Page 388 - Finite Element Modeling and Simulations with ANSYS Workbench

11

Design Optimization

11.1 Introduction
Optimization is an integral part of engineering design. Traditionally, optimization tasks
have been carried out mostly by trial and error, when unexpected failure of a design to
meet certain criteria is identified. Often, a best design is not obtained after many design
iterations. Only a feasible design meeting all the requirements is created. The conven-
tional way of changing a design when it is found to be deficient in certain criteria can be
incredibly costly and time-consuming. For today’s engineers, a more productive and cost-
effective practice is to use numerical optimization techniques to guide in the evaluation
of design trade-offs. Often, a best design is put forward after running simulation-based
optimization a few times. In this chapter, we will cover materials relating to the topics of
design optimization via simulation. The concepts of topology optimization, parametric
optimization, and design space exploration will be introduced, along with optimization
®
examples using ANSYS Workbench.

11.2 Topology Optimization

A design’s performance should be optimized from different perspectives as the design
process evolves. In the early stage of a design, topology optimization can be used to help
designers arrive at a good initial design concept. The goal of topology optimization is to
find the ideal distribution of material within a predefined design space for a given set of
loading and boundary conditions. The regions that contribute the least to the load bear-
ing are identified and taken out from the design to minimize the weight. As a result, an
optimal material layout is determined, from which a good design concept can be derived.
Figure 11.1 illustrates topology optimization of a bridge structure. The 3-D design space
of the bridge is shown as a solid rectangle box in Figure 11.1a. The bridge is fixed on the
bottom two edges and applied a surface load on the top face. In Figure 11.1b, an arch is
clearly suggested as the ideal layout by the topology optimization study aiming at 80%
weight reduction. Materials are removed from the least stressed regions in the simulation
model, that is, regions contributing the least to the overall stiffnesss of the structure. This
optimization study perhaps helps elucidate why the arch continues to play an important
part in bridge design after thousands of years of architectural use.

373