Nicholas E. Wierschem, Ph.D.
University of Tennessee
nwierschem.com
Problems
Extreme dynamic loads from earthquakes and wind events can damage or destroy civil structures. Furthermore, unwanted service-level vibrations can negatively impact the functionality of civil and mechanical systems. Through structural control, engineers and researchers seek to mitigate the effects of dynamic loads on systems and protect structures from damage or loss of functionality. However, many of the standard current structural control techniques, such as tuned mass dampers, have been developed based on linear dynamics; thus, these approaches may have a small window of frequencies they are effective over, they cannot be used to produce structures whose behavior adapts with the response level of the structure, and these approaches may be extremely vulnerable to detuning. Furthermore, many structural control approaches are large and expensive to implement in structures.
Approach
The Innovative and Smart Infrastructure Group (ISIG), which is led by Dr. Nicholas Wierschem at the University of Tennessee, seeks to overcome short comings of currently utilized structural control techniques by developing innovations and advances to passive structural control. While active and semi-active control types generally show more control efficacy, passive control techniques are focused on in this group as they are far more likely to be utilized in structures. In particular, the construction industry in the United States is very conservative and often will not accept the complexity, liability, and high upfront costs of active and semi-active control techniques. With this in mind, ISIG seeks to develop and investigate innovative passive techniques that control the vibration of structures including those that exploit repeatable nonlinearities to enable functionality not possible with linear techniques, such as the ability to adapt behavior with system response level. Additionally, ISIG seeks to also develop techniques that allow the vibrational energy of the structure to be benignly redirected and sequestered.
Findings
Rotational Rotational inertial mechanisms have been a key area of study of ISIG. These devices convert translational motion into the rotation of flywheels and in doing so provide a large inertia mass while utilizing a physically small flywheel mass. Recent findings related to these devices include:
- The large mass effects of these devices can be used to increase the efficiency and robustness of passive structural control devices.
- Adaptive geometry in the device’s flywheel can be used to create rotational inertial mechanisms that dynamically shift a system’s natural frequencies and enable resonance avoidance.
- Clutched versions of these devices can be used to extract and sequester energy from the main structure.
Another area of study is devices featuring impacts. Recent findings related to these devices include:
- Particle dampers can be adapted to control vibrations in multiple simultaneous directions.
- Impact damper geometry can be modified to create targeted behavior featuring adaptation to response level.
- Structural Control
- Structural Dynamics
- Nonlinear Dynamics
- Earthquake Engineering
- Vibration Isolation
- Experimental Methods
- Nicholas E. Wierschem
- Sima Abolghasemi
- Deidra Anderson
- Lydia Foster
- Anika Sarkar (PhD 24’, University of New Orleans)
- Wyatt Cupp (MS 24’, KPFF Consulting Engineers)
- Alex Shafer (MS 22’, Haines Structural Group)
- Lindsay Kirk (MS 21’, Haines Structural Group)
- Abdollah Javidialesaadi (PhD 20’, GE Vernova)
- Talley, P.C., Sarkar, A.T., Wierschem, N.E., and Denavit, M.D., (2022) “Performance of Structures with Clutch Inerter Dampers Subjected to Seismic Excitation,” Bulletin of Earthquake Engineering. https://doi.org/10.1007/s10518-022-01514-9
- Javidialesaadi, A., and Wierschem, N. E. (2019). “Energy transfer and passive control of single-degree-of-freedom structures using a one-directional rotational inertia viscous damper.” Engineering Structures, 12. https://doi.org/10.1016/j.engstruct.2019.109339
- Javidialesaadi, A., and Wierschem, N. E. (2019). “An inerter-enhanced nonlinear energy sink.” Mechanical Systems and Signal Processing, 129, 449–454. https://doi.org/10.1016/j.ymssp.2019.04.047
- Sarkar, A.T. and Wierschem, N.E., “Influence of the variable inertia rotational mechanism on natural frequency and structural response,” Smart Structures and Systems, 34 (4), 243-260, 2024, https://doi.org/10.12989/sss.2024.34.4.243
- Cupp, W. and Wierschem, N.E., “Clutching Inerter Damper for Multi-Degree-of-Freedom Base-Isolated Structures: A Numerical Study,” ASCE Journal of Engineering Mechanics, 150, 7 (2024), https://doi.org/10.1061/JENMDT.EMENG-7585
- Li, W., Wierschem, N. E., Li, X., and Yang, T. (2018). “On the energy transfer mechanism of the single-sided vibro-impact nonlinear energy sink.” Journal of Sound and Vibration, 437, 166–179. https://doi.org/10.1016/j.jsv.2018.08.057
Impact
By working with various stakeholders, the general findings on innovations in passive structural control techniques researched by ISIG are being translated into technological developments that will have real impacts with civil, mechanical, and aerospace applications.
Core Competencies
(Left) Linear rotational inertial mechanism (center) Example of a clutched rotational inertial mechanism – enables energy sequestration (right) Adaptive flywheel of a rotational inertial mechanism – enables resonance avoidance
Current Research Team Members
Recent Graduates
Funding Agencies
ONR, NSF, NASA