Variational approach to relaxed topological optimization: closed form solutions for structural problems in a sequential pseudo-time framework

TL;DR

This paper introduces a variational, closed-form solution approach for relaxed topological optimization in structural problems, utilizing a pseudo-time framework and fixed point algorithms, significantly reducing computational costs compared to traditional methods.

Contribution

It develops a novel analytical variational framework for topological optimization, providing efficient closed-form solutions and a pseudo-energy based smoothing technique to address ill-posedness.

Findings

Closed-form solutions enable efficient optimization in structural design.

The method reduces computational cost by approximately five times.

Solutions are comparable in quality to level set methods.

Abstract

The work explores a specific scenario for structural computational optimization based on the following elements: (a) a relaxed optimization setting considering the ersatz (bi-material) approximation, (b) a treatment based on a nonsmoothed characteristic function field as a topological design variable, (c) the consistent derivation of a relaxed topological derivative whose determination is simple, general and efficient, (d) formulation of the overall increasing cost function topological sensitivity as a suitable optimality criterion, and (e) consideration of a pseudo-time framework for the problem solution, ruled by the problem constraint evolution. In this setting, it is shown that the optimization problem can be analytically solved in a variational framework, leading to, nonlinear, closed-form algebraic solutions for the characteristic function, which are then solved, in every time-step, via fixed point methods based on a pseudo-energy cutting algorithm combined with the exact fulfillment of the constraint, at every iteration of the non-linear algorithm, via a bisection method. The issue of the ill-posedness (mesh dependency) of the topological solution, is then easily solved via a Laplacian smoothing of that pseudo-energy. In the aforementioned context, a number of (3D) topological structural optimization benchmarks are solved, and the solutions obtained with the explored closed-form solution method, are analyzed, and compared, with their solution through an alternative level set method. Although the obtained results, in terms of the cost function and topology designs, are very similar in both methods, the associated computational cost is about five times smaller in the closedform solution method this possibly being one of its advantages.