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Computational Methods for Debonding in Composites

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Chapter 12<br />

On Buckl<strong>in</strong>g Optimization<br />

of a W<strong>in</strong>d Turb<strong>in</strong>e Blade<br />

Erik Lund and Leon S. Johansen<br />

Abstract The design of composite structures such as w<strong>in</strong>d turb<strong>in</strong>e blades is a challeng<strong>in</strong>g<br />

problem due to the need <strong>for</strong> push<strong>in</strong>g the material utilization to the limit <strong>in</strong><br />

order to obta<strong>in</strong> light and cost effective structures. As a consequence of the m<strong>in</strong>imum<br />

material design strategy the structures are becom<strong>in</strong>g th<strong>in</strong>-walled, such that<br />

buckl<strong>in</strong>g problems must be addressed, and <strong>in</strong> this work the aim is to obta<strong>in</strong> buckl<strong>in</strong>g<br />

optimized multi-material designs of w<strong>in</strong>d turb<strong>in</strong>e blades. The design problem<br />

consists of distribut<strong>in</strong>g multiple materials with<strong>in</strong> a given design doma<strong>in</strong>, and the<br />

candidate materials may be fiber-re<strong>in</strong><strong>for</strong>ced materials, oriented at given discrete<br />

fiber angles, together with isotropic materials like foam materials used <strong>for</strong> sandwich<br />

structures. The discrete design optimization problem is converted to a cont<strong>in</strong>uous<br />

problem us<strong>in</strong>g the so-called Discrete Material Optimization (DMO) approach based<br />

on ideas from multi-phase topology optimization where <strong>in</strong>terpolation functions with<br />

penalization are <strong>in</strong>troduced. In this way traditional gradient based optimization<br />

techniques <strong>in</strong>clud<strong>in</strong>g efficient methods <strong>for</strong> design sensitivity analysis and mathematical<br />

programm<strong>in</strong>g can be used <strong>for</strong> solv<strong>in</strong>g the multi-material distribution problem.<br />

The multi-material topology optimization approach is demonstrated <strong>for</strong> buckl<strong>in</strong>g<br />

optimization of a 9 m generic w<strong>in</strong>d turb<strong>in</strong>e blade test section.<br />

12.1 Introduction<br />

Fiber-re<strong>in</strong><strong>for</strong>ced composite lam<strong>in</strong>ates are popular because of high stiffness-toweight<br />

and strength-to-weight ratios compared with isotropic materials, and they<br />

are, <strong>for</strong> example, used <strong>in</strong> naval, aerospace, automobile and other mechanical applications.<br />

Such composite lam<strong>in</strong>ates consist of layers of one or more materials stacked<br />

at different orientation angles, and they permit the designer to tailor the structure or<br />

component to achieve the specified objectives.<br />

E. Lund and L.S. Johansen<br />

Department of Mechanical Eng<strong>in</strong>eer<strong>in</strong>g, Aalborg University, Pontoppidanstraede 101, DK-9220<br />

Aalborg East, Denmark, e-mail: el@ime.aau.dk<br />

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