Hey Kyunghoon,
Unfortunately, I am not very familiar with
reduced basis methods (or with linear elasticity). If you were using
regular Finite Elements, then going by this formulation of linear
elasticity (
http://en.wikipedia.org/wiki/Linear_elasticity#Direct_tensor_form), the
strain is the gradient of the displacement that is solved for.
So I believe, one would use element_postprocess.C, but instead of computing
interior_value, one would use compute interior_gradient to compute the
strain, and then use Hooke's law to get the stress. This would work if you
needed average stress over a subset of the domain.
However, if you needed stress and strain at a point, you might want to use
point_gradient. See line 464 in
libmesh/examples/fem_system/fem_system_ex1/naviersystem.C , it gives an
example for point_value but the idea is the same for point_gradient. The
definitions for point_value and point_gradient are
in libmesh/src/systems/system.C .
Thanks.
On Sun, Jun 24, 2012 at 12:11 AM, Kyunghoon Lee
<aeronova.mail...@gmail.com>wrote:
> On Sun, Jun 24, 2012 at 11:33 AM, Vikram Garg <simulation...@gmail.com>wrote:
>
>> Hey Kyunghoon,
>> If you are using FEMSystem, see
>> element_postprocess.C and side_postprocess.C in this example:
>> libmesh/examples/adjoints/adjoints_ex1 (
>> http://libmesh.sourceforge.net/adjoints_ex1.php)
>>
>> If you are not using FEMSystem, I believe all you will have to do is to
>> write a loop over all elements, and then adapt the contents of
>> element/side_postprocess.C to the interior of that loop.
>>
>> Thanks.
>>
>
> Hi Grag,
>
> Thank you for the suggestion. I'm working on Reduced Cantilever Problem (
> http://libmesh.sourceforge.net/reduced_basis_ex5.php), so I guess I'm
> using FEMSystem. I checked the two files, element_postprocess.C and
> side_postprocess.C, but I cannot figure out how I can use them for my
> strain & stress evaluations. Can you elaborate, plz?
>
> K. Lee.
>
--
Vikram Garg
PhD Candidate
Institute for Computational and Engineering Sciences
The University of Texas at Austin
http://users.ices.utexas.edu/~vikram/
http://www.runforindia.org/runners/vikramg
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