P. C. Dunn

Bio: P. C. Dunn is an academic researcher from Massachusetts Institute of Technology. The author has contributed to research in topics: Aeroelasticity & Harmonic balance. The author has an hindex of 4, co-authored 4 publications receiving 194 citations.

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.

He-3 magnetic form factor

Abstract: The $^{3}\mathrm{He}$ magnetic form factor has been measured for momentum transfers between 0.7 and 11 ${\mathrm{fm}}^{\ensuremath{-}2}$ with improved precision over previous measurements. The charge form factor has been measured for momentum transfers less than 1 ${\mathrm{fm}}^{\ensuremath{-}2}$. The charge radius was determined to be 1.935\ifmmode\pm\else\textpm\fi{}0.03 fm, and the magnetic radius 1.935\ifmmode\pm\else\textpm\fi{}0.04 fm. Comparisons are made with calculations which include meson exchange corrections and reasonable agreement is found.NUCLEAR REACTIONS $d(e, {e}^{\ensuremath{'}})d$, ${q}^{2}=0.7 \mathrm{to} 11$ ${\mathrm{fm}}^{\ensuremath{-}2}$, $\ensuremath{\theta}=160\ifmmode^\circ\else\textdegree\fi{}$, measured magnetic form factor; ${q}^{2}l1$ ${\mathrm{fm}}^{\ensuremath{-}2}$, $\ensuremath{\theta}=60\ifmmode^\circ\else\textdegree\fi{}$, measured charge radius.

Nonlinear Aeroelasticity and Flight Dynamics of High-Altitude Long-Endurance Aircraft

Abstract: High-Altitude Long-Endurance (HALE) aircraft have wings with high aspect ratios. During operations of these aircraft, the wings can undergo large de∞ections. These large de∞ections can change the natural frequencies of the wing which, in turn, can produce noticeable changes in its aeroelastic behavior. This behavior can be accounted for only by using a rigorous nonlinear aeroelastic analysis. Results are obtained from such an analysis for aeroelastic behavior as well as overall ∞ight dynamic characteristics of a complete aircraft model representative of HALE aircraft. When the nonlinear ∞exibility efiects are taken into account in the calculation of trim and ∞ight dynamics characteristics, the predicted aeroelastic behavior of the complete aircraft turns out to be very difierent from what it would be without such efiects. The overall ∞ight dynamic characteristics of the aircraft also change due to wing ∞exibility. For example, the results show that the trim solution as well as the short-period and phugoid modes are afiected by wing ∞exibility.

Nonlinear Aeroelastic Analysis of Complete Aircraft in Subsonic Flow

Abstract: Aeroelastic instabilities are among the factors that may constrain the flight envelope of aircraft and, thus, must be considered during design. As future aircraft designs reduce weight and raise performance levels using directional material, thus leading to an increasingly flexible aircraft, there is a need for reliable analysis that models all of the important characteristics of the fluid-structure interaction problem. Such a model would be used in preliminary design and control synthesis. A theoretical basis has been established for a consistent analysis that takes into account 1) material anisotropy, 2) geometrical nonlinearities of the structure, 3) unsteady flow behavior, and 4) dynamic stall for the complete aircraft. Such a formulation for aeroelastic analysis of a complete aircraft in subsonic flow is described. Linear results are presented and validated for the Goland wing (Goland, M., The Flutter of a Uniform Cantilever Wing, Journal of Applied Mechanics, Vol. 12, No. 4, 1945, pp. A197-A208). Further results have been obtained that highlight the effects of structural and aerodynamic nonlinearities on the trim solution, flutter speed, and amplitude of limit-cycle oscillations. These results give insight into various nonlinear aeroelastic phenomena of interest: 1) the effect of steady-state lift and accompanying deformation on the speed at which instabilities occur, 2) the effect on nonlinearities in limiting the amplitude of oscillations once an instability is encountered, and 3) the destabilizing effects of nonlinearities for finite disturbances at stable conditions.

Elastic magnetic electron scattering from nuclei

Abstract: This paper is focused mainly on the subject of elastic magnetic electron scattering and how it has come to be a useful tool for studying the spatial distributions of convection and magnetization currents in the nuclear ground state. Using such a probe, emphasis is clearly placed on the electromagnetic currents provided by the valence nucleons in the nucleus, indeed, by neutrons as well as protons. These do not yield a complete description of the problem, however, and more complex nuclear many-body configurations are generally required. Various models are employed (shell-model configuration mixing, core-polarization effects, models of deformed nuclei, for instance), giving rise to quantitative comparisons with experimental measurements. Moreover, to achieve such successful descriptions, especially at high momentum transfers, it is frequently necessary to go beyond a purely one-body nucleonic reaction mechanism and to include the effects of two-body meson-exchange currents based on non-nucleonic degrees of freedom ($\ensuremath{\pi}$,$\ensuremath{\rho}$,$\ensuremath{\Delta},\dots{}$). The authors discuss all of these various facets of the problem, beginning with surveys of the historical development of the field and of the experimental techniques employed in such studies. They present a detailed treatment of the formalism needed in discussions of elastic electron scattering, including an introduction to the density-matrix approach to the nuclear many-body problem, with simple examples to clarify the ideas involved. For the nonspecialist a separate section of illustrative examples is supplied in which qualitative discussions of various aspects of the physics accessible in such ($e$,${e}^{\ensuremath{'}}$) studies are highlighted. Experimental and theoretical results for a large number of nuclei ranging from $A=2 \mathrm{to} 209$ are described in detail; this represents a compilation of virtually all of the high-quality data that are available at present. The paper concludes with projections as to which directions may be followed in the future, in particular, with a relatively complete discussion of the use of polarization in elastic electron scattering.