Thanks, Damian,
Yes, the degenerated 4-node shell elements can be easily converted
into 3-node elements by using many commercial software, i.e. Mcrash,
EasiCrash.
However it is not easy to quantify the effect of 4-node degenerated
elements on the FE results.
Thanks for any further discussion.
Will
--- Damian McGuckin <[log in to unmask]> wrote:
> On Sun, 5 May 2002, will kim wrote:
>
> > It seems well known that if a model contains many degenerated
> 4-node
> > elements, its results from the explicit algorithm will be less
> > reliable. Can anyone here provide a brief theoretical explanation
> > about the effect of degenerated 4-node element on FE calculation
> > results in the explicit algorithm.
>
> Avoiding your question (sorry), if you identify the 2 co-incident
> nodes,
> you can under many, if not most circumstances, use a routine ( if
> it is
> available ) which has formulated the algebra in terms of 3 nodes,
> not 4.
> While this does not consider the case where the 2 nodes not
> co-incident
> but simply very close to each other, this eliminates those
> numerical
> problems for the purely co-incident case. In most isoparametric
> shells,
> the algebra is a function of the number of nodes. Integration
> rules for a
> triangle are very different to those of a quadrilateral.
>
> Mind you, if you are stuck with somebody's package that has no
> triangles,
> you are a bit out of luck.
>
> The same applies for degenerated bricks but only where you have a 1
> or 3
> fully collapsed faces, i.e. it is a pentahedron or tetrahedron. A
> single
> collapsed edge is not sufficient to create a simple geometric shape
> which
> has an easily know algebraic solution. This case is so bad I would
> not
> begin to know where to start. With so many different combinations,
> this
> 3D case would be 100 times more complicated to implement than the
> 2D case.
>
> - Damian
>
> Pacific Engineering Systems International, 22/8 Campbell St,
> Artarmon NSW 2064
> Ph:+61-2-99063377 .. Fx:+61-2-99063468 | unsolicited email not
> wanted here !
> Views and opinions here are mine and not those of any past or
> present employer
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