Smart, connected testing for resilient, sustainable infrastructure
Real-world testing is physical, and simulation is virtual, computational. But the two worlds increasingly are being combined, in what is known as hybrid simulation, or cyberphysical testing. As our aging infrastructure must be more carefully inspected — and new infrastructure designed for enhanced resilience and sustainability — this real-time technique takes its cues from both the cyber and physical worlds. It blends the hard-nosed realism of a physical test with the numerical sophistication to simulate structural systems whose complexity and size make lab testing impractical.
In cyberphysical testing, sections of the structural system are tested in a laboratory while other elements are “virtualized” as a computational model. The technique traditionally has been used in earthquake engineering — picture the impracticality of testing a residential or commercial structure or its large components on a shake table in a lab. However, it increasingly is being used in scenario testing around encountering operational pitfalls like wind, flood and fire.
Essentially, in real-time hybrid simulation (RTHS), we take a structure or its parts that we do not fully understand — for example, new construction methods, new design techniques being adopted, or an unexpected behavior we’ve found in the field after an earthquake or a windstorm. We put those components in the lab, and couple them with a numerical model that is rich enough to induce the behavior we observed in the field, to generate information that helps us understand the physical behavior of the part in the lab.
These two tests — physical and cyber — run together. Sensors measure what’s happening in the physical specimen and feed the data into the computer model, which, in turn, feeds back commands from the numerically modeled part of the structure into our actuators to drive our physical specimen.
RTHS will play a significant role in the future of infrastructure. Society is interested in increasing sustainability and durability in our structures. That means we need to find ways to use fewer resources to build structures that also last longer. This goal requires that we exploit new materials, and come up with new designs that are slimmer and more careful about the use of resources. If we can learn more about their behavior, they may not need as much built-in redundancy as in the past.
If that’s the case, we need to do more testing and modeling. The idea of using RTHS is very attractive because it allows us to test things at low cost. It enables us to test new structural designs that are being thought up, and apply the extreme loads that those structures need to withstand onto the structures before they are built. Those are side-by-side capabilities — understanding observations in the lab and putting them into our numerical models. That’s where advances like parallel computing and machine learning can come into play.
Much of the work around hybrid simulation is being encouraged and promoted through the Multi-hazard Engineering Collaboratory for Hybrid Simulation (MECHS), where I currently serve as the director. MECHS is a National Science Foundation (NSF)-sponsored initiative to bring together an international community of researchers tackling the challenging scientific problems to realize this method. We hold workshops, training activities, and webinars, as well as generate videos, information, and publication lists. These resources are located in a single place, so people can find them and can learn about the latest and greatest research. In addition, we’re doing things like creating benchmark problems, which enable different people and research groups around the world to tackle a similar challenge in different ways to comprehend the pros and cons of alternate methods.
The practical application of RTHS is its ability to help us understand the things we see in the field whose causes we can’t discern because existing models didn’t predict what happened. We need to be able to forecast these events. Using hybrid simulation, when we find problems in the field and have research questions, we can develop ways to test, explore and validate new designs, in order to capture and embed that understanding as we improve our models.
Shirley J. Dyke, PhD
Professor of Mechanical and Civil Engineering
College of Engineering, Purdue University
Director, Multi-hazard Engineering Collaboratory for Hybrid Simulation (MECHS)
Director, Resilient ExtraTerrestrial Habitats institute (RETHi)
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