@article{kirschmeier_pash_gianikos_medina_gopalarathnam_bryant_2020, title={Aeroelastic inverse: Estimation of aerodynamic loads during large amplitude limit cycle oscillations}, volume={98}, ISSN={["0889-9746"]}, DOI={10.1016/j.jfluidstructs.2020.103131}, abstractNote={This paper presents an algorithm to compute the aerodynamic forces and moments of an aeroelastic wing undergoing large amplitude heave and pitch limit cycle oscillations. The technique is based on inverting the equations of motion to solve for the lift and moment experienced by the wing. Bayesian inferencing is used to estimate the structural parameters of the system and generate credible intervals on the lift and moment calculations. The inversion technique is applied to study the affect of mass coupling on limit cycle oscillation amplitude. Examining the force, power, and energy of the system, the reasons for amplitude growth with wind speed can be determined. The results demonstrate that the influence of mass coupling on the pitch–heave difference is the driving factor in amplitude variation. The pitch–heave phase difference not only controls how much aerodynamic energy is transferred into the system but also how the aerodynamic energy is distributed between the degrees of freedom.}, journal={JOURNAL OF FLUIDS AND STRUCTURES}, author={Kirschmeier, Benjamin and Pash, Graham and Gianikos, Zachary and Medina, Albert and Gopalarathnam, Ashok and Bryant, Matthew}, year={2020}, month={Oct} }
 @article{kirschmeier_gianikos_gopalarathnam_bryant_2020, title={Amplitude Annihilation in Wake-Influenced Aeroelastic Limit-Cycle Oscillations}, volume={58}, ISSN={["1533-385X"]}, DOI={10.2514/1.J058942}, abstractNote={This paper investigates the dynamics of a pitching and heaving aeroelastic wing undergoing large-amplitude limit-cycle oscillations influenced by a vortical wake from an upstream rectangular cylind...}, number={9}, journal={AIAA JOURNAL}, author={Kirschmeier, Benjamin A. and Gianikos, Zachary and Gopalarathnam, Ashok and Bryant, Matthew}, year={2020}, month={Sep}, pages={4117–4127} }
 @article{gianikos_kirschmeier_gopalarathnam_bryant_2020, title={Limit cycle characterization of an aeroelastic wing in a bluff body wake}, volume={95}, ISSN={["1095-8622"]}, DOI={10.1016/j.jfluidstructs.2020.102986}, abstractNote={This paper presents an experimental investigation aimed at characterizing the kinematics of a pitching-heaving aeroelastic wing placed downstream of a rectangular bluff body. The influence of the bluff body wake on the wing is twofold: a viscous wake which produces a velocity deficit downstream and an oscillating induced velocity field due to periodic vortex shedding. The latter effect is the focus of this paper, specifically, the interaction between the wake frequency and the wing limit cycle oscillation (LCO) frequency. Wind tunnel experiments showed that the presence of the upstream bluff body causes modulation of the LCO amplitude. The modulation resembles a beat phenomenon, however the modulation frequency is related to the third harmonic of fLCO rather than the fundamental frequency. The modulation behavior also differs from that of a beat in that the spectral content contains sideband frequencies, characteristic of a multiplication between a carrier wave and a modulation wave rather than a simple sinusoidal superposition. Additionally, the streamwise spacing between the bluff body and the wing significantly influences the wing kinematics, with a closer spacing between the two bodies increasing the intensity of the amplitude modulation. For shedding frequencies sufficiently close to the LCO third harmonic, reducing this streamwise distance was shown to induce an alternation between two distinct modes of amplitude modulation, each with its own intensity and frequency.}, number={0}, journal={JOURNAL OF FLUIDS AND STRUCTURES}, author={Gianikos, Zachary N. and Kirschmeier, Benjamin A. and Gopalarathnam, Ashok and Bryant, Matthew}, year={2020}, month={May} }
 @article{kirschmeier_bryant_2016, title={Toward efficient aeroelastic energy harvesting through limit cycle shaping}, volume={9799}, ISSN={["1996-756X"]}, DOI={10.1117/12.2218437}, abstractNote={Increasing demand to harvest energy from renewable resources has caused significant research interest in unsteady aerodynamic and hydrodynamic phenomena. Apart from the traditional horizontal axis wind turbines, there has been significant growth in the study of bio-inspired oscillating wings for energy harvesting. These systems are being built to harvest electricity for wireless devices, as well as for large scale mega-watt power generation. Such systems can be driven by aeroelastic flutter phenomena which, beyond a critical wind speed, will cause the system to enter into limitcycle oscillations. When the airfoil enters large amplitude, high frequency motion, leading and trailing edge vortices form and, when properly synchronized with the airfoil kinematics, enhance the energy extraction efficiency of the device. A reduced order dynamic stall model is employed on a nonlinear aeroelastic structural model to investigate whether the parameters of a fully passive aeroelastic device can be tuned to produce limit cycle oscillations at desired kinematics. This process is done through an optimization technique to find the necessary structural parameters to achieve desired structural forces and moments corresponding to a target limit cycle. Structural nonlinearities are explored to determine the essential nonlinearities such that the system’s limit cycle closely matches the desired kinematic trajectory. The results from this process demonstrate that it is possible to tune system parameters such that a desired limit cycle trajectory can be achieved. The simulations also demonstrate that the high efficiencies predicted by previous computational aerodynamics studies can be achieved in fully passive aeroelastic devices.}, journal={ACTIVE AND PASSIVE SMART STRUCTURES AND INTEGRATED SYSTEMS 2016}, author={Kirschmeier, Benjamin and Bryant, Matthew}, year={2016} }
 @article{kirschmeier_bryant_2015, title={Soap film flow visualization investigation of oscillating wing energy harvesters}, volume={9429}, ISSN={["1996-756X"]}, DOI={10.1117/12.2086523}, abstractNote={With increasing population and proliferation of wireless electronics, significant research attention has turned to harvesting energy from ambient sources such as wind and water flows at scales ranging from micro-watt to mega-watt levels. One technique that has recently attracted attention is the application of bio-inspired flapping wings for energy harvesting. This type of system uses a heaving and pitching airfoil to extract flow energy and generate electricity. Such a device can be realized using passive devices excited by aeroelastic flutter phenomena, kinematic mechanisms driven by mechanical linkages, or semi-active devices that are actively controlled in one degree of freedom and passively driven in another. For these types of systems, numerical simulations have showed strong dependence on efficiency and vortex interaction. In this paper we propose a new apparatus for reproducing arbitrary pitch-heave waveforms to perform flow visualization experiments in a soap film tunnel. The vertically falling, gravity driven soap film tunnel is used to replicate flows with a chord Reynolds number on the order of 4x104. The soap film tunnel is used to investigate leading edge vortex (LEV) and trailing edge vortex (TEV) interactions for sinusoidal and non-sinusoidal waveforms. From a qualitative analysis of the fluid structure interaction, we have been able to demonstrate that the LEVs for non-sinusoidal motion convect faster over the airfoil compared with sinusoidal motion. Signifying that optimal flapping frequency is dependent on the motion profile.}, journal={BIOINSPIRATION, BIOMIMETICS, AND BIOREPLICATION 2015}, author={Kirschmeier, Benjamin and Bryant, Matthew}, year={2015} }