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Using slidelines with higher order elements
The slideline algorithms in LUSAS only use corner nodes
in monitoring contact conditions and applying appropriate
restraints. For this reason low order elements are recommended
in general.
Slidelines may, however, be utilised with
higher order elements in which case Modeller will automatically
create a constraint equation to ensure that each midside
node occurring on a slideline displaces according to the
average of the immediately adjacent corner nodes, i.e. forcing
the slideline face to act as a linear element.
The disadvantage in using higher order elements
is that contact and, particularly, impact can excite element
mechanisms. This can be circumvented by specifying fine
integration for the element, but at the cost of an increase
in solution time as well as the correspondingly "stiffer"
solution normally expected with full integration. Moreover,
a refined mesh is generally recommended in the area of contact
which can result in significant analysis solution times.
The advantage is that classical higher order
elements have correspondingly higher order displacement
interpolation and can, therefore, simulate greater variations
in stress across a single element more accurately, enabling
fewer elements to be used. However, for the reason mentioned
above, this cannot normally be exploited. It should also
be noted that the low order, enhanced strain continuum elements
perform as well as the 20-noded at a fraction of the cost.
These elements are the default choices in LUSAS Modeller
where appropriate. In general they have an "m"
at the end of the element name - see the element reference
library manual for more information.
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