D3PLOT 22.1

How the "Closure" Calculation Works, and the Output it Produces

How the closure calculation works, and the output it produces

It is necessary to calculate the distance from each workpiece node to the nearest facet on the die. This is done by determining which facet a node will be projected onto when contact is made, and computing to the vector distance (less element thicknesses) between node and facet. This is very similar to the *CONTACT_NODES_TO_SURFACE problem in Ansys LS-DYNA, except that D3PLOT must consider nodes at some distance from, as well as in contact with, the die surface.

For nodes close to or in contact with a facet this is a simple calculation, but when a node is quite a long way from the die problems of ambiguity ("Which facet will I ultimately make contact with?") and complexity ("I need to be tested against many distant facets") arise.

To get round these problems, and to achieve a reasonably short computation time, a bucket-sorting process is used:

  • The volume of space around the workpiece, plus a margin, is calculated and then sub-divided by (x,y,z) coordinates into a 3D matrix of "buckets". Each bucket is a smaller, rectilinear volume of space.
  • Each workpiece node is assigned to a bucket, based on its coordinate. Die facets may lie in one or more buckets, or none at all if very distant.
  • For each die facet closure is only calculated for workpiece nodes that exist in the same or immediately adjacent bucket(s) as the facet.

D3PLOT uses a 10x10x10 (x,y,z) array of buckets, and chooses default dimensions such that closure values up to about 20% of the longest workpiece dimension will be calculated. Thus node closures will fall into one of four categories:

Node location
Meaning
Value
In Contact The workpiece node lies on or behind the die facet surface. (The penalty algorithm in Ansys LS-DYNA means that a node may penetrate an element.)
0.0
Near to contact The node is reasonably close to a facet, and a closure distance can be calculated.
> 0.0
Uncomputed The node is too far from the die for a closure distance to be computed, or has fallen into a "tunnel" between facets (see below).
-1.0 1
Uninvolved For nodes not in the workpiece, so not involved in the closure calculation at all.
-2.0 1

Closure categories and associated values

Note 1: These values are defaults which can be changed, see OPTIONS... below.



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