Loads and Boundary Conditions

Node Restrictions for Shape Optimization

Node restrictions in the Abaqus input file (command *BOUNDARY) are imported during the Tosca Structure preprocessing step if the following command is defined:

OPTIONS
 READ_BC = ALL
END_

By default, this command is already included in the configuration file command.ini. Therefore, it must not be defined explicitly in the parameter file.

Node restrictions defined in the FE-analysis (and maybe not used in the FE analysis) can be used as restrictions for design variables for shape and bead optimization (see command DVCON_SHAPE, DVCON_BEAD) to avoid optimization nodal displacements in specified places.

Contact Boundary Conditions

This behavior can be avoided by the definition of different restrictions in the optimization task (casting or minimum member size restrictions)

Sometimes the exact boundary conditions cannot be specified before designing the components. Often the exact boundary conditions are unknown early in the design phase. In addition, nonlinear boundary conditions such as contact definitions can change during designing. Linearized models often require several recalculations and reoptimizations with respect to the linearized boundary conditions and are therefore time-consuming. Thus, it is more efficient if the contact conditions are directly specified in the finite element input file applied for the optimization.

Tosca Structure is easy to operate for the familiar user of Abaqus. You create an analysis model for Abaqus with the relevant contact definitions. In addition, you define the design area for the optimization and the optimization task. Information for Tosca Structure regarding the actual contact problem is not required because Tosca Structure is a modular system. The contact problem becomes a part of the optimization through the forces of the nodes and the stresses. As a result, you can make full use of the capabilities in Abaqus for the contact calculations.

Contact conditions are permitted in the analysis model for topology and shape optimization. Defining a contact surface directly on the edge of the design space is allowed in topology optimization. The shape optimization algorithm must be inverted (see command OPT_PARAM, Parameter SCALE) if the design edge belongs to a contact surface in shape optimization. Convergence difficulties in the FE analysis might arise in cases of complex contact problems due to large changes in the model during optimization.