When the Word Hybrid Stops You in Your Tracks

Updated: May 21

After finishing the Hyperloop story, I started working on a success story about real-time hybrid simulation. If you, just like myself, have flunked practically every math exam as well as physics class, this hybrid simulation concept thing gets you. I got confirmation from a co-worker of mine, mind you a great engineer, that nonlinear structural Finite Element Analysis (FEA) can be quite tricky and is very challenging. That freaked me out, but also fascinated me from the get-go.


The success story was about structural tests. Basically, what they are simulating are hazardous scenarios on structures such as earthquakes and strong winds (I could ask a lead engineer if they are also testing blizzards, tsunamis and such if you wish). To simulate these forces, they have been developing algorithms and have built a huge testing facility. To get the most accurate test results, they have used hybrid real-time simulation (and the FEA thing that keeps freaking me out). Let’s dive into the hybrid simulation part: Basically, this means that you divide the whole structure under test into a numerical (analytical) and a physical (experimental) substructure. While the physical substructure encompasses all components that can’t be modeled numerically (this is, with the desired accuracy), the numerical structure describes all remaining non-physical components, also known as “somewhat the rest”. So where does FEA come into play here? In order to understand structural elements, engineers use this method to simulate them by applying a method called Finite Element Method (FEM). FEA is important, since it reduces the number of physical prototypes and optimizes the design much faster (mathematicians use partial differential equations to get to the best mathematical description of any physical phenomenon). In the case of structural experiments, engineers developed algorithms and used these computations to start a program called HybridFEM-MH. The algorithms can simulate the different scenarios on the physical structure.


It probably doesn’t surprise, that these large-scale experiments are conducted by the best in the field. The field of hybrid real-time simulation is still in its infancy, but by combining established understandings of physical systems through real-time nonlinear FEA with direct sensor feedback and command outputs to physical components, these experiments mark an important breakthrough!


For more information on these awesome experiments, click the links, read and get excited and freaked out about it at the same time. And as always: Stay hooked and enjoy the ride!

  • You can find this image and a great explanation about finite element analysis (FEA) and a video about the history of FEA (some say it dates back to Euler!) here. Also check out their library!

  • Check the link out to get to the experimental protocol. Furthermore, check out the paper regarding the HybridFEM-MH program, which facilitates nonlinear structural Finite Element Analysis in the Simulink environment: Kolay, C., Marullo, T. and J. Ricles, “HybridFEM-MH: A Program for Nonlinear Dynamic Analysis and Real-Time Hybrid Simulation of Civil Infrastructure Systems Subject to Multi-Hazards,” ATLSS Report No. 18-06, ATLSS Engineering Research Center, Lehigh University, Bethlehem, PA, 2018.

  • There are tons of other very fascinating papers released by the Natural Hazards Engineering Research Infrastructure (NHERI) Lehigh Experimental Facility (EF), you can find them here.

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