# Topology Optimisation in Structural Steel Design for Additive Manufacturing
## 8 Future Trends  
In the aftermath of the latest World Congress on Structural and Multidisciplinary Optimisation, held in 2019, surrogate-based optimisation and optimisation under uncertainty were highlighted as two trending issues for the future of TO [591]. In fact, the latter has a significant expression in recent studies by some of the leading researchers in the field, as one can regard in [PERSON] et al. 's work with the Augmented Lagrangian method for computing loading uncertainty [214; 454]. The prospective dissemination of TO in structural design, based on increasingly user-friendly and reliable software [2], is quite an undisputed prediction. However, the means to enforce such development are subjected to different views. As [PERSON] et al. reported the experience of inserting TO in engineering education as soon as in freshman levels at Johns Hopkins University both as a design tool and as a mean for understanding the force flows [592], [PERSON] [2] alluded to the role of the State to force practitioners to apply new technologies. Concurrently, [PERSON] et al. [530] pointed out to open academic research platforms and intellectual property expiry, but also governmental investments and expertise as catalysts for enforcing the application of emerging standards and fostering DfAM and AM processes integration and interconnectivity, potentially opposed by larger revenue companies. DfAM or AM-Oriented TO (MOTO) is envisaged to undertake the systematic study of trade-off relationships between TO and AM, unlike what has mostly happened to date [593]. \begin{table}
\begin{tabular}{p{142.3 pt} p{142.3 pt}} \hline \hline
**Development** & **Reference** \\ \hline A new perspective on overhang control, taking into account AM techniques specific features with a skeleton-based structure decomposition approach. TO approach to minimise supports in enclosed voids. Employs a Nonlinear Virtual Temperature Method (N-VTM) to find enclosed voids. & [575] \\ A TO approach for re-designing additively manufacturable parts. Integration with a commercial computer-aided design software is discussed, which enforces the study’s practical applicability. A TO approach for parts repair or upgrade with AM after subtractive machining. A TO approach for merging structural optimisation and WAAM deposition sequence. TO approach for taking into account the assembly design. A multi-objective minimisation TO approach which account for AM fabrication time and cost. Multiresolution Topology Optimisation (MTOP) method for high resolution AM with overhang and minimum length control. & [576] \\ An NRBTO method to account for additively manufactured materials’ properties local uncertainty. For such an end, Uncertainty Regions (UR) are defined within the design domain. TO with kinetic analysis added to the common FEA. Solid Anisotropic Material with the Penalisation (SAMP) technique better integrating process parameters into TO. TO of multi-material infills with a systematic multi-phase design method. Poisson’s equation-based scalar field constraint to suppress enclosed voids in TO. & [583] \\ \hline \hline \end{tabular}
\end{table} 
Table 7: Cont. This may also include considering fabrication models which integrate more conventional processes [530], as well as advancing in multi-material products, assisted by progress in simulation algorithms [530]. Nevertheless, an increasingly closer relationship between TO and AM is perceived as vital for the industry's development [594]. On the other hand, significant hurdles are yet to overcome in TO for AM. [PERSON] et al. reported the need for more advanced TO methods for multifunctional products, as well as for progress in multiscale TO [594] and [PERSON] and [PERSON] focused on the need for enhancing TO performance regarding aerodynamics problems [352].