki) and more particularly this one :

http://www.code-aster.org/wiki/doku.php … etisation2

Good luck.

TdS

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**todd_alan_martin****Member**- Registered: 2008-03-06
- Posts: 131

Hi Thomas

Thanks. That is exactly the sort of information I was looking for.

Todd.

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