Daochun Li

Development of piezoelectric actuated mechanism for flapping wing micro-aerial vehicle applications

Abstract Abstract A piezoelectric actuated two-bar two-flexure motion amplification mechanism for flapping wing micro-aerial vehicle application has been investigated. f r*A as an optimisation criterion has been introduced where f r is its fundamental resonant frequency of the system and A the vibration amplitude at the wing tip, or the free tip deflection at quasi-static operation. This criterion can be used to obtain the best piezoelectric actuation mechanism with the best energy transmission coefficient for flapping wing micro-aerial vehicle applications, and is a measurable quantity therefore can be compared with experimental results. A simplified beam model has been developed to calculate the fundamental resonant frequency for the full system consisted of piezoelectric actuator, motion amplification mechanism and the attached wing and the calculated values were compared with the measured results. A clear trend of the criteria f r*A varying with the two-flexure dimension, stiffness and setting angle have been obtained from the measured data and also the predicted results as a guideline for optimal design of the system.

Experimental study on the lift generated by a flapping rotary wing applied in a micro air vehicle

An experimental study was conducted to further validate whether the newly proposed flapping rotary wing is suitable for micro air vehicle design. First, the effects of two main kinematical parameters (flapping frequency and initial angle of attack) of flapping rotary wing on lift generation were discussed. It was found that a higher lift can be generated by flapping rotary wing through increasing flapping frequency at a proper initial angle of attack. Second, effect of coupled flapping motion with rotating motion on lift generation was analyzed. It is important that a larger lift was generated by flapping rotary wing than the superposition lifts from purely flapping and purely rotating motions when the initial angle of attack was less than a critical value. Finally, the comparison of the capability of lift generation from the flapping rotary wing and conventional rotary wing was given. It was indicated that the lift from flapping rotary wing was larger than that from conventional rotary wing in the range of Reynolds number from 2600 to 5000 as long as Strouhal number was determined appropriately. The present work suggests that flapping rotary wing may be a feasible and promising wing layout used in the design of micro air vehicle in terms of lift generation.

Modeling and nonlinear aeroelastic analysis of a wing with morphing trailing edge

An investigation was made into the nonlinear aeroelastic behavior of a composite wing with morphing trailing edge actuated by curved beams. Based on the design concept, an experimental wing model was built and a finite element model was created using MSC Patran/Nastran software. Impact test of the experimental model was carried out and the test data were used to validate the finite element models. In order to investigate the effect of freeplay nonlinearity between discs attached to the curved beams and wing skins, a nonlinear aeroelastic equation in modal coordinate was created. Generalized structural mass, damping, and stiffness matrixes were printed with DMAP language in Nastran. Doublet lattice method and Roger’s approximation were used to calculate unsteady aerodynamic influence coefficients matrix. In the analysis, the effect of morphing stiffness on critical flutter speed was studied. In addition, Hopf bifurcation and limit cycle oscillation were detected for the aeroelastic system with freeplay. The results show that the freeplay nonlinearity may reduce convergence speed and accelerate divergence of aeroelastic responses.

Aerodynamic Performance of the Locust Wing in Gliding Mode at Low Reynolds Number

Gliding is an important flight mode for insects because it saves energy during long distance flight without ing flapping. In this study, we investigated the influence of locust wing corrugation on the aerodynamic performance in gliding mode at low Reynolds number. Numerical simulations using two-dimensional Navier-Stokes equations are applied to study the gliding flight, which reveals the interaction between forewing and hindwing. The lift of the corrugated airfoil in a locust wing decreases from the wing root to the tip. Simulation results show that the pressure drags on the forewing and hindwing increase with an increase in wing thickness; while the lift-drag ratio of the airfoil is marginally affected by the corrugation on the airfoil. Geometric parameters analysis of the locust wing is also carried out, which includes the corrugation height, the corrugation placement and the shapes of leading and trailing edges.

Design, Experiment and Aerodynamic Calculation of a Flapping Wing Rotor Micro Aerial Vehicle

In this paper, investigation was made into the design, experiment, and aerodynamic analysis of a novel flapping wing rotor applicable to micro aerial vehicles (MAV). Attention was firstly focused on the design of a simple, reliable and lightweight flapping rotor configuration and wing structure to meet the challenging demands for high mechanical and power efficiency and vertical take-off and landing (VTOL) capability of an MAV. The experimental work demonstrated the feasibility and effectiveness of the innovative design. The paper presents an approach of experiment and processing the measured flapping wing total dynamic forces to extract the unsteady aerodynamic force. A potential-flow-based method, unsteady panel method was used to calculate the lift created by flapping wing system. As the method is two dimensional, strip theory is adopted to evaluate the aerodynamics of three dimensional flapping wings. Compared with measured data, the numerical results show good agreement with the first order lift component, which is caused by the rigid wing.

Design and Analysis of a Morphing Flap Structure for High Lift Wing

This paper presents the design, modeling and analysis of a morphing trailing edge (TE) flap for a large aircraft high lift wing. Attention was firstly focused on the design of an actuation system to smoothly deflect the flexible rear part of the flap to achieve a specified shape. An existing curved beam eccentuator design was adapted to the current structure together with an open sliding trailing edge. Additional connections were set between the upper and lower skins to ensure the integrity of the flap structure, under the aerodynamic and actuation loads, was maintained. Different types of connections were investigated and modeled to represent the practical design case. The effects of the aerodynamic pressure load on the flap structure and on the actuation load were analyzed. Subsequently a nonlinear structural modeling and analysis of the flap TE were carried out. A stress and strain analysis was performed to ensure a safe design and also to study the TE flap mechanical behavior under both actuation and aerodynamic load. The results showed that the proposed design solution is simple and able to achieve the desired flap morphed shape.

