Optimal frequency design of wind turbine blades

An optimization model for the design of a typical blade structure of horizontal-axis wind turbines is presented. The main spar is represented by thin-walled tubular beam composed of uniform segments each of which has different cross-sectional properties and length. The optimization variables are chosen to be the cross-sectional area, radius of gyration and length of each segment. The optimal design is pursued with respect to maximum frequency design criterion. Global optimality is attainable by the proposed model and a novel mathematical concept is given for placing the system frequencies. The problem is formulated as a non-linear mathematical programming problem solved by multi-dimensional search techniques. Structural analysis is restricted to the case of uncoupled flapping motion of the rotating blade, where an exact method of solution is given for calculating the natural vibration characteristics. Aeroelastic stability boundaries and steady-state response are calculated using Floquetʹs transition matrix theory. The results show that the approach used in this study is efficient and produces improved designs as compared with a reference or baseline design.