On Tue, May 5, 2015 at 6:34 PM, John Peterson <jwpeter...@gmail.com> wrote:
>
>
> On Tue, May 5, 2015 at 4:08 PM, David Knezevic <david.kneze...@akselos.com
> > wrote:
>
>> On Tue, May 5, 2015 at 5:48 PM, John Peterson <jwpeter...@gmail.com>
>> wrote:
>>
>>>
>>>
>>> On Tue, May 5, 2015 at 2:04 PM, David Knezevic <
>>> david.kneze...@akselos.com> wrote:
>>>
>>>>
>>>> Also, going back to my negative jacobian issue: I realized that this
>>>> element is actually not affine. So it seems like John's comment could be
>>>> right, i.e. that the jacobian is negative at at least one of the quadrature
>>>> points, and that Cubit doesn't pick this up because it's not testing the
>>>> jacobian at the same points.
>>>>
>>>
>>> Try initializing a CONSTANT order quadrature rule in your test code and
>>> see if that runs without hitting a negative Jacobian?
>>>
>>
>> That still gives a negative Jacobian.
>>
>> I can't imagine there's anything wrong with the libMesh code for
>> computing the jacobian, since that's used everywhere, so I guess this
>> element must be invalid. I pasted the node locations earlier in this
>> thread, and I was wondering if there is any "sanity check" I can run on
>> this element to confirm that it is indeed bad?
>>
>
> I plotted your element, and it looks pretty bad, almost completely flat.
> In the first image, you can see that the apex node and the mid-face node on
> the base are very close together. In the second image, you can see a
> reference Tet10, just to prove that Paraview displays these correctly. I
> really don't know how Cubit can claim that element has a non-negative
> Jacobian...
>
>
> https://drive.google.com/file/d/0B9BK7pg8se_iVUVpSUs4Y3J2dFk/view?usp=sharing
>
> https://drive.google.com/file/d/0B9BK7pg8se_ibUFKOHRDZ1FrTEE/view?usp=sharing
>
> Test code: https://gist.github.com/jwpeterson/c6c2fc8f627c02a0546b
>
Those figures are very helpful, thanks!! Definitely seems like CUBIT is in
the wrong here.
Thanks,
David
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