Session: 07-12-01: Optimization, Uncertainty and Probability

Paper Number: 116381

116381 - Stochastic Stability of a Torsional-Flutter Energy Harvester in Thunderstorm-Like Winds: Duffing vs. Hybrid Duffing – Van Der Pol Restoring Force Mechanisms 

Wind energy technologies are important because of the need for green energy sources. ``Specialized'' harvesters have been proposed to exploit wind energy in the low wind speed range and for medium scale applications, e.g., few residential housing units. These harvesters are triggered by various aeroelastic instability phenomena. For example, a torsional-flutter-based apparatus has been proposed for extracting energy from the wind flow. The apparatus is composed of a rigid, flapping blade-airfoil with variable pivot axis position. Typical dimensions of the harvester’s blade are half chord length 0.5 m and longitudinal (span) length between 4 and 10 times the chord. A nonlinear torsional spring mechanism (Duffing model), installed at equally spaced supports, has been used to enable stable limit-cycle, post-critical vibration. The conversion to electrical power is warranted by an eddy current converter with multi-loop magnetic coil and a translating permanent magnet. Energy is stored in a battery for re-use. 

Recent studies have examined the stochastic stability of the harvester and its post-critical operational conditions in turbulent wind flows, composed of horizontal mean speed and along-wind turbulence, both stationary and non-stationary. Non-synoptic, non-stationary turbulence has been considered to simulate urban settings and thunderstorm downburst gust fronts, in a non-ideal wind environment.

Physical states of the model are torsional rotation of the blade-airfoil, its time derivative with respect to dimensionless time. Aeroelastic torque is modeled by standard flow memory theory, indicial function based on Wagner formulation, corrected for three-dimensional flow effects that depend on aspect ratio of the flapping blade. Thunderstorm-like turbulence effects are both included in the drift and diffusion vectors of the stochastic dynamic equation through uniform modulation function; this function simulates the rapidly evolving, thunderstorm downburst landfall as well as the finite temporal duration of the gust front.

In this study a new model is proposed to examine the mean-square stability limits by replacing the Duffing restoring force mechanism, originally proposed, by a hybrid Duffing - van-der Pol mechanisms that couples a cubic torsional spring with amplitude-dependent structural damping. Various configurations will be considered with adjustable position of the blade-airfoil pivot axis: from the leading edge (windward point) to closer to the quarter chord position. Turbulence intensity will be varied to investigate various thunderstorms. Since the dimensions of the flapping blade-airfoil are small, a fully coherent gust front and load perturbation will be assumed. Mean-square stability will be studied by Moment Lyapunov Exponents, and will be computed numerically through Monte Carlo sampling.

Presenting Author: Luca Caracoglia Northeastern University

Presenting Author Biography: Luca Caracoglia is currently a Full Professor in the Department of Civil and Environmental Engineering of Northeastern University, Boston, Massachusetts, USA. He joined Northeastern University in 2005. In addition, Luca Caracoglia was granted two concurrent Full Professor Habilitations (accreditations) by the Italian Ministry of Public Instruction, University and Research (MIUR) in 2019. The first one is for the Scientific Discipline ICAR 08/B3, Civil Engineering/Structural Design (“Tecnica delle Costruzioni”). The second one is for the Scientific Discipline ICAR 08/B2, Civil Engineering/Structural Mechanics (“Scienza delle Costruzioni”). He received his Ph.D. in Structural Engineering from the University of Trieste, Italy in 2001.

Luca Caracoglia’s research and professional interests are in structural dynamics, random vibration, wind engineering, fluid-structure interaction of civil engineering structures, nonlinear cable network dynamics, wind energy and wind-based energy harvesting systems.

He has been author/co-author of 95+ peer-reviewed journal publications and book chapters (published or in press) and more than 110 conference proceedings / presentations in these fields. He has taught courses at the undergraduate and graduate levels in: Statics/Solid Mechanics, Structural Analysis, Steel Structure Design, Pre-stressed Concrete, Bridge Design, Wind Engineering and Wind Energy Systems.

Luca Caracoglia received the NSF-CAREER Award for young investigators in 2009. He co-chaired the 3rd Workshop of the American Association for Wind Engineering in 2012, and co-chaired the 8th International Colloquium on Bluff Body Aerodynamics & Applications (BBAA VIII), held at NU in 2016.

Luca Caracoglia was a member of the Board of Directors of the AAWE - American Association for Wind Engineering in 2020-2022, and is currently a member of the Executive Board of the ANIV – Italian National Association for Wind Engineering. He served as a member of the International Executive Board of the IAWE - International Association for Wind Engineering in 2012 – 2017.

Luca Caracoglia serves on four US national, technical committees of the American Society of Civil Engineers (ASCE). For his career accomplishments, Luca Caracoglia was granted the title of “Fellow ASCE” (held by 3% of the ASCE members) in September 2020. Furthermore, Luca Caracoglia currently serves as an Associate Editor for the ASCE Journal of Bridge Engineering and the Journal of Fluids and Structures (Elsevier). He is also a member of the editorial board for the journals Engineering Structures (Elsevier), Structural Control and Health Monitoring (Wiley), Structural Safety (Elsevier) and Wind and Structures (Techno-Press).

Authors:

Luca Caracoglia Northeastern University