TetrahedronElement.GetLocalInternalStress() + Robot Structural Analysis Comparison

[Murtasgh]

Hi,

I am aware that the TetrahedronElement is not fully implemented and may contain some bugs. For this reason I was comparing the output from BFE.NET with Robot Structural Analysis and the deflections are pretty much the same.

However, I'm having some difficulties extracting the stresses on TetrahedronElement by using GetLocalInternalStress(). I keep getting an IndexOutOfRangeException which seems to be because the res[,] variable is always [6x1] when I guess it should be at least [3x3] (see screenshot attached).

Are there any example on how GetLocalInternalStress() should be used to avoid this?

Many thanks for all the help in advance.

[epsi1on]

Hi there,
I need to check, seems the matrix dimensions are mismatch.
Formula for stress tensor would be DBU, but in this case...
Will update soon...
Also it's cool to hear the displacements are similar with robot structural, it could be a success validation of the library...
edit: for my own reference this is a formula for internal force of tetrahedron element: link

[epsi1on]

fixed in 89e3124,
can you please do a check?

[Murtasgh]

That's perfect, I'll do a check as soon as possible.

In a similar note, I was validating the TriangularShell elements but I'm having some difficulties with the LocalX and LocalY coordinates of the GetInternalForce method. Would you be able to confirm what coordinates would correspond to points 1, 2 and 3 of each triangle?

Thanks!

[epsi1on]

GetInternalForce usualy uses isoparametric coordinates. it is not a fixed point. do you mean integration points?

[epsi1on]

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