Abstract

Optimization of frame structures is formulated as a non-convex optimization problem, which is currently solved to local optimality. In this contribution, we investigate four optimization approaches: (i) general non-linear optimization, (ii) optimality criteria method, (iii) non-linear semidefinite programming, and (iv) polynomial optimization. We show that polynomial optimization solves the frame structure optimization to global optimality by building the (moment-sums-of-squares) hierarchy of convex linear semidefinite programming problems, and it also provides guaranteed lower and upper bounds on optimal design. Finally, we solve three sample optimization problems and conclude that the local optimization approaches may indeed converge to local optima, without any solution quality measure, or even to infeasible points. These issues are readily overcome by using polynomial optimization, which exhibits a finite convergence, at the prize of higher computational demands.

Highlights

  • Designing economical, efficient, and sustainable structures represents a major challenge of the contemporary society

  • We develop four different methods in Section 2: (i) general non-linear optimization solved by the interior-point method of fmincon, (ii) the first-order optimality criteria (OC) method [1, 5], (iii) reformulation of the problem into a non-linear semidefinite program (NSDP) solved by PenLab [6], and (iv) a suitably modified polynomial optmization (PO) problem (iii) solved globally using polynomial optimization methods [7] and the Mosek [8] optimizer

  • We show that the latter PO approach generates guaranteed lower and upper bounds on the solution, providing a means of assessing the design quality

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Summary

Introduction

Efficient, and sustainable structures represents a major challenge of the contemporary society. We develop four different methods in Section 2: (i) general non-linear optimization solved by the interior-point method of fmincon, (ii) the first-order optimality criteria (OC) method [1, 5], (iii) reformulation of the problem into a non-linear semidefinite program (NSDP) solved by PenLab [6], and (iv) a suitably modified polynomial optmization (PO) problem (iii) solved globally using polynomial optimization methods [7] and the Mosek [8] optimizer We show that the latter PO approach generates guaranteed lower and upper bounds on the solution, providing a means of assessing the design quality.

Solution techniques to frame optimization
Optimality criteria
Polynomial optimization
Solution process
Recognizing global optimality
Cantilever beam
I-shaped girder with self-weight
Conclusions

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