Thesis (M.App.Sc.) - Carleton University, 2007. / Includes bibliographical references (p. 78-79). Also available in electronic format on the Internet.

Thesis (M.S.)--University of Wyoming, 2009. / Title from PDF title page (viewed on June 15, 2010). Includes bibliographical references (p. 103).

Angle section members, used in open engineering structures, have been known to experience large amplitude oscillations when exposed to normal atmospheric winds, and in a few instances failure has been reported. The bluff geometry together with low natural frequency makes these members susceptible to aeroelastic vibrations of a vortex resonant or galloping nature. The thesis aims at studying the nature of the aerodynamic forces and the resulting instabilities for the safe design of the structures. It presents information on the aerodynamics and dynamics of the angle section during stationary, plunging, torsional and combined plunging-torsional conditions. From the measurements on stationary angle models, it is possible to predict the critical vortex resonant wind speeds for various angles of attack. The large variations of the unsteady aerodynamic coefficients indicate the dependence of the resonant instability on model orientation. Incorporating the stationary aerodynamic loadings, the quasi-steady analysis is able to predict the galloping instability and resulting amplitude and buildup time response. The absence of torsional galloping during the experiment is substantiated by the theory which shows the instability to occur only at high wind speeds or for systems with very low damping. The dynamical study demonstrates that structural angle sections are susceptible in general, to combined plunging and torsional vibrations. The nature of the instability depends on such system parameters as damping, natural frequency, angle of attack, section size, etc. However, due to the existence of two distinct families of virtual hinge points, it is possible to represent the motion as predominantly plunging or torsion. Furthermore, the frequency of the coupled motion as well as the type and range of the instability are found to be similar to those in the single degree of freedom. This makes it possible to obtain pertinent information by studying, both experimentally and theoretically, the plunging and torsional degrees of freedom, separately. During plunging resonance, the angle section experiences a vortex capture phenomenon where the shedding frequency is controlled by the cylinder motion over a finite wind speed range. On the other hand, the torsional vibration shows a vortex control condition over a large velocity range where the vortex shedding governs the frequency of oscillation and follows the stationary model Strouhal curve. Compared to the stationary and torsional results, the fluctuating pressures on the angle surface during plunging resonance are substantially larger in magnitude with less amplitude modulation and phase variation. Consequently, the unsteady aerodynamic coefficients increase with this instability. During resonance in either degree of freedom, the vortex velocity and longitudinal spacing remain essentially unaltered, however, the wake width experiences substantial increase with plunging motion. It appears that the torsional resonance has virtually no effect on the vortex shedding or wake characteristics. / Applied Science, Faculty of / Mechanical Engineering, Department of / Graduate

A procedure for the design of a scaled aircraft using linear aeroelastic scaling is developed and demonstrated. Previous work has shown the viability in matching scaled structural frequencies and mode shapes in order to achieve consistent linear scaling of simple models. This methodology is adopted for use on a high fidelity joined-wing aircraft model. Natural frequencies and mode shapes are matched by optimizing structural ply properties and nonstructural mass. A full-scale SensorCraft concept developed by AFRL and Boeing serves as the target model, and a 1/9th span geometrically scaled remotely piloted vehicle (RPV) serves as the initial design point. The aeroelastic response of the final design is verified against the response of the full-scale model. Reasonable agreement is seen in both aeroelastic damping and frequency for a range of flight velocities, but some discrepancy remains in accurately capturing the flutter velocity. / Master of Science

Aeroelastic scaling methodologies are developed for geometrically nonlinear applications. The new methods are demonstrated by designing an aeroelastically scaled model of a suitably nonlinear full-scale joined-wing aircraft. The best of the methods produce scaled models that closely replicate the target aeroelastic behavior. Internal loads sensitivity studies show that internal loads can be insensitive to axial stiffness, even for globally indeterminate structures. A derived transverse to axial stiffness ratio can be used as an indicator of axial stiffness importance. Two findings of the work extend to geometrically linear applications: new sources of local optima are identified, and modal mass is identified as a scaling parameter. Optimization procedures for addressing the multiple optima and modal mass matching are developed and demonstrated. Where justified, limitations of commercial software are avoided through development of custom tools for structural analysis and sensitivities, aerodynamic analysis, and nonlinear aeroelastic trim. / Ph. D.

