1,454 research outputs found
Hypersonic Flight Mechanics
The effects of aerodynamic forces on trajectories at orbital speeds are discussed in terms of atmospheric models. The assumptions for the model are spherical symmetry, nonrotating, and an exponential atmosphere. The equations of flight, and the performance in extra-atmospheric flight are discussed along with the return to the atmosphere, and the entry. Solutions of the exact equations using directly matched asymptotic expansions are presented
Li spectrum from Li fragmentation
A recently developed time dependent model for the excitation of a nucleon
from a bound state to a continuum resonant state in the system n+core is
applied to the study of the population of the low energy continuum of the
unbound Li system obtained from Li fragmentation. Comparison of
the model results to new data from the GSI laboratory suggests that the
reaction mechanism is dominated by final state effects rather than by the
sudden process, but for the population of the l=0 virtual state, in which case
the two mechanisms give almost identical results. There is also, for the first
time, a clear evidence for the population of a d resonance in
Li.Comment: 15 pages, 4 figures, 3 tables. Accepted for publication in
Nucl.Phys.
Solution of the exact equations for three-dimensional atmospheric entry using directly matched asymptotic expansions
The problem of determining the trajectories, partially or wholly contained in the atmosphere of a spherical, nonrotating planet, is considered. The exact equations of motion for three-dimensional, aerodynamically affected flight are derived. Modified Chapman variables are introduced and the equations are transformed into a set suitable for analytic integration using asymptotic expansions. The trajectory is solved in two regions: the outer region, where the force may be considered a gravitational field with aerodynamic perturbations, and the inner region, where the force is predominantly aerodynamic, with gravity as a perturbation. The two solutions are matched directly. A composite solution, valid everywhere, is constructed by additive composition. This approach of directly matched asymptotic expansions applied to the exact equations of motion couched in terms of modified Chapman variables yields an analytical solution which should prove to be a powerful tool for aerodynamic orbit calculations
Optimum three-dimensional atmospheric entry from the analytical solution of Chapman's exact equations
The general solution for the optimum three-dimensional aerodynamic control of a lifting vehicle entering a planetary atmosphere is developed. A set of dimensionless variables, modified Chapman variables, is introduced. The resulting exact equations of motion, referred to as Chapman's exact equations, have the advantage that they are completely free of the physical characteristics of the vehicle. Furthermore, a completely general lift-drag relationship is used in the derivation. The results obtained apply to any type of vehicle of arbitrary weight, dimensions and shape, having an arbitrary drag polar, and entering any planetary atmosphere. The aerodynamic controls chosen are the lift coefficient and the bank angle. General optimum control laws for these controls are developed. Several earlier particular solutions are shown to be special cases of this general result. Results are valid for both free and constrained terminal position
Response Function of Hot Nuclear Matter
We investigate the response function of hot nuclear matter to a small
isovector external field using a simplified Skyrme interaction reproducing the
value of the symmetry energy coefficient.
We consider values of the momentum transfer corresponding to the dipole
oscillation in heavy nuclei. We find that while at zero temperature the
particle hole interaction is almost repulsive enough to have a sharp (zero
sound type) collective oscillation, such is no longer the case at temperatures
of a few MeV. As a result a broadening of the dipole resonance occurs, leading
to its quasi disappearence by the time the temperature reaches 5 MeV. The
sensivity of the temperature evolution of the width when modifying the residual
interaction strength is also examined.Comment: 9 pages, IPNO/TH 94-15, DPT-IPN Orsay. Two figures available under
reques
Analytic theory of orbit contraction
The motion of a satellite in orbit, subject to atmospheric force and the motion of a reentry vehicle are governed by gravitational and aerodynamic forces. This suggests the derivation of a uniform set of equations applicable to both cases. For the case of satellite motion, by a proper transformation and by the method of averaging, a technique appropriate for long duration flight, the classical nonlinear differential equation describing the contraction of the major axis is derived. A rigorous analytic solution is used to integrate this equation with a high degree of accuracy, using Poincare's method of small parameters and Lagrange's expansion to explicitly express the major axis as a function of the eccentricity. The solution is uniformly valid for moderate and small eccentricities. For highly eccentric orbits, the asymptotic equation is derived directly from the general equation. Numerical solutions were generated to display the accuracy of the analytic theory
Minimum-fuel aeroassisted coplanar orbit transfer using lift-modulation
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/76271/1/AIAA-19945-331.pd
Optimal plane change during constant altitude hypersonic flight
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/76559/1/AIAA-1988-4341-460.pd
Orbital changes during hypersonic aerocruise
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/76648/1/AIAA-1987-2564-435.pd
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