Objectives

The Objectives command enables you to define optimization objectives and limits that the outcomes should satisfy. Access the command by selecting Objectives from the Design Criteria panel of the Generative Design toolbar.

You can select:

• Maximize stiffness - select it to achieve the maximum possible stiffness of the design for a given mass. You need to specify the value of the mass target for this objective.

  If you maximize the stiffness of the design, the design resists displacement caused by specified constraints and loads, but may be heavier. The mass is decreased by removing material in the areas that have the smallest impact on the stiffness of the model. The optimum stiffness to mass ratio is achieved, allowing the design to be as lightweight as possible for the application.

• Minimize mass - select it to achieve the minimum possible mass of the design. The solver removes mass through an automatically set number of iterations.

  If you minimize the mass, the resulting shape is light, but may be more prone to deflections caused by specified constraints and loads.

Limits

Optimization limits enable you to specify other requirements that the outcomes should satisfy. The solver tries to achieve the limits, though sometimes it may not be possible. The limits include:

• Safety factor – enables you to specify the ratio between the material’s yield strength and the maximum von Mises stress that the outcomes should satisfy. The Safety Factor value is based on the Yield Strength value of the material selected in your study.

• Mass target - enables you to achieve the desired mass of the generated shape. This limit is available, when you select the Maximize Stiffness objective. The mass target ensures that your design reaches the desired mass. For example, you can obtain a model that weighs 500 grams.

• Modal Frequency - enables you to include vibration limits in the generative design process. Specify Min. First Mode Frequency to define the lowest frequency at which the design's response occurs. The First Mode Frequency value should be greater than the frequency of the design when vibrating.

• Displacement - enables you to include displacement limits in the generative design process. You can specify global or local displacement limit.

  • Global - determines the maximum global displacement of your design.
  • Local - determines the maximum local displacement of a part of your design. You can define it for one or more locations in your design that belong to the preserve geometry, such as a face, edge, or vertex.

• Buckling - enables you to include buckling limits in the generative design process. Buckling causes the loss of stability of a design when under compression. Specify a Safety Factor value that is sufficient to avoid buckling of the design.

  If the safety factor of the initial shape is lower than desired, the solver increases the amount of material and the mass of your design. The solver continues increasing them until:

  • Your design reaches the safety factor target, or
  • Your design reaches the mass target.
  Note: The combination of the Buckling limit and the Remove rigid body modes option within the same study is not supported. If you use both of them, you won't receive any outcomes. Consider using them in different studies.

Example:

• Select Minimize Mass as an objective

• Enter 2 as the Safety Factor limit.

  The solver will minimize mass ensuring that the minimum factor of safety equals or is greater than 2.

The solver does not always remove mass until it achieves the Safety Factor limit. It tries to find the stiffest model while:

• Removing as much mass as possible
• And ensuring that the minimum factor of safety equals or is greater than the Safety Factor limit.