Engineering Optimization, 5th Edition

16 Multilevel and Multiobjective Optimization

16.1 Introduction

Although the practical aspects of optimization described in Chapter 15 can help in solving engineering optimization problems more efficiently, additional strategies are required for handling large practical engineering problems. For example, the optimum design of many practical mechanical, structural, and other engineering systems requires consideration of a large number of design variables, numerous constraints, and multiple objective functions. The design of an aircraft wing or complete aircraft, for example, involves not only the sizing of the overall wing (such as span, chord length distribution, and locations of nacelles/engines and controls), but also the determination of the spar and rib thicknesses, and areas and shapes of the stiffening members. In such cases, a multilevel optimization approach is often used with major dimensions decided in one level of optimization and the detailed dimensions computed in the second level. In addition, the analysis and determination of the aerodynamic and structural performance of the wing requires the use of large‐ scale finite element software such as NASTRAN, ABAQUS, and ANSYS. Also, the optimization problem involves not only the constraints on the stresses induced in different flight conditions (taxiing, take‐off, steady cruise, gust loads and turbulence and landing), control performance, stability, aerodynamic performance, drag, lift, buckling, and flutter ...