Mohamed Y. Zakaria

Experimental analysis of energy harvesting from self-induced flutter of a composite beam

Previous attempts to harvest energy from aeroelastic vibrations have been based on attaching a beam to a moving wing or structure. Here, we exploit self-excited oscillations of a fluttering composite beam to harvest energy using piezoelectric transduction. Details of the beam properties and experimental setup are presented. The effects of preset angle of attack, wind speed, and load resistance on the levels of harvested power are determined. The results point to a complex relation between the aerodynamic loading and its impact on the static deflection and amplitudes of the limit cycle oscillations on one hand and the load resistance and level of power harvested on the other hand.

Design Optimization of Flapping Ornithopters: The Pterosaur Replica in Forward Flight

There has been a recent interest to explore the shape and kinematics parameters of distinct pterosaurs from their fossil records. Clearly, far more evidence is needed to understand the nuances of dinosaurs flight. A multiobjective aerodynamic optimization problem of the wing kinematics and planform of a pterosaur replica ornithopter designed by Aerovironment is performed. Objective functions include minimization of the required cycle-averaged aerodynamic power and maximization of the propulsive efficiency. It is found that inclusion of the inertial power requirements is necessary for a physical and proper formulation of the optimization problem. Furthermore, the mere addition of the inertial power requirements is not enough to obtain reasonable results. Rather, one has to consider a partial (or even zero) elastic energy storage. The minimum power kinematic parameters closely match those of the previously designed pterosaur replica. Nevertheless, the obtained efficiency for such a design (minimum power) is...

Experimental-Based Unified Unsteady Nonlinear Aerodynamic Modeling For Two-Dimensional Airfoils

Unsteady force measurements of a plunging airfoil at different frequencies and mean angles of attack are used to construct frequency response models. The obtained frequency response models are then used to determine the linearized flow dynamics around each mean angle of attack, where an optimization-based linear system identification is performed to minimize the error between the predicted and measured frequency responses. Converting these models to state space form and writing the entries of the matrices as polynomials in the mean angle of attack, a global, unified unsteady model is developed. The developed reduced order model, represented in a state space form, is suitable for characterizing the nonlinear dynamical characteristics of the flow and the associated dynamics and control of a flying object.

Experimnetal Investigations of the Lift Frequency Response at High Angels of Attack

In comparison to the numerous theoretical research reports on the unsteady nonlinear aerodynamics, there has been very few experimental data available for validation purposes; particularly, at high angles of attack (40◦ and higher). We perform experiments on an oscillating two-dimensional NACA 0012 airfoil at various reduced frequencies (0.1 ≤ k ≤ 0.9) and mean angles of attack (0◦ ≤ α0 ≤ 65◦) that undergoes a plunging motion. For each case of the mean angle of attack, the plunging motion is performed with a small amplitude at different frequencies to determine the frequency response of the dynamics. The objective is to assess the effects of the mean angle of attack on the flow dynamics and determine specific aspects associated with unsteady motions at high values of the angle of attack and the reduced frequency.

An Experimental Study of Added Mass on a Plunging Airfoil Oscillating with High Frequencies at High Angles of Attack

Experiments are conducted to measure the unsteady plunging forces on an airfoil at zero forward velocity. The aim is to investigate the variation of the added mass with the oscillation frequency of the wing section for various angles of attack. Data of the measured forces is presented and compared with predicted forces from potential flow approximations. The results show a significant departure from those estimates especially at the high frequencies. The results show that the added mass varies linearly with the frequency of the oscillations. Furthermore, the added mass is largest for the cases of 10 and 20 degrees angles of attack. These results raise the question of how to account for the unsteady flow generated by the airfoil motion.

Piezoelectric energy harvesting using L-shaped structures:

Energy harvesting from an L-shaped structure, formed by two beams and corner and end masses, is investigated with the objective of expanding the bandwidth of the frequency range over which energy can be harvested. The structure is excited in a direction that yields the most uniform strain distribution along its main beam. The length of the auxiliary beam is varied to determine its effect on the level and breadth of the frequency range over which energy can be harvested. Results from experiments having different geometries are presented and discussed. It is determined that the frequency range over which energy can be harvested from such structures is much larger than levels harvested when using a cantilever beam. The experiments also show that L-shaped structures harvest more power when the length of the auxiliary beam is increased. On the contrary, the power density of the L-shaped structure is much smaller than that of the cantilever beam. The ability to control the bandwidth of frequency over which energy is harvested through proper adjustment of beam lengths is demonstrated.

Use of thermoelectric generator for water flow metering

We propose using a thermoelectric generator as a flow meter without requiring additional components. We do so by relating the power generated from the flow of hot water in a pipe to the flow rate. The results show that the steady state values of the power and voltage are more or less independent of the flow rate. On the other hand, the peak power varies significantly with the flow rate. As such, we develop through data analysis a relation between the nondimensional harvested peak power and the Reynolds number. Different sets of experiments are performed to assess the dependence of the developed relation on the boundary conditions. An equation governing this relation is obtained. The proposed approach provides a self-powered monitoring device for quantifying flow rates in pipes conveying hot water.

Shape and Kinematic Design Optimization of the Pterosaur replica

A multi-objective aerodynamic optimization problem of the wing kinematics and planform of the Pterosaur replica is performed. Objective functions include minimization of the required cycle-averaged aerodynamic power and maximization of the propulsive efficiency. It is found that inclusion of the inertial power requirements is necessary for a physical and proper formulation of the optimization problem. Furthermore, the mere addition of the inertial power requirements is not enough to obtain reasonable results. Rather, one has to consider a partial (or even zero) elastic energy storage. The minimum power optimum kinematic parameters are close to the operating design variables of the pterosaur replica compared to the maximum efficiency design; though the obtained efficiency for such a design (minimum power) is (10 %) which is relatively low. Furthermore, the optimized planform for maximum efficiency of the Pterosaur yields a propulsive efficiency of 46.0%.

A novel imaging technique for measuring kinematics of light-weight flexible structures

A new imaging algorithm is proposed to capture the kinematics of flexible, thin, light structures including frequencies and motion amplitudes for real time analysis. The studied case is a thin flexible beam that is preset at different angles of attack in a wind tunnel. As the angle of attack is increased beyond a critical value, the beam was observed to undergo a static deflection that is ensued by limit cycle oscillations. Imaging analysis of the beam vibrations shows that the motion consists of a superposition of the bending and torsion modes. The proposed algorithm was able to capture the oscillation amplitudes as well as the frequencies of both bending and torsion modes. The analysis results are validated through comparison with measurements from a piezoelectric sensor that is attached to the beam at its root.