Performance Analysis and Parametric Design of an Airfoil-Based Piezoaeroelastic Energy Harvester

Energy harvesters are designed to convert energy from ambient sources to recharge batteries or power low-power-consumption microsystems. The piezoelectric transduction of aeroelastic vibrations is a scalable option for energy harvesting. To design an efficient harvester, the harvesting performance needs to be studied and hence enhanced. The purpose of this paper is to analyze the dynamic response and harvesting performance of an airfoilbased piezoaeroelastic energy harvester by investigating the effects of the system parameters and external discrete disturbances. The airfoil, with plunge and pitch degrees of freedom (DOFs), is supported by linear flexural springs and nonlinear torsional springs. Piezoelectric transducers are attached to the plunge DOF. The unsteady aerodynamics due to arbitrary motions are obtained from Jones’ approximation of the Wagner function. A state-space model is obtained for numerical simulation. Parameters including the load resistance, the nonlinear torsional stiffness coefficient, the free play gap and the locations of both elastic axis and gravity center axis of the airfoil are concerned. In addition, the effects of 1-cosine gust disturbances are studied. The results show that: as the resistance increases, each of the plunge and pitch motions has a minimum amplitude. But the minimum response amplitudes do not affect the variations of the electric outputs. There is one optimal resistance maximizing the power output. Besides, the increase of the free play gap enhances harvesting performance linearly, whereas large nonlinear torsional stiffness would significantly decrease the power output. The variations of the voltage output with the structural nonlinearities resemble that of the plunge motion. Moreover, there is one optimal eccentricity of the airfoil for the highest harvesting performance as the elastic axis is fixed and the flow velocity is certain. The rearward shift of the elastic axis helps enhance the power output whereas it demands larger eccentricities to maintain limit cycle oscillations (LCOs). Last but not the least, under a relative large wind scale, the discrete gust loads may change the equilibrium position of both plunge and pitch responses under special gust vertical velocities. The jumps may affect the phase of the electric outputs, but they make no difference on the amplitude of power output.

NONLINEAR AEROELASTIC ANALYSIS OF A MORPHING FLAP

A morphing flap integrated with an actuation mechanism was designed and investigated. Based on structure parameters from static experiments, a finite element model of the flap was created within MSC Patran software. Normal modal analysis and linear flutter analysis were carried out firstly. V–g and V–f curves were obtained to determine the critical flutter speeds with and without the actuation mechanism. Structural mass, damping, stiffness, and aerodynamic matrixes were printed with DMAP language to form an aeroelastic equation in modal coordinate. The freeplay nonlinearity between disks attached to the curved beams and wing skins was considered in the aeroelastic analysis. An unsteady aerodynamic influence coefficients matrix was calculated by Rogers approximation. The nonlinear aeroelastic equation in modal coordinate was solved by an iterative program written with MATLAB software. Based on the reduced-order aeroelastic model, the effect of freeplay on aeroelastic responses was investigated. Numerical results show that the freeplay nonlinearity may reduce critical flutter speed, leading to supercritical Hopf bifurcation.

Active control design for an unmanned air vehicle with a morphing wing

Purpose – The purpose of this study is to develop an active controller of both leading-edge (LE) and trailing-edge (TE) control surfaces for an unmanned air vehicle (UAV) with a composite morphing wing. Design/methodology/approach – Instead of conventional hinged control surfaces, both LE and TE seamless control surfaces were integrated with the wing. Based on the longitudinal state space equation, the root locus plot of the morphing wing aircraft, with a stability augmented system, was constructed. Using the pole placement, the feedback gain matrix for an active control was obtained. Findings – The aerodynamic benefits of a morphing wing section are compared with a wing of a rigid control surface. However, the 3D morphing wing with a large sweptback angle produces a washout negative aeroelastic effect, which causes a significant reduction of the control effectiveness. The results show that the stability augmentation system can significantly improve the longitudinal controllability of an aircraft with a m...

Optimization of Composite Wing Structure for a Flying Wing Aircraft Subject to Multi Constraints

This paper presents a minimum weight optimization of a composite wing structure subject to multi constraints including strength, damage tolerance and aeroelastic stability. Based on preliminary design data, the investigation demonstrated an efficient optimization approach of a composite wing structure modeled by FEM in the detailed design phase for a flying wing aircraft. For potential application, the structure modeling and optimization process has been performed by full use of the commercial software MSC Nastran, which is widely employed in aerospace industry. First the wing structure FE model is divided into number of design zones along the span. A pre-process was proposed to group all plies in the same fiber orientation within one zone into a stack laminate and share one design variable. In each zone, the number of design variable in terms of skin ply thickness is reduced to the same number of fiber orientations used in the wing skin laminate. After the optimization, a post process was performed to trim the ply thickness and reset the skin laminate layup under the design and manufacture constraint. To keep the final design on the safe side, the thickness of an optimized ply is normally increased to the standard figure in the trim process. Consequently the trimmed structure weight is slightly increased after the post-process. However a practical optimum design of the composite wing structure in detailed FE model can be obtained. For the composite wing example, numerical results show that the optimized structure weight has been reduced by 16.3%. The results also show that the optimization approach is much efficient with little accuracy penalty.