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This document details the investigation of the aeroelastic behavior of very high aspect ratio cylinders. The difficulty in this investigation lies in the fact that there are two important length scales: the aspect ratio and the Reynolds number. The primary goal is to develop a method that properly represents both length scales during testing. The secondary goal is to develop a method that quantifies the cylinder motion. This paper describes a wind tunnel technique designed to account for the aspect ratio and the Reynolds number of a very high aspect ratio cylinder. This paper also describes the data acquisition and analysis techniques developed here to quantify the motion. As demonstrations, these techniques are then used here to study the motions of two cylinders that are the same in all ways except cross-sectional shape.

A robust technique for performing numerical simulations of nonlinear unsteady aeroelastic behavior is developed. The technique is applied to long-span bridges and the wing of a modern business jet. The heart of the procedure is combining the aerodynamic and structural models. The aerodynamic model is a general unsteady vortex-lattice method. The structural model for the bridges is a rigid roadbed supported by linear and torsional springs. For the aircraft wing, the structural model is a cantilever beam with rigid masses attached at various positions along the span; it was generated with the NASTRAN program. The structure, flowing air, and control devices are considered to be the elements of a single dynamic system. All the governing equations are integrated simultaneously and interactively in the time domain; a predictor-corrector method was adapted to perform this integration. For long-span bridges, the simulation predicts the onset of flutter accurately, and the numerical results strongly suggest that an actively controlled wing attached below the roadbed can easily suppress the wind-excited oscillations. The governing equations for a proposed passive system were developed. The wing structure is modelled with finite elements. The deflections are expressed as an expansion in terms of the free-vibration modes. The time-dependent coefficients are the generalized coordinates of the entire dynamic system. The concept of virtual work was extended to develop a method to transfer the aerodynamic loads to the structural nodes. Depending on the speed of the aircraft, the numerical results show damped responses to initial disturbances (although there are no viscous terms in either the aerodynamic or structural model), merging of modal frequencies, the development of limit-cycle oscillations, and the occurrence of a supercritical Hopf bifurcation leading to motion on a torus. / Ph. D.

High aspect-ratio, long-endurance aircraft require different design modeling from those with traditional moderate aspect ratios. High aspect-ratio, long endurance aircraft are generally more flexible structures than the traditional wing; therefore, they require modeling methods capable of handling a flexible structure even at the preliminary design stage. This work describes a design optimization method for combining rigid and inflatable wing design. The design will take advantage of the benefits of inflatable wing configurations for minimizing weight, while saving on design pressure requirements and allowing portability by using a rigid section at the root in which the inflatable section can be stowed. The multidisciplinary design optimization will determine minimum structural weight based on stress, divergence, and lift-to-drag ratio constraints. Because the goal of this design is to create an inflatable wing extension that can be packed into the rigid section, packing constraints are also applied to the design. / Master of Science

Thesis (Ph. D. in Aeronautical and Astronautical Engineering)--Naval Postgraduate School, June 2003. / Dissertation supervisor and advisor: E. Roberts Wood. Includes bibliographical references (p. 205-210). Also available online.

In this thesis we explore the relationship between aeroelastic flutter and multiparameter spectral theory. We first introduce the basic concept of the relationship between these two fields in abstract terms. Then we expand on this initial concept, using it to devise visualisation methods and a wide variety of solvers for flutter problems. We assess these solvers, applying them to real-life aeroelastic systems and measuring their performance. We then discuss and devise methods for improving these solvers. All our conclusions are supported by a variety of evidence from numerical experiments. Finally, we assess all of our methods, providing recommendations as to their use and future development. We do achieve several things in this thesis which have not been achieved before. Firstly, we solved a non-trivial flutter problem with a direct solver. The only direct solvers that have previously been presented are those that arise from classical flutter analysis, which applies only to very simple systems. Secondly, and as an extension of this first point, we solved a system with Theodorsen aerodynamics (approximated by a highly accurately) with a direct solver. This was achieved in an industrially competitive time (0.2s). This has never before been achieved. Thirdly, we solved an unstructured multiparameter eigenvalue problem. Unstructured problems have not been considered before, even in theoretical literature. This result is thus of significance both for multiparameter spectral theory and aeroelasticity. However, the single most important contribution of this thesis is the opening of a whole new field of study which stretches beyond aeroelasticity and into other industries: the treatment of instability problems using multiparameter methods. This field of research is wide and untrodden, and has the potential to change the way we analyse instability across many industries.

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