Defining a Maximum Truss Thickness (Maximum Member Size)

The definition of a maximum truss thickness is often necessary in order to design the components produced by casting. With this restriction, thick parts are avoided by splitting them into several thinner parts.

This task shows you how to:

Before you begin: The maximum member size constraint can only be used with the sensitivity-based algorithm. Maximum member size constraints with the controller algorithm are not supported.
Related Topics
In Other Guides
DVCON_TOPO

Context:

Normally, the maximum member size control is also a minimum member size control. In the restriction area, the resulting structure contains trusses mainly of the given defined diameter. Generally, no thinner trusses exist. Usually, the combination of a maximum member size control and a minimum member size control is not required.

The following figure shows a plate designed with and without maximum member size control:



Define a Maximum Member Size in Tosca ANSA® environment

  1. Choose DV_CONSTRAINTS and select New > MEMBERSIZE_CONTROL.

  2. In MEMBER_SIZE_CONTROL dialog, enter the element group and the desired minimum thickness, using MEMBER_SIZE = MAX.

Define of Maximum Member Size in Tosca Structure.gui

  1. Choose Command > DVCON_TOPO in Tosca Structure.pre.

  2. Define the Maximum Member Size as shown in the following figure:

  3. Or use the DVCON_TOPO command: 

    DVCON_TOPO
 ID_NAME = <Name of DVCON object>

 EL_GROUP = <Element group to be restricted>

 CHECK_TYPE = MAX_MEMBER

 THICKNESS = <maximum thickness of structures>
 MIN_THICKNESS = <minimum thickness of structures>
 DISTANCE = <distance between structural members>
END_

Define of a Maximum Membersize in Tosca Extension for ANSYS® Workbench

  1. To add a Membersize Control, select Topology > Membersize.

  2. In Details View window, select MAX_MEMBER as Check Type and insert the desired membersize as Thickness.

  3. If necessary, set more options like Distance or MinThickness.

    Important:

    The maximum member size restriction will usually not create thin parts in the area of boundary conditions and loads in the optimized structure. A reduction in these areas may result in collapsing the structure.

    The specified maximum diameter should not be smaller than twice the average element edge length because smaller values will create elements only connected by one or two nodes (point or line contact).

    The CPU-time for the calculation increases quadratically with the maximum member size. To save calculation time, the restriction should only be defined in the areas of the model where the thick parts are present. To identify these areas, the first step is to perform an optimization without restrictions.