Vagner Candido de Sousa

Enhanced aeroelastic energy harvesting by exploiting combined nonlinearities: theory and experiment

Converting aeroelastic vibrations into electricity for low power generation has received growing attention over the past few years. In addition to potential applications for aerospace structures, the goal is to develop alternative and scalable configurations for wind energy harvesting to use in wireless electronic systems. This paper presents modeling and experiments of aeroelastic energy harvesting using piezoelectric transduction with a focus on exploiting combined nonlinearities. An airfoil with plunge and pitch degrees of freedom (DOF) is investigated. Piezoelectric coupling is introduced to the plunge DOF while nonlinearities are introduced through the pitch DOF. A state-space model is presented and employed for the simulations of the piezoaeroelastic generator. A two-state approximation to Theodorsen aerodynamics is used in order to determine the unsteady aerodynamic loads. Three case studies are presented. First the interaction between piezoelectric power generation and linear aeroelastic behavior of a typical section is investigated for a set of resistive loads. Model predictions are compared to experimental data obtained from the wind tunnel tests at the flutter boundary. In the second case study, free play nonlinearity is added to the pitch DOF and it is shown that nonlinear limit-cycle oscillations can be obtained not only above but also below the linear flutter speed. The experimental results are successfully predicted by the model simulations. Finally, the combination of cubic hardening stiffness and free play nonlinearities is considered in the pitch DOF. The nonlinear piezoaeroelastic response is investigated for different values of the nonlinear-to-linear stiffness ratio. The free play nonlinearity reduces the cut-in speed while the hardening stiffness helps in obtaining persistent oscillations of acceptable amplitude over a wider range of airflow speeds. Such nonlinearities can be introduced to aeroelastic energy harvesters (exploiting piezoelectric or other transduction mechanisms) for performance enhancement.

Effect of pseudoelastic hysteresis of shape memory alloy springs on the aeroelastic behavior of a typical airfoil section

The literature on aeroelasticity includes studies on the use of smart materials as sensors and actuators in vibration control problems. Although different smart materials are available, shape memory alloys have received growing attention in aerospace applications. The hysteretic response of shape memory alloys exhibiting pseudoelasticity provides energy dissipating and damping capabilities for these materials, and therefore, the effectiveness of the pseudoelastic behavior of shape memory alloys has been investigated for passive structural vibration control. However, its effect on the aeroelastic behavior of lifting surfaces has not been covered in the literature. Hence, this article addresses the modeling and analysis of a 2-degree-of-freedom typical aeroelastic section with shape memory alloy springs introduced through the pitch degree of freedom. A state-space model is employed for the simulations of the coupled system, and a two-state approximation to Theodorsen aerodynamics is used for the determination of the aerodynamic loads. The effects of the hysteretic behavior of the shape memory alloy springs on the aeroelastic behavior of the typical section are investigated at the flutter boundary and at post-flutter regime.The literature on aeroelasticity includes studies on the use of smart materials as sensors and actuators in vibration control problems. Although different smart materials are available, shape memor...

Effect of constitutive model parameters on the aeroelastic behavior of an airfoil with shape memory alloy springs

The effects of the pseudoelastic hysteresis of shape memory alloy springs on the aeroelastic behavior of a typical airfoil section are numerically investigated for six different sets of alloy constitutive properties. A two-degree-of-freedom (namely, plunge and pitch) typical section is modeled. Shape memory alloy helical springs are considered in the pitch degree-of-freedom based on classical phenomenological models modified by the pure shear assumption. Tension–compression asymmetry and nonhomogeneous distributions of shear strain, shear stress and martensitic fraction in the cross-sectional area of the coiled shape memory alloy wire are considered. A linear model is used to determine the unsteady aerodynamic loads. Attractive alloy characteristics, which can enhance the aeroelastic behavior of the typical section at the flutter boundary and at the post-flutter regime, are identified and discussed in detail.

Experimental study on the aeroelastic behavior of a typical airfoil section with superelastic shape memory alloy springs

An experimental study on the aeroelastic behavior of a 2-degree-of-freedom typical airfoil section with superelastic shape memory alloy springs is reported. Shape memory alloy helical springs are included in the pitch degree-of-freedom of the typical section so that the effects of pseudoelastic hysteresis on the aeroelastic behavior of the system can be investigated. The experimental identification of the aeroelastic parameters is described. Wind tunnel tests are conducted for different shape memory alloy springs’ preload levels, airflow speeds, and initial conditions. It is shown that the linear unstable post-flutter behavior is transformed into stable limit cycle oscillations of acceptable amplitudes over a range of airflow speeds due to pseudoelastic hysteresis. Therefore, shape memory alloy springs can be effectively exploited to passively enhance the aeroelastic behavior of a typical section.An experimental study on the aeroelastic behavior of a 2-degree-of-freedom typical airfoil section with superelastic shape memory alloy springs is reported. Shape memory alloy helical springs are included in the pitch degree-of-freedom of the typical section so that the effects of pseudoelastic hysteresis on the aeroelastic behavior of the system can be investigated. The experimental identification of the aeroelastic parameters is described. Wind tunnel tests are conducted for different shape memory alloy springs’ preload levels, airflow speeds, and initial conditions. It is shown that the linear unstable post-flutter behavior is transformed into stable limit cycle oscillations of acceptable amplitudes over a range of airflow speeds due to pseudoelastic hysteresis. Therefore, shape memory alloy springs can be effectively exploited to passively enhance the aeroelastic behavior of a typical section.

