Novel Hybrid Simulation Improves Seismic Testing for Full-Scale Structures, Broadens Experimental Options for Engineering Research
EAGER: Next Generation Hybrid Simulation - Evaluation and Theory, Award# 1153665
Principal investigator: Khalid M. Mosalam, UC Berkeley
Even in our technologically advanced times, events such as Hurricane Sandy in 2012 can leave a heavily populated metropolitan area like the American Northeast without power for over a week. After such a disaster, having uninterrupted power is critical for relief, repair, and recovery efforts.
For years, engineers looking for ways to prevent disruption of electrical power after disasters have used full-scale testing to evaluate the performance of high-voltage disconnect switches, which are critical components of electrical substations. Substation disconnect switches are used to manage a network, shift electrical loads, and to turn off power in specific areas in case of danger. It’s vital that substations remain standing and fully operational – especially when subjected to the high dynamic loads from earthquakes and hurricanes.
Unfortunately, it is difficult to reliably assess the effect of these loads on the complex ceramic and polymeric materials used in these switches using mathematical techniques; as a result, the switches must be physically tested. However, conventional dynamic full-scale testing methods are expensive, inefficient and oftentimes not feasible. Few laboratories can accommodate the size of the specimens, and scale models may not be possible given the complex materials and components that comprise a disconnect switch.
Evaluating the earthquake response of electrical disconnect switches with full-scale testing
In a recent breakthrough, University of California, Berkeley civil engineering professor and researcher Khalid Mosalam, together with his research team, showed that advances in the engineering research methodology called “hybrid simulation” result in cheaper and faster data generation about the seismic behavior of disconnect switches in electrical substations.
As the name implies, hybrid simulation combines computational modeling with the physical testing of structures and components that are difficult to model mathematically – such as disconnect switches.
For the first time in earthquake engineering research, Mosalam and his team combined full scale testing of disconnect switches with numerical modeling of its structural components, including the support structure for the switch.
The Berkeley team’s innovative testing resulted in a novel framework for hybrid simulation, one that enables researchers to obtain the same amount of information as conventional, full scale, shake table testing – more quickly and inexpensively.
Advancing hybrid simulation techniques
In developing this framework, the research team achieved several other advancements in the hybrid simulation technique. First, by developing a system that integrates real-time and computer-generated data at very small intervals, in time steps as small as 1 millisecond, the team has enabled the application of hybrid simulation to a much broader range of structures.
Also, by applying new, more efficient algorithms for the numerical modeling, the team decreased the computational time by a factor of three – a significant improvement for hybrid simulation tests. Lastly, in a first for hybrid simulation using shake-tables, Mosalam’s team applied sophisticated new control techniques to test their physical samples, the disconnect switches, which enabled researchers to benefit from the combined acceleration, velocity, and displacement responses of the shake tables in hybrid simulation.
Mosalam’s multidisciplinary study of hybrid simulation, funded through the George E. Brown, Jr. Network for Earthquake Engineering Simulation (NEES), substantially advanced this earthquake simulation technique, which is one of the fundamental goals of the NEES Network. The hybrid simulation tools developed within the NEES Network were employed in various stages of the project.
The originality of Mosalam’s research is two-fold: it obtained valuable data about the safe operation of electrical disconnect switches after strong earthquakes, and it developed an advanced hybrid simulation technique that others can use to solve similar, real-world engineering problems.
Multidisciplinary hybrid simulation
In addition, this research brings together for the first time the two fields of hybrid testing and computational mechanics, a significant advancement in civil engineering research. In fact, the work represents a major conceptual shift in hybrid simulation techniques and establishes a thorough basis for hybrid simulations rooted on sound experimentation coupled with theoretical and applied multi-scale mechanics.
“Our multidisciplinary research shows that it’s possible to effectively utilize hybrid simulation to tackle today’s important engineering problems involving continuum structures, fluid dynamics, heat transfer, and energy concepts,” said Berkeley’s Mosalam.
Until now, hybrid simulation has been used as a tool to solve problems primarily in the field of earthquake engineering, with little effort dedicated to general engineering research. By investigating the method from a theoretical standpoint, this research shows that hybrid simulation techniques may be applied across multiple scales and engineering disciplines.
Mosalam explained, “Such effort requires input from experts in earthquake engineering, laboratory testing, control systems, numerical analysis and theoretical mechanics. In particular, the theoretical mechanics team devised the standardized analysis and testing procedure that will allow for accurate behavior prediction of new, cutting edge materials such as energy-efficient wall panels or structural components like triple friction pendulum isolators.”
Broader impacts in engineering research
In the future, the testing techniques developed in this study will increase substantially the reliability of hybrid simulation testing in engineering disciplines, and yet decrease the cost of experiments by two orders of magnitude.
Ultimately, the findings from this research will enable engineers to design more reliable, protective structures for the world’s electrical power lifelines in a more economical way.
Also Mosalam and his team hope that their more efficient and cost effective hybrid simulation methods will convince the broader structural engineering community outside the NEES earthquake engineering network to appreciate the value of hybrid simulation and employ it in their research and practice.