Browsing by Subject "aeroelasticity"
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Item A numerical method for fully nonlinear aeroelastic analysis(2009-05-15) Gargoloff, Joaquin IvanThis work presents a numerical method for the analysis of fully nonlinear aeroelastic problems. The aeroelastic model consisted of a Navier-Stokes flow solver, a nonlinear structural model, and a solution methodology that assured synchronous interaction between the nonlinear structure and the fluid flow. The flow around the deforming wing was modeled as unsteady, compressible and viscous using the Reynolds-averaged Navier-Stokes (RANS) equations. To reduce the computational time, a three-level multigrid algorithm was implemented and the flow solver was parallelized. The message-passing interface (MPI) standard libraries were used for the parallel interprocessor communication. The computational domain was divided into topologically identical layers that spanned from the root to past the tip of the wing. A novel mesh deformation algorithm was developed to deform the mesh as the structure of the wing was being displaced. The mesh deformation algorithm was able to handle wing tip deformations of up to 60 % of the wing semi-span. Besides being robust, the mesh deforming algorithm was computationally more efficient than regriding, since deforming an existing mesh was computationally less expensive than generating a new mesh for each wing position. Results are presented for the validation and verification of both the flow solver and the aeroelastic solver. The flow solver was validated using: (1) the flow over a flat plate, to validate the turbulent model implementation, and (2) the flow over the NACA 0012 airfoil and over the F-5 wing, to validate the implementation of the convective and viscous fluxes, the time integration algorithm, and the boundary conditions. The aeroelastic solver was validated using: (1) the unsteady F-5 wing undergoing forced pitch motion, and (2) the Nonlinear Aeroelastic Test Apparatus (NATA) wing. In addition, aeroelastic results were generated for the Goland wing. The aeroelastic solver developed herein allows the analysis of aeroelastic phenomena using a fully nonlinear approach. Limit cycle oscillations, which are highly nonlinear phenomena, were captured by the nonlinearities of the flow solver and the structural solver. The impact of the nonlinearities was assessed for the Goland wing, where nonlinear terms changed dramatically the aeroelastic behavior of the wing.Item An Efficient Nonlinear Structural Dynamics Solver for Use in Computational Aeroelastic Analysis(2011-08-08) Freno, Brian AndrewAerospace 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.Item Structural and Aerodynamic Interaction Computational Tool for Highly Reconfigurable Wings(2011-10-21) Eisenbeis, Brian JosephMorphing air vehicles enable more efficient and capable multi-role aircraft by adapting their shape to reach an ideal configuration in an ever-changing environment. Morphing capability is envisioned to have a profound impact on the future of the aerospace industry, and a reconfigurable wing is a significant element of a morphing aircraft. This thesis develops two tools for analyzing wing configurations with multiple geometric degrees-of-freedom: the structural tool and the aerodynamic and structural interaction tool. Linear Space Frame Finite Element Analysis with Euler-Bernoulli beam theory is used to develop the structural analysis morphing tool for modeling a given wing structure with variable geometric parameters including wing span, aspect ratio, sweep angle, dihedral angle, chord length, thickness, incidence angle, and twist angle. The structural tool is validated with linear Euler-Bernoulli beam models using a commercial finite element software program, and the tool is shown to match within 1% compared to all test cases. The verification of the structural tool uses linear and nonlinear Timoshenko beam models, 3D brick element wing models at various sweep angles, and a complex wing structural model of an existing aircraft. The beam model verification demonstrated the tool matches the Timoshenko models within 3%, but the comparisons to complex wing models show the limitations of modeling a wing structure using beam elements. The aerodynamic and structural interaction tool is developed to integrate a constant strength source doublet panel method aerodynamic tool, developed externally to this work, with the structural tool. The load results provided by the aerodynamic tool are used as inputs to the structural tool, giving a quasi-static aeroelastically deflected wing shape. An iterative version of the interaction tool uses the deflected wing shape results from the structural tool as new inputs for the aerodynamic tool in order to investigate the geometric convergence of an aeroelastically deflected wing shape. The findings presented in this thesis show that geometric convergence of the deflected wing shape is not attained using the chosen iterative method, but other potential methods are proposed for future work. The tools presented in the thesis are capable of modeling a wide range of wing configurations, and they may ultimately be utilized by Machine Learning algorithms to learn the ideal wing configuration for given flight conditions and develop control laws for a flyable morphing air vehicle.