Aeroelastic gust and maneuver loads have driven the sizing of primary aircraft structures since the beginning of aviation. Methodologies for determining the gust loads on aircraft have evolved over the last 100 years. There are three general approaches to gust loads analysis: quasi-static, transient, and continuous methods. Quasi-static analysis offers the greatest computational efficiency. A quasi-static formulation referred to as Pratt's Method is the current practice for FAR Part 23 certification requirements. Assumptions made in the derivation of Pratt's Method are acceptable for many conventional aircraft, but additional fidelity from transient and continuous analysis are required to certify FAR Part 25 aircraft. This work provides an assessment of the usability of Pratt's Method for unconventional high altitude long endurance (HALE) aircraft. Derivation Pratt's Method is reviewed and all assumptions are identified. Error of a key curve fit equation is quantified directly. Application dependent errors are quantified by comparing loads calculated using Pratt's Method to loads calculated from transient analysis. To facilitate this effort, a state of the art nonlinear aeroelastic code has been modified to more accurately capture the transient gust response. Application dependent errors are presented in the context of a SensorCraft inspired joined-wing HALE model, and a Helios inspired flying wing HALE model. Recommendations are made on the usability of Pratt's Method for aircraft similar to the two HALE models. It is concluded that Pratt's Method is useful for preliminary design of the joined-wing HALE model, but inadequate for the analysis of the flying wing model. Additional recommendations are made corresponding to subtleties in the implementation of Pratt's Method for unconventional configurations. / Master of Science

Ballute hypersonic aerodynamic decelerators have been considered for aerocapture since the early 1980's. Recent technology advances in fabric and polymer materials as well as analysis capabilities lend credibility to the potential of ballute aerocapture. The concept of the thin-film ballute for aerocapture shows the potential for large mass savings over propulsive orbit insertion or rigid aeroshell aerocapture. Several technology hurdles have been identified, including the effects of coupled fluid structure interaction on ballute performance and survivability. To date, no aeroelastic solutions of thin-film ballutes in an environment relevant to aerocapture have been published. In this investigation, an aeroelastic solution methodology is presented along with the analysis codes selected for each discipline. Variable-fidelity aerodynamic tools are used due to the long run times for computational fluid dynamics or direct simulation Monte Carlo analyses. The improved serial staggered method is used to couple the disciplinary analyses in a time-accurate manner, and direct node-matching is used for data transfer. In addition, an engineering approximation has been developed as an addition to modified Newtonian analysis to include the first-order effects of damping due to the fluid, providing a rapid dynamic aeroelastic analysis suitable for conceptual design. Static aeroelastic solutions of a clamped ballute on a Titan aerocapture trajectory are presented using non-linear analysis in a representative environment on a flexible structure. Grid convergence is demonstrated for both structural and aerodynamic models used in this analysis. Static deformed shape, drag and stress level are predicted at multiple points along the representative Titan aerocapture trajectory. Results are presented for verification and validation cases of the structural dynamics and simplified aerodynamics tools. Solutions match experiment and other validated codes well. Contributions of this research include the development of a tool for aeroelastic analysis of thin-film ballutes which is used to compute the first high-fidelity aeroelastic solutions of thin-film ballutes using inviscid perfect-gas aerodynamics. Additionally, an aerodynamics tool that implements an engineering estimate of hypersonic aerodynamics with a moving boundary condition is developed and used to determine the flutter point of a thin-film ballute on a Titan aerocapture trajectory.

Aerospace structures with large aspect ratio, such as airplane wings, rotorcraft blades, wind turbine blades, and jet engine fan and compressor blades, are particularly susceptible to aeroelastic phenomena. Finite element analysis provides an effective and generalized method to model these structures; however, it is computationally expensive. Fortunately, these structures have a length appreciably larger than the largest cross-sectional diameter. This characteristic is exploitable as these potential aeroelastically unstable structures can be modeled as cantilevered beams, drastically reducing computational time. In this thesis, the nonlinear equations of motion are derived for an inextensional, non-uniform cantilevered beam with a straight elastic axis. Along the elastic axis, the cross-sectional center of mass can be o set in both dimensions, and the principal bending and centroidal axes can each be rotated uniquely. The Galerkin method is used, permitting arbitrary and abrupt variations along the length that require no knowledge of the spatial derivatives of the beam properties. Additionally, these equations consistently retain all third-order nonlinearities that account for flexural-flexural-torsional coupling and extend the validity of the equations for large deformations. Furthermore, linearly independent shape functions are substituted into these equations, providing an efficient method to determine the natural frequencies and mode shapes of the beam and to solve for time-varying deformation. This method is validated using finite element analysis and is extended to swept wings. The importance of retaining cubic terms, in addition to quadratic terms, for nonlinear analysis is demonstrated for several examples. Ultimately, these equations are coupled with a fluid dynamics solver to provide a structurally efficient aeroelastic program.

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