Modeling and performance study of a beam microgyroscope

We develop a mathematical model of a microgyroscope whose principal component is a rotating cantilever beam equipped with a proof mass at its end. The microgyroscope undergoes two flexural vibrations that are coupled via base rotation about the microbeam longitudinal axis. The primary vibratory motion is produced in one direction (drive direction) of the microbeam by a pair of DC and AC voltages actuating the proof mass. The microbeam angular rotation induces a secondary vibration in the orthogonal (sense) direction actuated by a second DC voltage. Closed-form solutions are developed for the linearized problem to study the relationship between the base rotation and gyroscopic coupling. The response of the microgyroscope to variations in the DC voltage across the drive and sense electrodes and frequency of excitation are examined and a calibration curve of the gyroscope is obtained analytically.     

A unified model for electrostatic sensors in fluid media

Nonlinear Dynamics - We present a unified model of electrostatic sensors comprising cantilever microbeam resonators in fluid media. The model couples Euler–Bernoulli beam equation to the...     

Flutter control and mitigation of limit cycle oscillations in aircraft wings using distributed vibration absorbers

Nonlinear Dynamics - In this work, we demonstrate the application of the conserved-mass metamaterial concept to control the flutter onset in aircraft wings and mitigate their induced vibrations....     

Aeroelastic analysis and nonlinear dynamics of an elastically mounted wing

The response of an elastically mounted wing that is free to plunge and pitch, supported by nonlinear translational and torsional springs, and interacting with an incoming stream is analyzed. A tightly coupled model of the wing flow interaction is developed. A three-dimensional code based on the unsteady vortex lattice method is used for the prediction of the unsteady aerodynamic loads. The response of the wing shows a sequence of static and dynamic bifurcations and chaotic motions when increasing the flow speed. Pairs of stable solutions are observed over the different response regimes. The effects of the gust and structural nonlinearity on the wing's response are also investigated. The results show that gust may lead to jumps between the pairs of solutions for static and dynamic equilibrium responses without impacting the boundaries of the different response regimes. As for the effect of the structural nonlinearity, increasing the nonlinear coefficient of the stiffness of the torsional spring yields lower static deflections and amplitudes of the limit cycle oscillations.     

Role of wing morphing in thrust generation

In this paper, we investigate the role of morphing on flight dynamics of two birds by simulating the flow over rigid and morphing wings that have the characteristics of two different birds, namely the Giant Petrel and Dove Prion. The simulation of a flapping rigid wing shows that the root of the wing should be placed at a specific angle of attack in order to generate enough lift to balance the weight of the bird. However, in this case the generated thrust is either very small, or even negative, depending on the wing shape. Further, results show that morphing of the wing enables a significant increase in the thrust and propulsive efficiency. This indicates that the birds actually utilize some sort of active wing twisting and bending to produce enough thrust. This study should facilitate better guidance for the design of flapping air vehicles.     

Nonlinear analysis and effectiveness of weakly coupled microbeams for mass sensing applications

Nonlinear Dynamics - Kaplan turbines, also known as movable propeller turbines, are attractive for power generation from water currents. They are controlled by guide vanes and runner blades, whose...     

Nonlinear analysis and enhancement of wing-based piezoaeroelastic energy harvesters

We investigate the level of harvested power from aeroelastic vibrations for an elastically mounted wing supported by nonlinear springs. The energy is harvested by attaching a piezoelectric transducer to the plunge degree of freedom. The considered wing has a low-aspect ratio and hence three dimensional aerodynamic effects cannot be neglected. To this end, the three dimensional unsteady vortex lattice method for the prediction of the unsteady aerodynamic loads is developed. A strong coupling scheme that is based on Hamming's fourth-order predictor–corrector method and accounts for the interaction between the aerodynamic loads and the motion of the wing is employed. The effects of the electrical load resistance, nonlinear torsional spring and eccentricity between the elastic axis and the gravity axis on the level of the harvested power, pitch and plunge amplitudes are investigated for a range of operating wind speeds. The results show that there is a specific wind speed beyond which the pitch motion does not pick any further energy from the incident flow. As such, the displacement in the plunge direction grows significantly and causes enhanced energy harvesting. The results also show that the nonlinear torsional spring plays an important role in enhancing the level of the harvested power. Furthermore, the harvested power can be increased by an order of magnitude by properly choosing the eccentricity and the load resistance. This analysis is helpful in designing piezoaeroelastic energy harvesters that can operate optimally at specific wind speeds.     

Multifidelity modeling and comparative analysis of electrically coupled microbeams under squeeze-film damping effect

Nonlinear Dynamics - We investigate the nonlinear dynamic response of a device made of two electrically coupled cantilever microbeams. The vibrations of the microbeams triggered by the electric...     

Enclosure enhancement of flight performance

We use a potential flow solver to investigate the aerodynamic aspects of flapping flights in enclosed spaces. The enclosure effects are simulated by the method of images. Our study complements previous aerodynamic analyses which considered only the near-ground flight. The present results show that flying in the proximity of an enclosure affects the aerodynamic performance of flapping wings in terms of lift and thrust generation and power consumption. It leads to higher flight efficiency and more than 5% increase of the generation of lift and thrust.     

Uncertainty analysis near bifurcation of an aeroelastic system

Variations in structural and aerodynamic nonlinearities on the dynamic behavior of an aeroelastic system are investigated. The aeroelastic system consists of a rigid airfoil that is supported by nonlinear springs in the pitch and plunge directions and subjected to nonlinear aerodynamic loads. We follow two approaches to determine the effects of variations in the linear and nonlinear plunge and pitch stiffness coefficients of this aeroelastic system on its stability near the bifurcation. The first approach is based on implementation of intrusive polynomial chaos expansion (PCE) on the governing equations, yielding a set of nonlinear coupled ordinary differential equations that are numerically solved. The results show that this approach is capable of determining sensitivity of the flutter speed to variations in the linear pitch stiffness coefficient. On the other hand, it fails to predict changes in the type of the instability associated with randomness in the cubic stiffness coefficient. In the second approach, the normal form is used to investigate the flutter (Hopf bifurcation) boundary that occurs as the freestream velocity is increased and to analytically predict the amplitude and frequency of the ensuing LCO. The results show that this mathematical approach provides detailed aspects of the effects of the different system nonlinearities on its dynamic behavior. Furthermore, this approach could be effectively used to perform sensitivity analysis of the system's response to variations in its parameters.