Jinwu Xiang

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.

Meso-Scale Progressive Damage Behavior Characterization of Triaxial Braided Composites under Quasi-Static Tensile Load

Based on continuum damage mechanics (CDM), a sophisticated 3D meso-scale finite element (FE) model is proposed to characterize the progressive damage behavior of 2D Triaxial Braided Composites (2DTBC) with 60° braiding angle under quasi-static tensile load. The modified Von Mises strength criterion and 3D Hashin failure criterion are used to predict the damage initiation of the pure matrix and fiber tows. A combining interface damage and friction constitutive model is applied to predict the interface damage behavior. Murakami-Ohno stiffness degradation scheme is employed to predict the damage evolution process of each constituent. Coupling with the ordinary and translational symmetry boundary conditions, the tensile elastic response including tensile strength and failure strain of 2DTBC are in good agreement with the available experiment data. The numerical results show that the main failure modes of the composites under axial tensile load are pure matrix cracking, fiber and matrix tension failure in bias fiber tows, matrix tension failure in axial fiber tows and interface debonding; the main failure modes of the composites subjected to transverse tensile load are free-edge effect, matrix tension failure in bias fiber tows and interface debonding.

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...

Equivalent linear damping model of nonlinear hydraulic damper for helicopter rotor

An equivalent linear damping model is developed for forward flight condition, with the flap/lag/pitch kinematics and nonlinear characteristics of hydraulic damper taken into account. Damper axial velocity is analyzed from the velocities of the damper‐to‐blade attachment point in time domain. For the case of blade lead‐lag oscillations without forced excitation and kinematics, the equivalent linear damping is calculated from transient response with energy balance method, Fourier series based moving block analysis and Hilbert transform based technology, respectively. Results indicate that equivalent linear damping decreases significantly with lead‐lag forced excitation and flap/lag/pitch kinematics, especially with the latter in flight condition.

Control of an Aeroelastic System with Control Surface Nonlinearity

Nonlinearities in aircraft mechanism are unavoidable, especially in the control system. Correct modeling of the nonlinearities is necessary for the aeroelastic analysis and control . In this paper, a rational polynomial (RP) approximation model is introduced based on actual measured force-deflection relation in aileron system. Numerical examples prove that the model can be used to describe both freeplay and hysteresis nonlinearities. So the switching point problem may be avoided in the numerical integration process. Then state-dependent Riccati equation method is used to derive a state feedback suboptimal control law for flutter suppression of a three degree-of-freedom typical airfoil section with RP nonlinearity in control surface. With the control law designed in this paper, the closed-loop dynamic system is solved by Runge-Kutta numerical approach. Simulation results are presented to show the efficacy of the designed control system. And the effects of RP nonlinearity on aeroelastic closed-loop responses are also investigated.

Damage and perforation resistance behaviors induced by projectile impact load on bonding-patch repaired and scarf-patch repaired composite laminates

A three-dimensional continuum damage model is proposed to analyze the damage and perforation resistance behaviors of bonding-patch and scarf-patch repaired composite laminates under projectile impact load. Coupling with modified 3D-Hashin failure criteria, a linear-exponential law due to fiber pull-out failure and an exponential law are used to predict tensile and compressive softening processes of materials, respectively. A cohesive interaction based on triangle traction–separation law and mixed-mode fracture energy method is applied for interface debonding damages between patch/lamina, patch/patch and lamina/lamina. Comparisons are made between numerical results and several available test data for different impact offsets. The perforation resistance and interface debonding damage mechanisms are extensively discussed using finite element analysis. Further, perforation resistance behaviors of laminate with six different patch-repair patterns are assessed. Effects of initial velocity of projectile on residual velocity and energy-absorption are discussed. A residual velocity error within 7.3% and energy-absorption error within 9.2% is found between simulations and tests. Consistent failure modes including fiber fracture, matrix cracking, delamination and interface debonding are also identified. As the projectile invades patches, interface debonding damage in patches is accumulated rapidly, especially for larger impact offset. The combined patch-repairs show a reduction of at the most 48.3% in velocity and higher ballistic limit velocities which implies better perforation resistance capacity. The energy-absorption almost increases with increasing the initial velocity and a decreasing trend in average energy-absorption is found with the increase of impact offset.

Effects of micro-structure on aerodynamics of Coccinella septempunctata elytra (ladybird) in forward flight as assessed via electron microscopy

The effects of micro-structure on aerodynamics of Coccinella septempunctata (Coleoptera: Coccinellidae) elytra in forward flight were investigated. The micro-structure was examined by a scanning electron microscope and a digital microscope. Based on the experimental results, five elytron models were constructed to separately investigate the effects of the camber and the local corrugation in both leading edge and trailing edge on aerodynamics. Computational fluid dynamic simulations of five elytron models were conducted by solving the Reynolds-Averaged Navier-Stokes equations with the Reynolds number of 245. The results show that camber and the local corrugation in the leading edge play significant roles in improving the aerodynamic performance, while the local corrugation in the trailing edge has little effect on aerodynamics.