Topology optimization: from load path to a lighter part

What topology optimization does

You give the solver a design space, the loads and supports, and a goal, for example the stiffest structure that uses no more than a set fraction of the material. The solver then removes material where it carries little load. The result is a load path: a picture of where material is needed. It is a starting point for design, not a finished part.

The inputs decide the result

• Design space and non-design space. Make the design space as large as packaging allows, and mark bolt faces, bearing seats and mating surfaces as non-design.
• All load cases. A part optimized for one load case will be weak in the others. Include every relevant case, such as braking, cornering, bumps or lifting.
• Constraints. Mass or volume targets, displacement limits and minimum natural frequency all change the shape.
• Manufacturing constraints. Draw direction for casting or molding, extrusion direction, symmetry and minimum member size keep the result manufacturable.

From load path to part

The raw result is interpreted into CAD geometry that suits the process. Size and shape optimization then set the final thicknesses and dimensions, and a full analysis checks stress, stiffness and fatigue on the final design.

Skidmore, Owings & Merrill used exactly this sequence on a courthouse in Los Angeles: topology optimization in OptiStruct gave the load path, and beam optimization chose the steel sections. Steel was reduced by 10%. See the SOM case study.

Tools in HyperWorks

• OptiStruct for topology, topography, size, shape and free-size optimization, with the structural analysis in the same solver.
• Inspire for designers who want generative design and topology optimization early, in a simpler interface.
• HyperStudy for design of experiments and optimization across solvers and parameters.

Common mistakes

• Leaving out a load case that later drives the design.
• Making the design space too small, so the solver has no room to find a better path.
• Ignoring manufacturing until after the result, then losing most of the benefit when it is redrawn.
• Treating the raw result as the final geometry without a verification analysis.

Sources

• Skidmore, Owings & Merrill case study (Siemens)
• Simcenter OptiStruct (Siemens)

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