Dr. Ehrhardt’s research focuses on the intersection of test and analysis when considering the design and identification of nonlinear structures operating in extreme mechanical, thermal, and/or acoustic environments such as hypersonic flight. The coupled nature between the structure and environment leads to complex fluid-thermal-structural interactions (FTSI) increasing the need for compact nonlinear structural models. Nonlinear behavior is difficult to predict in these extreme combined environments as small variations in the structure can lead to large differences in the dynamic response and unexpected failures. When using the linear normal modes as a basis, the concept of nonlinear normal modes (NNMs) offers a compact definition of a structure’s nonlinear behavior with increasing amplitude. The NNMs can be tied to damped vibrations using the second order normal forms technique to identify phase-locked branches providing a means for the identification of modal energy transfer. This improved structural characterization is currently being applied to the design of additively manufactured metallic panels for investigation in supersonic and hypersonic tunnels as part of an Air Force Office of Scientific Research grant.
About the speaker: Dr. David Ehrhardt received his PhD in Engineering Mechanics from the University of Wisconsin-Madison in 2015 where his dissertation focused on a numerical and experimental exploration of nonlinear structures. After graduation, he went to the University of Bristol for a post-doctoral appointment where he designed a variable nonlinear structure to explore 1-1 and 1-3 coupling between underlying linear modes. Upon his return to the US, he started his own company, Ehrhardt Engineering LLC, which specialized in test support for supersonic and hypersonic wind tunnel test campaigns with the Air Force Research Laboratory. He has been a Senior Research Engineer at UIUC with a split appointment between the Applied Research Institute and the Advanced Material Testing and Evaluation Laboratory since February 2021.