Adaptive locally resonant metamaterials leveraging shape memory alloys

Locally resonant metamaterials leveraging shape memory alloy (SMA) springs are explored in this work in an effort to develop adaptive metamaterial configurations that can exhibit tunable bandgap properties as well as enhanced damping capabilities. An analytical model for a locally resonant metamaterial beam in transverse vibrations is combined with an SMA model for the resonator springs to investigate and leverage the potential of temperature-induced phase transformations and stress-induced hysteretic behavior of the springs. Two case studies are presented for this new class of smart metamaterials and the resulting finite metastructures. In one case, SMA resonators operate in the linear elastic regime, first at low temperature (martensitic behavior) and then at high temperature (austenitic behavior), demonstrating how the bandgap can be tuned to a different frequency range by altering the SMA elastic modulus with temperature. In the second case, the SMA springs are kept at high temperature at all times to operate in the nonlinear regime, so that the hysteresis associated with the SMA pseudoelastic effect is manifested, yielding additional dissipation over a range of frequencies, especially for the modes right outside the bandgap.Locally resonant metamaterials leveraging shape memory alloy (SMA) springs are explored in this work in an effort to develop adaptive metamaterial configurations that can exhibit tunable bandgap properties as well as enhanced damping capabilities. An analytical model for a locally resonant metamaterial beam in transverse vibrations is combined with an SMA model for the resonator springs to investigate and leverage the potential of temperature-induced phase transformations and stress-induced hysteretic behavior of the springs. Two case studies are presented for this new class of smart metamaterials and the resulting finite metastructures. In one case, SMA resonators operate in the linear elastic regime, first at low temperature (martensitic behavior) and then at high temperature (austenitic behavior), demonstrating how the bandgap can be tuned to a different frequency range by altering the SMA elastic modulus with temperature. In the second case, the SMA springs are kept at high temperature at all times to...

Tunable metamaterial beam with shape memory alloy resonators: Theory and experiment

We investigate and experimentally validate the concept of bandgap tuning in a locally resonant metamaterial beam exploiting shape memory alloy (SMA) resonators. The underlying mechanism is based on the difference between the martensitic phase (low temperature) and austenitic phase (high temperature) elastic moduli of the resonators, enabling a significant shift of the bandgap for a sufficient temperature change. Experimental validations are presented for a base-excited locally resonant metamaterial beam with SMA resonators following a brief theoretical background. It is shown that the lower bound of the bandgap as well as the bandwidth can be increased by 15% as the temperature is increased from 25 °C to 45 °C for the specific SMAs used in this work for concept demonstration. The change in the bandgap lower bound frequency and its bandwidth is governed by the square root of the fully austenitic to fully martensitic elastic moduli ratio, and it could be as high as 70% or more for other SMAs reported in the literature.We investigate and experimentally validate the concept of bandgap tuning in a locally resonant metamaterial beam exploiting shape memory alloy (SMA) resonators. The underlying mechanism is based on the difference between the martensitic phase (low temperature) and austenitic phase (high temperature) elastic moduli of the resonators, enabling a significant shift of the bandgap for a sufficient temperature change. Experimental validations are presented for a base-excited locally resonant metamaterial beam with SMA resonators following a brief theoretical background. It is shown that the lower bound of the bandgap as well as the bandwidth can be increased by 15% as the temperature is increased from 25 °C to 45 °C for the specific SMAs used in this work for concept demonstration. The change in the bandgap lower bound frequency and its bandwidth is governed by the square root of the fully austenitic to fully martensitic elastic moduli ratio, and it could be as high as 70% or more for other SMAs reported in the...

Locally resonant metamaterials with shape-memory alloy springs

Locally resonant metamaterials offer bandgap formation for wavelengths much longer than the lattice size, en- abling low-frequency and wideband vibration attenuation. Acoustic/elastic metamaterials made from resonating components usually do not exhibit reconfigurable and adaptive characteristics since the bandgap frequency range (i.e. target frequency and bandwidth combination) is fixed for a given mass ratio and stiffness of the resonators. In this work, we explore locally resonant metamaterials that exploit shape-memory alloy springs in an effort to develop adaptive metamaterials that can exhibit tunable bandgap properties. An analytical model for locally res- onant metastructures (i.e. metamaterials with specific boundary conditions) is combined with a shape-memory spring model of the resonator springs to investigate and exploit the potential of temperature-induced phase transformations and stress-induced hysteretic behavior of the springs. Various case studies are presented for this new class of smart metamaterials and metastructures.

Piezoaeroelastic Typical Section for Wind Energy Harvesting

In this paper an electromechanically coupled typical section is modeled for energy harvesting from the aeroelastic oscillations. An airfoil with three degrees of freedom is investigated. Piezoelectric coupling is introduced to the plunge degree-of-freedom and the influence of different load resistances on the overall system behavior is investigated. A free play region is considered in the control surface rotation axis. In the presence of such a concentrated structural nonlinearity, the flow-induced displacements can be harmonic, non-harmonic or chaotic. The presented model can simulate arbitrary airfoil motions as well as represent the nonlinear behavior. The Jones’ approximation to Wagner indicial function is adopted to approximate the aerodynamic loads. An optimal load resistance, which provides both the maximum power and the best passive control of vibration due to the shunt damping effect, is identified. Results show that airflow velocities close to the natural wind are enough to induce self-sustained oscillations and produce persistent power output from scaled piezoaeroelastic generators.