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OPTISTRUT Extracting Global stiffness matrix

Hello all,

I'm kinda new to this software and I want to extract the global stiffness (not reduced) of a model. Is it possible to print the mass and stiffness matrices in output file ?

Thanks for your time !

EDIT: Sorry I posted in wrong section. Please move it to Optistrut: solver section.

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Rahul_P1

This is possible by creating a super element with every GRID in the ASET and then using the resulting PUNCH DMIG.

See OS-2070: Topology Optimization of a Reduced Model using DMIG and the explanations of the related cards in the reference guide.

Altair Forum User

Could you please explain it little more in detail?

I don't know how to create a superelement, and which control card should I use: dmigmode oder dmigname?

Best

Michael

Altair Forum User

Hi @Michael Lauxmann

The part to be reduced out of the model through the static reduction model reduction technique is referred to as a superelement. In OptiStruct, ASET or ASET1 bulk data entries are required to indicate the boundary degrees of freedom of a superelement, meaning the set of degrees-of-freedom where the component (being replaced by direct matrix input) connects to the modeled structure. Both the accuracy and the cost of static reduction increase as the number of ASET entries is increased. For example, by using static reduction, the size of the matrix to solve will become smaller, but if the reduced matrix (DMIG) is very dense, then the solution time will become larger than the solution time for the full model where the matrix may be sparse. Hence, the selection of ASET entries is very important in performing an efficient analysis using DMIG.

In order to prevent the reduced matrix from being too dense, ASET entries are chosen carefully (see the next figure) instead of creating ASET entries for all of the boundary nodes between the design and non design spaces. Due to the small size of the problem used for this tutorial, the selection of ASET entries may not affect the solution time.

Please refer to this tutorial:

OS-2070: Topology Optimization of a Reduced Model using DMIG

Altair Forum User

Hi,

Prakash can please tell me where i could find this tutorial.

OS-2070: Topology Optimization of a Reduced Model using DMIG

Like this

Altair Forum User

How to begin studying on super elements

Altair Forum User

Hi,

PFA,

You can find all tutorial on OptiStruct help.

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