FE model check

[christophersrikanth]

Hi All,

I shall be grateful if you can point me in write direction.

I have some experience in writing FE codes for 1D elements (inclusing non linear) and have recently started using NX as a user in my workplace.

In NX (and I guess in all other FE softwares) we have FE model check based on the eblow criteria:


1)Aspect ratio
2)Warp
3)Skew
4)Taper
5)Jacobian ratio
6)Jacobian zero
7)Minimum angle
8)Maximum angle

A) I undestand aspect ratio might be ratio between shortesr and larges element sides. Am I right? How much that should be and what is the underlying physics here?
B) I'm not sure what the terminologies warp and skew mean here in connection with FE model checks. Can anyone help? As I would like to correct these entities based on my failed eleemnts (which are displayed following a check)
C) Now, JAcobian expresses the transformation bbetween mapped and real / geometric corrdinates. I'd heard of Jacobian determiannt but not clear of Jacobian ratio/Jacobian zero.Are warp, skew and JAcobian related?

Can anyone throw some light or perhaps a FE text that discusses these clearly

Chris

 

[christophersrikanth]

Another question- Are these checks at following the solution(i.e. after the analysis) or before analysis?

 

[rb1957]

the ideal quad is a square, aspect ratio 1 ... as you get away from that the results get unreliable.

skew is how much like a rhombus it is, skew zero is ideal.

warp is how much out of plane it is (3 points define a plane, if the 4th corner is on the same plane then warp = 0).

there's lots out there about sensivity of elements (user manuals, advanced manuals) check the autoexec to see the pre-set limits. the grand-daddy of most quad elements toay is the NASTRAN CQUAD4.

investigate it yourself with simple single element tests ... test aspect ratio 1, 2, 5, 10, 20, ... for a single element in tension

Quando Omni Flunkus Moritati

 

[GregLocock]

All except 5 and 6 are direct checks of element quality - simple geometrical analysis, ie preprocessing. The Jacobian ones I'm not sure about, it could refer to an element or a model. In context i suspect it is another element based check.

Cheers

Greg Locock


New here? Try reading these, they might help FAQ731-376

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[spongebob007]

A jacobian error indicates an element that is folded over on itself.