E.F. Crawley

Bio: E.F. Crawley is an academic researcher from Massachusetts Institute of Technology. The author has contributed to research in topic(s): Finite element method & Vibration. The author has an hindex of 1, co-authored 1 publication(s) receiving 74 citation(s).

Frequency determination and non-dimensionalization for composite cantilever plates

Abstract: A method for estimating the natural frequencies of composite cantilever plates and for non-dimensionalizing frequency data is developed and demonstrated. The scheme is based on a partial Ritz (Kantorovich) analysis, which reduces the problem to a set of uncoupled ordinary differential equations. The solution of these equations yields both the eigenvalues of free vibration and the proper forms of the non-dimensional frequency. Together these can be used to estimate the natural frequencies of laminated plates. In addition the non-dimensional frequency expressions can be used to reduce numerical or experimental vibration data. To demonstrate this the first five frequencies of a representative group of laminated plates are calculated by using a finite element model. The calculated frequencies are then non-dimensionalized by using the expressions derived from the Ritz analysis. The resulting non-dimensional frequencies not only show more consistency than the original data, but are shown to agree well with the eigenvalues of the Ritz analysis.

Aeroelastic tailoring - Theory, practice, and promise

Abstract: Aeroelastic tailoring technology is reviewed with reference to the historical background, the underlying theory, current trends, and specific applications. The specific application discussed include the Transonic Aircraft Technology program, an Advanced Design Composite Aircraft, the Wing/Inlet Advanced Development program, and the forward-swept wing. Finally, the future of aeroelastic tailoring and the development of an aeroelastic tailoring analysis and design tool under the Automated Strength-Aeroelastic Design program are examined.

Aeroelastic flutter and divergence of stiffness coupled, graphite/epoxy cantilevered plates

Abstract: An analytical and experimental investigation was conducted to determine the aeroelastic flutter and divergence behavior of unswept, rectangular wings simulated by graphite/epox y, cantilevered plates with various amounts of bending-torsi on stiffness coupling. The analytical approach incorporated a Rayleigh-Ritz energy formulation and unsteady, incompressible two-dimensional aerodynamic theory. Flutter and divergence velocities were obtained using the \ -g method and compared to results of low-speed wind tunnel tests. Stall flutter behavior was also examined experimentally. There was good agreement between analytical and experimental results. Wings with negative stiffness coupling exhibited divergence, while positive coupling delayed the onset of stall flutter.

Nonlinear Stall Flutter and Divergence Analysis of Cantilevered Graphite/Epoxy Wings

Abstract: The nonlinear, stalled, aeroelastic behavior of rectangular, graphite/epoxy, cantilevered wings with varying amount of bending-torsi on stiffness coupling is investigated. A nonlinear aeroelastic analysis is developed using the nonlinear, stalled ONERA aerodynamic model initially presented by Tran and Petot. Nonlinear flutter calculations are carried out using Fourier analysis to extract the harmonics from the ONERA aerodynamics, then a harmonic balance method and a Newton-Raphson solver are applied to the resulting nonlinear, Rayleigh-Ritz aeroelastic formulation. Test wings were constructed and subjected to wind-tunnel tests for comparison against the developed analysis. Wind-tunnel tests show reasonable agreement between theory and experiment for static deflections, for linear flutter and divergence, and for nonlinear, torsional stall flutter and bending stall flutter limit cycles. The current nonlinear analysis shows a transition from divergence to bending stall flutter, which linear analyses are unable to predict.

Aeroelastic and Aerothermoelastic Behavior in Hypersonic Flow

Abstract: The testing of aeroelastically and aerothermoelastically scaled wind-tunnel models in hypersonic flow is not feasible; thus, computational aeroelasticity and aerothermoelasticity are essential to the development of hypersonic vehicles. Several fundamental issues in this area are examined by performing a systematic computational study of the hypersonic aeroelastic and aerothermoelastic behavior of a three-dimensional configuration. Specifically, the flutter boundary of a low-aspect-ratio wing, representative of a fin or control surface on a hypersonic vehicle, is studied over a range of altitudes using third-order piston theory and Euler and Navier-Stokes aerodynamics. The sensitivity of the computational-fluid-dynamics-based aeroelastic analysis to grid resolution and parameters governing temporal accuracy are considered. In general, good agreement at moderate-to-high altitudes was observed for the three aerodynamic models. However, the wing flutters at unrealistic Mach numbers in the absence of aerodynamic heating. Therefore, because aerodynamic heating is an inherent feature of hypersonic flight and the aeroelastic behavior of a vehicle is sensitive to structural variations caused by heating, an aerothermoelastic methodology is developed that incorporates the heat transfer between the fluid and structure based on computational-fluid-dynamics-generated aerodynamic heating. The aerothermoelastic solution procedure is then applied to the low-aspect-ratio wing operating on a representative hypersonic trajectory. In the latter study, the sensitivity of the flutter margin to perturbations in trajectory angle of attack and Mach number is considered. Significant reductions in the flutter boundary of the heated wing are observed. The wing is also found to be susceptible to thermal buckling.

Vibration Tailoring of Advanced Composite Lifting Surfaces

Abstract: This paper discusses the free-vibration characteristics of directionally stiffened, laminated composite beamlike structures such as high-aspect-ratio lifting surfaces. A bounded nondimensional parameter, , is defined to describe the degree of elastic coupling between bending curvature and twist rate for a laminated beam. In addition, three different stiffness models commonly used to model laminated beam/tube deformation are described and compared. Using one of these models, the ability of the laminate design to control mode shape or node line characteristics is illustrated for a cross-coupled laminated cantilever beam. Finally, the effect of the nondimensional cross-coupling parameter, i/s on cantilever beam free-vibration node line positions and frequencies is illustrated, independent of a specific laminate design.