Defining Width Control (Minimum Cluster Width)

Small sheet parts in the resulting structure are often undesirable. Defining a minimum sheet width (minimum cluster width) avoids the creation of small substructures in the final result ( MIN_CLUSTER_WIDTH).

This task shows you how to:

See Also
In Other Guides
DVCON_SIZING

Context:

The minimum cluster width is often applied for avoiding high oscillations in the thickness distribution and that the structure has subcomponents with a minimum width.

In addition, the minimum cluster width for the width control can partly circumvent the two following problems:

  • First, checkerboards might appear if one is applying a minimal value of the lower bound of the thickness and applying lower-order shell elements as 3 node triangular shell elements. When using higher-order shell elements or the lower bound of the thickness is not minimal, checkerboards are not frequent.
  • Secondly, a minimum cluster width ensures uniqueness of the optimization solution independent upon the mesh size and discretization. A coarse mesh and a fine mesh lead to the same optimized structure if the minimum cluster widths for both cases are set to the same absolute size. Note that the size in both cases should be larger than the average element edge length.


Note:

Thin sheet thickness is controlled by lower and upper bound settings and not by the filter which controls the width.

Define a Minimum Cluster Width in Tosca Structure.gui

  1. Choose Command | DVCON_SIZING in Tosca Structure.pre screen.
  2. Apply an ID_NAME and select the element group. If the element group is not already defined, it is necessary to define it in advance using the GROUP_DEF command.
  3. Choose Type = Minimum Cluster Width and define a value:

Parameter File

The resulting command looks like: 

DVCON_SIZING
 ID_NAME    = <Name of DVCON object> 
 EL_GROUP   = <Element group to be restricted>
 CHECK_TYPE = MIN_CLUSTER_WIDTH
 WIDTH      = <minimum width of areas of same shell thickness>
END_