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fmpgomes
New member
Username: fmpgomes

Post Number: 1
Registered: 04-2010
Posted on Tuesday, April 20, 2010 - 01:37 pm:   

Hi, Mr. Nelson.
I'm using Flexpde 6.12, recently acquired by Furnas, company I work. And sorry for my bad english.

In elasticity, the stress tensor can be expressed in terms os principal stress (http://en.wikipedia.org/wiki/Stress_(mechanics)#Mohr.27s_circle_for_a_general_three-dimensional_state_of_stresses). I get the matrix associated with the tensor and calculate the three eigenvalues which are the three principal stresses. For each of 3 principal stress correspond a principal direction, and we really need this for the analysis in 3D domain.
Unfortunally, we don't understand the section "Eigenvalues" in Help. And we don't know "eigenfunctions" too... We see '3d_plate' and '
Please, help us.
Below, some try.
application/octet-streamexemple in 2D, with ERROR
TermBi-R1.pde (15.2 k)
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rgnelson
Moderator
Username: rgnelson

Post Number: 1350
Registered: 06-2003
Posted on Tuesday, April 20, 2010 - 06:05 pm:   

The short answer is that you can't use MODES and time dependence in the same problem.

MODES refers to computing the eigenvalues and eigenfunctions of the PDE, which in a stress problem would refer to the standing wave vibration patterns and frequencies for the structure.

Your temperature equation is time dependent, implying that you want to compute the evolution of the temperature and stress in your figure.

The stress invariants at any point can simply be computed by definitions in the DEFINITIONS section.

You may want to discuss this with Dr. Gitirana, who I believe is associated with your company.

Also, Dr. Backstrom has a book "Simple Deformation and Vibration by Finite Element Analysis" that is written for FlexPDE(5), availabe through the link on our web page www.pdesolutions.com/bookstore.html

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