1. Introduction
Topology optimization (TO) is a field of design optimization that determines the optimal material layout under
certain constraints on loads and boundaries within a given design space. This method allows the optimal
distribution of materials with desired performance to be determined while meeting the design constraints of the
structure (Bendsøe, 1989). TO is meaningful in that, compared with conventional optimization approaches,
designing is possible without meaningful initial design. Due to these advantages, various TO methodologies have
been studied to date (Bendsøe, 1989; Rozvany et al., 1992; Mlejnek, 1992; Allaire et al., 2002; Wang et al., 2003;
Xie & Steven, 1993). The following four TO methodologies are described in detail in Appendix A: density-based
method (i.e., the solid isotropic material with penalization (SIMP) method), evolutionary structural optimization
(ESO) method, level-set method (LSM), and moving morphable component (MMC) method.
Recent TO methods aim to solve various industrial applications. Examples include TO for patient-specific
osteosynthesis plates (Park et al., 2021), microscale lattice parameter (i.e., the strut diameter) optimization for TO
(Cheng et al., 2019), homogenization of 3D TO with microscale lattices (Zhang et al., 2021b), and multiscale TO
for additive manufacturing (AM) (Kim et al., 2022). Other notable works for more complex TO problems include
a multilevel approach to large-scale TO accounting for linearized buckling criteria (Ferrari & Sigmund, 2020),
the localized parametric level-set method applying a B-spline interpolation method (Wu et al., 2020), the
systematic TO approach for simultaneously designing morphing functionality and actuation in three-dimensional
wing structures (Jensen et al., 2021), the parametrized level-set method combined with the MMA algorithm to
solve nonlinear heat conduction problems with regional temperature constraints (Zhuang et al., 2021b), and the
parametric level-set method for non-uniform mesh of fluid TO problems (Li et al., 2022).
However, although the aforementioned TO methodologies can produce good conceptual designs, one of the
main challenges in performing TO is its high computational cost. The overall cost of the computational scheme is
dominated by finite element analysis (FEA), which computes the sensitivity for each iteration of the optimization
process. The required FEA time increases as the mesh size increases (e.g., when the mesh size is increased by 125
times, the required time increases by 4,137 times (Liu & Tovar, 2014)). Amid this computational challenge,
performing TO for a fine (high-resolution) topological mesh can take a few hours to days (Rade et al., 2020).
Furthermore, the 3D TO process requires much higher computational costs with increasing demands in the order
SIMP, BESO, and level set method in terms of the number of iterations (Yago et al., 2022). Therefore, various
studies have aimed to reduce the computation of solving these analysis equations in TO (Amir et al., 2009; Amir
et al., 2010). For instance, by using an approximate approach to solve the nested analysis equation in the minimum
compliance TO problem, Amir and Sigmund (2011) reduced the computational cost by one order of magnitude
for an FE mesh with 40,500 elements.
Similarly, aiming to improve this computational challenge, various methods have been developed to accelerate
TO (e.g., Limkilde et al. (2018) discussed the computational complexity of TO, while Ferrari and Sigmund (2020)
conducted large-scale TO with reduced computational cost. Martínez-Frutos et al. (2017) performed efficient
computation using GPU, while Borrvall and Petersson (2001) and Aage et al. (2015) attempted to accelerate TO
by parallel computing. Despite the aforementioned efforts to reduce TO computing time, the computational costs
remain high. This challenge has encouraged several researchers to develop ML-based TO to accelerate TO.
Figure 1 Overview of AI, ML, and DL (Kaluarachchi et al., 2021)