Researchers at MIT have demonstrated that by combining an automated design system with regular evaluations by human engineers produced results that performed better than those designed by the automated system alone. The process was also completed more rapidly than a fully manual approach.
Modern fabrication tools such as 3D printers can make structural materials in shapes that would have been difficult or impossible using conventional tools. New generative design systems can then take great advantage of this flexibility to create innovative designs for parts of a new building, car or virtually any other device.
However, such ‘black box’ automated systems often fall short of producing designs that are fully optimised for their purpose, such as providing the greatest strength in proportion to weight or minimising the amount of material needed to support a given load. Fully manual design, on the other hand, is time-consuming and labour-intensive.
The MIT team achieved some of the best of both of these approaches by running an automated design system and then stopping the process periodically to allow human engineers to evaluate the work in progress and make tweaks or adjustments before letting the computer resume its design process. According to assistant professor of civil and environmental engineering Josephine Carstensen, this basic approach can be applied to a broad range of scales and applications for the design of everything from biomedical devices to nanoscale materials to the structural support members of a skyscraper.
‘It’s a way to take advantage of how we can make things in much more complex ways than we could in the past,’ said doctoral student Dat Ha, adding that automated design systems have already begun to be widely used in the automotive and aerospace industries, where reducing weight while maintaining structural strength is a key need.
‘You can take a lot of weight out of components, and in these two industries, everything is driven by weight,’ Ha said. In some cases, such as internal components that aren’t visible, appearance is irrelevant, but for other structures, aesthetics may be important as well. The new system makes it possible to optimise designs for visual as well as mechanical properties, decisions in which the human touch is essential.
As a demonstration of their process in action, the researchers designed a number of structural load-bearing beams, such as might be used in a building or a bridge. In their iterations, they saw that the design had an area that could fail prematurely, so they selected that feature and required the program to address it. The computer system then revised the design accordingly, removing the highlighted strut and strengthening some other struts to compensate, leading to an improved final design.
The process, which they call Human-Informed Topology Optimization, begins by setting out the needed specifications – for example, a beam needs to be this length, supported on two points at its ends, and must support this much of a load. ‘As we’re seeing the structure evolve on the computer screen in response to initial specification,’ Carstensen said, ‘we interrupt the design and ask the user to judge it. The user can select, say, “I’m not a fan of this region, I’d like you to beef up or beef down this feature size requirement.” And then the algorithm takes into account the user input.’
While the result might not be as optimal as one produced by a fully rigorous yet significantly slower design algorithm that considers the underlying physics, according to Carstensen, it can be much better than a result generated by a rapid automated design system alone. ‘You don’t get something that’s quite as good, but that was not necessarily the goal. What we can show is that instead of using several hours to get something, we can use ten minutes and get something much better than where we started off.’
The system can be used to optimise a design based on any desired properties – not just strength and weight. For example, it can be used to minimise fracture or buckling, or to reduce stresses in the material by softening corners.
‘We’re not looking to replace the seven-hour solution,’ Carstensen said. ‘If you have all the time and all the resources in the world, obviously you can run these and it’s going to give you the best solution.’ But for many situations, such as designing replacement parts for equipment in a war zone or a disaster-relief area with limited computational power available, ‘then this kind of solution that catered directly to your needs would prevail’.
Similarly, for smaller companies manufacturing equipment in essentially ‘mum and dad’ businesses, such a simplified system might be just the ticket. The new system they developed is not only simple and efficient to run on smaller computers, but it also requires far less training to produce useful results, Carstensen said. A basic two-dimensional version of the software, suitable for designing basic beams and structural parts, is freely available now online as the team continues to develop a full 3D version.
The research has been published in Structural and Multidisciplinary Optimization.