In Lee

VIBRATION BEHAVIORS OF THERMALLY POSTBUCKLED ANISOTROPIC PLATES USING FIRST-ORDER SHEAR DEFORMABLE PLATE THEORY

Abstract Vibration behaviors of thermally postbuckled anisotropic plates are investigated. The finite element method is used for the analysis of thermal postbuckling and natural vibration of thermally postbuckled plates. The finite element model is based on the first-order shear deformable plate theory (FSDT) and von Karman strain-displacement relation to account for large deflection. Critical buckling temperature and the corresponding mode shape are determined from Euler buckling problem. In order to solve the thermal-postbuckling problem, the initial nonlinear stiffness is determined from estimated deflection of scaled buckling mode shape. The converged deflection at any temperature change is obtained using the Newton-Raphson method. The vibration analysis of thermally postbuckled plates are performed using the tangent stiffness obtained from the converged deflection. The effect of fiber orientation angle and aspect ratio on postbuckling and vibration behaviors are studied for simply supported laminated plates subject to steady-state uniform temperature increase.

Static and dynamic analysis of composite box beams using large deflection theory

The static and dynamic behavior of composite box beams is investigated using a large deflection beam theory. The finite element equations of motion for beams undergoing arbitrary large displacements and rotations, but small strains, are obtained from Hamiltons principle. The importance of non-classical structural phenomena is systematically investigated for composite box beams. The sectional elastic constants including warping deformations have been determined from the refined cross-sectional finite element method. The effects of fiber orientations and stacking sequences on the static deformation and vibration characteristics have been investigated. Numerical results are compared with the previously published experimental and theoretical results. The present results are proved to be very accurate.

Vibration analysis of anisotropic plates with eccentric stiffeners

Abstract The analysis of vibration characteristics of anisotropic plates with eccentric stiffeners has been performed using the finite element method based on the shear deformable plate theory. The stiffeners are modeled as a beam element based on Timoshenko beam theory. The present analysis presents the effects of fiber orientation, dimension and location of the stiffener on the vibration characteristics of anisotropic stiffened plates. The stiffened plates are composed of graphite-epoxy(AS1/3501-6) composite laminate with a symmetric stacking sequence. The present finite element model uses nine-node quadrilateral elements for the skin plate and three-node quadratic elements for the stiffener. The solution of the eigenvalue problems has been obtained by the subspace iteration method. The results obtained by the present finite element model are compared with previous results for the stiffened isotropic plates. Also, the result of the present beam model for the stiffener made of composite material is compared with that of the shell model. This result shows that the present model for the stiffened plate gives quite accurate results. The size, fibre orientation angle and location of the stiffener affect the natural frequencies and mode shapes of the stiffened anisotropic plate.

Aeroelastic stability of hingeless rotor blade in hover using large deflection theory

The coupled flap-lag-torsion aeroelastic stability of a hingeless rotor blade in hover is investigated using finite elements based on large deflection beam theory. The finite element equations of motion for beams undergoing arbitrary large displacements and rotations, but small strains, are obtained from Hamiltons principle. The stability boundary is calculated assuming blade motions to be small perturbations about the nonlinear steady equilibrium deflections, which are obtained through an iterative Newton-Raphson method. The p-k- mudal flutter analysis based on coupled rotating natural modes is used. Various unsteady two dimensional strip theories are used to evaluate the aerodynamic loads

Flutter analysis for control surface of launch vehicle with dynamic stiffness

Abstract The root locus and iterative V-g method have been applied to analyze the flutter for a control surface of a launch vehicle with control actuators. The actuator is considered as a spring with dynamic stiffness. The fictitious mass method is adopted for an efficient modal flutter analysis. The methods are applied to the flutter analysis of a control wing with a pneumatic actuator at a rotating axis in the supersonic region. The effect of the sweep angle on the flutter characteristics of the wing with dynamic stiffness is investigated and is compared with that of the wings with several values of static stiffness.

Aeroelastic analysis of composite rotor blades in hover

Abstract The aeroelastic phenomena of a composite rotor blade in hover is investigated using a finite element method. A large deflection type beam theory is used for the one-dimensional global deformation analysis of the hingeless, isolated rotor undergoing arbitrary large displacements and rotations, but small strains. The sectional elastic constants of a composite box beam, including warping deformations, are determined from the refined cross-sectional finite element method. A two-dimensional, quasi-steady strip theory is applied for the aerodynamic calculation. Complete nonlinear equations are solved by the Newton—Raphson method to obtain an equilibrium position and the stability equations are linearized about this position. The modal approach method based on coupled rotating natural modes is used for the flutter analysis. The effects of fiber orientation and stacking sequences on the aeroelastic stability have been investigated.

Supersonic flutter analysis of clamped symmetric composite panels using shear deformable finite elements

The flutter analysis has been performed based on the first-order shear deformable theory. Flutter boundaries have been obtained for both cross-ply and angle-ply composite plates. Also, the flutter analysis has been performed for both rectangular and trapezoidal plates with clamped edges.

Computation of Roll Moment for Projectile with Wraparound Fins Using Euler Equation

Flowe eld solutions of a projectile with wraparound e ns have been computed in a supersonic region with a time-marching, three-dimensional Euler equation. The roll moment coefe cients were computed from the e owe eld solution and compared with the experimental results. The roll moment coefe cient computations show good agreement with the experimental measurements for various e ight Mach numbers. This shows that the Euler equations can give comparably accurate solutions when computing the roll moment of wraparound e n cone gurations. Comparing the e owe eld solutions before and after the roll reversal, the roll reversal at higher Mach number than Mach 1 is thought to be due to the effect of a compression/expansion wave from a neighboring e n. Through the comparison with the previous results, it is shown that the tip shape, as well as the edge shape, has a signie cant effect on the roll moment of the wraparound e n.

Aeroelastic analysis of multibladed hingeless rotors in hover

The coupled flap-lag-torsion aeroelastic response and stability of multibladed hingeless rotors in the hovering flight condition are investigated. The vortex lattice method, with a three-dimensional prescribed wake geometry, is used for the prediction of unsteady airloads of multibladed rotors undergoing disturbed dynamic motions. Interblade unsteady wake effects due to vortex-phasing phenomena beneath a rotor are numerically calculated by the phase control of wake vortices shed from each blade. The aeroelastic equations of motion of the rotor blade are formulated using a finite element beam model that has no artificial restrictions on the magnitudes of displacements and rotations due to the degree of nonlinearity. Numerical results of the steady equilibrium deflections and the lead-lag damping and frequency are presented for two-, three-, and four-bladed stiff-inplane rotors, and are compared with those obtained from a two-dimensional quasisteady strip theory with steady and uniform inflow.

Refined aeroelastic analysis of hingeless rotor blades in hover

The aeroelastic response and stability of hingeless rotor blades in hover are investigated using both refined structural and aerodynamic models. Finite elements based on a large deflection-type beam theory are used for structural analysis. Although the strain components in the beam element are assumed to be small compared to unity, no kinematical limitations are imposed on the magnitude of displacements and rotations. A three-dimensional aerodynamic model including compressibility effect, which is a thin lifting-surface theory based on the unsteady vortex lattice method, is applied to evaluate the aerodynamic loads. A thin lifting-surface and its wake are represented by a number of the quadrilateral vortex-ring elements. The wake geometry is prescribed from the known generalized equations. Numerical results of the steady-state deflections and the stability for the stiff in-plane rotor blade are presented. It is found that the three-dimensional aerodynamic tip-relief, unsteady wake dynamics, and compressibility effects, not predicted in the two-dimensional strip theory, play an important role in the hingeless rotor aeroelastic analysis in hover.