Abstract

This contribution compares the performance of a monolithic and two staggered numerical update schemes for a coupled shape and topology optimization method for thin-walled beam structures. In order to limit the computational time of the optimization method, the thin-walled beam structures are modeled as 2.5D configurations. In this approach, 1D beam elements are used to simulate the beam response in the longitudinal direction, while the cross-sectional properties of the beam elements are calculated from additional 2D finite element method analyses. The sensitivities with respect to the shape and topology design variables are derived in closed form in order to take advantage of a computationally efficient, gradient-based optimization algorithm. The numerical examples concern basic circular and square thin-walled cantilever beam structures, as well as a more complex, non-prismatic thin-walled beam structure representative of a rotor blade used in a horizontal-axis wind turbine. For each numerical example the computational time and the solution computed by the monolithic and staggered update schemes are compared, which provides clear insight into the numerical efficiency of the solution procedure and the uniqueness of the computational result. Although the three different update schemes for the cases examined result in comparable optimized design concepts, the computational efficiency and the specific minimal compliance value found turn out to be rather sensitive to the algorithmic details of the numerical update scheme applied. Since the monolithic update scheme typically navigates a larger design space than the two staggered update schemes, for most cases examined it provides the lowest structural compliance. In the specific case whereby shape optimization (virtually) has no influence on the final, optimized beam configuration, the structural compliance computed by the monolithic scheme may relate to a local minimum that is less optimal compared to the value calculated by a staggered update scheme.

Highlights

  • Thin-walled beam structures are applied as load-bearing components in various engineering applications; illustrative examples are aircraft wings, wind turbine blades and hollow pile foundations

  • In order to limit the computational time of the optimization method, the beam structures are modeled as 2.5D configurations

  • A practical case study is considered of a horizontal-axis wind turbine (HAWT) rotor blade subjected to representative wind loading conditions

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Summary

Introduction

Thin-walled beam structures are applied as load-bearing components in various engineering applications; illustrative examples are aircraft wings, wind turbine blades and hollow pile foundations. Thin-Walled Structures 159 (2021) 107182 this typically leads to a considerable increase in computational time Another drawback of a fixed design domain is that it impedes the optimization of aeroelastic structures, such as aircraft wings and wind turbine blades. Since monolithic and stag­ gered update schemes follow different search paths in the design space, the numerical efficiency and the solution obtained by these update schemes in principle is different This sensitivity needs to be explored and well understood in order to develop a solid confidence in the results calculated by the coupled shape and topology optimization method.

Geometrical description and design variables
General framework
Sensitivity analysis
Topology sensitivities
Update of design variables
Numerical examples
Circular and square thin-walled cantilever beams
Findings
Conclusions
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