ME Faculty Candidate Seminar: Thomas Ward

ME Faculty Candidate Seminar:

“A study of vibrating semi-rigid cantilevers using soap-film experiments and a low-order math model”

Thomas Ward

Associate Professor

Iowa State University

Tuesday, March 28, 2023, 11:00 am

GM Conference Room

Lurie Engineering Center

Seminar Zoom Link

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Abstract:

Here, we investigate the transverse vibrational response of semi-rigid cantilevers to external forcing using both experiments and a low-order numerical model.  The purpose is to explore the energy harvesting potential of cantilever shaped-piezoelectric devices executing low-amplitude vibrations in low-speed wind.  Experiments were performed by placing cantilevers in a soap film tunnel.  The tunnel is capable of producing a range of uniform flow velocities 2-4 m/s, resulting in cantilever Reynolds numbers on the order of 10000-50000 based on length.  We consider the cantilever’s vibrational response to: 1) uniform flow at various cantilever inclination angles, and 2) placement downstream of vortices shed from a cylinder with cylinder Reynolds numbers on the order of 5000-25000.  Images captured using high speed video (~5000 fps) of the cantilever motion and wake vortex structure were analyzed to estimate vibrational amplitude, frequency, local phase angle and vortex shedding frequency.  We hypothesize, initially, that the cantilever’s vibrational response frequency measured at the free-end (tip) should be equal to either the cantilever’s natural frequency or cantilever/cylinder vortex shedding frequency.  The measured cantilever vibration frequencies not equal to either of these two values, therefore, must be driven by other sources.  For cantilevers undergoing small amplitude vibrations the linear-dynamic Euler-Bernoulli beam equation with damping is a valid model.  We show using numerical solutions to the Euler-Bernoulli beam equation that including two forcing terms of difference frequency can result in a quasi-periodic response.  We then investigate quasi-periodicity as an explanation for the measured cantilever vibrational response frequencies not equal to either the natural or vortex shedding frequency. The potential role of these measured frequencies and amplitudes in generating electrical power through energy harvesting of low-speed wind using cantilever shaped-piezoelectric devices will be discussed.

Bio:

Dr. Thomas Ward is an Associate Professor of Aerospace Engineering at Iowa State University.  He received a B.S. (1998) in Chemical Engineering from Missouri University of Science and Technology with a minor in Applied Mathematics, M.S. (2001) in Chemical Engineering from Stanford University and Ph.D. (2003) in Mechanical Engineering from University of California, Santa Barbara.  He worked in postdoctoral researcher positions at Harvard University from 2001-2003 in the School of Engineering and Applied Science, and at the University of California, Los Angeles from 2003-2005 in the Math department.  His research thrusts include studies in  .  He is the author or co-author of over 40 peer-reviewed publications, and his research efforts have been supported by NSF, AFOSR, AFRL and DARPA among others.